Experiment with the fineness of the crushed charcoal and the tension in the foil. The more squashed the charcoal is, the lower the resistance. Aim for a resistance of around 3k ohms and definitely 700 ohms < resistance < 14k ohms. | Experiment with the fineness of the crushed charcoal and the tension in the foil. The more squashed the charcoal is, the lower the resistance. Aim for a resistance of around 3k ohms and definitely 700 ohms < resistance < 14k ohms. |