[Coco] RGB to VGA boards, test equipment needed

[Barry Nelson]

What these people recommending expensive oscilloscopes are forgetting is that you want to look at the video SYNC pulses. The frequency of the horizontal sync from a color computer is only 15khz, which is in the audio frequency range. The vertical sync is even slower. That means, if all you want to see is the sync pulse even a cheap audio scope should give you a pretty good idea of what the sync pulse is like. The video pixels will be a fuzzy blur, but that shouldn't matter.

That means that these should work (at least somewhat):

http://makezine.com/projects/sound-card-oscilloscope/
https://www.zeitnitz.eu/scope_en
http://www.zelscope.com

Since your sound card can sample at up to a 44khz wave that means it should get at least 3 samples per period of a 15khz wave, it won't be pretty, but you should be able to at least see the H sync  pulse. You won't see the pulse shape but you should be able to see a spike and measure the amplitude and the timing. The vertical sync should show up in more detail as it is slower.

If you want to see the shape of the H sync pulse you will need a faster sample rate.

Something like this one:

http://www.ebay.com/itm/Hantek-6022BE-PC-Based-USB-Digital-Storag-Oscilloscope-2-Channels-20MHz-48MSa-s-/271265189899?hash=item3f28aa500b

Bandwidth: 20MHz; Sample Rate: 48MSa/s; 

Or this one

http://www.ebay.com/itm/SainSmart-DDS120-Pro-20MHz-PC-Based-USB-Digital-Storage-Portable-Oscilloscope-/300992154516?talgo=origal&tfrom=271265189899&tpos=unknow&ttype=price&ssPageName=STRK:MESE:IT

Bandwidth: 	20MHZ
Maximum sampling rate: 	50M/S





On Sep 6, 2015, at 10:22 PM, coco-request at maltedmedia.com wrote:

> Date: Sun, 6 Sep 2015 19:30:35 -0500 (CDT)
> From: "tim franklinlabs.com" <tim at franklinlabs.com>
> To: CoCoList for Color Computer Enthusiasts <coco at maltedmedia.com>
> Subject: Re: [Coco] RGB to VGA boards, test equipment needed
> Message-ID:
> 	<693991787.2888.1441585835674.JavaMail.vpopmail at atl4oxapp101.mgt.hosting.qts.netsol.com>
> 	
> Content-Type: text/plain; charset="utf-8"
> 
>   You might want to consider something like this... It's 100Mhz. There
>   are many of these from many different manufacturers. I can't speak for
>   this one personally but showing this for reference...
>   [1]http://www.circuitspecialists.com/usb-oscilloscope-dso-2250.html
> 
>     On September 6, 2015 at 6:43 PM Kandur <k at qdv.pw> wrote:
>     Thanks Gene.
>     What I really need these toys for is, to check the video signal's
>     sync pulses,
>     amplitude, shape and polarity.
>     Most of the time I would use these for to check audio signals.
>     Do these have X and Y direct inputs, like the analog scopes do?
>     I don't have room for large boxes anymore, like this
>     Tektronix 7623A 100 Mhz Storage scope, I used to have in my shop.
>     http://tinyurl.com/nbhla8n
>     Kandur
>     Sunday, September 6, 2015, 3:20:13 PM, you wrote:
>> On Sunday 06 September 2015 16:19:14 Kandur wrote:
>>> Would these pocket oscilloscopes do for checking video signals?
>>> If yes, wich one is better? Are there any others under $100?
>>> http://tinyurl.com/p9jx2ec
>>> http://tinyurl.com/ommymqs
>> eye.
>> above will, and because they are analog, often under priced on
>     ebay.
>> I have one of these:
>> 
>     <http://www.ebay.com/itm/Hitachi-V-1065A-Portable-Two-Channel-Analog
>     -Oscilloscope-100MHz-R-Type-w-Handle-/181840967212?hash=item2a5690f6
>     2c>
>> contains a good part you can use.
>> Cheers, Gene Heskett
>> "There are four boxes to be used in defense of liberty:
>> -Ed Howdershelt (Author)
>> Genes Web page <http://geneslinuxbox.net:6309/gene>
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