The effect of R17 (68Ω)

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marcelk
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Joined: 13 May 2018, 08:26

The effect of R17 (68Ω)

Post by marcelk » 11 Feb 2019, 14:54

Today I characterised the effect of the 68Ω resistors on the video output. Their purpose is to give some form of termination. We more or less copied these from a design on the Arduino forum, without much additional thought. Of course, in the Gigatron, the game controller shares these lines, so emission wise this can give all kinds of "interesting" behaviour: the cables are long transmission lines / antennas, and the fork is not exactly standard.

So it's about time to attach a scope and see what's happening. I compared the rising and falling edges on both sides of one of the resistors (R17), for every combination of devices attached. I did the same with the resistor bypassed. The results are just for info. See this PDF on HaD for details: https://cdn.hackaday.io/files/207818890 ... %20R17.pdf

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