555 Relay circuit

stolenfat · Posted: Mon Oct 13, 2008 9:10 pm Post subject: 555 Relay circuit

first off, i want to thank every one for all the assistance and inspiration that this forum has brought to me over the months. Much love.

And now, heres my request! Help!

Ok, so i have a circuit built up using a 555 as seen below, it's a modified LED blink circuit with a relay instead of a diode. It works alright, but there are power problems it seems: after a while of use, apparently the batteries drain past a certain point and not enough current is generated to create the magnetic field needed for the relay operation (this is my speculation, may not be correct). The relay itself is a "reed relay rated at .05 A at 125 VAC" not sure what that means, but i picked it from the others at radio shack because it seemed it required it the lowest amount of current. It seems to work better when connected to it's own independent power supply such as a 9volt instead of the internal SK-1 batteries.

more relay specs:
voltage: 12 VDC
coil restiance: 1050 ohms
nominal current: 11mA

My questions are, is there a better choice of relay i could have used here? Would a 4066 chip work better?

Also, at this point i cant get an LED to blink along with the relay switch rate by placing it in series before and after the relay. When i have tried to use one it makes the relay not function, or only for a few switches and then it stops. Very peculiar.
Could anybody suggest how I could get an led to operate right and not kill the function of the relay?

What does nominal current describe? Would a relay with lower/higher nominal current work better?

relay.jpg

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EdisonRex · Posted: Wed Oct 15, 2008 1:24 am Post subject:

Hi.

Couple of points off the top of my head. That relay is 1k and 11ma, so at a low voltage you're drawing a lot of power. Putting an LED (what rating, what current?) in series I can't think is going to help the poor 555 no matter how beefy it is - is it an LF555 or a NE555?

If you really want to drive a relay, best to drive it via a transistor.

I think you could probably use a 4016 or 4066 in place of a relay, but make sure you ground the switches you aren't using.

Oh yeah and that ".05A @125V" refers to the switching capacity of the relay, not the coil. That means if you can switch 5ma at 125V.

stolenfat · Posted: Wed Oct 15, 2008 2:53 pm Post subject:

could i add a tranny into my circuit that i already have built up? With the circuits shown in that pdf link, what could i do to add a timer to on/off the relay automatically?

The led came from a grab bag from radioshack, so i have no idea about the data regarding that...

But i did manage to get an led to blink opposite of the relay in the above circuit by adding it to point x and y shown above with a small resistor.

and the 555 is just a normal NE555, nothing special about it.

maybe if i added a power connection from the sk-1 internal batteries to the circuit with a diode and use it with another 9 volt to keep up some battery power?
I dunno, guess i gotta experiment.