This is my workshop, seen from inside. When I took this picture, the day was quite hot and sunny, so I decided to try out the marquee, installed on top of the shop window. I am living and working in this space now for over one year and I never tried it out, because I didn't have a crank to operate it. Well, I quickly built one out of an old water tube. Working inside on sunny days feels now like sitting in a small café.

This is the LDR-array with 32 LDR's. I've described this device in the PDF from 7.6.2006.
Because this piece so important, I've uploaded some more pictures. Together with the schematics, they can help you to rebuild it properly. Watch the other images here.

This is the LDR-array, together with the cold cathode tube, which lights the floor. The both parts are mounted on another sheet of PVC.

The same device, seen from top. The box behind the wires is the transformer, which generates about 800V for the cold cathode tube.

This is a close up of the same part. Here, I have also installed a 37pin SUB-D port. Everything, which is mounted under the wheelchair will be connected to the controllers via this SUB-D port. So, it will not only provide the connection to the LDR-array, but also the 12V power supply for the transformer of the cathode tube, a serial TXD line for the RFID reader and another TTL-level data line to read out the odometer. The fuse in front is for the RFID reader.

A later stadium of the same piece shows, that I have beveled the vinyl to let it slip easier over uneven surfaces.

This is the finished LDR-array in its aluminum cabinet.

I also decided to build an odometer for the wheelchair. The odometer will be placed exactly in the middle of the axis of the back wheels. The reason for that position is simple: If the wheelchair turns, but doesn't go forward or backward, it turns exactly around this point - and the odometer wheel won't detect any movement. It only detects the wheelchair's forward or backward movements. So when the controller gives out control voltages to the motor driver, it gets a feedback about the real speed of the wheelchair. This gives the opportunity to install a PID controller for the speed in the software as well, and it can also deliver a feedback about the current velocity of the wheelchair, which will change, if there are heavier or lighter people sitting on it. I guess, that I can use this data to adjust the PID controller for the line detection unit as well to the different people's weights.
The picture shows a plastic roll. I have drilled six holes into it and a small light barrier will encode the speed of it to a digital TTL-level signal.

These are all the parts for the odometer: The wheel, an aluminum cabinet, the axis, and a sheet of PVC with the light barrier installed inside.

This picture shows the light barrier in action. It is a very simple construction, which only consists out of a white LED, a photo diode and a voltage divider. It doesn't need to be more sophisticated, because there won't be any environmental light at this position.

This is the finished odometer.

Here, you can see the whole floor scanning device. When I took this picture, the aluminum cabinet was not set onto the LDR-array. On the right side, you can see the open LDR-array with the cold cathode tube and its transformer. On the left, next to it, is the RFID board. The big white sheet of plastic covers the RFID antenna. The construction is a bit asymmetric, because I have to keep at least 4cm distance between the RFID antenna and the cables, leading to the odometer. On the back (left) is the odometer.

Close up of the device, with the RFID board on the lower left corner of the image.

On the next photos, you can see, how I mounted the whole device under the wheelchair. It can be removed quickly for transport or maintenance, because it is only fixed by two splints.

The whole device hangs about 1cm above the floor.

Because of balancing problems, the odometer's wheel did not touch the ground. So I needed to attach an additional weight at the back. I found an old transformer, which had the perfect weight, and I screwed it behind the odometer. Now it works perfect, even if this transformer has no other function than being heavy.

These are older images with impressions of my workshop. The installed scanning device at the wheelchair on this picture is still the old one (version number two). Currently, The two car batteries are charged.

Here's a close up of the opened wheelchair with the connected chargers. I am using two 5Amps chargers, because the batteries have a capacity of 55 Ah. And if they are charged with more than 10% of their capacity, they start to produce bubbles, which consist of very explosive gases. So I decided to charge a bit slower and to live more safe.

In the foreground, you can see the last controller. Under the green sheet of plastic, there is the circuit with all the ADC's located. With the faders, I can adjust the PID-values.

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