Lesson 3 of 7

Potentiometer and PWM

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// A knob on A1 sets the brightness of the LED on pin 9 const int POT_PIN = A1; const int LED_PIN = 9; // a ~ pin, so analogWrite() makes PWM here const int BITS = 14; // 10 is the default; the R4's ADC goes up to 14 void setup() { Serial.begin(115200); analogReadResolution(BITS); pinMode(LED_PIN, OUTPUT); } void loop() { int top = (1 << BITS) - 1; int raw = analogRead(POT_PIN); float volts = raw * 5.0 / top; int duty = map(raw, 0, top, 0, 255); analogWrite(LED_PIN, duty); Serial.print("A1 = "); Serial.print(raw); Serial.print(" "); Serial.print(volts, 2); Serial.println(" V"); delay(250); }

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Read a potentiometer on A1 with the R4's 14-bit ADC and set an LED's brightness with PWM on ~9. Pick the resolution and see the same voltage as 0-1023 or as 0-16383.

Turn the knob in the figure
One voltage, three resolutions
map() turns any reading into a 0-255 duty

Pin	Connects to	What it does
`A1`	The potentiometer's middle leg (wiper)	Analog input, 0-5 V.
`D9`	1 kΩ resistor, then the LED	PWM output at 490 Hz.
`5V`	One end of the potentiometer	The top of the divider.
`GND`	The other end, and the LED's short leg	The bottom of the divider.

Wire it in

Sensors and actuators this board drives, with the real connections.

PotentiometerSupply 5 V
Ends to GND and 5V, the middle leg (wiper) to A1. analogRead(A1) goes from 0 to 1023 by default, or to 16383 after analogReadResolution(14).
Part pin Board pin
1 GNDWire colour black
2 A1Wire colour blue
3 5VWire colour red
SG90 micro servoSupply 5 V
Brown to GND, red to 5V, orange to D9. Servo.attach(9), then write(0..180).
Part pin Board pin
brown GNDWire colour brown
red 5VWire colour red
orange D9Wire colour orange
Careful
A starting servo can pull several hundred mA. On USB that comes straight from the computer's port, with no fuse on the board. More than one servo needs its own 5 V supply, with the grounds joined.

All 6 parts on the Arduino UNO R4 page

Connects to

What it does

A1

The potentiometer's middle leg (wiper)

Analog input, 0-5 V.

D9

1 kΩ resistor, then the LED

PWM output at 490 Hz.

5V

One end of the potentiometer

The top of the divider.

GND

The other end, and the LED's short leg

The bottom of the divider.

Wire it in

Sensors and actuators this board drives, with the real connections.

PotentiometerSupply 5 V

Ends to GND and 5V, the middle leg (wiper) to A1. analogRead(A1) goes from 0 to 1023 by default, or to 16383 after analogReadResolution(14).

Part pin	Board pin
1	GNDWire colour black
2	A1Wire colour blue
3	5VWire colour red

SG90 micro servoSupply 5 V

Brown to GND, red to 5V, orange to D9. Servo.attach(9), then write(0..180).

Part pin	Board pin
brown	GNDWire colour brown
red	5VWire colour red
orange	D9Wire colour orange

Careful

A starting servo can pull several hundred mA. On USB that comes straight from the computer's port, with no fuse on the board. More than one servo needs its own 5 V supply, with the grounds joined.

All 6 parts on the Arduino UNO R4 page

Potentiometer and PWM

Try it yourself

Serial monitor

Checks

Break it

Inputs

Parameters

Wire it in

Potentiometer and PWM

Try it yourself

Serial monitor

Checks

Break it

Inputs

Parameters

Wire it in