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I want to use a rotary DIP switch to set an ID number on a number of identical boards I am using for a project. I have run into the following three lines in the data sheet and I can't make sense of them:

Contact Rating:

  Non-Switching: DC 50V 100mA
  switching: DC 5V 100mA
  Minimum: DC 20mV 1uA

What do these lines exactly mean? What is the meaning of Switching as opposed to non-switching?

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  • \$\begingroup\$ Can you post the datasheet? \$\endgroup\$ – Butzke Sep 24 '13 at 16:17
  • \$\begingroup\$ Are you sure the switching voltage rating is higher than the non-switching? \$\endgroup\$ – JYelton Sep 24 '13 at 16:26
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Switching refers to the voltage and current that the switch can safely handle when transitioning from open to closed or closed to open without excessive arcing and damaging the contacts.

Non-switching refers to voltage and current that the switch can safely handle when the contacts remain in one position.

The minimum rating is a little more complicated. If the switch is operated with too little current, it can build up resistance (from dirt and corrosion) and eventually fail. A small amount of arcing is actually desirable to keep this accumulation from happening. This is also known as "wetting" current.

Reference: Switch contact ratings on AllAboutCircuits.com.


Edit, per comments:

BCD switch contacts from datasheet

I'm not sure which specific version of the rotary switch you have, as the datasheet is applicable to several variations. However most have the same pinout as above. The "C" terminals stand for common, meaning that an electrical connection is made from the common pin to any or all of the numbered pins based on the position of the selector.

For example, with a "real code" switch, if the selector is at position 3, then pins 1 and 2 will both be connected to common. The behavior of complementary code and gray code switches are different; this is outlined in the chart "Code Format" on page 2 of the datasheet.

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  • \$\begingroup\$ Thanks for the answer. Would you mind taking a look at the data sheet here: copal-electronics.info/en/0020f/02525.pdf And telling me how you think the two pins marked with a C should be connected up. I can understand the pins that provide the state of the switch, but the datasheet is vague on the two other pins. Many thanks \$\endgroup\$ – Essi Shams Sep 24 '13 at 16:28
  • \$\begingroup\$ "C" is what the other pins will be connected to when their switches are closed. Connect it to whatever voltage you want to read as "high" and put pull-down resistors on all of the switched pins. (or connect it to "low" and put pull-ups on the switched pins) \$\endgroup\$ – The Photon Sep 24 '13 at 16:34

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