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Tandy 1000 DIY Lightpen Shenannigans

Istarian said:
@Eudimorphodon And I'm pointing out that there should be a way to get similar technology if desired, even if you ending needing a more sophisticated sensor that can detect colors.

Of course, you could just use some sort of modern touch overlay/touchpad or even make a break-beam setup based on IR, visible light lasers, etc if desired. Even magnets and the right sort of hall effect sensor would work on a LCD which isn't remotely as sensitive as a CRT to an electrogmagnetic field...
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Unless you build something into to the LCD itself (maybe embed some kind of specialized "microdot" pixels that can refresh at a higher frequency and emit IR or soft UV specifically tuned to a matching light pen) anything along these lines is going to result in gross visual artifacts... and to what end? The reason the light pen was a popular technology in its day was it was cheap (just a photodiode and a bit of glue) and it worked on any CRT screen. In the modern world if you want a "pen" there are a *ton* of alternative solutions for getting an X/Y coordinate off a flat panel display that are cheap and completely agnostic to the display tech. You have touchscreen overlays (capacitive or resistive), both dirt cheap, which just require a sheet in front of the screen, there's EMR tech like used on Wacom (and knockoff) digitizer tablets... there are sonar-based systems for doing pens on large surfaces (I used to work in an office that had a thing that could digitize you drawing on a whiteboard; you just slipped a little collar over the pen and a couple of sensors flanking the board triangulated its location; similar things exist to stick on large TV sets), and for "light gun" applications where you want to be able to target things from a distance there's tech like the IR sensors used in Wii-motes. (Which, amusingly, is vaguely related in principle to how the heat seakers on the original Sidewinder air-to-air missile worked.)

An optical LCD light pen is a solution in search of a problem, and also not really on topic for vintage computing.
 
The Tandy 100 had a light pen bar code reader that was very popular in many stores for a short while back in the day. I've had a 100 (still works) since about 1985 but never sourced the light pen. Can't really see a use these days.
 
Quagmire said:
The Tandy 100 had a light pen bar code reader that was very popular in many stores for a short while back in the day. I've had a 100 (still works) since about 1985 but never sourced the light pen. Can't really see a use these days.
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Bar code reader wands were not the same thing as a light pens. I think maybe they did use the same body and cable for both, but the difference is that the bar code reader wand has an LED built into the tip to illuminate the bar code, whereas a light pen uses the CRT as the light source.
 
vwestlife said:
Bar code reader wands were not the same thing as a light pens. I think maybe they did use the same body and cable for both, but the difference is that the bar code reader wand has an LED built into the tip to illuminate the bar code, whereas a light pen uses the CRT as the light source.
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On that off-topic I have a USB bar code reader wand (found it in an electronic recycle bin), looks just like one to the right in your thumbnail other than the case is black. Pretty sure the old ones were serial, but the USB one looks like a keyboard; you plug it in and any code you scan ends up in whatever application you have open as if you typed it. I fooled around a little bit printing my own bar codes, but the novelty wore off pretty quick.
 
Thinking about old-timey equivalents to light pens I naturally remembered the infrared finger detector on the HP-150, a weird little not-PC-compatible MS-DOS computer from Hewlett-Packard. This system used rows of IR LEDs and sensors in a grid in front of the screen, which would get blocked by a stylus or finger; basically the same concept as those laser beam burglar alarms. Obviously the resolution was also very low; the tech manual on bitsavers puts it at 40x27, which is technically interesting because this is double than what the number of sensors would indicate; the system assumes you won't use a stylus much narrower (or wider) than a typical finger, so if the light is blocked on two adjacent sensors it assumes you're pointing at the cell *between* those rows/columns. Presumably if you had really bony fingers or poked it with too skinny of a pen the effective resolution would actually be more like 20x13.

A defect in this system is that dust would build up in the upward facing holes at the bottom of the screen bezel and block the beams. Ooops.

Of course this system should work okay if you substituted a different tech monitor for a CRT... and coincidentally enough, the "Hewlett Packard Company Archives Virtual Vault" has a picture of an LCD clock/watch tchotchke they made to promote the HP-150.. I don't think the touchscreen is actually functional on this, though... ;)
 
Eudimorphodon said:
On that off-topic I have a USB bar code reader wand (found it in an electronic recycle bin), looks just like one to the right in your thumbnail other than the case is black. Pretty sure the old ones were serial, but the USB one looks like a keyboard; you plug it in and any code you scan ends up in whatever application you have open as if you typed it. I fooled around a little bit printing my own bar codes, but the novelty wore off pretty quick.
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There are applications where you can scan book ISBN numbers in and they pull data from amazon into your collection database (including cover pics I think).
 
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