# Electromagnet coil circuitry

#### Turbo1zz

Joined Jan 25, 2012
2
I am making an electronic pendulum and have a very basic coil and circuit for sensing the magnet and driving the magnet which I was fortunate enough to get help with. I have a drawing of the circuit attached. My question is this... I want to place two LEDs in the circuit to pulse when the magnet enters and triggers the sensing coil and then another LED to fire when the Outer drive coil is triggered by the transister. Is it as simple as placing an LED in line with each coil or with so much I am learning about electronics it is not that simple.

Any and all help would be greatly appreciated in this matter.

Thank you,

Jeffrey

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#### wayneh

Joined Sep 9, 2010
17,473
Is it as simple as placing an LED in line with each coil ...
No, but you might get away with putting an LED plus a capacitor plus a resistor, all in series, all in parallel with the coil. The idea is that a voltage surge across the coil will send current thru the LED-cap-resistor, briefly lighting the LED until the capacitor charges and current stops. You may need to add another resistor across the cap to drain the charge off the cap during the "off" time. Do you know what voltage appears across the coils?

#### Turbo1zz

Joined Jan 25, 2012
2
Unfortunately I do not know the voltage across the coils and wouldn't know how to measure it since the coil resides inside a base below the pendulum with the magnet. I'd be completely fine with just an LED on the impulse coil so I can have a visual. a way of confirming the transistors operation. I really am running in the dark here so any help is greatly appreciated.

#### Bernard

Joined Aug 7, 2008
5,784
If the transistor is accesable, add a 2.7 K from collector to base of a PNP, 2N3906, emitter to + supply, collector to red LED anode, cathode to 100 Ω, other end to - supply.