diy light pen

#1
hi all me again,
i've had this thought in my mind for a while now
does everyone remember the crt based light pen, aka gun?

i want to build one for use as a pointing device on a laptop screen ironically to elminate the need for the touch pad which i hate passionatly as when go out anywhere there isn't always a suitable surface for my optical mouse
anyone got any ideas?
 
#2
No, sorry.
(I thought I'd better say that than leave it so it proves I read it :) ).

I doubt if you'll be able to use technique the old ones did.

Any plans on how you will pick up any synch pulses to base timing on?

Nothing on nerdynet to help?
 
#3
well as we know nothing is impossible..... just very very difficult

i was thinking a process that follows somthing like this...

firstly the pen is pointed at the screen
when the button is clicked a vb application can make the completely white then the vb app can via serial or usb interface to a pic chip can get adc readings while moving a sweeping bar across the screen twice 1 for each axis x and y
then the vb app moves the mouse resolved position and simulates a mouse click...
it's not without it's problems.....
i'm just hoping for a better idea
 
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#4
Sorry, can't follow that.
So you suggest getting X-Y based solely on ADC values?
No video signal synch? Do you remember/know how the old ones were done?

I can't see much PICAXE involvement here, so good luck. I'm sure you'll get it sorted.
 

boriz

Senior Member
#5
I completely sympathise. I hate those little touch pads too.
I think the CRT method was to measure the time between the start of the raster scan and the moment the beam passed the tip of your pen. An LCD system would need to be very different. I think the system you propose could work, but would be slow. If you want to generate the ‘scanning’ image yourself, it might be faster to use a divide by two zoning system. IE: Divide the screen into two, illuminate half of it, pen in illuminated half? YES> divide that section into two and repeat, NO, divide the other section into two and repeat. It might be a little faster that way, especially if you are happy with low positional resolution, but could still be an eyesore.
You can buy touch screen overlays of various sizes from Deal Extreme. See LINK1 and LINK2 and so on. No idea how to interface them.
You might also consider something like THIS or THIS. Never tried them but they look cool.
 

boriz

Senior Member
#6
Oh yes. One more thing. I hacked an old PS2 mouse and drove the x-y photo interrupters directly from a Picaxe just to see if it would work. It worked very well and was simple too. I’ll dig up some details if you need them. The beauty of such a system is that no software needs to run on the PC. The existing mouse drivers do all the work. All you need to do is think of a method of getting positional information into the Picaxe.
 
#7
well as we know nothing is impossible..... just very very difficult

i was thinking a process that follows somthing like this...

firstly the pen is pointed at the screen
when the button is clicked a vb application can make the completely white then the vb app can via serial or usb interface to a pic chip can get adc readings while moving a sweeping bar across the screen twice 1 for each axis x and y
then the vb app moves the mouse resolved position and simulates a mouse click...
it's not without it's problems.....
i'm just hoping for a better idea

Try this http://www.cw2.co.uk/lightpenprices.htm
 

BCJKiwi

Senior Member
#8
@DPG

1. buy one of the small mice designed for notebooks (usually have retractable cords as well)
2. organise a piece of plastic or other sheet that is the same size (or less) as your notebook so it will go in the bag without taking up (significant) space
3. When you don't have a flat surface for your notebook, place this sheet under your notebook with it extending out the side
4. Use your mouse in the normal way.

If necessary, increase the sensitivity of the mouse (in windows) to reduce the mouse movement required.
 
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