Hi all.
The title doesn't express it correctly. What I want to do is a simple circuit that drives some LEDs on when dark is detected (or sudden darkness occurred) for several seconds and then turns them off. The circuit's power supply is a PP3 9V battery (alkaline). The circuit should be as simple as possible and should draw the minimal possible current during when LEDs are off.
I design a circuit using LM358D op-amp using both halves as comparators, but after that I looked forward designing the circuit using only transistors. I design one using three 2N7000 MOSFEts and 3 resistors and a photoresistor and a capacitor and 3 super bright white LEDs.
The circuit draws about 0.1mA when the LEDs are off when there is light, and about 0.18mA at dark when the LEDs are off. When the LEDs turn on for some seconds when sudden dark happens, it draws about 10mA through the LEDs and the rest of the circuit.
Here is the circuit:
R1, R3 values are chosen after experimenting. There values determine at what light intensity should the LEDs turn on, and determine the current through the LEDs too. R4 and C2 values determine the duration for ON time. Q2 and Q3 function together like an AND gate.
The circuit still have a problem. When there is a little darkness, the LEDs light a little because the transistors' gate voltages are not zero.. This problem also creates another one which is the ON time of the LEDs where Q2's gate will not become zero after a while as C1 discharges. So this is a problem I want to solve. Any help is strongly appreciated especially because you read all my thread and gave me a period from your time .
I prefer to end my posts with "sorry for my bad English" because I really don't know if I have mistakes and how much, and to learn from these mistakes. So sorry for my bad English
Regards,
Hazim
The title doesn't express it correctly. What I want to do is a simple circuit that drives some LEDs on when dark is detected (or sudden darkness occurred) for several seconds and then turns them off. The circuit's power supply is a PP3 9V battery (alkaline). The circuit should be as simple as possible and should draw the minimal possible current during when LEDs are off.
I design a circuit using LM358D op-amp using both halves as comparators, but after that I looked forward designing the circuit using only transistors. I design one using three 2N7000 MOSFEts and 3 resistors and a photoresistor and a capacitor and 3 super bright white LEDs.
The circuit draws about 0.1mA when the LEDs are off when there is light, and about 0.18mA at dark when the LEDs are off. When the LEDs turn on for some seconds when sudden dark happens, it draws about 10mA through the LEDs and the rest of the circuit.
Here is the circuit:
R1, R3 values are chosen after experimenting. There values determine at what light intensity should the LEDs turn on, and determine the current through the LEDs too. R4 and C2 values determine the duration for ON time. Q2 and Q3 function together like an AND gate.
The circuit still have a problem. When there is a little darkness, the LEDs light a little because the transistors' gate voltages are not zero.. This problem also creates another one which is the ON time of the LEDs where Q2's gate will not become zero after a while as C1 discharges. So this is a problem I want to solve. Any help is strongly appreciated especially because you read all my thread and gave me a period from your time .
I prefer to end my posts with "sorry for my bad English" because I really don't know if I have mistakes and how much, and to learn from these mistakes. So sorry for my bad English
Regards,
Hazim
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