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Thread: Use Teensy 3.6 differential ADC to read analog pressure sensor?

  1. #1

    Use Teensy 3.6 differential ADC to read analog pressure sensor?

    Hi, I'm currently using a Teensy 3.6 with an external ADC to read an analog pressure sensor. I'm curious if there's any hope of reading the pressure sensor directly using differential ADC on the Teensy 3.6? (Pins A10 and A11.)

    If I got 6 bits of accuracy at around 60hz using the Teensy I'd be happy. (I'm unhappy with the data rate for my current ADC because it's intended for a digital scale and only runs at about 10Hz.)

    The ADC is an HX711 and the sensor is a MPX10GP. Currently the HX711 provides power to the sensor at around 2.4 volts and the sensor voltages are about halfway between at around 1.2 volts. (I am guessing it might be a Wheatstone bridge?) The voltage range for the measurements I'm interested in seems to be 13 to 18mV. I'm using the external ADC with its preamp set to 64x gain but that's actually a bit too high since it starts at around 75% and goes to max.

    Also, if you know of any alternate parts that might work well with a Teensy I'd be happy to hear it. This is for a breath sensor for a musical instrument.

  2. #2
    Senior Member
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    Due to the low output voltage change in the sensor alone, you would only get an ADC count range of 187 max. assume Teensy Vref=1.2v, 12-bits resolution (0.293mV/bit)and 55mV at 1.45psi 55mV / 0.293mv/bit == 187.7bits. If you want more bits of resolution, you could use a differential amplifier, here, see figure #5 and feed the result single ended into a Teensy.

    Also note that (per Google search) 'experienced trumpet players' can blow up to 1.9psi which is a bit above your sensor range.

  3. #3
    I went with an ADS1115 breakout board and it works well; the increased sample rate makes big difference. When powered from the Teensy's 3.3v pin with gain set to 16x (maximum) the input range is from 2300 to 4500 (out of 32k) if I blow hard, with 4000 as a more comfortable max pressure.

    I also tried setting the preamp to 1x and the range is 144 to 250 or so with 200 being a more comfortable max. I don't notice any effect on the audio from decreased resolution. It seems using the Teensy directly is worth trying. Since I soldered the Teensy to the Audio Shield before thinking of doing this, it looks like I'm going to have to start over with another one.

    I don't understand what the voltage reference has to do with a differential ADC read. How does that work?

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