One_hour_timer_with_manual_controls

Published:2009/7/24 23:30:00 Author:Jessie | From:SeekIC

This circuit uses an LM122 connected as a one-hour timer with manual controls for start, reset and cycle-end. S1 starts timing, but has no effect after timing has started. S2 is a center-off switch, which can either end the cycle prematurely or reset to 0 V. A new timing period starts as soon as S2 is released from the reset position. The average charging current through R1 is about 30 nA, so you must pay some attention to the parts layout to prevent stray leakage paths.The suggested timing capacitor has a typical self-time constant of 300 hours, and a guaranteed minimum of 25 hours at + 25℃.



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