Pebble V2.0 Instructions

// This is very rough, I need to work on it some more but it's a draft to get started.

This guide assumes that you already have all the SMD components pre-assembled on your board. Check that this is the case; if there are some SMD components that are missing or not assembled already then you should check this with Luke or Jon.

Your kit should come with the SMD ATmega8U2 pre-assembled on the board and the through-hole 16 MHz crystal next to it pre-soldered on the board, with the ATmega8U2 pre-flashed with its appropriate firmware and the USB ATmega8U2 circuit pre-tested. You should also be supplied with an ATmega328 DIP chip that is pre-flashed with an Arduino Uno compatible bootloader.

Check the status of the semi-permanent solder-jumper links - SJ1 (reset), SJ2 (USB ground) and SJ4 (+5V low-side drives) should be closed by default, whilst SJ3 (boot) should be open.

Now, let's start assembling some of the through-hole components on the board.

We will start by installing the 2-pin screw terminal block for the battery connection. Make sure that the holes where the wires are inserted face out towards the outside edge of the board.

Now, we will insert and solder the two-pin header which is used to connect or disconnect the USB power bus. We will also insert and solder the inductor - the inductor is a black cylinder with two wires, and it is not polarized.

Next, let's insert and solder the two 220 uF electrolytic capacitors - remember that these capacitors are polarized and they must be oriented with the correct polarity as marked on the board.

Next we will insert and solder the 6-pin ISP programming header (which may be optional if in-circuit programming is not required) and we will insert and solder the trimpot which sets the LCD contrast. Make sure that the side of the trimpot where you actually rotate it is facing towards the outside edge of the board.

Next, we will also insert and solder the 16-pin female header strip which connects to the LCD display. We will then also insert and solder the pair of 8-pin female header strips and the pair of 6-pin female header strips that are used to mate with Arduino "shields".

We'll now also insert and solder the 28-pin DIP socket for the AVR microcontroller, and the 16 MHz crystal for the AVR. The crystal is not polarized, but the IC socket should be inserted so that the indicator notch on the socket corresponds to the silkscreen marking. We'll also insert and solder the RGB LED, remembering that the RGB LED must be inserted the correct way, with the flat side of the LED corresponding to the silkscreen marking.

Now we can insert and solder the MCP9701 temperature sensor - make sure that you don't get the MCP9701 confused with the two similar-looking P2N2222 transistors. We can then also insert and solder the two P2N2222 transistors. Remember that the transistors and the temperature sensor must all be inserted the right way around, as marked on the silkscreen.

Now we can insert and solder the two 2.0 mm 10-pin female header sockets for the (optional) XBee module, as well as the 4-pin PCB-mounted screw terminal block for the two general-purpose low-side transistor outputs.

We can now insert and solder the rotary encoder. Finally, we’ll need to attach the LCD display. The easiest way to do this is probably to insert the 16-pin pin header strip into the 16-pin female header on the board, and insert the LCD module with the other end of the pin headers passing through the holes on the LCD.

Make sure that the LCD is in the correct orientation and that pin 1 on the LCD display corresponds to pin 1 on the board, and then solder the pin header onto the LCD module’s pads.

For future use, if the position of the LCD is not convenient, you might wish to construct a cable to move it away from the board.

Now, we’re ready for some testing.

Testing

Note: Once we’ve actually got the hardware, Luke/Jon/Andy etc. will perform some initial testing, and we’ll write a more simple, streamlined guide for miniconf use.

Insert a 0.1” shorting jumper (a little plastic thing, like the ones on older computer motherboards) onto the USB power header, and plug the Pebble into your computer with a mini-USB cable.

(Yes, jumper shunts were included on the BOM.)

Note: Oh, that’s a good idea. Maybe we can provide mini-USB cables with the boards like Freetronics usually does.

At this stage we won’t connect any batteries, and we won’t insert the AVR chip into its socket, and we won’t insert an XBee module, and we won’t connect any kind of shield.

As soon as you have connected the USB power, the power LED on the board should be illuminated and it should stay illuminated at all times. If it does not, then something is wrong. The first thing to check is that the USB power disconnection jumper is actually installed on its pair of pins.

At this stage, you should be able to talk to the ATmega8U2 USB-interface microcontroller from within the computer’s operating system. By default it’s programmed as a USB-to-serial bridge, just like an Arduino Uno.

Try inserting a little piece of wire to connect pin 0 and pin 1 on the Arduino shield header, then opening a terminal program and talking to the serial device. This simply creates a loop-back for the serial port, so you should be able to type in a string and see it echo back.

Now, if everything is good so far we can insert the ATmega328 microcontroller into its IC socket, making sure that it is inserted the right way around.

We should now be able to upload Arduino programs into the microcontroller using the Arduino IDE. Remember to select “Arduino Uno” as the target hardware type, and to select the appropriate serial device.

Batteries:

Now, if you want to use portable power without just being limited to USB use, let’s look at power options.

If you want to use a mains plugpack as the power supply, the kind of plugpack that provides a 5.0 V output onto a standard USB socket is a good choice.

The battery voltage input must be within the range of about 2.4 - 4.5 V for correct operation. Thou shall not ever exceed 5 volts, into either of the power supply inputs, on this device.

You can use two standard alkaline or NiCd or NiMH cells in series, for a voltage supply of 3.0 V (or 2.4 V if you’re using 1.2 V NiMH cells), or you can use 3.6-4.5 V from a set of three cells in series. The latter will provide an improvement in battery life. The 2.4 V you will get from two NiMH cells is OK, but it is towards the lower end of the operational voltage window.

You can use common “AA” or “AAA” cells, however the larger types such as “C” or “D” cells will provide greater charge capacity and a greater runtime. You could also use a 3.7 V lithium-polymer cell, where a small, lightweight battery with high energy density is desired.

There is no battery charging electronics built into the device - to recharge your batteries they must be disconnected and recharged externally.

A 2 x AA battery holder like the one pictured should be included in your kit. To use it, you’ll need to disconnect the USB power supply jumper (this does not affect USB programming and communications with the USB cable connected) and connect the wires from the battery holder to the battery connection terminals on the board.

Example battery holder, I need to nick a picture of one and insert it: http://search.digikey.com/us/en/products/BC2AAW/BC2AAW-ND/2190080

If you were using a different battery configuration, as per the examples and requirements above, you may wish to swap this over for a different kind of battery holder.

Make sure that the positive and negative wires from the battery holder are connected to the terminal block on the board with the correct polarity, as marked on the silkscreen, and ensure that charged batteries are inserted into the battery holder with the correct polarity.

With the batteries installed and wired up, you should then be able to turn on the power switch on the board, and the power LED should light up. (The on-board power switch has no effect if USB power is connected.) If you’re using a battery holder which has a built-in power switch then this power switch must also be turned on.

If you’re using battery power at the same time that you have the USB power jumper connected and USB plugged in, this should be OK and it should function normally with no weird issues or damage. However, I need to perform testing to double-check this once the production hardware arrives... until then, if in doubt leave the USB power jumper disconnected when battery power is connected.