Because volume control is free and for the people.™
KiCad 5.0 design files for a PCB that integrates an Alps RK16814MG motorized potentiometer with an H bridge to drive the motor using logic-level signals.
| Name | Function |
|---|---|
VOL_UP |
Logical input to rotate the potentiometer clockwise. |
VOL_DOWN |
Logical input to rotate the potentiometer counter-clockwise. |
V_MOT |
Power for motor drive. Nominally 6 VDC, but see comments below. |
+5VD |
Power for logic circuits. 5 VDC. |
DGND |
Ground for digital (logic) circuits. |
CHASSIS GROUND |
Ground for potentiometer case. Also labeled as C.G. on top side of PCB. |
A_TOP |
Potentiometer A input |
A_WIPER |
Potentiometer A output |
AB_COMMON |
Potentiometer A and B's common (typically connects to signal ground) |
B_TOP |
Potentiometer B input |
B_WIPER |
Potentiometer A output |
C_TOP |
Potentiometer C input |
C_WIPER |
Potentiometer C output |
CD_COMMON |
Potentiometer C and D's common (typically connects to signal ground) |
D_TOP |
Potentiometer D input |
D_WIPER |
Potentiometer D output |
There are two power inputs to the board, one for the 5 VDC logic (+5VD)
and the other to drive the potentiometer's motor (V_MOT). The board has a
jumper (J1) that when installed will connect V_MOT to +5VD---making it
possible to operate the module from just one +5VDC power source, albeit with
a couple caveats.
First, owing to the voltage drop across the Darlington H-bridge, the optimum
voltage for V_MOT is 6 VDC. When V_MOT is 5 VDC, the resulting voltage
delivered to the Alps RK16814MG's motor falls below Alps' specified minimum.
However, the motor seems to have no problem operating at this lower than
specified voltage. Second, the motor's maximum specified current consumption is
150 mA. This is beyond the capacity of, for example, the on-board regulators
found on many Arduinos. Therefore, if you opt to jumper J1, you may have to use
an external logic supply if you are using something like an Arduino for
control.
The logic supply ground is completely isolated from other grounds. For the love of all that is good, don't mix your logic and audio grounds. Connect the logic and audio grounds at one point only and as close to the main power supplies as possible.
It is assumed the case of the potentiometer is grounded through the chassis. A
ground pin labeled C.G. is provided if this is not the case. This connection
should not be used as a signal ground but rather only to provide a shielding
connection for the potentiometer's case.
The potentiometer internally connects the "ground" sides of both elements of
each gang. These are brought out as independent commons (AB_COMMON and
CD_COMMON). Typically, AB_COMMON and CD_COMMON will be connected to
signal ground.
While it's possible to use the Volume-AlpsRK16814MG PCB for applications other than volume control, we assume that you will be using it for volume control.
The Alps RK16814MG consists of two gangs of dual potentiometers. Refer to the table above for the PCB's I/O corresponding to these.
For regular (non-differential) stereo use, you have the option of using both elements of one gang (e.g., A and B) or one element from from each gang (e.g., A and C).
For differential stereo control, both elements on both gangs will be required.
To rotate the potentiometer CW (i.e., up), apply a logical 1 to VOL_UP and a
logical 0 to VOL_DOWN. To rotate the potentiometer CCW (i.e., down), apply a
logical 1 to VOL_DOWN and a logical 0 to VOL_UP. No harm will come if a
logical 1 is applied to both VOL_UP and VOL_DOWN simultaneously.
CERN Open Hardware License v1.2
Copyright (C) 2015 Mithat Konar.