Anti-Lost Alarm

Hi, I actually wanted to build an anti-lost alarm which has a transmitter and a receiver. Function of this alarm is to track a lost pet or child. So the transmitter will keep on sending the signal to the receiver as long as both device are on and synced. When the distance is too far away then the receiver would alert the user. For the transmitter i had decided to use NE555 timer as my IC to provide oscillation work, but for the receiver IC i have no idea, can anyone help for this?or any other information you need just let me know.

Much appreciated

I concur with Colin. Your choice of an NE555 for the "transmitter" indicates that you don't have the experience to tackle such a project -- i.e. one that requires a high level of reliability (where pets and human children are involved). So, do as Colin suggests and buy one -- and then choose a "beginners" project that doesn't affect the health/well being of pets or people.

I'm not that fond of 555's. They aren't that stable so you won't have that accurate a frequency and will have problems with the receiver. It will need to have a pretty wide range and then may pick up other stuff, which would be a bother.

A L4LS221 (dual 121) or some such would be much better, but why not a ceramic resonator and an op amp? That would be real stable and accurate and not much more than a 555.

I've never done a receiver, but there must be lots of circuits out there. Can you find anything by searching for carrier detector?

You could use saw filters such as used in remote control key fobs not only for transmitters but also for receivers

See below
http://www.freescale.com/files/microcontrollers/doc/app_note/AN3457.pdf

Think about common day usages example Rf door bell This also uses saw filters resonators to do exactly the same thing

See below
http://www.epcos.com/web/generator/Web/Sectio...F/PDF__AN1,property=Data__en.pdf;/PDF_AN1.pdf

You may not understand all of this but its still worth reading
http://www.meis.tu-berlin.de/fileadmin/fg54/AnalogWorkshop/2008/AW_Oheim_Stimman.pdf

OR

Simple Hartley oscillator or think about small radio controlled cars using the Rx-2B Tx-2B IC's
http://labmanual.blogspot.co.uk/2011/10/hartley-oscillator-electronic-devices.html

OR

Cmos logic oscillators using 4069 etc good enough for MW which is all you need

http://www.discovercircuits.com/DJ-Circuits/parallelosc.htm

Thanks for your help. I will look through all the link :)

Much appreciated.

I understood. Yes i have no experience about this. I shall learn from the basic Thanks
Your comment helped me alot.

Welcome

sorry just feel curious on this...is this circuit actually works? i got this from the internet...i tried to simulate using Multisim but i cant find those IC in the library...anyone can help on this?

Thanks and much appreciated.

Hi,
I just saw this page and wanted to let you know that the Epcos link has moved to:
http://www.epcos.com/epcos-en/529540/products...omotive-electronics-remote-control/resonators