It's time to get into the wiring for the rear case. We're going to do the following:
(The table gets kind of jumbled towards the middle, so pay attention to the numbers. Also, Solder points for the Raspberry Pi B+ are at the very bottom of this page!)
In order to trigger our Low Battery Red LED on the front panel, we're going to piggy back on the PowerBoost 1000s component T1's collector (Pin 3). This PNP transistor is in charge of switching on the red LOW LED on the PowerBoost when your battery is low. We're going to use it to feed our front panel LED as well! You should also solder the 500mA charge rate jumper on your LiPoly backpack, as we're dealing with large battery sizes that can take the extra juice.
It sounds like a lot of steps, but it moves a lot quicker than you think! Here's a diagram explaining the gist of it. We're going to put three connectors between the two halves so they can be separated for maintenance and further improvements! All of the connections have to be sealed with heatshrink to prevent shorts.
We're also going to snip off the power bus from a protoboard to use as our power distribution center for the post-PowerBoost 5V. This will allow for quick disconnects if any parts ever need to be replaced, or serviced. The entire design is setup to be modular, so that any given part can be released from the unit without a lot of effort or resoldering.
Note: There's a little more to the audio than this section covers, there is a dedicated page for the audio wiring. Also, some of the photos show the power switch originally being wired to the LiPoly backpack. This will reduce current draw to zero when the unit is off, however, the PowerBoost at full load can pull up to 4A. This will exceed the rating for the switch. To account for this, we toggle the PowerBoost's EN pin instead. Double However, the PowerBoost pulls up to 20uA when it's disabled. It's a tradeoff. If you're unhappy with the 20uA constant draw, then use a larger switch. If the 2500mAh battery is fully charged, it will take roughly 12 years to deplete the battery through this parasitic draw! The "schematic" and instructions use the EN pin, but some of the pictures are slightly different.
You can use a right angle header (instead of the JST male connector) for the PowerBoost, so a breakaway header can attach to it's IN side, as pictured above. There is also the header on the power switch, so that it can be disconnected easily, pictured below.
Next, we're going to create the Power Distribution Header. Time to whip out the large pilers for a second job, cutting the power bus off of this nice Protoboard. It's sad, but it's got two power buses, so it's perfectly usable still.
You should trim it to about half this size, as we don't have enough devices to even fill half of this board. After soldering on some break away headers, this should be the result. Now we have a central area to grab 5V from! Solder two wires from the PowerBoost OUT VCC and PowerBoost OUT GND onto the corresponding PDH buses.
Create a bunch of two pin connectors by trimming your breakaway headers into two pin pieces. Solder the VCCs and GNDs each to an individual connector, so that devices can be plugged into the PDH.
As there is no longer a need for them, we will remove the Rasberry Pi's built in USB connectors, and solder onto the pads underneath. The connectors can be removed by crushing them carefully with pilers. Do not try and pry off the connectors, or you will damage the Pi. You can also remove the Composite Video connector, and the Audio Jack.
Here is a photo of the main connector. It's pinout is as follows (left to right):
- AT42QT1010 (1) OUT
- AT42QT1010 (2) OUT
- MAX98306 LOUT-
- MAX98306 LOUT+
- MAX98306 ROUT-
- MAX98306 ROUT+
- RasPi USB(1) VCC
- RasPi USB(1) D-
- RasPi USB(1) D+
- RasPi USB(1) GND
The RasPi USB(2) pins go directly to the EXT Port USB A connector.
This is the display connector, and it's pins are (bottom to top):
- Raspberry Pi Composite SIG (Blue)
- Raspberry Pi Composite GND/GND (Green)
- GND (Brown)
- 5V (Red)
Here is which pads to solder onto the Raspberry Pi's Composite Connector. The Blue is Composite SIG and Green is Composite GND/GND.
If you have a Raspberry Pi B+, none of the solder points will match the Model A or B. So, you can use this handy guide to find the important ones! The USB ports will match up in the same order, when the Pi's are in the same orientation (USB ports facing left). That is: GND, D+, D-, VCC, just like in the diagram with the Model B.
Composite Video SIG
Test each connection with a multimeter as you progress, and double check your polarities! You'll be greeted by a happy Pi screen in no time!