ScriptOhio
Everybody is somebody else's weirdo.
Turn it into an oscilloscope:
Turning a TV (or monitor) into an oscilloscope?
This question comes up so often and it does sound like a neat project to give a defunct TV a second life. Don't expect to end up with a Tek 465 on the cheap when you are done. However, it could be a fun learning experience.
CAUTION: See the safety recommendations below.
You will be severely limited in the performance of such a scope. TVs and monitors are designed to operate at a very narrow range of horizontal scan rates and the high voltage is usually derived from the horizontal deflection. So, you would need to retain the original deflection system for this purpose at least.
Turning a TV (or monitor) into an oscilloscope?
This question comes up so often and it does sound like a neat project to give a defunct TV a second life. Don't expect to end up with a Tek 465 on the cheap when you are done. However, it could be a fun learning experience.
CAUTION: See the safety recommendations below.
You will be severely limited in the performance of such a scope. TVs and monitors are designed to operate at a very narrow range of horizontal scan rates and the high voltage is usually derived from the horizontal deflection. So, you would need to retain the original deflection system for this purpose at least.
- You will need to disconnect the deflection yoke from the horizontal and vertical deflection circuits of the TV or monitor without killing the HV. (also, doing all this without killing yourself as well). Depending on the design, this may be as simple as unplugging the yoke connector. More than likely, you will need to substitute a load for the horizontal deflection coil. A coil from another sacrificial similar TV or monitor would probably suffice.
Warning: at this point you have a really bright spot in the middle of the screen which will turn to a really black spot if the brightness is not turned way down really really quickly. - For the horizontal, you need a ramped current source. You are driving a non-ideal inductor (the deflection coil) so it has both inductance and resistance. Thus the waveform is a trapezoid - a voltage ramp (for the resistive part) superimposed on a voltage step (for the inductive part). This should not be too difficult. Don't expect to be able to achieve really fast sweep. Even running at normal TV rates is non-trivial.
- Similarly, for the vertical you need to drive with a voltage (your signal) controlled current source. However, if you are just screwing around, then the linearity etc. for the vertical may not be that important. In this case, one way is to put a current sensing resistor in series with the deflection coil and use this in a power op amp type of feedback arrangement. (You could do this for (2) as well.
- There is a good chance that the original brightness control will work as an intensity adjustment. However, with some TVs and monitors, this depends on receiving a valid video signal. You may need to improvise. If you do want to control the intensity from a signal source, you should be able to tap into the drive signals going to the little board on the neck of the CRT.
- Don't expect high bandwidth, uniform response, or any of the other things you take for granted with a decent scope. That takes work. However, as a fun project, this certainly qualifies. Interchanging the functions of the horizontal and vertical deflection yoke (and rotating it 90 degrees) may provide a better match of horizontal and vertical bandwidth to your intended applications or experiments.
- With a color TV or monitor, these experiments could be quite interesting and educational but there may be color fringing effects since you are not compensating for certain aspects of dynamic convergence at all.
- SAFETY: Once you disconnect the deflection yoke from the TV or monitor's circuits, move the original circuits out of the way and put a barrier between between you and the rest of the TV or monitor. All you will need are connections to the deflection yoke on the CRT (unless you want to do intensity modulation in which case you will need to drive the video output(s) to the CRT cathodes. I would recommend against doing this if your unit is one of those with a totally 'live' chassis as there would be additional safety hazards and circuit complications).
Upvote
0