On Sun, 28 May 2006 01:40:01 +0000, Matt J. McCullar wrote:


"Hamad bin Turki Salami" wrote in
message news
I'm just curious about a component that's on a board
in a synthesizer I have. It looks like a pot and it's
hooked to a knob that turns through about 315 degrees.
However, it has 4 leads instead of three. I've done
some measurements on it and they're not consistent
with it being a pot. What would it likely be?

When you turn the knob, does it feel smooth in its motion, as a volume pot
would? Or does it go through a series of "click-stops"?

You say it allows you to change a MIDI value. If the device has four leads,
and has click-stops in its motion, I would say it's a rotary switch. What
the switch is probably doing is connecting a nearby pullup resistor network
to Vcc and ground, or it could be doing it internally.

No, it's doesn't have clicks; it's smooth like a pot. In fact, this synth
has all three kinds of component: an ordinary pot for the volume control,
an encoder with click stops for selecting presets, and these 4 lead
components -- whatever they are -- for setting midi controller values.

I'm tempted to just bust one of these things open to see what's inside.