Classifications

• • H—ELECTRICITY
  • H03—ELECTRONIC CIRCUITRY
  • H03K—PULSE TECHNIQUE
  • H03K17/00—Electronic switching or gating, i.e. not by contact-making and –breaking
  • H03K17/94—Electronic switching or gating, i.e. not by contact-making and –breaking characterised by the way in which the control signals are generated
  • H03K17/96—Touch switches
• • H—ELECTRICITY
  • H03—ELECTRONIC CIRCUITRY
  • H03K—PULSE TECHNIQUE
  • H03K17/00—Electronic switching or gating, i.e. not by contact-making and –breaking
  • H03K17/94—Electronic switching or gating, i.e. not by contact-making and –breaking characterised by the way in which the control signals are generated
  • H03K17/96—Touch switches
  • H03K17/962—Capacitive touch switches
• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
  • G01R27/00—Arrangements for measuring resistance, reactance, impedance, or electric characteristics derived therefrom
  • G01R27/02—Measuring real or complex resistance, reactance, impedance, or other two-pole characteristics derived therefrom, e.g. time constant
  • G01R27/08—Measuring resistance by measuring both voltage and current
• • H—ELECTRICITY
  • H03—ELECTRONIC CIRCUITRY
  • H03K—PULSE TECHNIQUE
  • H03K17/00—Electronic switching or gating, i.e. not by contact-making and –breaking
  • H03K17/94—Electronic switching or gating, i.e. not by contact-making and –breaking characterised by the way in which the control signals are generated
  • H03K17/945—Proximity switches
  • H03K17/955—Proximity switches using a capacitive detector

Definitions

• the present invention is directed to methods and apparatus for interconnecting a field effect sensor with a control system or controlled device using only two wires.
• Mechanical switches are sometimes used to detect change in position of a mechanical part or level of a fluid, among other things. Such uses are particularly prevalent in
• Field effect sensors have been used as replacements for mechanical switches in many applications. Indeed, field effect sensors can be used to sense proximity of a mechanical part or a liquid. Field effect sensors have many advantages over mechanical switches. For example, they have no moving parts which can wear out or break. Also, they can be inexpensively mass-produced and customized for use in applications that would not readily accommodate mechanical switches.
• Mechanical switches in their simplest form are two-wire (input and output) devices that mechanically make or break an electrical circuit. They operate using mechanical force and do not require electrical power for their operation.
• field effect sensors are solid state-devices which require electrical power for their operation. Accordingly, a field effect sensor typically requires at least one more wire for its operation than does a mechanical switch. As such, known field effect sensors typically cannot be used as drop-in replacements for mechanical switches without some modification to the apparatus into which they would be installed.
• FIG. 1 illustrates schematically a first embodiment of the present invention
• FIG. 2 illustrates schematically a second embodiment of the present invention
• FIG. 3 illustrates schematically a third embodiment of the present invention
• FIG. 4 illustrates schematically a fourth embodiment of the present invention
• FIG. 5 illustrates an example of an application for the present invention.
• FIG. 1 illustrates a first preferred embodiment of the present invention wherein first, second and third field effect sensors S1,S2,S3 are connected to power supply 10 over two wires 12,14 in a daisy chain configuration.
• Sensors S1,S2,S3 preferably are embodied as field effect sensors using a TS100 integrated control circuit available from TouchSensor Technologies, LLC of Wheaton, Illinois.
• a corresponding load resistor LR1,LR2,LR3 is connected to the output of each sensor S1,S2,S3, respectively.
• Each load resistor LR1,LR2,LR3 has a unique value of resistance.
• Other embodiments can use more or fewer than three sensors and corresponding load resistors.
• Detection circuit 18 detects the current drawn by sensors S1,S2,S3.
• detection circuit 18 includes sense resistor 16 between power supply 10 and sensors S1,S2,S3.
• Detection circuit 18 detects the voltage drop across sense resistor 16 and provides an output line V out to a suitable decoding circuit, for example, an analog to digital converter, as would be known to one skilled in the art.
• a suitable decoding circuit for example, an analog to digital converter, as would be known to one skilled in the art.
• the design of detection circuit 18 is not critical to the invention. The design shown in FIG. 1 is for illustration and can be varied or substituted with another design as would be known to one skilled in the art.
• sensors S1,S2,S3 draw a baseline current from power supply 10.
• This baseline current can be detected as a voltage drop across sense resistor 16 or in any other suitable manner, as would be known to one skilled in the art. Typically, this baseline current will be negligible and, accordingly, will produce a negligible voltage drop across sense resistor 16.
• FIG. 1 illustrates an embodiment having a nominal 5 volt power supply
• the current through sense resistor 16 is substantially equal to the current through load resistor LR3, producing a corresponding voltage drop across sense resistor 16. Based on this voltage drop, detection circuit 18 outputs a signal V out of 0.714 volts. Based on this output voltage, the decoding circuit (not shown) determines that sensor S3, but not sensors SI and S2, must have been activated. Similarly, if sensors SI and S2 are activated and sensor S3 is not activated, the current through sense resistor is substantially equal to the sum of the currents through load resistors LR1 and LR2, producing a corresponding voltage drop across sense resistor 16. Based on this voltage drop, detection circuit 18 outputs a signal V out of 4.28 volts.
• the decoding circuit determines that sensors SI and S2, but not sensor S3, must have been activated.
• the table in FIG. 1 illustrates that a unique output V out is produced for each unique combination of sensors activated at any given time. Based on the value of V out at any particular time, the decoding circuit determines which individual sensor or combination of sensors is activated at that time.
• FIGS. 2 A and 2B illustrate a second embodiment of the present invention wherein a capacitor is used as a temporary local power supply for a field effect sensor.
• power input 102 of field effect sensor 100 is coupled through isolation diode 110 to a pulse generator and detection circuit via line 108.
• microcomputer 106 having a reconfigurable
• Port 104 through switched resistor 114 and FET 116.
• Port 104 selectively functions as an input port and output port, as discussed below.
• Capacitor 117 is coupled between ground and
• Pull-down resistor 118 is
• a first terminal of pull-up resistor 120 is comiected to a source of electrical potential, in
• pull-up resistor 120 is shown as a discrete component separate from microcomputer
• pull-up resistor 120 could be integral with, or its function otherwise could
• microcomputer 106 may be provided by, microcomputer 106, as would be known to one skilled in the art.
• microcomputer 106 With port 104 configured as an output port, microcomputer 106 outputs a pulse through port 104 over line 108 and through isolation diode 110. This pulse powers sensor
• capacitor 117 the energy stored in capacitor 117 continues to power sensor 100 for a short period of time. During this time,
• microcomputer 106 can read data from line 108.
• Microcomputer 106 senses this voltage through port 104 (while port 104 is configured as an input port) and determines, based on the sensed voltage, that sensor 100 is in the not activated condition.
• FIG. 2B differs from FIG. 2A in that FIG. 2B illustrates a second sensor 100' and corresponding circuitry (namely, sensor input 102', sensor output 112', capacitor 117', diode 110', FET 116', switched resistor 114', and pull-down resistor 118') coupled to microprocessor 106 through line 108 and port 104.
• the circuitry corresponding to sensor 100' is generally the same as the circuitry corresponding to sensor 100, except that switched resistors 114 and 114' have different values of resistance.
• a first voltage is present at the node between pull-up resistor 120 and switched resistors 114 and 114'. Based on the value of this first voltage,
• microprocessor 106 determines that sensor 100 is in the activated condition and sensor 100' is in the not activated condition. Likewise, when sensor 100' is activated and sensor 110 is not activated, a second voltage is present at the node between pull-up resistor 120 and switched resistors 114 and 114'. Based on the value of this second voltage, microprocessor 106 determines that sensor 100' is in the activated condition and sensor 100 is in the not activated condition. Similarly, when both sensors 100 and 100' are activated, a third voltage is present at the node between pull-up resistor 120 and switched resistors 114 and 114'. Based on the
• microprocessor 106 determines that both sensors 100 and 100' are
• FIG. 3 illustrates a third embodiment of the present invention wherein power input
• a pulse generator and detection circuit for example,
• microcomputer 206 via line 208 and output 212 of sensor 200 is coupled to line 208 via FET
• Pull-down resistor 218 is coupled between ground and the node
• a voltage source for example, a 5 V source
• the second terminal of a voltage source for example, a 5 V source
• pull-up resistor 220 is connected to line 208. Load resistor 214 and pull-up resistor 220 each
• pull-up resistor 220 is shown as a discrete component separate from microcomputer 206. Alternatively, pull-up resistor 220 could be integral with, or its function otherwise could be provided by,
• microcomputer 206 as would be known to one skilled in the art.
• pull-up resistor 220 and load resistor 214 form a voltage divider
• Microcomputer 206 senses the voltage applied to sensor 200 and thus
• pull-up resistor 220 can be omitted and/or current sensing techniques can be used to detect whether sensor 200 is activated or not.
• FET 216 when sensor 200 is not activated, FET 216 is in the "off state and the only current through line 208 is the negligible current required to power sensor 200.
• Microcomputer 206 perceives this condition as an open circuit, as it would a mechanical switch with open contacts.
• transistor 216 When sensor 200 is activated, transistor 216 is in the "on” state, enabling current through load resistor 214.
• Microcomputer 206 detects the increased current and determines that sensor 200 is activated. Indeed, if load resistor is selected to have a sufficiently low value of resistance, for example, 100 ohms, microcomputer 206 perceives the current through load resistor 214 as a dead short, as it would a mechanical switch with closed contacts.
• FIG. 4 illustrates a fourth embodiment of the present invention wherein a battery 320 provides power to sensor 300.
• Output 312 of sensor 300 is coupled to the gate of FET 316 and to pull-down resistor 318.
• output 312 is low, and FET 316 is in the "off state, emulating a mechanical switch with open contacts.
• output 312 is high, switching FET 316 to the "on" state, emulating a mechanical switch with closed contacts.
• Sensor 300 with battery 320 can be used as a drop in replacement for a mechanical switch because it does not require any wiring beyond that provided for the mechanical switch. The sensor input and output can simply be connected to the same wires to which the former mechanical switch was connected.

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• Physics & Mathematics (AREA)
• General Physics & Mathematics (AREA)
• Arrangements For Transmission Of Measured Signals (AREA)
• Electronic Switches (AREA)
• Switches That Are Operated By Magnetic Or Electric Fields (AREA)

Priority Applications (7)

Applications Claiming Priority (4)

Publications (2)

Family

ID=33313487

Family Applications (1)

Country Status (10)

Cited By (5)

Families Citing this family (38)

Family Cites Families (9)

• 2004
  • 2004-04-20 US US10/828,004 patent/US7023215B2/en not_active Expired - Lifetime
  • 2004-04-21 BR BRPI0409643-6A patent/BRPI0409643A/pt not_active IP Right Cessation
  • 2004-04-21 NZ NZ543435A patent/NZ543435A/en unknown
  • 2004-04-21 MX MXPA05011330A patent/MXPA05011330A/es not_active Application Discontinuation
  • 2004-04-21 AU AU2004232039A patent/AU2004232039B2/en not_active Ceased
  • 2004-04-21 JP JP2006513219A patent/JP2006524423A/ja not_active Ceased
  • 2004-04-21 WO PCT/US2004/012426 patent/WO2004095388A2/en not_active Ceased
  • 2004-04-21 EP EP04760123A patent/EP1623502A2/en not_active Withdrawn
  • 2004-04-21 CA CA002522909A patent/CA2522909A1/en not_active Abandoned
  • 2004-04-21 KR KR1020057019921A patent/KR20060006042A/ko not_active Ceased

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