I am Nikhil from India, working as an embedded programmer. I made half inch 7segment display based digital clock. But after few months few 7segment displays got damaged. I got same complaints in many boards. Please help me to debug the error.
5v dc power supply is used.Pic16f877a is used for controlling.74hc164 is the shift register ic used.
Bd140 transistor is used for on/off 7segment display.
5v is connected to the emitter of bd140.
Base is connected to pic microcontroller via resistor.Collector is connected to common anode of 7segment display.Cathode pins are connected to 74hc164 via current limiting resistors.
I think this is the recommended connecting method. But around 1/10th of the total segments used are getting damaged within few months.
I used 560e as current limiting resistor and increased its value upto 2k2, but no change only brightness is getting down.