Lesson 15 of 16

Strength tester

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#include <Servo.h> const int FSR = A0; const int BELL = 8; const long PULLDOWN = 10000; // must match the resistor on the breadboard Servo needle; int best = 0; // the hardest hit so far unsigned long bestAt = 0; // when it happened bool rung = false; void setup() { needle.attach(9); Serial.begin(9600); } void loop() { int force = analogRead(FSR); // harder press, higher reading // hold the best hit for a moment, then follow the pad again if (force >= best || millis() - bestAt > 1500) { best = force; bestAt = millis(); } needle.write(map(best, 0, 1023, 0, 180)); if (best > 880 && !rung) { tone(BELL, 1568, 400); // G6 for 400 ms rung = true; } else if (best < 880 - 100) { rung = false; } if (force > 10) { // work back from the divider to the sensor's resistance long ohms = PULLDOWN * (1023L - force) / force; Serial.print(force); Serial.print(" "); Serial.print(ohms); Serial.println(" ohms"); } delay(20); }

Stopped · Your code isn't running yet. Until you press Run, the board runs the program already on it.

Nothing printed yet. Press Run.

Hit the pad: a force-sensing resistor measures how hard, a servo needle swings to show it and holds the best hit, and a bell rings if you hit hard enough.

Hit it and watch the needle
How the divider gives you the sensor's resistance
Pick a pull-down to set the sensitivity
A peak hold, like a fairground strength tester

Pin	Connects to	What it does
`5V`	One leg of the FSR	The top of the divider.
`A0`	Between the FSR and the 10 kΩ resistor	Reads higher the harder you press.
`GND1`	The 10 kΩ resistor	The bottom of the divider.
`D9`	The servo's signal wire	Moves the needle.
`D8`	The buzzer	Rings the bell.

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 A0. analogRead(A0) then goes from 0 to 1023 as you turn it.
Part pin Board pin
1 GNDWire colour black
2 A0Wire colour green
3 5VWire colour red
Light sensor (LDR)Supply 5 V
From 5V to A0, with a 10 kΩ resistor from A0 to GND. More light, lower resistance, higher reading.
Part pin Board pin
1 5VWire colour red
2 A0Wire colour green
Piezo buzzerSupply 5 V
+ to a pin, − to GND. tone(pin, frequency) plays a note; a piezo draws only a few mA, so no resistor is needed.
Part pin Board pin
POS D8Wire colour orange
NEG GNDWire colour black
TMP36 temperature sensorSupply 5 V
Flat face toward you: left leg 5V, middle leg to A0, right leg GND. Degrees C = (volts − 0.5) × 100.
Part pin Board pin
VS 5VWire colour red
VOUT A0Wire colour green
GND GNDWire colour black
SG90 micro servoSupply 5 V
Brown to GND, red to 5V, orange to a pin (D9). Servo.attach(9) then write(0..180).
Part pin Board pin
GND GNDWire colour brown
VCC 5VWire colour red
SIG D9Wire colour orange
Careful
A moving servo can draw 250 mA and a stalled one 700 mA. More than one servo needs its own 5 V supply, with the grounds joined.
Capacitive soil moisture sensorSupply 5 V
AOUT to A0, VCC to 5V, GND to GND. The reading falls as the soil gets wetter.
Part pin Board pin
AOUT A0Wire colour yellow
VCC 5VWire colour red
GND GNDWire colour black
FSR 402 force sensorSupply 5 V
One leg to 5V, the other to A0, with a 10 kΩ pull-down from A0 to GND. Press harder, read higher.
Part pin Board pin
1 5VWire colour red
2 A0Wire colour green

All 16 parts on the Arduino Uno R3 page

Connects to

What it does

5V

One leg of the FSR

The top of the divider.

A0

Between the FSR and the 10 kΩ resistor

Reads higher the harder you press.

GND1

The 10 kΩ resistor

The bottom of the divider.

D9

The servo's signal wire

Moves the needle.

D8

The buzzer

Rings the bell.

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 A0. analogRead(A0) then goes from 0 to 1023 as you turn it.

Part pin	Board pin
1	GNDWire colour black
2	A0Wire colour green
3	5VWire colour red

Light sensor (LDR)Supply 5 V

From 5V to A0, with a 10 kΩ resistor from A0 to GND. More light, lower resistance, higher reading.

Part pin	Board pin
1	5VWire colour red
2	A0Wire colour green

Piezo buzzerSupply 5 V

+ to a pin, − to GND. tone(pin, frequency) plays a note; a piezo draws only a few mA, so no resistor is needed.

Part pin	Board pin
POS	D8Wire colour orange
NEG	GNDWire colour black

TMP36 temperature sensorSupply 5 V

Flat face toward you: left leg 5V, middle leg to A0, right leg GND. Degrees C = (volts − 0.5) × 100.

Part pin	Board pin
VS	5VWire colour red
VOUT	A0Wire colour green
GND	GNDWire colour black

SG90 micro servoSupply 5 V

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

Part pin	Board pin
GND	GNDWire colour brown
VCC	5VWire colour red
SIG	D9Wire colour orange

Careful

A moving servo can draw 250 mA and a stalled one 700 mA. More than one servo needs its own 5 V supply, with the grounds joined.

Capacitive soil moisture sensorSupply 5 V

AOUT to A0, VCC to 5V, GND to GND. The reading falls as the soil gets wetter.

Part pin	Board pin
AOUT	A0Wire colour yellow
VCC	5VWire colour red
GND	GNDWire colour black

FSR 402 force sensorSupply 5 V

One leg to 5V, the other to A0, with a 10 kΩ pull-down from A0 to GND. Press harder, read higher.

Part pin	Board pin
1	5VWire colour red
2	A0Wire colour green

All 16 parts on the Arduino Uno R3 page

Strength tester

Try it yourself

Serial monitor

Checks

Break it

Inputs

Parameters

Wire it in

Strength tester

Try it yourself

Serial monitor

Checks

Break it

Inputs

Parameters

Wire it in