My network master node is a Picaxe 08M running Jurjen's master node software. The
hardware is almost straight out of the description in the version 2 docs, build
on a breadboard and mounted on a piece of plexiglass.
The only minor change that I made was to move the indicator LED to pin 0 -- the
rest of my network nodes have an indicator LED on pin 0, and it makes it possible
to hook up an LED with a built-in dropping resistor by just plugging it into the
breadboard between pin 0 (leg 7) and ground (leg 8).
The picture over on the left is a picture of my master node in operation. I left
an extra three holes in the breadboard between the 08M and the rest of the interface
circuitry, that opens up enough room for a 14M if I ever need the extra I/O pins.
Since the master node on my network is only responsible for managing network access
time slots I don't think I'll ever need to use a 14M on this board.
Clockwise around the breadboard, starting on the left:
- First are a couple of binding posts to bring power onto the breadboard. I have an
old Wish 206 breadboard that I've used for 20 years or so that has binding posts,
I kinda liked the way it looked so I used 'em on the board that I built.
- On the upper left is the power supply, consisting of a 7805 regulator, a 1000uF
electrolytic capactor, a couple of smaller capacitors, and an power-on LED.
- Next to that in the center is the push-pull driver for the power MOSFET. I had a
heck of a time figuring out how to connect the NPN and PNP transistors that make
up the push-pull driver. Seems that you actually have to pay attention to the data
sheets once in a while to figure out which pin is which.
- On the extreme right on the top of the breadboard is an enhanced download circuit.
I don't much use it right now, because the master node software doesn't change very
often, but since it's 3 resistors and a diode I went ahead and added it.
- The only IC on the board is, of course, the 08M master processor. There is a green
indicator LED on the bottom right, it responds to 'flash master LED' messages sent
by other nodes.
- In the middle on the bottom are the MOSFET drivers for the network itself. the power
MOSFET is in the middle of the board, the smaller MOSFET for tri-stating the network
is next to it on the left. Various resistors live there, and the wiring is a bit
messed up. In fact, I mis-wired the tri-state MOSFET so badly that I managed to
let the magic smoke out of one before I figured out that the drain goes to ground,
not to the same pin as the gate.
- There is a red LED network activity indicator next to the tri-state MOSFET. It flashes
whenever there is activity on the network, for my network that means constantly.
- The blue box on the left is a terminal block for connecting the master node to the
network. Right now I'm using another breadboard as a punch down block, I want to
replace that with a telephone multiplexer so my wiring will be neater.
- The breadboard is a 480 tie point about 2x3 inches. It makes a great size for building
08M circuits on, I got it for $4.00 from
All Electronics.
- The whole node is sandwiched between two pieces of plexiglass separated by 1-inch
standoffs. Overkill for a "breadboard" circuit, but I think it looks way mass cool.