A brief history
The 7-segment display module (the DM1) was released at the same time as the V2 preamp controller. It was the only display module for the V2. Version A of the subsequent V25 preamp controller also used the same 7 segment display. The V25 RevA board had a pin header dedicated to the 7-segment display. It also had a header dedicated to the newer OLED display. The OLED display was released approximately 6 months after the V25 came out once the OLED driver/firmware was ready. Subsequent revisions B and C to the V25 board eliminated the dedicated 7-segment display interface header however the signals needed for the 7-segment display are still available from the 14 pin OLED interface.
7-segment display module
The 7-segment display module is a dual-digit display that uses 0.58″ tall 7-segment LED type display each capable of showing a 1 or 2 digit numbers – from 0 to 99. The display assembly provides visual (numerical) status information and indirectly connects the user control input devices (encoder & infrared receiver) to the V25 board.
A pair of display modules are needed to properly display information for the V25 preamp controller. One module acts as the master and displays the right channel volume. The slave module is controlled by the master and displays the left channel volume.
The picture below show both a front (right) and back view (left) of a master display module. The slave module has a second identical 2 digit 7-segment LED and its front view is the same as the master shown below on the right. The slave does not have its own driver hardware and must be driven by the master module. The master board has a special purpose 7-segment driver chip. The V25 communicates with the driver chip via an SPI serial data link.
7-Segment display assembly
A typical 7-segment display assembly is shown below in a front (left pic) and rear (right pic) view.
The 7-segment display assembly is composed of the following parts.
- Master Display Module – populated with chip, capacitor, conductor, resistor plus 2 digit display on reverse side
- Slave Display Module – 2 digit display only
- Encoder – rotary encoder with integral push button switch
- IR Receiver Module – 3 pin infrared receiver device (must be soldered to master display module)
- Ribbon Cable #1 – 2×5 pin cable connects master display module to slave display module
- Ribbon Cable #2 – 2×5 pin cable connects display assembly (via master) to the V25 board
- Cable #3 – 4 pin cable connects Encoder to master display module
V25 7-segment display connection
The connection from the V25 board to the DM1 7-segment display varies depending on the version of the V25 board. There are 3 versions of the V25 board – A, B & C. Both A & B use a single 10 pin ribbon cable from V25.J3 to DM1.J1. Version V25.C requires several individual female-female square pin jumper wires to connect from pins on V25 headers J8 and J9 to DM1 header J1.
In the case of versions A & B please note that the red stripe on the ribbon cable must be aligned with the side of the J1 and J3 headers that has the white dot.
The table below shows the V25 to DM1 connections for each of the 3 versions of the V25 board. Some of the version C connections are not strictly required for the DM1 itself but are signals for the IR remote sensor and manual encoder that interface on or through the DM1.
| V25 Version | Signal | From V25 | To DM1 (master module) |
|---|---|---|---|
| Versions A & B | All | Ribbon cable from V25.J3 header... | DM1.J1 header (align red stripe with white dot at each end) |
| Version C | +5V power | V25.J8.Vbus | DM1.J1.+5 (square pin female-female jumper wire - typical for all) |
| Ground | V25.J9.G | DM1.J1.G | |
| SPI chip select | V25.J9.CS | DM1.J1.CS |
|
| SPI serial clock | V25.J9.SC | DM1.J1.SC | |
| SPI serial data | V25.J9.SD | DM1.J1.SD | |
| Infrared (for Apple IR remote) | V25.J9.IR | DM1.J1.IR | |
| Encoder switch (for encoder) | V25.J9.ES | DM1.J1.S | |
| Encoder leg A (for encoder) | V25.J9.EA | DM1.J1.A | |
| Encoder leg B (for encoder) | V25.J9.EB | DM1.J1.B |
Encoder module
The encoder module is rotary encoder with integral push button that’s mounted on a small printed circuit board. The encoder circuit board has a 4 pin header labeled A, B, S and C which correspond to the master display module’s J2 pin header labeled A, B, S & G.
A & B are the encoder’s 2 rotary switches used to determine direction of turn and pulse counts and S is the push button. A, B & S are all referenced to G which connects to the V25’s ground.
Infrared receiver module
The infrared receiver module (“IR module”) is a single integrated infrared receiver with 3 pins as shown below. The IR module mounts to the master display module via solder pads IR1 such that the front of the IR module (the face with the bump) faces same direction as the display module digits.
