Posts: 30
Joined: Sat Aug 23, 2014 10:34 am

ADCPi Reading low voltages

Mon May 18, 2015 10:14 pm

I have an AbElectronics ADC Pi - ... -converter
Analog to Digital Converter based on the MCP3424.

Connecting a humidity sensor to it- the HIH4000, which is a 3 pin sensor (datasheet here- it should return anything between 0.8 and 4.5V.

When powered off the ADC-Pi boards 5v and ground the sensor measures 2.4V on the multimeter (which corresponds to a very sensible relative humidity). When I then plug the output pin of the sensor into the board it drops to 1.04V- and this doesn't change if you put the humidity up (breath on the sensor, etc).

Any ideas?

Have tried it both with a 100K resistor between GND and OUT (as the HIH4000 datasheet says), and without.. How is the ADC Board bringing the voltage down? Have tried 3 different sensors so its not a broken one. I'm out of things to try now!



Posts: 30
Joined: Sat Aug 23, 2014 10:34 am

Re: ADCPi Reading low voltages

Wed May 20, 2015 8:53 pm

Solved! I emailled this same question to ABElectronics, who make the ADCpi, and within 48 hours they'd ordered a humidity sensor and worked it out!

The HIH4000 needs at least 80KOhm between the output pin and ground, but the internal voltage divider arrangement inside the ADCPi wasn't putting enough load to get useful results.

Putting a 100K in series between the OUT pin of the sensor and the ADCPi solved the problem, then multiplying the output voltage by 6.95225 to compensate. The usual maths as on the HIH datasheet and I get a much saner humidity value!

All the clever working out goes to ABElectronics!

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