miniature running lights

elektor July/august 1985 The type UAA170 integrated circuit is normally used to drive up to sixteen LEDs, and the present circuit is no exception, as can be seen from fig- ure 1. The 555 is used as an astable multivibrator, but note that its output is not connected to the UAA170. Instead, the driver is fed from the junction of an RC network with a triangular voltage, the period of which is set with P1. It is advisable to use a tantalum capacitor in the C1position to keep the leakage current down. The voltage at the input of IC2must not exceed 6 V. To ensure that the triangular voltage remains below that value, the supply voltage of IC1is limited to 9.1 V by D17. If necessary, this zener diode may be replaced by an 8.2 V or even 6.8 V type. The voltages on pins 12 and 13 determine the voltage range swept by the LEDs. The reference voltage for D16 is pro- vided via pin 5 of IC1and amounts to about 2/3 of the supply voltage to the 555. The reference voltage for D1is 81 12 V 10 11 13 ...