555 simple exposure timer circuit

Published:2011/5/21 5:58:00 Author:TaoXi | Keyword: simple, exposure timer | From:SeekIC

As the figure 17-5 shows, the photo exposure timer circuit uses the 555 as the core. This circuit is one kind of artificially start monostable circuit. If you press AN, the timing capacitor C1 immediately discharges to zero, 555 sets, the timing begins, J closes, the light H turns on. The lighting time is the time of C1 charges to 2/3VDD td=1.1(R1+RP1)C1. The length of time can be set by the photo typy. When the time is up, 555 returns to the reset state, pin-3 has the low level voltage, J releases, H turns off automaticly. The parameter's td in the figure is about 2 minutes.



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