# How to reduce the effect of electric lighter noise on Micro controller?

I am using a kind of electric lighter in my circuit in order to turn the fire on.

And also i have used some sensors that alert in danger by sending a signal to the MCU (ATmega 32) interrupt. The lighter works with 220 V AC in its input so I used a relay to switch it on and off. Also I used emitter common transistor to make the relay controllable from MCU. Right before it I have used an optocoupler to separate the power supply. But when the lighter starts working, the interrupt program begin and this is my problem.

I have used many methods for example i placed small capacitors on Interrupt's pin, used sound insulation cover around MCU, covering the lighter, covering lighter wires, using ferrite bead (on the output of the power supply of MCU), using big capacitors. They helped me to reduce this noise But not enough to solve my problem. What should I do? Maybe the lighter is too powerful!

• Do you have a circuit? – Jason Han Aug 5 '17 at 5:57
• I'll draw it now – Mohammad Reza Hasanpour Aug 5 '17 at 6:02
• Where do MQ2 and MQ5 come from? You want to do the filtering there, not at the MCU pin. – Vince Patron Aug 5 '17 at 7:24
• They are independent module. I just use its TTL answer. – Mohammad Reza Hasanpour Aug 5 '17 at 7:44
• Have you measured the noise? If so, please post a screenshot of your measurement. – Daniel Aug 8 '17 at 23:34

I would try to filter the signals befor U2:A. If you filter it after U2:A such as in the circuit the noise will already have influenced the TTL signal and it can't be differentiated any more if the signal got generated thru noise or the MQ2 / MQ5 modules.