Step 1

Building North Paw V1.0

Step 1: Electronics

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1: Assembling the circuit board …
The little electronics bag includes all of this.

  • Custom North Paw V1.0 PCB
  • 2 10kOhm resistors
  • 1 green LED
  • 2 0.1uF caps (little blue ones)
  • 1 large 47uF electrolytic cap
  • Battery jack + black cover + socket
  • ATMEGA168 28DIP IC
  • 1×3 and 2×3 right angle female header sockets for compass
  • 3 pin resonator (blue)
  • switch STDP
  • 2×5 male right angle motor socket
  • HM55B compass module (comes in silver bag)
  • ribbon cable snap
  • 8 coin-type vibrating motors

For this set of instructions, you won’t need either the ribbon cable snap or the motors, so set them aside in a safe place.

You’ll need a solding iron and some solder.
Start soldering with the shortest components first… this makes it easy to turn the board over and solder on the bottom, where nothing is in your way. So we start with the resistors, they are both the same so bend them up and put the through the holes marked R1 and R2 (both are near the ATMEGA footprint)

Next do the two ICs. Be careful to get the orientation of the ICs correct – the ATMEGA pin one is to the right, whereas the TPIC pin one is to the left.
Next mount the 1×3 female header on the *back* of the board. The HM55B compass will slot into this later. Solder it tightly in place
For the other half of the compass socket, you’ll need to chop the shorter pins on the 2×3 female header socket. This should leave 3 longer legs. Chop the short ones all the way back – otherwise the little leftover leads could contact the pins from the 1×3 from the other side
Once you’ve got the short legs cut, place the 2×3 into the holes, and before soldering mount the HM55B compass into the resulting socket (the RoHS label goes towards the center of the board. If your HM55B lacks the RoHS mark: the three small surface mount resistors go towards the board). You’ll see that the 2×3 actually doesn’t quite touch the PCB. Also make sure that the short leads that you cut are not contacting the pins from the 1×3 socket. Once you’re happy square it all up and then solder the 2×3 in place.
Now do the switch and the barrel connector. For the switch, there are two much larger holes, these will need a lot of extra solder. They provide a firm mechanical hold to the board, so that you can flip the switch without worrying. The barrel connector has two little pegs at the front which should fit into the holes provided.
Now solder on the three pin blue resonator (orientation does not matter) and the two 0.1uF caps (orientation does not matter)
The large electrolytic capacitor is polarized. The stripe down one side is the negative terminal. On the board, the negative hole is marked. The negative side is towards the barrel jack. If you’re not sure, compare to the photo.
Solder in the motor socket. You’ll also need to bypass “T2”, which is a switch controlling the actions of motors 1-8. Use one of the leads that you cut off a resistor or cap. Bend it over and solder it between the two outside pins of T2 (see photo).

The North Paw V1.0 circuit board supports up to 16 motors via the T1/T2 switch. The kit contains only 8 motors, so for the kit, it makes sense to simply bypass the switch by hardwiring it high.

Put the battery wires through the black cover (very important – impossible to do later!). Cut the wires down to ~2 inches in length. Tin the wires with solder.
Solder the red wire unto the outside contact, and the black wire unto the inside contact. (yes we know this is backwards, our bad). Make sure not to put any solder/bumps/wires/etc on the outside of the outside contact, as this makes it difficult to get the cover over later.
Once both leads are soldered, use pliers to close the strain relief crimp at the end of the outside contact. Then you should be able to slide the cover over the contacts and screw it shut.
The final step is the LED. If you check carefully, you’ll fine that the package has a flat side. The silkscreen on the PCB shows a flat side, simply align the two. Alternately, the silk screen also shows a small “+” on the bottom side of the LED footprint. The longer leg of the LED is positive side and should go through the bottom hole.

Your circuit board is done! Take a couple of minutes now to inspect all of your solder joints, make sure they are all shiny and complete. A quick glance now could save you the agony of a flaky North Paw later.

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North Paw V1.0, for help contact

First published July, 2009