EMP shopping cart locker

Step 6 Populate the board

This board does not require any advanced soldering skill - just a steady hand, some reasonably fine solder, and a pointy iron. Here are the steps and their justifications - note that we found all of these to be absolutely necessary:

1) Reinforce high current traces with solder and wire

These are the fat traces along the top of the board, and also connecting to the capacitor. Even a thick wire trace won't be able to carry enough current to power the cart-locker. We have blown up our first few boards due to this issue. We find it best to reinforce the traces by soldering wire along the trace.

2) Solder sockets

Since this is a high-power board, you want to be able to replace chips should they blow up. This will allow you to simply pop in a new one and continue wreaking havoc.

3) Solder other components-- resistors, capacitors, resonator, switch, 5V regulator

4) Attach wires

As detailed in the pictures below, the middle two are the battery leads, with the + terminal on the left. Reversing these will blow up the board. The outer two are for the inductor. Order doesn't matter for these.

For now, just attach about 2-3 feet of wire to each large solder pad. The four large pads need ~18 gauge wire. The two small solder pads at the bottom can be much smaller wire, and the leads should be able to reach from your pocket to your hand, about 4-5 ft.

5) Solder MOSFETs and protection diodes last (note directions of diodes)

The protection diodes will prevent all sorts of nasty voltages produced from frying most of the components on the board. Bend the MOSFETS to be in plane with the board before soldering. You want the completed board to be low profile.

6) If you are programming the PIC in circuit, solder the header and socket the PIC. Otherwise, program before inserting.

7) Attach heat sinks to MOSFETs with heat pads and screw insulators.

Don't forget those insulators! Depending on how you wield this beast, you may come into intimate contact with a heatsink, and when that happens you'd better hope it's not electrically energized too!!! The parts list calls for the purchase of 4 heat sinks, but since we had aluminum scrap sitting around, we used that on our version instead.

8) Encapsulate the board to prevent smoke leakage. We were lazy and used electrical tape. We have also been so lazy as to wrap it in a heavy plastic bag. If you want to do things better, put it in an electronic enclosure or tupperware.