Better Homemade Resistors

 I figured the easiest way to make a metal oxide resistor would be to fill a tube with iron oxide and put wire in the end. I did just this. A got a short length of 3mm OD glass tubing, placed a peice of 14AWG copper wire in one end, poured powdered iron oxide (made from steel wool) into it, and placed another wire in the other end. When I connected my meter I discovered an annoying fact. Iron Oxide (FeO2) is completely non-conductive. I think after that fail carbon composite is my best shot.

To try to increase the strength of the resistors I replaced the clay with plaster. I mixed 5/8 of a teaspoon plaster of Paris with  1/8 of a teaspoon powdered graphite and 3/4 of a teaspoon water. I poured it into a narrow rectangular mould about 1/4 of an inch wide by 1 1/4 inches long and embedded leads. When I removed it from the mould in the morning there were two problems. Firstly it was actually likely weaker than the clay ones. Secondly and more importantly its resistance read infinite on my multimeter. Back to the drawing board I guess. 

My first attempt at carbon composite resistors was rather simple. I mixed powdered graphite (from pencil leads) with clay, formed it into cylinders and stuck wires in the ends. They showed resistance values well into the kilohm range. I got pretty excited but soon realized a problem. They were far too brittle. they would never have the strength to allow their leads to be bent. The cover picture shows one of these early prototypes with it's resistance being measured. Ways to increase their strength are currently in the works.