using NTC Temp on 2 inputs

rolsen

Member
I am using an two NTC resistor/47K devider first on adc 1 into b0, and second on adc 2 into b1. On debug b0,b1 I am getting mixed readings, ie when i heat up the first the second seems to follow, then both remain unchanged. How can I keep them seperate? If I remove one the other works fine.
 

hippy

Technical Support
Staff member
http://www.rev-ed.co.uk/picaxe/forum/Topic.asp?topic_id=1993

You need to use an extra 'dummy' READADC when using two separate analogue inputs with PICAXE-08M Firmware Version 9.0 -

This doesn't work ...

- READADC 1,b0
- READADC 2,b1
- DEBUG b0,b1

This does ...

- READADC 1,b0
- READADC 1,b0
- READADC 2,b1
- READADC 2,b1
- DEBUG b0,b1
 

wardbob

Member
You should have one thermistor between 5 V and your first adc pin and then your 47 k resistor between the 0V and the same adc pin.
You should have the other thermistor between 5 V and your second adc pin and then your second 47 k resistor between the 0V and the second adc pin. Is that what you have?
Also, which two actual pins on the 08M are you using for adc (should be either 3, 5, or 6 but not 4)?
I am doing the same thing on an 18X but they do not affect each other.
Is yours a 50 k thermistor (at 25 C) or what? My thermistors are 10 k at 25 C and I'm using a 10 k resistor. I am only looking for small changes near room temperature.
 

wardbob

Member
Rolsen, if hippy's fix works, ignore my questions. I hope it works for you. Hippy is right 99+%, it seems.
I never saw that info before, hippy. Where did you dig that up?
 

rolsen

Member
Thanks hippy & ward bob for the fast response.
Hippy will do as you advised and many thanks.
Ward Bob the themisters are 100K and connected as you indicated. Pin 1 & 2 (Physical Leg 5 & 6)
I was thinking of trying the same with LDRs.
 

wardbob

Member
Rolsen, if hippy's fix works, ignore my questions. I hope it works for you. Hippy is right 99+%, it seems.
I never saw that info before, hippy. Where did you dig that up?
 
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