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muruga81
04-30-2005, 09:00 PM
hai,
i have an application using pic micro 16f877 powered by 9v transformer via 7805 regulator 1000uF and 100uF bulk decoupling cap near regulator, and an RC filter 1ohm with 0.1uF. the problem is when any high voltage AC motor connected to the same power line with micro is switched on, during few seconds my micro behaves abnormally and displays junk value and then return to normal agter few seconds. can any one give me a suggestion about the easiest way to over come this power line noise problem.

thanks in advance

Murugan

vidur
04-30-2005, 09:41 PM
try a few things

put a freewheeling diode between the input & output terminals. A reverse biased diode at the output will also act as a fast capacitor & provide some protection........use 1n4007 s

you need bulk capacitors both at output and input terminals. The capacitance at input must be higher than output. say 1000uF at input & 470 uF at output, The faster 0.1uF should be at output

Put a heavy series inductor-resistor for surge supression ( i've not tested any particular values, so experiment & find out)

muruga81
05-02-2005, 10:58 AM
thanks for ur advice,
many of friends advice me to use inductor coils of .1 milli Henry between reg and micro and many sort of things. can any one provide with me a rough schematic or links for typical power ciruit for micro working in noisy environments where high power AC motors were used..

thanks in advance

murugan

muruga81
05-03-2005, 03:17 PM
i have one another problem the application which i have build calulate the speed of a 3HP AC motor by using M18 proximity sensor and display its RPM using 7 seg display. for each revolution the proximity gives a active low output which is coupled by using optocoupler pc817 and given to RB0 as interrupt. during normal running this arrangement works fine but during running when i switch on/off the motor during that brief moment numerous interrupts occurs and RPM display shows unusual values. (i found out by displaying the number of counts of interrupts occured). micro never resets how to avoid this problem it is due to power fluctuation in 5V power to micro or 12V supply to proximity. please advice me how to condition dignals comping going to interrupts

thanks in advance

murugan

nchinoy
05-23-2005, 04:13 PM
For your noise problem ....

Check if your AC motor has proper earthing ! Secondly use a capacitor say (104 / 1KV / Ceramic) between your system ground and earth. This way most of the noise that comes through your system from the external ground is bypassed. I have used this and it works fine...

My circuit (micro) is placed in a very high frequency environment.. with a lot of noise EMI (and Induction Feilds) and using this technique helped me get rid of that unwanted noise.

For your speed display using a proximity ... Average out your reading per/min or per/15sec... This way you will avoid burst effects... Also use a debounce circuit or implement it in your software, since ON/OFF of the ,motor is bound to induce a lot of noise and you 817 might not be able to cope with it and will give you pulses instead...

Debouncing the ciruit will help with that too ..

Just my 2 cents worth...

Nimesh

vidur
05-24-2005, 10:09 AM
Secondly use a capacitor say (104 / 1KV / Ceramic) between your system ground and earth. This way most of the noise that comes through your system from the external ground is bypassed. I have used this and it works fine...

Nimesh


can you elaborate on this....with a circuit diagram or something like that

nchinoy
05-24-2005, 10:35 AM
You have a common supply for your AC motor and your micro based card correct ? As in this might be 230V .. So what you need to do is the neutral line (Ground connection on your PCB), should have one end of the 104/1KV/Ceramic capacitor and the other end of the capacitor should be earth i.e. the green wire of the 3 core cable... Ensure that your AC motor also has proper earthing ... i.e. the green wire...

You can check for proper earthing by using a multimeter... measure the voltage between the PHASE and EARTH (Should be 230V) and then between NEUTRAL and EARTH (Should be less than 8V)...

See if you can put up your schematic card and for the motor wiring... I will try and see if i can show you where to PUT the capacitor in your circuit....

just my 2 cents worth....

Nimesh