Probably An Issue With HG7881 Motor Driver - Arduino Forum

Probably an Issue with HG7881 Motor Driver Other Hardware Motors, Mechanics, Power and CNC system August 31, 2014, 10:46pm 1

I am a newbie to the Arduino world and been recently busy testing and playing with some of the common cheap modules and sensors available for direct interfacing with Arduino.

One of the most interesting modules is the dual channel motor driver based on HG7881 available on the following link: http://www.lctech-inc.com/Hardware/Detail.aspx?id=155c73e2-e972-473f-913d-ec443dbef0be

This module has 6 input header pins and 4 output driven power for stepper or normal DC motors.

The issue I have noticed (which can be a very serious one) is that when you drive the motor with an external power supply that has a voltage less than the Arduino Vcc (say 2.5v), the module will start to sink current from the Arduino PWM pins, and can go very high even for a small 3v dc motor.

What I have done is connecting the external 2.5v power supply to the Vcc and Gnd pins of the module. The Gnd of Arduino connected to the power supply Gnd, and the control pins (A-IA, A-IB) to Arduino PWM pins 10 and 9.

I wish someone with more experience to confirm this as it might be considered an issue with the design of the module.

system August 31, 2014, 11:39pm 2

While at first glance it looks like a cool motor driver, epecially because of the 800 mA current capability, on closer inspection, the absence of a second ground pin for the motor power supply sets it apart from the better L298 motor drivers that have a separate ground for the motor power supply. One poster had one like that and he said there was no continuity between the two grounds confirming that the motor supply was indeed isolated from the arduino interface side. That being the case , the motor power supply SHOULD be GREATER than the motor rating by at least 1.5 to 2V because the driver has an overhead and requires more voltage to compensate for the voltage dropped across the devices. For 3V motors you should set your motor supply to 5V , not 2.5V.

MarkT September 1, 2014, 4:07pm 3

Abulafi: The issue I have noticed (which can be a very serious one) is that when you drive the motor with an external power supply that has a voltage less than the Arduino Vcc (say 2.5v), the module will start to sink current from the Arduino PWM pins, and can go very high even for a small 3v dc motor.

Yes, this is common in H-bridge chips like this, you have to be sure your motor supply is present and strong enough to keep the motor supply higher than 5V at all times to avoid this.

For instance the L298 and L293D chips have this property too I believe. Couldn't find the datasheet online for the HG7881 - I personally would be put off using a device without a datasheet, because there's no way to check if you are using it correctly...

system September 3, 2014, 8:27am 4

Thank you raschemmel and MarkT for your comments. I believe this module should not be considered safe for direct interfacing with Arduino and those who sell it should put all the warnings and facts in the device description.

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