Assistance with a voltage sensor switch

[jmaurer]

I'm connecting a digital doorbell to a 16v AC doorbell circuit. Using a Spore doorbell switch which is lighted by 4 LEDs. Worth noting because it does not behave like a normal doorbell switch. In the 'off' position it still passes about 6v through the circuit. When pressed the voltage spikes up to 16v during contact.

The digital doorbell unfortunately 'sees' the 6v as a button press, so it activates once when connected to the circuit then sits there basically assuming that someone has continuously pressed the button. It has two sets of leads: one for a hot circuit (assumes 0v = no button press, 6-16v AC/DC as button press) and one that is self-powered by an onboard 9v battery (assumes no external power and closed circuit as button press, open circuit as not).

I would like to front-end the digital doorbell with a voltage sensing switch that converts 6-8v and below to 0v (open circuit) and 9-16v and above to a button press (closed circuit). I could use a transistor switch to change the state of a mechanical relay, using the relay contacts to activate/deactivate the second set of doorbell contacts. The voltage sensing switch would either have to be powered by an onboard battery or by the doorbell circuit itself. I could use a full-wave rectifier to convert doorbell current to DC.

I have some electronics experience but am a long way from being able to identify what components would be needed to build this circuit up. A pointer to an existing circuit diagram/thread or some explicit directions would really be welcome! I've searched pretty extensively and found some automotive control circuits that come close but not quite there.

Thanks in advance!
Jeff

 

[Diver300]

Put a resistor in parallel with the doorbell.

Try 330 R, 1 W.

That will should keep the voltage down so that the doorbell doesn't see the voltage until the button is actually pressed.

 

[jmaurer]

Got it - thanks!

I had tried a parallel resistor earlier but a 1k ohm - no go. The 330 ohm was still too much resistance, but a 1 watt, 100 ohm worked great. Thanks so much.

Jeff

 

[Diver300]

Thanks for the feedback. You maybe should be aware that 16 V across 100 ohms will generate 2.5 W of power in your 1 W resistor. It's probably fine as the bell push is only pressed briefly.

 

[jmaurer]

Current across the resistor

I worried after that as well. Guess I'd better drag out Ohm's Law and attempt to be more precise in my work, and less ham-fisted.

The button press is momentary as long as someone isn't trying to goof around with it.

thanks, appreciate the advice!
Jeff