Measurements during experiments are mostly analog in nature and is to be digitized before feeding into the computer for recording and further processing. Phoenix box has Four Analog input channels that can digitize voltages ranging from 0 to 5V and a digitization time of 100 microseconds. . The 8 bit ADC chip ADC0809 uses internal multiplexing and uses the same ADC to digitize all the inputs. Input signals are generally in the millivolts range and some of them may be bipolar, swinging to both positive and negative sides. They need to be amplified using the gain stages provided to utilize the full range of the ADC. One amplifier with offset is provided to convert a bipolar, -5V to 5V signal to a unipolar, 0 to 5V, signal. The required ADC channel must be selected in software before digitization using the software routines provided in the library. A 0 to 5V input gives output from 0 to 255.
    A Sample and Hold circuit is implemented using CD4066 switch and TL084 opamp. The start convert pulse keeps the ADC input in Sample mode for 2 -3 microseconds and Holds it during conversion. All the four input capacitors will be holding the voltages. To read them without sampling again add 4 to the channel number. For example, selectADC(5) will make the voltage held by channel 1 ( 5-4) to be converted during the next ADC read command like zeroTo5000() , minus5000To5000() or getRawADC().

ADC0809 Datasheet (PDF file)