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Topic: Thermocouple (Read 2 times) previous topic - next topic

Graynomad

The A0:1 lines appear to be floating, if so what MUX IO is being selected?

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Rob
Rob Gray aka the GRAYnomad www.robgray.com

J T

I've not tried with the thermocouple connected directly to the MAX6675 yet, but that seems like a logical step in trouble shooting.

As I understand the data sheet on the ADG609 putting 5v on the EN leg will "connect" the S1A to DA and S1B to DB, putting 5v on combination of A0 and A1 bring the other pairs to DA and DB. Perhaps A0 and A1 "must" be connected and pulled low?

I'm really new at this stuff and really appreciate the help.

Thanks
John

Graynomad

Quote
Perhaps A0 and A1 "must" be connected and pulled low?

It's possible that chip has internal pull downs or something, but good practice (and removes one variable) to tie them yourself.

______
Rob
Rob Gray aka the GRAYnomad www.robgray.com

Jack Christensen

I'm using the following, not sure about the 0x00 vs. 0xff, but easy to try.
Code: [Select]
    digitalWrite(_ssPin, LOW);
    tcData = SPI.transfer(0x00) << 8;
    tcData |= SPI.transfer(0x00);
    digitalWrite(_ssPin, HIGH);


Definitely test initially with the TC connected directly to the MAX6675.  Theoretically an "ideal" mux would work, but thermocouples deal in microvolts, so a mux would have to pass the signal through pretty darned faithfully.  So I'm also dubious, but I'd encourage you to try it since you have the parts.  I'd be interested to hear the results.  The MAX6675 senses its own temperature to do the cold-junction compensation, so as long as the mux is kept close by, that shouldn't be a huge issue.
MCP79411/12 RTC ... "One Million Ohms" ATtiny kit ... available at http://www.tindie.com/stores/JChristensen/

J T


The A0:1 lines appear to be floating, if so what MUX IO is being selected?

______
Rob



Bingo Rob! You were correct the A0 and A1 lines can not be left floating. I connected them up and set them to low in my setup loop and walla she works...

A big thanks for spotting that.

Onward and forward...

Thanks
John

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