Fig. 06 · Robotics Lab · Why not to use it

L298N driver

Arduino Nano

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Bench

No reading yet

+12V (motor supply)

No reading yet

Current draw

0 mA

Build and break

1BuildNext up
Strip to the bare PCB
Take every part off the red board. You will put it back the way a factory would: SMD parts first, then the low through-hole parts, the tall ones, the solder joints and the jumper caps last.
2
Pick and place the SMD parts, then reflow
3
Fit the low through-hole parts
4
Fit the tall parts
5
Solder the through-hole joints
6
Put the jumper caps on
7
Wire the Nano to IN1-IN4 and GND
8
Wire the two motors
9
Wire the LiPo to +12V and GND
10
Power the bench
11
Upload Forward
12
Upload Reverse
13
Upload Spin on the spot
14
Upload Brake
15
Upload Half speed
16
Put the LiPo on backwardsBreak it
17
Fit C1 backwardsBreak it
18
Power it from 4 x AABreak it
19
Power it from 36 VBreak it
20
Leave a cold joint on motor A's terminalBreak it
21
Leave the 5V-EN cap offBreak it
22
Leave out the GND wireBreak it
23
Hold both wheelsBreak it
24
Exploded view

Break it on purpose

Each fault is one that catches real builders. Trigger it, read the symptom on the bench, then fix it.

LiPo on backwards
reverse polarity
Why it happens
Symptom: The power LED stays dark, nothing turns, the diodes and C1 get hot within seconds and the battery leads warm up.
There is no protection diode or fuse. Reversed, the eight flyback diodes conduct from GND through the outputs to +12V and put two diode drops, about 2 V, straight across the pack. Several amps flow through 1 A diodes and C1 sees reverse voltage.
Fix: Unplug at once, check the diodes and C1 for damage, and put red on +12V. A connector that only fits one way prevents it.
C1 in backwards
part in backwards
Why it happens
Symptom: A hiss and a pop when the pack goes on, a bulging can, a fishy smell.
An aluminium electrolytic only holds voltage one way. Backwards, its oxide layer breaks down, it conducts, heats and the electrolyte boils until the vent opens.
Fix: Replace C1 with the stripe (minus) toward the front edge, as printed.
6 V is too little with 5V-EN on
brown-out
Why it happens
Symptom: The power LED glows dimly, the motors twitch or do nothing and the logic keeps dropping out.
The 78M05 needs about 2 V more at its input than it puts out. From 6 V it manages about 4 V, below the 4.5 V the L298N's logic needs. And the motors would only see about 4.4 V after the bridge's drop anyway.
Fix: Use a 2S LiPo (7.4 V) or more. On a 6 V pack, pull the 5V-EN cap and feed the +5V screw from the Nano's 5 V.
36 V on +12V
wrong voltage
Why it happens
Symptom: A pop from the regulator or C1, the power LED dies, and the 5 V screw may carry the full supply.
The L298N is rated to 46 V, but the module's 220 µF capacitors are 35 V parts and the 78M05 takes 35 V at most. When a regulator fails it often fails short and passes the full supply to everything on +5V.
Fix: Stay at 12 V or less with the 5V-EN cap on. Above that, pull the cap and feed 5 V yourself, and keep under 35 V on this board.
Cold joint on motor A's terminal
cold solder joint
Why it happens
Symptom: Motor A stutters, cuts out on bumps or runs only one way; the terminal pin gets warm.
The terminal pins carry the full motor current. A dull, grainy joint makes contact only part of the time and its resistance turns current into heat.
Fix: Reheat the joint with fresh solder until it flows into a shiny cone around the pin.
5V-EN cap missing
missing part
Why it happens
Symptom: The pack is connected but the power LED is dark and no command does anything.
The cap connects +12V to the 78M05. Without it the regulator is off, the +5V rail is dead and the L298N's logic has no supply, so its switches never turn on.
Fix: Put the cap back, or with supplies over 12 V feed 5 V into the +5V screw from the controller.
No common ground
floating input
Why it happens
Symptom: The motors twitch, run the wrong way or ignore the sketch, and touching a wire changes what they do.
A logic level is a voltage between two points. With no wire between the Nano's GND and the module's GND, the L298N measures the Nano's pins against nothing: the inputs float and drift with every bit of noise.
Fix: Run a wire from the Nano's GND to the GND screw on the power terminal.
Both wheels stalled
overheating
Why it happens
Symptom: The heatsink gets too hot to touch, then the motors stutter: they stop, start again a few seconds later and stop again.
A held TT motor draws about 1.1 A from 7.4 V. The two conducting switches lose about 2.7 V at that current, about 3 W per bridge, 6 W for both. The L298N has no current limit; only its overtemperature cut-out stops it, and it restarts as soon as it has cooled a little.
Fix: Free the wheels and cut the power to a stalled motor in the sketch. Better: a MOSFET driver like the TB6612FNG, which loses a tenth of the power.

Meet the bench

power it, pick a direction, feel the heat

The L298N is the motor driver in nearly every starter kit: a red 43 mm square board with a black heatsink, two blue motor terminals and a 2S LiPo on its power terminal. Inside the chip are two H-bridges built from bipolar transistors, a 1990s design. IN1 and IN2 pick motor A's direction, IN3 and IN4 motor B's, and ENA and ENB switch each bridge on; as the module ships, two jumper caps tie both enables to +5V, so the motors run at full speed. A 78M05 regulator behind the 5V-EN cap makes the chip's 5 V logic supply from the battery. The catch is the drop: two bipolar switches sit in series with every motor and lose 1.4 + 1.15 x I volts between them, about 1.6 V with a free-running TT motor and 2.7 V with the wheel held, and all of it turns into heat. Build the module, wire the Nano, the motors and the pack, drive it in every direction, then hold the wheels and watch the heatsink climb until the chip cuts out. The TB6612FNG on the bench before this one does the same job and loses about 0.1 V.

Sources

On the bench

Selected

Sketch uses 2,252 bytes of program storage

Code: Forward

// L298N: IN1 and IN2 pick motor A's direction, IN3 and IN4 motor B's
const int ENA = 9, IN1 = 8, IN2 = 7;   // motor A: enable and the two direction inputs
const int ENB = 3, IN3 = 5, IN4 = 4;   // motor B

void drive(int in1, int in2, int in3, int in4) {
  digitalWrite(IN1, in1); digitalWrite(IN2, in2);
  digitalWrite(IN3, in3); digitalWrite(IN4, in4);
}

void setup() {
  for (int p = 3; p <= 9; p++) pinMode(p, OUTPUT);
  Serial.begin(9600);
  analogWrite(ENA, 255);      // full speed (the cap holds ENA at 5 V anyway)
  analogWrite(ENB, 255);
  drive(HIGH, LOW, HIGH, LOW);   // both forward
  Serial.println("forward: IN1 H, IN2 L, IN3 H, IN4 L");
}

void loop() {
}

Practice tasks

0/2 tasks

Write the code, then run the checks. The run uses a virtual clock and a scripted world, so the same code always gives the same result.

Soft start on ENA

Arduino C++

Pull the ENA cap and wire ENA to D9. Drive motor A forward (IN1 on D8 HIGH, IN2 on D7 LOW) and ramp ENA from 0 to 255, one step every 10 ms, so it reaches full speed in about 2.5 s. Hold full speed for 2 s, then brake by taking IN2 HIGH and print "stopped".

Checks

Not run yetRuns for 5.5 s
Not run yetIN1 (D8) is HIGH
Not run yetIN2 (D7) is LOW while driving
Not run yetAt 0.25 s ENA (D9) is at about 10%
Not run yetAt 1 s ENA is at about 40%
Not run yetAt 3.5 s ENA is at full duty
Not run yetAt 5 s IN2 is HIGH: braking
Not run yetPrints "stopped"

Hints

Set the direction once, before the ramp: digitalWrite(IN1, HIGH); digitalWrite(IN2, LOW);
A for loop from 0 to 255 with analogWrite(ENA, duty) and delay(10) inside gives the ramp.
Brake is IN1 = IN2 with the bridge enabled: IN1 is already HIGH, so set IN2 HIGH too.

Code for Soft start on ENA

Drive a square

Arduino C++

Make a two-wheeled robot drive a square: four times, both motors forward for 1 s, then pivot for 0.5 s (motor A forward, motor B reverse) and print "corner" with the count. After the fourth corner, brake both motors. IN1 is D8, IN2 D7, IN3 D5, IN4 D4; the enable caps stay on.

Checks

Not run yetRuns for 6.5 s
Not run yetFirst side: IN3 (D5) is HIGH
Not run yetFirst side: IN4 (D4) is LOW
Not run yetFirst corner: IN3 is LOW
Not run yetFirst corner: IN4 is HIGH, motor B reverses
Not run yetFirst corner: IN1 (D8) stays HIGH, motor A forward
Not run yetSecond side: IN3 is HIGH again
Not run yetPrints "corner 4" by 6.2 s
Not run yetAt the end IN2 (D7) is HIGH: motor A braking
Not run yetAt the end IN3 is HIGH: motor B braking

Hints

A helper drive(in1, in2, in3, in4) that writes all four inputs keeps each move to one line.
for (int side = 1; side <= 4; side++) { ... } in setup() runs the square once; loop() can stay empty.
Brake both: drive(HIGH, HIGH, HIGH, HIGH).

Code for Drive a square

Build and break

1BuildNext up

Strip to the bare PCB

Take every part off the red board. You will put it back the way a factory would: SMD parts first, then the low through-hole parts, the tall ones, the solder joints and the jumper caps last.

Pick and place the SMD parts, then reflow

Fit the low through-hole parts

Fit the tall parts

Solder the through-hole joints

Put the jumper caps on

Wire the Nano to IN1-IN4 and GND

Wire the two motors

Wire the LiPo to +12V and GND

Power the bench

Upload Forward

Upload Reverse

Upload Spin on the spot

Upload Brake

Upload Half speed

Put the LiPo on backwardsBreak it

Fit C1 backwardsBreak it

Power it from 4 x AABreak it

Power it from 36 VBreak it

Leave a cold joint on motor A's terminalBreak it

Leave the 5V-EN cap offBreak it

Leave out the GND wireBreak it

Hold both wheelsBreak it

Exploded view

Meet the bench

power it, pick a direction, feel the heat

On the bench

Selected

Sketch uses 2,252 bytes of program storage

Code: Forward

// L298N: IN1 and IN2 pick motor A's direction, IN3 and IN4 motor B's
const int ENA = 9, IN1 = 8, IN2 = 7;   // motor A: enable and the two direction inputs
const int ENB = 3, IN3 = 5, IN4 = 4;   // motor B

void drive(int in1, int in2, int in3, int in4) {
  digitalWrite(IN1, in1); digitalWrite(IN2, in2);
  digitalWrite(IN3, in3); digitalWrite(IN4, in4);
}

void setup() {
  for (int p = 3; p <= 9; p++) pinMode(p, OUTPUT);
  Serial.begin(9600);
  analogWrite(ENA, 255);      // full speed (the cap holds ENA at 5 V anyway)
  analogWrite(ENB, 255);
  drive(HIGH, LOW, HIGH, LOW);   // both forward
  Serial.println("forward: IN1 H, IN2 L, IN3 H, IN4 L");
}

void loop() {
}

L298N driver

The bench

Build and break

Strip to the bare PCB

Pick and place the SMD parts, then reflow

Fit the low through-hole parts

Fit the tall parts

Solder the through-hole joints

Put the jumper caps on

Wire the Nano to IN1-IN4 and GND

Wire the two motors

Wire the LiPo to +12V and GND

Power the bench

Upload Forward

Upload Reverse

Upload Spin on the spot

Upload Brake

Upload Half speed

Put the LiPo on backwardsBreak it

Fit C1 backwardsBreak it

Power it from 4 x AABreak it

Power it from 36 VBreak it

Leave a cold joint on motor A's terminalBreak it

Leave the 5V-EN cap offBreak it

Leave out the GND wireBreak it

Hold both wheelsBreak it

Exploded view

Break it on purpose

LiPo on backwards

C1 in backwards

6 V is too little with 5V-EN on

36 V on +12V

Cold joint on motor A's terminal

5V-EN cap missing

No common ground

Both wheels stalled

Live status

Current draw

Check yourself

After: Put the jumper caps on

After: Upload Brake

After: Hold both wheels

End of bench quiz

Meet the bench

Sources

On the bench

Practice tasks

Soft start on ENA

Checks

Drive a square

Checks

L298N driver

The bench

Build and break

Strip to the bare PCB

Pick and place the SMD parts, then reflow

Fit the low through-hole parts

Fit the tall parts

Solder the through-hole joints

Put the jumper caps on

Wire the Nano to IN1-IN4 and GND

Wire the two motors

Wire the LiPo to +12V and GND

Power the bench

Upload Forward

Upload Reverse

Upload Spin on the spot

Upload Brake

Upload Half speed

Put the LiPo on backwardsBreak it

Fit C1 backwardsBreak it

Power it from 4 x AABreak it

Power it from 36 VBreak it

Leave a cold joint on motor A's terminalBreak it

Leave the 5V-EN cap offBreak it

Leave out the GND wireBreak it

Hold both wheelsBreak it

Exploded view

Break it on purpose

LiPo on backwards