This is going to be a weblog post with lots of pictures…
The Graphics Board is easy to assemble, but there are two things to watch out for:
- the polarity markings for two of the electrolytic 1µF caps are reversed
- if you solder the display onto the board, then you can’t easily reach the back anymore
The former is a mini goof-up by yours truly, the latter is something to keep in mind when deciding which headers you are going to use (you can side-step the issue by mounting the display using headers, but that will increase the height of the entire stack).
Here goes. As usual, I’m going to proceed from low to high-profile components, because that lets you put the components in, flip the board over, and press on it to get the components soldered closely to the board.
First the 100 Ω backlight series resistor:
Note that there’s a solder jumper right above it. The default is to connect the middle pad with the leftmost pad marked “P”. This connects the backlight permanently to the PWR line. If you want to control the backlight through the IRQ signal, you can set the solder jumper to the “I” position instead (see the backlight() docs). This can be changed later if you change your mind.
Then 5 yellow decoupling caps. These are not polarized, but make sure you put them into the right holes:
Update: The latest kit version ships with ceramic capacitors replacing the electrolytic capacitors. This gives longer life and simplifies the construction detail since these capacitors are not polarised. See the Wiki for more detail
The next step needs some care, because these two electrolytic caps are marked the wrong way on the silkscreen – they should be placed as follows:
The proper way to connect these, is to put long lead on the right and on the bottom, respectively. Or, same thing: put the gray stripes of the plastic case insulation on the left and on the top.
Note: the two caps on the left will only just barely fit when a JeeNode v5 is added on later. If you use a JeeNode v4, it is probably better to place them flat on their side pointing left. When in doubt, make sure you check the mechanical layout before soldering these two leftmost caps!
The other two 1 µF caps go as indicated on the board, they will in fact be oriented exactly opposite to the caps right next to them:
The next step is to solder the 6-pin female headers onto the board. A very easy way to do this is to place the headers into a JeeNode… and then place the PCB on top of the JeeNode (face down) to solder all of them at once:
The result should be like this:
Congratulations – if you’ve made it this far, then you’ve got the minimum set of parts in place to drive the display. This requires loading the glcd_demo.pde sketch onto a JeeNode. But since there’s no backlight, it’ll be very hard to see whether it is working. I tried it, by pushing the display pins through the 20 holes, and bending them slightly so I could photograph the display against a white background:
You can also power it off a BUB or USB, and there’s no need to bend those pins – just beware that the display is hard to read, and that it has to make contact from the moment the JeeNode has been powered up (or reset).
Seeing the image will give you confidence that all the components have been soldered on correctly and are working properly. FWIW, I managed to wire almost all the caps wrong on my first unit and it still worked!
Anyway – now is the time to decide which headers you want to attach to the board.
I decided I just wanted the inner two ports headers, so I took two 6-pin female headers:
… and bent the pins at a right angle:
This is the final board:
The last step will be to attach the backlight and the display:
The backlight is a small white plastic panel, lit by an internal white LED. The silvery tape around the panel prevents most of the stray light by reflecting most of the light back into the panel.
The panel has a front and a back! And the polarity of the LED wires matter!
The side with a small ridge on top is the front. If you check very closely, you’ll see that it has a protective plastic film on it. Take it off, and avoid touching the panel surface afterwards:
Now turn over the panel and bend the LED leads as shown here – note the difference in the length of both wires:
Insert the wires in the two holes next to the resistor marked “Backlight”. Make sure the panel is on the back side, i.e. not where the components are. What you want is to get the panel into approximately this position:
It doesn’t need to touch the circuit board. Solder the leads on the front side and then cut the ends off:
Note: due to the lighting, you can’t see the panel itself in the above picture – the leads you see are the ones between board and LED – not the snipped off ends!
The last step is the display itself. You will need to decide whether you want it attached directly (and more permanently) to the board, or whether you want to use 0.1″ female headers (these are not included with the kit).
Note that only the 20 pins one one side are actually connected – the 2x 3 pins on the other side are just to hold the display in place.
BEFORE YOU PROCEED: carefully remove the thin protective plastic film on BOTH sides of the display!
Careful: only remove the TRANSPARENT film – not the silvery one!
I’m going to solder the display directly onto the board. It looks a lot nicer that way, IMO. So the first step is to carefully insert the display pins:
Then flip the whole package over and solder all 20 pins. Note that the pins only stick out a little bit:
The goal is not to squish everything tight against the board – that would probably just scratch and damage the backlight panel. What I do is press it in far enough for the the backlight to press gently agains the display, with hardly any gap. In fact, I can still move the backlight around a bit, which is useful to align it properly with the viewable LCD area.
Then I solder just one pin of each of the 3-pin headers on the other side to hold the display in place. That way, it will be easier to undo – in case I ever need to reach the back side of the pcb again:
Here’s one more picture of the whole thing with a JeeNode USB attached:
That’s it – it’s ready to inform and amuse us!
Update: If your display looks uneven with vertical “black bars”, please refer to the Wiki for comments about setting the optimum display contrast.