This is a simple divide-by-10,000,000 using an 8-pin AVR, the ATtiny13. It can be used to lock the QRP Labs kits (Ultimate3S QRSS/WSPR Transmitter, VFO/Signal Generator, and ProgRock) to a 10MHz frequency reference.

The ATtiny13 is clocked at the 10MHz input frequency from the frequency reference. You may need a buffer amplifier here if the amplitude of the 10MHz Frequency reference is not enough. The leading edge (low-to-high transition) of the 1pps output is very accurate. The pulse width is approximately 100ms (0.1 seconds). There is also a sync signal input. A low-to-high transition on this input restarts the timers, so that it synchronises the 1pps output with the incoming pulse input. Connect it to ground if not used. 

Pin connections

Pin 1 (processor reset) connect to +5V
Pin 2 is the 10MHz input frequency
Pin 3 is the output 1pps, i.e. input divided by 10,000,000
Pin 4 (Gnd) connect to 0
Pin 6 is the sync signal. A low-to-high pulse here syncs the 1pps 
Pin 8 (Vcc) connect to +5V


Hex file for installation on an ATtiny13
C source file


The hex file should be installed on the ATtiny13. There is no EEPROM file (.eep). The fuses need to be set for external clock and remove the divide-by-8 fuse setting.