Date: Tue, 16 Aug 2005 00:36:31 -0500 (CDT)
Subject: more robot electronics
X-UID: 79
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It's funny as pictures don't reveal how much work is required to do simple 
things. I picked up three plastic parts boxes for under $5 (discontinued 
product) from Fry's in Dallas. This is a good buy. None of the parts boxes 
fit the STK500 board except for one huge one. I wanted something the size 
of a Japanese bento or sandwich box.

So I had to cut away a lot of plastic with a hacksaw blade and X-acto 
knife (two very useful tools). I tried using epoxy at one point. It just 
peeled off. Epoxy does not stick to high density polyethylene.

Quite a bit of the bottom of the box is cut away to make it flat. Then the 
plastic from the front of the a microwave oven door (found by the dumpster 
- this broken microwave has been useful) is cut to size and stuck to the 
bottom using 3M aerosol contact cement. This works. The microwave oven 
plastic is some kind of very high density polycarbonate (my guess). That's 
probably for safety, to prevent a microwave oven door from being broken 
open and the radiation leaking out.

Now the microcontroller programmer board fits in a nice box along with 
lots of cables and jumpers. It came in a cardboard box (nice enough) 
without any obvious way to otherwise store it for use.

The USB to serial conversion cable had #4 nuts on the DB-9 end that get in 
the way. So I ended up cutting off the plastic cover and sawing off the 
nuts with a hacksaw blade. There's quite a bit of electronics inside the 
conversion cable. It's impressive inside. After I had cut everything 
apart, it was obvious that I didn't have to do that. I could have just 
sawed the nuts off. But now it's reassembled and stress relieved with a 
zip-tie and black electrical tape so it looks cooler. Also, if it breaks, 
I guess I have a good idea how to attempt a repair.

The green thing with the white carpet thread wrapped around it is a $3 ZIF 
(zero insertion force) socket from Altex in Carrollton. There are only a 
few electronics parts stores in Dallas (I have not explored them). I can 
only imagine how much nicer it is in Silicon Valley. Anyway, it could be a 
lot of work to mount this ZIF socket in durable way as the pins on the 
bottom are the wrong size and orientation. So I instead went for an 
improvised solution and just wrapped carpet thread around the ZIF socket 
and a machined 40 pin IC socket. There is enough tension to maintain 
electrical contacts. The IC pins just fit between the threads. It looks 
weird but seems to work.

I wired in the optical isolators and connected them to the MOSFET driver 
ICs and socket for the microcontroller. So most stuff is wired now. I 
don't want to put a microcontroller into the socket until I have a decent 
idea that the firmware is correct. I do plan on having some provision for 
ISP (in system programming). But I also realized that if I want to 
re-flash the microcontroller without powering the single board computers, 
then I have to open the enclosure and disconnect them. So it's not 
completely painless.

Behind the motor control board is a box full of the MOSFETs I soldered 
about two weeks ago. I hope these hold up as I didn't do a very good job. 
The MOSFETs are literally bolted through the six small holes on the left 
edge of the motor control board, six FETs and heatsinks on the bottom and 
six on top. There's just a mass of 18 gauge wires. I don't know how much 
that will affect airflow. It can't be good.

I'm going to try something new - five to six hours of sleep per night. I 
do know that I must be sleep deprived in order to make progress. There's 
just not enough time to have a full time job and still work on the robot. 
I've been sleeping too much lately. But I also notice that when I'm tired, 
I start to slow down. I think there is a balance between sleep and work 
that is optimal. I do try not to waste time now. I used to get home after 
work and relax for an hour or two. That time is too precious to waste.

Also, I'm going to go on vacation again in October. This time, I'll 
allocate the entire day for travel. RoboNexus is in San Jose from the 6th 
to the 9th. So I may go and take lots of pictures. It's not as cool as the 
robot expositions in Japan. But it's probably the closest in the US to 
that.