Light pen having actuating accelerometer

• US 4,695,831 A
• Filed: 05/06/1985
• Issued: 09/22/1987
• Est. Priority Date: 05/06/1985
• Status: Expired due to Fees

• Current Assignee: Carl Zeiss Inc (Carl-Zeiss-Stiftung)
• Original Assignee: Humphrey Instruments, Inc.
• Inventors: Shinn, Alan L.
• Primary Examiner(s): Brigance, Gerald L.
• Assistant Examiner(s): Brier, Jeffery A.
• Application Number:
  US06/731,416
• Time in Patent Office: 869 Days
• Field of Search: 340/707, 340/708, 340/709, 340/710, 178/18
• US Class Current: 345/180
• CPC Class Codes: G06F 3/0386 for light pen

Abstract

A light pen of the type having a photoreceptor for sensing the signal from a CRT computer display and outputting to computer logic the location of the photosensing light pen is disclosed. The improvement herein is the incorporation of an accelerometer on the light pen actuated by tapping the pen gently on the screen. The accelerometer has the preferred form of a microphone acoustically deadened as by the placement of silicone rubber over the acoustical channel. The rubber acts as an accelerometer mass outputting a high frequency signal upon tapping of the light pen on the glass covering a CRT screen. A monostable amplifier opens a signal gate to conventional computer measuring logic for that duration necessary to assure one complete raster sweep of the screen. A light receptor at the screen end of the light pen outputs through a video amplifier and fast comparator to measure the precise moment of video raster passage. This light measurement is transmitted to conventional gate logic interior of the computer and compared to raster location, and converted into pen location.

Claims

1. In the combination of a cathode ray tube display having a transparent screen, a raster for writing to said display and a light pen having a photosensor for detecting raster passage from the front of said cathode ray display and relaying raster passage to software logic interior of a computer;

and a switch in combination with said light pen for gating a signal from said photosensor to circuitry for locating position of said photosensor in relation to said display, the improvement to said switch including an accelerometer mounted to said light pen actuated by the tapping of said light pen on the transparent screen of said CRT, said accelerometer including a mass movably mounted to said light pen and a transducer for detecting movement of said mass upon acceleration of said light pen upon tapping said light pen, and actuating said switch in response thereto.

2. The invention of claim 1 wherein said accelerometer comprises a condensor microphone covered with a silicone rubber mass.

3. A light pen in combination comprising:

a cathode ray tube having a scanning raster;

a pen having output to logic interior of a computer;

a photoreceptor communicated to the tip of said pen;

an accelerometer mounted to said pen for detecting tapping of said pen on a cathode ray tube, said accelerometer having an output, said accelerometer including a mass movably mounted to said light pen and a transducer for detecting movement of said mass upon acceleration of said light pen upon tapping said light pen, and actuating said switch in response thereto;

a monostable circuit for outputting the output of said accelerometer for a time period sufficient for a complete raster sweep of said display; and

a comparator connected to said photosensor for outputting to software logic interior of said computer the moment of raster passage at said light pen whereby a location of said light pen can be determined.