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?

Hamad bin Turki Salami wrote:

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?

Leads or terminals ? You can get pots with centre taps making 4 terminals. It
might also be a rotary encoder although these normally turn continuously and
don't typically have 4 connections.

Graham

In article m.net,
(known to some as Hamad bin Turki
Salami) scribed...

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.

snippety

It could be a Hexadecimal or BCD-output rotary switch. See if you
get continuity in a binary-like sequence.

Happy hunting.


--
Dr. Anton T. Squeegee, Director, Dutch Surrealist Plumbing Institute
(Known to some as Bruce Lane, KC7GR)
http://www.bluefeathertech.com -- kyrrin a/t bluefeathertech d-o=t calm
"Salvadore Dali's computer has surreal ports..."

On Fri, 26 May 2006 21:45:30 -0700, Dr.Anton wrote:

In article m.net,
(known to some as Hamad bin Turki
Salami) scribed...

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.

snippety

It could be a Hexadecimal or BCD-output rotary switch. See if you
get continuity in a binary-like sequence.

Hmm. This thing determines a MIDI controller value that varies between
0 and 127. Maybe it's doing 2 Hex digits and throwing away one bit?
But the resistances between the various leads do vary as I turn the knob;
they go up and then down in a non-linear and non-monotone way.

On Sat, 27 May 2006 14:25:23 -0600, Hamad bin Turki Salami
put finger to keyboard and
composed:

On Fri, 26 May 2006 21:45:30 -0700, Dr.Anton wrote:

In article m.net,
(known to some as Hamad bin Turki
Salami) scribed...

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.

snippety

It could be a Hexadecimal or BCD-output rotary switch. See if you
get continuity in a binary-like sequence.

Hmm. This thing determines a MIDI controller value that varies between
0 and 127. Maybe it's doing 2 Hex digits and throwing away one bit?
But the resistances between the various leads do vary as I turn the knob;
they go up and then down in a non-linear and non-monotone way.

What are the various resistances at min (0000 0000), centre (0011 1111
or 0100 000), and max (0111 111)? Is there a common terminal?

- Franc Zabkar
--
Please remove one 'i' from my address when replying by email.

Hamad bin Turki Salami wrote:

On Fri, 26 May 2006 21:45:30 -0700, Dr.Anton wrote:

In article m.net,
(known to some as Hamad bin Turki
Salami) scribed...

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.

snippety

It could be a Hexadecimal or BCD-output rotary switch. See if you
get continuity in a binary-like sequence.

Hmm. This thing determines a MIDI controller value that varies between
0 and 127. Maybe it's doing 2 Hex digits and throwing away one bit?
But the resistances between the various leads do vary as I turn the knob;
they go up and then down in a non-linear and non-monotone way.

Probably an encoder then.

Graham

"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.

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.

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.


Hmm... you've got me curious, too. I don't know. Only thing I can suggest
now is to send a detailed e-mail to the service department of the
manufacturer and ask. Be sure to specify the component location silkscreend
on the circuit board to make things easier. And please get back to the rest
of us about it!

Who _is_ the manufacturer of this synth, by the way?

On Sat, 27 May 2006 23:47:49 -0600, Hamad bin Turki Salami
put finger to keyboard and
composed:

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.

If these devices span 315 degrees, and if they are meant to "encode"
128 discrete values, then each binary increment must correspond to 2.5
degrees of rotation, assuming the devices are "linear".

I think your best approach is to measure the voltages on each pin as
you select known MIDI values. Otherwise look for changes as you switch
from 63 to 64 in midrange. This is the point at which all the bits
change state. To identify the "least significant pin", look for the
pin that changes state most often as you rotate the dial.

- Franc Zabkar
--
Please remove one 'i' from my address when replying by email.