Go Down

Topic: External reset button? (Read 608 times) previous topic - next topic

TheAliw1

Oct 10, 2019, 12:47 pm Last Edit: Oct 10, 2019, 12:49 pm by TheAliw1
Hi everyone,
I was wondering about external reset buttons and I found two schematics:
#1 from: https://programmingelectronics.com/how-to-use-an-external-reset-button-with-arduino/

#2 from: https://content.arduino.cc/assets/NANO33BLE_V2.0_sch.pdf

What is the function of this capacitor in parallel in #2 and what is the value of the DNP resistor and what does DNP stand for?

jackthom41

What is the function of this capacitor in parallel in #2 and what is the value of the DNP resistor and what does DNP stand for?
It's always a best practice to use capacitors coz they reduce any noise or fluctuations in power line. If you are using a simple push button with Arduino then you can use a resistor of 1 K ohm. Don't know what's DNP.
My collection of Arduino Projects ====> https://www.theengineeringprojects.com/2015/03/arduino-projects.html

sterretje

The combination of R5 and C2 form a filter and is used for debouncing.

From what I can find that relates to electronics, DNP probably indicates 'do not place'.
If you understand an example, use it.
If you don't understand an example, don't use it.

Electronics engineer by trade, software engineer by profession. Trying to get back into electronics after 15 years absence.

raymw


MorganS

"Do Not Populate" is used when there are optional components. There will be holes or pads on the board but the normal manufacturing process won't place any component there. You can add that to the board yourself, if it turns out that your application needs it.

The capacitor is used to ensure a consistent reset when the power is first applied. It takes a little while for the capacitor to charge, so it holds the chip in reset state until (hopefully) the power voltage has come up enough for the chip to run properly. Without that, the chip may attempt to start in the first nanosecond that power starts coming up, which may be insufficient voltage for the chip to run properly.

If you are adding a reset button to an already-working Arduino board, use the first schematic.
"The problem is in the code you didn't post."

Paul__B

Without that, the chip may attempt to start in the first nanosecond that power starts coming up, which may be insufficient voltage for the chip to run properly.
Although that functionality is necessarily built into the chip.

MorganS

So why does the datasheet say it is required?

The chip will start up by itself under most, but not all, conditions. The cap just helps with a wider range of crappy power supplies.
"The problem is in the code you didn't post."

TheAliw1

Quote
If you are adding a reset button to an already-working Arduino board, use the first schematic.
This is what I am going for. Thanks!

I'm still quite interested to what you guys are saying about the capacitor. I understand I don't need it for an external reset button but I'd love to learn more about it so I'm watching your posts :)

Go Up