I found this forum and thought this was really cool. I have no electronics knowledge what so ever. So if this is horribly remedial then please disregard.

I am building a small project that is a simple announcement tone in our house to let me to let me know when someone is at our dock. I am using components from an old garage door opener. A simple push button system from a garage door opener transmitter for when boats arrive at the dock or to signal someone up in the house from the dock. There is no power at the dock and I keep losing walkie talkies. So a simple button attached to a garage door opener transmitter in a weather proof box box is what I am making. Simple, cheap and replaceable. I enjoy doing simple projects like this. I know there are several systems I can buy but what's the fun in that?

Here is my question. Is there a simple way to put a low battery light at the transmitter side on the battery? Simple, LED so I can see it when I pass by.

 

I somehow get the feeling that you may soon be losing garage door opener transmitters.

If the battery is getting low, turning on an LED constantly will rapidly make the battery much lower, to the point where the LED will no longer glow. To maximize the battery life, the circuit would need to just flash the LED intermittently.

Another thought might be to have the low battery condition ring the doorbell occasionally, but limit it to ringing only during daylight hours (being summoned to the dock at 2AM to replace a battery would make me a tad surly.) This might be arranged by using a solar cell, phototransistor, photodiode, or CdS resistor (photoresistor, cadmium sulphide, sometimes called LDR). When the low battery condition rings the doorbell, it could also flash an LED to get your attention.

You might also consider using a solar cell array to charge a NiMH battery, so you would need to replace the battery much less frequently - if at all.

 

Though not convenient, you could add a momentary switch that you would have to "push-to-test". This would address the problem of having the LED indicator constantly on.

hgmjr

 

Since you like to MacGyver things together, I offer you this as a possible solution:

Go to the hardware store and buy one of those outdoor hanging lights with the solar cell for recharging its two AA batteries (~$30-$40). Disconnect the LED that is used for the light, and hook some wires into the battery compartment to run your garage door opener. During the day the solar panel circuitry will keep the batteries charged, disconnecting the LED will prevent it from draining the batteries at night.

You may occasionally need to replace the batteries, but much farther between than non-rechargeable types.

 

I assume this replies to all who answered. Thanks, I like the photcell and battery suggestion. Never thought of that. I also liked gutting the outdoor light. I may gut a smoke detector and look at the low bat chirp in them. Awesome, site. I am sure I will be back with more questions.

 

If you gut a smoke detector, remember that many of them have radioactive components in them that must be disposed of properly.

More info: http://www.google.com/search?hl=en&q=smoke+detector+disposal