Make normally closed switch act as normally open

[acehobojoe]

can it be done?

[GibsonGM]

Depends on where you are using it, for what, and why.  An inverter (do a net search, "BJT inverter") will do the INVERSE of what you feed it....so, a low signal going to a BJT inverter will give a high output, and vice versa.  Your switch would then have the "opposite property", and look like normally closed...ideally...

You'd have to use an inverter anywhere the switch is, and there are places this just makes no sense, such as in bypass situations...I can see places where you'd have serious problems routing audio thru the switch (wiser minds know what this is called).   

Guess the answer is  - sometimes you can hack them, sometimes not...

[PRR]

The universal way is a relay. Normally-closed relay through NC switch and battery is Open until you hit the switch, then it closes. When not hit, power is consumed.

You need to say more about the job before we can sensibly explore other options. We "could" use a NC switch to shut-off a light until pressed, just by shorting the light. A 60 Watt house-lamp, this would burn-up the wires or pop the fuse, not good. However an LED and 10K resistor, shorting the LED is quite practical and the increased power is tiny. Same ideas apply to making/breaking signals, with the same concerns about shorting things that resent shorts.

[noisette]

Not sure if it addresses your question, but it might be of  interest anyway...
http://www.nicolascollins.com/texts/superswitch.pdf

[nocentelli]

Nice link, noisette, thanks! I'll have to draw myself a schematic to understand how it works: Perfect trigger control for a simple synth I'm working on.

[acehobojoe]

Noice! Thanks guys.

[acehobojoe]

I will be using it with high amps on a mosfet switch (that works well) but the control voltage is pretty small. The BJT sounds like it will work, but I'll have to test it out.

The idea is that the mosfet should be able to turn on with either a NO switch or NC for input.

[R.G.]

You need to say more about the job before we can sensibly explore other options.

I will be using it with high amps on a mosfet switch (that works well) but the control voltage is pretty small. The BJT sounds like it will work, but I'll have to test it out.

The idea is that the mosfet should be able to turn on with either a NO switch or NC for input.

Translating:
"I got the MOSFET well pump power switch that you guys suggested running, now I need help getting the drive to the MOSFET running for different circumstances."

[acehobojoe]

I'm sorry.

[acehobojoe]

I guess I should explain a little bit to you the full backstory.

The question should really be, can I ask work related questions to you all? I understand that this is a hobby forum and meant for stompbox questions, so I'll understand if you want me to keep posts gear related.

I need to conduct research elsewhere when designing stuff for a company. This is really my first time doing anything like this.

I actually got the job because of this forum and a comment RG made a while back. He told me to find someone to help me work with high voltages safely before attempting to design a power supply. This led me to a man who works independently on solar energy and alternative energy near my house. I asked him a question, and he gave me a job. It's a lot of manual labor, but it sure is fun. One of our first jobs involved converting three phase AC to DC for this water turbine thing. We use a modules mostly, so very little soldering.

I wanted to use this mosfet switch design to control the well pump as mentioned above, because I remembered that you can use this little transistor thing to turn on a higher voltage with a lower one! Much like our distortion and boost pedals. And I knew the idea of it, but didn't ever use it as a power transistor. So I did a lot of video watching and looked at a few ways of doing it, and came up with a design that used the transistor like a relay.

The reason this pump should have a solid state relay, is because it needs a few specific charactaristics that a simple high amp relay wouldn't provide. There are great relays out there that would work fine for us, but the normally open normally closed deal and a few other little tricks were why I thought it would be better to design a mosfet PCB.

You all have helped me tremendously as friends or acquaintances that are on the internet while I dove into pedal building, and I understand if you want to keep this forum focused. I really shouldn't have asked.

[Transmogrifox]

There are off-topic threads that might be a little more appropriate.  I do think there are many in the lounge who might like the little brain-teasers.  These things with solar systems, pumps and other practical electrical systems are really interesting and fun to toy with, and there is a good chance somebody will give advice in the Lounge.

Just my opinion, but I think most will agree that commercial interests aren't taboo (it appears many who use this forum are making money on what they learn and that seems a perfectly sensible thing to do) ... just non-guitar stuff doesn't really fit in "Building your own stompbox".

However, if this thread could be steered back to the more vague form in which it was started, the idea of inverting a switch function I think is relevant and useful in the building your own stompbox setting, and I see this thread invoked the answers that are not entirely OT.

[acehobojoe]

There are various stompboxes with a tap tempo function that can be controlled with either NO or NC, changed by a switch.

[acehobojoe]

Here's the final design I went with. You can see that the power transistor is turned ON when a voltage is applied to it. In this case, it's 24v. It will work with 48 50, 60, doesn't matter. The magic is happening with the PNP transistor at the top.

The PNP transistor works by allowing current to flow out of it's base. The way to use this to my advantage is to simply always allow a small current out of it (via the 2k resistor), making it normally closed, and apply a positive voltage to the base to open the switch. With this setup I have two switches that can do two different things.

The NO switch simply allows the circuit to have power. The NC switch allows it to have power but be operated by a different kind of switch. It's mainly supposed to be an idiot proof design, so that someone can't buy the wrong kind of switch. It will always work.

Unfortunately, there still has to be a toggle switch to choose NC "mode" or NO "mode", but that should be pretty user friendly. The Switch not put on the schematic is between the R1 power and the Emitter of the PNP transistor.

This has many stompbox uses, if anyone needs it. You could use it to power a pedal , or the most obvious use to me is for a tap tempo that you want to make versatile. Many people know about those pesky boss tap tempo pedals that only work with NC switches. With this design, you could allow a pedal to work with either type of switch. Usually the delays and controllers use some sort of 5v pulse that would work just fine with the PNP setup. So it's easy to "trick" your setup into thinking you have a NO switch or viceversa.

I've not looked into boss pedals much, but I'm sure you could use a pnp to accomplish the reverse of what I did.