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A SIMPLE ADC ON AN LTC1286 CHIP

by Yuri Magda

Start ý The Software ý The Input Signal Handler and Interface ý Code Concerns ý The Design and Details ý Sources and PDF

The purpose of this article is to attract your attention to a A/D converter circuit designed on a popular low-cost chip, the LTC1286. Iýve used this converter for about a year now in my home laboratory for measuring voltage in electronic circuits. The circuit allows the measurement of an input voltage ranging from 0 to 5 V and is controlled through a PC parallel port. The converter consumes a low supply current equal to only 250 ýA. The control program of the converter can work on any PC running Windows98.

I would like to begin by describing the electrical circuit of the device (see Figure 1). As you see, the circuit is straightforward. It uses the LTC1286 chip in a single-ended connection.

Figure 1ýThis schematic shows the interfacing of the ADC to the PC parallel port. (Click to enlarge)

The analog input voltage ranging from 0 to 5 V is accepted through pin 2 (+IN). The conversion result is provided on pin 6 (Dout) as a serial datastream. The chip select (*CS/SHDN) input on pin 5 initiates the conversion and frames the serial data transfer. And, pin 7 (CLK) is used as a serial clock for accessing data from the LTC1286 chip.

The converter works with a sampling frequency of up to 12,500 measurements per second. It has 12-bit resolution, which means that there are 4096 (2¹²) values recognized. Therefore, with an input range of 0 to 5 V, the resolution is 1.22 mV (5/4096).

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