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An LED Daylight Sensor with PWM Brightness Control

An LED Daylight Sensor with PWM Brightness Control

This blog adds a PWM brightness control to the circuit from the previous post A Quick and Simple LED Daylight Sensor.

I have added a 555 timer circuit to give the LED daylight sensor circuit PWM brightness control. See the schematic here:
(to see a bigger version of any of these pictures click the image, then click the image on the following page, it is a weird wordpress issue)

Adding a variable PWM control to the previous circuit only uses eight more components.

Using the 500K potentiometer the PWM can be set for ~1% to ~99% duty cycle.

I have also increased the resistance going to the photo-transistor to further reduce the off state current draw and increase the dark sensitivity ( the circuit turns on later, when it is darker, and back off earlier in the morning ).

Since I am running my circuit with the PWM duty cycle set to 30% I have increased current to the LEDs to get more light out with less average current draw ( Note the 68 Ohm resistor that were 100 Ohms in the previous circuit ). The LEDS appear brighter because of persistence of vision from the human eye.