This document describes how to implement a 10-bit Sigma-Delta A/D converter using a simple external circuit and a Sigma-Delta conversion program. The ST7FLITE05(09) has an on-chip ADC with 8-bit resolution and an input range of 0-VCC. The external Sigma-Delta ADC described in this application is designed for relatively slow alternating signals (0,2 - 5Hz) in the range 0 - 10mV(p-p). The focus of the project is to provide good relative accuracy, repeatable parameters and simplicity, resulting therefore a low cost of the device (in its simplest form, apart from the microcontroller, only three RC elements are necessary).