Thursday, September 21, 2006

Digital Medal sort of working Part 2

So, some heat applied to the row seven current limiting resistor fixed the dead row number seven. As for the doubled up column, I've determined that the column is shorted to Vcc on the MCU to transistor array link. That has to be an assembly issue. An unpopulated board doesn't have the problem.

So now the only worry is the soft power. Can it handle the load? Why is it dropping out to two volts in the present circuit? The short doesn't draw that much current, but since I don't know exactly where it is, I can't be sure of its full effect on the circuit.

I'd like to just cut the column signal line to see if I can get rid of the soft power problem, but its really hard physically. Plus there is no guarantee the as to the extent of the short. Maybe I should just test the load carrying capability with a false load? But what if the load is not the real issue? Hmmm. Hmmm. I will have to ponder it for a while.

Tuesday, September 19, 2006

Arrrr



My pirate name is:


Black Roger Rackham



Like anyone confronted with the harshness of robbery on the high seas, you can be pessimistic at times. You have the good fortune of having a good name, since Rackham (pronounced RACKem, not rack-ham) is one of the coolest sounding surnames for a pirate. Arr!


Monday, September 18, 2006

Li-ion Batteries



So today, bored at work, I began to think of the Li-ion batteries I got from Eddy some time back and how I might connect them. A lot of folks just solder the pads, but I kinda wanted to do a removable pressure contact type thing similar to what cell phones do. (The battery is actually intended for a cell phone.) I remember my old cell phone had theses sort of spring loaded plunger style contactors the rear battery door pushed the battery pads onto.

Anyway I went looking for the contactors, thinking they were custom and I'd never find them. I found these .1" Mill-Max spring loaded headers but, having only my faulty memory, felt sure that the battery pads were well over a .1" pitch. To my delight, when I returned home and bothered to check I discovered that my cell phone plunger things looked exactly like the Mill-Max headers and that the battery pads were in fact .1" pitch.

This looks like it will be a cool way to connect my batteries if I can come up with a good way to put pressure on the battery.

Digital Medal sort of working

Well I made some progress tonight. I have to short out the soft power circuit, but I can get the digital medal to mostly run. One column appears to be doubled up and the bottom row is completely dead. But the text is scrolling! Woot! I'll review the PCB design for the affected row and column, but it could easily be a drilled out hole issue. Its possible that heating the affected pad for a bit will get me a connection.

Anyway I'm happy to have progress.

Digital Medal Struggle

Sigh. So, the digital medal has problems. Not the least of which is the time and energy I have available to work on it. The worst problem is the damn hole sizes. I trusted the print out as a sort of eye-ball measurement that all the hole sizes were OK. They weren't. I have to drill out a lot of holes. The worst of that is for the LED displays that can't be soldered on both side. I have to drill a second hold very close the pad and run wire-wrap wire through it and the main hole to get a good mechanical and electrical connection to both sides of the pad.

The next problem is the third transistor array that was thrown in at the last minute. I guess I miscommunicated with the fellow who did the schematic for me. I though I had understood him to say that he'd prototyped the circuit. He hadn't done it for this last minute add. First I discovered that power was backwards. I should have looked more carefully once I discovered that. But, no. I started on a second drilled out board only to discover that the inputs and outputs were also backwards.

So now I'm onto to the third drilled out board. Ironically this board is a touch easier because I don't have to cut traces to fix the power. Since the inputs and outputs on the UDN2981 were also reversed, if I solder the chip to the other side it will be connected perfectly on the current board. If this works I don't think I'm going to edit the board except for hole sizes.

Anyway, I should be able to get a bit of work on it tonight. Maybe I'll be able to light it up, who knows. *I WILL* get it working for the November games dammit.

Tuesday, September 05, 2006

Digital Medal

Well the Digital Medal Project has been consuming almost all my free time for what seems like a month now. It's almost done! Today I got the prototype boards and tried placing the components. It was designed to be tight. I was astounded when the components snapped into the center hole with the precision that I had measured them for. Its a perfect fit.

All was not perfect, however. The PCB program I used to make the board shows the .02 in holes a lot larger on print out than .02 really is. Either that or the board shop used the wrong size bit. $90 worth of prototype board an I have to drill out half the damn holes and solder on both sides. That going to be a bit of a trick for the LEDs but I think I know how to do it.

Oh, well, the finals should be damn near perfect.

Now to solder up a board and see if the circuit actually works! Boy that it would be amazing to have everything fall into place right at the last minute here. The Table top competition is this Sunday!