TC4 + HTC roast controller for Hottop available

Discuss roast levels and profiles for espresso, equipment for roasting coffee.
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Randy G.

Postby Randy G. » Sep 04, 2012, 3:55 pm

Jim has announced the availability of the new HTC Hottop interface board. Plugged into the TC4C and a few added components, you end up with a computer-controlled home roaster ("just add computer). Owner's manual to follow soon we hope. It's in the works.

In the meantime, I thought I would post some specific info on my installation...

Here is a photo of the installation I did in my KN-8828B-2K. As you can see (hopefully) there is plenty of room to mount the two boards.
1 - HTC board. A custom-designed board to create an interface and control system
2 - The TC4C board provides USB I/O and Thermocouple connection point.
These two boards are powered through the USB connection. Plug in the USB cable and control functions are through the USB. Unplug the USB and the Hottop operates as intended by the factory through the Hottop control panel as if the HTC system were not installed.
The aluminum shelf upon which they are mounted is attached through the side panel. I drilled and tapped two holes in the bracket which is pop-riveted to the fabricated aluminum shelf.
3 - Thermocouple leads.
4 - USB cable. I later removed that cable and used a "Cables-To-Go" 28071 male to panel mount cable. I installed it in the rear cover and it is the only external sign that the roaster has been modified:
5 - The two Hottop ribbon cables

Basically, you have three tasks for physical installation:
A - Install two K thermocouples (bean temperature and environmental temperature). These vary widely. I started with bayonet mounted from e-bay, but the thermocouples themselves were of low quyality. I kept the mounting but just used the leads and twisted the wire ends. These are a lot tougher than the fine-wire exposed thermocouples, faster responding than stainless covered thermocouples, yet still seem accurate enough. I inserted them through a short piece of silicone tubing so they are easy to remove for maintenance and replacement. The mounts are shown here, epoxied in place:

B - Mount the boards
C - Wiring.
i -connecting the thermocouples leads
To run the thermocouple leads I enlarged the existing opening in the frame and routed the leads under the main board. This brought them up in the rear of the roaster (as seen in thr first photo). This makes them ore accessible when connecting them. The two clamps seen here are 1/4" pipe clamps modified to hold the leads. I insulated them using insulation covering from an electrical extension with the internals removed:

ii - connecting the two ribbon cables (one from the control panel to the HTC and one from the HTC to the Hottop Main Board
iii - connecting a USB cable to go from the TC4C to the computer.
The two boards come with a few other connecting wires, and there is an LED on a long lead that is illuminated anytime the heating element is sent power. This is optional and works well as a troubleshooting device.

What you end up with is a control system that gives a repeatability and control level that is astounding.
I have only used it with RoastLogger so cannot comment on functioning with Artisan. Not brave enough to deal with the reprogramming at this point. When things settle down I will contact Jim and Tom and see about that. The programming instructions I had previously seen were unclear, and I am too busy to deal with the possibility of screwing up my control system at this time.

Being able to visually see (on a graph) what the roaster is doing in real time along with the control that this system (HTC+TC4C & RoastLogger) is addicting. I am still fine tuning (and probably always will be), but RoastLogger lets you load a previous roast's data into the graph and then you can roast "over" that for comparison as seen here (previous roast in pastel colors, current roast in dark colors):

It allows you to be sure a roast is duplicated (like when you change air filters, put in a new heating element, or are roasting somewhere with a different line voltage), and it allows you to verify programming changes you have made. RL also gives you the opportunity to save the programming and later load it, so you can have various roasting parameters for different coffees, different weather conditions, or different brewing methods, and the like.
Espresso! My Espresso!

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Postby Bob_McBob » Sep 04, 2012, 4:25 pm

Thank you for the installation photos, Randy. I'll be ordering my HTC+TC4C combo this evening. Would it be possible to see the how your thermocouples are installed inside the drum chamber? Also, do you have a specific recommendation for appropriate thermocouples and routing material?

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Randy G.

Postby Randy G. » Sep 04, 2012, 4:37 pm

The leads for the thermocouples go through the enlarged opening (mentioned in the OP) in the frame. Dremel strikes again. A bit of hand filing to radius the edges. The fiberglass covers were discarded and replaced with teh thick rubber ones shown originally in this thread.

These were the original probes I used. I did not like them so I cut the ends off, pulled out the thermocouple wires, cut the ends off, and just twisted them together. These are "stuffed" through a short length of silicone tubing and that stuffed into the tube.
Espresso! My Espresso!

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Postby Italyhound » Sep 04, 2012, 5:31 pm

Thank you Randy and Jim

Using such boards has always been the stuff of tech-tinkerers - of which I am not. I did install the TCs but that was manual labor, not actual thinking stuff like TC4s :D

With the preprogrammed boards, does this allow a tech newbie like me to use it without a problem of having to mess with, maintain or mod the electronic innards?

If so, me likey.
@evshack on Twitter

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Randy G.

Postby Randy G. » Sep 04, 2012, 5:38 pm


Jim and Tom have done all the work so installation is fairly straightforward. There really is no electronics knowledge needed beyond knowing the difference between "+" and "-" with the thermocouple leads where they attach to the TC4C board. The most difficult part (IMO) is the thermocouple installation. Everything else is just, as you surmised, plugging in of wires. The only exception to that would be the mounting of the boards inside the Hottop and the running of the USB cable out to the computer. The RoastLogger app is now well documented (if I do say so myself) using my well-known step-by-step theories of manual creation.

And really, it was Jim and Tom who did virtually all the testing, and they cooperated on the programming. The electronics are mostly Jim iirc. Me? I am just the manual-writing grunt.
Espresso! My Espresso!

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Postby GreenBean » Sep 05, 2012, 5:05 am

Thanks for starting a new thread for this Randy. :D For anyone thinking of installing thermocouples in the rear wall of the roast chamber they can find a lot of information available in various forums on how people have done this in the past. The following are a few general pointers that may be helpful:

1. Randy has shown the ideal location for the thermocouples in his photo in the above post.
2. I would strongly recommend that you insulate the thermocouples, both electrically and thermally, from the roasters frame this can save much heartache later and will ensure accurate results. This can be done by:
    2.1 Using bare wire thermocouples protruding about 4 mm into the roast chamber insulated from the frame by their own insulation or as Randy describes in his above post. They would, of course, need to be insulated with suitable material such as glass fibre that can withstand the temperature in the roast chamber.
    2.2 Using grounded sheathed thermocouples (the thermocouple hot junction is welded to the sheath) but insulate the sheath from the roasters frame. I have been using silicone tubing to do this for well over two years and hundreds of roasts without problems.
    2.3 Using insulated sheathed thermocouples (the thermocouple wire is insulated from the sheath) will provide electrical isolation but not thermal. These thermocouples are a little slower responding to temperature changes. I would still recommend thermal insulation as in 2.2.
3. If using any of the above sheathed thermocouples ensure that the sheath diameter is no more than 3 mm. Larger diameters will conduct more heat to the rear wall (even with the insulation) which will result in low readings. This is especially the case for the bean temperature thermocouple as the protrusion into the roast chamber is limited by the proximity to the drum vanes (larger diameter sheaths and lower protrusion increase the error in readings).

In case anyone misses the link in the previous thread some further photos showing the installation of the HTShield version of the HT Roaster Interface in a Hottop and links to download Randy's excellent RoastLogger user manual are available in this thread on TMC.

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Postby Bob_McBob » Sep 05, 2012, 5:21 am

My HTC+TC4C combo is ordered, and I am waiting to hear back from Hottop USA about shipping a control panel cable to Canada. I intend to place the thermocouples as shown in Randy's photos. I would definitely appreciate some specific product recommendations for thermocouples and shielding/insulation material, if possible.

Bak Ta Lo

Postby Bak Ta Lo » Sep 05, 2012, 6:01 am

Wow, this is really cool! Awesome work, if I was just now looking at getting a roaster I would get a HT, and not my Quest M3. I love the M3 but this looks really fun to play with.
LMWDP #371

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Postby iginfect » Sep 05, 2012, 8:47 am

Bob McBob asked
I would definitely appreciate some specific product recommendations for thermocouples and shielding/insulation material, if possible.

Jim Shulman in DIY tc recommended Kapton® Insulated Thermocouple Wire type K 30 gauge available from Omega Sorry I can't give the URL of Jim's post as my home computer is down where all my info is stored.


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Team HB

Postby drgary » Sep 05, 2012, 9:13 am

This is an exciting project to see as I'm finishing eliminating electrical noise in the TC installation in my Hottop. I'll be watching this thread.

What I WOULD do for a good cup of coffee!