I have a sensor which switches on mains (AC 220v) for roughly 5 secs each time it is activated. and I have this wired to a relay. I want the time period the relay is activated to be reduced by about 1/10, what is the easiest way to do this without messing with the sensor?
Thanks.
More information is needed to judge - how is it wired? what is it? what is
the relay? How are the sensor and relay powered?
MarkT:
More information is needed to judge - how is it wired? what is it? what is
the relay? How are the sensor and relay powered?
See diagram for wiring.
It is a system with a sensor which when activated rings a doorbell by way of a relay. The relay is a spdt 220v coil. The sensor is powered by 220v mains as is the relay. The sensor is mounted outside far from the relay which is inside. The doorbell is remote. At the moment the doorbell rings for a prolonged period as the switch remains on for 5 secs rather than being momentarily on when pushed manually.
CR network (capacitor then resistor) as a differentiator, short pulse then triggers a 555 monostable. Wire the relay contacts in so it is normally high and creates a short 0V pulse.
I can draw you a circuit when I'm home later.
polymorph:
CR network (capacitor then resistor) as a differentiator, short pulse then triggers a 555 monostable. Wire the relay contacts in so it is normally high and creates a short 0V pulse.I can draw you a circuit when I'm home later.
Thanks. I thought about a 555 circuit but had the impression they were more or less obselete these days and it would mean havng to have a low dc voltage to power the circuit. I also thought about a mechanical rather than electronic solution using two relays - see diagram. I was kind of hoping there might be a nicer, neater solution!
Obviously the 555 timer is not obsolete, there are at least a half-dozen manufacturers making different kinds of them.
Good point about requiring a low voltage. I'll have a think.
polymorph:
Obviously the 555 timer is not obsolete, there are at least a half-dozen manufacturers making different kinds of them.Good point about requiring a low voltage. I'll have a think.
Yeah ok but the last time I mentioned it I got the strong impression it was outdated. Anyway it seems like there isn't a neat solution, at least not an obvious one so the double relay might actually be a contender.
The 555 timer has been around for a long time, and some scoff at it, but it is still a lot simpler to use for simple tasks.
I think what you've drawn might work. Although you might need to do something to slow the relay on the left a bit. If it were DC, I'd suggest a shorted turn around the relay coil, but that won't do for AC. A bit more mass on the contacts, maybe?
Have you tried it yet? I don't see any inherent problems with it. Although the relay coils are inductive loads and so will cause arcing, an RC series snubber could solve that, and a relay is a very light load for another relay to switch, so maybe not necessary to worry about it.
You do realise that when you do this your sensor will be dead for the 5 seconds anyway?
Since it rings a doorbell, and he doesn't want it going off for 5 seconds, I suspect it doesn't matter.
Just tried it and it doesn't work. Yes I need more than a few milliseconds. I'm not keen with mains voltage, least of all messing around with the relay. Even if I got it working with weights or such I'd surely end up throwing the house into darkness at the least convenient time in the near future - probably when the wife is alone!
Yeah, I certainly want to kill the sensor for the 5 seconds!
Reducing the active time by 1/10 would reduce the active time from 5 seconds to 4.5 seconds.
michinyon:
Reducing the active time by 1/10 would reduce the active time from 5 seconds to 4.5 seconds.
Sorry I meant to 1/10 not by 1/10.
What voltage is coming from the sensor to power the relay?
If 220V, then perhaps that could power a power supply that would power up a 555 timer wired as a one-shot that only triggers when the power turns on and won't retrigger until power is cycled off and back on again. A 5V relay could replace the 220V relay.
polymorph:
What voltage is coming from the sensor to power the relay?If 220V, then perhaps that could power a power supply that would power up a 555 timer wired as a one-shot that only triggers when the power turns on and won't retrigger until power is cycled off and back on again. A 5V relay could replace the 220V relay.
Yes 220V. I would appreciate a circuit diagram.
I am currently a college student and so by no means am I guaranteeing this circuit will work, but out of curiosity after reading this thread I drew up a circuit I thought might work. If it doesn't work no worries and I will remove it or correct it and change the picture.
Crop and resample, please. 3264x2448 pixels is -way- to big.
My apologies I took the picture with my phone and had no idea it was so large, I just re-sized the image.
I think the OP was hoping for a schematic, not a block diagram.
I'll try to find some time to draw something up later today.
