Ideas in Electronics
What I plan to do here is to present some ideas for electronic projects,
and show you how far I have gotten with them.
In this section you will find the following:
What I plan to do here is to present some ideas for electronic projects,
and show you how far I have gotten with them.
In this section you will find the following:
In order to maintain sanity, I always prefer to use DOS and QBASIC. Why?
1. QBASIC is easy to work with.
2. It handles port-mapped I/O and RS232 routines directly. Visual Basic will
handle RS232 only with a plug-in, and port-mapped I/O only with a driver written
in Visual C++.
3. DOS does not crash whenever it feels like it.
4. QBASIC is right there, ready to go.
Before deciding how to lay out a project like this, you need to decide if you
want to build a huge breadboard system, or build a smaller I/O board for each
project you want to automate.
Finally got to do some more planning on this project.
Last week, I picked up a DVM from Radio Shack which has an RS232 interface.
It works well, but it has two limitations:
The baud rate is fixed at 600, which makes it rather slooow. If I try to take readings more often than 1 second, it will backlog the previous reading, then eventually crash.
The other problem is that the function can't be changed under software control. I am spoiled by the Fluke 45 meters I use at work. They are much faster, and may be completely controlled remotely.
Overall, it's a good meter.
I still want to develop a meter based on the ADC0809 A/D converter, which will give me fast readings with 8-bit resolution. This will be good enough for general work. After that, I plan to use a 16-bit DAC along with an SAR done in software, driven either by the host computer, or an on-board Z80.
I have also sketched out the basics of an IC tester.
I still haven't decided whether to use an array of independently controlled tri-state drivers, or to have hard-wired test sockets dedicated to individual pinouts.
2-17-2001
I have completed several more pieces.
The 16 bit A/D converter is working. It consists of a 16 bit DAC, a sample/hold chip, and some software. It performs a reasonably fast 16 bit successive approximation conversion. The input range is -10 to +10 volts, and of course, it may be used as a 16 bit DAC. The schematic is nearly finished, and I'll be putting it up soon.
The 8 channel 8 bit AD converter is also working.
I have breadboarded a bipolar driver, which works like an op amp, except that it can put out over 1 amp over the range of -12 to +12 volts. I had it connected to a motor which is linked to a rack-and-pinion actuator. Varying the input voltage plus and minus a few volts causes the rack to go in either direction. Hooking it up to a function generator set to about 1 Hz causes it to smoothly go back and forth. Using a square wave makes it dart back and forth. A good basis for a simple motion control project. The driver can be driven by one of the DACs, controlled by the computer.
The output voltage swing is limited by the op amps max rated supply voltage, and the max current is limited by the gain of the darlington drivers.
It works fairly well as an audio amplifier.
I have also started on a regulated supply with a selectable output, based on the LT1038. This is a 3-terminal adjustable regulator similar to the LM317, except that it handles 10 amps. It can be adjusted with a pot, or with switched resistors controlled by the computer. The next step is to determine whether standard opto-isolators are suitable to switch the feedback resistors. It's not practical to use a transistor in the feedback circuit to make it voltage controllable. Using opto-isolators eliminates grounding problems in the drivers, and makes it easy to build a negative adjustable regulator by just reversing the output terminals. Of course, a floating raw supply is also needed.
The breadboarded version puts out 1.2 to 28 volts regulated, up to 6 amps.
9-13-04
Didn't make too much progress here. I has to step back and take a good look at all the
"treasures" I had lying around (read: in the way) and make a little room. Since then, I got
sidetracked, then ham radio came along.
More to follow at a later date
There is some restriction on which tuners are usable - the OLD VCR's with the two
click-stop channel selectors are too bulky. The newer tuners require a digital coded
data stream, which makes them useless if you don't have the programming data.
The most useful ones have a voltage control input, and three select lines
for LO VHF, HI VHF, and UHF. I have built a fixture which makes it easy to check them
out. It's just a 12 volt supply, a three position switch and a variable 0-30 volt supply
for the tuning voltage.
At a later date, I'll post some pictures of the tuners I have managed to figure out, and
show how to get them working.
It's getting easier to find old video cameras and camcorders. Each one contains a
tiny CRT which would make a tiny TV set which could be hidden just about anyplace -
tucked away inside one of your computer speakers, strapped to you hat, or hidden inside
what looks like the pencil sharpener on your desk.
As with the tuners, it's important to find a viewfinder which accepts a supply voltage
and composite video. Many of them require separate vertical and horizontal drive signals,
which makes them not worth the trouble.
More to follow at a later date
Neon flashers are far more efficient, but they aren't used as much these days. Way back in the
1950's, many people still had portable radios with tubes in them. I had a few myself. The B battery
which supplied the plate voltages was usually 67.5 to 90 volts. After these batteries ran down to
the point where the radio quit, there was usually enough energy to flash the NE-2 neon lights. It
only takes a few microamps to run them, so the flashers were usually soldered in place, and they
ran 24/7 for a LONG time. (Of course, they didn't use the term "24/7" back then.)
The major drawback here is the size of the B batteries. Some of them were as big as a pair of VHS
tapes, and somewhat expensive for their time. Nowdays, you can still buy them for industrial use,
but they're VERY expensive. How to get around that? I built several inverters which draw 10 mA from
a single flashlight cell, and provides 100 to 120 volts DC, with enough power to flash 10 neon lights
for many hours. In normal use, one AA cell will last a whole season.
More to follow at a later date
9-13-04
At the Rochester hamfest, I found luminescent cable. The same as the luminescent panels which
first came out in the 50's, but in the form of a wire. It's actually a sort of coax - one electrode
is the center wire, covered by electroluminescent phosphor. The other electrode is two very fine
wires over the phosphor. They can be found at lumi-line.com at very reasonable prices.
Let's go to another page titled
Tiny CRT's.
Finished a dipper. Found a simple Hartley circuit which works beautifully through VHF. The only reason I didn't add VHF is because there wasn't enough space on the dial to add another range.
Also finished a noise bridge. Works great - I found out that my random length dipole is only slightly capacitive, and very close to 50 ohms without any tuner attached.
