# Circuit that pulses ground?

Discussion in 'General Electronics Chat' started by Alvin, Aug 27, 2008.

1. ### Alvin Thread Starter Member

Jan 22, 2008
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Hey Guys,

I'm looking into making a circuit that pulses a ground to replicate a signal in a vehicle. The voltage is 12vdc.. I have a few PWM circuits but they all provide a +12dc square wave.

Should I use one of these circuits with the output on say a NPN to ground?

2. ### blocco a spirale AAC Fanatic!

Jun 18, 2008
1,455
369
Do you need a negative pulse i.e from 12V to 0V and back to 12V? You can invert a positive pulse with an NPN transistor and a pull-up resistor.

3. ### antseezee Active Member

Sep 16, 2006
45
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I like the idea of using a transistor or MOSFET to pulse the ground. Have a voltage source along with a resistor to give your predetermined amount, and feed it into the collector of the transistor. Your base will have a control signal that will determine whenever the transistor gets switched on to bring ground into the picture.

Sometimes these circuits are used in driving LEDs (where you pulse ground to light the LED as opposed to pulsing the LEDs directly).

4. ### LearningElectrician New Member

Aug 24, 2008
9
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What's up. I'm don't know very much about circuit design as you could probably tell by my Grounding101 thread, but But i'd like to contribute to this forum on "grounds" other than that one thread I made.

I have seen before how pulsating signal can be created. On a speed senser that goes into a vehicle wheel to provide a signal for speed and/or anti-skid or something. Basically it's a regular circuit with a positive and negative hooked up between the source and load like any working circuit would be. But on the negative side of the conductor there is a tiny wheel contraption hooked up to in between the wire. On the wheel there are like 2 strips of conductor across it. I think this wheel part of the circuit is actually located in the middle of the car's actual wheels. When the car moves and therefore the circuit's wheel moves/spins. As the wheel spins in the circuit it creates a connection each time one of the strips contacts the circuit. The faster the acceleration or deceleration, the faster the little wheel in the circuit spins, therefor created a faster signal....

I drew a picture to illustrate...

I drew the wheel in a position where there is no connection, but as it turns (probably due to being connected to the actual vehicle's wheel) each time the blue conductive material contacts the wire, a complete circuit is created...this on off, on off, acts as a really fast switch....creating a pulsing signal....