{"id":11,"date":"2010-08-23T22:33:33","date_gmt":"2010-08-24T02:33:33","guid":{"rendered":"http:\/\/hackspot.net\/iSpotBlog\/?p=11"},"modified":"2010-08-24T01:45:17","modified_gmt":"2010-08-24T05:45:17","slug":"adding-a-serial-console-port-to-the-ispot-with-ispot-teardown","status":"publish","type":"post","link":"http:\/\/hackspot.net\/iSpotBlog\/?p=11","title":{"rendered":"Adding a serial console port to the iSpot (with iSpot teardown)"},"content":{"rendered":"

This is my first blog entry.\u00a0 I’m not much of a writer, but will hopefully describe things well enough for people to understand.<\/p>\n

Thanks to my friend Al for the hardware help.<\/em><\/p>\n

I wanted to add a serial port to my iSpot, so I’d have access to the RedBoot serial console (runs before the kernel loads).\u00a0 This will hopefully make it safer for experimentation – I should be able to recover from ‘bricking’ by using the serial console\/RedBoot commands.<\/p>\n

What follows are step-by-step instructions for adding a serial port to your iSpot.\u00a0 I am assuming that you have basic hardware knowledge, and are very comfortable with disassembling hardware (and feel confident that you can reassemble it!)<\/em><\/span><\/p>\n

WARNING: You could very easily DESTROY your iSpot if you make a mistake!\u00a0 Also, modifying your iSpot in any way will likely VOID your warranty!\u00a0 Proceed with caution!<\/em><\/strong><\/p>\n

Here’s the iSpot with battery cover removed.<\/p>\n

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Remove the 3 indicated screws, then use fingernail\/other thin tool to separate the front\/back plastic (they snap together).<\/p>\n

Here’s the iSpot with the plastic cover removed (showing “component side” of board – the side opposite the battery compartment):<\/p>\n

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Pop the PC board out of the plastic (be careful in the area of the power switch).\u00a0 Make a note of the orientation of the board (use mini-usb port as a reference for when you reassemble it).<\/p>\n

Here is the PC board removed, showing the battery compartment side:<\/p>\n

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Notice the 12-pin header along the top – we’ll be attaching the serial port to some of these pins.\u00a0 Sadly, the serial port signals from the CPU don’t connect directly to the pins on this header – they go through some ‘zero ohm’ resistors, which are NOT populated by default.\u00a0 So, to enable the serial port, you need to install those resistors (or just short the connections with small wires or solder-blobs).<\/p>\n

The serial port resistors are located underneath<\/em> the WiFi daughtercard.\u00a0 So, this must be removed.\u00a0 Flip the board back over, and carefully<\/em> disconnect the white antenna cable near the top of the board (sorry, I don’t have a photo).\u00a0 Then, carefully<\/em> remove the plastic cover that holds-down the WiFi daughtercard.\u00a0 Do this by pushing the plastic snaps through from the back side, one at a time.\u00a0 NOTE that the interconnect between the main board and daugtercard is along the bottom of the daughtercard (when viewing with antenna cable along the top).\u00a0 It came apart pretty easily for us.<\/p>\n

Here’s a photo of the main board (component side) with daughtercard removed (daughtercard has been ‘flipped up’ in this photo – notice the antenna wire sticking out at the ‘bottom’ of the daughtercard – it’s along the top when the board is flipped back over\/oriented correctly):<\/p>\n

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(ignore the wires coming out the left-side of the main board in the above photo – we temporarily soldered some on to the battery contacts so we could connect to a bench power supply)<\/p>\n

The resistors we need to populate are underneath the small rectangular grey piece of foam (with a notch in it)\u00a0along the top of the main board (was separating the main board and daughtercard).\u00a0 NOTE: it is taped-down with double-sided tape.\u00a0 When we removed it, the double-sided tape was left behind.\u00a0 We needed to remove the tape in order to get access to the resistors, and destroyed the tape in the process.\u00a0 You may want to be more careful – although it wasn’t a problem to put back together (WiFi daughtercard causes enough of a compression fit to hold the foam in place).<\/p>\n

Here’s a photo with that foam removed, and a circle around the pads for the two resistors which need to be installed:<\/p>\n

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The two resistor sites are outlined by white silkscreen.\u00a0 In this photo, they are oriented vertically – one resistor is on the left, one on the right.\u00a0 You need to install resistors (or short wires\/solder blobs) vertically – connecting the left-top pad with the left-bottom pad, and (separately) connecting the right-top pad with the right-bottom pad.<\/p>\n

Once that is done, reverse your steps to reconnect the WiFi daughtercard.\u00a0 Be careful about the alignment of the interconnect between the two boards.\u00a0 Also, don’t forget to re-connect the white antenna cable.<\/p>\n

Now, flip the main board over again (showing battery-compartment side, with 12-pin header along the top).\u00a0 Notice that the left-side pin is square, where the rest are round.\u00a0 The square pin is pin #1.<\/p>\n

We need to solder wires to the UART “TX” (output from CPU to PC) and “RX” (input from PC to CPU) lines.\u00a0 NOTE that these are 3.3V signals<\/em> – you will probably need a level-shifter in order to connect to a PC serial port.\u00a0 Do NOT connect a standard PC serial port with +\/- 12V signals directly to these points!<\/em><\/p>\n

The level-shifter we use at work requires a 3.3V power supply (in addition to the TX\/RX lines), so we decided to tap-into 3.3V and GND signals (also found on the 12-pin header).\u00a0 Here’s the pin numbers for each of the signals:<\/p>\n