Wiring Schematic Diagram

This circuit is intended as a reliable replacement to thermally-activated switches used for Christmas tree lamp-flashing.

The schematic diagram formed by Q1, Q2 and related resistors triggers the SCR. Timing is provided by R1, R2 & C1. To change flashing frequency do not modify R1 and R2 values: set C1 value from 100 to 2200µF instead. Best performances are obtained with C1= 470 or 1000µF and R4= 12K or 10K. Due to low consumption of normal 10 or 20 lamp series-loops intended for Christmas trees (60mA @ 230V typical for a 20 lamp series-loop), very small and cheap SCR devices can be used, e.g. C106D1 (400V 3.2A) or TICP106D (400V 2A), this last and the suggested P0102D devices having TO92 cases.

R1    : 100K
R2,R5 : 1K
R3,R6 : 470R
R4    : 12K
C1    : 1000µF/25V
D1-D4 : 1N4007
D5    : P0102D
Q1    : BC327
Q2    : BC337
PL1   : Male Mains plug
SK1   : Female Mains socket

Warning! The device is connected to 220Vac mains, then some parts in the circuit board are subjected to lethal potential! Avoid touching the circuit when plugged and enclose it in a plastic box.