Re: SPST Frustration

[K3yPr0gg3r]

Hi,

I've got a bug about building some discontinued circuits, (thought my Pepper Spray wouldn't work but sounds great!). Anyway, the build docs call for SPST ON/ON for Deadpool (Body & Comp), Doombutter (Fuzz Lift), and Uproar (Pres.). I've been banging my head trying to find ON/ON, when all I'm finding is ON/OFF. I found an example of wiring an SPDT ON/ON so it acts like an SPST ON/ON, (See Attachment Pic), in the Mysterioso Jr. doc. Would this be the best way to go as an alternative?

Thank you

[jimilee]

Yep. I use spdt instead of spst because they serve the same purpose, but I usually keep some in hand too.


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[K3yPr0gg3r]

Thank you. For the "jumper", should I just use a small bit of wire or a resistor lead, (for a PCB jumper)?

[davent]

SPST can only be on or off, spdt gives you ON/ON.



dave

[midwayfair]

It's helpful to get a better visualization of what a switch actually does.

Grab your favorite toggle, preferrably a 3-lug SPDT switch, though a center off is also fine (and instructive). Use an actual toggle, not a stomp switch, because it's easier to see what's going on.

Now get your multimeter and put it on continuity.

A switch is nothing but a way to connect two wires some of the time.

Any given switch can have at least two positions (or else it isn't switching anything): It can connect the wires, or it can not connect the wires. We call that "on" or "off."

In davent's picture, the spst part of the graphic shows you a single switch. It's open in the picture (per the general schematic icon).

So turn on your multimeter, and touch the probes to two lugs at a time until it beeps. That tells you how they're connected. Flip the switch. Those two lugs are no longer connected, so it doesn't beep. If you have three lugs, though, you'll find that the other outside lug is now connected to the center.

In this type of switch (on-on), the center is called a COMMON lug. If you're using all three lugs, that's the one that's in the circuit regardless of which outside lug is connected to it.

Look at the toggle's bat. You'll see that when it's switched one way, if you follow it like it's a straight line diagonally, it moves the connection to the lug at the end of that line. Like this:

\ < top of the bat
  \
    \ < inside the switch
|  |  | < the third lug is the one that's connected now.

      /
    /
  /
|  |  |

This is flipped the other way and the first lug is the one connected.

So a SPDT has "two throws." That actually means that it's like two switches in one. One switch can be on while the other is off, but you have to have a single connection that's common between the two switches. If you want to switch two things with nothing in common, you need to add a "pole" (another row of lugs).

Anyway, what's the deal with the picture you found? After all, they connected two lugs (the two at the top) and then show you using just the bottom one, while I'm sitting here telling you that you only need to use two lugs.

This is basically just a safety thing. If something happens to your switch, you have a little bit of redundancy with the extra connection. The only thing being switched is still the bottom.

[K3yPr0gg3r]

Thank you, again. So when the build doc states SPST (ON/ON) it's a type-O. Am I able to use ON/OFF switches, for the Doombutter Fuzz Lift for example or the Pres. switch for Uproar? Flip the switch to turn "whatever" on, flip again to turn it off. Don't mean to be OCD, but I've had such a good run with builds of late, I don't want to ruin a circuit because of a stupid switch! If there HAS to be something ON/ON in order for the circuit to work, I'll order SPDTs and wire as "midwayfair" suggested.

Thank you

[midwayfair]

Look at the schematic. Count the connections the switch is required to make. Use a switch that can make those connections. Refer to Dave's diagram if you're not sure. Confirm with your multimeter if you haven't.

While we can certainly sit here and tell you what's appropriate for every circuit, it would be far better for you and us if you internalized what the schematic symbols mean are needed and how the physical device works with hands-on experience.

[K3yPr0gg3r]

Just need some clarification before I order...don't want to waste $! In the schematic the SPST is labeled with a 1 and a 2. Doomsch1 pic shows the "Fuzz Lift" part of the Doombutter circuit which, if I'm reading the schematic correctly, brings in or takes out C2 (47uf). Anyway, 1 is underlined in purple and 2 in green. The Deadpool build doc wiring page shows two SPDTs, (versus SPST), being used for "Body" and "Comp". Deadpoolwiring1 pic shows this. My question is on an SPDT ON/ON toggle does 1 get wired to the center lug of the switch, and does 2 get wired to the right lug as shown in the pic?

Thanks

[davent]

Just need some clarification before I order...don't want to waste $! In the schematic the SPST is labeled with a 1 and a 2. Doomsch1 pic shows the "Fuzz Lift" part of the Doombutter circuit which, if I'm reading the schematic correctly, brings in or takes out C2 (47uf). Anyway, 1 is underlined in purple and 2 in green. The Deadpool build doc wiring page shows two SPDTs, (versus SPST), being used for "Body" and "Comp". Deadpoolwiring1 pic shows this. My question is on an SPDT ON/ON toggle does 1 get wired to the center lug of the switch, and does 2 get wired to the right lug as shown in the pic?

Thanks

In the first circuit the switch controls a feedback loop around the amp chip, the cap is always in circuit.

One wire always goes to the center lug, doesn't matter which outer lug the second wire goes to but with two switches you'd want the switches oriented the same way when mounted in the enclosure so the toggle off/on of the switches are oriented the same.

dave

[K3yPr0gg3r]

That's what I needed to know. Thanks Dave!

[beneharris]

don't want to waste $

I'd encourage you to waste the money. Especially for the cost of a couple switches. I can't tell you how many things I've picked up and have had stick because I used the wrong part or tried something that didn't work. And I've only been doing it for a year or two.