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Powering mcu and dc motor from same battery source

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Full Member level 6
Dec 22, 2006
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Delhi , India
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Dear friends ,

I need to design a circuit where a battery is connected to a dc geared motor .

When the motor runs the entire platform which includes the battery mounted on it runs forward.

Now i need to install a real time rtc ds1302 to start the motor automatically at a particular time .
I have to install mcu and rtc on the same platform to turn on the relay at desired time .

My concern is since the motor and mcu with rtc ( after 7805 5V regulated ) have to be powered from battery 12v dc .What are the chances of motor noise disrupting the mcu or resetting it or creating error while reading rtc data ......

How do we design such circuit where mcu and rtc , relay and Battery , Motor share the same ground .

Please suggest .


I think you can separate mcu supply from motor by proper EMI filter and regulate and filter it's supply by proper supply capacitor after regulator.


the key to success is to know about the currents and the current paths.
Frequency, magnitude, impedance.

One way is to seperate the GND paths of both circuits. The separation should be done in a way so that the microcontroller and all it´s sensitive circuit - including - 7805 - works in a small area with a common GND plane.

If you connect the PCB GND and the motor GND with different wires directely form the battery, then the PCB voltage is as clean as can be. But filters in the wires may improve noise additionally.
The problem is when you have a motor power control that needs the same GND reference for any signals, like PWM control signals, analog measurement signals.. Then both system GNDs may have a voltage difference leading to malfuntion.

A solution to this problem could be to wire GND from battery to the motor control and supply the microcontroller with extra wires from the motor control. Since the GND lines from motor control to microcontrolelr won´t have much current then voltage drop is minimized. (It may differ to the battery GND, but this is no problem)

Maybe draw a picture of your circuit: Battery, motor, motor control and microcontroller circuit and additional circuitry, if there is any.
Then with a colored marker show the high current path, especially where is pulsed current.

Then you should see where you can expect voltage drop, and where you can rely on the voltage reference.

Show us your picture and we can better assist you.

However separation is necessary and separate wire to battery, but EMI filter for damping noise on VCC and GND is very important. also sometimes problem intensify when battery isn't full charged. so I think we can put a proper capacitor after regulator for this problem.

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