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4-channel TC meter and datalogger project

I've seen some mention of meter and datalogger projects recently, so I thought I may as well jump in too.

I'm taking a modular approach, so folks can pick and choose what features they want and omit features they don't want.

Main features
1. Arduino-compatible platform
2. 4-channels. May be downsized to fewer channels and save on connectors if you prefer.
3. LCD and some buttons, for standalone operation
4. Rise-per-minute display, per channel
5. Enclosure: Unknown. suggestions welcome.

Datalogger - not required, but could choose from:
1. local storage - flash memory
2. wired - usb, serial, ethernet
3. RF: radio, bluetooth, wifi, etc.
4. SD card

1. graphical LCD display
2. overlay of desired roast profile
3. PID option
4. tweet your roast
5. text your roast
6. webcam

Comments welcome. -bill
My current project won't need it, but the next one will.
Interested to see more.
Help me to understand '4 channels'. (i'm currently still in the world of thermometers).
Randy G
If bluetooth were implemented and it was bi-directional then there would be little or no need for an LCD display since all parameters could be remotely dealt with. The benefit is that a bluetooth dongle can usually be had for less than $5 so can easily be added to a notebook. Would also eliminate all but maybe one USB port. This would make the packages more compact and robust. ET and BT would be great, so really, two channels would be sufficient for most folks. Larger roasters would probably like a third for exhaust temperature.

That would make a great monitoring device, depending on the software that came with it. Now, if it had proportional output control, then it could control the roaster remotely as well... Two proportional (heat and fan) and one binary for eject/end roast. That could come in V.2.

But I can contribute with testing as well as writing the manual for it (I have a lot of experience in that area). AND.. I have a spare Hottop (how many people can say that? LOL) which I could use for a testing unit...

We could package the entire thing, sell it, and use the profit for Coffee Kids... just a thought.

Life's too short to drink bad coffee.
Hi Scott - by 4 channels, I just mean you could monitor and/or log 4 temperature probes at the same time.

Randy - thanks for your interest, I'd like to hear more of your ideas. While I like the idea of realtime data between the 'device' and a computer, some folks may want a nice standalone unit. Handheld is possible in fact.

Bluetooth is fine, but might involve 'pairing' and so a minimal display might be called for, although admittedly BT mice get by without one.

When you talk about the 'software', are you talking embedded software or PC/host computer software? I can do both, but enjoy the embedded side the most.

Licensing- I'm thinking of this as an open-source project, with MIT software license and CC-BY for hardware.

Edited by bvwelch on 05/13/2010 7:17 PM
Randy G
I was thinking about PC/host software that could take the data in real time, show it on a graph, and save it in a file (comma delimited, open source format. My thinking is that the device could then be built INTO a roaster with minimal (or no) external evidence that it existed. Power up the roaster and the host recognizes the BT. As far as embedded software, I am clueless, and even less helpful writing it.

But a stand-alone device could also work. My head is swimming with possibilities at the moment. But since I do not know the capabilities or limitations of the device it is hard to make a wish list.

My skills are in teaching, writing, document creation, and photography. I created the Hottop owners manual and the entire Hottop USA website and I wrote the Vibiemme Domobar Super owner's manual. [I like to think] I am very skilled at creating and documenting step-by-step instructions. It's waht folks tell me, anyway... :)

Life's too short to drink bad coffee.
Hi Randy,

Putting one of these inside a roaster is great. It simplifies things as you say. We can do standalone also. Both approaches have many common building blocks/modules.

The PC/host software is great too - I can provide a functional program but I'd welcome someone else who enjoys/excels at desktop software to take on that task. Again, we may be able to use much of the PC software for both scenarios.

I'd say, go ahead and 'brainstorm' what you might want to see, in terms of functions that would be embedded inside the roaster or in a stand-alone device. There is a wide range of 'horsepower' available that is 'Arduino compatible', so really the sky is the limit. -bill
Edited by bvwelch on 05/13/2010 8:28 PM
I have only had a bit of a read about the Arduino board over the last few weeks and it ticks most of the boxes for flexability and externally modding.

Stand alone roaster with displays, keypads storage etc will simply up the costs so go the PC based control I reckon. We all own one if not more or a laptop these days and any old P2 or P3 with XP for a platform would be a good place to go. If you need to buy one they are as cheap as chips too, the last 2.8Gig machine I got was $150 locally including a flat screen etc. I doubt you could do the LCD keypad storage etc for much under $100

Data transmission wise Bluetooth is the obvious way to go simplier and cheaper than 2.4G but I would allow on the board a mini USB plug for debugging if required or some may even like the wired option.

If you then wanted to "add" the stand alone capabilities as an option then that should be considered as an extra rather than as the stock version. SD card for storing programming, profiles etc, simple LCD 2 or 3 line display and a small keypad should suffice with all the profile changes or logging data being done on the PC then uploaded to the SD card by bluetooth or directly.

some random thoughts based on the KISS principle for a start :)
Edited by beanflying on 05/14/2010 12:50 AM
My name is Tim and I have a coffee equipment addiction problem :)

Two Hottops - modded
TJ 067 Electric 1kg 5+years old
Insert new 5-8kg Roaster here urgently BBQ grill
Thanks for all the good feedback.

The standalone mode is of interest to me, in particular the rise-o-meter idea that Farmroast and others are doing, so that is what I am working on first. The UEi APOLLO II DT302 and DT304 are popular handhelds so I'll be mindful of their costs and features.

With a modular approach, you won't have to pay for things like LCD, keypads, storage, etc unless you want those features.
I'm watching & waiting. The rise-per-minute is very appealing. Would you be able to have a deltaT between whichever probes you select, like [(environmental temp)-(bean temp)], and work that into a profile...


Edited by seedlings on 05/14/2010 7:51 AM
Roaster: CoffeeAir II 2# DIY air roaster
Grinder: Vintage Grindmaster 500
Brewers: Vintage Cory DCU DCL, Aeropress, Press, Osaka Titanium pourover
Adding to the wish-list; Has anyone taken a stab at monitoring pressure? It would make a big difference for the next project. -Scott
Pressurestats I've worked with output in resistance... Surely the audrino could handle that?


*edit, correct term is 'pressure transducer'
Edited by seedlings on 05/14/2010 11:09 AM
Roaster: CoffeeAir II 2# DIY air roaster
Grinder: Vintage Grindmaster 500
Brewers: Vintage Cory DCU DCL, Aeropress, Press, Osaka Titanium pourover
Hi CHAD, thanks for joining in - please go into more detail about your deltaT idea.

And by the way, I'd appreciate your insights on the 'user interface' for those PID units you've got. Eventually we'll need those things unless folks are willing to sit at a computer and make adjustments. How big are the displays? Actually folks will be able to pick their favorite LCD, up to a point, but some software mods may be required now and then.

I did the boiling water test yesterday, so today may be a good roasting day.

Also, what's your preference on TC connectors? Right now I'm using screw terminals, but I notice some other guys are using the blade-type connectors from Omega. I'm thinking to go with the screw terminals - cheaper.
What's a pressurestat? Links? manual?
Randy G
The pressurestat would be used to control boiler temperature by monitoring the pressure. Not applicable for the roaster plan...

It seems we need to define the levels of application and function, and then decide which way to go. I will brainstorm a bit here.. "Let's throw some beans into the grinder and measure the crema..."

I was thinking about this device last night. It is only worth its weight in transistors if the device to which it is connected gives the user some control over the heat source. This revelation comes from some recent experiments I have been doing with the Hottop KN-8828P. It electrical heating element, as controlled by the programming, is binary. When it reaches the currently programmed temperature he heating element turns off, and the ET drops quite a bit, and is slow to recover. So much so that unless this project can be created in a way to totally control the roaster it will have little value. The KN-8828B controls the heat through wave form modification and so has incremental control over heat and so this project would have value with that roaster.
I do not know what other roasters do so others will have to comment. I suspect that the "B" Hottop is the only home electric roaster that does this.. My point? If your roaster does not have variable control over heat then the best bet is to either modify it so it does, or just add a digital thermometer:
Like THIS display with THIS Thermocouple.

basic, minimum requirements for all levels:
- real-time, two channel thermocouple monitoring (ET and BT)
- display rate of rise (third display line or with button press)
- USB for programming or streaming of data to PC.

Level 1 - Project-box, external mounted. Display of two concurrent temperatures.

Level 1a - as level one, but built-in, with the display on the roaster.

Level2 - add Bluetooth to the above with various abilities of PC software to be discussed later.

Level 3 - add ability for device to control the roaster (specifically, incremental control of heating element).

Others- please add to this or modify it. It is just a beginning outline (brain flatulence).
Edited by seedlings on 05/14/2010 10:51 AM

Life's too short to drink bad coffee.
Actually for roasting, the pressure monitor before combustion as well as below the bean mass would be very helpful. I'll keep my fingers crossed. -Scott
Hi Randy, thanks for the good feedback.

I'd like to amend your Level2 to just say "wireless" Bluetooth may be best, but there are other wireless options I'd like to explore. Bluetooth can be pricey on the embedded side, and problematic on some computers.
Edited by seedlings on 05/14/2010 10:52 AM
I should have said "pressure transducer." Pressurestats have on/off at a set value. Looks like they can output voltage or current (the resistance application I used was telephone related).

DeltaT might be a misnomer. If you want to prevent divots, say, you might want to keep the difference between ET(environmental temp) and BT (bean temp) to a certain maximum. If you start with 600F air, that's a difference of 540F. With a DT set to 250F, then the air temperature would stay no more than 250F above the bean temp, until the final ET is reached. It's another way to profile that I've been thinking about. Change DT for a different profile. Longer? Lower it. Faster? Raise it.

Edited by seedlings on 05/14/2010 11:01 AM
Roaster: CoffeeAir II 2# DIY air roaster
Grinder: Vintage Grindmaster 500
Brewers: Vintage Cory DCU DCL, Aeropress, Press, Osaka Titanium pourover
Randy G


bvwelch wrote:
Hi Randy, thanks for the good feedback.

Go to eBay and look up seller procon-products or procon products and check their store. Thay have a thermometer display unit for about $20 using K probes (screw terminal). It's cheap weay to add a temperature display.


Edited by seedlings on 05/14/2010 11:10 AM

Life's too short to drink bad coffee.
Sounds good CHAD. We can start by just displaying the info. Any thoughts on the display format? LCDs are available in all sorts and sizes. Example: 2x16, 2x20, 4x20. If you're like me, you want all the info available during the roast, without having to push buttons.

Make a little sketch of what you'd like to see by default. Sounds like 2 channels is sufficient, so we can show ET and BT, and the temp rise for each, and the delta/difference between the two, and may as well have elapsed time on-screen?

I was also thinking of having a BT 'profile' that you'd manually follow at first ( you are the PID :-) So you'd want to see that 'delta' also...
Pressure transducers- which ones from that Omega link are most useful for your roasters? I think we can handle any of the output they mention: millivolts, volts, or 20mA.


bvwelch wrote:
Pressure transducers- which ones from that Omega link are most useful for your roasters? I think we can handle any of the output they mention: millivolts, volts, or 20mA.

Looking through, I believe they're cost prohibitive.

Roaster: CoffeeAir II 2# DIY air roaster
Grinder: Vintage Grindmaster 500
Brewers: Vintage Cory DCU DCL, Aeropress, Press, Osaka Titanium pourover
Randy G
How would one make use of pressure display or control when roasting?

Life's too short to drink bad coffee.
Speaking for myself, pre-combustion pressure would relate to combustion efficiency.
Below the bean mass; Reducing air flow thru-out the roast is just a reality. I currently monitor that visually or by sound . There is likely a pressure that would be most efficient(depending on RC design). At least monitoring
would be helpful. I haven't got my head around the auto-control yet.
Reducing air flow almost always requires a drop in throttle.
Maintaining the balance automatically would be handy.
Randy G


freshbeans wrote:
Speaking for myself, pre-combustion pressure would relate to combustion efficiency.

Ahh.. so we are talking about gas fired roasters (Probat ..

Interesting. I have no personal experience with gas fired roasters, so this is interesting.. I wonder what would be better.. pressure or air flow? I would theorize it would be the one with the easiest to install, lowest-maintenance, and least expensive transducer.

Would possibly work on the Hottop since the fan speed can be adjusted. Could help compensate for the age and efficiency of the filter medium.

Life's too short to drink bad coffee.
I'd like to think pressure. As the beans loose wieght,they offer less back-pressure. That's the point where air-flow gets dumped(or blower turn-down) to keep the beans from flying.
Looking forward to the developments! -Scott
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