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Blanking the retrace - Analog scope

:: EPE Chat Zone ­:: ­Radio Bygones Message Board :: » EPE Forum Archives 2007-2009 » Archive through 28 July, 2009 » Blanking the retrace - Analog scope « Previous Next »

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atferrari
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Username: atferrari

Post Number: 737
Registered: 05-2005


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Posted on Sunday, 19 July, 2009 - 03:45 pm:   Edit Post Delete Post Print Post    Move Post (Moderator/Admin Only)

I managed to show on my scope a symbol formed by several dots by controlling voltages at the X-Y axis.

To make it neat I would need to blank the retrace between dots.

My scope is an old analog TRIO 10 MHz CS1562A. Couldn't find the manual but a PDF version found in the Web says that "modulation" may be done "at TTL" levels.

Just in case, I tried myself bringing the Z axis input to 0V and 5V, getting only a change in brightness.

Is it any way I could blank completely the retrace in between spots?

(Message edited by atferrari on 19 July, 2009)
Agustín Tomás - Buenos Aires - Argentina
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joe
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Post Number: 588
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Posted on Sunday, 19 July, 2009 - 04:10 pm:   Edit Post Delete Post Print Post    Move Post (Moderator/Admin Only)

I created a scope display for my Z80 system many years ago.

It was tricky to work out how long to keep the beam in one place to display the "dot" against the persitance of the scopes display to fool my vision.

I never had to blank the display tho if I had the brightness turned up too high, you could sometimes see the traces between the dots and the fly-back, as the display went back to the start of the display.

If you display a dot for a period of time, and then move quickly to the next location, I would be supprised if you saw the trace between the two points.

I can't think how you would blank the actual display on a scope without making modifications to it.

Joe
Do one thing each day that scares you – work here !
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atferrari
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Username: atferrari

Post Number: 738
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Posted on Sunday, 19 July, 2009 - 04:24 pm:   Edit Post Delete Post Print Post    Move Post (Moderator/Admin Only)

Hola Joe,

Were you bringing both axis back to position zero (0,0) after "making" every dot?

My initial attempt was made jumping straight from one dot to the next.

I am not using latches so I update ports one after the other what contributes to the blurr.

Had I been able to blank the retrace between updates I could see only the spots free of any trail.

While I believe that a voltage out of "TTL levels" could actually blank all, I am affraid to put in risk the only scope I have.

(Message edited by atferrari on 19 July, 2009)
Agustín Tomás - Buenos Aires - Argentina
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joe
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Post Number: 589
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Posted on Sunday, 19 July, 2009 - 05:21 pm:   Edit Post Delete Post Print Post    Move Post (Moderator/Admin Only)

Hi Agustin,

If I remember correctly, and its going back a good few years now, I used 2 x 8 bit digital to analogue converters, connected to the X and Y scope inputs respectfully; this gave me a matrix of 256 x 256 dots. I can't remember if I used bought IC's for this or just made a simple D to A using resistors. Since I was on pocket money I may well have used just resisors, at the start of the project anyway.

All I then did was to select each "dot" that was required, wait a little while for it to be shown and my eye to register it, and then move onto the next one.

The spacing between each dot is controled via the voltage on each step of the D to A converter and the Volts/Div control on the scope of course. I have a feeling that I never ran it to 256 x 256 but only 64 x 64 but I can't remember why.

However, thinking about it, because you have to "wait" whilst each dot is displayed, it may have been that if a lot of the dots were active, the display ran too slowly and flickered but I really can't remember now.

I also remember experimenting with placing small capacitors on the outputs of the D to A converters to cause lines between the dots to be displayed; I was experimenting with wire-frame graphics at the time.

I do remember that the software I wrote was horrible. I used loads of memory to store the patterns to be displayed and didn't have much left for my actual program; that could also be why I never ran at 256 x 256 as I was short on very expensive RAM (in those days).

Joe

Sorry, never answered your question.
I moved from position to position (top left of the display to the bottom right), and then back to the top left. That may not have been the best way, I don't know.

(Message edited by joe on 19 July, 2009)
Do one thing each day that scares you – work here !
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atferrari
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Username: atferrari

Post Number: 739
Registered: 05-2005


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Posted on Sunday, 19 July, 2009 - 05:34 pm:   Edit Post Delete Post Print Post    Move Post (Moderator/Admin Only)

Before commenting, let me tell you that the problem is solved: applying -5V did the trick.

Well, it seems that I am also doing more or less like you with two R2R networks including a CA3140 as a buffer fed by +9V in singe supply. The whole carefully breadboarded to speed up the hardware part, being concerned more about the software side of this.

The micro is a PIC at 16 MHz.

I need now two lines of code to trigger/stop the trail blanking to make it neat.

Eventually I will start a new post if I come out with something worth to be shown.

Gracias Joe for replying.
Agustín Tomás - Buenos Aires - Argentina
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atferrari
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Post Number: 743
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Posted on Sunday, 26 July, 2009 - 11:44 pm:   Edit Post Delete Post Print Post    Move Post (Moderator/Admin Only)

After solving (temporarily) the blanking pulse (0 to -3V) at the Z axis input, I got a neat image on the screen eliminating the trails when the beam changes the position along the x and z axis.

Just for the sake of completness see somewhere else in this forum, my post about switching a 2N2222 with a 1.8 usec pulse.
Agustín Tomás - Buenos Aires - Argentina

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