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.
(http://thumbnails102.imagebam.com/26917/68ab10269164027.jpg) (http://www.imagebam.com/image/68ab10269164027)
The arduino code I used for fsr sensor is here under In-Depth Code for Analog FSR Measurements on this website, http://learn.adafruit.com/force-sensitive-resistor-fsr/using-an-fsr.
The problem I face is there's analog reading for port 4 & 5 as shown
(http://thumbnails105.imagebam.com/26917/310358269164022.jpg) (http://www.imagebam.com/image/310358269164022)
Supposingly, it should be zero value if I didn't apply any force.
(http://thumbnails104.imagebam.com/26917/ee274f269164016.jpg) (http://www.imagebam.com/image/ee274f269164016)
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,
Lub/OLIMEX