Hi everyone!
Can someone please educate me on the simplest way to turn a relay on and off automatically?

I tried using an automotive flasher (for turn signals etc) but it didn't work. The circuit is operating on 12v DC. The relay that is being switched on and off is controlling a PC relay and toggles btwn 2 lights.

I was doing research and read about that 555 implementation but that seemed too involved for what I need to do.

Thanks!

 

555 would really be a very simple way to do it.

just have a 555 osscilator (only requires the 555 chip and a few extra components), turning on and off a transistor, which controlls the relay. There are other ways, but this is probably the nicest and simplist way.

So your saying you've got a relay controlling a relay?? Why not miss out the first relay and controll the 'PC Relay' directly? Or is a 'PC Relay' somthing I've not heard of...?

On a side note, how fast are you wanting to turn this relay on and off?

Tim

 

I had the relay control the other relay because I wasnt sure if the automotive flasher would work with all of the resistance of the whole circuit, so I kind of isolated it in its own circuit. If it would work with out that first relay, then out the window it goes. So, 555 is the best way to go? Maybe I was reading about something else. So what would a 555 setup cost me?

Also, I want it about as fast as turn signals, so about 1 second cycles.

 

ok, basic 555 circuit as shown below.

couple of capacitors, couple of resistors, and one IC. Max cost about £1. Transistor to power relay - depending on the type of relay, probably no more than £1.

Total cost, therfore - about £2.

1 Second cycles should be fine - do they need to be extremely accurate?
components for 1 second cycles - I assume that means that it flashes once a second, not on for a second,and then off for a second?
Anyway, for a frequency of 1Hz, use this formula:

Frequency = 1.44/((R1+R2+R2)*C)
(i will work out the values when i've woken up)


Also, if you are not using a solid state relay, you will probably hear the 'clicking' sound of the relay - which presumably you don't want.

Tim

Attached Images

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Thanks for the post. The cycles dont have to be exact. And I dont care about the sound at all. I will go to Radio shack and start buying stuff (=

 

my brain hurt trying to solve that formula, so I used the calculator at (just for future reference): http://www.priory.bromley.sch.uk/stu...555astable.asp

it reckons something like R1=2.2K, R2=68K, C=10uF will give an approx 1Hz output. Duty cycle is roughly 50% - i.e. the light would be on for about the same time as it is off.

You may want to play with the values until it suits you.

Have fun.

any other questions just ask,

Tim

 

Well, I got the 555 to work. For R1 I used 1K, for R2 I used 1000k. I used .1uf for C. It gave me a 50% duty and just the speed I need. Thanks alot guys for your help!

 

no probs