Nuts and Volts - September/October 2018

20 mA, which a dead 9V battery seems to do on its own due to its higher internal resistance.

We can make the circuit by simply connecting the battery to the resistor and LED in series, with a switch to turn it off by disconnecting the battery from the resistor. Schematic 1 shows the circuit using the on-off-on switch with the resistor across the two outputs of the switch.

Photo 1 shows the simple circuit using the on-off-on switch to either use the resistor or not use it, depending on the voltage the battery can maintain while driving the LED. It’s not easy to tell if the 9V battery is weak enough to drive the LED directly, so the safest way to tell is to use a voltmeter, or to wait until the LED is obviously getting dimmer and try it without the resistor.

After I built this circuit, I came up with a much simpler way to attach the resistor. In my new approach, the resistor is soldered to the two ON sections of the on-off-on switch, and then one wire from one of those ends is connected to the cathode of the LED. This reduces the amount of wire needed. I hope you enjoy building this circuit. Now, you can use those dead 9V batteries as small flashlights or even as personal nightlights.

The Simple Joule Thief Night Light as a Soldering Island Project

My use of the term “soldering islands” here is similar to the

Manhattan style of circuit building. One can do searches online to find articles on this construction technique. A good one I’ve come across is by K7QO. Manhattan Style construction uses small islands for solder points. These are usually cut from double-sided copper-clad circuit boards. The bottom side is then soldered to another single-sided copper-clad board and positioned to follow the circuit; either to make it easy for the signal, easy to construct, or both. The top side of each little island is then used to connect various leads. These islands can be either round or rectangular. The difference between Manhattan style construction and these soldering islands is that there is no way to connect the soldering islands to a copper-clad circuit board without shorting out the entire circuit. These islands must either be glued to something — another board or the bottom or side of a box, for example — or float with enough room between them that they will not short out. Another method is to use very high-valued resistors — 1 MΩ or more — to keep all the solder islands at a good distance from each other. When using these with a joule thief circuit, we have the stiff resistor, LED, and transistor leads to help maintain the distance between the solder islands. I use this island method because there are times when I need to connect more than just two wires or leads together. I find that a small solder island makes this very easy to do. Using only the wires or leads is far more frustrating because the lead or wire never wants to stay in the position I need long enough for me to solder it to the other leads. Or, as I warm up the other two or more leads already soldered together, one of them pops off and I have to fight with all the leads to get them back together. Other than using a soldering island,