Pull-up resistor - which value?


I need a pull-up on D13 to control a PSU with high as off. I need at least a 470Ohm resistor? Is this fine for pull-up? The arduino can bring down the output without any problems. If I use higher values the voltage is too low at boot of the arduino.


Your description is a bit vague without a schematic, but 4k7 on an Arduino pin is not going to harm anything. If it works then it's OK.

No, it’s 470.

The resistor is R11. I planned 10kOhm but the voltage is too low then.


Sicherheitsschaltung_Ladekoffer_Schaltplan.zip (1.08 MB)

No, it's 470.

Sorry, I read 407Ohm as 4700 Ohms :confused:
470 Ohms will give just over 10mA at 5V, which is fine.
(5 / 470 = 0.0106)

You can calculate that quite easily using an ohm's calculator, they are available on line. Look at what the arduino can supply as far as current etc on its D13 pin, remember it is already connected to the on board led. DO NOT run these pins at max output, 1 or 2 possibly but no more, the chip has limits which can be gotten from the data sheet. This pin will cycle at unexpected times when download code etc, this could damage your PSU. I would suggesting using another pin if you can. Ohm's law calculator: http://www.ohmslawcalculator.com/ohms-law-calculator This response is to help you get started in solving your problem, not solve it for you.
Good Luck & Have Fun!

Still checked this and 470 is fine.

The tip with D13 during firmware uploads is good. I like to use it to check the PSU controloutput without a PSU connected. But during testing it would be better to use another one. So every other Pin should stay on its status or become floating during firmware upload? Will check this...

BTW. Connecting USB and Vin in parallel is not a problem?


Is there a reason you need to use D13?

I ask because the reason you need such a strong pullup is probably because of the load from the LED on that pin (I'm guessing the board isn't an Uno or Mega, as those two buffer pin 13 so the LED doesn't load down the pin). With literally any other pin except 0 or 1 (which are used for serial, and hence have all sorts of other complications), a 10k pullup would be fine.