Digistump Forums
The Digispark => Digispark (Original) Support => Topic started by: DuinoSoar on July 18, 2019, 02:14:08 pm
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Hello, again.
For some of my potential DigiSpark projects, I am wondering about using pins PB1, PB3 and PB4 for functions where the on-board LED (for PB1), or the USB port (for PB3 and PB4), are not required for the application.
With the various resistors, Zeners, and the LED hanging off of these pins (and, don't forget about that 1.5 K pull-up on PB3 near the USB connector!), what special precautions (if any) need to be considered when using these pins in any of their available functions?
For example (and without limiting the discussion to these), in reference to the "official DigiSpark schematic" at https://s3.amazonaws.com/digistump-resources/files/97a1bb28_DigisparkSchematic.pdf (https://s3.amazonaws.com/digistump-resources/files/97a1bb28_DigisparkSchematic.pdf) [PDF]:
- How would the USB components (R1, R2, R3, D1 and D2) affect using PB3 or PB4 in the various digital or analogue modes?
- Could PB3 even be used as an analogue input, given the R3 pull-up (1.5K)?
- What about trying to use PB3 as digital input WITHOUT pull-up? Is that even possible?
- How would the LED and the R5 "pull-down" affect the use of PB1?
Is there a web page or document somewhere that describes these issues?
Oh, and while I am at it, is diode D3 (connected between the USB +5V pin and the board's +5V Vcc "rail") being used in some kind of special mode, or is that an error in the schematic (i.e. it looks backward)? And if it is an error, why has this "official schematic" never been corrected?
Thanks and best regards,
DuinoSoar.