Schematics > Oscillators and timers > Photo Timer Circuit
Photo Timer Circuit
Time is set by potentiometer R2
which provides a range or 1 sec. To 100 seconds with timing capacitor C1 of
100uF. The output at pin 3 is normally low and the relay is held off. A
momentary push on switch S1 energies the relay which is held closed for a time
1.1 X (R1+R2). C1 and then released. The exact length of the timing interval
will depend on the actual capacitance of C1. Most electrolytic capacitors are
rated on the basis of minimum guaranteed value and the actual value may be
higher. The circuit should be calibrated for various positions of the control
knob of R2 after the timing capacitor has had a chance to age. Once the
capacitor has reached its stable value, the timings provided should be well
within the photographic requirements.
Parts List
C1 - 100uF, 25V electrolytic
C2 - 0.01uF, disc ceramic
D1, D2 - DR50 or 1N4001
R!,R2 - 10K ohms, ¼ watts
R3 - 1 M ohms, potentiometer
RLY1 - 12V, DC relay, operating current less than 200mA
S1 - Push-to-on switch
U1 - NE555 timer IC
P1 & P2 are for exposure lamp ckt.
Title: Photo Timer Circuit
Source: www.electronics-lab.com
Published on: 2005-02-03
Reads: 502
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