21 Jan
2011
21 Jan
'11
12:22 a.m.
Vidicon - 1949 - 1953 CBS
CCD - 1969 - Bell Labs
Regards
?
Rod Smallwood
-----Original Message-----
From: cctech-bounces at classiccmp.org [mailto:cctech-bounces at classiccmp.org]
On Behalf Of Tony Duell
Sent: 20 January 2011 19:56
To: cctalk at classiccmp.org
Subject: Re: HP150 Touchscreen diagnostic
On 2011 Jan 18, at 10:51 AM, Tony Duell wrote:
Narrows the problem down, but then you still don't know whether it's
the emitter or detector.
If the logic analyser gives indication of blocked beams as you stated
in your original message, why not just poke a finger around on the
screen to find which locations don't change the data stream (or change
it for only one axis). Appropriate poking sequences should distinguish
between X & Y blockages. (Assuming the detectors feed selectors giving
individual time slots in the data stream, as opposed to being
wire-ORed.) Or finger poking on the good beams to map out the data
stream.
Oh, I know the format of the data output -- and I have schematics for the
touchscreen PCB, which cotnains just 4000-series CMOS logic chips, a quad
op-map (324 I think) and the LED drivers. Nothing custom, nothing
programmable. The microcontroller I mentioned is on the CPU board and
interfaces between the 8088 bus and the touchscreen, keyboard interface
(simuilar, but IIRC the microcontroller, not the device provides the sync
pulse), and the beeper. If I look at the ribbon cable to the
touchscreen, I am looking at the raw signls before the microcontroller
has a go at them :-)
The format is something like : X axis in oder (L->R), one unusued, Y
sesors in order (Top->Bottom), Sync pulse (on the other output), repeat.
That's from memory, I can find the exact details if you want them.
But I have heard it said that a 'hacker' is somebody, who, if he has to
do a task a dozen times and each time takes 5 minutes, he'll happly spend
a day finding an automatic to do it. So yes, I could just count pulses on
the logic analyser, but the hacker in me (is there one?) says that I
whould be finding a way to avoid doing that ;-)
-tony
Similarly, power up an IR LED and run it past the holes of the
detectors and look for activity/change on the detectors data line.
It may be less work in the end to make up some kind of tester to plug
into the touchscreen PCB and display the status of all the beams...