HT Roaster Interface devices

[JimG]

A new gizmo for messing with your Hottop roaster has finally escaped my basement.  Think of it, maybe, as "milowidget lite."

The devices are optimized to work with Tom Coxon's RoastLogger software, which allows both monitoring ET and BT, as well as control of the roaster's heater and fan.  Tom's method for semi-automatic roasts on the Hottop works very well for me and is fully supported by the new interface devices.

The gizmo comes in two forms:  1) as a shield that can be stacked on an Arduino/TC4 combination, or 2) in a form that can be either piggybacked on to a TC4C, or connected using cables only.

For several months now there have been prototype versions out -- and the devices have been improved greatly as a result of reports and suggestions from the testers (thanks Tom and Randy, in particular).

Here is a link to a pretty crude web page that attempts to describe the new interface boards:
http://www.mlgp-llc.com/htri/index.html

Randy is working on an excellent user guide (I have seen a draft).  But for the short term I hope there is enough information on the web page to at least get the word out.

Jim
 

[smico]

I was lucky to be beta tester of the Jim's widget on my Hottop B2 and I already posted here, in different thread, my satisfaction with it. This is perfect external heat controller for HT as it preserves all original safety features, with flexibility of unlimited number of profiles.

And profiles for the HT interface in Roast Logger are ingenious.  They exactly follow my thoughts during the roasting: before first crack I change heat and fan on target temperatures to get desired roasting curves. After first crack, I count seconds, change heat and fan and finally eject at certain times.

I am sure Jim will answer all your questions, but if you want to hear my experiences from daily use, fire away any question here or through PM.

If you live close to Montreal you can swing by my place to see the HT Interface live, or we can test it on you very roaster to help you make educated decision.

Regards
Miroslav

[JimG]

The HT Roaster Interface Users Guide version 1.00 is now available for download.

Thank you to Randy for another excellent piece of writing, and to Tom for his helpful reviews and comments.

Jim

[JimG]

There have been some ground loop and noise issues with the TC4 system, but that is unrelated to the new roaster interfaces. 

With the TC4 system, when there are problems it has been associated with grounded thermocouples.  What I think happens is that the roaster frame is floating, i.e., not earth grounded.  If you measure the voltage between the roaster frame and earth ground with a DMM you will read a pretty high number -- usually 50 to 80 VAC.  If the TC4 is powered by an AC source (like a wall wart or USB cable), you will measure a similar voltage difference between the GND plane on the TC4 and earth ground.

When you use grounded thermocouples then these two big voltages "meet" at the chip that reads the thermocouple signal.  The chip takes a dim view of any voltages over 2.0VDC, so the readings get very flaky.

The best solution is to completely isolate/insulate the thermocouples from everything (except of course the TC4 or other measuring instrument).  In particular, there should be no path from either of the thermocouple wires to earth ground or to the roaster.

A solution that has also worked is to tie the roaster frame to the GND plane on the TC4.  This forces the roaster frame, thermocouples, and TC4 to all be referenced to the same voltage.  On my roaster I used a series 1K resistor to give a little protection to the USB port on my computer.  A 10K series resistor is probably safer.

For some reason, the thermocouples on eBay with all of the braided shielding have really been a problem.

Jim

[smico]

HTC is the coolest Hottop roaster device ever. 
The main reason is that now I save Heat-Fan settings in RoastLogger for every roast, along with log, and I can re-roast the same beans and get identical results.

Heat-fan settings for Java Jampit that I roasted yesterday, and just repeated roast today for a friend.  Curve was followed almost perfectly.

@actionT1Table
100|90|20
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152|55|45
165|90|20
180|50|50
185|60|40
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@actionSecsFCTable
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@actionResetTable
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@loadBeansTable
160

[JasonG]

There have been some ground loop and noise issues with the TC4 system, but that is unrelated to the new roaster interfaces. 

With the TC4 system, when there are problems it has been associated with grounded thermocouples.  What I think happens is that the roaster frame is floating, i.e., not earth grounded.  If you measure the voltage between the roaster frame and earth ground with a DMM you will read a pretty high number -- usually 50 to 80 VAC.  If the TC4 is powered by an AC source (like a wall wart or USB cable), you will measure a similar voltage difference between the GND plane on the TC4 and earth ground.

Wow is this ever true. Quite fiddly and awkward when things stop monitoring mid-roast!

[JimG]

Fortunately there are a number of good solutions that allow you to avoid the problem altogether.

Jim