Author: Dirk Uffmann . . . Original version published: April 6, 2007 . . . Last update June 28, 2010

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Content


The Story
The fischertechnik model described here is the realisation of a dream I had in my youth (around 1976-1980). It was inspired by a picture in a fischertechnik flysheet of 1974/75. In this flysheet you see an elevator with 3 levels. The control electronics is built with the old silver electronic modules (called "Silberlinge" in german due to the silver colour of their surface) of the fischertechnik hobby4 series (5 Flip-Flop, 1 Mono-Flop, 1 NAND, 1 NOR, 2 Dynamical AND, 1 Relais RBI and 1 rectifier).

I have never owned the necessary 12 fischertechnik electonics modules as shown in the picture. Therefore, in 2003 I decided to built an elevator controlled by digital logic built from devices like in the fischertechnik set "IC Digital Praktikum". I started the elevator with 4 levels but without doors at that time. To implement the logic I needed 6 of the logic ICs of the TTL 74xx series. For that purpose I used 3 identical self-made boards each with 2 sockets for the 14-pin modules and 1 board for the relais amplifiers and IC voltage supply. Below you see pictures of the boards used for the TTL digital control. Interconnections were made using self-made cables with the same joints as in the original fischertechnik set. The digital signals then switch 2 fischertechnik relais of type RBII via a relais amplifier. The 2 relais switch the direction and power of one motor driving the elevator.

I built up the elevator like described above. One drawback was an interference of the motor switching lines with the TTL input lines coming from the push buttons. The TTL inputs are very sensitive. By physical separation of the lines I sucessfully decoupled them to avoid the disturbance. Another drawback were the missing control lights showing the elevator level. Generally, it soon becomes quite an effort if you want to extend the control to include more features. And so I decided to replace the digital TTL circuits by computer control via the old fischertechnik computer interface. In each elevator level 6 lights display the status of the elevator: movement down, up and the 4 levels. A further extension were the safety light barriers and the automatic doors. On the top left is a picture of the final version with all features.

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Figure Captions: Printed circuit boards used for the original version with TTL digital control
    Left: Function of two IC14 modules
    Right: Function of voltage regulation 5V + one IC14 module + four relais amplifiers for fischertechnik RBII module (Silberling)


The boards were designed using Eagle light (Freeware version) by CADsoft. If you are interested in reproducing these boards you may download the Eagle schematics and board layout files here:

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Details of the Construction

Overview
In the following some details of the construction are given. Below you see a picture of two levels of the elevator and another picture of one level.


Here on the left the door is sliding and on the right it is open. You can see the mechanics of the door's sliding mechanism and its motor drive.


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Automatic Sliding Door
This is a view from an inclined angle: on the left the door is closed and on the right it is sliding.


Here you see a closed sliding door from the back side (left) and a detailed view of the door's sliding mechanics and motor drive.


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Safety Light Barriers, Reed Switches and Display
The position of the cabin on the four levels ist detected using a permanent magnet mounted on the cabin and one reed contact switch in each of the four levels. Each sliding door is equipped with a safety light barrier. When entering or leaving the cabin, the cabin doors are prevented from closing as long as the light barrier is interrupted. The reed contacts are original fischertechnik parts. The safety light barrier is built with high power orange LEDs and BPW40 Phototransistors. These Devices were mounted and soldered in original fischertechnik lamp sockets. The LEDs use a resistor of 220 Ohm each with 9V supply. Since the phototransistors do not give enough current to switch the 1 kOhm pull-up resistors of the fischertechnik computer interface, I integrated a standard pnp transistor (BC337B) for current amplification of the photo current. These pnp transistors can be seen mounted in the fischertechnik connectors above the phototransistor of each safety light barrier.


In each level a display shows whether the elevator cabin is going downwards or upwards and in which level the cabin has arrived.


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Cabin Drive
The cabin is running with 4 wheels on 2 guide rails (left). It is lifted by a rope drawn on a cable winch (right).


Here you see views of one elevator level from the sides.


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Computer Control and Software
For the computer control two of the first fischertechnik computer interfaces were used (connected to the parallel or printer port of the computer). However, you could also use the newer intelligent interface (on the serial port) instead with the same software. Or use the actual Robo Pro interface and code a new software. To save inputs and outputs I combined each safety light barrier with the according level push button of the same level on one common input (logical OR). One motor output drives two display lamps with his two directions. The other node of the lamps is common ground. This is the connection scheme:
The control software for the elevator using the fischertechnik computer interface was developed using fischertechnik LLwin3.03. You may download the control software file here:

http://home.arcor.de/uffmann/Elevator-Dateien/Elevator.mdl


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