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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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isotope's picture
Looks like a bad batch of BD681... (((
ignoblegnome's picture
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.
e-square12's picture
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...
ignoblegnome's picture

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.

isotope's picture
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.
maneuver's picture

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. 

OddBot's picture

When soldering components into any circuit board, be carefull to put the components in the correct way. Many components such as transistors, diodes etc. are polarised and either wont work or will be permanently damaged by incorrect installation.

If you wish to have a circuit board "pre-assembled" then tell Claudia this when ordering. There will be an additional fee but we will send you a board that has been assembled and tested.

isotope's picture

This reminder is very good, especially for beginners!

For this case I'm pretty sure I have everything soldered correctly, I have checked datasheet for pinout of BD681 and compared to schematic you posted. I started doing this checks after I got shipment from Picaxe with 3.3v regulator pinout different from PCB layout, which I have burnt :)

OddBot's picture
If you can send me clear closeup photos of the PCB and setup then I can look to see if there is another problem.
isotope's picture
I'll post pics as soon as I get home today... Thanks.