Help with circuit

Thread Starter

Mr6ft6

Joined May 6, 2024
3
What would be the best way so when any one switch is pushed all of the others will not be able to supply voltage. Only one switch in the circuit could be live at any time. 12 vdc 3 Amp load max1000000480.jpg
 

WBahn

Joined Mar 31, 2012
30,303
So what should happen if SW3 and SW5 are closed at the same time?

Which one should be the one that is supplying power?
 

MrChips

Joined Oct 2, 2009
31,088
You could do it if the switches were prioritized, e.g. SW1 has highest priority and SW6 has lowest priority.
For example, if SW6 is already on, any other switch could steal the power from SW6.
 

SamR

Joined Mar 19, 2019
5,081
Not sure just what your circuit is but multiple switches for the same load to be disabled after any one pushed can be done using a seal-in and disable relay contacts arrangement.
 

Irving

Joined Jan 30, 2016
4,065
Simplest mechanical solution is a piano switch... eg

https://www.amazon.co.uk/uxcell-Interlock-Button-Switch-Piano/dp/B07PCKVNXX, but expensive, maybe $18-$20+

1716228818042.png


Doing it purely with relays might be possible, but I couldn't see a simple solution with just SPST or DPDT relays, maybe with expensive set/reset latching ones.

The easiest/cheapest solution, IMHO, is a <$2 micro-controller, eg PIC or ATtinyxx, driving 5v relays (< $1 each for 10), here shown for 3... but a 6-channel version will be about 1/2 the price of a piano switch...

1716230803368.png
 

Tonyr1084

Joined Sep 24, 2015
7,998
I have a three speed fan in my shop. It's made from an old furnace blower, built into a box with air filters. The attached switching arrangement gives priority to HIGH speed, (SW1) rendering Medium (SW2) and Low (SW3) inactive. You can switch ALL three switches on and only one will power the fan, the HIGH. If the High is off then MEDIUM is the next priority. Switch it off and the last switch, Low, is active. Of course if all three switches are off then the fan is off.
Screenshot 2024-05-20 at 1.23.50 PM.png
 

Thread Starter

Mr6ft6

Joined May 6, 2024
3
So what should happen if SW3 and SW5 are closed at the same time?

Which one should be the one that is supplying power?
So I'm sorry I'm not clear. I would like to change the circuit so that only one switch at a time could ever be powered up. Even if someone were to push the button for one or even all those switches only one first pushed would complete the circuit at a time until power is shut off
 

WBahn

Joined Mar 31, 2012
30,303
So I'm sorry I'm not clear. I would like to change the circuit so that only one switch at a time could ever be powered up. Even if someone were to push the button for one or even all those switches only one first pushed would complete the circuit at a time until power is shut off
There are a number of ways to do it -- largely depends on the basic technology you are looking to use. A microcontroller? Relays? Mechanical?

A simple relay-based approach would be to use a relay with each button configured as a latch that supplies power not only to the relay to keep it latched, but to it's load. Then, put another set of switch contacts on each relay in series to supply power to the buttons when no relay is latched. The first button to get pressed latches itself and robs all of the others of power. Cycle power on everything will open the latched relay and return the system to its initial state. No switch has priority over another.

There IS the possibility that, if two buttons were pressed at the same time, that both of them could latch. Would be unlikely to happen, but possible. So how likely is it to occur that multiple buttons are pressed with a few milliseconds of each other? And how devastating would it be should two or more circuits happen to latch closed?
 

panic mode

Joined Oct 10, 2011
2,880
without using selector switch or logic circuitry, this is as far as you can go.
if the switches are piano type, pressing any switch would reset others.

the elegant solution is to use programmable device since very few parts are needed and the switches can be buttons (no need for mechanical interlocks). also this can ensure dead time on each transition if required.

1716252017315.png
 

PeteHL

Joined Dec 17, 2014
479
Is there a single load or does each switch supply voltage to a separate load? Must the switches be single pole single throw (SPST)?
 
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Irving

Joined Jan 30, 2016
4,065
Game show "first who buzzes in locks the other contestants out".
That's exactly what the microcontroller example I gave was used for, wthout the relays just a transistor on each channel, as it only needed to light a big LED and operate a buzzer. After 0.5 sec the buzzer was silenced and the LED went out after 5 sec.

but the TS wants 3A capability per channel... hence the relays
 

panic mode

Joined Oct 10, 2011
2,880
many ways to do this... the easiest is to use smart relay or small PLC. but one can also use 6 buttons and 6 relays. buttons would need plenty of normally closed contacts therefore industrial style would be needed (contacts can be added and removed at will). using just buttons and relays would be a lot of wiring. ok for one time thing but not something to mass produce. for something to be mass produced it would be better to use PCB and additional relays with more contacts.
1716293781224.png

using programmable controller things can be very flexible. for example using 2s complement one can get this to work with just two instructions while number of channels can be as large as register size of the instructions. here is an example of 32 bits/channels.
1716294573383.png

or just one instruction if your controller allows expressions:
1716294864012.png

and if that is not enough, one can use loops so there is practically no limit...


correction...
above example would clear outputs when no button is pressed.
this can be fixed by only processing the code when some button is pressed

1716295169834.png
 
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Tonyr1084

Joined Sep 24, 2015
7,998
Game show "first who buzzes in locks the other contestants out".
That's exactly what the microcontroller example I gave was used for, wthout the relays just a transistor on each channel, as it only needed to light a big LED and operate a buzzer. After 0.5 sec the buzzer was silenced and the LED went out after 5 sec.

but the TS wants 3A capability per channel... hence the relays
Yes. I understand the 3A capacity. It seemed to me like some comments were going a little off track. So I posted with the intention of bringing the subject back into clarity. I'm sure I could figure out a way to do the game show buzzer thing but I've been busy in the wood shop and don't have much more time than a brief visit before opening shop. So my comment wasn't posted to answer the question but just to bring it back on the track I thought the TS wants.
 

panic mode

Joined Oct 10, 2011
2,880
1. the problem with game show circuit is that it needs reset, before it can work again.
2. the simplest option is selector switch. the problem is that one may not want to energize "in between" channels while changing selection. the advantage of selector switch is that it retains the state during power outage. programmable systems can do the same by using nonvolatile memory.
3. the piano key is mechanical contraption that works but it is from the old days that most newcomers have never seen and may have problem finding/selecting right one.
4. using series of SPDT switches will work just fine. the only issue is that one need to turn off previous one off.
5. the microcontroller is the ideal option but requires programming which not everyone will be happy to do.
6. version with relays and seal in circuit does the same thing but requires either buttons with a lot of NC contacts or interposing relays. no programming but lots of wiring and easy to make a mistake.
7. the circuit in post 12 will do exactly the same without programming. need an oscillator (555 will do) to create clock. replacing LEDs and series resistor with transistors and relays (or ULN200x) will do exactly the same function as microcontroller.
8. using smart relays or PLC is great if you already have one and know how to use it
9. XOR logic. (still needs relays)
10. using ROM... (still needs relays)

well...

not sure what Tonyr1084 was concerned about. i think that is quite a list of things that are very much on topic.
 

Tonyr1084

Joined Sep 24, 2015
7,998
not sure what Tonyr1084 was concerned about. i think that is quite a list of things that are very much on topic.
Didn't say it was off topic. Was just noticing that a few comments were going off in a different direction from what the TS was asking for.
What would be the best way so when any one switch is pushed all of the others will not be able to supply voltage. Only one switch in the circuit could be live at any time. 12 vdc 3 Amp load max
Here's the point I was following on: Assume 10 switches. Suppose switch #3 is pressed. All other switches are locked out. Once the other switches are locked out - if you press any other switch nothing would change. There MUST be some way to reset the switches.

In post #6 I gave an example of a way to have a priority switching system. It works well for my 3 speed fan, but it doesn't seem to be quite what the TS is searching for. XOR gates, µC and programming along with relays to handle the higher power - yeah, those are in keeping with the thread. But things like the Piano switch - while that's a very close proximity to what is being asked for - it's not quite there. You can push #2 and 2 is on. Then you can push #4 and 2 shuts off and 4 turns on. That's not what I'm picking up on.

For sure I could be the one on the wrong track. I'm not right, just trying to be of help.

I think the paint should be dry enough by now. Be back tonight.
 
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