Isolation between high and low voltage side?????

[xischaune]

Hi all...
i have made a small circuit with 89C51 microcontroller acting as a counter...there is the low voltage side with a simple bridge-rectifier based dc supply which gives 5volts to microcontroller
There is a 220V AC lamp which operates with the help of a relay. The relay is controlled by microcontroller...
The switch on the lamp if pressed....give a 5volt to zero volt transition and the microcontroller counts 1....
But
The problem is that due to AC switching in the relay....the microcontroller counts erratically....i.e. even if the switch is not pressed...it counts one....
I need some help on how to isolate the high voltage side from the low voltage side....
I need a simple solution...maybe discrete component based solution...i know about optocouplers...or triac based solution...but can there be any shortcut...by connecting some diode across relay etc.....
Thanx in advance

 

[Verba]

microcontroller is connected directly to relay ?
reverse diode in paralel with the reley should help, i think.
Do you have any schematic ? Your explanation is not completely clear for me.

 

[nguyennam]

As you did not post your circuit, so it is hard to pinpoint the problem.

Maybe your power supply for the MCU is too noisy, you should use the voltage regulator of 5V, filtering capacitors of 1,000uF, 0.1uF before and after the regulator. If the power supply wire is too long, above 15cm, you had better place a cap of 0.1uF right between Vdd and Vss pin of the MCU.

nguyennam

 

[budhy]

For reactive load (e.i. relay) you should anti-parallel a diode (connect cathode to Vcc) accross the relay coil. And remember use other dc supply for relay coil, don't mix with your 5 Volt Vcc for micros.
Are you direct connect 89C51 output pin to drive relay coil? Don't do that, use a transistor switch between 89C51 pin and relay coil.

And... do you realize your switch is bouncing?