5.8. Tips and Tricks

We expect you to look to outside resources for information on practical skills; we have some starting points on the Essential Skills List. For specific problems with the lab equipment, you might the Errata section handy. However, this page also includes some miscellaneous notes you may find useful.

5.8.1. Soldering

My essential soldering tips:

1. Lead is poisonous: wash your hands afterwards.
2. Turn on the fan to absorb the rosin fumes.
3. Put a little water on the sponge.
4. Melt a little solder on the tip to “tin” it.
5. Use the sponge to clean off excess solder and flux from the tip.
6. Soldering is all about heat, oxides, and surface tension: the rosin flux vaporizes in the heat and removes oxides so the solder can wet the metal; the melted solder wicks into the freshly cleaned gaps.
7. Heat the joint with the iron; let the hot joint melt the solder. The solder is applied to the joint, not the tip.
8. Look for a shiny, symmetrical meniscus of solder when you’re done.

5.8.2. Electronics

1. If an analog sensor doesn’t emit the right voltage to drive a particular circuit, it is possible to construct a passive resistor network to add an offset voltage, or an active op-amp circuit to offset and scale the signal to the appropriate level. E.g., the Sharp rangefinder output is too low a voltage to directly trigger our MOSFETs. For more discussion see the Op Amp Level Translation Exercise.
2. If you are unclear on the wiring of a stepper motor, use a DMM to measure the resistance between the wires. A bipolar stepper will have four wires, two per coil, and the low-resistance of the coil should be unambiguously measurable.