Electronics > Beginners
Pulling down voltage to zero on parallel circuit elements
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wesley1:
Hello!

I tried searching for a solution to my problem, but could not find any related topics so far. Perhaps I'm missing the right terms..

There is a simplified circuit like in the attached picture.
I am looking for a method to drive the voltage to zero on R1 with access only to the point in the circuit marked with the question mark.
It is clear that I can control the voltage and current for the rest of the circuit (i.e. R2 and R3).
But what are my options if I want to influence the R1 part of the circuit by putting components where the question mark is..?



I suppose shorting the circuit there is not a great idea. Putting a low value resistor with high wattage to let most current bypass the rest of the components..?

Thanks!
Zero999:
The only way to force the voltage across R1 to 0V is by short circuiting it, which will cause a large current to flow.

What does the circuit do? Can we please see the bigger picture.
macboy:
Nothing you can place at the question mark can affect the voltage across R1 in any way... not without knowing more about the 12 V source at least. If it is an "ideal" 12 V source, with zero internal resistance, and the wires are also ideal, then no amount of load will drag it down. Since the 12 V source is connected directly across R1, the voltage at R1 is simply exactly equal to that source voltage, period. Nothing you can place at the question mark can create a short across R1 or across the 12 V source. Even placing a voltage source at the question mark can't change the voltage across R1.
You said it's a simplified circuit. Has it been "simplified" correctly? Is everything you know about the circuit (especially the 12 V source) shown? Unless something is wrong or missing, there is no solution.
wesley1:
It is an intercom circuit with a proprietary one wire protocol. The master provides the 12V to the slave devices in the appartments which use parasitic power from the line.
There is a two-way communication between the master and the slaves.

I'd like to experiment with arduino to be able to trigger my intercom without the real master.
I assumed the slaves pull the signal level to ground for sending. Maybe my assumption was wrong and they reply by some different technique.

One thing to note is that I have access also to GND at the question mark, R2 is the device in my appartment.
About the voltage source, it's a 12VDC power supply driven by a 230VAC to 12VAC transformer with a 100mA fuse. That's everything I could figure out from the docs.
Kirill V.:
Firstly, you should consider internal resistance of 12 V source and add it to your simplified circuit
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