TV to Oscilloscope conversion.

[Ferroto]

I saw a project awhile back where a TV was converted into an oscilloscope. Basicly on the back of a CRT there are two coils one that controlls the x deflection of electrons and the other that controls the y deflection. According to the tutorial all you do is connect the x defliction coil to a sawtooth generator and the y defliciont coil to your test signel.

Recently I was at a yard sale and found an old portable black and white TV for 5 bucks and figured I'd give it a try.

This is the tutorial I'm following. It tells me to connect the horizontal deflection coil to the location on the board where the vertical coil used to be but I want to be able to adjust the timebase which means some type of variable sawtooth generator I'm thinking a 555 timer. I still don't know how I'm going to do the triggering circuit.

I was wondering has anyone here taken on this type of project before.

[saturation]

In the 1970s, a TV to scope converter was my very first scope, but what I built included an RF  modulator so the TV needn't be opened and hacked for safety reasons.  You could also use any TV tuned to channel 3 or 4.  The downsides were many, but it was cheaper to build then than buy or have nothing at all.  Today, the quality will be far less than if you simply refurbished a used Tek.   You could also do this with an old CRT monitor on the same principle.

http://markbowers.org/home/crt-oscilloscope

[IanB]

The major issue with X-Y deflection coils is that real oscilloscopes use X-Y deflection plates (electrostatic instead of electromagnetic). I think the use of magnetic coils will produce major bandwidth and signal distortion problems.

These days you could do much better by using a USB scope or a computer sound card and plotting the results on the computer display. For sure you would be limited to low frequencies, but I guess a converted television would have much the same limits.

[EEVblog]

It's a very 70's type project to build.
Few would build one these days for anything useful, but I have seen a few recent builds around. Sorry, no links to hand.

Dave.

[deephaven]

The 'modern' way of doing it would be to create a frame store out of memory. This is then addressed with horizontal and vertical address counters which correspond to the H and V timing required to make a valid TV signal. The input side would write into memory to produce the desired display waveform.

The above is a slightly simplified explanation of what would be needed!

[RCMR]

Wow... brings back memories.

Back in the 1970s I made a lot of beer-money by converting old B&W TV sets into oscilloscope-like displays that were very popular at discos.

You'd simply hook the Y-axis of the yoke up to the output of the audio section (ie: instead of the speaker) and feed the music into the top of the volume pot.

The X-axis of the yoke would be hooked up to the output of the vertical output stage (thus giving a 20mS scan rate).

Some strips of coloured cellophane over the front of the mono CRT and you'd get a truly excellent multi-coloured oscilloscope-like display.

I'd buy the old TV sets for about $20 each and sell the "DiscoWave" units for about $50 each (remember 1970s dollars).   I used to earn about $50/hour doing this and couldn't keep up with the demand.

Works really well for audio frequencies.