As requested by firmware we are including:
Two green power on LEDs, one for 5V and one for 3V3
Two blue debugging LEDs on the H7 Chip
Three red debugging LEDs on the F0 Chip
For the package I went with 0603 for the LEDs and resistors I sourced. When connecting the debugging LEDs to the microcontroller they are connected with any GPIO pin that isn’t already being used by something more important. In order for the LEDs to be turned on the microcontroller pulls the pins high and the power on LEDs are perpetually on when power is applied.
For determining the resistor resistance that is required the following formula was applied:
V(applied to LED by circuit) - V(feed forward of LED) = I(desired current draw of LED) x R(resistor in circuit)
For determining the ideal current value there was much deliberation, but after talking with mentors we decided that we should target I=0.5mA. Keep in mind for our calculations we will use “standard” units so I=0.5mA means I=0.0005A for our calculations.
The voltage applied to the LED by circuit is nominally 3V3 as that’s what the circuit voltage is. The Feed Forward voltage can be found on each LEDs datasheet and each different colored LED I found had a different feed forward value so these calculations were done multiple times.
The resistance value is what we are trying to determine and is what we will use for the resistor in the LED. It should also be noted we can swap these LEDs after the fact if the LEDs are too bright or too dim, but these estimations should be a good start.
LED selection was fairly simple, sorted by color and package and then went by cheapest with stock. They all contain curves showing how bright they should be for the amount of current they draw, but all of this isn’t very important as long as the feed forward voltage of the LED is less then the voltage we have in the circuit which is 3V3.
For the 5V power on LED we see (5V)-(2.1V)=(0.0005A)x(R) leads us to R=5800ohms=5.8kohms. However, this is a fairly non standard part and stock was not available for the part so I went forward with a 5.9kohm=5900ohm resistor which redoing the calculators (5V)-(2.1V+=(I)x(5900) shows that we get I=0.00049A=0.49mA which is close enough.
For the 3V3 power on LED we see (3.3V)-(2.1V)=(0.0005A)x(R) leads us to R=2400ohms=2.4kohms.
For the F0 debugging LEDs we see (3.3V)-(2.8V)=(0.0005A)x(R) which leads us to R=1000ohms=1kohms.
For the H7 debugging LEDs we see (3.3V)-(2.0V) = (0.0005A)x(R) leads us to R=2600ohms=2.6kohms. This is once again a nonstandard resistor that either isn’t produced or isn’t widely in stock so I rounded down to 2.55kohms resistors which is extremely similar.
One thing to note about the LEDs is that they are diodes, hence the reason why they have a feed forward voltage, and therefore must be oriented the proper direction with ground on pin 1 and the resistor and power being on pin 2.