analogpotentiometer
I want to measure degrees using linear potentiometer, so I thought to use the AD 676 analogue to digital converter (ADC) IC.
Is this a good ADC for monitoring a potentiometer?
If so, how can I use it? A schematic of an example implementation would be helpful.
This is a very general question and there are lots of app notes with reference designs for mixed signal boards. "mixed signal", "digital analog", "design" and "ground" are your keywords. In addition, usually every datasheet of a mixed signal controller or DAC contains a reference design.
A common method for protecting analog inputs is a Z-Diode and a series resistor. You have to realize the overvoltage protection requirements and the DAC leakage current to calculate the series resistor value. As you can see in http://www.atmel.com/dyn/resources/prod_documents/doc2508.pdf a series resistor can protect an analog input even from mains voltage.
Yes, you can use a resistor divider for scaling an analog input. If the input resistance is too low, use an transistor/opamp as a voltage follower.
For digital inputs you can use resistor dividers/series resistors, too, which is the slowest of the mentioned methosd. For up to 15V you can use a 74HC4050 buffer. If it need to be really quick, you're probably better off with a dedicated level shifter IC.
Draw on paper.
Post anywhere OR email to me and I will post. apptechnz@gmail.com.
ANY diode in the signal path will affect accuracy badly.
Probably error of about +/- 0.1V best case or 2% at 5V or 20% at 0.5V.
If you must multiplex ADC use a "real" multiplexer IC to start.
The cheap CD4051 (HEF4051 etc) 8:1 multiplexer will do well enough for playing.
Pricing here - in stock from 52 cents US in 1's.
eg see below. They use an external ADC but the method is identical for onboard ADC.
Best Answer
Why did you choose the AD676 in particular? It's a 16-bit ADC, which is much more than you need. A potmeter rotates over about 270°, so an 8-bit ADC would give you a resolution of about 1°. Nowadays it's often easier to find a 10-bit ADC, and they don't cost much more.
Normally you should also look at the ADC's speed, but for reading a potmeter 10 samples per second should do and any SAR (Successive Approximation) ADC will do here (most will easily be a thousand times faster).
How do you want to interface it to your microcontroller? I2C, SPI?
A standard serial protocol makes it ridiculously easy to interface your ADC with your microcontroller. As an example the following "schematic" from the Microchip MCP3021 datasheet:
The MCP3021 is a 10-bit ADC which interfaces through I2C. It comes in a 5 pin SOT23 package:
That's all you need.