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I understand the use for two binding posts on a breadboard: namely to connect the + and - of a DC power supply. But what it the purpose of breadboards with three binding posts?

In this tutorial I read: "Typically, you only need to connect a power and ground wire from the posts to the breadboard. If you need an alternate power source, you can use the third post." But would I not need a third and fourth binding post to connect a second power supply?

So how do you make use of just a third binding post?

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    \$\begingroup\$ if you need +15 V, -15 V, and ground? Really common with op amps and the like. \$\endgroup\$
    – Hearth
    May 11 at 19:29
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    \$\begingroup\$ signal in or signal out ... i use it to connect an external switch ... that way i do not pull on wires that are connected to the breadboard ... not really an electronics design question though \$\endgroup\$
    – jsotola
    May 11 at 22:23

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Some components need a positive and negative supply voltage, and also ground, eg OpAmps. This can be achieved with voltage-splitters or just plain old resistors. For basic dc electronics you won't really need dual-supply.
Or if you need for example 15V and 5V you could also use the three points, but thats probably a bit messy.

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  • \$\begingroup\$ Ah, I see. So I would use a single power supply and converter to generate different voltages which all share the same ground? \$\endgroup\$
    – Linus
    May 11 at 21:46
  • \$\begingroup\$ @Joel Rupp I would recommend against creating dual supply rails using "voltage-splitters or just plain old resistors." Not really sure what a voltage splitter is and you should almost never use resistors to generate power rails. These dual positive/negative voltages are usually generated by dedicated power supplies or supply ICs. \$\endgroup\$ May 11 at 21:52

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