Fig. 05 · Robotics Lab · H-bridge, PWM

TB6612FNG driver

Arduino Nano

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Bench

No reading yet

PWMA duty

No reading yet

Current draw

0 mA

Build and break

1BuildNext up
Strip to the bare PCB
Take every part off. The red 20 mm square holds only four parts and two headers: you will put them back in the order a factory would.
2
Pick and place the SMD parts, then reflow
3
Fit JP1, the power and motor header
4
Fit JP2, the control header
5
Solder the header joints
6
Wire the Nano to JP2 and VCC
7
Wire the two motors
8
Wire the LiPo to VM and GND
9
Power the bench
10
Send Forward 50%
11
Send Brake
12
Send Coast
13
Send Reverse
14
Send Forward 100%
15
Pull STBY low
16
Break it: C3 in backwardsBreak it
17
Break it: LiPo plugged in backwardsBreak it
18
Break it: a 4S pack on VMBreak it
19
Break it: motors on the Nano's 5 VBreak it
20
Break it: cold joints on the control headerBreak it
21
Leave U1 out
22
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.

C3 fitted backwards
part in backwards
Why it happens
Symptom: Pop: C3 cracks and smokes as soon as the battery is on, and the battery current jumps.
A tantalum capacitor is polarised. Reverse voltage breaks down its oxide layer, it turns into a near short across VM, and the battery pushes amps through it until it burns.
Fix: Unplug, desolder C3, and fit a new one with the band (+) toward VM on the left.
LiPo connected backwards
reverse polarity
Why it happens
Symptom: U1 and C3 get hot within seconds, there is a burnt smell, and nothing turns.
The SparkFun board has no reverse protection. Current flows from GND through the lower switches' body diodes, out through the upper ones to VM: two diode drops across the battery, a near short through the chip. C3 is reverse-biased at the same time.
Fix: Unplug at once and swap the leads: red to VM, black to GND. On a real board U1 and C3 are usually dead; Pololu's carrier adds a reverse-protection MOSFET on VM.
16.8 V on VM
wrong voltage
Why it happens
Symptom: The driver fails at once: VM shorts to GND and the battery leads get warm.
VM works up to 13.5 V and survives 15 V. A full 4S pack (16.8 V) is above both, and every braking spike adds more on top.
Fix: Use a 2S pack (8.4 V full) or at most a 3S (12.6 V full, little margin for braking spikes).
Motors on the Nano's 5 V
brown-out
Why it happens
Symptom: The Nano resets every time the motors start: the sketch restarts, the serial line repeats, the wheels jerk.
Two TT motors take about 1.6 A for a moment when they start. The Nano's USB supply is fused at 500 mA and sits behind a diode, so its 5 V rail sags below the ATmega328P's 2.7 V brown-out level and the chip resets.
Fix: Feed VM from the battery, keep VCC on the Nano's 5 V, and join the grounds.
Cold joints on the control header
cold solder joint
Why it happens
Symptom: The motors stutter, worse when the board is tapped or vibrates.
A cold joint is dull, grainy and cone-shaped: it touches the pin only now and then. When the STBY joint opens, the 200 kΩ pull-down drags STBY LOW and the chip sleeps until the contact comes back.
Fix: Reheat each joint with fresh flux and a little solder until it flows into a shiny, concave fillet.
STBY low or unconnected
floating input
Why it happens
Symptom: Powered, the sketch runs, IN1, IN2 and PWM look right, and nothing turns.
STBY LOW turns every output off. An unconnected STBY reads LOW because of the internal 200 kΩ pull-down, the commonest first-day trap with this chip.
Fix: Wire STBY to a pin and drive it HIGH in setup(), or tie it to VCC.
U1 left off
missing part
Why it happens
Symptom: Both supplies are on, but nothing turns and nothing gets warm.
Without U1 there is nothing between the battery and the motors: the board is only headers, three capacitors and copper.
Fix: Unplug, place U1 with pin 1 top left, and solder it.

Meet the bench

power the bench, then send drive commands

A Nano pin gives about 20 mA at 5 V. A TT gear motor wants 150 mA just to turn and about an amp when it starts or stalls, at 6 to 7 V. The TB6612FNG sits in between: two H-bridges, each four switches that connect the motor one way, the other way, or short its leads together to brake. IN1 and IN2 pick the direction and PWM sets the speed by switching the bridge on and off almost a thousand times a second (977 Hz on pins 5 and 6). Motor power (VM, 2.5 to 13.5 V, here a 2S LiPo) and logic power (VCC, 2.7 to 5.5 V, here the Nano's 5 V) are separate supplies with one common ground, and STBY must be HIGH or the whole chip sleeps. Its MOSFET switches lose about 0.5 V at 1 A and only about 0.15 V at 0.3 A, against about 2 V for the L298N's bipolar switches, so this is the driver to use. Build the breakout, power it, then try brake and coast back to back: brake stops the wheel hard, coast lets it spin down.

Sources

On the bench

Selected

Instant: switches at once, no upload

Code: Forward 50%

// TB6612FNG: IN1 and IN2 pick the direction, PWM sets the speed
const int PWMA = 5, AIN1 = 7, AIN2 = 8;
const int PWMB = 6, BIN1 = 10, BIN2 = 11, STBY = 9;

void drive(int in1, int in2, int pwm) {
  digitalWrite(AIN1, in1); digitalWrite(AIN2, in2); analogWrite(PWMA, pwm);
  digitalWrite(BIN1, in1); digitalWrite(BIN2, in2); analogWrite(PWMB, pwm);
}

void setup() {
  for (int p = 5; p <= 11; p++) pinMode(p, OUTPUT);
  digitalWrite(STBY, HIGH);   // LOW, or left unconnected, puts the whole chip to sleep
  Serial.begin(9600);
}

void loop() {
  drive(HIGH, LOW, 128);      // forward, half speed
  Serial.println("AIN1=H AIN2=L PWMA=128 -> forward, ~3.7 V average");
  delay(3000);
}
// IN1 IN2 PWM -> H L pwm: forward | L H pwm: reverse | H H x: short brake | L L H: coast

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.

Five speeds, both ways

Arduino C++

Drive motor A forward at five PWM steps (51, 102, 153, 204, 255), one second each, brake for half a second, then do the same in reverse and brake again. Keep STBY HIGH the whole time.

Checks

Not run yetRuns for the whole 11 s
Not run yetSTBY (D9) is HIGH
Not run yetForward: AIN1 (D7) is HIGH
Not run yetForward: AIN2 (D8) is LOW
Not run yetFirst step: PWMA at 20%
Not run yetThird step: PWMA at 60%
Not run yetFifth step: PWMA at 100%
Not run yetReverse: AIN1 (D7) is LOW
Not run yetReverse: AIN2 (D8) is HIGH
Not run yetReverse, first step: PWMA at 20%
Not run yetReverse, fifth step: PWMA at 100%

Hints

Direction is AIN1 and AIN2, speed is analogWrite(PWMA, …): set the direction once, then step the PWM.
51 × i for i = 1 to 5 gives the five steps; delay(1000) after each one.
Brake is AIN1 = AIN2 = HIGH. Write both pins every time; never rely on the pull-down.

Code for Five speeds, both ways

Exactly one turn

Arduino C++

A 20-slot encoder disc on motor A's shaft gives one rising edge on D2 per slot. Count the edges in an interrupt and brake motor A after exactly 20 slots, one wheel turn, then print the count once. Because you stop on the count and not on a timer, it turns once whether the battery is full or nearly flat: your first closed loop.

Checks

Not run yetCounts the encoder with an interrupt and a volatile counter
Not run yetDrives motor A at PWM 150
Not run yetStill driving after 19 slots
Not run yetBrakes (AIN2 HIGH) right after slot 20
Not run yetStays braked
Not run yetPrints "one turn: 20 slots"

Hints

The interrupt only counts: count++ in tick(), nothing else. Do the deciding in loop().
count is a 32-bit long on an 8-bit chip: read it between noInterrupts() and interrupts() so it cannot change halfway through the read.
AIN1 is already HIGH, so setting AIN2 HIGH gives the short brake. Use a flag so you brake and print only once.

Code for Exactly one turn

Build and break

1BuildNext up

Strip to the bare PCB

Take every part off. The red 20 mm square holds only four parts and two headers: you will put them back in the order a factory would.

Pick and place the SMD parts, then reflow

Fit JP1, the power and motor header

Fit JP2, the control header

Solder the header joints

Wire the Nano to JP2 and VCC

Wire the two motors

Wire the LiPo to VM and GND

Power the bench

Send Forward 50%

Send Brake

Send Coast

Send Reverse

Send Forward 100%

Pull STBY low

Break it: C3 in backwardsBreak it

Break it: LiPo plugged in backwardsBreak it

Break it: a 4S pack on VMBreak it

Break it: motors on the Nano's 5 VBreak it

Break it: cold joints on the control headerBreak it

Leave U1 out

Exploded view

Meet the bench

power the bench, then send drive commands

On the bench

Selected

Instant: switches at once, no upload

Code: Forward 50%

// TB6612FNG: IN1 and IN2 pick the direction, PWM sets the speed
const int PWMA = 5, AIN1 = 7, AIN2 = 8;
const int PWMB = 6, BIN1 = 10, BIN2 = 11, STBY = 9;

void drive(int in1, int in2, int pwm) {
  digitalWrite(AIN1, in1); digitalWrite(AIN2, in2); analogWrite(PWMA, pwm);
  digitalWrite(BIN1, in1); digitalWrite(BIN2, in2); analogWrite(PWMB, pwm);
}

void setup() {
  for (int p = 5; p <= 11; p++) pinMode(p, OUTPUT);
  digitalWrite(STBY, HIGH);   // LOW, or left unconnected, puts the whole chip to sleep
  Serial.begin(9600);
}

void loop() {
  drive(HIGH, LOW, 128);      // forward, half speed
  Serial.println("AIN1=H AIN2=L PWMA=128 -> forward, ~3.7 V average");
  delay(3000);
}
// IN1 IN2 PWM -> H L pwm: forward | L H pwm: reverse | H H x: short brake | L L H: coast

TB6612FNG driver

The bench

Build and break

Strip to the bare PCB

Pick and place the SMD parts, then reflow

Fit JP1, the power and motor header

Fit JP2, the control header

Solder the header joints

Wire the Nano to JP2 and VCC

Wire the two motors

Wire the LiPo to VM and GND

Power the bench

Send Forward 50%

Send Brake

Send Coast

Send Reverse

Send Forward 100%

Pull STBY low

Break it: C3 in backwardsBreak it

Break it: LiPo plugged in backwardsBreak it

Break it: a 4S pack on VMBreak it

Break it: motors on the Nano's 5 VBreak it

Break it: cold joints on the control headerBreak it

Leave U1 out

Exploded view

Break it on purpose

C3 fitted backwards

LiPo connected backwards

16.8 V on VM

Motors on the Nano's 5 V

Cold joints on the control header

STBY low or unconnected

U1 left off

Live status

Current draw

Check yourself

After: Solder the header joints

After: Send Coast

After: Break it: motors on the Nano's 5 V

End of bench quiz

Meet the bench

Sources

On the bench

Practice tasks

Five speeds, both ways

Checks

Exactly one turn

Checks

TB6612FNG driver

The bench

Build and break

Strip to the bare PCB

Pick and place the SMD parts, then reflow

Fit JP1, the power and motor header

Fit JP2, the control header

Solder the header joints

Wire the Nano to JP2 and VCC

Wire the two motors

Wire the LiPo to VM and GND

Power the bench

Send Forward 50%

Send Brake

Send Coast

Send Reverse

Send Forward 100%

Pull STBY low

Break it: C3 in backwardsBreak it

Break it: LiPo plugged in backwardsBreak it

Break it: a 4S pack on VMBreak it

Break it: motors on the Nano's 5 VBreak it

Break it: cold joints on the control headerBreak it

Leave U1 out

Exploded view

Break it on purpose

C3 fitted backwards

LiPo connected backwards

16.8 V on VM

Motors on the Nano's 5 V

Cold joints on the control header

STBY low or unconnected