Hi there,
I'm building a timer for stairs. You can see the attached schematic.
The circuit is working well.But I'm meaning to make some changes in it for some reasons:
You know, the circuit is drawing current all the time even when nobody is using the light. I have seen the timers that one head of the switch in them is connected to the mains so whenever the switch is hitted the timer starts to work. But I can't figure out the trick for this circuit. Do you know the trick?
The other benefit of this circuit is that the number of the outputs reduce to 4 and so it's more commercial in wiring.
Appreciated for your assit.

You mean when you step your foot onto the fist stair, the timer starts and turns on & after while its turning off like that?

I think you have already done that.

Monstable mode switch is the trick there’s no any other trick.

hi fahime,

I see that you are switching the 'neutral' line with your relay contacts.

The problem is that the light socket and all the wiring from the mains supply
to the relay contact is 'live' all the time!

Ideally you should switch the 'live' side of the light.

There are circuits using the 555 that will give a delay/timing period when the power is applied to the 555. Simliar to what Gayan is suggesting.

A pressure pad placed under the stair carpet, at the foot or at the top of the stair makes a good trigger switch. You can buy pressure pads designed for stair tread sizes.

Is a inversed diode needed for the coil of the relay? Otherwise the ouput pin of the 555 timer may be destroyed, right?

Originally Posted by bananasiong

Is a inversed diode needed for the coil of the relay? Otherwise the ouput pin of the 555 timer may be destroyed, right?

Yes I agree!

I have seen a 555 driving a relay coil with two protection diodes. The 2nd one is in series to prevent the clamped flyback voltage from exceeding the supply voltage.

Which won't happen and the 0.7V across the diode isn't going to hurt.

Originally Posted by audioguru

I have seen a 555 driving a relay coil with two protection diodes. The 2nd one is in series to prevent the clamped flyback voltage from exceeding the supply voltage.

Why the series diode is needed? I thought the reversed parallel diode limits the flyback voltage to 0.7 V? Is it needed for every relay switching design?

The diode across the coil clamps the flyback voltage to be 0.7V higher than the supply voltage. I have seen many circuits with two diodes for a 555 that drives a relay.

I just looked through a few datasheets but I couldn't find a word anout it.

Fahime sorry for changing your circuit.

But for the staircase to turn on & off a relay you don’t need a timer or an electronic circuit. Have you heard about two way switch method? Can do from it.But practically its hard to place the on off switch instead of push on switch.

Now I don’t have the diagram. If need I’ll draw & give.

But you have to step the last step also to turn off the relay.

Your comments are very useful. Thanks everyone.
But I haven't gotten my answer yet.
In my design the switch is on the way of trigger signal. And it doesn't cut the mains when it's up. I wanna to put the switch on the way of the mains. What changes should be done in the circuit to fulfill this ?
If I'm not so clear please tell me to explain more.

hi fahime,
Is this what you were asking???