Momentary push button DPDT switch with alternate action

[Western]

Hi guys,

I am wondering if there is such an animal as a DPDT momentary push button switch where it is normally open ... press it once and it rocks to one side to close contacts ... release it and it opens ... press again and it rocks to the other side closing those contacts.

Have someone who wants help with a project and they are talking H-Bridges and Arduinos, which are all fun and stuff ... but unecessary complication for his purpose.

Thanks.

 

[augustinetez]

If there is an Arduino involved, any reason it can't be done in software and just use a simple push to make switch?

 

[Western]

No, he has no idea what an Arduino even is ... that was what was recommended to him.

Since he has asked my opinion, I'm suggesting he avoids using an Arduino to keep his job as simple as possible ... and I'm just trying to come up with ways to help solve his problem.

 

[augustinetez]

I've checked some of my regular suppliers and they don't have anything like what you are asking for - they are mostly one set of contacts is closed and then when you push the button it switches to the other set and releases and goes back to the first set when you let go (if that made any sense).

You may be able to rig something using two of that type of switch.

C&K Switches 'may' have something in their 'Alternate Action' switch range, but it is a large website and will take some searching as the website and their datasheets are not all that informative.

 

[Visitor]

Would a DPDT center-off momentary toggle switch work? Push one way for forward, the other way for reverse, and when you let go, the switch is off. Digikey has a bunch of options for this. DPDT, mom - off - mom or sometimes shown as (on) - off - (on) where the parenthesis indicate a momentary position.

 

[Western]

Thanks Terry, that was the same conclusion I came to after spending ages going through catalogues and datasheets.

I was hopeful when I saw 'Alternate Action' as well ... but I ended up with the impression that was for latched switches, where one push closes one set of contacts and the next push changed to the alternate set.

Thanks for your help.

 

[Western]

Would a DPDT center-off momentary toggle switch work? Push one way for forward, the other way for reverse, and when you let go, the switch is off. Digikey has a bunch of options for this. DPDT, mom - off - mom or sometimes shown as (on) - off - (on) where the parenthesis indicate a momentary position.

Yes, that is exactly what I thought of too ... but when I put it to the guy, he was adamant that he wanted a pushbutton switch.

I did find a fairly flat rocker switch that appeared to work like the toggle switch you mentioned above ... maybe that'll appeal to him.

 

[AnalogKid]

Your problem description is nice and clear (thanks), so I'm pretty sure the answer is no. There is no catalog-standard, off-the-shelf pushbutton switch that has a four-state cycle. A common switch for ceiling fans has a four-state cycle, but it is off - A on - B on - A&B on. and it is pull-chain, not pushbutton.

Two DPST relays can be controlled with a SPST pushbutton switch through a small circuit that is way less complex than anything Arduino. And of course, the relays can be replaced with solid state switching devices (BJT, MOSFET, SSR, etc.)

1 - CD4017
2 - 2N7000 (relay drivers)
2 - DPST relay
2 - 1N4004 (transient suppression)
1 - SPST switch
1 - resistor
2 - capacitor
optional R-C power-on reset

ak

 

[Visitor]

If there was an alternate action pushbutton, you'd never know if the next push would give you forward or reverse. It would be opposite what the last push did with no indication of what that will be.

 

[Western]

Preview

AnalogKid said:
Your problem description is nice and clear (thanks), so I'm pretty sure the answer is no. There is no catalog-standard, off-the-shelf pushbutton switch that has a four-state cycle. A common switch for ceiling fans has a four-state cycle, but it is off - A on - B on - A&B on. and it is pull-chain, not pushbutton.

Two DPST relays can be controlled with a SPST pushbutton switch through a small circuit that is way less complex than anything Arduino. And of course, the relays can be replaced with solid state switching devices (BJT, MOSFET, SSR, etc.)

ak

Thank you AK ... and I was slowly coming to the same realisation about the switches.

Edit:

Sorry, the rest of my reply vanished!!!

I definitely agree that an Arduino would be overkill and should be able to do it far more simply ... in fact I think it could be done with a 'normal' DPDT momentary pushbutton switch, an electro and a resistor ... though still would have been easier with my mythical switch.

 

[Western]

If there was an alternate action pushbutton, you'd never know if the next push would give you forward or reverse. It would be opposite what the last push did with no indication of what that will be.

Nah, he'd know when it swapped. It is to turn on (and off) a firehose nozzle so I'm pretty sure it'll be obvious.

 

[Pommie]

It is to turn on (and off) a firehose nozzle

So why does it need the second set of contacts? A simple push on/push off will do what's needed or I'm missing something.

Mike.

 

[Visitor]

So why does it need the second set of contacts? A simple push on/push off will do what's needed or I'm missing something.

Mike.

I think that a motor is being used to open a valve, then close the valve – screw the handle out, then screw it back. So momentary power to the motor in one polarity, then off. Then in the reverse polarity then off. I think.

Too sleepy at the right now to have coherent thought about solutions, but I think I understand the problem now.

 

[Les Jones]

Is this relating to the same question that was asked on the AAC forum relating to solenoid actuated points on a model railway ? If so it took a long time to find out what the tread starter wanted. several solutions were provided.

Les.

 

[Western]

So why does it need the second set of contacts? A simple push on/push off will do what's needed or I'm missing something.

Mike.

Sorry, been working.

Okay, the firefighting nozzle has a latching solenoid in it to turn on and off the flow.

From the guys explanation, it requires a 12v pulse to latch it on, and a reversed 12v pulse to turn it off.

He explained that from his experience fighting fires, it was really difficult to keep holding a pushbutton down for half an hour at time perhaps ... so the latching solenoid solves half his problem.

That's why I was after a DPDT push button switch that can be wired to reverse the voltage to the solenoid ... but they only seem to be available in toggle or rocker switches with a centre off and momentary either side ...

... and he specifically argued that a rocker switch is difficult to make work in this situation. I am assuming he means difficult to physically operate ... rather than it won't work technically.


And good guess Visitor, very close to the mark.

And no Les, definitely notthing to do with model railways.

 

[Visitor]

Where does the 12v come from?

 

[Western]

Where does the 12v come from?

I didn't ask that question, but he did say the switch is on the hose near/next to the nozzle ... and not remote ...

... so it seems to me it must be fed along the hose ... tied to or taped ... dunno.

Apparently this is for small mobile units where the driver hangs (his arm) out the widow and tackles the fire while driving.

 

[AnalogKid]

With that extra detail in post #15 - ! (tsk), it is clear why an H-bridge was in the discussion.

But ...

If it is "latching" solenoid, why does the button have to be held down continuously? Or are you saying that *changing* to a latching solenoid removed the continuous requirement - ?

And to be clear, both the switch and the solenoid are out at the nozzle, and the only thing running up and down the hose is continuous +12 Vdc?

ak

 

[eTech]

That's why I was after a DPDT push button switch that can be wired to reverse the voltage to the solenoid ... but they only seem to be available in toggle or rocker switches with a centre off and momentary either side ...

Momentary center-off switches are designated (ON)-OFF-(ON). You are looking for an ON-OFF-ON switch.
I've seen those in toggle and rocker type switches

 

[Visitor]

So let's go back to the beginning here, and what I think the story may be.

The nozzle requires 12 volts to activate it. Originally, it was operated via a momentary push button switch. Press the button, and it's on, release the button and it's off. This seems like the likely scenario.

So why not replace the momentary push button with a push-on / push-off button and eliminate the latching relay and all the rest? That seems like a needlessly complex and potentially unreliable solution that depends on using a switch that doesn't exist.