BLOCKHEAD

I started with a piece of stripboard about 4inches by one inch, cut it in half so I now had two bits two by one. I put the power part of the circuit on the first board (top left and right). The only difference to the original circuit was the addition of the tiny Germanium diode (circled left). We don’t get much sun in the UK so I didn’t want to waist any with it flowing back out when the sun goes in! The cap is a 5.5v 1F memory cap from Maplins. You can see the socket pins to the right of the GE where the solar cell plugs in.

The next photos are the uppermost board containing the “guts” of the circuit. I used a 74AC240 in a socket. Again you can see the use of socket pins for the PD’s and resistor allowing easy “tinkering”. Again on the right photo you can just make out pins at the rear of the board for the motor connections.

The LED’s are held off the rest of the circuit by little rubber rings found on an old board from a VCR. The exposed leads had tape or cable insulation slid on where appropriate. I probably could have made the circuit more compact but this was my first time with stripboard and I wanted to make sure I could see what I was doing.

Here you can see how it was all put together. The solar cell is stuck with double sided tape to the chip. I’ve used glue in the past but once it’s on you can’t get it off without wrecking the cell.

The top board is not actually attached to the bottom board with anything more that the strength of the cables going from one to the other, this is quite handy as it disassembles very easily. One thing I found was if your using socket pins, put them on both boards, especially if you need to do lots of troubleshooting (as I did). The advantage of this is that  after pulling things apart repeatedly sometimes a cable end will break off! If it’s attached to one board you have the hassle of de-soldering and      replacing the cable. If you use pins on both boards you simply replace the whole cable.

The motor is a Nihon (BG Micro) gear motor part no LEN 1022. At the moment they still have a few at $9.99, they will even remove the motor at no extra cost, saving a lot on shipping costs. I soldered a ring of copper wire around the motor then two wires from the motor mounting holes to the ring and then on to the board. I also soldered a wire from the ring to the board at the back to stabilize things.          Remember to cut the tracks if you solder directly to the board saving problems later.

The PD’s are standard silicon photodiodes part no CY90X from Maplins. I did try the same ones with a dark daylight filter case but the clear ones seem to work better. They are mounted in LED covers to shield them from to many sources of light, again found on an old VCR board, and mounted at about 80 degrees to each other. This you will have to play with to find the optimum angle.

The base is an old stainless steel fitting which came in a job lot from an auction. I drilled a “tight” hole in the top and simply pushed the motor shaft in.

Click here for a short video of him following a light. If you look closely you can just see Trevor exiting the shot!