MCU noise with drive relay

[mshh]

I designed this pcb with the help of people in this forum to drive relay with ac motor(thanks to them). the circuit still has noise problems when relay switch the motor. it's good with ac lamp but the problem happen with ac motor. external interrupt is disturbed, reset and sometimes random characters on lcd appears.
I put aluminum paper on lcd cables
I separated the power supplies with common ground
I put the push buttons all on the board directly and capacitors across them
Then i connect the relay and disconnect it manually fast
It resets and random number appears on lcd but not every time.
Is there any thing not on its place on pcb or trace path is wrong.

 

[barry]

If I remember correctly, people kept telling you to add ground plane and it looks like you ignored their advice and added no ground plane (unless there's a bottom layer you're not showing.) The copper you've got on the top layer is useless.

Obviously your problem is noise generated by the AC motor is getting into your circuit. I presume it's an induction motor. Induction motors don't generate a lot of electrical noise (compared to commutated DC motors), but they can generate magnetic fields. How close to the circuit is your motor? Have you tried moving it away to see if that helps? The other thing to consider is that when the motor initially powers on it will draw a LOT of current (inrush). Is it pulling your supply down?

 

[mshh]

I didn't understand them that they were talking about double layer. Is it obligatory to use double layer to avoid noise?
I use ac small grill motor and the relay board is far from the MCU 10 cm. the supply is almost constant when relay is on (it changes from 5.1 to 5.07v)

 

[barry]

I didn't understand them that they were talking about double layer. Is it obligatory to use double layer to avoid noise?
I use ac small grill motor and the relay board is far from the MCU 10 cm. the supply is almost constant when relay is on (it changes from 5.1 to 5.07v)

Well, yes, they were talking about double layer. You say the supply is 'constant' but have you looked at it with an oscilloscope during the initial turn-on? Have you tried putting an RC filter on the reset line? How long is the trace on your reset signal?

 

[mshh]

Yes, it was also constant during far switchings.but if i switch relays fast every second , there are spikes on vcc so i think that it nay be the diode of relay coil is slow i replaced it with 1n4148 fast diode and i will see its effects.

 

[barry]

What do you mean "far switchings" or "switch relays fast every second"? Once a second is pretty slow. If you see a spike once a second, you'll see one once an hour, too. It's the initial inrush that's the problem, not how often you're switching.

 

[KlausST]

Hi,

Is it obligatory to use double layer to avoid noise?

Asking such questions is a good start.

With a double layer PCB - or better say "with a solid GND plane" - you can't avoid the existance if noise. But you can minimize the influence of noise to your circuit.
In my eyes a good GND plane is the key to success.

Thus I wrote in post #22:
* Still no GND plane: We don´t need to talk about noise improvements without GND plane.

I recommend you to re read the complete other thread...and ask questions about things you don't understand.

Imagine:
You can't avoid earthquakes ... but you may build houses that can withstand earthquakes.

Klaus

 

[mshh]

I measured VCC and reset pins using scope, there are spikes when relay is off how to eliminate them?

 

[KlausST]

Hi,

if you ask me... I can only repeat:

I wrote in post #22:
* Still no GND plane: We don´t need to talk about noise improvements without GND plane.

Klaus

 

[barry]

I measured VCC and reset pins using scope, there are spikes when relay is off how to eliminate them?

Spikes with the relay off? Where are they coming from? Maybe you should have a ground plane. Just a thought.