ITP Notebook

Abacusynth: PCB Development

April 11, 2022

Homemade HardwareThesis

Sketch of my thesis project: Abacusynth Sketch of my thesis project: Abacusynth

For my thesis project I am creating a synthesizer inspired by an abacus. Its interface consists of four rods, each holding a spinning object. These four objects represent oscillators in the synth. A user can spin them and move them left and right along the rod. Each rod needs a distance sensor facing inwards to measure the object’s position and an encoder facing outwards which is used to adjust the harmonic of the oscillator and change the waveform. A breakbeam sensor is used to detect rotation, but this is separate from the PCB — for that I am using these sensors.

Board Design

PCB Schematic PCB Schematic

PCB board design PCB board design

The board runs on 2.8V — a requirement of the VL6180X distance sensor. It is single sided, since the sensor faces forward and the encoder sits on the back, meaning all connections are on the front. The schematic is pretty simple, including pulll-up resistors for the SDA and SCL connections and capacitors to help smooth the signal.

Bill of Materials

PartValueDevicePackageDescription
C110ufCOMPONENT_CAP-08050805Capacitor
C40.1uFCOMPONENT_CAP-08050805Capacitor
MT3PEC11R-4215F-S0024PEC11R-4215F-S0024XDCR_PEC11R-4215F-S0024Incremental Encoder, 12 Mm, Contact Rating 10 Ma - 5 Vdc Check availability
SCL_PULLUP10kCOMPONENT_RESISTOR-08050805
SDA_PULLUP10kCOMPONENT_RESISTOR-08050805
U$1HEADER-7-DIPHEADER-7-DIPHEADER-7-DIPNPTC081KFXC-RC: Vertical Female SMD Headers
U1VL6180XVL6180XVL6180VL6180x Proximity and Light Sensor with Gesture Recognition

Milling V1

The milled board The milled board

To start I milled one board to make sure everything worked.

Adding the components with solder paste Adding the components with solder paste

I added the components by hand with solder paste and soldered them with the heat gun. I then soldered the larger components with the iron.

Soldering using a heat gun Soldering using a heat gun

The back of the board The back of the board

Once everything was connected I tested the board by connecting 2.8V power and the sensors to my main board. It worked!

Testing the distance sensor

The board mounted on the inner wall The board mounted on the inner wall

The mounting configuration with the breakbeam sensor attached.

side view side view

One limitation I noticed was that the distance sensor picked up on the inside of the wall if it was any thicker than a half inch thick. I had initially thought that the thickness would be a bit wider, giving me more room for the wiring.

The distance sensor aligns with the hole The distance sensor aligns with the hole

The other side screws into the board and encoder The other side screws into the board and encoder

Multiples

Now that I was sure the design worked, I needed to multiply it x4.

4 Milled Boards 4 Milled Boards

The milling went pretty smoothly. Since there aren’t too many parts, I added them by hand.

The soldered components The soldered components

I then tested each one by connecting it to my circuit. Out of the four new boards, all but one worked. So I kept my first prototype and soldered the encoders to the 3 new working ones.

Four working PCBs Four working PCBs

Mounting the circuits Mounting the circuits

I mounted the components fit in the new wooden housing and wired everything up. It was a little tight but everything fit.

Wiring everything to the main board Wiring everything to the main board