GrafBar Digitizer

[DanBoris]

I ran across an article about this interesting digitizer in the February 1984 issue of Microcomputing magazine. It is the Grafbar GP-7 and it's kind of cool how it works. When the pen is pressed it emits a brief ultra-sonic tone. The control box has an ultra-sonic receiver on each side that picks up the tone. The unit times how long it takes each receiver to pick up the tone and from that can triangulate the position of the pen. The results are then transmitted out a serial port to the host computer. The labels Origin, Line, Metric, Stream and Cancel are commands that can be issued by tapping the pen close to the box in front of the label. 

 

 

Edited September 28, 2020 by DanBoris

[mr_me]

Digitizer tablets were pretty common in the 1980s, they varied in size,  accuracy,  and price.  I wonder how accurate this thing is.

[DanBoris]

8 hours ago, mr_me said:

Digitizer tablets were pretty common in the 1980s, they varied in size,  accuracy,  and price.  I wonder how accurate this thing is.

The article doesn't give any details on accuracy, but the article does say that the shipping versions of the unit will have a software update to compensate for temperature differences since the speed of sound changes with temperature. That change is pretty small for all reasonable temperatures so that indicates to me this this is pretty accurate. I did some searches but haven't been able to find any information online for this device with the exception of an E-Bay auction for the main unit. I would love to see the manual since the article says it contains the schematics.