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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.
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