An RS-485 Pressure Sensor Interface Board Compatible with Arduino

This project brief describes how to build and use an Arduino-compatible interface board that reads an on-board pressure sensor and reports the measurement over an RS-485 network.

Project one hour ago by Rajkumar Sharma, All About Circuits

This board is built around an ATmega328 microcontroller, an SN65HVD08DR half-duplex RS-485 transceiver, and an MPXV5010DP pressure sensor. Screw terminals bring out the RS-485 A and B lines for the twisted-pair bus cable, and the remaining I/O signals are available on pin headers for expansion (Figure 1).

The MPXV5010DP outputs an analog voltage proportional to applied pressure, which the ATmega328 samples and transmits over RS-485. A practical use case is a pressure-monitoring node on an RS-485 network, reporting back to a central controller or a companion display board.

This board suits pressure-sensing applications and other sensor nodes that need a reliable, noise-resistant RS-485 link, including hospital beds, HVAC systems, respiratory equipment, process control, and liquid-level or pressure measurement in appliances.

Figure 1. The assembled RS-485 pressure sensor interface board.

Specs and Features

Supply voltage: 5 V DC
MPXV5010DP pressure sensor on board
Pressure sensor output: 0.2 mV to 4.7 V
Half-duplex RS-485 communication (SN65HVD08DR transceiver)
Screw terminal for RS-485 A/B connection
Glitch-free power-up and power-down bus inputs and outputs
Multiple Arduino I/O lines broken out to headers
On-board power LED and function LED (tied to D13)
Optional 0.96-inch OLED display footprint
Optional 433 MHz RF module footprint
Four 4 mm mounting holes
PCB dimensions: 72.39 x 26.51 mm

How It Works

The ATmega328 reads the MPXV5010DP's analog output on pin A1 and drives the SN65HVD08DR transceiver to send the pressure reading out over RS-485. The transceiver connects to the microcontroller as follows:

RO (Receiver Output) = Arduino D10
RE (Receiver Enable) = Arduino D2
DE (Driver Enable) = Arduino D3
DI (Driver Input) = Arduino D11

The MPXV5010DP is a piezoresistive, monolithic silicon pressure sensor designed for microcontroller-based analog-to-digital measurement. It combines micromachining, thin-film metallization, and bipolar processing to produce an accurate, high-level analog output proportional to applied pressure. This device is rated for a 10 kPa range, with a sensitivity of 450 mV/kPa and an output swing from 0.2 mV to 4.7 V DC.

The SN65HVD08DR combines a three-state differential line driver and receiver in a single SOIC-8 package, compliant with the ANSI TIA/EIA-485-A and ISO-8482E standards. It operates from a 3 V to 5.5 V supply, draws less than 90 mW of quiescent power, and includes glitch-free failsafe biasing on its bus pins during power-up and power-down, so the bus stays clean when nodes are hot-plugged or power-cycled. An optional 0.96-inch OLED display can be soldered to the underside of the board for local status readout, and an optional 433 MHz RF module footprint is provided for wireless retransmission of the pressure reading.

The included test firmware receives pressure data over RS-485 and compares it to a threshold; the matching RS-485 relay driver board (published separately) can then trigger a relay once the reading crosses that threshold.

Schematic and Bill of Materials

Figure 2. Schematic for the RS-485 Pressure Sensor Interface Board.

The bill of materials is shown in Table 1.

Table 1. BOM for RS-485 Pressure Sensor Interface Board.

REF	DESCRIPTION	QTY	MFG	SUPPLIER	PART NO.
ANT1	Antenna (optional, not populated)	1
CN1	2-pin screw terminal, 5.08 mm pitch	1	Phoenix	Digi-Key	277-1247-ND
CN2, CN3, CN5, CN6	4-pin male header, 2.54 mm pitch	4	Würth	Digi-Key	732-5317-ND
CN4	8-pin male header, 2.54 mm pitch	1	Würth	Digi-Key	732-5321-ND
CN7, CN8	6-pin male header, 2.54 mm pitch	2	Würth	Digi-Key	732-5319-ND
C1	10 µF / 16 V ceramic, 0805	1	Yageo/Murata	Digi-Key
C2, C3, C4	100 nF / 50 V ceramic, 0805	3	Yageo/Murata	Digi-Key
C5, C6	22 pF / 50 V ceramic, 0805	2	Yageo/Murata	Digi-Key
R6, R7, C7, R12	Do not populate	4
D1, D2	Red LED, SMD 0805	2	OSRAM	Digi-Key	475-1278-1-ND
R1, R2, R3, R4, R5	10 kΩ 5%, SMD 0805	5	Yageo/Murata	Digi-Key
R8, R9, R10, R11, R14	0 Ω 5%, SMD 0805	5	Yageo/Murata	Digi-Key
R13	1 MΩ 5%, SMD 0805	1	Yageo/Murata	Digi-Key
R15, R16	1 kΩ 5%, SMD 0805	2	Yageo/Murata	Digi-Key
U1	SN65HVD08DR, SOIC-8	1	TI	Digi-Key	296-39173-1-ND
U2	ATmega328, TQFP-32	1	Microchip	Digi-Key	ATMEGA328-AU-ND
U3	SM712, do not populate	1
U4	MPXV5010DP pressure sensor	1	NXP/Freescale	Digi-Key	MPXV5010DP-ND
X1	16 MHz crystal	1	ECS Inc.		X1103-ND