Re: Scope using TV
Hello rx5,
Echo47 has a good idea there. The problem with trying to build an oscilloscope is that you tend to need an oscilloscope to find the bugs in it!
I bought a really cheap one (not working) from eBay a few years ago just to play with - I am still fiddling with it, trying my own input circuits etc. If you get one with the HV section working and just faulty input amps or timebase, it can be good fun making your own bits for it. But as I said, you really need another 'scope to test your bits.
Building one from a TV can be done in two ways:
1. Force the TV into "oscilloscope" mode, making the beam scan the screen and draw your input. This is quite easily done (there are several circuits on the web, all similar). This will suffer from very low bandwidth as the TV tube is simply not intended for this type of use.
2. Use the TV (or monitor) simply as a monitor and make a circuit that takes a signal, digitises it, buffers in a frame memory and outputs frames to the monitor. This can be much better as an oscilloscope (as echo47 said, it's what a digital 'scope does) but is more complicated to make.
Personally, if I wanted to try making a 'scope and did not want to buy one to test it with, I would use a PC soundcard and oscilloscope software (search the web). This should have similar or better bandwidth than an analogue-TV 'scope and is a lot easier to get!
My final advice (for what it's worth
) is:
First: buy a cheap, working 'scope or use a PC soundcard and software
Then: if you still want to experiment with 'scope building, buy a non-working basic 'scope (hopefully with a working beam so you know the tube and HV are OK) and design your own timebase and input circuits. I'm sure I have seen such circuits on the web, but I can't find the links. Try searching.
Ideally, get a service manual for the 'scope so you know what is what inside it. You might even find somewhere that will give you a junk scope for nothing.
Whatever you do:- enjoy it, learn, ask here when you get stuck, and don't get zapped by the HV (it hurts!!!)
FoxyRick.