the efficiency of the power conversion process.
Unless you have a large supply of free power IGBTs
(Insulated Gate Bipolar Transistors) or power MOSFETs
and have a lot of experience tracking down and eliminating
stray capacitances and inductances, a vent hood for
venting the magic smoke that you are sure to let out of the
power transistors, and a lot of life insurance, building your
own inverter is to be avoided at all costs. I suggest buying
a Variable Frequency Drive (VFD). At least some of them
will work from a DC supply. Here is just the first site I found
Bay Village, OH
[4045 — April 2004]
Many years back, there were ads in the electronics
magazines about converting a TV to an oscilloscope.
Does anyone remember how this was done?
The best article of that time period was in Popular
Electronics, September of 1982, page 63. The title was
"Turn Your TV Screen Into an Oscilloscope. Low Cost
Device Operates Without Modification on Connections to
Your Television Receiver."
This unit sensed the television vertical sweep magnetic
field with an antenna outside the case of the TV. Each
successive TV horizontal line then became another step in
the time base, i.e., rotated 90°. The horizontal oscilloscope
time base (X) was displayed on the TV as a vertical line
starting at the top left and moving to the lower left. The
sweep rate was always fixed at the TV vertical refresh rate
of 30 Hz.
Oscilloscope amplitude informa-tion (Y) was
presented as the displacement to the right of the horizontal
trigger line, presently described as the left side of the
screen. To allow viewing negative as well as positive
signals, the TV horizontal hold control could be adjusted so
the TV horizontal sync bar would be displaced to the
middle of the screen. This was usually rather unstable and
not always a straight vertical line.
The oscilloscope vertical signal information was
coupled back into the TV as interference into the TV
antenna so that it bled through the tuner. There is no signal
trigger, but some synchronization was accomplished by
adjusting the vertical hold control.
The circuit is pretty slick: a + 6 and - 6 power supply, a
741 opamp with input signal range scales, a 555 timer for
output, a transistor for sync input, and an antenna to do
the input and the output coupling. Unfortunately, it was
limited to the lower audio frequencies with a fixed 30 Hz
time base and the time base was unstable with only the TV
vertical hold control to help position the signal.
Although limited, the author deserves a compliment
for innovative thinking. It is a pleasure to see what was
attempted with limited resources over 20 years ago.
This is all that I can reconstruct. A good online search,
the Popular Electronics archives, or a scientific
library is probably a good place to find the magazine
[5046 — May 2004]
I have owned a Fluke 8020A multimeter for about
10 years. It is no longer usable, as the display has
turned black. I have contacted Fluke and they do not
have a replacement display for this meter — their
solution is to buy a new one. Does anyone have a
solution to my problem?
#1 I had the same problem with a Fluke 8024 15 years
ago. The problem is caused by prolonged storage at high
temperature — over 130° F. A week in the refrigerator (not
the freezing compartment) cured it. It is still in regular use
today. I don't know if your display is too far gone to be
restored this way, but it worked for me.
#2 Buy a used unit for parts/replacement on eBay. The
day I checked, there was one for $9.99. I suspect, given the
cost of new LCDs, that this is a cheaper route.
Jon H. Peterson