Using this circuit diagram can be made a very simple charger for NiCd batteries, using a timer 555. Internal comparison window is fixed at 4.7 V by Zener diode D1. If potential of pin 6 exceeds this level, the output voltage at pin 3 is "0". If potential pin 2 drops below half the reference voltage (2.35 V), the output voltage becomes "1".
Using a 555 timer circuit and some other electronic components can be made a small voltage converter that provides a negative voltage of 12 V at a rate of a few milliamps. 555 circuit is connected as astabil frequency of 125 kHz. Network C1-C5-D2-D3 form a cascade circuit which provides a negative DC voltage. Since in the scheme was not used either a transformer or inductor, converter efficiency is not very high: up to 16% at a current of 20 mA output.
Using this circuit diagram can be built optocoupler electronic circuit resistant at incident light. This optocoupler resistant at incident light is simple to make and is built using a 555 timer and some passive electronic components.
Timer 555 provides the optocoupler LED pulses at a frequency of 10 kHz. If at the receiver output will only be amplified signal having this frequency, no natural light or artificial light of day and will not disrupt the functioning of intense light barrier.