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11 years ago.
Analog Inputs
Hi Mbed Community!
I'm new and excited to be working on my current project. I'm trying to make a box that will make my life a lot easier but need some direction and input from the community.
I have to be able to read differential analog input signals. My first thought was I would take two single line analog inputs and subtract them to get the differential value. Will this work?
Second, the analog inputs ranges from -5V to 5V for some devices and 0V to 5V for others. How can I go about scaling these signals accordingly while guaranteeing I have a constant scaling? I am taking readings from signal conditioners that are used to read Load Cells and Linear Pots.
I can elaborate more if needed
Thanks!
Josh
1 Answer
11 years ago.
The scaling should not be a problem. A network of 2 or 3 resistors is sufficient. Calculating the values involves some math. Look for superposition and thevenin equivalent. Converting a differential signal with two adc inputs will only work for very slow signals and common modes. The mbed has only one adc with a multiplexer on the input, so there is a time difference between the sampling of your two inputs. Unless your signal and the common mode are constant, this will result in a voltage error. Hence your common mode will not be completely eliminated and you will lose some of your signal. Therefore it is better to use an opamp or instrumentation amplifier.
Some random question, are you from Ngee Ann Polytechnic?
posted by WB Tan 30 Apr 2013