Counter Using RF

Thread Starter


Joined Mar 12, 2007

I need to build a counter that is triggered by presence of a RF field in a particular area.For this a constant RF field transmitter(fixed at a place) has to be built. and also a portable RF receiver along with a counter circuit to count the no. of times I enter the RF field has to be designed. I am having trouble selecting the proper transmitter and receiver and the output formats. A detailed explanation for this project from you guys is expected. I want the whole model to come out very cheap.Your suggestions and help is needed.

Venu Madhav


Joined Feb 24, 2006
I don't think your requirements are clear enough to even imagine a reliable design. Did you have a geographic range over which the device is to operate and some idea of the frequency you would use, and some idea of the power level.

I don't know about where you live and work but such a transmitter would be highly illegal in many parts of the world.


Joined Nov 17, 2003
It might also be an idea to state what specifically is posing you problems with your selection of the proper transmitter and receiver, and the output formats.



Joined Mar 22, 2007
It all depends on the frequency, area, power transmitted and such.

For the recieving part if the chosen frequency is around 1GHz, and this has been checked not to interfere with any surrounding objects, like your mobile phone then a simple diode detector could be one choice. You could have a small monopole antenna which has been tuned to the given frequency using lumped elements on microstrip transmission line.

The diode (schottky barrier) will then rectify this signal, and produce an output voltage. Something like 45mV/µW could be used. So as you get closer to the RF source, the signal strength will get higher and so the voltage output, with a RF choke, will increace also.
You could then have a transistor to act as a switch, so once the current gets to a certain level, the transistor switches 'on' which could be recorded with some sort of counter circuit.