Here’s a way to avoid
winding the pickup coil for the inductive speed sensor used in projects
such as the Speed Alarm, Gearshift Indicator, etc. All you need to do is
carefully break open the plastic case of a small relay and cut away the
armature mechanism, so that you are left with the relay coil and core.
If you are careful you can retain the terminating pins that are moulded
in the plastic former to solder the shielded cable to.
The relay coil can then be mounted on a strip of aluminium which can
then be used as a mounting bracket. Fishing rod binding thread can be
used to fix the coil to the bracket, after which you can use binding
varnish to protect it after the wires have been soldered. You can then
dip the whole lot in epoxy for further protection or just use a small
piece of heatshrink.
Author: Rick Goodwin – Copyright: Silicon Chip