(Deutsche Übersetzung im nächsten Beitrag)
Some time ago I came across a Wikipedia article describing a fascinating invention that is obsolete now but was revolutionary in the 1830s: the Cooke and Wheatstone Telegraph. It worked by rotating needles via electromagnetic coils so that they pointed to letters on a dial. They made several models, but the most famous one used five needles. The transmitter and the receiver were interconnected with five wires, one for each coil, over several miles.
- Cooke and Wheatstone Telegraph.jpg (127.05 KiB) 189 mal betrachtet
The article describes the device thoroughly, and it even includes a very nice schematic. A faithful copy would require ten electromagnets and ten fixed magnets connected to the needles, but I realized I could make it work with mini-motors. The principle worked, so I set out to build a complete model. It has one simplification: the model is unidirectional, that is, one unit is always the transmitter and the other is the receiver. I could made it bidirectional (i.e. half-duplex), but the wiring would require a lot of extra labor. It looks like this:
- telegraph model.jpg (788.54 KiB) 189 mal betrachtet
In the original, two buttons must be pressed for a character to be transmitted. I added rotating handles to press the buttons, both to avoid short-circuits (which are very likely to happen otherwise) and to make transmission more user-friendly. Turning a pair of handles each time drives two motors on the transmitter and two on the receiver, sending one character. The whole switch assembly can be pivoted for easier storage. The panels are printed on 240 g paper and have lines, circles and typography similar to the original. Five needles give only 20 characters; I decided to copy the original English layout (which omits the C, J, Q, U, X and Z, so it can't quite spell "fischertechnik"
). Perhaps some of you will try a German version with different letters? A bigger, 6-needle model which would allow up to 30 characters.A classic ft challenge: how to drive a snap-in axle 130593 directly from a mini-motor? I used white differential bevel gears 31413 (like in the roller coaster model). The connection is not very solid, but it works. The motors are driven by three 9-Volt batteries connected in series, which gives around 6.75 per motor. With four batteries the motors may turn too fast and the gears might slip.
Here are some cool links:
Wikipedia article
High resolution photo
Patent illustration
Best regards,
Rubem
