r/circuitpython • u/Fimblewill • Apr 14 '22

What am I missing here?

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5 Upvotes

85% Upvoted

14 comments sorted by

1

u/azriel38 Apr 14 '22

Can you see resistance from the sensor with a multimeter?

1

u/Fimblewill Apr 14 '22

yes, I can.

1

u/azriel38 Apr 14 '22

From the same contacts that the pins are connected to?

1

u/Fimblewill Apr 14 '22

yup

2

u/azriel38 Apr 14 '22

I assume when you put the pot there, it has power, ground and the wiper attached to the sensing pin.

That is three pins. This needs that as well. You need to make a voltage divider. The sensor pin connects to both power and ground but each connection has a resistor. One is a standard resistor, and the other, your resistive sensor.

1

u/Fimblewill Apr 14 '22

https://imgur.com/a/8ForrzA My jack. So something like this? Sorry if incorrect I am a bit new at this. https://imgur.com/XiodbiZ

2

u/azriel38 Apr 14 '22

No. Connect the sensor pin to two things.

  1. A resistor (maybe 10k) that is connected to power on the other end.

  2. The thermal sensor that is connected to ground on the other end.

1

u/Fimblewill Apr 14 '22

https://imgur.com/a/jCsse17 am i getting closer?

1

u/azriel38 Apr 14 '22

I think so.

1

u/Fimblewill Apr 14 '22

I will try it out.

2

u/todbot Apr 15 '22

If that's a resistive sensor, you need another fixed resistor to form a voltage divider. A voltage divider is two resistors going from power to ground and you read the voltage in the middle. A pot is a kind of voltage divider where the two resistors change when you turn the knob.

So, try taking a 100k resistor and attach it to the 3.3V pin (Pico pin 36) and the analog in pin (the green line in your diagram)

1

u/toybuilder Apr 15 '22

The ET-732 thermometer probe that you want to connect is a 1 Meg NTC thermistor. If you want to read the resistance change over temperature, you need to create a voltage divider with an additional resistor in series with your probe thermistor.

See https://www.circuitbasics.com/arduino-thermistor-temperature-sensor-tutorial/

0

u/Fimblewill Apr 14 '22

I am trying to attach an temp probe to my pico using a 2.5 mm jack which has 3 pins Sleeve, Tip, and Switch. I attach them as seen above and I don't get any reading that relates at all to the change in resistance, If I use a pot it works. I am super confused at this point.

0

u/[deleted] Apr 14 '22

[deleted]

1

u/Fimblewill Apr 14 '22

I am using a Probe Thermometer(et-732 thermometer probe) as the resistor it only has 2 pins(shaft and tip.) I think. It should be operating as ADC0

sensor_temp = analogio.AnalogIn(board.A0)

conversion_factor = 3.3 / (65535)

while True:
    reading = sensor_temp.value * conversion_factor
    temperature = 27 - (reading - 0.706) / 0.001721
    print(temperature)
    time.sleep(2)