# Sending an impulse with pauses

Discussion in 'General Electronics Chat' started by orwikcons, May 7, 2008.

1. ### orwikcons Thread Starter Member

May 2, 2008
22
0

Depending on impendance that comes in the circuit (R1<R2<R3<R4), on B will go short impulses +12V (0.25 - 1 seconds) in a periods of 3 seconds, responding to R1, up to 14 seconds, responding to R4.

I am trying to improvise the windwasher work, where I can define the pause lenght, by these four values. So the pauses should be proportional to impendances. Lenght of impulse don't need to be precise value, but to be under one wiper period (cycle), so it can be proportional to resistors too.

2. ### Papabravo Expert

Feb 24, 2006
12,279
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Is there a question in there?

3. ### SgtWookie Expert

Jul 17, 2007
22,201
1,809
Sounds like you want to vary the time between wipes of a windshield wiper.

In order for this to work properly, you'll first need a way to detect when the wiper is at the end of it's travel.

4. ### Wendy Moderator

Mar 24, 2008
21,838
3,047
The classic way to do this is a variable timer, where the wiper goes the same speed but pauses between wipes in variable increments. Is this what you're trying to do?

5. ### orwikcons Thread Starter Member

May 2, 2008
22
0
Sorry, my English is not so good, so I couldn't explain what I had wanted.

The factory circuit gives an impulse to the wiper-motor, every 6 seconds. That impulse is enough to move wipers from the start, then automatic circuit in the motor drives wipers to the end of there way, and back them to start (because the length of impulse is not so important, it only has to move wipers from the start, but masn't be longer than one cycle, because then two cycles would happen). So, I want to make the circuit which will give such impulses, but pause between wipes will be defined with those four impendances (the switch is from other car). For example the circuit which will give an impulse, and then wait a few seconds, and depending on selected resistor, the lenghts of pause and impulse will be multiplied with proportional coefficient.

Last edited: May 7, 2008
6. ### beenthere Retired Moderator

Apr 20, 2004
15,808
295
Many years ago, I put together a kit that allowed a variable time between strokes of the wiper blades. The active part was a unijunction transistor that pulled in a relay briefly when it went into conduction. The control was a pot configured as a variable resistor that controlled the rate of charge onto a capacitor.

If you look up "unijunction relaxation oscillator", you can find how the control worked.