Wireless doorbell battery monitor

wireless-doorbell-battery-monitor

We know exactly what [Dan] is going through. We also bought a cheap wireless doorbell and are plagued by the batteries running down. When that happens, the only way you know is when people start pounding on the door because you’re not answering the bell. Well no more for [Dan]. He built a backup system which monitors the voltage of the batteries on the chime unit.

You can see the small bit of protoboard he used to house the microcontroller and the UI. It’s an ATtiny13 along with a green LED and a single push button. The idea is to use the chip’s ADC to monitor the voltage level of the pair of batteries which power the chime. When it drops below 3V the green LED will come on.

First off, we wish these things would come with better power supply circuits. For instance, we just replaced the CR2032 in an Apple TV remote and measured the voltage at 2.7V. That remote and the chime both run from a 3V source. Can’t they be made to work down to 1.8V? But we digress.

In addition to monitoring voltage [Dan's] rig also counts the number of times the chime has rung. Every eight seconds it flashes the count in binary, unless he presses the red button to clear the count. This is shown in the video after the break. We guess he wants to know how many times this thing can be used before running the batteries down.

Seriously though, for a rarely used item like this how hard would it be to use ambient light harvesting to help save the batteries? Looking at some indoor solar harvesting numbers shows it might be impossible to only power this from PV, but what if there was a super-cap which would be topped off with a trickle from the panels but would still use the batteries when that runs down?

Comments

  1. J. Peterson says:

    We have a light switch based on Enocean’s “energy harvesting” switches. The motion of the switch itself provides the energy to send the RF signal to the receiver. The switches were expensive ($200+ for the transmitter + receiver switch) but it works reliably and we never have to worry about replacing batteries.

  2. Anybodysguess says:

    I had the same problem, but it was reverse of his. The indoor unit I have, plugs into the wall. But the transmitter runs on a 12 volt battery that is very expensive and had to be replaced ever 6-8 months so I replaced it with a 9 volt battery, hidden behind the door frame! Just make sure you get a good name brand battery that uses a plastic bottom, because the ones that use a card board bottom will crumble in the humid air.

  3. Smonson says:

    By the time a lithium cell is down to 1.8v it is basically dead, there’s not much point trying to squeeze it any harder.

  4. browsem says:

    I just wired the send units of mine, to my inhouse 12v system. For some reason they include a blue led, that just drains the battery. Now for getting some cheap solar panels on the receiving end :-)

  5. echodelta says:

    Duino? Bigger battery or wall wart. Easy. It’s that tiny stacked 12volt battery, as another has noted. I will have to try the 9volt though. Combine the other hack today and like the $200 dollar switch, use a pull weight to set up a generator. Or the old fashioned turn-key dinger with a multipole generator under the housing. Steampunk.

  6. cde says:

    Funny, my like 10 year old wireless doorbell for the house uses 4 D cell batteries and tells you “Chime battery low” when it gets low. The door part uses 2 (or 3) cr2032s and those don’t tell you though.

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