problem controling a nicrew 50W lamp

theatrus · Feb 7, 2023

The 400pF limit on I2C is generally fairly lenient. Its not a fast bus my any means, but thats why DDC over longer cables usually ends up with a more powerful driver to overcome the rise time issue. And VGA and HDMI cables where the link is used are shielded.

Longer runs? Just use RS485.

robsworld78 · Feb 7, 2023

theatrus said:
The 400pF limit on I2C is generally fairly lenient. Its not a fast bus my any means, but thats why DDC over longer cables usually ends up with a more powerful driver to overcome the rise time issue. And VGA and HDMI cables where the link is used are shielded.

Longer runs? Just use RS485.

Yeah but if drivers are being used then wouldn't that mean it's no longer what it was designed for? Those all came after. I can find a driver claiming 100 feet but that certainly wasn't the original intent. You're statement for 1 - 2 meters being ok I think is misleading if you meant with a driver. I know people and personally have experienced issues with just 1 meter of cable, it's not a good idea in my opinion.

theatrus · Feb 7, 2023

robsworld78 said:
Yeah but if drivers are being used then wouldn't that mean it's no longer what it was designed for? Those all came after. I can find a driver claiming 100 feet but that certainly wasn't the original intent. You're statement for 1 - 2 meters being ok I think is misleading if you meant with a driver. I know people and personally have experienced issues with just 1 meter of cable, it's not a good idea in my opinion.

Its kinda being pedantic, but its still electrically the same bus. Similar effect with increasing pull-up strength. Again, its a niche application, and all of the usages are shielded and at slow speed (100kHz). YMMV, and I agree its hard to recommend running it off board :)

Sral · Feb 7, 2023

Well, scaling down the frequency to 10kHz due to the pH circuit likely makes the I2C pretty forgiving, so I believe this shortening of tracks and avoidance of „Y“ shaped splits might be unnecessary.
Doesn’t hurt though, if you still have enough space for everything else ^^