I found a circuit on a electronic racing car that works, and measure the Bemf of a motor, but i can't understanding how it works.
On A and B is the motor. The motor uses 24Volts.
C is in one pin of an Atmega. Perhaps this change between 0 and 5 Volts so it can measure the Bemf in low speed.
My question is, is it safe for the ADC input of the Atmega ?
I doubt anyone else will be able to understand it either if that's all the information you give.
With the motor connected directly across the 24 volt supply line, 'c' will sit at 12volts
If however the motor is run up and then the voltage is disconnected the motor will generate a voltage across its terminals which can be measured.
Looking at your picture, I guess you have to apply Kirchhoff's circuit laws. Kirchhoff's circuit laws - Wikipedia
billys7:
I found a circuit on a electronic racing car that works, and measure the Bemf of a motor, but i can't understanding how it works.
Well its not measuring the back EMF across most of its range, since the output will be above 5V, and
only the resistance of the resistors protects the ADC pin from damage. I suspect the resistor to the motor
is actually 150k
That would then make more sense - it would map +/-24V to approximately the range 5--0V
My question is, is it safe for the ADC input of the Atmega ?
It's hard to say... The ATmega chip has small internal "protection diodes" but I'm not sure what the current rating is and since we don't know the back-EMF we can't calculate how much current you'll get through the resistor when the protection "kicks in".
The back-EMF can be thousands of volts if it's not somehow "constrained".
Please provide the full circuit that you "found" and a ;ink to the actual article so's we can maybe make a sensible response to your enquiry
My question is, is it safe for the ADC input of the Atmega ?
Only as Douglas Adams says, with a “strange new usage of the word safe to which I was previously unaware.”
Hi,
Does the motor have a model/maker/part number on it please?
A picture of the motor and controller would be good.
Thanks.. Tom... 