Intro: Building a Custom Shield for the Gangster Gadget Propeller Platform
Breadboards can be quick for trying out a simple circuit, but they are really clumsy when it comes to actually USING that circuit.
So step up to the next level of circuit prototyping with a custom shield like this one for the Propeller Platform from Gangster Gadget.
The picture below is a general purpose prototyping board - called a "shield" in modern terms.
It is used to wire to a custom circuit that can be plugged into the host computer.
So we can try out something without hacking the host itself.
This shield offers:
Stereo audio output
A great big LED to blink
A switch connector
and four efternal power connectors.
On the right side of the shield the processor pins and power pins are labeled with a stick-on.
That makes it a lot easier to wire to the right pin.
This shield plugs into the low order connector on the GG Propeller Platform board. (the red board)
1 each "Perf Board" circuit board with holes on .1" centers and a solder pad per hole big enough for the circuit you want to build.
2 each Wire wrap header - male - 20 pins
Soldering Iron with a fine point
Small diameter solder.
A circuit to build (I'll add that in a while)
software to drive the circuit you added!
First, lets build the bare shield...
Pin spacing for the headers on the GG Prop Platform are standard .1" spacing.
So regular perf board (from Radio Shack even) will work fine.
First step is to trim the perf board to size.
It can be snapped apart by carefully aligning a row of holes along the edge of a table and just snapping the free end down.
Hold the side on the table firmly to the table and it will break cleanly (sort of) along that row.
Clean up the snapped edge by rubbing the edge on sandpaper, just so it is neat and doesn't snag on stuff.
For this Instructable we will make a full shield - it will attach to both headers and sit over the host board.
Next step is to trim the wire wrap header strips to the correct length.
They can be broken across the table edge, but a more precise method is to cut them apart with snips.
A single 20 pin header will make two parts - 4 pins for power and 16 pins for signals.
Note that there is a gap of .1 inches between them so you can tell which end is which.
Plugging shields in backwards is a bad thing. Very bad!
So it's nice they way Nick separated the headers that way. (Thanks Nick!)
Now fit the pin strips through the perf board.
I stick them through from the top and so I can solder the pins to the board on the bottom.
Check the locations and spacing carefully. As you can see, I'm using the actual host board to make absolutely sure
that the pins will hit he header sockets below.
Now comes the fun/hard/challenging/interesting/painful part - soldering!
Each pin is soldered to the copper pad on the bottom side of the perf board.
I guess you don't HAVE to solder every pin, but it does make it more mechanically solid.
Start by tacking a pin at each end of the board. Make sure the pin is seated all the way down flush on the other side!
If not, touch the iron to the pin/pad and press the board against the table to seat the pin.
Too much heat can make the pad release from the board. That's not a disaster by itself.
But it get's wobbly (we'll fix that in a minute).
DOUBLE check (AGAIN) that the pins are in the right rows! (don't ask how I know to double-double check)
Then solder the rest of the pins.
When that is done. I run a tiny bit of superglue between the plastic strip and the perf board.
That's just to really hold everything together nice and tight.
Be neat. Superglue is not an electrical conductor and can insulate a pin when it shouldn't be insulated!
Now it's time to build up your circuit.
This board was mainly needed to play audio.
So it has an audio connector (stereo 3.m mm socket) to allow the board to be plugged into an audio amplifier and speaker.
There is some other stuff on it too.
Like the great big LED that I used to develop the LED THROB code.
And a pin header that I can plug an external switch into so the software can read it.
But for the moment, this is what he wiring side looks like.
I am using proper wire wrap techniques on the wire wrap pins, and soldering the short pins.
(More on that in the next Instructable)
Properly done, the insulated part of the wire should partially wrap around a pin before
the bare wire. That makes the wire less likely to unwrap a bit and short this wire to that
wire (when you are digging around under it trying to find a problem?) and makes the
connection quite a bit stronger.
For the soldered ends, I first tin the pin with a dab of solder.
Then make a tiny hook in the end of the wire, slip it over the pin and hold it steady while
you solder it together. Usually that means just touching the tip of the iron to the connection
for a second or two.
Those connections tend to be more fragile as the wire is connected solidly and wiggling
it can cause it to fracture at the solder joint.
The circuit is wired and ready to test!
Note the stickers that identify the pins on the bottom of the board too.
I make these with a CAD program to get really accurate spacing and font size,
printed them on sticky label paper, cut them out and stuck them on.
Prevents a lot of confusion about which-pin-is-which that often happens when
working upside down on the bottom of the board.
The finished shield is attached to the Propeller Platform and the program is loaded via USB cable (black wire).
A nice feature of the Gangster Gadget Propeller Platform is that is can be powered by the USB cable.
It's Up and Running!
The video is from the breadboard development version (also home brewed).
The Propeller has sometimes been maligned for having no dedicated hardware, or that it takes processor
power to run the software driven peripherals.
But that's really short sighted. Thre is awesome flexibility here!
If you need a video display, dedicate a cog (or two) to it and - it's running.
If you don't need a video display, those cogs and counters are available for other f\unctions.
Can you imagine playing a wave file like this with ANY other micro-controller?
Hardware interface -
Two resisters and two caps make the audio filter.
I've added two more to AC couple the signal to the amplifier.
The software and wave file all fit in a single cog.
Total cost for the audio demo? Less than a buck.
The circuit wired up here is very straight forward - a resistor and capacitor filter for each "side" and a miniature stereo connector.
Pins 10 and 11 of the Propeller processor chip are used to make audio signals.
The rest is up to software.
There are literally hundreds of software "objects" to play with at the Parallax Propeller Object Exchange.
When you are ready to rumble, visit the object exchange at http://obex.parallax.com/