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My circuit has a microcontroller, it uses power from a DC transformer (120V to 12V DC). My circuit also control an pneumatic valve which also use 12V DC. Almost every time when the pneumatic valve opens, the current becomes unstable. This makes the microcontroller restart.

Some guy suggested me to use two power sources. In my case, it is very rare for a microcontroller and a pneumatic valve to use two DC transformers. How can I build "two power sources" in a microntroller circuit?

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    \$\begingroup\$ What microcontroller are you using that can run from 12V? \$\endgroup\$ – Matt Young May 1 '13 at 7:11
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    \$\begingroup\$ Please include your circuit schematics. \$\endgroup\$ – shimofuri May 1 '13 at 8:12
  • \$\begingroup\$ What is the rated current of your 12V supply? How much current does the valve draw? What is the supply voltage when the valve is open? \$\endgroup\$ – Phil Frost May 1 '13 at 10:49
  • \$\begingroup\$ @MattYoung I use a 5V voltage reference and an Opamp to create the power source for the Mircocontroller \$\endgroup\$ – Superhero May 1 '13 at 14:33
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Sounds like the back-EMF from the solenoid is disrupting the micro. There are a few potential issues / solutions here;

1st, read up on snubber diodes/protection used with relays/solenoids, it's been covered many times here on all the hundreds of variations on "how do I switch a relay from my *duino?" questions.

2nd, look at the smoothing and grounding of the micro's supply.

3rd, you may need to separate the "power" side of your circuit from the "logic" side using something like an opto-isolator and perhaps splitting the power supply - this does not mean you need two separate PSU's, just that the delicate side of the circuit could include a power supply/conditioning circuit that isolates it from the noisy side.

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