MicroPython Forum (Archive)

Hello pyboard community.

I was playing with my extension board LCD32MKv10 (LCD screen plus four buttons); when I noticed that the buttons are handled by a capacitive touch sensor: the MPR121.

This means that the same extension board is equivalent to having
http://www.exp-tech.de/sparkfun-mpr121- ... kout-board
or a
https://www.adafruit.com/products/2340

thus enabling cool stuff like https://vimeo.com/127429518 (minus the PC)

Looking at the schematic all 12 capacitive touch sensors are exposed on J3 http://micropython.org/resources/LCD32M ... matics.pdf.
(similar to the sparkfun breakout board http://dlnmh9ip6v2uc.cloudfront.net/dat ... ut-v13.pdf )

My question is simple: what is the role of R8-R11 ? are they really 0 Ohms ?

thanks for your replies !

Zero ohm resistors have many purposes. I'll list some general purpose reasons.

1 - They could be replaced by non-zero ohm resistors (perhaps for tuning)
2 - They're often used as test points, especially when using chip packages like BGA or multilayer boards. Having a zero ohm resistor forces the traces to come to the surface (otherwise some traces might wind up only being on inner layers)
3 - They can be added/removed to modify functionality. For example, the discovery boards come with a bunch of onboard peripherals which are connected using SB (solder ball) connections, which are effectively zero ohm resistors. These can have the solder balls removed and then the pin could be used for a different purpose.

In the case of the LCD32MK board for the pyboard, the MPR121 actually supports upto 12 capacitive touch switches. So if you wanted to add an external panel with 12 switches you might not want to use the 4 on the board. Removing the zero ohm resistors would allow that to happen.

Thanks for the answer, that makes sense ! (zero ohm resistors are there to allow to remove them)

The removal of 0 Ohm resistor will allow you to add extra touch switches in case of LCD32MK board for the Python Board. 0 ohm resistors have many purposes like they are used for tuning. Also sometimes they are used for the test points. Also sometimes they gives the flexibility to modify the design.