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Topics - sts70nl

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IR Pens / tip-push IR-pen
« on: June 30, 2008, 02:01:52 PM »
As promised a guide on how to build a tip-push IR-pen.  The key component is an Edding Retract 11 Permanent Marker.

The beauty of the Edding Retract 11 Permanent Marker comes from being well over engineered.  Amazing how much effort went into designing and producing this marker.  However, for building a IR-pen it is great for it comes already with its own battery holder.

The complete materials list:

- 1x Edding Retract 11 Permanent Marker (for Dutch: found at Primera @ Ä2,70)
- 1x Metal ring 4 mm diameter
- 1x Screw with flat head (5mm 20mm)
- 1x IR-LED (5mm, 940 nm)
- 1x ball point spring
- A bit of tin foil
- 1 piece of wire (8-9 cm, thin; I used one of the four inner wires of a phone wire)
- Small bit of sticky tape (for insulation purpose on the IR-LED)

A soldering set is required, although soldering is limited to two joints (which Iím more than happy about for Iím not that good at it).

Most difficult thing I found, besides the soldering, was to remove a spring near the tip.  This took me a couple of minutes.

Initially I was a bit worried about getting the tip-push good enough. However, in hindsight, due to the design I came up with, the error margin in building/constructing is pretty big.  This was additionally proven when I built tip-push IR-pen number two and recorded mean while my actions and steps (see the YouTube video).

What you get, is an easy to fine-tune tip-push IR-pen with an internal battery holder. The IR-pen does have the look and feel of a white board marker.

[youtube] [/youtube]


Using the instructions available I made my push-button IR-pen.  As a push-button a small keyboard button was used.  Very nice, however there was a need to constantly remember when to push and most importantly when not to push the button.  It works great, but not a real white board experience.

Like some others the idea came up to build an IR-pen that when pushed against the white board for writing will turn on the IR and will turn the IR off when the pressure is released. 


Hopefully soon I will have the time to build and record the building of the push-tip IR-pen.


Have a rule of thumb to quickly setup the Wiimote for use with a beamer and whiteboard.

Consistent and very optimal tracking on a white board

The more angles, the more skewed and the less optimal the tracking

- no beamer (haven't got one to play around with)
- real whiteboard
- Wiimote
- Boonjin's 0.2.2 beta
- Living room (daylight)

The Wiimote has a 90 degree angle on the whiteboard, however it is slightly angled upward (see picture attached).

- Start the calibration procedure
- Trial & error to find the maximum view of the Wiimote camera
- Repeat until the maximum area is found

     d   WT   WB   HL   HRresolution    W:H
104cm      78cm      77cm      53cm     47cm       114%  3.1:2
  50cm 36cm34cm 25cm 25cm  120%  2.8:2

  • - width / height ratio of the Wiimote is 3:2
  • - distance and height seem to have an easy ratio

The distance of the Wiimote to the whiteboard follows: d = 2*H
Where (d) is the distance Wiimote to whiteboard, and (H) = projected height

It would be very nice to get additional measurements as well to get a good rule of thumb.  For instance, I couldn't use a beamer (was not required for I was looking for the maximum area) and my whiteboard isn't one of the largest so I could take only two measurements.

Stefan van Aalst

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