Wireless Coupled Frequency Meter

A 0 to 2 MHz ferquency meter with a Minimum Mass Wireless Coupler, based on the ATMega8.Range to the Minimum Mass Base Unit is 10 to 15 cm. Since the frequency meter is battery operated, it can be floated from ground, making life in and around the test bench a lot simpler. No need to connect it to the computer or LCD display - just turn in on and place it next to the base unit. A simple one chip frequency meter was the first instrument I updated with the Minimum Mass Wireless Coupler. The frequency meter is self-contained, including batteries. The only external electrical connection is pair of wires to connect to the signal being measured.
Wireless Coupled Frequency Meter - schematic

To use it, I merely attach the input leads to the signal I want to measure, place the meter next to the base unit and switch it on. The activity LEDs blink on both enclosures as the frequency meter sends its command menu and -voila! -the menu prints on my computer screen and the system is ready for taking measurements. After the frequency meter sends its command menu, it "disconnects" from the RF channel. In other words, it does not respond to commands or send data until it receives an ASCII control-A character, which is its reconnect command. A control-B character from the keyboard disconnects the meter from the channel again. Other devices use different control codes, for example, the scanning voltmeter uses control-C do connect and control-D to disconnect. This discipline allows multiple Minimum Mass Wireless Coupler equipped devices to share the same Base Unit without interfering with each other. The circuit shown on this page uses the simplest possible implementation of the Minimum Mass Wireless Coupler. As long as the input signal swings through the chip's logic switching thresholds, it will be counted. As the battery voltage drops lower and lower, the 1N916 protection diodes will keep the input pin on the controller from exceeding the maximum current shown on the data sheet. A further protection is the upside-down transistor connected as a low current zener diode, just in case the batteries a large signal...

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