Something wrong with port 4 & 5 for olimex 328 board

Started by leochengboon, August 06, 2013, 05:16:34 PM

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Hi, I'm actually using olimex 328 board with 2 EMG shield. The AIN_SEL for first shield is 1. The AIN_SEL for second shield is 3. Supposingly, it means that the analog port for 1 and 2 are taken. I plan to have the remaining 4 analog ports for my 4 force sensitive resistor sensor.

The arrangement of my FSR is similar to this, except the ports taken are 2,3,4,5.

The arduino code I used for fsr sensor is here under In-Depth Code for Analog FSR Measurements on this website,

The problem I face is there's analog reading for port 4 & 5 as shown

Supposingly, it should be zero value if I didn't apply any force.

Is it related to the SDA and SCL of the ports?

I've tested the port 4&5 with only olimex 328 board, it shows the same results.
Please give me advice. Thank you.


Hello Leong,

Sorry for the delay in answering – we had summer vacations!

There are pull-ups on the analog 4 and 5 lines near the UEXT! They are causing the troublesome readings.

How to proceed would depend if you have revision B or revision C of the board. If you have revision C then unsolder and cut between the pads of the R23_E and R24_E jumpers – this would remove the 3.3V from the analog 4 and analog 5 lines. If you have revision B of the board there are no such jumpers and you would have to unsolder resistors R23 and R24.

Hope this helps.

Best regards,
Technical support and documentation manager at Olimex