When monitoring the output to a speaker from one of my wireless doorbells, I see that when the speaker would previously have sounded (before I removed it from the circuit), the voltage drops from 0.27v to 0.
I've never come across something which is turned 'on' by an absence of voltage and is 'off' when given voltage - and such a low voltage at that.
The other doorbells in my repertoire are to my mind 'conventional' - they're off when I measure no voltage and 'on' when given 3v or 4.5v....
Speakers respond to AC current - you are measuring a DC voltage on no-load I suspect. The 0.27V is likely to be due to residual charge on the output electrolytic capacitor in the output circuit (adding the speaker will quickly discharge this, a high-impedance voltmeter is only going to slowly discharge it).
Not sure why it drops to 0V though, but I wouldn't worry about it, set your meter to AC volts and re-measure...
MarkT:
Speakers respond to AC current - you are measuring a DC voltage on no-load I suspect. The 0.27V is likely to be due to residual charge on the output electrolytic capacitor in the output circuit (adding the speaker will quickly discharge this, a high-impedance voltmeter is only going to slowly discharge it).
Not sure why it drops to 0V though, but I wouldn't worry about it, set your meter to AC volts and re-measure...
You're right Mark, I am measuring DC on no-load.
Can the Arduino accept an AC input? It seems to be the only one of my wireless doorbells (I am using three different types) which uses AC current.
It looks like doorbell had a piezo buzzer as a sounding device, not a real speaker. Piezo doesn't require AC, so it was driven by modulated DC w/o ant electrolytic caps. And it explains 0.25V - logic "low" level.
If there is no AC, it could be connected directly to arduino, analog or digital port.
