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Oldbitcollector (Jeff)
05-11-2008, 09:33 AM
I noticed that Radio Shack still had some old fashion Photoresistors (http://www.radioshack.com/product/index.jsp?productId=2062590&cp=&sr=1&origkw=photo+cell&kw=photo+cell&parentPage=search) so I grabbed a pack.

As it turns out they function nicely as an old-fashion light pen connecting them between IO and 3v with
the IO side pulled down using a 10k resistor. I've got it drawing on the screen. (slowly) in Femto.
A decent object could yield a snazzy lightpen or add a switch and you'd have a light-gun.

OBC

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Beau Schwabe
05-11-2008, 11:19 AM
Oldbitcollector,

I've thought about doing something like this for quite sometime, but haven't gotten around to doing anything yet... similar to a light pen project I entered into an SX contest.

Only coming from the Propeller itself, it might actually be a lot easier, since you "know" where the vertical and horizontal sync are, or at least you have a better reference to where they are.

What's essential is a good "trigger" circuit on the front end with your photo-transistor. I ended up settling on a basic current mirror design to act as a buffer to the photo-transistor which worked really well... better than just a pull-down resistor. I'll see if I can find a schematic.

I'd be very interested to see a Light Pen object for the Propeller!!!

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Beau Schwabe (mailto:bschwabe@parallax.com)

IC Layout Engineer
Parallax, Inc.

Kaos Kidd
05-22-2008, 01:28 AM
Funny, I was looking at how light pens work and everything for the exact same reason....

KK

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Propeller + Hardware - extra bits for the bit bucket = 1 Coffeeless KaosKidd
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Beau Schwabe
05-22-2008, 02:48 AM
Oldbitcollector,

Here is the conditioning circuit that I used for a Light-Pen project that provided a nice signal to the SX.

http://forums.parallax.com/attachment.php?attachmentid=40329

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Beau Schwabe (mailto:bschwabe@parallax.com)

IC Layout Engineer
Parallax, Inc.