# solve the problem of noise

#### mah

Joined Mar 15, 2010
348
i use external interrupt pin on atmega 8(INT1) to do action, but there is a relay and motor in my circuit which activated the interrupt and execute the action. i used switch debounce but no vain how to solve this problem?

#### Papabravo

Joined Feb 24, 2006
14,659
i use external interrupt pin on atmega 8(INT1) to do action, but there is a relay and motor in my circuit which activated the interrupt and execute the action. i used switch debounce but no vain how to solve this problem?
Examine your Ground (GND) connections. Best is to use one pair of power and ground leads/traces for the ATmega8, and a separate pair for the motor and solenoid. There should be only one common point -- at the power supply. That should be your first effort. A schematic of your entire system would be most helpful. Can you please provide one.

#### mah

Joined Mar 15, 2010
348
i have gnd plane and power plane and i put capacitor 100nf across each switch also relay board is separated from MCU board

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Joined Mar 10, 2018
4,057
Using scope in one shot mode can you capture pin interrupt is tied to to
see if thats the problem ? Also is pin operated in a high Z environment,
eg. the drive to the pin is from a high z source ? This causes C coupling,
best way to get rid of noise is to lower pin Z and/or use a ferrite bead.

But confirm your changes with scope captures to make sure you have
created a wide margin suppression of noise.

Regards, Dana.

#### KeithWalker

Joined Jul 10, 2017
1,291
i have gnd plane and power plane and i put capacitor 100nf across each switch also relay board is separated from MCU board
The relay and motor are not shown in your schematic. What kind are they and how are you powering them?

#### mah

Joined Mar 15, 2010
348
The relay and motor are not shown in your schematic. What kind are they and how are you powering them?
this is the relay board drive small ac motor, i tried to use snubber rc circuit 100nf,47 ohm but there was leakage and the relay was always on

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#### Papabravo

Joined Feb 24, 2006
14,659
i have gnd plane and power plane and i put capacitor 100nf across each switch also relay board is separated from MCU board
I know what you have, and that is a problem. If you take my suggestion you will have less of a problem. Go back and read it again. Do not pass Go and do not collect $200.00 #### SamR Joined Mar 19, 2019 2,763 Couple of things. Relay coils can backfeed when field collapses and same for motor winding. Use diodes to prevent backfeed. #### Papabravo Joined Feb 24, 2006 14,659 Couple of things. Relay coils can backfeed when field collapses and same for motor winding. Use diodes to prevent backfeed. Is backfeed a technical term? What exactly are you talking about? Without a schematic we don't know if he has them or not. #### SamR Joined Mar 19, 2019 2,763 Backfeeding is flow of electrical energy in the reverse direction from its normal flow. For example, backfeeding may occur when electrical power is injected into the local power grid from a source other than a utility company generator. Backfeeding - Wikipedia en.wikipedia.org/wiki/Backfeeding As happens when a coil or motor field collapses. Also can be a source of circuit noise and hence diodes to prevent. #### KeithWalker Joined Jul 10, 2017 1,291 this is the relay board drive small ac motor, i tried to use snubber rc circuit 100nf,47 ohm but there was leakage and the relay was always on The second diagram you posted is the same one you posted above. We still don't know what type of relay and motor you are using, how they are connected and how you are powering them. #### Papabravo Joined Feb 24, 2006 14,659 Backfeeding is flow of electrical energy in the reverse direction from its normal flow. For example, backfeeding may occur when electrical power is injected into the local power grid from a source other than a utility company generator. Backfeeding - Wikipedia en.wikipedia.org/wiki/Backfeeding As happens when a coil or motor field collapses. Also can be a source of circuit noise and hence diodes to prevent. So turning off a switch on a solenoid leaves no path for the current to flow which makes backfeeding, as you put it, impossible. It physically cannot flow if there is no path so I think we are talking about different things. What you get without a current path, is a large voltage spike proportional to the inductance and the time rate of change of the current. A diode will provide an alternate path for the current in a coil to flow when the switch turns off, but it may or may not do much to help the TS's problem if his layout does not have a better grounding strategy. #### Sensacell Joined Jun 19, 2012 2,621 Is it possible to disable the interrupt synchronously with the relay activation? If the same MCU controls the relay, then you might be able to mask the problem. #### Papabravo Joined Feb 24, 2006 14,659 Is it possible to disable the interrupt synchronously with the relay activation? If the same MCU controls the relay, then you might be able to mask the problem. Seriously? #### Sensacell Joined Jun 19, 2012 2,621 Seriously? Sure, just trying to think like a Boeing engineer for a minute or two. Not the correct solution, but maybe it could work, keep it quiet, save money for shareholders... #### SamR Joined Mar 19, 2019 2,763 Yep it's not a switch controlling it if the signal is from the MCU. Or any other IC. Thread Starter #### mah Joined Mar 15, 2010 348 Backfeeding is flow of electrical energy in the reverse direction from its normal flow. For example, backfeeding may occur when electrical power is injected into the local power grid from a source other than a utility company generator. Backfeeding - Wikipedia en.wikipedia.org/wiki/Backfeeding As happens when a coil or motor field collapses. Also can be a source of circuit noise and hence diodes to prevent. l293d driver has already internal diodes for this mission Thread Starter #### mah Joined Mar 15, 2010 348 Is it possible to disable the interrupt synchronously with the relay activation? If the same MCU controls the relay, then you might be able to mask the problem. good idea, but Is it the right choice ? I mean Is it one of our options #### Papabravo Joined Feb 24, 2006 14,659 Yep it's not a switch controlling it if the signal is from the MCU. Or any other IC. A quaint notion, but nonsense. A digital output from an MCU is a lot of things. One of them is a switch. #### KeithWalker Joined Jul 10, 2017 1,291 I know what you have, and that is a problem. If you take my suggestion you will have less of a problem. Go back and read it again. Do not pass Go and do not collect$200.00
He mentions that the motor is "a small AC motor". We do not yet know how it is powered so it may not be a very good Idea to connect it to circuit ground.