The Analog of Things Part 3
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When working off a project that you found online, we are often happy with the result once we see the analog value is being read and then converted. Case in point in Part 2 (The Analog of Things Part 2๏ปฟ), the moment we measured the 0.275mV on the sensor and then saw the 27.5 'C on the LCD display, we were happy - it's working.
Performing analog to digital conversion however is not that simple, especially when you are looking for accuracy. The 8BIT ADC for example has a lower resolution than a 10BIT or 12BIT ADC. The higher resolution may require a more accurate way to read the input value and ensure that the minor "step" that was converted to a digital value is not actually noise.
In most cases when you are getting to grips with ADC, you are using the single-ended input. There are a number of reasons for this.
- In most cases its performance is sufficient
- The code required to implement the solution is simpler
- Less wiring requirements
- It's cheaper
You may notice that from time to time real-world elements are mentioned. If you are going to have a successful career in this field, understanding the factors driving the success of a design is essential.
The inherent issue with the single-ended approach is that the moment the application is measuring a voltage differential in the mV spectrum, the noise or interference it generates automatically negates the value of its advantages.
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Single-ended and differential refer to the reference for a voltage. Single-ended is referred to as ground while differential is referred to as a secondary input or reference voltage.
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Single Ended: In this application. they are designed to be connected to the same ground level as the microcontroller and to provide their measurement result as an analog voltage signal on a single wire referenced to this common ground. All basic ADCs support single-ended operation.
Differential: A differential ADC measures the voltage difference between two inputs, one of which is the sensor, and the second is a reference voltage.
There is also the consideration that you may need to dust off a maths textbook to remember of these things worked. Shown below is the formula used to perform the calculation and to derive the value.
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If you are starting to focus on analog systems, working with these various options would assist in determining which is the best route to follow. There are a number of fixes that can be implemented to get around the noise and inherent drawbacks of a single-ended system.
Where a differential system is needed, the Radix Duo with a PIC16F1784 included offers this feature integrated with the device. You also have integrated opamps on the micro, so potentially a low part-density application could be achieved.
Fortunately, there is help, and a reference is provided below.
