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How to wire 2 regulators, 1 for motor 1 for MCU?

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AceOfHearts

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Due to large and irregular current draw from motors I have the motor connected to one regulator and the microcontroller unit (MCU) to another. Though this technique worked before, for some reason, the MCU regulator is affected and so Im getting wierd and random MCU outputs when the motor runs.

I am using one power pack, both regulators are connected to the same ground and same +Vs. Am I doing some thing wrong?

Appreciate any thoughts.

PS. I have decided to have a regulator for the motors due to other reasons.
 
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Could be a number of reasons... Do the two regulators share the same input rail? If so, perhaps the input to the regulators is not capacitively coupled well enough. Does the input dip significantly when the motors draw more current? This could be causing a reset on the MCU supply.
 
Have you got a decent size capacitor on the output from the 5V regulator and the normal decoupling capacitors?

Mike.
 
PS. I have decided to have a regulator for the motors due to other reasons.
You may want to share what the reasons were. It could be related. (Or Not)
EDIT:
In my mind it is hard to justify regulating the motor power. Motors are such a mixed bag that if you want constant speed you need to monitor the speed, regulating the input will not do it.
 
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Thanks for all the help.

I finally determined what the problem was. It was my L293D IC which stopped working and was outputting erroneous high voltages (which also had damaged the microcontroller conencted to it).

Both parts have been replaced and all is working fine now.

Thanks again.
 
Thanks for all the help.

I finally determined what the problem was. It was my L293D IC which stopped working and was outputting erroneous high voltages (which also had damaged the microcontroller conencted to it).

Both parts have been replaced and all is working fine now.

Thanks again.

Maybe it's nothing, but do you know why the L293D gave up the ghost? There's a chance that it's something in the circuit (maybe back EMF from the motors) which will shorten the life of any replacement as well, unless the root cause is identified and fixed.

Then again, like I said--maybe it's nothing. Could just have been a bum/damaged part.

How long was the original part working in the circuit?


Torben
 
I'm with Corben here. You might still have an issue with your design. You might consider powering the motor from a seperate source.
 
Thanks for the tips! Well, I have had the L293D on this project for about 3 months now, and then used it for a year on another application...So I it could be that it had its fair share of experimentation.

Though I am not ruling out other causes. I am not using a "decouping capacitor". I have never used one, how do I implement one, how do I know what values to use? And how does it help a circuit with motors in it? I will read online material, but as we know, first-hand experience is always invaluable.

Many thanks.
 
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When a motor starts up it initially draws a large current which can overwhelm the power supply and drop the voltage below the reset voltage of the microcontroller. To overcome this a large electrolytic capacitor is places on the 5V line to act as a reservoir (think battery) for the MCU during startup. Electrolytic capacitors are like little batteries and charge up by changing an electrolyte, because of this they cannot react very quickly to demand and therefore don't work very well at high frequencies. MCUs work at high frequencies and cause spikes on the supply that can cause problems. To overcome these spikes we use small fast capacitors close to the MCU. Fast capacitors are the little ceramic caps and we normally use a value of 100nF.

So, you want a large (100uF) electrolytic on your 5V supply and a small (100nF) ceramic capacitor as near to the MCU power pins as practical.

Mike.
 
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