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
Hi, jtjohnston, welcome to the forums. The only way I can see this working is to use a relay coil that's half or less the supply voltage, and then the wiring up is something like this: On switch-on, the capacitor charges up through R1 until it reaches a high-enough voltage to pull the relay arm over and make the switch. Now the switch puts a second smaller resistor R2 across the cap so it discharges faster than it charges until its potential is too low to keep the relay on. It's going to need a massive capacitor for 1-second delays and not be very accurate, a 555 solution is cheap and precise. If above was practical, they'd maybe have used such a system in car turn indicators before semiconductors got going. They didn't, they used a heater wrapped round a bi-metallic strip that bent to make/break the lamp circuit.
Your with the Mexborough & District Lions Club. Ever hear of the Masons? When I was younger and worked for an alarm company, I had my paws on big, honking 12 v aircraft relays. I got it to work, can remember how. I remember someone saying that that was how they did it in school buses. Anyhow, I'll play with this. Start with a 6 v relay, huh? Any specific calculation for the capacitor? Tantium better?
Only as in the New Masons boozer where I've spent many a happy hour. For the cap, it will have to be an aluminium electrolytic, tantalum don't come in such large sizes. You'll probably need over 10,000uF; it depends how much range the relay has between pick-up voltage and drop-out voltage.
New Masons boozer? Tsk, tsk. We're a tea-totaling crowd around here: www.glquebec.org (I'm Web master and ISP) Thanks, I'll let you know how it works.
