## Simultaneous A/D and D/A Conversion

Equipment needed: IBM-PC, PCL-812 analog data acquisition/control board, digital volt meter, operational amplifier manifold, resistors, diode.

1. Install the PCL-812 board into any available slot of the IBM-PCs bus. The base address A is determined by the base address switch on the board; the factory default is hex 220 (544 decimal). The PCL-812 board has a 12 bit ADC with 16 input channels and an output range of -10 to +10 volts. Refer to the manual to find out how to program the ADC.

2. The objective of this experiment is to construct and test a system to record the current-voltage characteristic curves of unknown two-terminal devices, that is, to apply a range of voltages across the device and measure the resulting current flow. You will use the DAC in the PCL-812 board to generate the voltages and the ADC to measure the voltage across the device and (by the application of Ohm's Law) the current through the device. Such a setup might be used, for example, to measure the characteristics of an electrochemical cell or a new organic semiconductor. We will test our setup first with a simple resistor (which has a linear IE curve whose slope is given by its resistance) and then use it to test a small diode (which has a more interesting non-linear, temperature-sensitive, IE curve).

3. In the circuit shown here, an operational amplifier boosts the 5 volt output of the DAC to 10 volts and applies it to the Device Under Test through a 10K Ohm series resistor. ADC channel 1 measures the voltage across the device. The current through the device is given, according to Ohm's Law, by the ratio of the voltage across the 10K Ohm series resistor divided by its resistance (assuming that no current is drawn by the channel 1 input - a reasonable assumption). The voltage across the series resistor is the difference between the channel 1 voltage and the channel 0 voltage. Therefore, the computer can easily calculate the current through the device.

4. Write a program to measure the IE curve from 0 to 10 volts total applied voltage and save the data as a text file containing two columns of data (E across device and I through the device).

Lab report: Submit your program listing (print-out only) along with a print-out of the data.

This page is maintained by Tom O'Haver , Department of Chemistry and Biochemistry, The University of Maryland at College Park. Comments, suggestions and questions should be directed to Prof. O'Haver at to2@umail.umd.edu.