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Cerbuino & 5v tolerance


#1

“Digital I/O are 3.3V but 5V tolerant (except reset and 2xDAC pins)”

What about pins A3 & A4 which are listed as Analog/TBD pins?


#2

Link please?


#3

It’s on the Cerbuino Bee page:
http://www.ghielectronics.com/catalog/product/351

The pins are here:
http://www.ghielectronics.com/docs/45/fez-cerbuino-bee-developer

Also, what’s the max amps it can handle? I want to do some battery level measuring.

Its a 2 cell lipo battery - each Cell is supposed to be between 3.7 & 4.2v. I want to hook up the balance charger to read off the voltage from one of the cells only. I will need to use a voltage divider eventually.


#4

Analog pins will only read up to 3v3 so you will need a divider from day 1.

Amps? Mmm, you realise amps is what something draws from a battery, so the answer here is that it doesn’t matter how big a battery, you’ll be able to measure it’s voltage.


#5

I understand about the divider.

My reason for asking about the amps, was that I connected the battery’s balance plug outputs to my breadboard and the wires got hot and started to melt the plastic. The wires were not shorted as far as I can tell. Nothing else was on ghe board, i was trying to get some readings with my volt meter.


#6

Figured out my melty issue … the pack is a 2S, so the cells are wired in series. I was trying to use the juice coming of the balance connector in parallel. The wiring in the pack was “shorting” out my connections. **edit - see diagram attached

Warning: programmer doing hardware!!!

Still curious about my original question - are the Analog pins 5v or 3.3v? The info page says “digital” pins are 5v, except for the DAC. What about these analogs?


#7

Well the answer is that at 3v3 they will max out the reading of the ADC, so doing anything that introduces above 3v3 to them is pointless since you can’t measure it. The fact that the information explicitly mentions the DAC pins, means that you will damage the DAC if you connect greater than 3v3 to the AOUT pins. The 5v tolerance of the ADC is documented on the processor datasheet http://www.st.com/st-web-ui/static/active/en/resource/technical/document/datasheet/DM00037051.pdf starting page 44. But again, the fact that you can’t measure anything above 3v3 means you should always control voltage to under that.

And yes, melty issue was a short :slight_smile: Glad you didn’t connect anything else to that.


#8

I understand about the 3v3 max reading. I was worried that if the voltage goes over (meaning that if the voltage divider calculation is off) that I might ruin my Cerb.

Thanks!


#9

Make sure you read the specs, it is NOT tolerant :wink: so yes you will fry Cerb’s ADC or the multiplexer if you hook up more than 3v3.