Let's Make Robots!

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 have mounted Motor Driver PCB on top of Mr. Basic, and found another possible cause of fault: Very first time I powered up board on Mr. Basic, just like on picture, and there is high chance of shortening components by touching motor housings. I have put a piece of cardboard to prevent it for now. Will replace it by plastic insulator soon...


That would be possible, but my first test was outside the Mr. Basic... so I'm still trying to figure out what happened.

But it's true. I had the same problem with my Arduino in a r/c car chassis. I measured and cutted a calculator's cover and mounted it with screws where the original circuit used to be. In the Mr. Basic, I'm using some plastic spacers from aTamiya kit to cover the 3 screws in the board; in my case they make contact with the pins of the Arduino.


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...

I was a little confused trying to follow the description of your problem. So I'm not sure if you have the same issue or not. Did OddBot's reply to you help you in troubleshooting at all?

If you can get the BD681s easily, stick with those. I still have to do some testing on the TIP120s, though it seem to work so far.

If you are sure you have same problem, I'd suggest just go ahead and buy new transistors locally. Even in my country they were available :) Price here was ~$1 each.