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Mark asked

temperature sensor readings working in reverse

Ok so heres a weird one! Hopefully someone can help as I'm loosing my will lol.

I'm using rpi3b+ with latest venus 260-34. I've made a circuit using mcp3208 and resistors and lm335 sensor.

I have my temperature reading no problem but...... as the temp goes up the reading goes down and if I cool the sensor the reading goes up??? If i swap the terminals around I get either the disconnected or reverse polarity or unknown message.

The tank sendors/reading is correct and stable using the same vref and mcp3208.

Any help ideas greatly appreciated


Venus OSRaspberry PiTemperature Sensortemperature
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laurenceh avatar image laurenceh commented ·

I have the mcp3208 working, I used a readily available purchased custard pi analogue board. One thing is certain swapping the terminals on the lm335 won’t fix anything. The lm335s should be wired as per the beagle bone cape circuit. The voltage across the lm335 rises and falls with temperature they go between ground and a pull up resistor. For reliable long term use the inputs should be protected with clamp diodes.

My project is documented here:

You are not clear if your talking about the raw value from mcp3208 going the wrong way, or the temperature reported on the Venus console going the wrong way? From memory raw values should be around 2015 at 1 degree and 2167 at room temperature.

Raw values available at /sys/bus/iio/devices/iio:device0

I did Try a 2.60 release and had no problem.

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