L293D motor shield power sources

I have a 4xAA battery powering the 4 dc motors on a typical plastic chassis via a L293D motor shield. The car uses the ultrasonic sensor and code to avoid obstacles. The issue Im having is that when the UNO is plugged into the 5V from the usb cable and the 4xAA are powering the L293D shield, all works well.

But when I remove the USB cable and use just the 4xAA to power the L293D, the motors just buzz as if not getting enough power. I guess this means the power transfer from the L293D shield is either not enough or not even supposed to happen, although some power does spill over from the shield to the UNO because the code runs fine, however the motors just buzz when they are supposed to move and of course, they dont turn the wheels. The servo works fine.

So I tried plugging a 9V battery clip to the UNO's barrel jack, but it drained the 9V instantly. I then tried another 9v and it drained it again. It drains them from 9.2V or so that they come with, to about 8-7.5V and then they're useless.

Why does this happen?

You need separate power supplies. Use a 4xAA for the motors and a 9V for the Arduino.
There is a jumper next to the motor power in plug which is labeled "PWR." (the little yellow thing)
That jumper connects the motor power to the Arduino power.

Pull it off and plug it back in on only one pin so you don't lose it.

You may want a heftier motor driver. The L293 cannot pass much power because it uses bipolar transistors internally which have a very high voltage drop.

Thanks I am using separate power sources. I was just wondering why the 9v on the ArduinoHonduras barrel Jack was draining. I guess it's related to they jumper so I looked at the diagram and found this. Can someone explain how the jumper keeps the power sources separate and why the 9v Greta dragones when using separarte sources but leaving the jumper on?

If the motor supply is absent or inadequate the L293D internally routes current from the logic supply to
the power side of its circuitry. This is bad news and you should avoid this by ensuring the
motor supply is adequate for the load, and always connecting it first if possible.

But why when I connect the 4xAA batteries to the shield and the 9v to Arduino does the 9v battery get drained?

If the motor supply is absent or inadequate the L293D internally routes current from the logic supply to
the power side of its circuitry.

Clearly the batteries are failing to provide enough current on their own.

Have you thought to measure the currents and voltages with a multimeter?

Ok so the 4xAA's are insufficient. It's just surprising because I've seen 4wd car projects where they run all 4 motors on a 9v and the Arduino on a 9v and it's enough.

So it surprised me that my setup is worse.

The jumper shorts the Arduino power to the motor power when connected. So when you had the 4xAA and 9V both plugged in they were shorted to each other. Take the jumper off, power the motors with the 4xAA (6xAA is probably better) and power the Arduino with the 9V.

Hi, just browsing information on this as I am a noob on this stuff.

Can I use this motor shield with Bluetooth?

I have pretty much the same kit and set-up with L293D and the ultrasonic, but I also want to make an app for it to use Bluetooth, (power on/off, ultrasonic off (driver mode)) etc.

As far as I know the Bluetooth needs Tx and Rx, can I get to these with the shield in place?

Or is there another solution using the analog pins?

Cheers much if anyone can help,

Alanthas.

Hey, I have a doubt. I have a l293d motor shield and I want to connect 4 dc motors (the yellow cheap ones that come in arduino car packs), 2 servos, 2 hc-SR04 and a bluetooth module (the SR04 and the bluetooth module would be connected to the analog pins). I was wondering how many AA batteries could I use without damaging the board or the arduino so the motors are faster. Can I use up to 8?? 6?? or should I stick to four?