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Limits the time a device can be switched on. Could be useful for any place where people keeps forgetting to turn off the light... |
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Parts: |
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Device purpose: This circuit is intended to be used in various places, where a device haven't to be turned on too long. When a voltage is applied to P1, then the C1 capacitor starts to load, trigerring some current to flow trough the base of the T1 transistor, which stays "on" until C1 is loaded. The transistor's base current is limited by R2. D1 is here to protect the transistor from destruction (relay's coils are known to generate some voltage spikes when turned on/off). When there is no voltage anymore on P1, then C1 is discharging through R1, allowing the circuit to be used again. In some applications (eg. low power bulbs) the S1 switch can be replaced by the final device. You will have to adjust C1 and R1 to your convenience. |
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