Building the Handy Board

Build or Buy?

I decided to build my own Handy Board rather than purchase a fully assembled version. Partly, this decision was based on the fact that I already had a number of the components, thus building the board myself was significantly cheaper than buying one. For my purposes, I decided that I did not require IR support, so I did not purchase the relevant components. In addition, I already had an AC adaptor, the 68HC11, SRAM, and some assorted resistors, capacitors, etc. The total for my purchased parts was $101.85 (see below), but your mileage will vary.

The assembly manual is quite detailed, making this board a very straight forward project if you are reasonably handy with a soldering iron, but I would not suggest this as a first time electronics project.

 

Parts

The parts for a complete handy board and interface should run between $100 and $150. My total was about $102, but I left out a few components, had a number of others already on hand, and upgraded a few. My "Bill of Materials" (BOM) is available either as an Excel Workbook or as a text file. A few notes about the BOM:

The PC boards can be purchased from Douglas Electronics. My price reflects a slight discount based on volume (I think the cpu board is normally $16). Only two of the remaining parts were hard to find: L293 and DS1233. I was able to locate both of these at Newark Electronics. The remaining parts were stocked at Digi-Key.

 

Assembly

The assembly of the board was quite easy, but then again I do this sort of thing for a living. It took me about 4 hours to assemble the entire board including running the tests after each step of the assembly. There were no problems, and no rework was required. Actually, the tests took almost as much time as the soldering, but I would not suggest skipping the tests. The assembly manual is designed such that you can catch a mistake very early on with little debugging. If you just solder everything down and it doesn't work, it may be difficult to debug - especially if you don't have a scope.

If you decide not to install the IR components, you should wire a couple of additional pins together so that the extra gates on U7 and U9 don't oscilate needlessly (and thus consume power). If you do not place C6 and R4, then you should short the contacts for C6 together (just put a plain wire between the pads instead of a capacitor). Similarly, if you do not place R7, then you should short it. The reasons for these changes is that the logic parts are all CMOS logic, which exists in an undefined (and often power hungry) state if one or more INPUTS are left floating. Leaving OUTPUTS unconnected is not a problem, but all unused INPUTS should be connected to either Vcc or ground.

Although the Optrex LCD panels are electrically compatible with the Handy Board, the particular panel I used had its contacts in the wrong position and order to allow connection straight through to the board. Instead, I wired up a 14 conductor ribbon cable from the LCD to the main board.

Interactive C is used to test much of the board's functionality, and it will not boot properly if the LCD panel is not connected.

If your AC adaptor has a slow response time, it is possible for the board to get locked up during reset - especially once the L293 chips are placed. Once the battery pack is connected (and charged), it will act as a large capacitor on the power bus, and prevent lock up from happening. Of course, another option would be to get a better power supply.

Another option for battery packs is to use an R/C style battery connector on the board, and then use commonly available R/C racing battery packs. This is a good approach if you want to be able to easily switch to a higher capacity pack. The battery uses a receptacle (WM2309-ND) with 2 pins (WM2310-ND). The board should have a plug (WM2308-ND) and 2 sockets (WM2311-ND). I haven't tried the Digi-key parts myself since I already had the right connectors, but the specs on the parts look right.


I have tried to be as accutate as possible with the information presented here, but there is always some chance of an error. Use at your own risk.


 [Dave's Lego Site]