Intelligent Flickering Light

Whether it is required to simulate an open fire in a nativity scene, a forest fire in a model railway landscape, a log fire in a doll’s house or simply for an artificial candle, neither steady light nor the commercially-available regularly flickering lights are very realistic. The circuit described here imitates much better the irregular flickering of a fire.For maximum flexibility, and to reduce the component count to a minimum, a microcontroller from the Atmel ATtiny range has been selected to generate the flickering pattern. Two miniature light bulbs, each driven by a transistor, are controlled using a PWM signal to produce eight different light levels. Potentiometer P1 in the RC network adjusts the speed of the clock to the microcontroller, and hence the speed of the flickering.

Resistors:
R1,R4,R5 = 4kOhm7
R2 = 10kOhm
R3 = 1kOhm
R6 = 220Ohm
Capacitors:
C1,C2 = 100nF
C3 = 10µF 16V
Semiconductors:
D1 = 5.1V zener diode, 400 mW
T1,T2 = BC547
IC1 = ATtiny11-6PI (programmed)
Miscellaneous:
L1,L2 = 6V / 80mA miniature lamp
PCB no. 040089-11, available from The PCBShop
Project software: file 040089-11, Free Download