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[Q] Cutting Solder Pads on Chip

OP jennarachelle

17th May 2014, 04:50 PM   |  #1  
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Join Date:Joined: May 2014
Hi all,

Iím connecting 4 MPR121 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 GNDÖ

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?
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18th May 2014, 08:49 AM   |  #2  
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Join Date:Joined: May 2014
the add pin seems to be routed via the second jumper pad (counted from the bottom when looking on the picture youve posted)
just cut the trace between the solder pads with an exacto and measure with a multimeter if it is routed to ground at the left side (going to the chip) if it is not routed to ground you can connect to that pad.

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