Assembling the Handy Board, Part 6

Fuse, Battery Wiring, and Final Assembly

This is the final series in the Handy Board assembly. In this sequence, the PolySwitch© resettable fuse and the 9.6v rechargable battery pack are installed.

For this assembly sequence, collect the following parts:


Fuse Installation

Assembly

Install the rectangular fuse element (PolySwitch© RUE250) in its designated location (near the upper left corner of the Handy Board).

Testing and Debugging

There are no testing and debugging instructions for this assembly step.

Battery Installation

CAUTION: BATTERY PACKS ARE OFTEN DELIVERED FULLY OR PARTIALLY CHARGED, AND EXTREME CARE MUST BE TAKEN NOT TO SHORT THE TWO BATTERY TERMINALS TOGETHER.

In practice, this means that you must not let the two exposed wire ends inadvertently come into contact with each other, nor should you cut through pre-attached wires in the same snip.

The reason for this is that Nickel Cadmium batteries are capable of driving huge amounts of current through a short circuit, far more than common household Alkaline batteries. Shorting out Nicad batteries, even for a brief interval, CAN POSE A SERIOUS EXPLOSION AND FIRE HAZARD.

Assembly

If the pack does not some with wires pre-soldered, solder a three to four inch length to each of the the battery terminals. Use a reasonably heavy gauge (20 or less) and preferably stranded rather than solid wire. Color-code the positive terminal with a red wire and the negative terminal with a black wire. Do not yet strip off the insulation at the ends away from the battery.

If the pack comes with pre-soldered wires, individually clip the wires to approximately three to four inches in length. Do not yet strip off the insulation at the ends away from the battery.

Position the battery pack in the lower half of the LMB enclosure (the half with the taps for screws). Route the wires around the screw posts as indicated in the diagram.

Make sure the Handy Board's main power switch is turned off.

Strip about 1/4 inch of the insulation off of the red (positive terminal) wire. Twist the wire strands together, and insert into the round battery hole (marked with a + on the component side). Insert the wire from the bottom of the Handy Board and solder from the top.

Now do the black negative terminal wire in the same fashion, soldering it into the square hole (marked with a - on the component side). Be careful not to let the exposed black wire touch any point of the Handy Board other than the hole in which it is mounted. This could apply the 9.6v battery voltage to components that are only rated for 5v, causing those components to be destroyed.

If you have a hot glue gun, add a dab of hot glue to the battery wires on the underside of the board.

Testing

Plug the DC adapter into the Handy Board's battery charging jack. The Handy Board's yellow CHARGE LED should light continously.

Now plug the adapter into the Interface/Charger Board, and connect to the Handy Board with the telephone cable. Put the Charge Rate switch on the I/C Board into the NORMAL position. The yellow CHARGE LED on the Interface/Charger Board should now light. Flip the Charge Rate switch to ZAP!!, and the CHARGE LED will turn off.

Battery charging tips:

Debugging

If the CHARGE LEDs do not light as expected, check their polarity.

Final Assembly

Flip the Handy Board on top of the battery pack, and use the self-tapping screws to mount it in place. Do not tighten the screws so much as to dig the screw heads into the printed circuit wires that pass underneath them. If nylon washers are available, mount them between the board top surface and the screw heads. Do not use metal washers; they will short the wires printed into the circuit board.

Note that only half of the plastic enclosure is used in the final mounting (holding the battery pack underneath the Handy Board).

If the Handy Board is to be used with LEGO parts, glue four flat LEGO pieces to the underside of the case. Make sure to first mount the LEGO pieces on a baseplate so they are installed at valid LEGO spacings! Cyanoacrylate glues (e.g., Crazy Glue©) are recommended for affixing LEGO pieces to the Handy Board case.

Congratulations! The Handy Board assembly is complete.

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Fred Martin / MIT Media Laboratory / fredm@media.mit.edu / Sun Feb 4 09:09:56 1996