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microcontroller and noisy environment ...

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Junior Member level 1
Jun 16, 2006
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high noise environment power supply circuit


I have a trouble in my project.... :cry:

I design a circuit which use 7 relay and atmel 89c4051 (also 89s52) microcontroller and uln2003 which drive the relays.
This circuit should working near a gas cooker. Everything is ok until the gas cooker electrical spark generators activate for burning the gas on …

At this time system goes in abnormal (reset, halt or change function or do undefined function …) but when I put the system far from the gas cooker it works good …

It seems the electromagnetic generated with the spark generator make the trouble …

Is any body known what is going on, and what should I do to prevent this?

microcontroller proper grounding

I had a similar problem near some motor contactors. The contact arcing broadcast some very high energy noise and caused all sorts of problems. There is no quick easy solution is some cases, but good grounding and shielding is vital. Physical isolation is also important. Put the uC and it's immediate components inside a grounded metal box and as far away as possible from the noise source. Isolate the power supply and use good filtering. Decouple the power pins of the uC. Cross your fingers and keep testing.

microcontroller grounding

Now picture the spark hitting your board. This is similar to one of the tests for TUV certification, although TUV certification just requires your board to restart properly. After shielding your board, protect each input and output. I have personally seen where an enclosure needed to be made from a ferus metal to shield from the magnetic portion of the EM pulse from a spark (it was a REALLY big spark). I too wish you luck, because you can have it fixed for a given installation just to find that the next installation gives you grief. I do think that you can design the cicuit to operate in those conditions though, hopefully within budget.

drive ssr or solid state relay microcontroller

Try isolate both side of the noise source and the microcontroller system.

microcontroller + noisy envirnment

try to isolate all inputs and oupts from the microcontroller by opto couplers like pc817


make a metal enclouse to avoid EM hitting directly to the board

microcontroller noisy environment

Put decoupling capacitors near every chip's power point entries such as Vcc pins.
The value can be 0.1 micro farad disc capacitors

you use Isolate between microcontrol with output drive = solid state relay for AC drive


Iam giving some suggestions for your problem

1.Use snubber (capcitar+resistor) circuit or snubber across the load relay.

2. Use different power supplies for relays and for controller.
For relays 12V supply and for controller 5V supply

3.proper grounding


My experience with this problem is:

1. Decoupling capacitors beside each IC on the PCB
2. A separate transformer for each part of the design (the digital and the analogue)
3. Do not use a high speed crystal if you do not need it.
4. Do not use long PCb tracks for the relays
5. switch off every module you do not need inside your MCU
6. Use a grounded small metal piece as a box around your MCU
7. Use fast recovery diodes with the relays.
These made me able to reduce the noise in dspic30 running 164 relays in a really big project.

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