Am I about to do something foolish (Power Question)

Projects General Guidance
1

Hi,

I have an existing motor (90v) controlled by a pwm board.

The pwm boards has on it a 10k pot and the voltage across this pot measures 12v.

I have replaced this pot with a digital 10k pot which is controlled via my arduino. (I have connected the grounds of the 2 circuits as previously advised)

Yesterday I had the thought that I could eliminate the 9v battery by powering the arduino from the 12v which are across the potentiometer from the other circuit.

Is this line of reasoning sound or am I about to do something foolish? Perhaps there are some checks I need to do or components I need to put in between?

Any help appreciated

Krish

2

unfortunately - it depends
if the original pot is simply connected across the boards 12 volt supply - then yes
if the pot is somehow buried inside the circuitry (more likely) then no as the load of the arduino will appear as a short across the pot

3

Assuming you haven't done anything weird, my understanding is that the control inputs of a digital pot are relatively isolated from the potentiometer part. From how I understand what you are saying, you are probably okay, but a schematic will help immensely. I'm assuming you are feeding the 12V into the on-board regulator of the Arduino board, and not trying to apply it to the 5V or 3.3V pins.

4

I think that you will find that a "digital pot" is good only in an application where the "top of the pot" is at a potential <= its [the device's] VDD.
Perhaps a link to your device (pdf) ?

5

widget:
Yesterday I had the thought that I could eliminate the 9v battery by powering the arduino from the 12v which are across the potentiometer from the other circuit.

Is this line of reasoning sound or am I about to do something foolish?

I don't see any problem with it, as long as the ground for the 12V supply you're planning to adopt is the same as the Arduino's existing ground (I think it is, but if I've misunderstood then that might be a problem).

12V is on the high side for powering an Arduino and it won't be able to supply much current but as long as you aren't expecting the Arduino to power anything it should be OK. If the regulator starts getting hot then you could always help it out by adding an external regulator. For 12V - 5V conversion you should be able to use an automotive USB charger.