Lab 5 explores analog input and output using variable resistors. You will learn to read sensor values to the serial monitor and vary the brightness of LED lights using pulse width modulation (PWM).

Lab Objectives:

• Read Analog sensor values using analogRead()
• Print sensor values to the serial monitor
• Use analogWrite on a PWM pin
• Learn to fit an analog input reading into a single byte using the map() function

Lab 5 Resources:

• Videos: Analog Input 1 and Analog Input 2
• Adafruit’s guide to Forse Sensitive Resistors (FSR)

Parts:

• Solderless Breadboard and hookup wire
• Arduino microcontroller module & USB connector
• LEDs of different colors
• 560 ohm (or anything from 220 to 1K) and 10 Kilohm resistors
• 10Kohm potentiometer
• 2 Variable Resistors

Part 1: Potentiometers

Build a circuit with a potentiometer as the input, and an LED as the output. Use analogRead() for the incoming potentiometer value, and analogWrite() to set the brightness of the LED.

Setup the breadboard
Connect a potentiometer to analog in pin 0 of the module, and an LED and a resistor to digital pin 9:

Program the Module

First, establish some global variables at the top of the program -

	// declare a global constant to give the LEDs pin number a name

	// declare an int to hold the value returned by the potentiometer, use analogValue

	// declare int for brightness value - to use for writing PWM to LED

In the setup() method -

	void setup() {

	    // initialize serial communications at 9600 bps
	    
	    // declare the led pin as an output:
	    
	}

In the main loop - read the analog value using analogRead() and put the result into the variable that holds the analog value. Then divide the analog value by 4 to get it into a range from 0 to 255. Then use the analogWrite() command to face the LED. Finally, print out the brightness value to the serial monitor.

	void loop() {

		// read value from the pot and put results into analogValue

		// get analogValue it to fit into a byte - this is the brightness

		// PWM the LED with the brightness value

		// print the brightness calue back to the serial monitor
	}

When you run this code, the LED should dim up and down as you turn the pot, and the brightness value should show up in the serial monitor.

Part 2: Other Variable Resistors (going a bit further…)

Build a circuit with at least 2 different variable resistors that output brightness values to two different colored LEDs

Build two voltage divider circuits that connect to A0 and A1, using variable resistors for R3 and R4 (try a photocell or an FSR). To both pin 9 and 10, connect a resistor + LED. Use different colors for LED1 and LED2.

The circuit above works for any variable resistor. It’s called a voltage divider. There are two voltage dividers, one on analog in 0 and one on analog in 1. The fixed resistor in each circuit should have the same order of magnitude as the variable resistor’s range. For example, if you’re using a flex sensor with a range of 50 – 100 kilohms, you might use a 47Kohm or a 100Kohm fixed resistor. If you’re using a force sensing resistor that goes from infinity ohms to 10 ohms, but most of its range is between 10Kohms and 10 ohms, you might use a 10Kohm fixed resistor.

In Part 1, you used a potentiometer as input which always gives the full range of analog values, which is 0 to 1023. You can divide this value by 4 to get a range of 0 to 255, which is the full output range of the analogWrite() command.

A voltage divider circuit, on the other hand, can’t give you the full range. The fixed resistor in the circuit limits the range. You’ll need to modify the code or the resistor if you want a different range.

Use the serial monitor to find your sensor range. Then use the map() function to map the actual range that the sensor gives as input to the range that the LED needs as output.

A Note on soldering sensor leads - Flex sensors and force-sensing resistors melt easily, so unless you are very quick with a soldering iron, it’s risky to solder directly to their leads. Here are three better solutions:

1. Use female headers
2. Use screw terminals (if you have a row of three you can attach the fixed resistor as well)
3. Use wire wrapping wire and a wire wrapping tool

Lab 5 is due before class on Tuesday February 14th

Your blog response should include a schematic, a clear video of your working circuit and a brief description of what the circuit does and how you made it. Submit a link to your blog post on Edmodo.