No voltage across L293DNE output. DC motors not working

[sajan45]

Hi.
I am a returning newbie. I tinkered around a couple of beginner-level Arduino projects 8 years ago but then I dropped out of Electronics and pursued a career in Software Engineering.

I remember the basics of electronics but still, I am missing something, as the motors are not running. I am using an Arduino UNO board.
Here is my circuit diagram.

This is the first time I am drawing a circuit diagram, that is not on paper, please excuse me if it is messy,

Both the batteries are 1000mAh and 8.4v and fully charged.
Specification of the motors are:
Operating Voltage: 3V~6V DC
No-load speed(5V): about 208RPM
Load current: 170mA (when it is 4.5V)

I have tried moving the IC to different positions on the breadboard, and also tried with a L293D driver shield. When trying with the driver shield, I can see 2 LEDs out of 4 are ON, on the shield, but still no voltage across output pins.

Since I am trying to figure out the problem, I have removed everything else from the breadboard and the code is straightforward as well.

#define left_motor_pin_1 4
#define left_motor_pin_2 5
#define en_left 9
#define en_right 10
#define right_motor_pin_1 6
#define right_motor_pin_2 7

void setup() {
  pinMode(left_motor_pin_1,OUTPUT);
  pinMode(left_motor_pin_2,OUTPUT);
  pinMode(en_left, OUTPUT);
  pinMode(en_right, OUTPUT);
  pinMode(right_motor_pin_1,OUTPUT);
  pinMode(right_motor_pin_2,OUTPUT);
}

void loop() {
  analogWrite(en_left, 255);
  analogWrite(en_right, 255);
  moveForward();
}

void moveForward() {
  digitalWrite(left_motor_pin_1,HIGH);
  digitalWrite(left_motor_pin_2,LOW);
  digitalWrite(right_motor_pin_1,HIGH);
  digitalWrite(right_motor_pin_2,LOW);
}

This is my first post on the forum, if this is not the correct place to post this, please guide me about the right channel for this post.

Thanks

[TomGeorge]

Hi, @sajan45
Welcome to the forum.

Do you have a DMM?
Can you please post a picture of your project?
Do you really have a 3.7V battery connected to Vin and Gnd?

I think a hand drawn picture will be so much better, you can then use and label your components.
Including the real power sources.
Please use component names and pin labels to give a clear diagram, do not try to make it a small diagram, spread it out to show your wiring.

Thanks.. Tom...

[sajan45]

Hi @TomGeorge . Thank you for your response.
Yes, I have a DMM. I was using that to check the voltage across output pins.
I have an 8.4V LiPo battery connected to Vin. Same capacity battery for the external power source of L293DNE as well. I just could not find that in Fritzing, so I used a 3.7V image and mentioned the battery details in the post.

I thought a digital image will be cleaner but since you suggested, I will try to draw the circuit by hand. I can take a picture but my wiring is not that neat, I am afraid it will not show you anything useful.

[PaulRB]

@sajan45

Here is my circuit diagram.

Can you please post a schematic? I can't check your wiring because I haven't memorized the pin layout for L293. With a schematic I would not have to know the pin layout because in a schematic, every pin is labelled. Fritzing has a schematic editor. Switch the view to Schematic View and rearrange the components and draw in the connections. Fritzing will draw in some temporary dotted lines on the schematic for you, based on the connections from your breadboard view. Use plenty of the "power" symbols (5V, GND and other voltages) to help keep your schematic neat and avoid criss-crossing wires as much as possible, these make the schematic harder to read.

[PaulRB]

Many breadboards have breaks in the power bus lines, half way along the breadboard. This may mean that your grounds are not connected, so the L293 can't receive signals from the Uno.

[sajan45]

I did a continuity test and also I moved the ground connection wire to the same side. It still does not work.

Here is the schematic that Fritzing generated. I just added wire color. I know there is a few crisscrossing but could not find a way to edit it and it's only 4 connections, so I hope it's not too hard to understand it.

Thanks

[TomGeorge]

Hi,
This might help;

I think you need to gnd all those pins, 4, 5, 13, and 12.
Tom...

[runaway_pancake]

This took me < 5 minutes

[TomGeorge]

@runaway_pancake

This took me < 5 minutes

Nice, my hands won't work that neat or nice anymore.
When I reverse engineer I hand drawn circuits are real electronic MUD MAPS...

mud map | What is it? A Definition | Mud Maps®

Tom...

[sajan45]

This is really nice, I guess I imagined a different and complex way. Thanks.

[sajan45]

Tried that too. Didn't work.

[TomGeorge]

Hi,
With the code in post#1;
Check with your DMM that the ;

  digitalWrite(left_motor_pin_1,HIGH);
  digitalWrite(left_motor_pin_2,LOW);
  digitalWrite(right_motor_pin_1,HIGH);
  digitalWrite(right_motor_pin_2,LOW);

Pins are respectively HIGH or LOW.
And check;

  analogWrite(en_left, 255);
  analogWrite(en_right, 255);

Pins are HIGH.

Can you please post some images of your project?

Tom....

[PaulRB]

@sajan45

Here is the schematic that Fritzing generated. I just added wire color

You generate the schematic, Fritzing just helps. You clearly didn't spend as much time and effort drawing that as you did with the breadboard wiring diagram, or it would look a lot better!

[sajan45]

Yes, that's true. I wanted to post the schematic as soon as possible, as I was afraid that when the post gets older, I will lose people's attention and will be stuck in this situation. I will spend some time on this and clean it more.

[sajan45]

@TomGeorge

Check with your DMM that the ;

I checked. I am getting 4.98V and 0V for the pins that were supposed HIGH and LOW respectively. I will post some pictures after a few hours when I get back home.