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rjrouquette / rgb_matrix_udp

udp based rgb panel driver using raspberry pi
The Unlicense
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Support separate +5V for RPi and LED panels #13

Open marekm72 opened 3 years ago

marekm72 commented 3 years ago

Considering a project to use this with a CM4 on a CM4IO board. This has its own +12V to +5V buck for the CM4 itself, but not enough power for the LED panels. So the panels need to be powered separately - but they (at least the one I have) clamp their inputs if higher than their power supply, so need correct power sequencing (panels first, then the driver).

If the '16244 drivers accept inputs (3.3V levels from RPi GPIO/DPI) without clamping to unpowered Vcc, I'd suggest to power them with +5V from the panels (not from the RPi GPIO connector) as they need a big power supply anyway, and you avoid putting extra load on the RPi power. Or alternatively - if drivers still powered by the RPi, they could be tristated if panel power is off (less than 0.5V below RPi Vcc). The Xmega would need to handle this too (disable output ports / protect input ports if Xmega unpowered but still driven by RPi).

I have just one 32x32 panel (1:8 scan) for now, and would like to free up some RPi GPIO by using one of the the 565 modes (if more panels needed, chain them by their hub75 out/in connectors), is this reasonably possible with this design?

rjrouquette commented 3 years ago

The schematics and board layout are already available and you are free to make your own changes per the terms of the [un]license. All you need to do to support a different GPIO mapping is change the DPI RGB bit mappings to match your preferred GPIO pinout. You will also need to alter the board layout if you drop any of the GPIO pins used by the XMega to capture the ABCDE bit banging values.

marekm72 commented 3 years ago

Thanks. Not sure if KiCAD imports from Eagle PCB properly yet (I see a few unconnected nets). The 18-bit RGB666 format would be good fit for 3 panel connectors (6 bits each), and the spare buffers could then drive separate CLK for each panel. 74ABT Voh_min specs seem a bit low for 5V 74HC inputs on the panels, does it work well for you? 74AHCT may be better (has all of: +5V power, TTL 3.3V compatible inputs, CMOS 5V output levels, inputs not clamped to Vcc when powered off). BTW, Xmega AU has USB which could be useful for remote upgrades from the RPi.

rjrouquette commented 3 years ago

The 74ABT series worked fine with my panels. The series doesn't matter much as long it has sharp output transitions and TTL compatible inputs.