Hello to all,
these days I had the need for a “Dusk to Dawn” switch completely electronically (without relay) and a made with just few components.
I initially opted for a single transistor solutions, but unfortunately there were two drawbacks: the change of status was not quick but very gradual and the transistor generated a slight dropout that drastically decreased the brightness of the LED Strip.
At this point I opted for a N mosfet and in this way the change of status much better and the dropout was just a few mV.
The final circuit is the following:
The operation is very simple: the photoresistor (LDR) has a value of about 100kΩ in the dark and when this is illuminated the resistance decreases and the voltage divider between R1 and R2, means that the gate of Q1 goes below the threshold level (between 2V and 4V) turning off the the Led Strip. With R1 I can set sensitivity, while reversing R1 and R2, I reverse the operation (it turns on with light and turn off with the dark).
See you soon!
Electronics & Arduino 