555 timer circuit for darkroom 3

Published:2011/10/18 3:44:00 Author:Ecco | Keyword: 555, darkroom , timer circuit | From:SeekIC

As the figure 17-16 shown, the timing circuit is composed of two branches of 555, IC1 forms a timer, IC2 is a second signal metronome. AN1 is the timer button, clicking the AN1, 555 sets, J pulls in, light exposure lamp H1 is lit, safelight H2 is off. K1 is regular file, when the C1 (or C2) is charged to more than 2/3 threshold level, the 555 resets, J releases. H1 is off, H2 is lit, exposure ended. IC2 and RP2, R4, R5, C4 etc. form astable multivibrator, adjusting the RP2 can make the oscillation be 1Hz. The output of it drives red LED lighting by VT1.



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