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SELF POWERED ADC INTERFACE TO PARALLEL PORT

Project for connecting analogue signal to LPT printer port. Included Visual Basic 6 software and a circuit diagram. The MCP3201 is a micro-power 12 bit analogue to digital converter. The conversion selector selects the MSB when it sets to 8 Bit or 10 Bit and ignores the rest of the bits. With less resolution the reading is more stable. The supply to the circuit is via the 5V at pins that are switched to logic high by the software.
The VB6 software includes a freeware DLL from http://logix4u.net/ ,keep the .dll file and the .exe file in the same folder.
Datasheet for the MCP3201 can be downloaded from http://ww1.microchip.com/downloads/en/DeviceDoc/21290D.pdf
VB6 code (30KB). You are free to use the circuit diagram and the VB software with no limitations.

The VB6 application is a combined digital and analogue voltmeter.

Circuit Description
See also Technical Tips

MCP3201
Input at pin 2 of the ADC is 0 to 2.5 volts full range positive voltage only. The chip over voltage protection is 5V max.
Pin 8 is the supply to the IC and it is about 3.2 V.
Pin 1 is reference voltage for the ADC and cannot be changed because it regulates the supply to the IC.
Pin 6 is the serial data out of the ADC, BC237 is a TTL level drive.
Pin 7 is the clock for reading the data, 100pF is for filtering crosstalk from the cable.
Pin 5 is the Chip Select.
100R resistors and diodes on these lines are for clipping the voltage to the Vcc of the IC.

LPT plug
Pins 23,34,25 are earth. Pins 1,11,14 are inputs and outputs used for reading the ADC data. Pins 8,9 are switched to 5 V ,output high, by the software and are used for powering the circuit.