Hardware Integration – Pexla Sensors

Supply Voltage 3.0 – 6.0 V

I/O Logic 3.3 V

Default Baud 9600 bps

Thread ¾″ NPT

Sleep Current 3 – 8.5 µA

Pinout Overview

Pexla sensors expose all interfaces on a single 6-pin JST connector. UART TX/RX, I²C SDA/SCL, and a configurable GPIO/threshold pin share the same harness. The Modbus RS485 variant substitutes the UART lines for A/B differential pairs.

1 VCC 3–6V supply

2 GND Ground

3 TX UART transmit

4 RX UART receive

5 SDA I²C data

6 SCL I²C clock

7 GPIO Threshold/wake

Connection 1

Generic MCU via UART / RS232

UART is the primary interface for all Pexla models. A direct 3-wire connection (TX, RX, GND) is all that's needed. The sensor transmits distance frames immediately on power-up at 9600 bps — no initialization required. For 5V MCUs such as Arduino Uno, a simple voltage divider on the RX line protects the sensor's 3.3V input.

Wiring Table — UART (3.3V MCU)

Pexla Pin	MCU Pin	Wire	Notes
VCC	3.3V	●	Max 6V; 3.3V or 5V both work
GND	GND	●	Common ground required
TX (sensor out)	RX (MCU in)	●	Direct — no level shift needed at 3.3V
RX (sensor in)	TX (MCU out)	●	For API commands only; leave open for read-only
GPIO	Any digital in	●	Optional: threshold alert / wake

⚠️

5V MCU (Arduino Uno): add a 10kΩ / 20kΩ voltage divider on the MCU TX → Pexla RX line. The sensor TX → MCU RX line works directly as 3.3V is a valid HIGH for 5V CMOS.

Default UART Settings

Baud Rate	`9600 bps (configurable up to 500,000)`
Data Bits	`8`
Parity	`None`
Stop Bits	`1`
Flow Control	`None`
Logic Level	`3.3V`
Output Frame	`R{distance_mm}\n @ 1 Hz`
Maxbotix PWM	`Available on GPIO pin`

💡

Maxbotix pin-compatible: Pexla MX is a drop-in replacement for HRXL-MaxSonar-WR sensors. Same pinout, same PWM output format, same operating voltage range.

Connection 2

MCU via I²C

I²C allows up to 127 Pexla sensors on a single 2-wire bus, making it ideal for multi-point monitoring arrays. The sensor appears as a 7-bit I²C peripheral. Pull-up resistors (4.7 kΩ typical) must be present on SDA and SCL. The I²C interface supports 100 kHz (Standard) and 400 kHz (Fast) modes.

Wiring Table — I²C

Pexla Pin	MCU Pin	Wire	Notes
VCC	3.3V	●	3.3V or 5V
GND	GND	●	Common ground
SDA	SDA	●	4.7 kΩ pull-up to 3.3V required
SCL	SCL	●	4.7 kΩ pull-up to 3.3V required
GPIO	INT pin	●	Optional: data-ready interrupt

I²C Configuration

Default Address	`0x52 (7-bit)`
Speed	`100 kHz / 400 kHz`
Pull-ups	`4.7 kΩ to 3.3V`
Max Bus Length	`~1 m at 400 kHz`
Multi-sensor	`Up to 127 devices`
Data Register	`0x00–0x01 (distance MSB/LSB)`

💡

Multi-sensor arrays: each Pexla sensor's I²C address can be configured via the API. Deploy up to 127 sensors on a single bus for distributed level monitoring across a treatment facility or stormwater network.

Connection 3

Modbus Host via RS485

The Pexla ModBus model implements Modbus RTU over RS485 — the industrial standard supported by virtually every SCADA system, PLC, and data logger. RS485 differential signaling allows cable runs up to 1200 m and multi-drop networks of up to 32 devices on a single twisted-pair cable. The Pexla sensor acts as a Modbus slave (server) responding to function codes 03 (Read Holding Registers) and 06 (Write Single Register).

Wiring Table — RS485

Pexla	RS485 Bus	Wire	Notes
VCC	+12V or +5V	●	Sensor powered from bus or separate supply
GND	GND	●	Common ground
A (D+)	A (D+)	●	RS485 positive (non-inverting)
B (D−)	B (D−)	●	RS485 negative (inverting)

⚠️

Termination: add a 120 Ω resistor across A/B at each end of the bus for cable runs over 10 m or at speeds above 9600 bps. Bias resistors (560 Ω) should be present at the master end.

Modbus Configuration

Protocol	`Modbus RTU`
Default Address	`0x01 (configurable 1–247)`
Baud Rate	`9600 bps default (configurable)`
Parity	`None, 8-N-1`
Cable	`Twisted pair, shielded`
Max Nodes	`32 (hardware), 247 (protocol)`
Max Distance	`1200 m at 9600 bps`
Register 0x0000	`Distance in mm (uint16)`
Register 0x0001	`Temperature × 10 (int16)`
Register 0x0010	`Threshold high (mm)`
Register 0x0011	`Threshold low (mm)`
FC 03	`Read holding registers`
FC 06	`Write single register (config)`

Connection 4

PC via USB-C

The Pexla USB and Pexla SD models include a USB-C connector that presents as a virtual COM port (USB CDC) on Windows, macOS, and Linux — no driver installation required on modern operating systems. The USB connection simultaneously powers the sensor and provides full bidirectional API access. Use any serial terminal or Python script to read live distance data and configure all parameters.

USB Connection

Connector	`USB-C (Pexla) ↔ USB-A/C (PC)`
Protocol	`USB CDC (virtual COM port)`
Driver	`None required (Win 10+, macOS, Linux)`
Windows Port	`COMx (Device Manager)`
macOS Port	`/dev/cu.usbmodem*`
Linux Port	`/dev/ttyACM0`
Baud Rate	`Any (USB is not baud-sensitive)`
Power from USB	`5V, up to 500 mA`
Firmware Update	`Via USB — drag-and-drop or CLI tool`

Recommended Serial Terminals

PuTTY Windows

Free. Connection → Serial. Set port and baud.

CoolTerm Windows / macOS

Graphical, logging support, timestamps.

screen macOS / Linux

screen /dev/ttyACM0 9600

Arduino Serial All platforms

Built into Arduino IDE. Tools → Serial Monitor.

pyserial Python (all)

pip install pyserial — see API Integration docs.

minicom Linux

minicom -D /dev/ttyACM0 -b 9600

Comparison

Interface Selection Guide

All interfaces expose identical distance data and API functionality. Choose based on your host platform, cable length, and deployment context.

Criteria	UART / RS232	I²C	Modbus RS485	USB-C
Best For	MCUs, Arduino, RPi	Multi-sensor arrays	SCADA / PLC / DCS	Development, logging
Max Cable	~15 m (RS232: 15 m)	~1 m	1200 m	5 m (USB spec)
Multi-device	1:1 only	127 on one bus	32–247 on one bus	1:1 only
Wires Required	3–4	4 + pull-ups	4 (A, B, PWR, GND)	1 cable
Noise Immunity	Moderate	Low (short runs)	Excellent	Excellent
Protocol	ASCII frames	Register-mapped	Modbus RTU	USB CDC / ASCII
Power from Host	No	No	No	Yes (5V USB)
Driver Needed	No	No	No	No (Win10+/mac/Linux)
API Access	Full	Full	Full (via registers)	Full
SDI-12 (Pexla MX)	✓ on TX pin	—	—	—