Browse Prior Art Database

Single Digital I/O Line Analog to Digital Conversion

IP.com Disclosure Number: IPCOM000104711D
Original Publication Date: 1993-May-01
Included in the Prior Art Database: 2005-Mar-19
Document File: 2 page(s) / 65K

Publishing Venue

IBM

Related People

Smith, GJ: AUTHOR

Abstract

A method of monitoring an analog sensor with a digital microprocessor is disclosed. Integration of the current out of a sensor following an initial charging step produces a decaying voltage level that is detected as the level crosses the threshold of the microprocessor digital input port logic.

This text was extracted from an ASCII text file.
This is the abbreviated version, containing approximately 53% of the total text.

Single Digital I/O Line Analog to Digital Conversion

      A method of monitoring an analog sensor with a digital
microprocessor is disclosed.  Integration of the current out of a
sensor following an initial charging step produces a decaying voltage
level that is detected as the level crosses the threshold of the
microprocessor digital input port logic.

      The invention exploits both the power of a microprocessor and
the threshold nature of digital logic.  The combination of these
together with the non-obvious use of digital line source current for
providing power to the analog sensor electronics makes the
combination novel.  To make the invention clear, a simple example is
given in the figure.  This example is only meant to show a very
simple embodiment using minimal parts.  In the figure, a temperature
sensor (thermistor) is placed in parallel with a capacitor.  Data
acquisition takes place in two phases.

1.  In the first phase, a digital input/output (I/O) line is
    programmed by the host microprocessor to be an output and is set
    at a high level for a given length of time.  In the simplest
    case, the line remains high until the capacitor has fully
    charged.  As will be shown later, this is not required.  A series
    resistance, Rs, has been added to limit the source current for
    this example.

2.  The actual measurement is performed in phase 2.  In phase 2, the
    host microprocessor programs the digital line to be an input.
    After this is done, the microprocessor repeatedly polls the line
    to see when it reaches a low state.  The time required for the
    line will reach a low state will depend on the I/O line voltage
    in pha...