Analogue Input

[Hafslo]

I’ve been playing with the analogue input – trying to get Crumble to read temperature from a potential divider made up of a themistor and similarly rated fixed resistor. Running on 4.5v battery. End aim is to make a light whose colour changes according to temperature.

Problem is sparkles draw differing current as they change, and battery drain varies, so analogue reading varies giving a misleading impression of temperature.

Has anyone got a simple circuit that will allow me to measure a variable resistance consistently? From what little I know, I would have thought it needs a voltage regulator but I can’t find one listed that will work from 4.5v.

Any help / ideas gratefully received!

Phil

[Joseph]

Hi Phil,

I think the problem is the potential divider is across the battery voltage, while the Crumble is using the USB voltage as a reference. If you run the program without USB connected, you might see an improvement, but no monitoring!

One way round this is to use an output set to HI as the +ve side of the divider. So you could have each ‘end’ of the divider wired to – and B, with the centre connected to A. You would then set B HI and read the analogue value off A.

Also, you can actually use thermistors and LDRs directly on the crumble (each I/O has a 100k pull-down resistor): connect the thermistor across A and B, set B HI and read analog A. Ideally you would use a 100k (approx.) thermistor, but it should work with other values.

I’m thinking about adding blocks that say something like:
(LDR on A&B/C&D)

I hope this makes sense without any diagrams!

All the best,

Joseph

[Hafslo]

Yes, it does thanks!

I just couldn’t face indoor electronics whilst the sun was shining but now we have some rainy days forecast, I’ll give it a go and report back!

Cheers.

Phil

[Author]

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