I have 9 wires normally held at 12 volts but occasionally pulled to ground that I want to monitor with an arduino without disrupting the circuit they are part of.
Some explanation is in order. The wires go to a set of self playing Christmas bells. 9 small actuators inside brass bells controlled by a small circuit board and run from 12v DC create very nice music and my plan is to synchronize lights to them. I already have a setup that lets me control lights with an arduino I just need to tell the arduino when each bell is actuated. The problem I'm having is that after probing with my voltmeter I've learned that for whatever reason the circuit for each bell is held high at 12v then drops down (presumably to ground but it's too quick for my multimeter and I don't have an oscilloscope) to trigger the actuator. I know the arduino can detect a low voltage just as well as a high but I don't know how to get the 12v down to something the arduino can handle without grounding out the circuit and breaking the bells. Any help would be appreciated.
Look up voltage dividers.
Ah I didn't realize you could use capacitors in a voltage divider. My first thought was to use high value resistors but even then I'm providing a path to ground. Thank you for your help. If I remember correctly you are the same person who helped me over a year ago when I last posted a question.
Can you or anyone else make a quick estimate of the approximate component values I should use? Ohms or kilo ohms or mega ohms? Nano or pico farads? I'm happy to fine tune on my own I just want to start in the right ballpark.
try 10K and 6.8K for the resistors. Your voltage divider offers 16,800 ohms resistance to your 12 volt lines, which taps off 0.7 milliamp from your power. Trust me, your circuit won't be affected by that.
Thanks for the suggestion. I'm really wary of interfering with the existing circuit since there is virtually no chance I could fix it if I damaged it and they don't make new ones any more but you make a good point that 0.0007 amps is practically nothing. With any luck I'll have a great Christmas tree this year.
Which side of the coil are you looking at?
Sounds like the bells work with a pull to ground. The circuit is floating , so you see 12 volts on either side of the coil. To ring the bell, one side is pulled to ground.
If you are looking at the sourced side of the circuit (12V), you will never see a voltage drop. Need to be looking at the ground side.
The bells share a wire which I thought originally was ground but now I guess is the 12 volt source. I am of course looking at the other side of the loop for each bell which I originally assumed to be the source but now seems to be where they are pulled to ground for a split second.