Joule Thief: Making a Quick and Dirty PCB Joule Thief
Here I show how easy and quick it is to make a simple printed circuit board for your Joule Thief.
Copper clad board, the resist pen, and Ferric Chloride etching solution are available at your favorite electronic supply house.
Lay out your circuit in some logical manner and draw it onto the cladding with the resist pen. You can also use packing tape or pre-made PCB transfers, but for simple circuits the pen works fine.
Then in a plastic or glass container, cover the board with the Ferric Chloride etchant. Don’t use metal, and don’t make a mess or you’ll get in trouble with SWMBO. The stuff will stain your hands, too, and is corrosive and toxic so be careful.
Agitate with plastic utensil. It took about 20 minutes at cool room temperature, but if you warm the solution a little bit it will go quicker. Follow the directions on the bottle. Don’t put the thing in the microwave, silly!
You can pour the used solution back into the original bottle; it will last for many boards, getting a little slower as the iron is replaced by copper in the solution. The iron will precipitate out as a fine dust, so don’t shake the bottle before pouring for a new board.
Rinse well, and clean off the resist with acetone, or peel away your tape or prefab pads.
Drill the holes for the component leads. I used a #55 bit which is a little large. Check your layout before soldering anything to the board and make sure all the copper is removed from where it should be removed. If you have excess you can scrape it away with a sharp knife blade, and if you have interrupted traces you can jump them with solder or fine wire.
Mount and solder your components. A little rubbing with ScotchBrite pad or a pencil eraser will make the soldering a bit easier.
Test, and enjoy!!
I used an LR44 button cell that was down to around 1 volt. If you are very careful and don’t use too much heat you can solder directly to the cell… but be careful, they can explode, so use minimum heat and wear eye protection if you try this part.
The extra holes in the board are for current and voltage monitoring test points, which I installed after making the pictures. The one-ohm resistors are current viewing resistors: looking at the voltage drop across these resistors will give the current flowing in them by Ohm’s Law.
Thank you for watching!!
Copper clad circuit board material
Ferric Chloride etchant
plastic pan and fork
Basic JT components, including 1 ohm Current Viewing Resistors, a 2n2222a metal can transistor, a 1K base resistor, and a toroid with 10:40 windings.
The toroid is from an old PC power supply, it originally was 10:10, so I stripped off one of the windings and replaced it with 40 turns of #22 magnet wire.