US 4,291,303 A · Touch pad and display tube circuitry

Abstract

Improved touch pad and display tube circuitry including a touch pad circuit, a tube circuit, and a scan voltage pulse drive circuit for generating scan voltage pulses applied to the touch pad and display tube circuits. The touch pad circuit receives scanning voltage pulses having very fast rise-times, to reduce the effects of contaminants which may be present on the surface of the touch pad panel. The display tubes of the display tube circuit each include an anode, a plurality of display cathodes and a control cathode. The current flowing through the control cathode is proportional to the current in the associated display cathodes. The control cathode current is utilized by the drive circuit to adjust to a desired value the value of the magnitude of the scan voltage pulses applied to the anodes of the display tubes. The drive circuit utilizes a substantial portion of common circuitry to generate both the touch pad and display tube scan voltage pulses. The control circuit also functions to isolate the touch pads and display tube anodes in such manner that the fast rise-time pulses applied to the touch pads are not coupled to the display tube anodes.

Claims52

Dependent claims

A touch pad circuit comprising:

first and second touch pads each having an input and an output, and having a common face plate which permits contaminants located on said face plate to form ohmic and/or dielectric couplings between said touch pads;
scan pulse generator means for applying touch pad scan pulses to said inputs of said touch pads to cause first and second touch response signals to appear at the outputs of said first and second touch pads, respectively;
said touch pad scan pulses having a sufficiently fast rise-time that said first and second touch response signals initially pulse to an initial level determined by the capacitance to ground of said first and second touch pads, respectively, and thereafter change their value due to ohmic and/or capacitive coupling between said first and second touch pads caused by contaminants on said common face plate if contaminants of a sufficient amount are located on said face plate;
and
detector circuit means coupled to said touch pads for determining which, if any, of said touch pads is being touched by an operator of said touch pad circuit by examining said initial level of said touch pad response signals.

2 more elements

A touch pad circuit, comprising:

a plurality of touch pads, each of said touch pads including an input and an output and having a common face plate which permits contaminants on said face plate to ohmically and/or dielectrically couple adjacent touch pads;
scan pulse generating means for sequentially applying touch pad scan pulses to said inputs of each of said plurality of touch pads to cause touch pad response signals to sequentially appear at the outputs of each of said touch pads, each of said touch pad response signals being associated with the touch pad at whose output said touch response signal appears, said touch pad scan pulses having a sufficiently fast rise-time that each of said response signals initially pulses to a value indicative of the capacitance to ground of its associated touch pad and thereafter changes its value due to ohmic and/or dielectric coupling between adjacent touch pads if contaminants of a sufficient amount are located on said face plate;
and
detector circuit means for sequentially examining said touch response signals and for generating a touch condition output signal indicating the presence of a touch condition whenever said initial value of the last generated touch response signal has a magnitude which indicates that the capacitance to ground of its associated touch pad is at least equal to a predetermined value, said detector circuit means including means for suppressing the generating of a touch condition signal responsive to said last generated touch response signal whenever said initial value of the next-to-last generated touch response signal indicates that the capacitance to ground of its associated touch pad is at least equal to said predetermined value unless said initial value of said last generated touch response signal has a magnitude which indicates that the capacitance to ground of its associated touch pad is greater than said predetermined value.

1 more element

A touch pad and display circuit, comprising:

a plurality of display tubes, each of said display tubes adapted to display a desired indicia when a display scan pulses is applied thereto;
a plurality of touch pads, each of said touch pads having an input and an output, said touch pads sharing a common face plate which permits contaminants on said face plate to ohmically and/or dielectrically couple adjacent touch pads;
detector means for determining which, if any, of said touch pads is being touched by an operator of said touch pad display circuit by examining response signals appearing at said touch pad outputs responsive to the application of touch pad scan signals to said touch pad inputs;
and
driver circuit means for sequentially applying touch pad scan pulses to said touch pad inputs and for sequentially applying display tube scan signals to said display tubes;
each of said touch pad response signals examined by said detector means being associated with the touch pad at whose output said touch pad response signal appears, said touch pad scan pulses having a sufficiently fast rise-time that each of said response signals initially pulses to a value indicative of the capacitance to ground of its associated touch pad and thereafter changes its value due to ohmic and/or dielectric coupling between adjacent touch pads if contaminants of a sufficient amount are located on said face plate.

3 more elements

Dependencies are inferred from the claim text.

Touch pad and display tube circuitry

Life of this patent

Touch pad and display tube circuitry

Life of this patent

Abstract

Claims52