The Main PCB

This is the most complicated and delicate board of the whole robot, as it contains the main microcontroller and a lot of small-pitch connectors.

Take your time with this one, and make sure to follow the instructions carefully to avoid damaging the board or the components.

As this board is pretty big, the assembly process will be split in 7 parts. Starting with soldering the board's surface-mount connectors and components, and then the through-hole ones.

1 - The audio management

We'll start with the audio section, which is located on the left side of the board. This section contains the PAM8406 audio chip as well as filtering and power management components.

For this section, you'll need :

ID	Component	Description	Quantity
1	PAM8406 Audio Chip	Main audio processing chip	1
2	0603 100nF Capacitor	Decoupling capacitor	3
3	0603 Ferrite Bead	EMI filtering component	3
4	0603 220pF Capacitor	Decoupling capacitor	2
5	0603 1uF Capacitor	Decoupling capacitor	2
6	0603 10nF Capacitor	Low-pass filter capacitor	1
7	0603 1kΩ Resistor	Low-pass filter resistor	1
8	0603 22kΩ Resistor	Gain control resistor	1

2 - The USB connexion

The USB section is located on the top right of the board, and it contains the USB-C connector as well as the necessary components for programming and communication with the ESP32-S3.

For this section, you'll need :

ID	Component	Description	Quantity
1	USB-C Connector	Main USB connector for programming	1
2	CH340C USB-to-Serial Chip	USB-to-Serial converter chip	1
3	0603 10uF Capacitor	Decoupling capacitor	1
4	SOT-23-3L BJT Transistor	Used for programming sequence	2
5	0603 10kΩ Resistor	Resistors for programming	2
6	SOT-23-6 USB Protection IC	ESD protection for USB lines	1
7	0603 1uF Capacitor	Timing capacitor for reset sequence	1

3 - The camera components

The camera section is located on the bottom center of the board, and it contains all the components necessary for powering and connecting the camera module to the board.
This section is particularly delicate, as it contains a lot of small components and a fine-pitch FPC connector.

For this section, you'll need :

ID	Component	Description	Quantity
1	FPC 24-pin Connector	Camera connector	1
2	0603 100nF Capacitor	Decoupling capacitor	4
3	0603 10uF Capacitor	Decoupling capacitor	2
4	0603 15pF Capacitor	Decoupling capacitor	1
5	0603 4.7kΩ Resistor	Pull-up resistor	1
6	0603 1kΩ Resistor	Pull-down resistor	1
7	SOT-23-3L 1.2V LDO	Digital supply for camera	1
8	SOT-23-3L 2.8V LDO	Analog supply for camera	1

4 - The power management

The power management section is located under the USB connector, and contains a few components for power supply management.

For this section, you'll need :

ID	Component	Description	Quantity
1	SOT-223 3.3V LDO	Main power supply	2
2	SMA-L4.3 Power Diode	USB vs Battery selection	2
3	F1812 Fuse	Short-circuit protection	1
4	SMA-L4.3 TVS Diode	Short-circuit protection	1

5 - The ESP32-S3 and LED

The main section of the board is located in the center, and contains the ESP32-S3 microcontroller as well as the RGB status LED for debugging.

For this section, you'll need :

ID	Component	Description	Quantity
1	ESP32-S3 N16R8	Main microcontroller	1
2	XL550 WS2812B LED	RGB status LED	1
3	0603 2.2kΩ Resistor	I2C pull-up resistor	4
4	0603 10kΩ Resistor	Enable pull-up resistor	1
5	0603 100nF Capacitor	Decoupling capacitor	1
6	0603 10uF Capacitor	Decoupling capacitor	1
7	0603 220pF Capacitor	Noise filtering capacitor	1

6 - The back connectors

Now that all the SMD components are soldered, we can move on to the through-hole ones. But before doing anything, we'll solder the USB-C connector's housing pins, to make sure it is securely attached to the board.

Soldering the USB-C connector

Flip the board to access the back of the USB-C connector. Push the connector flush against the board, and solder the 4 housing pins on the back of the board.

Use a little bit of solder flux to make sure the solder flows well, and be careful not to use too much heat or pressure on the connector to avoid damaging it or the PCB.

Soldering the other connectors

The board contains 7 other JST connectors on the back for power supply and communication with the rest of the robot. These connectors are pretty big and easy to solder, but make sure to align them properly.

For this step, you'll need :

ID	Connector	Description	Quantity
1	JST PH 2-pin	Power supply connector	1
2	JST PH 4-pin	IMU & Plug PCB connectors	2
3	JST PH 5-pin	Motor Driver connector	1
4	JST PH 7-pin	Analog Reader connector	1
5	1.25 mm 2-pin	Speaker connector	1

7 - The front connectors

Moving on the front of the board, we have 5 more JST connectors to solder, and a 470uF capacitor for the speaker power supply.

make sure to solder the capacitor in the correct orientation, as it is polarized.

For this step, you'll need :

ID	Connector	Description	Quantity
1	JST PH 3-pin	Left & Right buttons	2
2	JST PH 4-pin	Laser & Screen connectors	2
3	JST PH 5-pin	I2S Microphone connector	1
4	470uF Capacitor	Speaker capacitor	1

Final inspection

After soldering all the components, inspect the PCB carefully to ensure that all joints are solid and there are no solder bridges or cold joints. Use a magnifying glass if necessary to check for any issues.

If you have a multimeter, you can also check for continuity between the pins of the connectors and the corresponding pads on the PCB to ensure that everything is properly connected.

If all the checks are good, you can also try powering the board on for the first time to see if your PC recognizes the USB device.

All good ? Well, congratulations! You've just soldered the most complicated PCB of the whole robot!

Let's do a bit more soldering now, but to prepare all the other components and boards !