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The "DOLLAR" Light
These dollar-store camping lights are very easy to convert to LED use. By replacing the 3-volt incandescents with a simple (5 components plus LEDs) circuit to drive a couple of wide angle LEDs, we cut battery drain to 1/10 while producing a very usable amount of light.

LIST OF PARTS:

2SD965
Low-voltage, high-current transistor. Available as FJN965 from Fairchild. You can substitute a 2N4401 or MPS651 NPN with reduced efficiency.
1mH Inductor
If you get a commercial unit, you have to add a secondary coil. Using 30-guage (or thinner) enamel wire, add another winding over the existing coil with a similar number of turns, and in the same direction. I used a small (.4" od) toroid with 2 coils of 15 turns each. With high-performance transistors, any value from 200uH and up will work.
5uH Capacitor
Any value electrolytic or tantalum from 2uF and up is suitable, so long as voltage limits are observed.
10K resistor
This controls the brightness - adjust for different requirements
1N5819
Or any similar shottky diode. Most rectifiers (1N4001 etc) will work with a small reduction in performance.
1N914
Or any similar small signal silicon diode. Used as a simple regulator. May be left out.
LED
2 are used in this circuit. The Design will drive up to 5 LEDs in parallel. Any 25mA light will work, but I found these, available on eBay to be very effective.

The simplicity of the design allows us to 'space-form' the components. Here are the 3 major sections at the beginning of our assembly. If you want to use this minimalist approach, all components, especially the inductor coil, must be small enough to fit through the neck of the light where the light bulb used to sit.

A closeup of our main circuit.

After unsoldering the incan socket, mark the positive supply wire so there is no mistake later!

Finally, everything's snug inside our light. And it WORKS!

Performance is very good - with the suggested parts both LEDs run at 25mA with a supply of 4.5v at about 93% efficiency.

With their light baffle, there is still glare and hotspots.
But apply a layer of glow powder from Glow Inc and the light becomes smooth and even. A layer of contact cement was applied with a Q-tip on the inside of the baffle, and the powder sprinkled on. Do it over a sheet of paper so the excess can be reused. These 2 pictures were taken using the same exposure - you can see that there is little effect on the total brightness.

Of course, this also means you can find your light in the dark!
The insides of the light.

Go to Quantsuff's BASIC LED page - More LED circuits - Regulated LED circuits - The HAK-Lite

See my other Projects on Instructables.com

Questions? Suggestions? Send me email!

The "DOLLAR" Light
These dollar-store camping lights are very easy to convert to LED use. By replacing the 3-volt incandescents with a simple (5 components plus LEDs) circuit to drive a couple of wide angle LEDs, we cut battery drain to 1/10 while producing a very usable amount of light.

LIST OF PARTS: 2SD965 Low-voltage, high-current transistor. Available as FJN965 from Fairchild. You can substitute a 2N4401 or MPS651 NPN with reduced efficiency. 1mH Inductor If you get a commercial unit, you have to add a secondary coil. Using 30-guage (or thinner) enamel wire, add another winding over the existing coil with a similar number of turns, and in the same direction. I used a small (.4" od) toroid with 2 coils of 15 turns each. With high-performance transistors, any value from 200uH and up will work. 5uH Capacitor Any value electrolytic or tantalum from 2uF and up is suitable, so long as voltage limits are observed. 10K resistor This controls the brightness - adjust for different requirements 1N5819 Or any similar shottky diode. Most rectifiers (1N4001 etc) will work with a small reduction in performance. 1N914 Or any similar small signal silicon diode. Used as a simple regulator. May be left out. LED 2 are used in this circuit. The Design will drive up to 5 LEDs in parallel. Any 25mA light will work, but I found these, available on eBay to be very effective.
The simplicity of the design allows us to 'space-form' the components. Here are the 3 major sections at the beginning of our assembly. If you want to use this minimalist approach, all components, especially the inductor coil, must be small enough to fit through the neck of the light where the light bulb used to sit. A closeup of our main circuit.	After unsoldering the incan socket, mark the positive supply wire so there is no mistake later! Finally, everything's snug inside our light. And it WORKS! Performance is very good - with the suggested parts both LEDs run at 25mA with a supply of 4.5v at about 93% efficiency.
With their light baffle, there is still glare and hotspots.	But apply a layer of glow powder from Glow Inc and the light becomes smooth and even. A layer of contact cement was applied with a Q-tip on the inside of the baffle, and the powder sprinkled on. Do it over a sheet of paper so the excess can be reused. These 2 pictures were taken using the same exposure - you can see that there is little effect on the total brightness.
Of course, this also means you can find your light in the dark!	The insides of the light.

Go to Quantsuff's BASIC LED page - More LED circuits - Regulated LED circuits - The HAK-Lite