The drawing below illustrates a multistage light sequencer using
descrete parts and no integrated circuits. The idea is not new and
I hear a similar circuit was developed about 40 years ago using
germanium transistors. The idea is to connect the lights so that
as one turns off it causes the next to turn on, and so forth.
This is accomplished with a large capacitor between each stage
that charges when a stage turns off and supplies base current
to the next transistor, thus turning it on. Any number of stages
can be used and the drawing below illustrates 3 small Christmas
lights running at about 5 volts and 200mA. The circuit may need
to be manually started when power is applied. To start it,
connect a momentary short across any one of the capacitors
and then remove the short. You could use a manual push button
to do this.
Detailed operation:
Assume the circuit doesn't start when power is applied amd
all lights are off and all three capacitors are charged to
about 5 volts. We connect a jumper across the 220uF capacitor
on the left which discharges the capacitor and turns on the
2nd stage transistor and corresponding light. When the jumper is
removed, the capacitor will start charging through the
base of the stage 2 transistor and stage 1 light.
This causes
the stage 2 transistor to remain on while the capacitor continues
to charge. At the same time, the capacitor connecting stage 2
and 3 will discharge through the 100 ohm resistor and diode and
stage 2 transistor. When the capacitor charging current falls
below what is needed to keep stage 2 turned on, the transistor
and light will turn off causing the voltage at the collector
of the stage 2 transistor to rise to 5 volts.
Since the capacitor
connecting stage 2 and 3 has discharged and the voltage rises
at the collector of stage 2, the capacitor from stage 2 and 3
will charge causing the 3rd stage to turn on and the
cycle repeats for sucessive stages 4,5,6,7.... and back to 1.
The sequence rate is determined by the capacitor and resistor values
(220uF and 100 ohms in this case), load current (200mA in this case),
and current gain of the particular transistor used. This arrangement
runs at about 120 complete cycles per minute for 3 lights, or about
167mS per light. Faster or slower rates can be obtained with
different capacitor values.
Sourced by : bowdenshobbycircuits.info