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I have external switch with 24v/open circuit. I think that I only need voltage divider and drive the FPGA input, but something feels weird for me, maybe I need some capacitor for noise? maybe some buffer to protect the FPGA? enter image description here EDIT: Please see the attached DC electrical characteristics On my board when external switch leaved the voltage will be ~0v when pressed the voltage will be 24*1.5/12.5= ~2.9V enter image description here

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  • \$\begingroup\$ Do you plan to debounce it in the FPGA? \$\endgroup\$
    – winny
    Commented Sep 7, 2023 at 7:43
  • \$\begingroup\$ Are you sure that will even present the FPGA with correct logic voltage levels? \$\endgroup\$
    – Justme
    Commented Sep 7, 2023 at 7:46
  • \$\begingroup\$ @Justme please see my edit \$\endgroup\$
    – Knowledge
    Commented Sep 7, 2023 at 7:57
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    \$\begingroup\$ ESD protection etc. is pretty important to consider if it is an external connection. \$\endgroup\$
    – Klas-Kenny
    Commented Sep 7, 2023 at 8:07

2 Answers 2

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There are tons of example input circuits. Just google it. Some very simplistic ones are below. You can keep adding more to them as you want to add more protection, or debouncing etc.

schematic

simulate this circuit – Schematic created using CircuitLab

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You should consider adding ESD protection devices, such as TVS (Transient Voltage Suppression) diodes, to your input lines.

To filter out noise caused by switch toggling, you can add a small capacitance to smooth the input signal before it reaches the FPGA.

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  • \$\begingroup\$ can you show me how to connect it ? \$\endgroup\$
    – Knowledge
    Commented Sep 7, 2023 at 11:09

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