SMCSKart Mainboard

Custom PCB integrating every system in the SMCS Robotics 8th period go-kart. The board acts as the central hub between a Raspberry Pi 4, a Teensy 4.1, all motor controller I/O, sensors, and peripherals.

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Components

Component	Description
Raspberry Pi 4	Main compute; connected via 40-pin header
Teensy 4.1	Real-time microcontroller with onboard Ethernet
NEO-M9N	GPS module (connected to Pi I2C + PPS to Teensy)
MPU6050	6-axis accelerometer/gyroscope (connected to Pi I2C)
MCP4725	12-bit DAC for throttle signal generation (connected to Teensy I2C)
MCP2562-E/P	CAN bus transceiver
IRLZ44N	Logic-level N-channel MOSFETs for all toggle/switch outputs (with pulldown resistors)
ND721000	FarDriver BLDC/PMSM speed controller (RS232 interface)

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Power Rails

The board supplies three voltage rails available on the extra power port:

Rail	Voltage
3V3	3.3 V
5V	5 V
24V	24 V (also used for LED strip)

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Teensy 4.1 Pin Assignments

Serial / UART

Pin(s)	Interface	Connected To	Notes
0, 1	Serial1 (TX, RX)	ND721000 ESC	RS232 level — programming/telemetry port on ESC
7, 8	Serial2 (TX, RX)	Raspberry Pi 4	UART bridge between Teensy and Pi
14, 15	Serial3 (TX, RX)	Transceiver module	RF/wireless transceiver comms
34, 35	Serial8 (TX, RX)	FPV camera	UART control for FPV camera

I2C

Pin(s)	Bus	Connected To
18, 19	SDA, SCL	MCP4725 DAC (throttle control)

CAN Bus

Pin(s)	Signal	Notes
30, 31	CRX, CTX	Via MCP2562-E/P transceiver; 120 Ω termination required at each end

Digital I/O — ESC Control & Sensors

All toggle output pins drive an IRLZ44N MOSFET with a pulldown resistor, providing an active-low ground signal to the ESC connector.

Pin	Function	ESC Signal	Direction
2	Hall Pulses input	Hall Pulses (ESC pin 18)	Input from ESC
3	Reverse toggle	REV (ESC pin 8)	Output to ESC
4	Brake toggle	Low Brake (ESC pin 21)	Output to ESC
5	High speed toggle	High Speed (ESC pin 3)	Output to ESC
6	Low speed toggle	Low Speed (ESC pin 2)	Output to ESC
9	Cruise control	Cruise/Boost connector	Output to ESC
10	PPS	NEO-M9N GPS pulse-per-second	Input from GPS
32	Contactor toggle	Main contactor relay	Output

PWM — LED Strip (24 V)

Pin	Channel
37	Red
36	Green
33	Blue

Auxiliary (EX1–EX5)

Pin	Label
25	EX1
26	EX2
27	EX3
28	EX4
29	EX5

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Raspberry Pi 4 I2C Bus

Device	Address	Function
NEO-M9N	—	GPS module
MPU6050	0x68	Accelerometer / Gyroscope

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ND721000 ESC Interface

The Teensy communicates with the ND721000 over Serial1 (pins 0/1) at RS232 levels (programming/telemetry port). In addition, discrete signals are routed between the board and the ESC's connector harness.

ESC Connector Pin Reference

ESC Pin	Color	Signal	Direction	Teensy Pin	Notes
1	Yellow	Hall A	→ ESC	—	Motor hall sensor A
2	Blue-White	Low Speed	← Teensy	6	Ground to activate low speed profile
3	Yellow-White	High Speed	← Teensy	5	Ground to activate high speed profile
4	Red	HALL+	—	—	~14 V supply to hall sensors / encoder
5	Brown-Yellow	CAN L	↔	—	CAN bus low (optional; 120 Ω termination required)
6	Black	GND (Hall)	—	—	Hall sensor ground
7	Black	B− / GND	—	—	Battery negative / signal ground
8	Brown-White	REV	← Teensy	3	Ground to request reverse direction
9	Purple	Speedometer signal	→	—	Analog speed output for speedometer gauge
10	Orange	Key	—	—	Main power-on input (connect to key switch via 5A fuse)
11	Gray	High Brake	← Teensy	4	Active-high (12 V) brake input
12	Green	Hall B	→ ESC	—	Motor hall sensor B
13	Light-Blue	SPD (digital speed pulse)	→	—	Square-wave RPM output for digital speedo / ECU
14	Black-White	FW (anti-theft)	←	—	Ground to activate anti-theft lockout (error code 6)
15	Red-Yellow	CAN H	↔	—	CAN bus high (optional; 120 Ω termination required)
16	Black	GND (serial/switch)	—	—	Signal ground for serial and switch circuits
17	White	Hall P (encoder index)	→ ESC	—	Once-per-revolution encoder reference pulse
18	Brown	Hall Pulses signal	→ Teensy	2	Speed pulse output used as tachometer reference
19	Brown-Red	Lock Phase	—	—	Anti-theft motor phase lock wire
20	Orange	Key (anti-theft)	—	—	Secondary key input for anti-theft subsystem
21	Yellow-Green	Low Brake	← Teensy	4	Active-low brake input; ground to signal braking
22	Blue	Hall C	→ ESC	—	Motor hall sensor C
23	Brown-Blue	TxD (serial)	→ Teensy	0 (RX)	ESC serial transmit → Teensy Serial1 RX
24	White	Motor Temp	→ ESC	—	Motor temperature sensor (PTC/NTC/KTY)
25	—	—	—	—	—
26	Black	GND (throttle/brake)	—	—	Shared signal ground for throttle and brake circuits
27	Green-White	TPS (throttle)	← DAC	—	Throttle position signal (0.5–4.3 V); driven by MCP4725
28	Red-White	ACC+ (5 V)	→ throttle sensor	—	5 V regulated supply for throttle sensor
29	Brown-Green	V+ (serial power)	→ adapter	—	5 V supply for USB-TTL programming adapter
30	Pink	B+ (anti-theft)	—	—	Always-live battery positive for anti-theft device
31	Brown-Red	RxD (serial)	← Teensy	1 (TX)	ESC serial receive ← Teensy Serial1 TX

Note: High Brake (pin 11) is active-high (12 V) while Low Brake (pin 21) is active-low (GND). Both can signal braking; the board uses pin 21 via MOSFET toggle (Teensy pin 4). Note: Medium speed mode is the ESC default when neither High Speed nor Low Speed is grounded.

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External Connectors / Ports

Port	Description
40-pin header	Raspberry Pi 4 HAT connector
USB-A	HID peripheral (keyboard, gamepad, etc.)
Ethernet	Networking (Teensy 4.1 native Ethernet)
CAN × 3	CANBUS + I2C interface ports
Contactor	Trigger port for main contactor relay (Teensy pin 32)
FPV camera	UART port (Teensy Serial8, pins 34/35)
Transceiver	RF transceiver UART port (Teensy Serial3, pins 14/15)
Power port	Extra 3V3 / 5V / 24V supply breakout
LED strip	24 V RGB PWM output (pins 37, 36, 33)

For images of each port's annotated pinout, see ./docs/PINOUTS.md

Made by Eli Ferrara, SMCS Class of 2026 MIT License