How to Add a Second Power Button

[FreeRangeRon]

Hi All,

I’ve recently added an additional power button to my PBP and I thought I'd share the process. This button is located on the side of the machine so that the PBP can be powered on and off when the laptop is closed.



This is useful if you want to switch the machine on when it’s docked (i.e. using an external monitor) or if you need to power it up with the bottom case panel removed, for example when working on the hardware.

This guide will cover mounting the button on the right side on the machine next to the USB A port, the position is roughly equivalent to the barrel jack but on the opposite side. This position allows all parts to fit neatly in the space under the smallboard. This mod involves some disassembly of the PBP, small solder joints, and working with small parts. The soldering is quite forgiving but if this is your first time with a soldering iron you might want to practice some basics before diving into this. That said, if you take your time you shouldn’t have any problems.

Proceed at your own risk, any PBP modifications are your responsibility alone, modifications will void your warranty.

Here’s what you’ll need:

• Solder Iron - A small tip, around 2mm, will make the job easier. 
  
• Push Button Switch - STSP NO 3mm x 6mm x 5mm. I used a through-hole part.
  
• M3 Drill Bit - This one came out of a tap and die set but any sharp bit will do.
  
• Insulated Wire - 30awg (or smaller) cut to  2x32cm lengths.
  
• Button Cap - This is the bit you press, which in turn pushes the switch. 3D printed but could be fabricated by any means (ButtonCap.stl)
  
• Button Support - This part holds the switch in place. 3D printed but could be fabricated by any means (ButtonSupport.stl)
  

Step 1. Dissemble the PBP

Follow the normal disassembly procedure for the PBP removing the mainboard, battery and smallboard from the case.

Step 2. Drilling the Button Hole

Drill a hole in the mid-case for the new power button. My hole centre is 8.3mm from the edge of the USB port and 3.5mm from the keyboard deck. There’s a little room for error here, you should be okay up to +0.3mm on either measurement.



tip:The plastic is quite soft, a sharp drill bit will cut through with finger strength alone, if using a power tool take it slow to prevent melting or cracking.

Step 3 - Wiring up the Button.

The PBP’s power button is on the keyboard but it's wired up differently from the other keys. It's a switch with a discrete connection to the RK808 power management chip. Here's the schematic for the keyboard connector.

The power button is triggered (the switch is closed) when pin 26 is connected to ground. You can try this by bridging pins 25 & 26 on the keyboard connector. We're going to tap into the circuit here to build our new button, but luckily we don't have to solder onto the keyboard connector. Pin 26 is connected to a test point on the reverse of the mainboard. Test points are PCB pads used in the factory to validate the assembly and operation of the board during manufacturing. In the schematic above you can see that T64 is connectected to pin 26. T64 is on the reverse of the mainboard, toward the bottom right hand corner.



To complete our switch we also need a ground and it just so happens that the test point right next to T64, test point 88, is a ground. So, let's solder on our switch wires. Go ahead and peel back the (very sticky) insulating plastic that covers the rear of the board. Tin both test points by adding a little flux and then solder to each. Prepare two 32cm lengths from the insulated wire and wind them together into a twisted pair (this isn't essential but makes them easier to manage). Bare a tiny bit of each of the wires, 2mm should be good, and tin them. Finally, solder the wires to the pads by holding them together and touching them with the solder iron.



Route the wires up to the corner of the board and replace the sticky plastic insulator (ignore the two wires on the left near the USB, they're not part of this project).



Next, attach the switch to the other side of the wires. If you're using a through-hole switch, trim down the legs so that they're level with the switch body and then solder one cable to each leg (it doesn't matter which way round you attach them).



Now fit the mainboard back into the PBP's case and route the new switch wires along the top edge, just under the hinges, following the path of the microphones and antenna. (Leave the battery removed to give yourself more space to work).



Step 4. Fitting the Switch

With the mainboard wired up let's go ahead and put the switch in place. Two 3D printed parts constrain the switch and hold it in position, in combination with the smallboard everything is stable without glue or tape. However, if you don't have access to a 3D printer I'm sure you could glue things down, or fashion something out of other material. This is a drawing for the parts used

Drop the button support and the button cap into the PBP case and squeeze the button in between. I like to press it against the button cap and slide in, letting it push back against the button support.



The button support pivots against the plastic strengthening ribs of the case, this constrains the button but still allows it to be pressed. There's some room for improvement here, the part could be made to better fit the cavity, but with the smallboard in place it's plenty secure.

Finally, fit the smallboard back into the case, making sure to route the switch wires below the screw insert, this allows the board to seat correctly.



And with that, your second power button is now installed. Well done!

This button behaves exactly like the original, as far as the system is concerned it is the original, so anything you can do with the keyboard button you can do with this one.

If you have any problems, check all your solder joints, there are very few points of failure here some of the possibilities are:

Bad solder joints
Faulty switch
Broken wire
Board damage as a result of heavy handed soldering
Board shorts due to poor reseating, or failure to apply insulator layer

Good luck and let me know if you give this a try.

Cheers,
Ron