Step 9: Cables

Correctly connecting USB cables can cause confusion between the four different wires in each cable. The USB standard uses Red, Black, Green & White wires, each must be correctly matched or the devices wont work. I used the Wikipedia USB Page as a guide.

1 | Where the USB cable was detached from the hub we now need to reattach the new, shortened USB cable, along with a +5v input from the LDO. Using the same USB lead measure the cable so there is enough wire to go from the hub to the Raspberry Pi. Connect the White (D-), Green (D+) and Black (gnd) wires to the hub. Do not connect the Red (+5v) wire from the USB cable connected to the Raspberry Pi. We leave the +5 cable out so that we do not draw any power from the Raspberry Pi's USB connection. Instead power comes from the +5v LDO.

2 | To the USB hub attach a Red (+5v) & Black (gnd) wire, at the other end of this cable attached male DuPont connectors into a two-pin plug. This wire will connect to the regulated +5v & gnd lines from the LDO.

The slide switch will be used to direct power from either the battery pack (on position), or the DC socket (off position). When there is no jack in the DC socket the LapPi will be powered down. There are no charging circuits inside the LapPi so the batteries will need to be removed from the holder when the time comes to recharge them.

3 | The centre two poles of the switch will be the main power line. Connect the PP3 connector lead to one end of the switch, cover the connections with heat-shrink. At the other end connect lines which will come from the DC socket, connect and heat-shrink the DC supply wires. I have used DuPont connectors to make it easier to dismantle the LapPi should the need arise.

4 | The centre two poles need to be split into three outputs; 1 to the Raspberry Pi, 1 to the USB Hub's LDO, and the last will provide power for the screen pack. Again I have used DuPont connectors where appropriate. To make it simple to keep track of the different connections I have put a small length of heat-shrink tube on the corresponding positive wires for each connection. For example I have used blue to highlight the DC sockets wires.

5 | Connect a measured length USB cable to the GPS dongle.

6 | You now have to create the opposite end of the IDE cable used in the screen pack, the process is exactly the same as last time. I began working with the two USB connections. Once a set of four wires was finished I tested it worked correctly by plugging the cable into a USB port while the Bluetooth/WiFi dongle was connected to the other end. For the power supply to the screen use DuPont connectors to match the power supply from the switch.

7 | Connect the panel mount USB socket to a USB plug. Check the cable length before hand.