Ready to deploy design #7

March 24, 2025 · View on GitHub

Read this document from start to end before building anything. Ensure you understand everything. This setup was tested (with an external power source only).

Hardware features

Bluetooth Low Energy
Powered through rechargeable batteries or external power source (but not both)
Built-in battery monitor
Analog clutch paddles (x2)
Shift paddles (x2)
Relative rotary encoders (with push button): x3
Up to 20 additional push buttons

Button mapping

Bite point calibration: rotary #1 clockwise and counter-clockwise (while holding one and only one clutch paddle).
Next clutch function: Left shift paddle and START.
Calibrate analog clutch paddles: Left shift paddle, Right shift paddle and START.
Power on: rotary #1 clockwise or counter-clockwise.

Needed parts

Common:

Item	Quantity	Notes
Bare bone rotary encoder	3	With built-in push button
Roller lever	2	For shift paddles (maybe they are included with your wheel's case)
Linear potentiometer (10K-ohms to 100K-ohms)	2	For clutch paddles (maybe they are included with your wheel's case)
Push buttons	up to 20	General purpose inputs (up to you)
PISO shift register	3	74HC165N (mandatory)
Resistors	25	Any impedance in the range from 1K-ohms to 10K-ohms
Standard perfboard sized 24x10 holes	1	Single-sided or double-sided
LilyGO T-QT PRO DevKit board	1	With male pins already soldered
Pin header (male or female up to you)	37	For external wiring
External Antenna with proper connector	1	Optional

Battery-operated:

Item	Quantity	Notes
LiPo Battery 4.2V (max)	1	Must fit T-QT specification. Capacity and size up to you
Both male and female GX16 (5 pins) connectors	1 male and 1 female	For the charging port
USB-C spiral cable long enough	1	For charging. Must match your T-QT USB connector.
Battery connector	1	Should be included in your T-QT purchase

External power source:

Item	Quantity	Notes
External connector	1	Depends on your external power source

Other parts (quantity unknown):

Wire with Dupond terminals (for external wiring). A kit for protoboards will do the job. ¿Male or female? the opposite to pin headers. Sacrifice some of them for other wiring.
Welding tin.

Other notes:

The GX16 connector may be replaced by any other kind. The GX16 features a knot that prevents accidental unplug. The 5 pins flavor allows to build a fully capable USB port, not just a charging/power port, if you want.
The packaging of the shift registers will show a small circle next to pin #1, which is tagged as ~LD here.
There are several flavors of the T-QT DevKit board. Choose the "PRO" flavor, since it features a built-in powerboost module, unless you don't need the battery.
The T-QT DevKit board is sold with some wires included for the (optional) battery.

Pin-out plan for the T-QT DevKit board

GPIO	Input	Output	Usage	Notes
34	OK	OK	SERIAL
33	OK	OK	NEXT
39	OK	OK	ROT1_B
38	OK	OK	ROT2_A	outputs PWM signal at boot
37	OK	OK	ROT2_B	outputs PWM signal at boot
36	OK	OK	ROT3_A
35	OK	OK	ROT3_B
48	OK	OK	LOAD
18	OK	OK	ROT1_A
17	OK	OK	POT2_OUT	outputs PWM signal at boot
16	OK	OK	POT1_OUT

Circuit layout

We are reusing the shift registers example from the switches subsystem as a satellite circuit:

shift registers satellite circuit

External wiring goes as follows:

External wiring image

This layout includes the following subsystems (read for an in-depth explanation):

Power through a powerboost module already built in the DevKit board or an external power source.
Battery monitor through a built in voltage divider.
Switches through shift registers.
Relative rotary encoder bare bone type.

Notes and build tips:

Some components may look very small, not matching their actual size. This is not a mistake. They must be placed in vertical position, so they lie in a minimal surface of the perfboard.

External wiring

Each input has an assigned number in the circuit layout. Certain inputs have a particular function, so attach them properly.
The POTn_GND and POTn_VCC terminals of each potentiometer are interchangeable. If the clutch (or axis) goes to 100% when idle, swap those terminals. If you don't have the chance to swap those terminals, the companion app has the ability to swap axis polarity by user request.
Push buttons:
- There are two COM pins. They are intended for the left and right sides of the steering wheel, but you may use any of them.
- Wire COM to just one terminal of each push button in a chain.
- Wire the other terminal of each push button to one of the light-blue pins.
- Bare bone rotary encoders: their built-in push button must be wired like any other push button, being SW and SW COM the involved terminals.
In a battery-operated setup:
- Solder the battery connector to the small solder pads on the back of the T-QT devkit board.
- Battery(+) is the positive pole of the battery.
- Battery(-) is the negative pole of the battery.
- Attach Battery(+) and Battery(-) properly. Take care not to swap those terminals. There are two small solder pads on the back of the T-QT for them.
- EXT_GND is used as an additional COM pin header.
- Battery charge port:
  - Cut the USB cable near the USB-C end, but leave enough length to reach the GX16 plug.
  - Make sure matching GX16 pins in both male and female connectors are soldered to the same wire (same color).
  - Red and black wires are mandatory. Others are optional.
In an externally powered setup:
- Solder the external connector to Dupond wires matching the pin header of EXT_5V and EXT_GND.
- Leave Battery(+) and Battery(-) unwired (obviously).
- EXT_5V is the positive terminal of the external power source. Any DC source from +5V to +7V is suitable.
- EXT_GND is the negative (or ground) terminal of the external power source.
Rotary encoder #1 is mandatory as well as the Start button.

Firmware upload

At Arduino IDE, configure the board manager as this:

Board: "ESP32S3Dev"
USB CDC on boot: "Enabled".

You may need to edit the sketch.

In a battery-operated setup:

You should calibrate your battery first. See the Battery calibration procedure.
Locate the #define BATTERY_ENABLE_READ_GPIO directive and rewrite, so it looks as follow:
```
#define BATTERY_ENABLE_READ_GPIO GPIO_NUM_4
```

When using an external power source:

Locate the #define BATTERY_ENABLE_READ_GPIO directive and rewrite, so it looks as follow:
```
// #define BATTERY_ENABLE_READ_GPIO GPIO_NUM_4
```

Plug the USB cable to the DevKit board and upload the sketch with Arduino IDE. If required, in order to enter "boot mode" click the reset button while holding "IO0".
Open the serial monitor (Arduino IDE).
Reset.
Check there are no error messages.