AVR Frequency Meter

Posted on Dec 5, 2012

This is design for a frequency meter based on AVR microcontrollers. Maximum input frequency is specified to be 30 MHz in the multi-chip configuration, and in single-chip configuration, there are both 5 MHz and 10 Mhz versions operating with 10 and 20 MHz crystals, respectively. All versions have 9 1/2 digit resolution. I have used multi-chip version at 40 Mhz, and depending upon the actual chips you use and your layout, it can work at much higher input frequencies. The 10 MHz single-chip version using the ATtiny2313 is ideal for use with a X10 or X 100 prescaler.

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

As for microcontroller choice, the requirements for this firmware are that the controller be an AVR with a 16 bit counter, has a ram stack and UART or USART, and the ability to operate at 10 MHz. Some modification may be required to the code to accommodate a USART instead of a UART, a 16 bit stack pointer instead of the 8 bit pointer on the AT90S2313, and the specific controls of the 16 bit counter registers. I used an AT90S2313 because they are available to me and suitably small. For the 10 MHz input single-chip configuration, you need to use an AVR that can clock at 20 MHz. I used an ATtiny2313-20. When programming the ATtiny2313, remember to select a fuse setting for the internal clock oscillator. The AT90S2313 does not have clock fuse settings. The first phase was to make a high resolution frequency meter/counter just using the AT90S2313 ot ATtiny2313, then to add the external prescaler. Without the prescaler, the maximum input frequency for the frequency meter is 5 MHz or 10 MHz, depending upon the chip you use and the firmware version you choose. With the multi-chip version that includes a prescaler, the maximum input frequency, according the the component specifications, is about 30 Mhz - this will vary with individual external prescaler chips and your circuit layout. To summarize, there are three versions of the code available at the top of this page: The 5 MHz single-chip version, which is basically an...

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