Compatible SPI ADCs?



  • I have a machine I am retrofitting with a Duet Ethernet board. The machine has K-Type Thermocouples which go through a AD597A. The AD device outputs the temperature reading of the thermocouple as a voltage. (-1.4volts @ -200 degC to 12.428 volts at 1250 degC).

    I was originally planning on swapping in new TC boards using the MAX31856 chips, but I want to keep all the electronics as stock as possible, and instead install an interface board between the electronics and the Duet.

    It looks like I'm going to need a SPI ADC, with a decent resolution (12 or 13-bit) over the suitable range from 0-5V (0 degC to 500 degC). Are there any ADC's off the shelf that are out of box compatible with the Duet that I can install on one of the numerous available channels using M305?

    It seems like all I will need to do is specify offset, gain and voltage difference and then assign that to one of the channels, but I'm not 100% sure if there is a specific way to do it already that isn't documented?



  • Whoops! Just stumbled upon this topic made just a few days ago: https://forum.duet3d.com/topic/7125/use-of-linear-output-temperature-sensors

    Looks like I can use Sensor type 300. Will report back with more information for anyone else trying to implement something similar.

    https://github.com/dc42/RepRapFirmware/blob/6b835cb3c8e9aa10113ae750151d9f9065116cd4/src/Heating/Sensors/CurrentLoopTemperatureSensor.cpp

    Looks like MCP3204 is supported, which is exactly what I was thinking of using!



  • Follow up update! I have submitted a revision to the Firmware, which hopefully will be accepted: https://forum.duet3d.com/topic/7151/linear-adc-thermocouple-improvements

    It is indeed possible to use the MCP3204 or MCP3208 ADC chip with the Duet!

    Once the firmware is updated, it should also be possible to use all 4 or 8 channels of ADC in either single mode or differential mode. (Right now, only 1 channel is able to be used at a time).


 

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