If you can't beat 'em, join 'em.
Following a discovery that the I am working on a revised design based on SN7407 level shifters.
(If you want a board from the the buffers work as expected, please PM me for details.)
Simple enough circuit but I have several questions.
First off: any problem with cascading the buffers this way? The idea is to have a switchable output between +5 (also serving as Vdd for the ICs) and an adjustable voltage which is derived from a low-dropout regulator (say 12 V or higher).
It is more simple to route when the output of the first buffer connects to the input of the second, but would it be better to tie the inputs of both buffers together instead?
What should the handling of MIDI IN 3 and MIDI OUT 3 be?
Presumably MIDI IN 3 should go through an optocoupler with a 3.3 V pull-up on the Core side:
http://ucapps.de/mbhp/mbhp_core_lpc17_midi3_midi4_extension.pdf
Hence, no level shifting is necessary I think.
But for MIDI OUT 3?
From the Quad-IIC schematic it is not clear whether the signal needs to be level-shifted. Will a 3.3 V output be compatible with the 8-bit core of the BLM?
In this case, MIDI OUT 3 is level shifted:
http://ucapps.de/mbhp/mbhp_core_lpc17_output_buffers.pdf
For these two, it isn't:
http://ucapps.de/mbhp/mbhp_core_stm32_midi3_extension.pdf
http://ucapps.de/midibox_blm/blm_connector_mbseq.pdf
There is a 3.3 V pull-up for the LPC core:
http://ucapps.de/mbhp/mbhp_core_lpc17_midi3_midi4_extension.pdf
Even though I will not use the LPC core, I plan to make it compatible with both for the greatest flexibility.
Some clarification would be welcome.
Cheers,