debouncing on NRF52 Preview DK

[Lakerno]

infocenter.nordicsemi.com/index.jsp

I see a debouncing filter in the block diagram of NRF52 preview DK. Isnt debouncing implemented in software? So why need a HW debouncing filter?? which part of the schematic (ie. component numbers) refers to this debouncing filter from the block diagram?

thanks

[MartinBL]

Hi

Short answer: The debouncing filter is not inside the nRF52 IC. The filter is only used when you are using an external shield on top of your nRF52 DK. When using a shield the buttons get disconnected from the GPIO pins on the nRF52 IC and are instead routed to an I/O expander which is susceptible to "button noise" and needs a filtered input signal. Below I have posted parts of the nRF52 DK schematic (found here) showing how the blocks in your link are connected electrically.

The switching block, U4, is a NX3DV2567) double throw analog switch that connects the button inputs either to the nRF52 IC directly or to an I/O expander depending on whether or not a shield is detected on the SHIELD_DETECT line. If no shield is detected then the button inputs are routed directly to pin 13-16 on the nRF52 IC. If a shield is detected then the button inputs are routed through a filter to an I/O expander, U7, which is a PCAL6408A. This expander allows you to use TWI to control GPIOs on the shield and hence, save some GPIOs on the nRF52 IC.

Summary:

If you are not using a shield, buttons are connected directly to a nRF52 and you are expected to do debouncing in software, e.g. by using the Button Handling Library.

If you are using a shield the buttons need to be filtered because they will be routed to an I/O expander that doesn't do software filtering.

[oliverhu]

since i found NRF52 has inside pull up resistor, could I directly connect the button to the reset pin without pull up/ pull down network.

[Lakerno]

Clear Explanation. Thank you! Martin. Also can you clarify, if a pullup/pulldown resistor is required if a pushbutton switch is connected to P0.21/Reset to ground?

[Lakerno]

I have connected a push button switch to generate an interrupt as below. Based on your explanation, I am not adding any HW debouncer to this pin. Also may I know, if I need to add any pullup/pulldown resistors? thank u

[MartinBL]

There is an internal pull up on the reset pin of about ~13kOhm so unless you are particularly vulnerable to ESD or noise an external resistor should not be necessary.