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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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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.

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...

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.

I cannot help you on this one, I just want to send a message to everybody else:


A title that explains what sort of problem you have.

A description of what you want the circuit to do, and how it fails to do so.

A short summary of what sort of troubleshooting you've done before posting here.

Detailed descriptions of what happens when you try fixes suggested by other LMRers.


If everybody asked for help this thoroughly, LMR would be able to fix any problem and win the Google X-price Lunar challenge within next summer...

Sorry for hijacking your thread. Please refrain from replying to my rant in this post. 

Dear LMR,

I'm just back from the shop, fortunately they had BD681 in stock, so I got hold of few. Set up breadboard tester, and, OMG, it worked!!!! I've got them soldered on the board and tested, works fine! btw they have hFE of 1 as well on my multimeter, I think it reads what's called "hfe small signal dc gain = 1" in datasheet, whatever... Thanks to all of you for help!!! Mr. Wake is back on track! :D

To conclude, I think I have burnt transistors somehow... But... provided e-square has same problem??? I believe it worth checking the batch at DAGU, OddBot??? Just in case???

I have the same kit, which I assembled but have not tested yet. I'll give it a try if I get a chance, just to be sure we didn't get a bad lot of BD681s.

Uh oh! I'm having the same problem. The relays work just fine, but I get no motor action when I apply voltage to the PWM inputs of the board.


Looks like a bad batch of BD681... (((
Yep. I confirmed with my multimeter that the BD681 is getting VCC to the collector, the emitter is grounded, and the base gets voltage when the PWM input is high. So the transistor is bad.  Both of 'em.
So, should I buy replacements or wait for an answer from DAGU / Oddbot / Claudia? Since my arduino motor shield's death is still a mystery, my only option at the moment would be this controller...but seems I'm stuck again...