LEDs to show IO-status influence on connected hardware

StefanL38

I want to build a propeller-chip experimentation board.

For easy watching the status of the IO-pins I would like to connect LEDs through some kind of
a driver-chip (74HC244? LM324 as voltage-follower?). combined with a current-limiting resistor.

Propeller-IO-Pin

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390 Ohm---x---> to peripheral chips.

At "x" connected to the driver-chip. My knowledge about electronics is quite good except for things
like parasitic capacitance, and the influence of resistors on the perfomance of high frequency signals.

What kind of driver-LED-circuitry would you suggest and what would be the limits on high-frequency signals? (I mean things like
- would a 400 kHz I2C-bus still work properly with these status-LEDs connected?

- would a 1 MHz SPI-bus still work properly with these status-LEDs connected?

- would a TV-signal still be possible with adpated DA-resistorvalues?
- would a VGA-signal still be possible with adpated DA-resistorvalues?

any kind of comments and ideas are much appreciated
best regards

Stefan

kwinn

I would go with high efficiency leds and a 2K7 to 3K3 resistor to the pin being monitored. The prop drive capability should ensure there is no issue due to parasitic capacitance or other effects.