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Circuits > Motor, light and power control > Christmas Star
Christmas Star
This circuit can be used to construct an attractive Christmas Star. When we
switch on this circuit, the brightness of lamp L1 gradually increases. When it
reaches the maximum brightness level, the brightness starts decreasing gradually.
And when it reaches the minimum brightness level, it again increases
automatically. This cycle repeats. The increase and decrease of brightness of
bulb L1 depends on the charging and discharging of capacitor C3. When the output
of IC1 is high, capacitor C3 starts discharging and consequently the brightness
of lamp L1 decreases. IC2 is an opto-isolator whereas IC1 is configured as an
astable multivibrator. The frequency of IC1 can be changed by varying the value
of resistor R2 or the value of capacitor C1. Remember that when you vary the
frequency of IC1, you should also vary the values of resistors R3 and R4
correspondingly for better performance. The minimum brightness level of lamp L1
can be changed by adjusting potentiometer VR1. If the brightness of the lamp L1
does not reach a reasonable brightness level, or if the lamp seems to remain in
maximum brightness level (watch for a minute), increase the in-circuit
resistance of potmeter VR1. If in-circuit resistance of potmeter VR1 is too high,
the lamp may flicker in its minimum brightness region, or the lamp may remain in
‘off’ state for a long time. In such cases, decrease the resistance of potmeter
VR1 till the brightness of lamp L1 smoothly increases and decreases. When supply
voltage varies, you have to adjust potmeter VR1 as stated above, for proper
performance of the circuit. A triac such as BT136 can be used in place of the
SCR in this circuit. Caution: While adjusting potmeter VR1, care should be taken
to avoid electrical shock.
Title: Christmas Star
Source: www.electronic-circuits-diagrams.com
Published on: 2005-02-01
Reads: 478
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