The Solar Garden Light: adding the Flash

In the previous attempt to increase the output from a basic Solar Garden Light (SGL), publishedhere, we quickly reached a limit: the brighter we make the light, the quicker we deplete the battery, or more properly, the charge we can obtain from the sun during the day.

The solution was apparent: make a flashing SGL. Not only is it much more readily noticeable, and hence, more effective against would-be intruders; it also conserves battery power, so that the battery will last a long time.

The difficulty was designing a circuit that could be made from easily obtainable and inexpensive parts. The result is a simple flashing circuit using only ONE transistor, powered by a single rechargeable battery.And, a simple enhancement of 2 parts will more than triple the light output.

And it is effective - after 4 days of storm & rain, with only the rechargeable from the old light, it's still going strong.

Step 1 The circuit

The material you will need for the light:

R1,R2,R3,R4: 1.5K-ohm resistor
C1: 470uF (micro Farad)
C2: 1nF (.001uF) or 680pF for 2 x orange or red LEDs
D1,D2: 1N4148 or 1N914 (any low-power signal diode)
Q1,Q2: BC337 (do not substitute!)
T1, made from 3 pieces of thin, insulated wire each 8ft (2m5) long
Solar cell, 1.2volt battery, LED, casing: from old Garden Light

The hi-lited components (Q2,R2) are optional, but will greatly increase the brightness.

The basic circuit is a Joule Thief which is designed to drain the charge in C1 to light the LED. This causes the LED to flash. After that C1 has to recharge through R3, which takes about 3/4 seconds, at which point the cycle repeats. The optional parts increase the power to the LED, and make the flash longer as well.

This circuit is also unique in that not only will it switch off the flashing when the battery begins to charge; it will also turn the light back on to avoid overcharging the battery.

Comments

[hehinckley]

Would that design work for making an LED flashing sign?

[qs]

No reason why not - depending on the size of the sign, you may need multiple LEDs.

[dezignable]

I would like to make the flashing LED(s) light up fiber optic strands (encased in something like concrete) that spell out a name or address. Will 30 AWG wire-wrap wire work as well as 32 AWG wire-wrap? I would like to buy no more than needed (8 feet) if possible, but can't find a source for 32AWG wire-wrap.

[qs]

You can substitute any copper wire as long as it's insulated. The only constraint is the size of the coil when you use thicker wires.

I've never had any luck bonding fibre optics to naked LEDs - is there a special technique?

It would be awesome if you can combine 3 or more flashing LEDs each with its own group of fibres!

[sasaa]

in some communities, red and/or blue flashing lights are used to signify a crime or emergency. TRUE don't use red lights!

[ralegg]

Do you have a video of it in action?

[qs]

For sure!

[ralegg]

very nice!
haha, I just went to your site and realized I had been there before to read about your fake flourescent, keep up the good work!

[wierd idiot]

Well that's a flash circuit you got there. :)

[qs]

Thanks, it's the only design I know of that can work off 1.2-volts using only 1 transistor.