Master Node

someone's got to be in charge

Master Node 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 docs, built on a breadboard and mounted on a piece of plexiglass. I updated the circuit to the version 3.0 circuit in August, 2009.

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 on the left is my master node in operation. I left an extra three holes in the breadboard between the 08M and the rest of the circuitry -- that opens up enough room for a 14M is 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 capacitor, a couple of smaller capacitors, and a power-on LED and dropping resistor.
  • 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 have to actually pay attention to the data sheets once in a while to figure out which pin is which.
  • On the top right 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 three resistors and a diode I went ahead and added it.
  • The only IC on the board is, of course, the Picaxe 08M processor. There is a green LED on the bottom right, it responds to "flash LED" messages sent to the master node.
  • 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 Plexiglas separated by 1-inch standoffs. Overkill for a "breadboard" circuit, but I think it looks way mass cool.


  • 08M running network master software.
  • Provides regulated 5V power to the rest of the network.
  • LED network activity indicator flashes to show when there is traffic on the network.

Node message table

The master node sends the following messages:

Message Description
CMDactivateNode Requests that the node identified in the node field register to send messages.
CMDavailableTimeSlot Grants a network time slot to the node identified in the node field.

The master node implements handlers for the following messages:

Message Description
CMDregisterNode Adds a sending node to the node table.
CMDunregisterNode Removes a node from the node table.
CMDflashLED Flashes the master node indicator LED.
Log in