# Ambient Light Powered LED Flasher

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This LED flasher circuit is optimized to run from the ambient light present in your room and no other power source. A small photovoltaic cell converts the light to electricity and that weak current charges a 1000uF capacitor. After a time period of around 1.5 seconds, the stored energy is discharged through an LED.

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## Step 2: Circuit Diagram & Main Components

FV cell: should deliver at least 2.5v (no load open circuit) and 0.5mA short circuit current (under room lighting)

Incandescent / halogen lighting is the most efficient for F.V.cells (after daylight) and fluorescent is the least.

Q1-Q2: BC549 npn transistors

Q3: 2N7000 N-channel mosfet. You may have to select it for lowest gate threshold voltage or use a low threshold BSH103

LED: use a high efficiencyred LED . (red LEDs have the lowest forward voltage (Vf) )

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## 2 Discussions

At first I was kinda disapppointed that it required an additional solar panel to work, I expected that the LED would be use as a mini solar cell. That duty cycle couldn't be aquired though.

However I was curious about the actual power consumtion and efficiency, so I quickly scatched it in LTSpice. Since there was no solar cell available I "made" my own with a 2k impedence, I think that is a realistic value. Ive atache a the simulation below.

green: system voltage

blue: LED current consumption

red: total system current consumption

Hats off for archiving a standby cnsumption of 24uA, this is amazing considering you only used discrete components. I've played a bit with the values and figured out that (at least in the simulation) R1, R2, R3 can be set to 10M and R4 to 1.5M to decrease the standby current consumtion to only 2uA!

Still a great design, love it!

If anybody wants the LTSpice files to play around with just drop a PM.

1 reply

Nice to see you again ! . FET input has a relatively high capacitance, so increasing R4 to 1.5M will slow down rise time of gate voltage considerably, discharging C4 prematurely. Your simulation is awesome. Thank you!!!