How To Build A Psychedelic Light Show Circuit


The output from the speakers is directly connected to the input of 

the unit (a parallelconnection). The audio input received is stepped

up by the respective audio transformer (left speaker input by left

section and right speaker by right section (SEE FIG) and fed to the

base of transistor via a potentiometer. The audio transformer also

acts as an isolation transformer keeping the mains supply isolated

from the input sockets. The design of the audio amplitier is not

critical and so any audio transformer of mediunr size may, be used

for this purpose. The side having lesser number of turns is connected

to the inputand the

side having greater number of turns is connected

to the potentiometer. The output from the transistor is used for trig-

gering) SCR (Silicon Controlled Rectifier).

An SCR can only be triggered when a positive pulse is applied to ‘

its gate. When the SCR is triggered, it comes into conduction and

allows the current to pass through it. The gate loses its control

once the SCR gets triggered and the control can be restored only

when the current through the SCR is interrupted. When smooth DC

is applied across the SCR, and then triggered, the SCR comes into

conduction. lt stays in this stage even when the gate is left open.

(i.e. ho pulse) showing thereby that the gate has no control over the

conducting SCR. But here, for this electronic unit to function, we re-

quire a condition such that the SCR switches off when the pulse from

the gate is removed. In other ‘words, we want that the gate should

have full coutrol over the current passing through the SCR.`To

achievelthisgcondition we supply AC or un·filtered DC to

the SCR

tliisicase after every half cycle the current crosses the zero level line

and so thecurrent through the SCR is interrupted twice in each cycle

(i.e. 100 times/sec.), Thus, whenever there is a pulse at the gate, the

SCR triggers and the lamp lights up. When the pulse comes down

to zero, tne SCR comzs into non-conducting state and the lamp

switches off. When AC supply is used the intensity of the lamp

reduces as only positive half cycle can pass through the SCR to fthe

load. In th: case of full wave unfiltered supply full brilliance is

attained. The potentiometer controls the intensity and the flashing



Parts Required for building psychedelic light show circuit

I. Transistors : ‘ BC 107 (2 Nos) .

2. SCR : 600 PIV 3 Amps (2 Nos)

3. Diodes : 1SMl (5 Nos)i

4. Audio Transformer : 2(Nos) il

5. Condenser : clcctrolytic 1000 mfd 15 volts (I No.)

Article Written By Swagatam

Swagatam is a blogger at

Posted on: Last updated: 25-07-2016 209 0

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