I'm trying to built a key ringer (which can be attached to the key as key chain so that it can be easily found out with the help of the beep sound when misplaced). I know its available in the market but wanted to make one of my own.i figured it out that it should have a RF transmitter receiver with a beeper attached tot he receiver ,but dunno really where to start. This is the one I'm talking about http://www.keyringer.com/ .Saw many circuits like whistle key finder etc but this the one i really want to make.

 

Yeh, but how do you find the key ringer when you lose it?

 

I remember seeing those years ago. They were not activated by a remote. You would only lose the remote anyway

They were activated by clapping your hands - making some noise - and the device would respond by chirping.

So I reckon you need a device with a small microphone and a small speaker. It would have to come on only in response to a sudden sharp sound, otherwise it's battery would run down with ambient noise.

No remote control device would make sense.

Good luck

 

Hey! I've just read the full site you referred to http://www.keyringer.com/

and it does seem a sensible solution. Each device can find another. So you keep one of them safe always - as suggested - stuck to your fridge.

Still - the temptation to walk about with the 'safe' one when something is lost, would inevitably lewad to its loss also

It's easier to make a whistle or clap as neded

D.

 

Unless you want to build an RF receiver/transmitter from scratch I recommend low power RF ICs from Micrel or Linx Technologies.
There are several different types available.

Example:http://www.micrel.com/_PDF/micrf002-022.pdf

Your major obstacle is battery capacity. There exist "long" range passive transponders but that's a much more complicated project.

The above mentioned low power UHF receivers need to be used in polled operation, in order to save current.