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Mr. Basic Motor Driver Kit Problem

Hi, LMR!

I need some help with troubleshooting Mr. Basic Motor Driver board. Basically, I couldn't make it work. I use 4xAA Alkaline batteries [5.8V actual voltage] as power supply. MC Picaxe 18X. Relays are working fine, but Motors are not. With my little experience in electronics I guess BD681 does not open for some reason. But not sue, I might be wrong...

My setup:


Troubleshooting done:

First I checked setup with only VCC and GND connected to motor driver board. I have VCC and GND potentials on respective board outputs with motors disconnected. Is this ok?? Well, as long as there is no current between them... But I'm not realy sure... Then I have checked picaxe actually sets out pin high. and connected PWM input of the board. At this point with PWM high, I have 5.8 (VCC) and 4.6v on motor outputs (motors disconnected.) And no current drawn by motor when connected..

Anyone could help???

Am I doing something wrong ??

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The relays are switching, but the motors aren't turning. The Arduino code works fine. They do run when one of the cables is plug directly into the ground pin. They also run with a jumper from ground to the normally open pin of the relay, but when it swicthes, there seems to be some sort of short. Many combinations of the ground pin are making the motors turn which makes me think I may have a grounding problem. I'm not so good with this type of troubleshooting, so any help would be appreciated. Thanks.
The power leads of the Mr. Basic motor controller should go directly to your batteries. When both motors are stalled they will draw about 4A. If you try to run this through an arduino you could fry it. The only connections you should have from your arduino to the controller are 4 digital outputs to the F/R and PWM connections of each motor.

There are 6 connections in total on the board (not counting the motor outputs). 2 for power and 2 for each motor. Each motor has a F/R (forward/reverse) input and a PWM (Pulse Width Modulation) input. These are both connected to digital outputs of your processor.

Once you have the power connected, your processor should drive the PWM input high to turn on the motor. The relay only controls direction of the motor.

I checked my board phisically and found no defects, soldering points are ok as well... Tried to connect board inputs to VCC neither of motorw work. Motos themselves are ok. They go spinning when conneced straight to batteries. Next step I desoldered BD681 and set up circuit on breadboard but could not drive anything with it. Is there any way I could have burnt both of them??? My multimeter hFE checks results in 1 which is absolutely ok as per datasheet. I'll try to catch my local electronics shop for parts today... And probably after doing some tests on motor current, I will try to use BCX38C for purpose...

I am not sure what you have done unless you have put the BD681 in backward. To make the motors run you need to have the PWM input high. The relay only selects the direction.

The BD681 is a very tough component. It can withstand fairly high temperature during soldering and has a built in flyback diode. The BD681 has a HFE of greater than 750 which also makes me think you had it in backward as you said it only had a HFE of 1.

Thanks for reply, OddBot. I'll try to get some BD681s locally. Is there any substitute for this part? Should I try tosolder it back different way?

I'm sorry to say I do not know of a good substitute. I chose that transistor because it is a darlington transistor (two transistors in one to give a high hfe) so that a digital output could drive a high current load such as the motors. Many other transistors with the same power rating have a much lower hfe (about 40-80).

Try soldering it back in the correct way. (the exposed metal back towards the outside of the PCB).

That is the way it was initially: metal back facing out.... Hmm...
That is the way it was initially: metal back facing out.... Hmm...

I suggest you removed the PICAXE from the troubleshooting to simplify and verify operation of the board itself.

I always find it best to start troubleshooting at the "physical layer".  First visually inspect your board and look for any solder bridges or poor solder joints. If you have a multimeter you can test for continuity between connection points on the circuit board. 

Next, with VCC and GND connected to your battery pack, and one motor connected, connect the respective PWM input to VCC and see if the motor turns. Although the input is labeld PWM, simply attaching a logical high to it will drive your motor at full speed. You only need PWM from your uController if you need speed control.

If this works, try also applying VCC to the F/R input for that motor, and see if the relay switches and drives the motor in reverse.

If you have problems, try connecting your motor to the other motor driver output (left, if you were testing with right) and try the same thing. In fact, even if the right motor driver worked, verify the left one too. 

If both work OK in forward and reverse, It's time to re-introduce the PICAXE and see what it is doing.