Thermocouple board

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Thermocouple board

Postby chense » Wed Mar 10, 2010 6:47 am

Jean - somewhat off-topic - I think this concept (external board) would be good for TC (EGT) amps - imagine this: small board with 4 TC (EGT) amps, with small screw-in/push in terminals all around the board, and 0-5 V outputs.

This way, one would avoid using (expensive and bulky) special TC connectors for TC wires and one would also avoid soldering the TC wires to the board (supposedly bad because of extra transition resistance that solder introduces, this would eliminate at least one junction). And since you already have the EGT amp layout worked-out on the logger board :D.

I for one would buy one 8) . And if this new MS3 EGT fuel trim is as good as James reported, a board like that would be popular.

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Re: New dual VR board V2.0

Postby jsmcortina » Wed Mar 10, 2010 7:42 am

Something like this prototype:
100_1199.jpg
100_1198.jpg

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Re: New dual VR board V2.0

Postby chense » Wed Mar 10, 2010 12:02 pm

That's just what I had in mind. Just a little bit smaller.

Plan on doing a batch / sending it to a PCB manufacturer? (if yes, count me in for 1)

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Re: New dual VR board V2.0

Postby racingmini_mtl » Wed Mar 10, 2010 1:05 pm

Since James is not planning on doing a batch (from what he told me), I'm thinking of doing this since it does make a lot of sense both for MS3 and for the base I/O Extender board.

I'll check for the best enclosure option and I'll reproduce the same circuit as for the I/O Extender logger board. The plan is to have 4 EGT conditioners with plug in screw terminals for both the EGT probes, the outputs and the 12V supply/ground. It will have 0-5V outputs that will just need to be connected to generic ADC inputs (ADC6,7 on the MS board would require a couple of caps and a resistor but the MS3X inputs should work as is if I understand correctly the MS3 doc).

That should be quite quick to design since the only thing I need to check are the screw terminals and the enclosure.

Let me know if you have requests or suggestions. It might be better to start a new post for it though.

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Re: New dual VR board V2.0

Postby jsmcortina » Wed Mar 10, 2010 1:30 pm

racingmini_mtl wrote: It might be better to start a new post for it though.

here it is..

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Re: Thermocouple board

Postby SordFish » Wed Mar 10, 2010 3:06 pm

will the board be for ad595's or something else? either way Id definitely buy a few of these.
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Re: New dual VR board V2.0

Postby chense » Wed Mar 10, 2010 3:51 pm

racingmini_mtl wrote:That should be quite quick to design since the only thing I need to check are the screw terminals and the enclosure.

Let me know if you have requests or suggestions.


I wouldn't worry too much about the case - in my usage scenario, I would prefer a tiny, low profile SMD board so I can wrap it up in some self-bonding insulating tape and be done with it.

And another thing that would be ideal - on the MS side add pads for a DB-9 connector (cable version, like on 4-Channel Ignition/Injection Driver Board). That would solve the problem of freeing up enough pins on DB-37 and provide some mechanical protection, since the TC board would be plugged besides big and bulky, tightened DB-37.

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Re: Thermocouple board

Postby racingmini_mtl » Wed Mar 10, 2010 7:04 pm

First, thank you James for splitting this up from the other thread.

Second, the plan is to use the AD597 which is similar to the AD595 but is available in a smaller SMD package (as seen in James picture). It is slightly less accurate but it is more than accurate enough for the purpose. And the board would be sold fully assembled (or at least the SMD components).

I was thinking of using this case: http://www.hammondmfg.com/pdf/1551KFL.pdf. This would provide a convenient way of installing the case in the car. And the idea was to have a 6-way connector (4 outputs plus 12V and ground) and an 8-way connector (4 EGT probes + and -). The connectors would be something like this: http://www.molex.com/pdm_docs/iso/39530-001.gif and http://www.molex.com/pdm_docs/iso/39532-002.gif. These plug-in screw terminals make it easy to connect the wires and probes without having to do any crimping or soldering.

Chense, it would not be a big deal to add the pads to be able to use a DB9 instead of the 6-way connector. That would allow to us it instead of the plug-in connectors. The board may be a bit bigger than needed because the case is larger than what is strictly needed for the components but it's still not very big at 74mm x 34mm (2.913" x 1.339"). And I think that the majority of people will want a case so I will have to design the board accordingly.

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Re: Thermocouple board

Postby chense » Thu Mar 11, 2010 2:48 am

racingmini_mtl wrote:Chense, it would not be a big deal to add the pads to be able to use a DB9 instead of the 6-way connector. That would allow to use it instead of the plug-in connectors.

Great!

racingmini_mtl wrote:The board may be a bit bigger than needed because the case is larger than what is strictly needed for the components but it's still not very big at 74mm x 34mm (2.913" x 1.339"). And I think that the majority of people will want a case so I will have to design the board accordingly.

OK.
For me, it would be good if the connectors (or at least the DB-9) would be on the shorter side of the board (so I can plug it directly into the MS case).

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Re: Thermocouple board

Postby racingmini_mtl » Thu Mar 11, 2010 8:25 am

I'll look at using the smaller case: http://www.hammondmfg.com/pdf/1551RFL.pdf. This means the board would be 44mm x 44mm (1.732" x1.732") but it also means that the screw terminals would be 3.5mm pitch instead of 5.08mm. And the DB9 wouldn't have to be on a different side but used instead of the 6-way connector on the same side.

The 3.5mm screw terminals are the same ones I use with the logger board and they are fine for the EGT probes. However, it does require the use of a small flat head screwdriver because the screws are small.

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Re: Thermocouple board

Postby chense » Thu Mar 11, 2010 2:22 pm

This is the basic layout mock-up I had in mind (imagine screw-in terminals instead of angled headers):
img_1381_s.jpeg


I don't really care if you make it longer, shorter, or even put the terminals on the side, just make it (so I don't have to :mrgreen: ).

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Re: Thermocouple board

Postby racingmini_mtl » Sat Mar 13, 2010 2:09 pm

This is what I have now:
quadEGT.png

This would go in the 1551KFL case (linked above) and the board itself is 74mm x 34mm. The screw terminal are 5.08mm pitch (0.2"). These are actually cheaper and more common than the smaller 3.5mm pitch terminals. There are pad for plug-in terminal blocks and for fixed terminal blocks for both the inputs and outputs and there's the option of using a DB9 for the output and power supply.

I have added reverse polarity protection and over voltage protection as well as some noise filtering of the power supply.

So if there is enough interest, I'll have a batch made.

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Re: Thermocouple board

Postby chense » Sat Mar 13, 2010 3:05 pm

Looks good ... I'll take one.

[If it's not too much trouble, please route the 5V/chip PS to one pin of DB-9]

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Re: Thermocouple board

Postby racingmini_mtl » Sat Mar 13, 2010 3:20 pm

chense wrote:Looks good ... I'll take one.

[If it's not too much trouble, please route the 5V/chip PS to one pin of DB-9]

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The chips are powered by 12V (protected and filtered). But I can route this to one of the DB9 pins if you want.

However, I don't see what you'd do with it since the chip simply outputs a voltage proportional to the temperature (10mV/°C which is then divided by resistors to 4mV/°C) and not related to the power supply. The output at a given temperature will be the same for a 12V or 14V supply. The only difference is the maximum temperature (the output is limited to the supply voltage minus 2V).

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Re: Thermocouple board

Postby chense » Sat Mar 13, 2010 4:13 pm

racingmini_mtl wrote:
chense wrote:Looks good ... I'll take one.

[If it's not too much trouble, please route the 5V/chip PS to one pin of DB-9]


The chips are powered by 12V (protected and filtered). But I can route this to one of the DB9 pins if you want.


Ooops :oops: , sorry, didn't check the datasheet (thought you were putting an on-board 5V regulator such as on VR2.0).

So scratch that, not important.

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Re: Thermocouple board

Postby racingmini_mtl » Sat Mar 13, 2010 6:24 pm

No problem. That was a valid concern.

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Re: Thermocouple board

Postby SordFish » Sun Mar 14, 2010 9:39 am

the board looks good :D also any ideas on price?
also is the output 0-12v or does the board include a voltage divider?
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Re: Thermocouple board

Postby racingmini_mtl » Sun Mar 14, 2010 11:07 am

I need to check a few more things because there's a huge difference in price for the connectors so I'll have to get back to you about final pricing. But I'll probably have 3 options: the assembled board with all the surface mount components but no connector or case, the complete kit which contains the assembled board, the connectors and the case, and finally, the complete assembled unit which comes ready to use.

My first approximation is that the assembled board will be about $65-$70, the complete kit about $15-$25 more, and the assembled unit another $15-$25. If you compare that to getting 4 AD595 from Digikey to make your own, you'll see that this will be a bargain.

And the voltage divider is on the board with values such that 0-1200°C is 0-4.8V (or 4mV/°C). However, the ADC filter components (2 caps and a resistor) are not on the board since these need to be close to the CPU.

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Re: Thermocouple board

Postby msoultan » Mon Mar 15, 2010 7:04 pm

I'd be very interested in one of these!
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Re: Thermocouple board

Postby racingmini_mtl » Wed Mar 31, 2010 12:52 pm

I have finished the board and have ordered a batch. I should have them available in about 2 weeks. I have modified it compared to the last one as can be seen below. It will still fit in the same case mentioned before but I have removed the "wings" since they didn't provide anything other than filling the box. The board is now 61.5mm x 34mm (2.42"x1.34"). The plug in screw terminal blocks and the fixed screw terminal blocks will fit in the same holes.

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