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Using the ADC

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So far you have set up two interrupts, and three macros which are called from the main routine. In this next part of the project you will set up a further macro that will measure the signal on an analogue input.

1. Add an ADC component onto your project panel. Alter the connection so that it is connected to ADC 1 - this is the potentiometer on the Sensor board.
2. Add a new macro and call it 'ADCmeasure'.
3. Add a Component macro to the 'ADCmeasure' macro. Set it to 'GetInt' to read the value of the ADC into the variable 'ADCreading' that you set up previously.
4. Drag a Calculation icon into the macro and enter 'volume = ADCreading / 10' into the Calculation field.

You should have something like this:

The process of sampling the ADC is a two stage one: first sample the value and then read the value into a variable. The PICmicro we are using here actually has up to 8 ADC inputs - AN0 to AN8. Internally however the PICmicro only has one Analogue to Digital Converter. Each of the 8 inputs can be switched to the ADC using internal analogue switches. This gives you a clue as to why the process of getting an analogue input into your program is a two stage process: internally Flowcode sets up the analogue switch to connect to the relevant input, then it takes a reading.

The ADC inside the PICmicro has a resolution of 10 bits. This means that to make use of the full range of the ADC you need to use a variable of type Int: a 16 bit variable. The value you read will vary between 0 and 1023. However we are used to seeing Volume presented as 0 to 10, or 0 to 100. Because of this we can quickly divide the ADC reading by 10 to get a scale of 0 to 102 as our volume setting. You should by now be able to think of programming techniques to cap the value at 100.

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