This time I wanted to build a prototype fairly quickly and increase the budget to do so.  Moving motors from a computer has been done many times before and it has been broken up into modular components.  So, I only had to determine what I wanted to move and get that connected to one of many types of PC ports.

The type of motor I wanted to start with was a servo.  So, I did some searching on the web and located a reasonably priced Pololu Servo controller that receives commands over an RS-232 DB9 port.  Now, since most modern PC’s don’t have serial ports, I purchased a cheap USB to Serial adapter, the TU-S9.  The adapter would also be useful for other projects since the serial interface is fairly basic.  Since I already had a servo from Parallax, that was all I needed.

Parts:

• USB-Serial adapter: TRENDnet TU-S9
• Serial Servo Controller: Pololu 8 Servo Serial Controller
• Servo Motor: Parallax Standard Servo

The TU-S9 is a nice adapter since it is built with the PL-2303 chipset and is supported on most Linux distros.  Once you plug it in your PC, you should see ‘/dev/ttyUSB0′ appear.  This worked without problems on my Ubuntu Netbook Remix distro.

The servo controller is nice, but I initially had some problems with getting the configuration right.  I started with a modified test application with a tcl UI (created for the 16 servo controller).  When that didn’t work, I moved on to a Python test script.  The servo’s didn’t budge with it either.  The only thing that worked was a .Net test application on an old Windows PC.  It was odd since running the Python script on that same PC wouldn’t work, even when the transfer signals were identical for both.

Since I didn’t have the source code for the .Net test app, I couldn’t find out what serial configuration could be different between the other applications.  At one point, I simply pulled out the default DTR/RTS jumper and gave it a go.  This ended up being the problem.  The .Net app must have handled the RTS line properly so that it didn’t reset the controller.  Wow!  I wish I tested the other RS-232 lines!

In the end I was able to whip together a simple python demo script (see below) that moves the servo to various positions.  Feel free to use it, I got inspiration from a previous test script.

(Wordpress doesn’t like source code. So bear with me.)
# servoDemo.py
import serial
import sys
import time

# send some position commands and watch it move
setpos(7,30)
setpos(7,90)
setpos(7,180)
setpos(7,45)
setpos(7,135)
setpos(7,90)
setpos(7,45)
setpos(7,30)
setpos(7,45)
setpos(7,30)
setpos(7,45)
setpos(7,30)
setpos(7,135)
setpos(7,30)
setpos(7,90)

LinuxDevices.com has a good overview of the device.  More detailed specs can be found here.

Of course, there is potential for the many thinclient devices out there.  They are getting more beefy and much, much smaller.  The Jack PC, from Chip PC, is small enough to fit in the wall socket itself and can even be powered via LAN.  The abundance of ports is useful, but the low performance, less RAM, and higher price (higher than $300) makes it less desirable.  However, Chip PC did just release a Linux version of the Jack PC, which does pull some extra attention.

However, a bunch of other junk is left on the walks of San Francisco. Junk that is worthless to others can be valuable in the eyes of others. For instance, a broken coffee brewer probably has a kick ass timer and liquid switch system that you could rig up so that your plants don’t dessicate during long vacations. (Yeah, sure… you could probably water your cat with it too.) I’ve seen cordless phones, TV’s, a mini counter top dish washer (a tad strange), clock radios, and other electronic gadgets. But, last weekend I ran across a somewhat historical find that tugged enough on my curiosity to induce me to lug it up my four flights of stairs to my home. It was an antique radio in a wooden housing.

This radio is an eye sore. It is about the size of luggage people take on airplanes because it has those nifty wheels. I actually thought it was an ugly brown suitcase the way it was propped up. On closer inspection I saw that it had a couple of dials and a record player behind an obtrusive door. The record player was what convinced me to take it. I had a record I wanted to hear for a while and didn’t want to shell out money to do so.

With the box on the floor and the door closed, I couldn’t believe how some hayseed had this in his barnhouse for decades rocking out to Bob Wills thinking it was the best thing since sliced bread. “Damn straight Maude! We’re a part of the MODERN age. We got tech-nolgy and we’re doin’ jus fine.”

Opening the door I saw the moldy turn table and took special notice how the felt protective layer would disintegrate under the most tender touch. Those little fragments were fond of clinging to vinyl. So, it kind of made the whole ‘protection’ thing pointless. After more examination I peeked in the back vent and lo and behold were a few columns of vacuum tubes standing there like weary monoliths of a forgotten age. When I plugged in the radio they glowed like a soft warm ember and emitted that dry smell I remember as a child when I played with my father’s old receiver that also had an array of vacuum tubes.

The power is turned on by turning the volume knob and it was beautiful. It had such a warm analog slow power up that it made me curl up inside my head with a wonderful grin of contentment. Rotating the tuner produced a fuzzy calming noise that was pleasant all on its own. This was unlike scanning the frequencies on today’s radios, which produces such a sharp screeching that it makes you want to grind your teeth. Amazingly this thing worked. I rolled around the dial trying to find a hip station, “Wow, there’s a lot of talk on the radio today.” It took me a little while to realize the radio only got AM broadcasts.

The center knob was missing. It was used to change the sound from treble to bass, as well as to switch to amplify the record player. After fumbling with some pliers I gave the turn table a whirl. My record was a Shins single I got free for some sort of promotion or CD release. It was a 45 rpm disc with one of those wide holes in the center. The record player only had the ~5 millimeter pin, so I rigged up some cardboard (that was handily within an arms length) and kept the record center. The turntable still worked and spun the disc, so I grabbed the needle and carefully dropped it on the warped surface (By the way, don’t store records at a 45 degree, boys and girls).

“Damn. It works!” I thought. But it sounded funny. Everything was high pitched and the beat was too fast. As far as I knew, record players ran at 45 rpm or at 33 rpm, so I couldn’t figure out why I was hearing the Chipmunks. It turns out that this thing was old. It ran at 78 rpm.

Now that the diagnostic testing was completed and the stereo monophone worked, I began examining it. The vacuum tubes were warming up and the heat belched out the vents in the back. The smell of that fume was so nostalgic. I took a closer look inside and noticed there was a plate of glass that had fallen into the back. It turns out that it was the front plate for the tuner needle. Once I saw that, I became determined to restore it and see how it looked.

Lifting up the box, there was an old tattered paper plastered to the wood with a surprising number of patents. I was impressed, but a little disheartened since I couldn’t find a date. I still don’t know how old this thing is. Conveniently on the bottom there were four nuts for easy access. After a few twists of a wrench I was able to gut the thing. “Wow. Those old fogies knew how to design something for later maintenance.”

Looking at the core tuner and sound components I felt like I was on some archaeological dig. On the side there were some scribblings for which tube goes where. Someone obviously serviced this machine and it made me feel giddy that someone would have enough appreciation for something they would spend the time to get it repaired. Now days, people buy something new when something breaks. However, in this day and age, we don’t have much choice given the lack of modular (non-PC) based devices that are built from cheap circuit boards. But still, that lack of affection is disturbing.

As usual, I began to take everything apart even though I was only intending to remount the glass. I took out the vacuum tubes and looked through one that was smoky and was probably burned out. I also discovered this neat tuning capacitor that looked like a heat sink because it was built from plates and used the air as an insulator.