Alvin,
I found your post hard to understand.
>>sorry for my poor command in english. To simplify the setup, I had built 3pcs of 8
channel relay module. Excatly what I had installed at site. Module A, Module B and
Module C. All are link via Rs485 communication line. Each module is connected with 2
load. Which means i only use 2 relay channel for the trigerring. The purpose is to
monitor the switching, if it will affect the rest of the modules if Module A being
switched.
{first trial in my office without Ecap install after the bridge}
All the module works perfectly. While switching on and off any channel will not affect any micro to reset.
I really hope the resetting does occur so I can identify{simulate} the same problem at site.
{second trial in my office with Ecap 1000uF install}
Everything runs perfectly.
If there is no Ecap after the rectifier bridge, you will have a full wave rectified waveform at the input to the voltage regulator.
>>the purpose of using the recrifier is the prevent reverse polarity of the input voltage. However I'm using the 12Vdc 3.5A (very regulated DC voltage) adapter since it
had already rectified to a stable DC.
Therefore, you're expecting the regulator to eliminate this very large ripple signal.
>>i beliv there would not have any large ripple after the bridge as I'm using a regulated 12Vdc not 12Vac.
Is your comparator circuit designed as a Flip Flop or just a comparator?
>>it is design as a comparator with the Vref 4.92V. Building this comparator is to monitor the 5V line if it drops during the switching process. Since I do not have any
Scope to check on the 5V line.
If the latter is true, then the drop in voltage may be too brief for you to see the LED
flash.