Vermes
Advanced Member level 4
Electronic part
The counter 4017 was used to multiplex. The counter enables the transistors of successive displays. It receives a clock signal and reset signal to return to the first display. The counter has to be reset by uC, because if it resets itself, there would be some problems with the order of numbers. The reset signal had to be extended to 3us, because it does not react to shorter pulses. The clock signal does not cause such problems.
Atmega8 with external quartz 8MHz was used, PCF8583 calculated the time. Communication was made using TWI (hardware equivalent I2C).
The temperature measurement is done by DS18B20. It was put outside the housing, because the temperature inside is about 1-2 degrees higher (heat from the transformer and stabilizers).
DCF77 receiver was made on u4224b system. Ferrite core was taken from an old radio.
The display brightness can be regulated by PWM. ADC measures the voltage at the photoresistor, it uses 8 older bits of the result and enter them as PWM value.
Housing
The housing used for this device is from a radio-alarm.
Program
The program was written in C. Most functions are in the interrupt, only read and write by TWI are in the main loop.
T0 is responsible for multiplexing, T1 for PWM, T2 for reading the keys and auxiliary counters. There is another interrupt from ADC and external INT0 from DCF77.
Link to original thread (attachment) – Zegar LED z DCF77 i termometrem