Hardwired Circuit

[Steve Etter]

First, thanks to all for your comments. This is all really good information and I always like learning how to think a little differently about a problem than I already do.

Archie - Looking at your scheme (Momentary Pushbutton Control Full Circuit), I agree that it will work perfectly for PLC control but could potentially have one problem in the hardwired world if not taken into account...your pushbutton must have the N.C. contacts "making" before "breaking" the N.O. contacts. If you don't, the latching circuits will drop out as you let off the pushbutton.

pkshaver - I thought about using a programmable relay, but in the industry I am in (as an OEM), the lower tech I can go, the better. I would prefer to stick with old technology if possible..even if it is slightly more expensive..to keep from having to store and/or keep track of additional programming.

Gerry - I still haven't looked at the ratchet relay yet, but I believe it will be one of the two solutions I will end up using. Thank you.

Eric - First, yes, I do need to toggle with each press..but your point is well made. Second, thanks for pointing out the maintained foot switch option. I have never had to find and order a foot switch before, so I was not aware of this option. This is my favorite solution and, provided I can get one from my supplier, it will be how I go. Thanks.

Steve

 

[Eric Nelson]

Yeah, we're just full of ideas around here... and sometimes full of other stuff too...

What brand (and part number) switch do you have currently? I can probably help you find where to get a similar or even identical maintained version...

-Eric

 

[Steve Etter]

The one I am currently looking at is a model 83895101 made by Crouzet. The only reason I am looking here is because they were the first ones to walk through the door. Any and all manufacturers you could point me at would be appreciated...especially those you have good experience with.

Steve

 

[Eric Nelson]

For some reason, Crouzet's website is M.I.A., but I see that Allied Electronics used to sell that particular model for $150, so I guess that's about what you plan to spend.... That's a reasonable budget for a decent guarded foot switch.

I don't use foot switches that often, but when I do, it's usually one from Linemaster mainly because they're readily available for places like Grainger, MSC, and McMaster-Carr. Linemaster makes very good switches, but there are plenty of others...

Check with companies like Conntrol or Altech. Nearly every switch they sell can be ordered with maintained contacts. Don't forget that companies like Square-D and A-B also sell these...

Or just search for "foot switch" at Google.... Lotsa links!

-Eric

 

[Archie]

Steve

I agree with you on the problem of a make before break requirement.
So I have put out on the site another solution based on one-hot design, in which one relay is energized representing each state. This design does require more relays and contacts.
The bottom line is that this design does not require make before break contacts.

http://www.geocities.com/plctech99/index.html

Once again, I have not built this one in hardwire to test it, but the theory is there.

BTW, when using DC voltage, this can be done with 3 SPDT relays. I have used that circuit in the field multiple times. Works great in automotive applications when you only have a negative pulse to switch with.

 

[Dave]

Hi Steve

Yes you can do this circuit hard wired. I have myself, for a conveyor. Press a foot switch to start the conveyor then press it again to stop it. But always use positively guided contacts e.g. a contactor. I used three relays for my circuit and 50% of the time worked fine, but every now and then a contact would make before another and would fail to work properly.

Dave

 

[[email protected]]

My 2 cents

I dunno, but I think some of you may be making this harder than you think. I believe what he is trying to accomplish can be done with 3 regular ice cube relays, one pushbutton, and his solenoid. Take this and see if you can see my point. CR1 is used for direct control of the valve, relay on, valve on, etc. CR2 is merely a relay to acknowledge that CR1 is on and the pushbutton is not depressed. (use a NC of the PB) Lastly, CR3 is used to drop out CR1 and CR2. I won't go any further into details on this, cause I probably already lost ya, but just take the idea and play with it once. If no one else can understand where I went, I'll try and post the wiring diagram. I feel as though this should work. It's a piece of cake to draw.

Russ

P.S. Just another hint, I used N.O. contacts of each relay to latch themselves on, but what they latch around varies, meaning the switch, or other relays in the rung.

 

[Eric Nelson]

Re: My 2 cents

I won't go any further into details on this, cause I probably already lost ya

Nah, we do a lot of wanderin' around here, but we NEVER get lost!...

I understand your idea, but when was it mentioned that there's a NC contact available??? And even if there was one, can we be sure it's a break-before-make? Sure, you could create the contact by adding yet another relay in sync (no, not n'sync) with the PB (er, I mean foot switch).

I think the "challenge" of the original question was to create a flip-flop output from a SINGLE dry contact.

beerchug

-Eric

 

[[email protected]]

More meaningless jargon

First, I don't think that there are ever limitations. The initial idea was to create the circuit with a single pushbutton, nothing said about only one set of contacts. To try to do this with one set of switch contacts is not smart anyways, being they are available so abundantly and cheaply. That being said, this is what I proposed. Maybe my thinking is wrong, but to the best of my knowledge, this should work regardless of whether the contacts are make before break, etc. If the man wants to try to use this great, if not, then it just helped me kill a few slow moments at work.

PB1 CR3 CR1
1---1 1-----1-------1/1-------------1---( )--------1NEUTRAL
1 CR1 1 1 SOL 1
1---1 1-----1 1----( )-------1
1 1
1 1
1 PB1 CR1 CR2 1
1---1/1----1--------1 1------------------( )-------1
1 CR2 1 1
1---1 1----1 1
1 1
1 PB1 CR2 CR3 1
1---1 1--------1----1 1-----1------------( )-------1
1 CR3 1
1----1 1-----1



I will assume that you understand this the way I do. I will acknowledge the trouble with using one dry contact, but that to me is pointless running of the mouth and mind. No one in the real world would do that. If the point is to use one pushbutton as a start stop circuit to start a solenoid, etc, this will work, every time, until a component fails. Granted, this does need two separate normally open contacts, and one set of normally closed, but it does utilize only one pushbutton, and it is a fairly simple application to do. I have seen pushbuttons with 6 different contacts on them before, no harm nor foul. Hopefully this helps the man in his quest, if he wants simple and cheap, I give him just that.

Russ

 

[[email protected]]

sorry about all that

Please forgive the sloppiness. That was my first attempt, and it went as well as most of mine do. The instructions got messed up, but I think you guys are smart enough to see what I am doing.

PB1 is a normally open, CR3 is a normally closed, then CR1 coil.
CR1 Normally open latches around the PB1.

PB1 is a normally closed, CR1 is a normally open, then CR2 coil.
CR2 normally open latches around the PB.

PB1 is a normally open, CR2 is a normally open, then CR3.
CR3 is normally open in parallel with CR2.

The solenoid is tied in parallel with CR1, so when it is on, so is the solenoid.

Operation:

Push PB1, CR1 comes on, latching itself on.
Release PB1. CR1 stays latched, on rung 2, the PB1 NC and CR1 NO allow CR2 to energize, which latches itself on around PB1.
Push PB1, CR3 comes on. When CR3 comes on, it drops out CR1, which unlatches CR2. CR3 stays energized, keeping CR1 from energizing until PB1 is released. Then the process starts again. I think this will accomplish everything the original author wanted. Can you guys tell how busy I am tonite?

 

[Ukrainian]

Developing your idea

Here is differente picture. I took off several contacts from your diagramm.

 

[rsdoran]

Why not just use a maintained foot switch thats designed for this type application?
http://www.linemaster.com/hercules.shtml

I missed that Eric had already provided this.

 

[Eric Nelson]

I missed that Eric had already provided this.

Easy to miss that since this thread is sooooooooo old...

beerchug

-Eric

 

[Lancie1]

Guys,

All the different circuits is very interesting, but I believe that Tom Jenkins solved the real problem back at the beginning. He suggested an "alternator relay". If Tom says it will work, then you can depend on it!! Yes that's all you need, just the foot switch and one alternator relay. I have used them many times. Every time you energize an alternator relay, the relay energizes either Output 1 or Output 2. Use Output 1 to turn on the solenoid, second foot press will turn it off again. These relays are not hard to find either. Square-D, Allied Electronics, Newark Electronics, Allen-Bradley, Grainger, and others have these in the ice-cube form with plug-in bases.

Now, don't let this dampen your enthusiasm for creating yet more circuits! They are always appreciated.

 

[Voltimus]

I have to stress my agreement with Mr. Nelson.

All my guitar effects use maintained foot switches, and being the logic based people that we are, we keep trying to add or take away from logic something that has basically a mechanical answer.

K.I.S.S. less contacts means fewer chances of failure. And easier replacement.