CB SNIFFER PROBE

It’s often difficult if not impossible to detect RF in mini-power RF circuits such as used in walkie-talkies; generally, service grade test equipment just isn’t sensitive enough. Next time you are working on a CB walkie-talkie and can’t tell if a lower power RF amplifier is working, just throw together a CB Sniffer Probe from remains of the old junk box. Better yet, why not be prepared in advance because all new components will cost less than $10. A small plastic rod about 6 inches long, cemented to L1, will allow you to se the sniffer as a probe. To align, place the sniffer near the antenna of a known good walkie-talkie, key the transmitter, and using an insulated alignment screwdriver adjust trimmer capacitor C1 for maximum brilliance of neon lamp l1.

Parts List For CB Sniffer Probe

C1 – 5 to 30 pF trimmer capacitor

l1 – NE-2 neon lamp

L1 - RF choke, ohmite Z-144 or equiv.

HOW TO MAKE HEART RATE MONITOR RECEIVER By RICK MOLL?-BIOMEDICAL PROJECTS

IDEA

Commercial HRM transmitters are available from several manufacturers. The HRM receiver

described here allows these transmitters to be interfaced to a small microcontroller or PC.



The HRM receiver is built on a 2.5 x 1.8 inch printed circuit board. It can be interfaced to just about any microcontroller that has an analog input. It will operate from the same 5V supply that powers the microcontroller. With each heart beat signal it receives from a wireless HRM transmitter, it outputs an analog pulse. These pulses are typically sampled with a microcontroller ADC port.

HRM Transmitter

This wireless HRM transmitter was manufactured by Polar, who claims to be the world's leading producer of wireless HRM equipment. Cardiosport and Sports Instruments manufacture similar equipment.

These transmitters are worn around the chest and generate a 5kHz magnetic pulse with each heart beat they detect. The transmitted magnetic signals are fairly weak, but typically have a range of over 3 feet.

These HRM transmitters can be purchased for as little as $40 (USD), or along with a no frills wrist style receiver for around $50 (USD).

circuit description

schematic

code


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