Dual Sensor Measurement Using Single Current-Loop with FSK Modulation Reference Design


Design files


The TIDA-00483 reference design demonstrates a 4-20mA current loop subsystem capable of measuring the surrounding environment and communicating the temperature, humidity, and ambient light over the loop. The small footprint of the design contains all sensors, filters, and control circuitry to calculate and communicate the sensor data. The reference design is intended for process measurement applications in factory automation, field transmitters and building automation. The sensors, MCU and communication modules all run from the current loop power, requiring less than 3.5 mA.

  • Reduce cabling and installation cost by transmitting two variable parameters simultaneously on a 4-20mA current loop
  • Expandable to additional sensor parameters via FSK-modulated digital data stream
  • Dual op-amp 4th order Butterworth filter for FSK generation reduces BOM count
  • Ultra Low power MSP430 consumes less of the 3.5 mA budget allowing more current for sensors in the loop
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A fully assembled board has been developed for testing and performance validation only, and is not available for sale.

Design files & products

Design files

Download ready-to-use system files to speed your design process.

TIDUAH2.PDF (2208 K)

Reference design overview and verified performance test data


Detailed schematic diagram for design layout and components


Complete listing of design components, reference designators, and manufacturers/part numbers


Detailed overview of design layout for component placement

TIDRIM4.ZIP (3187 K)

Files used for 3D models or 2D drawings of IC components


Design file that contains information on physical board layer of design PCB

TIDRIL9.PDF (1901 K)

PCB layer plot file used for generating PCB design layout


Includes TI products in the design and potential alternatives.

Precision DACs (≤10 MSPS)

DAC161S99716-Bit Precision DAC With Internal Reference and 4mA-to-20mA Current Loop Drive

Data sheet: PDF | HTML
General-purpose op amps

LMV342Dual, 5.5-V, 1-MHz, high output current (75-mA) operational amplifier

Data sheet: PDF | HTML
Humidity sensors

HDC1000Low Power, 3% Accuracy Digital Humidity Sensor with Integrated Temperature Sensor

Data sheet: PDF | HTML
Humidity sensors

HDC1010±2% low-power digital humidity and temperature sensor in WCSP

Data sheet: PDF | HTML
Light sensors

OPT3001Digital ambient light sensor (ALS) with high-precision human-eye response

Data sheet: PDF | HTML
Linear & low-dropout (LDO) regulators

TPS7A400150-mA, 100-V, low-IQ, adjustable low-dropout voltage regulator with enable

Data sheet: PDF | HTML
MSP430 microcontrollers

MSP430FR596916 MHz MCU with 64KB FRAM, 2KB SRAM, AES, 12-bit ADC, comparator, DMA, UART/SPI/I2C, timer

Data sheet: PDF | HTML

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Technical documentation

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Type Title Date
* Design guide Dual Sensor Measurement Using Single Current-Loop Design Guide Aug. 26, 2015

Related design resources

Reference designs

TIDA-00095 RTD Temperature Transmitter for 2-wire, 4 to 20-mA Current Loop Systems

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