What is it?

The gated GPS locked frequency counter or frequency standard is a standalone unit which uses the pps signal from the GPS module to calibrate its internal frequency and locks to it to be able to read other frequencies in frequency counter mode or provide a frequency standard when in that mode. An SI5351 module is used for the reference frequency standard mode together with the GPS lock to accurately set the frequency.

Why did you make it?

I always was looking after building such a unit and my old faithful counter always was few Hz off. So this project uses a dual 16 bit counter to form a 32 bit counter where the frequency to be read is converted to a square wave and fed to the counter chip which is then represented as a 32 bit long binary number. This is read by the avr atmega328 and converts it to and show it as the measured frequency.

The board features an input transistor amplifier and also a frequency standard output and gps Connection by means of a side sma connector. Display is a 20x4 and can be driven by the i2c adapter or onboard pcf8574 expander chip. The board was designed to accommodate the si5351 with a tcxo and optional a si5351 can also be used.

What makes it special?

• Calibrates by GPS Lock

• Shows current GPS Time and date

• Serial Output for monitoring

• Powered by 9v with on Board Regulator

• Gate Switch with selection 1,2,5,10 seconds

• 10Mhz or any other frequency(set in code) Output

• 1PPS Output

Assembled Board with 20x4 lcd