Triple Play Solid State Limit Switch Noise Filter


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Thread: Triple Play Solid State Limit Switch Noise Filter

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    Thumbs up Triple Play Solid State Limit Switch Noise Filter

    I have had issues off and on with VFD noise coupling onto my limit switches and causing false trips on the inputs. I have used software filtering with some success and also a relay voltage level conversion circuit. But I wanted something more robust. Long story short, I built a solid state filtering board that eliminates noise three ways:


    1. High voltage (24V) is used for all switch and input wiring. The 24V signaling is then attenuated down to 5V before being passed through step 2 below. The 24V to 5V conversion reduces all signals, including noise, by about 80%.
    2. Low pass filter slows down the signal edge and eliminates all high frequency noise
    3. Schmitt trigger buffering cleans up non-monotonic signal edges to prevent multiple triggers and produce a crisp clean signal. Using shmitt triggers instead of relays means no moving parts to fail over time.


    The circuit logics, calculations, BOM, board, and some scope shots are included. I may do a PCB later to clean things up.

    -Enjoy!

    Similar Threads:
    Attached Thumbnails Attached Thumbnails Triple Play Solid State Limit Switch Noise Filter-limitswitchfilter-ckt-jpg   Triple Play Solid State Limit Switch Noise Filter-limitswitchfilter-bom-jpg   Triple Play Solid State Limit Switch Noise Filter-filterboard-front-jpg   Triple Play Solid State Limit Switch Noise Filter-filterboard-back-jpg  

    Triple Play Solid State Limit Switch Noise Filter-rdivider-filter-png   Triple Play Solid State Limit Switch Noise Filter-schmitt-filter-png  


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Triple Play Solid State Limit Switch Noise Filter
Triple Play Solid State Limit Switch Noise Filter