Cellular Phone Jammer Detector

Use an old analog cellular phone to verify the integrity of the cellular phone network in your local area.

A neat thing about old cellular phones is that when they power on they switch to a local roaming network.  On Motorola handsets, the yellow "Roam" LED will start to flash, even if the phone is not activated.  If for whatever reason, say ladyada is on a jamming spree, the phone will then begin to light the red "NoSvc" LED.

If we tap the "NoSvc" LED and add a simple digital logic counter and 555-timer circuit, you can trip a relay to activate a buzzer or a pager whenever the cellular phone is out of service or jammed.  The counter circuit waits until the "NoSvc" LED lights pulses on-and-off eight times, then it activates a piezo buzzer for three seconds.

By adding an external duplexer and a little attenuation, you can increase the jammer's detection capability.

Block Diagram




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