Frequency Meter

Posted on Jul 19, 2012

This basically the frequency meter section of the frequency meter/pulse generator based on the AT90S2313 described elsewhere on this site, combined with the 100 MHz RF interface described in the page about the RS-232 to 100 MHz RF desktop channel adapter. Built and align this is the same manner as the 100 MHz RF desktop channel adapter. The frequency meter has a maximum input frequency of 4 Mhz and counts up to 65535. Time bases of 10 ms, 100 ms, 1 second, 10 seconds, and 100 seconds are selectable from the keyboard via the RF link.

Frequency Meter
Click here to download the full size of the above Circuit.

I would suggest adding a 5 volt zener from pin 9 of the AT90S2313 to ground to reduce chances of damage to the input from electrostatic discharges. I did not put it on the schematic because I did not build this and try it. Take a look at the frequency and pulse generator project on this web site to see how I used the reverse base-emitter junction of a transistor to accomplish the same thing because I didn't have any appropriate zeners at the time of the project. The frequency meter sends to address $02 (the RS232 to RF Data Channel receive address) and receives address $03 (which is coded as $18 in the firmware because of the position of the address within the header byte). Firmware This firmware was a combination of the firmware from two projects, with the irrelevant parts removed. There are several assembler warnings of registers being assigned more than once -don't worry about it, there aren't any conflicts but it made hooking the two pieces of code a little easier and made the resulting file a little easier to read doing it this way. Here is the Assembler source file. In case its helpful, here is the hex file At power-on a greeting and menu is displayed. Individual readings are taken whenever the "R" key or return key are pressed. Variations A low battery indicator would be a nice improvement so that the terminal would be alerted when a low battery was detected. Additionally an LED could be added as a...

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