Heatermeter Aux. Thermocouple And two probe board V6.1(Final Version)


John Bostwick

TVWBB Wizard
Hey guys, I was wondering if any of you knew what is the best place to jump to the thermocouple output on the HM board? I assume I should do it to one of the pins on the AT Mega?


Ralph answered your question, but I wanted to say if others read this before they make their build. I have heatermeter boards that are designed to eliminate all wires. You can solder a small switch directly to the heatermeter boards.

I dont have it posted on OSH just yet, though.

Danny C

New member
Ralph answered your question, but I wanted to say if others read this before they make their build. I have heatermeter boards that are designed to eliminate all wires. You can solder a small switch directly to the heatermeter boards.

I dont have it posted on OSH just yet, though.

Thanks, I'll keep this in mind. I may give this heatermeter to my father in law for his bday.

Dominick A

Ralph - do you have better close ups of the pictures you posted on page 39 in the Roto Damper thread? I think I'm good with everything on the RDTC board, except I can't see exactly what is on the board showing how the servo and blower are connected. I ordered all of the parts earlier listed earlier in this thread, but can't see how they go together.


Also, are the reference voltage parts already included in this project, or would that be something different? I'm a midwest guy and it would be cool to see sub-zero temps even if I'm not grilling.
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Dave Smith

TVWBB Super Fan
should be marked on board which is what.


TVWBB Diamond Member
The other side of the board has the labels for the header, because the header sits there in that box and it would cover over the labels after it is installed.

Dominick A

The other side of the board has the labels for the header, because the header sits there in that box and it would cover over the labels after it is installed.

I know they go in that spot, I just couldn't see how the connections are made. I've got the TE Connectivity parts, just wanted to be sure I used them right.


TVWBB Diamond Member
Oh, sorry, I was confused and thinking Dave was saying there should be labels on the board there.... I didn't realize he was responding to your question....

As for your question... I am not sure I am clear exactly what you are asking, so I will just elaborate a bit about the header and how I use it...

There are 6 pins, the servo takes 3 and the blower takes two, leaving one unused pin in between them. I generally do not install the pin in between so the header has a set of two pins and a set of three pins. This makes it very easy to see where the servo plugs, obviously the side with 3 pins. Also, we purposefully put the GND pin for both the servo and the blower on the OUTSIDE PIN. So now you can see easily which side the servo and blower plug (because of 2 and 3 pins) and also know that the ground on both of them go to the outside pin. No labels needed once you look at it that way.

As for header style and use, it may vary, I don't think JohnB and I do things the same. I use a right angle header with the pins horizontal across the board, I think John may use a straight header and let the pins stick upright? You can really do it any way you want, including not using a header at all and soldering the wires from your blower and servo right to the board. Any way the header fits into your rig is fine, straight, right angle, top or bottom of the board.... There is really no right and wrong way to setup the header, it's whatever works for you.

As for the REF offset parts, IDK if they are on the basic BOM or not, chicken and egg here, I got my parts before there was a BOM. But from memory an OP Amp IC, a 1M resistor and a trim pot are the unique parts for the REF Offset circuit. The trim pot is a white box with 3 legs with a screw slot adjustment on it. If you've got that then you probably have all the REF Offset parts. If you don't have them and want them shoot me an email at rotodamper AT hotmail DOT com, I might have the parts here and could send them along with OKI board when I ship that to you.
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TVWBB Diamond Member
Dominick, what did you find on the REF offset parts, do you have them or need them? I have them here if you need them, shoot me an email if you could so I know whether to ship out your OKI alone today or if you need the REF stuff too...

Dominick A

Looks like I have what I need from Mouser:
TC AMP (P/N 584-AD8495ARMZ)
Prec RRO SGL Supply (P/N 584-OP777ARZ)
0805 1Mohm 1% Tol (P/N 756-WCR0805-1MOFA
1/4" SQ 100K 10% (P/N 3361P-1-104GLF)


New member

i was wondering if someone would sell me one of these boards? paypal ready.

i figured id ask here before placing an order for 3....



TVWBB Diamond Member
I put together a v6.3 (RDTC) board today and took pics along the way, I will attempt to put together a bit of a build guide here as requested. There are many ways to go about this, you could use solder paste and a hot air soldering gun or a reflow oven, or specialty small soldering tools etc, this guide will cover how you can do it with average stuff you can get at a radio shack type store.

Before I begin the build I should note on V6.3 we added a space for a Standard Pit Probe jack. This means you can use this board without any of the SMD components installed to wire a Roto Damper for a Standard Pit Probe, Two Food Probes and CAT5 jack, as well as connect the blower and servo using the header on the RDTC board. So you can use this board as an alternate to the hand wiring method using the punch down CAT5 jack from Home Depot. It will cost more but is easier to assemble.

First thing to do is clean up the board. When you receive the board from OSH Park there will be little sections on the edges from where the boards were attached for manufacturing. You should clip/file/sand them way until the edges of the boards are even, as shown in the board on the bottom in the following picture. If you don't do this they may interfere with fitting the board in its case (btw, you should do the same on your HM board before you build it)


Here is a pic of the tools I used to do the assembly. A standard Weller 25 Watt soldering iron, thin solder, solder wick, and flux, as well as some tweezers and a pick to help with placing the very small SMD components. I also wore a magnifying visor that I got from Harbor Freight for about $3 bucks so it was easier to see when working.


I put a thin coating of flux on the board and then placed the TC amp IC in place, noting the dot on the board and the IC which is in the upper right corner in the picture below (though not visible at this resolution). After I lined up the IC on the board I soldered one corner leg in place, which you can see in the following picture. After you tack down this one leg make sure the IC is still aligned, if not then reheat the leg and nudge the IC into position.


If you have a very fine soldering iron tip you can attempt to solder one leg at a time and do it cleanly (without creating solder bridges to the adjacent legs). I have done it before but it is extremely difficult. I find it easier not to worry about the bridge, I still solder each leg individualy and try not to flow too much solder to each leg, but don't worry too much about the invitable bridge across all 4 legs as shown in the pic below:


It usually works out quite easily to remove the solder bridge and excess solder using solder wick as shown in the pic below. I first dip the wick in flux (and wipe leaving a thin coat over the entire braid) then place the braid across all 4 legs of the IC. Press the soldering iron down on the braid somewhat horizontal across the IC legs and the wick will get hot, flux will melt and the excess solder will be drawn up from the IC legs. In the picture below you can see the top row of legs has been cleaned up in this manner already, and have things in position to do the bottom row.


After you get all the SMD components soldered on the board you can test the TC amp with the same procedure detailed in the HM build guide. I tend to prefer doing a quick continuity test on the IC after I have done the soldering and cleanup, making sure the IC legs have continuity to the right places and there are no shorts between the legs. Below is a pic of the RDTCv6.3 board that I have added a color code to, showing the nearest direct connections to each IC leg. You can use this to make sure the IC legs are soldered well to the board and having continuity to the nearest connected component, and you can also use it to make sure the adjacent IC legs are not shorted to each other. It's easier to test for shorts between the legs using the larger solder pads for resistors/caps that have the same color as shown on the IC legs (instead of trying to put meter leads on two very tiny legs right next to each other on the IC). Note that two legs (yellow) are connected together (bridged by a trace on the board), and the one leg with the X on it is not used, so you don't have to worry about bridges in those places.


After the IC is installed and tested as above it's time to install the SMD Caps and resistors. I did them in this order:

3X .1uf caps
2X 1nf caps
1X 10nf cap
2X 10K resistors
1X 1K resistor
1X MCP1700 3.3v Regulator
1X 1M resistor (Optional, only if installing REF offset circuit)

I find it easiest to place the parts with tweezers, when oriented properly press them down on the board a bit, this seems to help hold them in place a bit (they kinda sink into the flux that is on the board). Then I lightly solder one side of the component, if it moves out of place reheat the solder and use the pick or tweezers to push the part into place, let that solder cool briefly and then solder the other side of the component. Here is a shot of the board with all the SMD parts in place.


The board looks a mess with all that flux, particularly with all the reflection in a picture, but it cleans up really nice with a little isopropyl alcohol and a soft bristle brush.


The TC circuit on the HM bottoms out around roughly 37F, so the HM will just flat line at 37F no matter how cold the TC gets. If you live in an area where it gets sub zero and want your TC to have the ability to measure lower temps you can install the REF Offset Circuit. I should note, the HM/RDTC will function fine without the REF Offset circuit even in sub zero weather, you will just not be able to see the actual temperature when it is below 37F.

The REF Offset circuit consists of the OP777 Op Amp, the 1M resistor, and the trimmer potentiometer. The OP777 IC is on the other side of the RDTC board. It has a bit more space between the legs than the TC amp so it is much easier to solder, you shouldn't have any problem getting this done without solder bridges. Note the dot on the lower right corner of the part and on the board for orientation. Here's a pic of the OP777 installed.


With the REF Offset circuit installed, when the trim pot is fully counter clockwise the TC should read actual room temperature, as you rotate the trim pot clockwise you will see the temperature reading on the HM for the TC rise upward a bit over 100F at max. To set the offset decide how low you need the TC to register first. If you want the TC to register to 13 below zero, for instance, use the REF Offset Trim Pot to raise the TC temp 50F (37 + 13) and then in the HM Config for the TC set an offset of -50F. After you change the offset setting in the HM config the TC will show proper room temp and will now register temps down to 13F below zero. (50F below the normal low end reading)

If you are not installing the REF Offset circuit you can omit those parts and just make a solder bridge across the solder pads labeled REFG. Also note, if you are not using the REF Offset circuit you don't have to worry about cleaning up a solder bridge between the green and purple legs of the TC amp IC.

That covers all the SMD work on the board, I will continue in the next post with installing the larger pieces of hardware to finish the board. (I have hit the limit of pics I can include in this post)
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TVWBB Diamond Member
Here is a pic of the board with all the larger pieces of hardware required. The RDTC board uses the same CAT5 jack and TC Jack as the HM board, the Food Probe jacks are NOT the same as the HM board however.


I tend to install the larger parts in order of height from short to tall, so I can press them against the table while I solder to make sure they are seated fully against the board. (this helps the board fit the case easier) The TC jack is very close to the food probe jack next to it, if solder runs to the top side of the board on the staple-like retainer it can prevent that food probe jack from seating flat on the board. If this happens use solder wick to remove the solder there and make sure the food probe jack seats flat on the board before you solder it in place. The following pic shows the excess solder on the staple-like retainer, you can see the dent in the solder where the food probe jack was biting into it. I removed solder there before I put the food probe in place.


After the TC Jack I install the food probe jacks. Solder one leg, make sure the jack is seated flat against the board, then solder the rest. Finally, install the CAT5 jack using the same method. Your board is basically finished now.


The last thing that needs to be done is connect the blower and servo to the 6 pin header. The easiest way to do this is to cut the wires and solder them directly to the board. The holes are labeled on the board showing what wires go where.

You can optionally install the right angle header on the board so you can use the connector on the servo (and add a 2-pin connector to the blower) so you can plug/unplug these items. If you are installing the right angle header, first trim the food probe legs down as close to the board as possible. The header has one extra pin purposefully, two pins for the blower on one side, 3 pins for the servo on the other side, with a dead pin in between. I like to remove the dead pin from the header before I install it, this way I can tell very easily how to plug in the blower and servo. 2 pins for the blower, 3 pins for the servo, with the GND being on the outside pin for the both of them.

Install the header so the pins just barely protrude from the other side of the board, solder both sides of the board for extra durability. Put the servo plug on the header, bend them up slightly if the connector wont slip past the food probe legs below. The legs on the header are a bit long and they will make the servo plug protrude beyond the edge of the board as shown in the following picture.


The servo plug will interfere with the case if it overhangs as shown above, so trim down the header legs a bit as shown in the pic below.


You can also see the REF Offset Trimmer Potentiometer in the above pic, I think I forget to cover installing that. previously. That part remains in the clear when the board is finished, so you can install that last. It is very easy to solder in place, I solder the single leg first, re-align if the other 2 legs are out of place, then solder the other two legs in place. Again, make sure this part is flat against the board and inside the box outline on the board for the part or it may interfere when installed in the case.

Here are a couple shots of the board going in the case.


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Tim Loftus

TVWBB Member
Thanks for the write up on this Ralph! I want to build one of these soon. I am just holding off as I hope to sell my house and now sure if one would be viable in the new house. I hate to hold off as my current house is set up perfectly for one of these. my heater meter could set in the garage and just have a cat 5 cable running to the aux board.


TVWBB Diamond Member
You're welcome.
Just FYI, in my experimentation the CAT5 cable length can run about 50Ft or so before it starts effecting things.

John Bostwick

TVWBB Wizard
I'd love to see a version of this with all thermocouple probes.

You could possibly have 3 thermocouples but using a cat5 cable that's the maximum. The time involved to make the board and the added cost for the thermocouples would neglect any advantage.