Mault / Hardware build guide

Build the card sorter

01 / Set up

Set up your build

Choose how you're building the sorter. The parts list, wiring and assembly steps below follow these choices, which are saved in this browser.

Where are your parts from?

Controller board

Sorting modules

Each module adds two bins. With the catch-all at the bottom, that's 7 bins.

Module 1

Bin 2

Bin 1

Module 2

Bin 4

Bin 3

Module 3

Bin 6

Bin 5

Bin 7catch-all, all 3 bottoms open

Each module has three servos, a bottom trapdoor, a paddle gate, and a left/right pusher, plus an IR sensor. Closing every trapdoor above the target bin and opening only the ones beneath it lets a card fall to the right module before the pusher ejects it.

02 / Parts

Bill of materials

Quantities scale with the number of modules you're building: 3 modules × 3 servos, 1 feeder, 4 IR sensors, 10 of the PCA9685's 16 channels in use. The remaining channels are free for additional sorting modules (up to 5 modules on a single PCA9685). Check off each part as you gather it. Checkmarks are saved in this browser.

Building forOwn partsUno R43 modulesChange

Would rather not source every part yourself? The Mault shop sells kits with everything except the 3D-printed parts. You'll still need to print those yourself.

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Electronics

Qty	Part	Notes
1	Arduino Uno R4	Runs `firmware/main/main.ino`; USB connection to the host computer for Web Serial
1	Adafruit PCA9685 16-channel 12-bit PWM/servo driver	I²C servo driver, drives all 10 servos
9	SG90 micro servo, positional (180°)	3 per module × 3 modules: bottom trapdoor, paddle gate, pusher Buy digital SG90s. Analog SG90s, and Tower Pro servos in particular, don't hold their calibrated positions reliably in this sorter.
1	MG90S servo, 360° continuous rotation	Feeder, drives cards out of the hopper into module 1

Sensing

	Qty	Part	Notes	Buy
	4	Reflective/obstacle IR sensor module (3-pin: VCC, GND, digital OUT)	One at the gate of each module (1-3), plus one in the hopper throat

Power

Qty	Part	Notes
1	6V regulated power supply, 3A	Dedicated servo bus power into the PCA9685 V+ terminal. Do not power 10 servos off the Uno R4's onboard 5V. 5.5mm x 2.5mm barrel plug, center positive.
1	USB-A–to–USB-C cable	Arduino Uno R4 ↔ host computer
1	DC barrel jack or screw-terminal pigtail	Adapts the PSU output to the PCA9685's V+ / GND terminal

Structural

Qty	Part	Notes
-	PLA or PETG filament	Quantity per your slicer's estimate for the model above
6	20mm ID 26mm OD 3mm Width O-Ring	Fitted onto the feeder roller for grip on the card face
4	9.2mm ID 14mm OD 2.4mm Section O-Ring	Fits onto the hopper roller
1	3D-printed Servo Controller Plate	Printed once, regardless of module count
2	3D-printed Bins Plate	Catches the cards the pusher ejects to each side
1	3D-printed End Bin Plate	Used alongside the Bins Plates to complete the bin assembly

Fasteners & wiring supplies

Qty	Part	Notes
24	M3×6 screw	14 attach each bin base to the housing; 8 attach the base panels to the base; 2 mount a camera or phone bracket
8	M3 nut	Paired with the base panel M3×6 screws
2	M3 washer	Used with the M3×8 screws that mount the hopper roller
2	M3×8 screw	Mounts the hopper roller
1	M3×25 screw	Adjusts the hopper roller tension with the spring
1	7/32" x 11/16" spring	Tensions the adjustable wall against the card stack
59	M2×6 screw (17 per module, +4 for the board mount, +3 for the servo driver board, +1 for the feeder)	17 per module (3 modules): flapper (bottom/sides) and pusher arms, plus 6 to screw the bottom and side paddles into the housing; +4 to mount the Uno R4; +3 to mount the PCA9685 servo driver board; +1 for the feeder
6	M2×8 screw	2 per module (3 modules), to mount the pusher. M2×10 works fine if you don't have M2×8 on hand.
10	Servo horn screw (Included with servos)	Included with each servo; secures the horn to the shaft
1 pack	Jumper Wires	IR sensor/Servos. Using these you may have to daisy chain some together, just electrical tape them to make sure they don't come apart.
2	Wago connectorsOptional	Splices power and ground to each IR sensor without twisting/soldering wires together
~50	Dupont ConnectorsOptional	These are only needed if you're making your own custom length wires.
1	Dupont CrimperOptional	These are only needed if you're making your own custom length wires.

Optional

Qty	Part	Notes
1	Logitech C920 webcam	This is the one I use. Any webcam works as long as you can manually adjust focus, brightness, etc. (auto-adjusting can throw off scans)
1	Anker PowerConf C200 webcam	Recommended alternative to the C920. Also lets you manually adjust focus, brightness, etc.
1	1/4"-20 camera mount screw	Standard tripod-mount thread, screws into a webcam or phone mount's socket
0-25	Hopper sled weights	Drop into the weighted hopper sled to press the stack down so cards feed more reliably. Add up to 25
1 pack	Servo extension cables	Only needed for more than 3 sorting modules, where the stock servo leads won't reach the servo driver board

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03 / Assembly

Assembly

Eight phases, structural work first. Checkboxes are saved in this browser, so you can close the tab mid-build and pick back up later.

Stuck on a step? Join the Discord if you need help.

Building forOwn partsUno R43 modulesChange

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Phase 03

Flash the firmware

Download the code from the GitHub repository (Code → Download ZIP) and unzip it, then open the firmware folder with the Arduino IDE (File → Open → firmware/main/main.ino).

The Arduino IDE needs a sketch to live in a folder with the same name, so open main.ino from inside firmware/main rather than moving it elsewhere.

In the Arduino IDE, install the ArduinoJson, Adafruit PWM Servo Driver, and ArduinoBLE libraries.

Library Manager → search each by name. ArduinoBLE powers Bluetooth on the Uno R4 WiFi. The Uno R4 Minima has no Bluetooth hardware and doesn't use it, so Minima builds can skip it.

Select board "Arduino UNO R4 WiFi" (or "Arduino UNO R4 Minima" if that's the one you have), select the correct port, then upload firmware/main/main.ino.

Picking the exact board matters: Bluetooth is only compiled in when the WiFi board is selected.

Open the Serial Monitor at 9600 baud and confirm you see {"status":"ready"} after the board resets.

Phase 04

Wire and calibrate

Everything hangs off one I²C bus (PCA9685) and 4 digital input pins (IR sensors). The PCA9685's logic side runs off the Uno R4's onboard supply; its V+ servo rail must come from the external supply, and that supply's ground must be tied back to the Uno R4's ground. A floating servo ground is the most common reason a freshly wired unit won't move.

Wire colors vary between parts and suppliers, so don't rely on the colors in the diagram or photos. Trace each wire from its pin label and make sure it ends up at the correct place.

Use a 6V 3A power supply for the servos. Anything higher can burn out the servos or the servo control board.

Wire the PCA9685 to the Uno R4's I²C bus (SDA/SCL) and logic power/GND.

The PCA9685's header pins point straight out to the side. You may need to bend them 90° upward so they clear the panel and stay easy to reach when wiring to the Uno R4. Use the table below. The logic voltage is 3.3V on ESP32, not 5V.

I²C bus

PCA9685 pin	Arduino Uno R4	Wire in diagram
`SDA`	`SDA`
`SCL`	`SCL`
`VCC` (logic)	`5V`
`GND`	`GND`

Wire all 10 servos into PCA9685 channels 0–8 and 15 per the channel map. The feeder always takes the last channel.

There are wire channels, that use zip ties, in the side of the base to help keep everything neat.

PCA9685 channel map

Ch.	Assignment
0	Module 1, bottom
1	Module 1, paddle
2	Module 1, pusher
3	Module 2, bottom
4	Module 2, paddle
5	Module 2, pusher
6	Module 3, bottom
7	Module 3, paddle
8	Module 3, pusher
9	Unused, available for additional sorting modules
10	Unused, available for additional sorting modules
11	Unused, available for additional sorting modules
12	Unused, available for additional sorting modules
13	Unused, available for additional sorting modules
14	Unused, available for additional sorting modules
15	Feeder (continuous rotation)

Wire the 4 IR sensors to the digital pins in the table below. Module gates and the hopper throat sensor don't all fall on consecutive pins.

For the power and ground, you will have to combine 4 wires into one, either with a breadboard or by twisting and soldering them together. You will need to manually calibrate the sensors to have a shorter throw, as to not get false positives.

IR sensors

All 4 read active-LOW (pin goes low when a card is present) using the Uno R4's internal pull-up. Wire the sensor's digital OUT straight to the pin, no external pull-up resistor needed.

Sensor	Pin	Signal wire in diagram
Module 1 gate	`D2`
Module 2 gate	`D3`
Module 3 gate	`D4`
Hopper throat	`D5`

Bring the external 6V supply into the PCA9685 V+/GND terminal, and tie its ground to the Uno R4's ground.

Skipping the common ground is the #1 cause of servos that twitch but never move correctly.

Servo power

From	To	Wire in diagram
External 6V PSU, +	PCA9685 `V+` terminal block
External 6V PSU, −	PCA9685 `GND` terminal block and Uno R4 `GND`

Connect the Uno R4 to the app via Web Serial, then open /app/calibrate.

In the setup wizard (Set up your sorter, which opens the first time the sorter connects, or from the help (?) menu on /app/calibrate), install the horns (with their flapper or pusher arm already fitted) one servo at a time. For the bottom paddle and the side paddles, move the slider to 90%, then press the horn onto the servo shaft with the paddle in its closed position. For the pusher, move the slider to 50%, then press the horn onto the shaft. Secure each horn with its horn screw, for all 9 module servos.

Fitting a horn off-center biases the whole linkage. The exact open/closed and left/right pulses get fine-tuned in the next step.

Module Calibration Grid, set the open/closed pulse for each bottom and paddle, and left/neutral/right for each pusher, module by module.

For pusherLeft/pusherRight, swing the arm toward the inner wall but stop before it touches, about 10-12% away from neutral. The pusher doesn't need to hit the wall to fling the card, and pressing against it strains the servo. The app warns you past 16%.

Feeder Calibration Panel, tune feed speed, pulse/pause timing, and settle duration against your actual hopper.

Set the detection distance of all 4 IR sensors so each one sees a card 1 inch (2.5 cm) in front of it. With the board powered, use a small screwdriver on the screw of the blue box (the potentiometer) on each sensor: first turn it until the sensor's indicator LED goes off with nothing in front of it, then hold a card 1 inch in front of the sensor and turn the screw slowly back the other way until the LED just comes on.

Check it by pulling the card back to about 2 inches (5 cm): the LED should go off again. If it stays on, back the screw off a little. A sensor set too far reaches past the card path and reports cards that aren't there.

IR Sensor Panel, verify all 4 sensors report present/absent correctly with a card in hand.

If a sensor doesn't trigger, or triggers with nothing in front of it, repeat the previous step for that sensor.

Bin Routing Controls, send a test card to each of the 7 bins in turn and confirm it lands correctly.

Phase 05

Load and run

Load the hopper and confirm the feeder stops pulsing once the hopper IR reads empty.

Run a full scan-to-bin pass end to end before leaving the unit unattended.

Build the card sorter

Set up your build

Where are your parts from?

Controller board

Sorting modules

Bill of materials

Electronics

Sensing

Power

Structural

Fasteners & wiring supplies

Optional

Assembly

Print the structural parts

Assemble the modules

Flash the firmware

Wire and calibrate

I²C bus

PCA9685 channel map

IR sensors

Servo power

Load and run

Build the card sorter

Set up your build

Where are your parts from?

Controller board

Sorting modules

Bill of materials

Full parts list

Electronics

Sensing

Power

Structural

Fasteners & wiring supplies

Optional

Assembly

Print the structural parts

Assemble the modules

Flash the firmware

Wire and calibrate

Full wiring diagram

I²C bus

PCA9685 channel map

IR sensors

Servo power

Load and run