Hi,
I am trying to connect my 12V AC doorbell into a wireless transmitter. This is to notify me when someone rings the doorbell.

I built a simple circuit which works BUT only if a doorbell button is pressed for ~1.5 or more seconds - while most of the people press it for a fraction of second.

Here's the link to the circuit: http://tinyurl.com/y8ckn5l2

The wireless transmitter (on the right) needs approx 0.75 second to be react. I think the relay (middle box) needs another 0.75 second from the time the doorbell button to close the circuit. How can this be addressed? Adding a capacitor? Replacing relay with a transistor?

Thank you,
Jack


Mods Note:
The circuit was copied from #4.

 

Please post your circuit here. Many people at AAC won't go to unknown sites.

A relay will typically pull in no more than a few tens of milliseconds, so the problem should be soluble. You may need a "pulse stretcher" of some sort (555 timer is very popular).

 

Try a large electrolytic cap across the DC out.
Max.

 

Here's the drawing...

Thank you,
Jack

 

Easiest/simplest way is try the cap version first.
Max.

 

Easiest/simplest way is try the cap version first.
Max.

Thanks! I will give a try.

 

I would personally use a one shot ic 9r pulse stretcher. You can accomplish this with a LTC6752 or really any dual comparators.

The first comparator detects the start pulse. When it is closed the timing capacitor is charged. The capacitor then discharges through a resistor to the gate of the second comparator closing the circuit for the transmitter. Once the capacitor is depleted then the gate is open again, however I would personally have either a relay or optocoupler in between the doorbells rectified AC and your circuitry.