After I've bought my strida folding bicycle, one of the first things I've done was to check out instructables.com for any strida related projects. And quite astonished to see that there wasn't any.
So I've planned to make an instructable that can be used on my (and also others') strida.
I think this is the first (and only so far) project in instructables, which is built around the strida.
Though my expertise is electronical engineering and solar lighting systems, I've chosen to build a propel light for the strida. The improvement to the other propel lights around the web is to use solar power and to create a totally independent light system that "lives" inside the strida wheel. There is no wires to the outside world and no need to charge either.
The image generated is much better than the shaky photo below ;)
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Step 1: Electronical Preparations
For the electronics, you may either go for scratch building or using some parts of a cheap solar garden light. I've done both ways. I've used this solar light that was wandering around my terrace for 2 years, one of which it was out of order.
I've disassembled it and found out it has perfectly good parts for this project.
first of them was a round solar panel. There is no fork in the unique strida bike design neither at the front nor rear. The folding ability is dependent on the magnet which connects the front-rear wheel axises. I've widened the small hole in the middle of the round solar panel wide enough the magnet mechanism of the strida wheel. By putting the solar panel in the middle, I also eliminated the balance problems of the wheel.
There are all kinds of small solar panels in these solar lights available everywhere. I guess finding a round solar panel which has got enough empty space in the middle which is enough wide to house the strida wheel axis is hard. But any other panel is ok too. all you have to do is obtain a power source which is able to deliver around 2.3v open circuit voltage and 50-200mA short circuit current. Mine is delivering 2.3v and around 200mA. its really perfect, a very lucky find.
Step 2: Circuitry
I've designed a simple solar lighting circuit. It has got a small microcontroller a very simple charge controller and a voltage multiplier. The part at the lower left of the schematic is the voltage multiplier. It transforms the voltage generated by the 1.2V nimh cell to almost 4V which is enough for the ultrabright LEDs to run properly. The PIC12F675 microcontroller can work with voltages 2-6V so it is not problematic.
some of the solar garden lights have an internal voltage doubler too. Mine has got one too. But I've sticked to the circuit schematic. If you find one in your solar light, then you can use it instead of the one in the schematic. All you have to do is open circuit the LDR (light sensor, if there is any). I've did that to the doubler I've took from the disassembled light and put it a side for further use.
Next thing is to assemble the circuitry on multi holed prototype board. This will require some soldering and electronics assembly skills. I'm sure there are many instructables around this subject. You may take a look at them so I'm not mentioning about the assembly here. The photos are of the first light I've tried. It had 10 ordinary LEDs. I've designed a resistor network method for driving 10 leds with a controller having only 5 output pins. The method increased power consumption so I've gave up that. Later I'll make a second version with a bigger controller and 10 or more LEDs. This version of the circuit has got 5 LEDs.
The circuit is secured to the air valve of the tire. I've used a metal valve cap and used hot silicone to glue circuit to the cap.
The proteus simulation file (demo is available on labcenter.co.uk ) is also included for the ones who want to see the circuit working.
Step 3: Solar Panel Montage
I've used hard silicon and some wire for the solar panel montage.
The panel fits to the wheel like a charm and even improves the looks of the bike by giving a higher tech look :)
You can see the 5 LED circuit under the panel.
It is secured to the air valve of the tire. The cable between the panel and the circuit has a socket which further secures the circuit and in case of a flat tire can be disconnected easily.
Step 4: Microcontroller Code & Hex File
They are here too. The code is written in C by using the CCS C compiler. It is a great compiler to start, I recommend to everyone.
Hex code is also included directly programmable to the controller.
Here is my strida5 resting in my terrace, with its new CPU and solar system onboard, charging its battery.
Step 5: Some Videos
The videos don't actually show the full graphic drawn by the LED system. I guess its due to the low framerate of the cell phone which used to record the movies.
The graphic in fact covers all the rotation of the wheel, 360 degrees.
Participated in the
Light Up Your Ride