Displaying video on a Trio 10MHz scope using the Z input.
Considering the postings in sci.electronics.design, memories of old analog electronics came,
so I decided to also show some stuff on a scope.
But why not real video? Why so difficult with X, Y only, when we have a Z axis input?
So I started soldering some components together, a so called 'haystack'.
Wanted to use a 9V battery, but it turned out to be flat and a bit low voltage for the output swing I needed,
the Trio's Z input seems to drive drive the CRT directly, soldered in a 12V DC adapter (not stabilised).
This is what the haystack looks like:
Connected it to my Cyberhome DVD player, And this is what it looks like in stop mode.
And this is what it looks like in play mode:
Even subtitles are very readable (sorry for unsharp pictures, this camera has fixed focus lens and gets no closer,
had to use 'nightshot' to get any picture at all.. Image is not that bright).
And here is the diagram:
Just used parts from the junk box, whatever I found...
The scope timebase is triggered from the video input in 'external' mode, and 'TV trigger' is selected, adjust for 64 us full screen sweep (H),
The video is first amplified and inverted by J1, so sync pulses are positive, and then fed to sync separator Q3.
It is also fed to the output stage Q2, that inverts again, driving the scope CRT grid negative on sync,
so sync is black, and white becomes green.
The vertical 'timebase' does not exist, C3 , R6, R12 form an integrator to filter out the V pulses from the composite sync at the collector of Q3.
Q1 shorts C6 against + at each V sync pulse, while J2 (yes I used 5 transistors!) is a current source that slowly in a linear way
discharges C6 so we have a nice linear ramp in V sync at C6, that we feed into the Y input of the scope.
We do NOT use the X input, just normal one channel scope mode.
One note, the V ramp will stop if no input signal, the scope will not burn in with just a H trace,
but in a real TV application one would for example use an UJT, also for H osc.
Do you see that adding just _5_more_ transistors will make this a monitor?
One V oscillator, one H oscillator, 2 drivers for the deflection plates - or coils -, and one to generate the HV voltages.
And the same if driving a real magnetic defection CRT.
Analog TV was so simple.
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