Build a complete industrial-ADC interface using a microcontroller and a sigma-delta modulator

摘要

Designers commonly use 0- to 20-mA, 0 to 10V isolated inputs for industrial-application-control signals. A combination of isolated supplies, the built-in isolation of an Analog Devices (www.analog.com) AD7400 sigma-delta modulator, and a Texas Instruments (www.ti.com) MSP430 microcontroller creates a design for industrial designers requiring complete, isolated, and robust analog-signal interfaces. A precise signal-conditioning circuit generates the small differential voltage that the AD7400 requires (Figure 1). The circuit generates the required 200-mV differential voltage. For clarity, the figure omits overvoltage diodes and protection circuits.