Reading a thermocouple ?

also digikey has the adafruit breakouts so, i grabbed on to give it a try

Thanks again for the suggestion

C

calvin.d wrote: so if I wanted to get 4 separate temp readings, could I use the set of pins on a mesa card to read the input ?

Yes, one output pin for clock, one input pin for data and then one output pin per thermocouple channel for select.

Though, you could also use the Mesa version of SPI for a much faster update rate. The HAL component works at 1 kHz, whereas the Mesa firmware SPI is (up to) MHz. But 1000 bits of data is still 5 thermocouple channels at 1Hz.

So I have hardware in hand to go the MAX ic spi route.

I now have a hardware question that breakout board ( www.adafruit.com/product/269 ) is expecting 5v in and has 3.3v io lines for the data

I have my 7I76 setup to use 24v for the general IO

anyone have an opinion on the right way to get the GPIO voltage down to 3.3v or 5v

or should i just grab a separate mesa board to extend off the 7i76 to deal with this IO.

Thank You
C

You could use a parallel port or serial port, if you have one.
(There are enough IO pins on the serial port to use it for a few GPIO lines )

There is also the option of using the second port on the 5i25, or adding something like a 7i73 to the 7i76.

No eBay APP ID and/or Cert ID defined in Kunena configurationMight be a bit late to the party here but another simple option where you are using a Mesa card with analog ADC inputs would be to use something like this
www.sparkfun.com/products/10988

And scale the voltage to suit the Mesa 36.3 V ADC range with one of these:


I've ordered one of the amplifiers to read an analog output current sensor this way on my 7i76e. The analog pin shows the ADC voltage so then it would be a simple matter to scale the output in hal with mult2.

I have played around with temperature sensing on an Arduino and I will say that Andy is on the right track. The SPI or one wire interfaced sensors are superior but the analog devices are easy to implement with the Mesa devices.

the sparkfun option will not work for what I am looking for I need actual thermocouples for what I want to do.

I think you are correct though, doing this via analog or PWM into the GPIO on a Mesa board is starting to make more sense to me. I think I want a board that has a micro controller and a max3155. The code to go from spi to a khz PWM output is easy and if I just use a mosfet to switch a 24v line then I am right in voltage range for the GPIO on the board I am using.

anyone have any thoughts on reading a 10kHz PWM on a 7i76 GPIO ?

Thank You
C