testeur de transistors

This circuit is intended to give clear warning when it is time to replace the stylus in a record-player car-tridge. The unit indicates the `playing time` that has already elapsed, using five LEDs. The f irst LED lights after the stylus has been in actual use for 100 hours, and each following LED lights after a further 100 hours. After 500 hours all LEDs are lit, indicating that it is time to replace the stylus. Otherwise, after a further 100 hours the f ive LEDs start flashing on and off -signal ing that it is now high time!