Society of Robots - Robot Forum

Electronics => Electronics => Topic started by: declanshanaghy on March 10, 2011, 03:46:26 PM

Title: How to avoid separate power supplies
Post by: declanshanaghy on March 10, 2011, 03:46:26 PM

I'm just starting out on this robotics lark so i figured i should get some experts to weigh in on this question that popped into my head.

So far i haven't come across a decent solution to get me off the ground.

I'd like to avoid having separate power supplies for my motors and MCU.
Is it possible to a constant current source component directly from the supply for the motors? Any suggestions?

The MCU would then draw its power from the supply through an LM7805

Any hints as to pros and cons of this approach are appreciated.

Thanks,
Declan

Title: Re: How to avoid separate power supplies
Post by: Soeren on March 10, 2011, 04:15:13 PM

Hi,

Quote from: declanshanaghy on March 10, 2011, 03:46:26 PM

I'd like to avoid having separate power supplies for my motors and MCU.
Is it possible to a constant current source component directly from the supply for the motors? Any suggestions?

The MCU would then draw its power from the supply through an LM7805

Apart from the "constant current source component", yes, it's possible - but it will need good filtering to avoid noise from the motor entering the logic and sensors.

What voltage are you planning on feeding your motors?
What's the drive current and stall current  of the motors?

Title: Re: How to avoid separate power supplies
Post by: Cyntrox on March 12, 2011, 07:18:59 PM

Also, note that the LM7805 needs a about 7.2v, if I remember correctly. Otherwise you won't get 5v out.

Title: Re: How to avoid separate power supplies
Post by: Soeren on March 12, 2011, 09:13:52 PM

hi,

Depending on manufacturer, the 7805 has a drop out of 2.5 to 3.5V (a few even higher) - 3V is the rule of thumb here for a reasonable regulation with most of them.