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Mr. Basic PCB with motor controller

Mr._Basic_motor_driver_Schematic.jpg333.35 KB
Vendor's Description: 

During the first Mr. Basic contest some people had trouble driving their motors because of the current required and because of the low voltage provided by Mr. Basic's 3xAA battery holder. I posted a blog showing a schematic for a controller which DAGU has now produced as a replacement PCB for Mr. Basic.

This controller will work on voltages from 3.6V to 7.2V. Higher voltages can be used if the relays are changed. Although designed for Mr. Basic this PCB can be used on any robot and has room for additional circuitry to be added. This board comes as a kit (PCB and components) so you will need to solder it yourself.


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Does it drop the voltage


There is a voltage drop across the BD681 transistor used for PWM. This varies depending on the individual transistor and the load but is usually less than 1V.

Hi, photo here now. I am also thinking of using a 9v battery for the pic, with a 7805 regulator.

As you can see on the photo, it isent the same print as the 1 you have posted at the top.

photo of motor controller

Ok, I don't see a photo, the diagram looks fine.

I don't know what you mean by "The 2 BC547 transistors and some of the resistors are placed different on my print." This is where a photo would be useful.

If your motor controller works fine when you touch a wire connected from +V to the direction and PWM inputs of the motor controller then it is ok.

One possibility is your power supply / batteries cannot deliver enough current to drive the motor. As each motor has a stall current of about 2A you need to use NiMh or NiCd batteries. Alkaline batteries have too much internal resistance.

When your Pic tries to drive the motors, the voltage drops and the chip resets. This would explain the change in PWM frequency. Put some big capacitors (2200uF or higher) on the motor controller power connections.

Try running your PIC off a different (regulated) supply with a common ground.

Hi, not sure if it just is me, but cant find any that will fit into the batterie case that where with the LMR Mr. Basic that are either NiMh or NiCd. Do you know any?

Any battery that looks like this and says "rechargeable" is OK.


Now with a photo :0) . A friend told me, that it could be noise from the motors, if so how do i remove that?

I have tried to test it manually, and there it worked. The motor controller circuit board dont look like the picture here on this trophic. The 2 BC547 transistors and some of the resistors are placed different on my print.




Just got the motor controller, but when i fixed it up with my PIC16F876A i coudent get it to work. I can feal that the motor get a regular bumb, but it wont start driving. And when i put a scope on the PWM output from the PIC, i get a fine puls, but when i then connect it to the motor controller circuit it is not so fine any more. Any1 know what i am doing wrong?

The funny ting is also that this is the same problem i had with the motor controller i tried to build my self.

Can you post a photo of your setup showing how you have connected it? Unless you have damaged a transistor by overheating or put one in back to front then I suspect you are not connecting everything up properly. Especially as you say you had this problem with another speed controller.
Have you tried testing the motor controller manually, i.e. just using wires to apply the input signals?