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Minimum Mass Wireless Coupled Frequency Meter
Near Field Communications (NFC)
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.

The basic Minimum Mass Wireless Coupler technology is described and links to other projects on this site that use the Minimum Mass Wireless Coupler are located on the web page, Minimum Mass Wireless Coupler.

Downloads
Download the AVRStudio assembly source for the program: vlffmtr2313.asm
Download the AVRStudio assembly source for the include file: vlfcw2313.inc




The all parts except the loop antenna fit inside a battery case.
The loop was squashed a little bit to make it fit the shape of
the case.






The circuit is as simple as it can get and still work.
Wiring is not critical.

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. 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 is applied to the input leads when the power is off.

A battery saver shuts down the controller and power to the bias resistors if the circuit does not receive a command for a long period of time. This one feature has saved me from having to replace the batteries a number of times already.

With respect to firmware, this is basically the RS-232 Freq. Meter/Pulse Generator Based on Atmel AT902313  from elsewhere on this site. I just removed the pulse generator part of it and replaced the calls to the UART with calls to the Minimum Mass Wireless Coupler driver, which are provided by the .inc file.

The red "operating" and the green "ready" LEDs from the original design were not used becasue this is a battery powered device, and with that scheme, one LED is to be on all the time the unit is powerd up. As it is, there is one yellow LED that indicates activity on the Minimum Mass Wireless Coupler and that is enough.


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Contents ©2005 Richard Cappels All Rights Reserved. http://www.projects.cappels.org/

First posted in March, 2005

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(Summary: No warranties, use these pages at your own risk. You may use the information provided here for personal and educational purposes but you may not republish or use this information for any commercial purpose without explicit permission.) I neither express nor imply any warranty for the quality, fitness for any particular purpose or  user, or freedom from patents or other restrictions on the rights of use of any software, firmware, hardware, design, service,information, or advice provided, mentioned,or made reference to in these pages. By utilizing or relying on software, firmware, hardware, design, service,information, or advice provided, mentioned, or made reference to in these pages, the user takes responsibility to assume all risk and associated with said activity and hold Richard Cappels harmless in the event of any loss or expense associated with said activity. The contents of this web site, unless otherwise noted, is copyrighted by Richard Cappels. Use of information presented on this site for personal, nonprofit educational and noncommercial use is encouraged, but unless explicitly stated with respect to particular material, the material itself may not be republished or used directly for commercial purposes. For the purposes of this notice, copying binary data resulting from program files, including assembly source code and object (hex) files into semiconductor memories for personal, nonprofit educational or other noncommercial use is not considered republishing. Entities desiring to use any material published in this pages for commercial purposes should contact the respective copyright holder(s).