Cutting solder pads on chip

Other Hardware General Electronics
1

Hi all,

I’m connecting 4 MPR121 (https://www.sparkfun.com/products/9695) chips to an Arduino Mega. My schematic is fairly straight forward:

The 4 are going to a breadboard. Breadboard is going to Arduino.

PWR > 3.3v
GND > GND
SDA > Digital 20
SCL > Digital 21

IRQ > Sensor 1 - Digital 2
Sensor 2 - Digital 3
Sensor 3 - Digital 19
Sensor 4 - Digital 18

Now, so that the 4 sensors can have separate addresses, I need to modify 3 of the sensors, via the ADD pin, as the MPR121 address is configured by connecting the ADD. By default, ADD is connected to GND, so I have to open this jumper.

Sensor 1 - unmodified (0x5a)
Sensor 2 - ADD to 3.3v
Sensor 3 - ADD to SDA
Sensor 4 - ADD to SCL

I have two questions:

  1. Can I open the jumper by simply severing/damaging the ADD solder pad seen on the back of the MPR121 attached? Thus disconnecting ADD from GND…

  2. Next, to solder this ADD to 3.3/SDA/SCL, do I solder a connection from/to the tiny hole (one of 4) beside the ADD to the tiny hole (also one of the 4) beside 3.3 / SDA / SCL?

Thanks in advance!

09695-03.jpg
09695-03.jpg600×600 129 KB

2

  1. Between each pair of solder pads there's an existing, very short trace -- it's barely visible. To disconnect you just need to use a razor knife between the pads.

  2. I think the easiest way would be to add a wire between ADD and 3.3V, SDA, or SCL between the larger, six holes on the left edge of the board. You can do that on either the top or bottom side of the board so it shouldn't interfere with any pin headers or other wires you're planning on connecting those those holes.

The "four tiny holes" are "vias". They're there to provide a current path between the top and bottom of the board. I don't think it's a good idea to attempt to solder anything to them; they're not designed for that.

3

Chagrin,

Thank you so much. I'm ready to get work.

Much appreciated.