Tag Archives: fresh roast

FreshRoast SR500 Wattage

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Earlier in the blog I posted photos showing the circuit boards inside the roaster that were labeled 1000W.  The roaster was reported as being 1500W and it’s a pretty major deal to be 1000W vs 1500W.  After looking back at the blog and some of the things I’ve worked with and struggled it made me wonder more about the wattages used by the SR500.  Additionally it seems there are a lot of people that come to this blog looking for information about how many watts the SR500 is.

In the interest of providing accurate information I went out and got a device for measuring wattage drawn by a device.  Upon plugging it in I discovered that the SR500 draws .8 Watts in “idle” mode.  For comparison a coffee pot I had here with only an Off/Timer/On toggle button and a button to let you change the clock and a tiny little LCD you can’t even REALLY see except when trying to look at it to program the start brew time was drawing 1.2-1.5 watts.  When I turned on  the coffee pot it went to around 1460-1470 watts.

Back to the coffee roaster the manufacturer reported it as 1500watts.  Looking at the circuit board it seemed to show 1000W on one of the labels.  Turns out it is indeed 1500 watts when running full force as described.  I have no idea why the circuit board reports 1000 watts.  I started thinking maybe there is something with the electronics and mainly the fan that would suck up a significant amount of wattage while it was turned on.  Knowing the model of processor inside the circuit and the other parts there was not a lot of electric being consumed.  This was proven when looking at the cool cycle.  First let’s start with the typical roast numbers.

Starting we have .8 Watts  in a sort of standby mode waiting for the controls to turn the roast on. [Edit 4/14/11 – The meter in a sort of standby of its own with nothing plugged into it runs about .5 watts.  This means the roaster in standby probably consumes something more like .3 watts.]  Once I turned on power it lurched upward and for many of the settings hovered +/-  one to five watts one way or the other from the following numbers:

Fan / Heat / Wattage Reported

Low / Low / 1420
Med / Low / 1475
High / Low / 1500
Low / Med / 1420
Med / Med / 1475
High / Med / 1508
Low / High / 1420
Med / High / 1475
High / High / 1505 to 1520

The wattages slowly ticked up and down without seeming to be connected too heavily to anything in particular that was going on.  This was measured WITHOUT the roasting chamber in place allowing the roaster to simply run full force.  When I have more time I’ll run a regular roast through and see if there is any significant peak points where the numbers differ much fluctuating during the roast and if there is a pattern to any of it.  This leads to cooling.

Cooling for all intents and purposes is the roaster running with all electronics EXCEPT for the heater.  This is particularly interesting because the amounts that the wattage changes is not necessarily reflected on each of the tiers for the fan/heater combo.

High Fan / Cool / 182 watts
Med Fan / Cool / 148 watts
Low Fan / Cool / 107 watts

As you can see the wattage of the roaster is pretty reasonable to be called 1500 watts.  You cannot say that the HEATER is 1500 watts….  but it IS a 1500+ watt device like most other items advertised that way.  Why the internal parts are labeled 1000w I cannot imagine.  My guess is there may have been an earlier design that reused the same circuit board to control things and it just needed a stronger heater element.

The roaster appears to not vary the heat outside of the full power to the heater element and then it turns off when the LOW/MED/HI threshold is met.  I expect to see the wattage go from 1400-1500ish down to the 140-180 range every time the heater cycles the way this looks.

For those looking for an update on SD memory I am pleased to say that I found the problems with the SD memory wiring that were actually conflicting with more pins than I knew.  I also found a couple other places that were conflicting randomly that I had odd symptoms that I had not traced yet.  How did I do this?  I blew up the datasheet pin diagram from 8.5 x 11 to 3 feet by around 2 feet something after color coding a few of the pin types and then systematically crossing out a few pins that I have no control over which ones are used because they either HAVE TO be used due to existing circuit boards on the development kit or else there are so many other pins being used in a “set” that I cannot use that function.  Examples would be if you needed to use UART1 TX/RX.  These are on pins RF2 and RF8.  ALSO living on these pins are SDI and SDO #3.  Obviously if you use UART 1 those pins are tied up and now you cannot use SPI (SDI/SDO) set number 3.

Once I cross those functions off the list it makes it soooo much easier to find all the other functions that I need to place or can place in other locations.  I’m gradually transferring these items into a schematic building power supplies and VGA interfaces etc onto them.  I’m beginning to get closer and closer to having created a full schematic for the entire project up to this point.  I can convert that schematic into a circuit board layout and after a few more rounds of tests and seeing if I can figure out a few more sensors I’ll probably be ready to test out a preliminary test board that will become a “condensed” development platform.  This will let me test 1) building circuit boards, 2) knowing that I’m close to getting a functional system, and 3) having a lot less junk on my desk.

I’ve now managed to get time and date stamp and temperature readings sending to a CSV file that loads easily into Excel that I can apply a chart to.  Next up — Roasting something to get real temperature numbers.

MAX6675 with PIC32MX795F512L

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As I mentioned earlier I’m using the USB Starter Kit II, the PIC32 Expansion Board, the SSD1926 PicTail Plus board, and a Truly 3.2″ 320×240 LCD display board to develop the roaster system. This has resulted in some “fun” trying to figure out which pins are really going where on the board and the PicTail cards that you can build your own circuits on. Occasionally some of the pins are not exactly labeled the right way or else there are a few pins that are wired together on the circuit boards making you unable to use one of the pins that are wired together or in some cases both cannot be used etc.

I’ve been working through various demos and trying to understand some of the libraries and still trying to identify all of the pins on the expansion board that are already attached to the LCD / graphics chip. So far I have not found any that involved the SPI1 Pins, which I’m sure is incorrect now.

I’ve now managed to get real time readings to occur while using SPI2 instead of SPI1. Originally I was using pins B2 (SS1), C4 (SDI1) , and D10 (SCK1). to communicate with the MAX6675 thermocouple. When the system launched it would begin to read temperatures from those pins properly but only while in animate debug mode. As soon as I would let it run in full speed to get to a break point later it would be partially or completely erroneous in the received readings. I’ve now switched it to the SPI2 pins and using G9 (SCK1), and G7 (SDI1). (The MAX6675 does not use the SDO pins since it only transmits readings and does not receive using SPI data)

I’m now opening the SPI port to communicate with the MAX6675 using 16bit word mode:
OpenSPI2(SPI_MODE16_ON | SPI_SMP_ON | SPI_CKE_ON | MASTER_ENABLE_ON | CLK_POL_ACTIVE_HIGH | SEC_PRESCAL_8_1 | PRI_PRESCAL_16_1, SPI_ENABLE);

[After I clean up all the “Dead code” that I’ve been testing various things with I’ll insert some additional SPI stuff HERE]

Which appears to work properly talking to the MAX6675. Further I’ve gotten the text to display on the screen of the current temperature where it runs a rolling average of the last 3 readings updating the screen after each additional reading. At the moment it flips on one of the starter kit’s LEDs based on the temperature when it needs to heat and turns it off when it’s reached a preset temperature.

I need to work more on getting the LCD display to show the activity that is going on in terms of heating/cooling and run a timer to begin estimating what stage the roast would be in based on temperatures and time-wise. Additionally I’ll need to figure out how to graph the temperature across the bottom of the screen too. I’m thinking screen real estate is somewhat limited so I may want to upgrade the LCD to the wider board to move some of the data to the side leaving a larger graph area to represent the roast curves.

Early July Update. Observation on SR500.

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Having been offered full time employment starting the middle of July after approximately 2 years of unemployment things are looking good for getting some progress on this project. LOL! While this may sound odd this is actually good due to the fact that I’m building (if all goes properly) a somewhat professional-esque coffee roasting computer. It takes a lot of money and resources to design this thing. I’m already into the project around $300-400 worth of circuit development kit gear and need a lot more stuff. In the end I’ll have a complete system that will be significantly cheaper to build but still have all the development kits to make other projects. I chose that route because of the “other projects” for down the road instead of only buying the things I need right now. While having full time employment will limit my available time it DOES however allow me money to keep purchasing all the parts.

Most projects you find on the internet for a coffee roaster use something like a Basic Stamp or some other very limited processor. It also usually involves hooking together a few things someone finds off eBay hooked together with some various wires and connectors salvaged off some old computer equipment and other devices abandoned in the garage. By the time it’s done you get a picture on the internet of some “finished” popcorn popper that looks like it’s about 30 seconds from taking out a corner of your house into a huge crater or like it’s some sort of industrial wiring project of conduit and electrical boxes.

I’m intending on making this thing as small as I can make it and sealing it up inside a electronics case with a single cord or perhaps a cord and a sensor wire that plugs into the back of the case that leads to the roaster. I don’t want 50 million little cords and sensors and clunky switches and other doo-dads spread across my counter. I also want to be able to pick the whole thing up and move it somewhere else without accidentally cracking off a wire and needing to re-solder it. I don’t know about you but I love my coffee. I don’t love having to re-solder the wiring just to roast some more or being unable to use my kitchen for anything else.

My Kitchen is not that big. It cannot accommodate a lot of “stuff” strewn around it. so the entire thing will need to be compact. As a result I intend on having a case that has a LCD touch screen installed. It will probably have a LED or two and at most probably a single power switch on the front edge or side. I will likely try to design the circuitry so that it fits onto one or more circuit boards stacked on top of one another. The LCD will be mounted on top with various connectors and other items stacked below it. I’m reasonably sure I can shrink the majority of this down into a space about 4″ by 6″ and about 1.5 to 2″ tall.

As mentioned I recently purchased the PIC32 development gear. At the moment I’ve been working on the GUI. This is a lot more complicated programming than I’m used to. Additionally I’m having a few “weird” situations where LED’s on the starter kit are lit that I don’t seem to understand why. When I turn on an LED that is normally off things work fine but then when I programmatically turn that one off the LCD turns off too though they shouldn’t be connected at all. The other LED works fine turning it on and off the same way. One of these LEDs simply stays on all the time no matter what.

At the moment I now have a “splash screen” functioning. I touch the screen and it continues to a “Home” menu. From there it offers several buttons to run the manual or the automatic roasting menu. There is also a provision for a Setup menu. I am still waiting for the ethernet to arrive that will allow me to download roasting data out of the system or pre-configure a roast from a web page. It currently draws temperature onto the screen from some “made up numbers” I have the thermocouple and the chip that will convert the sensor reading to numbers but need to solder it to a board that I can connect to the processor. I also need to do the same with the clock chip that I have as well. The processor has built in clock routines but they only work while the system is turned on. As soon as you cut power that clock loses it’s data. As a result I will program the system to read the clock chip every time the system turns on.

Over the next few days I will program the roasting screens to change certain display areas based on the simulated temperature numbers and then integrate the “control” portion where it then stops the increase in temperature and then tries to increase it appropriately. I still need to figure out the timer stuff… it doesnt seem to run on the demo and I was thinking it had to do with an oscillator being missing but this seems to be related to USB stuff in the documentation for the starter kit. This doesnt seem right though. I need to figure that out and then the next step is to start ordering all the pin headers and not included on some of the other boards. I’ll try to figure out a few more of the parts that I’ll need and order those in the next few days as well so I can keep working on this. Assuming I’m right that the crystal is required apparently Microchip decided to save 83 cents by not including the oscillator.

Also as a side note. Due to the job offer I completed a move to Northern California from Central California which has kept me from messing with the coffee much until now. A variety of coffee that I roasted here with the Fresh Roast +8 took approximately 6 minutes to hit second crack. Using a SR500 where I used to live took about 6 minutes as well while running the fan at half speed for the first two minutes. To do the same thing here with the SR500 appears to take around 7-8 minutes with a lot more slowing down the fan to around the 25% setting once movement starts to flow more easily and first crack was reached.

Roast temperature probe sweet spot in Fresh Roast

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As I mentioned previously there appears to be a “donut” shaped sweet spot in the roast.  I had been testing my SR500 with a K type thermocouple in various spots.  Most of the time people run their roasters with the thermocouple shoved straight down the middle in a lot of the photos I’ve seen.  With the SR500 I’ve found this region to be very sparse with beans due to the high flow of air up the middle.

As shown in this diagram the center portion at the bottom shoots up the middle in the air column grabbing beans on the edges of the two green zones.  They are then tossed outward in the orange circular zone represented on top.  The beans that sit out on the purple areas on the bottom tend to burn due to low circulation.  Ultimately I would expect some sort of triangular slanted chute sealed to the edge would allow beans to be directed away from this burn zone and closer to an area where movement would be possible will help improve this.

I have not written much lately because I’m currently not at home using my roaster.  Prior to leaving I did some testing of the sweet spot ultimately getting pretty close to the middle of that sweet spot.  No matter which beans I roasted and the length the beans were being roasted I always noticed, while adjusting fan and temperature settings on the controls, that the beans always had first crack at the expected temperature +/- 1 degree Fahrenheit.    The same with second crack seemed to hold true as well.

Based on those readings and the reproducibility of that it is my opinion that the ideal thermocouple position in the SR500 and probably the SR300 is as I described earlier.  The height seems to be just below the surface of where 120 grams of beans fills the roasting chamber to for the tip.  This keeps it from the bottom where the heat is somewhat higher and allows it to be centered in contact with the main mass of beans once they expand slightly and begin to float more easily in the air column above his position.

Regarding the coffee’s I’ve roasted.  I previously mentioned some by name and certain characteristics of the roast as I was roasting them.  I had decided until I can track the actual temperatures and accurate times to share it was probably best not to continue posting the resulting curves as I roasted them.

Experimenting with a thermocouple.

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So now that I have a faster responding thermocouple I’m finding that the  sensor works better closer to the edges of the roaster.   When thinking of the bean mass on the SR300 and SR500 you probably need to consider the bean mass as if it is a donut at the bottom of the chamber.  You want to get the tip of the probe centered in the middle of the donut and not the middle of the chamber.

Most modifications people have shown put the probe drilled straight down the middle.  This has the advantage of clearing the “chaff grate” on the sides down a natural hole in the roaster.  The problem with this is that the very center is actually a sort of “fountain” of beans and hot air.   The probe has very little contact with any of the roasted beans and is mostly picking up the air put out by the roaster.

Many people who have sensored this middle area report temperatures in the 420 to 425 degree range.  At the very end all of the beans are very fluid and filling almost the entire chamber area moving freely.  Once this finally happens the temperature readings then reach the 440-450 range showing a typical second crack area that coincides with actual second crack occuring.  Often second crack ACTUALLY happens while the probe is showing 400 degrees when placed in the middle.  This is likely due to the bean mass thermic reaction being hotter than the air rushing up from below and only a few minutes later does the air column catch up.

I’m starting to get low on beans from the samplers  with only a pound or two left of all the varieties.  I’m feeling that the probe placement I used initially in the middle helped stall a few roasts due to inaccurate temperatures of the bean mass that I responded to.  I’m testing a roast where the probe was moved closer to the “donut” range to see what sort of tastes develop but this one is pretty close to a standard roast.

My feelings are there is a “donut” sweet spot.  In the diagram below there is a Orange region [1] that is the normal plume of bean being pulled from the middle area on the bottom and [2] tossed up on top to the left and right.  As you descend into that area you enter part of the sweet spot [Green].  In the far left and right corners [Purple] you have a “burn” zone due to very low circulation of the beans.  This is caused by the more central area of the donut [3] falling towards the middle and then being jetted to the top [1] repeating the cycle.  Only when the beans have sufficiently roasted does the bean mass begin to rise above the initial [Yellow] fill line.  As the mass makes it above the silver metalic band there is enough movement to cause beans to leave the “Burn Zone” and make it easily into the column.  This initial burn area is where the stray first cracks are likely to originate and the uneven roast occurs.

Freshroast "Sweet Spot" created in roasting chamber.

I would thus interpret the space where the D on the left donut and the t on the right donut would be the approximate ideal locations to sample bean mass temperatures due to the piling on of beans from the fountain [1] above it.

Freshroast SR500 apparent “safety” mechanism. Adding new thermocouple.

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Due to the microprocessor installed and the sensor mounted at the top of the roaster base where you install the roasting chamber.

NTC Thermistor mounting

It appears that when you turn the roaster on to High and lower the fan knob to the lowest setting the roaster will reach (unloaded) 430 degrees.  At that point the fan automatically revs up slightly (possibly due to the heater being off)  and the heat stops climbing at 433 degrees.  Occasionally it drops sooner but always between 430 and 433.  It then drops from 430ish degrees down to approximately 420 degrees and then resumes climbing again.  The heat appears to always stop at 420 and then goes back up.  The highest it stops dropping at is 422.

Temperatures were measured with a new K type thermocouple mounted approximately where the center of the bean mass would be.  I obtained this at OSH (Orchard Supply Hardware) since I needed some sort of multimeter for the moment.  They had one inexpensive “Craftsman” model with the ranges I need for measurements with the Digital Multimeter side with an included K type thermocouple mode.  I’m expecting the thermocouple to not last very long due to the temperature rating they put on it.  I will likely get one from eBay or something that is compatible with the K thermocouple sensors in the meter.  I’m guessing the protective covering they put on the tip end insulation area to keep the insulation from unraveling is not able to withstand the high temperature for very long but the insulation looks like it can take a lot more.   I’m going to probably get some high temperature silicone and put a little dab right at the end above the tip to hold the insulation better so it won’t fray.

Ultimately I’ll source out a thermocouple that can do more properly as I get further into this.   I’m going to switch to using the previous thermometer as a timer (was a secondary feature… you get one or the other on screen at any point in time) and the thermocouple as the new temperature sensor since it actually responds faster on temperature changes.

Modified Thermometer Test w/ Rwanda Gkongoro Nyarusiza

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So as mentioned previously I took the thermometer probe and used one of those pipe cutters with the “wheel” for cutting things like copper pipe and sliced off part of the probe.  Due to the fact that this sort of cutter “crushes” slightly while it cuts this ended up making it so I could not slide the inner electronics out without fear of not getting it back in or damaging it (without having a soldering iron currently).  I instead slid all of the formerly connected probe upwards and taped it to the probe’s plug using electrical tape.  I then crimped the remaining probe in place at the top against the braided cover.

My initial test seems to have yielded a technically proper heat ramp based on what was happening.  Additionally the cooling cycle appears to have been pretty normal too.  It appears that when the cool cycle halts the beans are approximately 158 degrees and linger there while in the roasting chamber even when removed from the roaster.  They drop to around 130 degrees after being dumped out into another container within about 20 seconds and then they hang around 130-120 degrees for several minutes if undisturbed.

Here is my heat readings for a standard roast.  In this case I was roasting the Rwanda Gkongoro Nyarusiza.

Markers are A= Rolling First Crack, B= Second Crack.  Fan speed is shown as 100% for the knob being set all the way to the right.  50% is fan knob set in the middle position (straight up).

I was not able to keep track of any additional details due to manually tracking the roast on paper.  Cooling with fan speed increased to 100% starting at 6.1 was as follows:

Bean mass started at 120g and reduced to 102g for a loss of 18g or 15%

Problems with thermometer – YAY!

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So I finally got a chance to try a roast with the thermometer.  At approximately 3.5 minutes into the roast in the reading it crossed 482 and would no longer read.  This is OBVIOUSLY not a correct reading.  I expected some imperfection in the readings due to this probe expecting liquid/solid meat as opposed to air/dry readings but everything is significantly off.  First crack came as a reading of 449 which puts me a good 50 degrees above where I expect to be and follows about 50 degrees over everything I expected during the roast for the color changes etc.

My theory is that the probe is so long that it has to be inserted through the grate on the chaff collector on top.  The probe is then picking up heat transferred by the chaff collector that it is touching and particularly the metallic disc embedded in the lid being transferred through the plastic.

The cooling cycle lasts approximately 2.5(ish) minutes and it ends at an unusually high number.  With the probe and chaff covered removed and sitting 5+ minutes it still shows a temperature in the 90s so this is certainly picking up the temperature from the cover.  At this point I will need to attempt to remove the probe in some way and see what else I can do to “shrink” the size of the probe and find an alternate place to put it.

[easychart height=”300″ type=”line” title=”Heat Results” groupnames=”Temperature F” valuenames=”0.0,0.5,1.0,1.5,2.0,2.5,3.0,3.5,4.0,4.5,5.0,5.5,6.0″ group1values=”78,222,366,402,413,428,460,482,482,482,482,482″ group1markers=”6.1″ hidechartdata=”true” ]

[easychart height=”300″ type=”line” title=”Cool Results” groupnames=”Temperature F” valuenames=”0.0,0.1,0.2,0.3,0.4,0.5,0.6,0.7,0.8,0.9,1.0,1.1,1.2,1.3,1.4,1.5,1.6,1.7,1.8,1.9,2.0,2.1,2.2,2.3,2.4,2.5″ group1values=”482,482,474,402,320,262,240,212,201,183,172,167,158,152,147,141,140,138,138,132,129,127,127,127″  hidechartdata=”true” ]

While the HEATING is flawed with the metal disc and the cooling is most certainly flawed at the end as well it is interesting to witness the significant drop in heat from the cooling cycle.  The beans (by touch) clearly release heat faster than the metal mass does and they are quite cool in the end.  In about 30 seconds the heat has dropped  to around 250 with the metal heat skewing the readings.  It is my guess that all cooling readings are approximately 30-40 degrees higher than actual in the bean mass meaning the real “roasting” has stopped before 30 seconds of cooling are up.

Lesson Learned: The chaff collector gets significantly hot enough that you need to avoid ANY contact to any probe devices with the top and try to steer clear of the metal disc at all costs.

Update: I have used a copper pipe cutter to slowly slice a ring around the metal casing of the thermometer allowing me to shorten the probe.    I googled around and found this article http://brettbeauregard.com/blog/2009/09/anatomy-of-a-digital-thermometer-probe/ which shows the inner guts of a typical probe.  As you will see this is mostly the braided wire until the very end where the actual sensor is.  I’ve sliced off several inches of the casing and slid it up the wire towards the socket.  Once I determine if this seems to work I will try to figure out a way to slide this off without mucking things up too much and permanently removing it and crimping the end of the probe onto the braid.  New article once I get to that stage if it works out.

Temperature and the “pause” when pressing Up/Down button on FreshRoast SR500

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So as mentioned before there appears to be some sort of temperature sensing device built into the base that interacts with the Atmel processor.  There appears to be potentially power dimming circuits in there as well but I need a multimeter to verify all that which I do not have at the moment.

I’ve mostly been roasting the past few days “by sight, smell and sound”  the various coffees.  I logged some details on some of the coffees I roasted and they turned out ok when I brewed them but without temperature data to go with my timings I figured reporting the results was pretty useless so I stopped mentioning the other beans and what I roasted.

Initially my plan was to roast the coffee and see which ones tasted good or “bad”.  So far the only one that I have had any issues with is not necessarily “bad”…. but just not “really good”… it is only good.  That of course is a horrible horrible crime in the world of coffee.  [/sarcasm].   Even the “only good” coffee will be given a chance to redeem itself after reading the details provide on SweetMaria’s regarding the coffee and seeing if there are any nuances of needing to be darker or lighter or perhaps made into espresso or left for resting for additional days etc before I decide where it belongs in my ordering of new coffee for the “longer term” than the initial sampler.

I have now set up a digital gram scale (sensitivity 1.0g) with a small plastic measuring cup that I “tare” on the scale prior to pouring the beans in.  I’m finding that the amount is sensitive for only a couple beans that seem to roast “weird” compared to the rest where the others do just fine with a higher amount of beans.  These beans that are “weird” have little movement until the last 60-90 seconds of the roast.

The factory suggested amount is 120 grams while Tom @ Sweet Marias suggests 100 as being more realistic.  While I cannot claim to be any sort of coffee snob and certainly not an expert at roasting/cupping etc I’m finding the coffees I listed in my first blog…  by starting them on a completely level surface, and running the fan at 100% with the heat on low until a slighter amber color is achieved will result in pretty decent coffee with no more than one or two dark “spots” beans.  It seems on very small beans that apparently get stuck in the mesh before the fan starts.  They will end up scorching but the rest of them circulate quite well and explain why the “stirring trick” works due to this taking place while the fan is blowing.  Once you stir all the beans free from the screen they begin to free-float in the stream like the larger ones that never got stuck.  Everything else seems to roast gradually and without signs of burning though heavier beans will start to darken faster due to spending more time lower in the chamber.  I believe the roaster being level to be quite important as a result and starting off with a lower temperature and the “cool trick” artificially keeping the temperature low in the startup to help limit any burning.  This would side with people that declare a pre-heat cycle with the FreshRoast to be unnecessary since it would probably burn the beans worse than starting off slowly.  Ultimately a much lower temperature than “low” perhaps by around 100 degrees would be better as a “dry” cycle.

Today I managed to find a temperature probe in the grill section that makes it into the upper 400s Fahrenheit.  Most thermometers stop at 392 degrees or they have a lot of plastic that would prohibit you being able to have them near the heat of a roaster.  It is a BBQ grill thermometer made for Kenmore and was sold at my local Sears store.  It does NOT fit the roasting chamber without some convincing.  Convincing involves some very gradual bends being applied to the thermometer probe to allow it ot sit further down in the chaff collector putting the tip in the middle of the roasting chamber.  To convince it to turn I ended up utilizing the combination of a small gap on the rounded handle on a vise for some MINOR adjustments and the major adjustments being convinced with a large Maglight flashlight.  If you have ever bent metal electrical conduit you will get the idea.  You need to gradually support the pipe as it bends sit that it does not kink.  The temperature probe is actually a hollow shaft with a pointed tip on it.  The hollow shaft contains a set of twisted wiring that is actually a thermocouple.  It connects to the braided wire cover for that wiring which leads to the socket on the display.  You don’t want to kink the probe so it has to be slow bends in the probe to keep it from crimping on the thermocouple and potentially weakening things.

I have not roasted a batch using the new thermometer yet due to the fact some things came up today where I was not in the house and as a result we didnt really drink much coffee today to use the beans we’ve already roasted leaving me nowhere to place the finished roast.  As a result I now have a 2 day rest on most of these beans that are in there.  Today I get to see if the probe will pickup any appropriate temperature readings that match up with what would be expected at First Crack and/or Second Crack or if it is simply not sensitive enough and is actually picking up the roaster air only.

I have already attempted to run the roaster without beans for a brief time to inspect the temperature readings and see if there is any sort of ramp involved.  The temperatures did not seem to pass the mid 300s no matter what the setting while on high. Apparently with that level of airflow (if things are working with the sensor)  the heating elements needs to have back pressure from the beans in the roaster to reach the 400s.  As a result if running too small of a batch it will likely not roast properly thus never reaching a high enough temperature like too much beans could result in too high of a temperature being applied.  With the use of the Atmel processor and that possible NTC Thermistor Diode it probably means that the heater will cut out to not result in an overheat situation temperature wise BUT ultimately the beans in the roaster will probably burn without enough movement.

FYI the Atmel datasheet HERE shows that the processor has interrupt capabilties.  The buttons seem to be wired to two of the pins that have interrupt capabilties.  Due to there not being any chips to buffer the button pressing it would be my guess that the program made any pressing of Up/Downl to be an interrupt to the existing programming.  It seems to be part of the “Analog Comparator” which treats the status of two pins as a logical on/off.  If you press up it counts that button as pressed (1 or on) to the other button (down) as not pressed (0 or off).  It compares the two settings and initiates an interrupt.  As a result whatever signals being received for fan or heat control would be interrupted resulting in a “drop” to a minimum level that we are seeing.  This interrupt stops normal interpretation of the voltage in/out on the other ports and triggers a counter to go up or down.  There is circuitry built in apparently to do limited “debouncing” which is why holding the button does not make it continue to go up or down.  With the use of more expensive complex circuitry the variation in speed that we see would go away but due to cost savings this is a side effect.  The only way to eliminate such a pause is to use a different controller than the Atmel or potentially include extra chips to handle these changes.  The length of the pause is directly related to how quickly you can trigger the button.  I would suspect if you had “two bare wires” instead of the push button and you quickly tapped them together rapidly the up/down reaction would not be noticeable.  Due to the type of button used there is a long “click” in the button that makes the interrupt obvious.  The faster the contact and release of the button the shorter the interrupt allowing the circuit to continue on as programmed.

Inside the Freshroast SR500

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As I’ve mentioned it is my intention to try to improve on the control of the Freshroast SR500 by automating some of it with a microchip circuit.  I’ve got a lot of crazy ideas of things to do with this but most of it will take some time.

At the moment I’ve been unemployed for quite some time.  At my last employer I ran the IT department for a community bank.  That means I was in charge of the network, email, spam, spyware, virus protection, servers, desktops, printers, we had a Cisco Voice over IP phone system, and a variety of other things.  I got to deal with all the regulatory requirements from the Federal and State government writing policies, procedures, and supervising the IT staff as well doing budgets etc.  Anyway they outsourced the whole thing when the economy started getting bad probably because my salary and those that I would work with are not cheap and there were a lot of things that were changing and needing done.  Ultimately it was technically cheaper to just turn it over to a company that only does banks as an all inclusive package.  Since the economy has not improved much I’m still looking for employment which of course limits my funds to work on building control systems.  It does allow me a lot of time to work on projects such as learning to program microcontrollers.

Update July 2011 – Please check out my multi-part Teardown posting showing step by step taking apart a FreshRoast SR500 roaster after reviewing this post.

At this time I’ve written a significant amount of code that in simulators appears to operate in the proper voltage ranges and will turn on and off the heat and vary the speed of the fans.  Once I get the ability to start purchasing some of the devices and equipment necessary to build a prototype making circuit boards and programming the actual processors etc I will begin to blog about that as well.  For now I will write about what makes the SR500 work and my impression of what it does…

The Brain
Obviously the roaster has a fan, a heater, a roasting chamber, a chaff collector, a two number display, a switch, and fan speed knob.  What is not so obvious is what makes it work on the inside.  What you find inside are two circuit boards.  One has the knobs and switches connected to it.  The other board has all the power connections on it.  The control system for the knobs has what most people would refer to as “the brain”.  This is a 20 pin Atmel processor connected to a 12MHz oscillator running with about 2K of memory available to it.

Alternate view NTC Thermistor, ATmel AT89C2051-24PU

Next to the processor is a plug marked “NTC” where this is connected to a NTC Thermistor.  This is a type of resistor commonly used to test temperatures.  They typically have a narrow range of temperatures they operate in  but they are quite effective for the price.  The NTC is attached to some of the pins on the Atmel processor allowing it to sense temperature by measuring the electric resistance which changes with the temperature.

The NTC Sensor
Without knowing the specific NTC I cannot tell you how exact the temperature sensing is but while noticing that the switch has a high, medium, and low.   The temperatures listed by the manufacturer that it runs at are 490, 455, and 390.  These are 35 and 65 degrees apart from one step to the next.  This is a very large difference in temperature meaning it does not have to be very precise to tell the difference from one another.

The sensor is mounted in the path of the heater’s air.  You can see it through the grate at the top of the roaster.

NTC Thermistor mounting

As a result of the placement of the sensor this can measure how hot the air is coming off of the heater coils.  It does not get wired directly to power anywhere along the way.  Instead it connects directly to the Atmel processor which then feeds out to a MOC3043 Zero-Cross Opto-Isolators TRIAC Driver.

Left of High voltage board.

The MOC TRIAC is a special type of chip that isolates DC voltage from high voltage AC typically.  It often figures out when the AC voltage crosses zero volts.  In the US power runs at 110/120 volts and 60Hz.  Hz is a “times per second” rating.  In Europe the power tends to be somewhere in the 220+ volt area but at 50Hz… most parts in the roasting equipment are rated at either 400V or 250V so that it can be adapted to run using US or European (and other areas of the world) voltage without changing too many parts.  The Zero-Cross part of the chip helps to determine when the AC voltage goes from 0 volts up to +110/120/220/240 for example and then back down to 0 volts and then down to -110/-120/-220/-240 volts and back to 0.  That 0 to +volts  to 0 to -volts  pattern occurs 50 or 60 times per second or twice that when you just look at hitting the peak voltage from 0.  Effectively what happens when you try to “dim” the power (fan speed control, temperature control etc in some cases) it often is controlled with this sort of circuit.  In that sort of circuit (in otherwords) what happens is when you say run at 50% you let it go from 0 to +110 (0, 10, 20, 30, 40, 50, 60, 70, 80, 90, 100, 110)  and then immediately slams it to 0 instead of rolling it down gradually (110, 100, 90, 80, 70, 60, 50, 40, 30, 20, 10, 0)  and then repeats it for the negative voltage.  Every time a MOC with Zero Cross connected to some TRIACs detects 0 point it gets reset and timing triggers occur to start over on the dimming at the appropriate points.

In the middle of the board are two devices that could be a TRIAC or a DC voltage regulator.  There are also numerous devices that could be TRIACS scattered over the board too.  The larger devices are attached to a large heat sink to keep them cool since they tend to generate a lot of heat.  Since I no longer have a multimeter to test some voltage I cannot determine whether the output of these devices are AC or DC voltage but there is obviously devices on here for creating DC voltage as well as those for switching and/or dimming AC voltage.

Fan, Bridge Rectifier KBPC606

This is one example of a place where DC voltage appears in the system.  Without being able to fully trace all of the wiring yet since this effort was only for a quick inspection and not to dismantle it I cannot see where this comes from and goes to but ultimately such a device (the black box) would normally take power coming in on two pins and through a series of diodes inside convert coming out the other two pins to DC voltage.  I am not sure where the fan knob (which connects to the two pins next to the MOC chip I believe)  is ultimately getting voltage from and whether it is AC or DC and if it is a lower voltage or higher one etc but it obviously controls some sort of dimming to this fan that apparently has AC voltage coming to the rectifier being converted to DC as it goes in.

Soooo… in the mean time I need to obtain a few things to get started….

  1. PIC Microprocessor and/or development kit – I have decided I will be using a PIC micro-controller for this project.  At the moment I am working on a simulated PIC18 but will probably move to a PIC24 and perhaps if I can get a development kit circuit board will use the new PIC32 to allow for some “additional” ideas I have for the roaster and perhaps some “accessories” to make it even more useful than “just” roasting.  I had started with a Basic Stamp 2 series microprocessor and quickly overwhelmed it quite some time back and then began learning PIC microcontrollers.  At this time I can only use a PIC32 if I can get a physical chip and board to work with.  PIC24 options are very limited in the simulation and will likely be a stage before reaching the PIC32 physical hardware.  If I can get the right development kit I can swap the PIC24 and PIC32 interchangeably on the development board.
  2. A lot of connectors similar to those used on the Fresh Roast boards pictured above.
  3. A replacement Multimeter since I no longer have mine… I had a rather substantial professional quality one but after several moves it was lost.
  4. A “rework” or “reflow” capable soldering system. These are typically used when prototyping SMD/SMT and high density chip based circuits.  There will be many miniature resistors and other devices that are actually soldered to the surface of the circuit boards rather than installed through holes.  Some of the communication types and chips for many of the sensors and devices require enough pins (or just that ultimately are not available any other way) that surface mount is the only option.  Many of these devices are extremely small and the simplest way of mounting them involves Infrared pre-heaters or hot air soldering and desoldering techniques.
  5. Real Time Clock chip.  Used for realistic good time stamping and tracking of the roast including the actual date for…
  6. Ethernet chipset and connectors. To allow a log tracking the roast information to be accessed from your computer including details form the …
  7. K or J Thermocouple and management chips to enable the PIC to know the various temperatures logging and responding to them from the air, the bean mass and other locations to control the heat and fan speeds as well as to…
  8. Display the results on a LCD Screen in real time to allow you to access a….
  9. Control interface such as buttons or touch device to configure the roast or select  a stored profile speeding things up or slowing them down or changing the temperatures etc in real time as well as access profiles or other details in
  10. Built in Flash memory or possible….
  11. SD Memory slot to transport profiles to the roaster or to archive them.
  12. Various power control parts such as TRIACs, IGBT, etc for phase control (dimming/speed control)
  13. PCB manufacturing materials such as photosensitive boards, chemicals, trays, transparency, etc…
  14. Small precision drill press to place any required through holes in circuit board too to allow “test” prototypes to be built
  15. PCB Vendor to produce a permanent solution once the prototypes are complete for me to transfer everything to since I need a couple of these for my roaster, my girlfriend’s roaster, and probably one for my landlord who is addicted to good coffee now and will end up getting her own eventually when I need to move out 😛
  16. Eventually I’ll need to figure out what sort of box to put it all in.

At this point I’m pretty confident I’ve identified all of the required actual components at least in general.  I need to finalize the power control requirements with a multimeter figuring out what all the actual roaster parts need/use and select those final parts and do some testing with lightbulbs and fans before I start connecting them to the roaster as well as do some testing of actual temperatures being put out by the SR500 as it comes from the factory.  Once those are finished I need to finalize the method of configuring the profiles using the final controls and display and I’m pretty much set.   I have not interfaced SD into the circuits yet but the communication systems are already there for other sensors.  The “file system” will be a bit of a problem programming FAT/FAT16/FAT32 into it due to some apparent Microsoft thing *makes rude gesture* so I need to look into that some more.

Theoretically I have a functioning controller in simulator.  It does not currently access AC voltage directly in the simulator though because I still need to determine the actual voltages being used to establish the amperage requirements of the various parts.  One area that is confusing is on the bottom of the roaster it shows 1600watts.  Well it’s a small fan and a heater coil and a TINY bit of electronics that uses less than an amp for that last part.  The fan seems to be deriving power from a plug marked 100W as shown in the “Left of High Voltage Board” photo.  Where the real problem comes in is with the heater causing the most concern.  You would assume the heater was 1400 or 1500 watts on its own with the unit showing 1600 watts on the bottom.  When you look at the board though….

1000W to heater coils?

Oh… and that device marked Q5 below it.  There’s a similar one next to it to the left.  That is one of the devices I have not determined exactly what it is yet.  There appears to be no identifying marks on it for a part number.  It might be creating DC voltage as a regulator or it could be one of many types of TRIAC.  The white stuff is a typical lithium thermal grease like the use on computer CPUs to make sure they don’t overheat by having a good thermal connection to the heatsink.  In this case some regulators depending on the voltage and amps or and pretty much most TRIAC dimmer devices generate a LOT of heat.  I’m thinking it’s a TRIAC due to the Q numbering being used since a voltage regulator typically uses a U number pattern.