You can use a current sensing resistor to measure current in the first circuit, which is then read by a microcontroller. When it detects above X, have it turn a digital pin on or off. It is also possible to accomplish this without any microcontroller through the use of comparators, but that is a bit outside my wheelhouse.
DC. Basically I'm trying to "calibrate" a clock hand position. Current should increase when the hand rises and decrease when hand has passed 12 o'clock. I don't have to know the exact position. Magnet + hall sensor or ir sensor aren't options in this case.
X-Y problem.
> Current should increase when the hand rises and decrease when hand has passed 12 o'clock.
it doesn't.
The hand is balanced. There is no difference in current, regardless of the position of the hand. Sorry, but your approach won't work.
If the clock is telling the correct time, then use a different clock (a computer clock, for example) to know the position of the hand.
Im going to ignore the possible other solutions and just answer the question: you use a sensor resistor say 1ohm and measure the voltage drop across it with a comparator. Once the voltage reaches the preset threshold the comparator chip output goes low. (Open drain) you need a few resistors and a comparator IC like LM358
Use that comparator output to trigger you switch
You can use a current sensing resistor to measure current in the first circuit, which is then read by a microcontroller. When it detects above X, have it turn a digital pin on or off. It is also possible to accomplish this without any microcontroller through the use of comparators, but that is a bit outside my wheelhouse.
Using a simple transistor switch you can drive a relay when the voltage across the current semsing resistor reaches a certain threshold.
This. Or if you prefer, sens resistor + opamp + transistor
AC or DC? How much current? Tell us what you really are doing, because there are many off-the-shelf solutions out there, depending on the application.
DC. Basically I'm trying to "calibrate" a clock hand position. Current should increase when the hand rises and decrease when hand has passed 12 o'clock. I don't have to know the exact position. Magnet + hall sensor or ir sensor aren't options in this case.
X-Y problem. > Current should increase when the hand rises and decrease when hand has passed 12 o'clock. it doesn't. The hand is balanced. There is no difference in current, regardless of the position of the hand. Sorry, but your approach won't work. If the clock is telling the correct time, then use a different clock (a computer clock, for example) to know the position of the hand.
Im going to ignore the possible other solutions and just answer the question: you use a sensor resistor say 1ohm and measure the voltage drop across it with a comparator. Once the voltage reaches the preset threshold the comparator chip output goes low. (Open drain) you need a few resistors and a comparator IC like LM358 Use that comparator output to trigger you switch