Need Some Help With A Electronic Timer

[Roytoner]

HELP

Need to get hold of a timer for our alarm for the windows at the mo it is draining power all the time, so if any one knows how this will wire up Lookie it would be a great help!!

need it to work when the earth become active so the + power will time out as well

Paul.

[sotal]

What exactly do you want to do?

We used to have to make loads of circuits with 555 timers in A level electronics. I've still got a load of circuit diagrams somewhere but the 555 curcuits are fairly simple anyway.

Do you just want to alter it so the alarm is only active for 1 second every 5 seconds or something like that? To save power

[Roytoner]

What I am looking for is a timer that is only on for about 1 min, as it is at the mo the relay for the windows is live all the time

[sotal]

Still not completley with you! Probably me though I'm knackered!

So let me get it right first....

You've fitted an alarm to the MR2 which I presume shuts the windows??? but it keeps sending power to the relay??? Is that right or am I barking up the wrong tree??

If that is how it is, then you want to build a timer so that the alarm output only sends power for 1 minute until it is reset?

If so then you need to make a monostable circuit. The bottom one on this image shows a monostable circuit, which would give power out for 1 second:

To get a minute use any of the following combinations of resitor/capacitor

Capaci Resitor

470uF - 116.05K

220uF - 247.93K

100uF - 545.45K

47uF - 1.16M

22uF - 2.48M

Then wire the old output from the alarm up as the trigger and use the output from this circuit to your relay.

Let me know if that isn't what you wanted!

[Chyownster]

Might need a Mosfet to drive the relay

[Roytoner]

Might need a Mosfet to drive the relay

Sotol you hit the nail on the head need something that kills the power after about 30 sec .

Chyownster what the hell is a Mosfet??

[DaveSR]

Might need a Mosfet to drive the relay

Sotol you hit the nail on the head need something that kills the power after about 30 sec .

Chyownster what the hell is a Mosfet??

Metal Oxide Semiconductor Field Effect Transistor ...... and that's all I can remember

The circuits posted will do the job fine ..... however pop in to maplins and see what kits they do as they are sure to do some 555 timer circuits

[Roytoner]

Thanks going down there on Sunday

Hate it when one thing leads to another

[Chyownster]

Indeed it is DaveSR :) It is used to drive the relay to initiate the relay. Its better due to its hight saturation of outputs