jtjohnston Posted March 14, 2007 Report Share Posted March 14, 2007 I'm a 41-year old newbie. Haven't played with this stuff since I was 20. I still know a few principles. So be gentle. Here goes.I want to create an RC circuit to create yee old alternating, blinking relay.Instead of powering the relay through the coil, (pin 1) I'm juicing it through pin 4 by placing a jumper between pin 1 and pin 4. Therefore, when 12 v dc passes through pin 4, it will activate the coil, pin 1, and fire to the normally open position. When it looses juice it pops back to the normally closed position. The question is how to keep the relay alternating every 1 second.If I use a RC circuit between pins 1 and 4, using an RC circuit charge and decay, I should be able to make the relay alternate. That is as far as what I remember what to do.I have a regular automobile SPST relay, the coil measures about 900 ohms.What values do I need for R1, R2 & C1. My idea of using R2 was to help C1 decay faster. Eventually I would put a pot for R2 to control the decay rate of the RC circuit.Can anyone help? Am I looking at this the right way?I do plan to experiment with a 555 circuit later, but want to try and do this old-school first.John Quote Link to comment Share on other sites More sharing options...
Kevin Weddle Posted March 14, 2007 Report Share Posted March 14, 2007 Probably what will happen is that it will cycle the relay very fast, wearing it out. A large capacitor will hold the voltage on the coil for a period, a larger capacitor might make a noticeable difference. Quote Link to comment Share on other sites More sharing options...
jtjohnston Posted March 14, 2007 Author Report Share Posted March 14, 2007 Any idea on how to calculate C1, R1 & R2? Quote Link to comment Share on other sites More sharing options...
Fowkc Posted March 15, 2007 Report Share Posted March 15, 2007 Clarify what's happening here... in the first diagram, pin 4 is normally closed. In the second, it's normally open...You'll have to experiment to see what voltage your relay turns off at. I'm not sure how your second circuit is meant to work, but I can see the principle (using a capacitor to keep the relay on). Assume the capacitor starts charged at 12V, work out how the voltage on the capacitor changes with time, then use that equation to get the capacitance you need for a 1s pulse. Quote Link to comment Share on other sites More sharing options...
Kevin Weddle Posted March 15, 2007 Report Share Posted March 15, 2007 Just a parallel capacitor is what you want. But you need a relay with a 10Kohm coil to slow the relay down. Quote Link to comment Share on other sites More sharing options...
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