Hardwired Circuit

[Steve Etter]

I know this is slightly of subject, but I need some help creating a hardwired circuit.

What I am trying to accomplish is cycling a single solenoid off and on using one pushbutton. In other words, press and hold the button once and the solenoid engages. Let off the button and then press and hold it again to disengage the solenoid.

I know this is an easy program to write in a PLC using latch/unlatch coils and a one-shot, but I need a simple way to hardwire one with minimal components. Does anyone have a clean little method for this? I guess the real problem I have is effectively creating the one-shot.

Thanks in advance.

Steve

[PLucas]

The thread below dealt with this question using logic, as there are no one shots in the replies, it should be quite easy to convert this to relays

http://www.plctalk.net/qanda/showthread.php?s=&threadid=150

Paul

[bernie_carlton]

The thread quoted uses - like many other PLC baased single pushbutton alternators - the fact of the program scan for part of the logic. REAL WORLD relays, in effect, solve ALL the logic at the same time (within limits of contact closing times etc). I have had problems going back to a REAL RELAY circuit of any moderate complexity with my mind still in the PLC scan mode. This is not to offer a solution, just a caution.

[Steve Etter]

Thanks for the lead. I knew I had seen this but could not remember just when....anyway, I don't think any of these schemes work in hardwired state. All of them seem to rely on sequencial logic in order to operate correctly.

It looks to me like all of these solutions would have the solenoid chatter on and off while the button is being pressed and then finishing by chance in one of the two states. Unfortunately the hardwired world will not submit to my desire to have it read top-to-bottom and left-to-right.

If I am missing something or reading these schematics wrong, I sure need some help getting my blinders off.

Thanks

[Rick Densing]

I am curious as to why it has to be a pushbutton. Why not a standard lever switch. It does what you want and is self indicating. Is it that you always want it to be off at power up?

[Tom Jenkins]

You are essentially trying to create an alternator circuit. This is pretty tough with relays (unless you use a time delay for one of them) because of the relay races that ensue.

Fortunately, Square D, Cutler Hammer, Time Mark, and goodness knows how many others, have two pump alternator relays available with everything canned in an octal or 11-pin socket relay. Check them out.

[Gerry]

You need a "ratchet relay". Google will tell you where to find them.

[godfrey]

This sounds like the toggle button on my night stand lamp. Press it once and the light is on. Press it again and the light is off. I think I have seen these buttons at Radio Shack. Will this work for you?

[Steve Etter]

Sorry it took so long to get back to this..got called out of town at the last minute and just got back.

Rick/Godfrey - In truth, it is a foot switch. The application is to energize/de-energize a brake with the same foot switch in an industrial application. The least expensive industrial unit we have found (and hence most desirable) is a simple switch type.

Tom/Gerry - I am not yet familiar with the alternator or ratchet relays..sounds promising..I will look in to those today. Thanks.

And I think I have worked out a circuit that will work using four relays. I will attempt to post a schematic of it later this morning for anyone else is who is interested. I may not have to use it though once I learn about the alternator/ratchet relays.

Steve

[Don]

An impulse relay may work out.

[Steve Etter]

This is my first attempt to post code, so I hope you will forgive me with regards to its look....anyway, here goes:

Relay R1 directly controls the solenoid (Y0).
Relay R2 must be low in order for relay R1 to engergize
and energizing relay R3 will cause it to drop out.


PB R2 R3 R1
--| |----|/|----|/|----( )--
+
R1 +
--| |---------


Relay R2 is used to signal that the pushbutton has been pressed
and then released to energize the solenoid.

Relay R1 must be high in order for relay R2 to engergize.
Energizing relay R4 will cause it to drop out.

PB R1 R4 R2
--|/|----| |----|/|----( )--
+
R2 +
--| |---------


Relay R3 is used to drop out R1. Relay R2 remains energized
thereby preventing R0 from re-energizing while the pushbutton is pressed.

Relay R2 must be high in order for relay R3 to engergize.
This prevents R3 from energizing when the pushbutton is pressed the first time.

PB R2 R3
--| |----| |-----------( )--


Relay R4 is used to drop out R2.

Relay R1 must be low in order for relay R4 to engergize.
This prevents R4 from energizing when the pushbutton is release the first time.

PB R1 R4
--|/|----|/|-----------( )--

Solenoid is energized whenever relay R1 is.

R1 Y0
--| |------------------( )--


Keep in mind that this is hardwired code so the left-right top-bottom thought process does not work here.

If anybody sees any problems with this code, please let me know.

Thanks
Steve

[Archie]

Steve

This is a very interesting problem, that I have used many times to challenge people in training sessions.

I have many solutions to this using DC Voltage, AC Voltage, and PLC ladder. I have one posted at a web site that works with all three.

The down side to this solution for hard wire is that it requires a PB with 2 NO and 2 NC contacts, One relay with 3 NO contacts, and one relay with 1 NO and 1 NC contacts. You can reduce the 3 NO contacts to 2 NO on the first relay by putting the light/coil in paralell with the coil.

If you have only one contact on the PB, you may add a third relay, a DPDT to fill in for the PB contacts.

Enough of all of the variations, the posting is at...

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

I have not actually hardwired and tested this circuit for race condition, but I have built and used a DC version that uses 3 SPDT relays and 2 diodes.

Hope this helps
Archie

[pkshaver]

IMO, by the time you mess with all of the relays, you're better off with a small programmable relay, (like the Klockner EASY). Program the basic ladder right there on the screen and be done with it.

-Phil

[Gerry]

The ratchet relay solution:
- 1 PB or FtSw with 1 NO contact
- 1 ratchet relay with one contact

A ratchet relay can be thought of as an electro-mechanical flip-flop. When you energise the coil, the armature moves the pawl on a ratchet wheel, indexing it by one tooth. The wheel turns a cam which operates the contacts. For each increment of the wheel, the contacts change state.

Very simple.

[Eric Nelson]

Takoga,
Though this has been a nice exercise for everyone, re-reading your second most recent post got me thinking... http://www.peyups.com/images/phpbb/icons/think.gif

Since I'm not sure of the actual function of the foot switch, I can only go by your description of it's application...

First off, do you really need the brake to toggle state with each press of the foot switch? Could you possibly just use the foot switch to disengage (or engage) the brake only while pressed?

If you need it to toggle, you may want to revisit your actual cost savings of a "simple switch" (momentary) version vs. a slightly higher (if any) cost push-on/push-off (maintained) foot switch. Most foot switch manufacturers offer both styles for roughly the same cost... Just change the part number and you're done! This may be cheaper than adding multiple relays to accomplish the same task. It also makes it a LOT less complicated and therefore more reliable. If you are an OEM, do you really want the customer (or you in the field) to have to troubleshoot this system rather than simply replacing ONE worn out foot switch?

IOW, always remember the K.I.S.S. principle! http://www.peyups.com/images/phpbb/icons/headbang.gif

Just my 2¢,

-Eric

[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... :rolleyes:

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 (http://www.alliedelec.com) 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 (http://www.linemaster.com) mainly because they're readily available for places like Grainger (http://www.grainger.com), MSC (http://www.mscdirect.com), and McMaster-Carr (http://www.mcmaster.com). Linemaster makes very good switches, but there are plenty of others...

Check with companies like Conntrol (http://www.conntrol.com) or Altech (http://www.altechcorp.com/HTML/FS.HTM). 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! :cool:

-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

[russrmartin@hotmail.com]

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]

Originally posted by russrmartin@hotmail.com
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!... :D

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

[russrmartin@hotmail.com]

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

[russrmartin@hotmail.com]

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]

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]

Originally posted by rsdoran
I missed that Eric had already provided this.

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

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.

[Koldwater]

Try This !

http://www.koldwater.com/images/flipflop.jpg

[Rod]

The press brakes I work on also have an auto/manual or jog postion switch.
In auto the press bottoms out to return either by a limit switch or another push of the foot switch. The latter is to allow the metal to relax to it's new deformation.

In manual-jog mode each time the switch is pressed the ram extnds until the switch is released. Repeated pressings of the switch will continue extending the ram.
All done with icecubes.

I don't have a schematic in front of me, but any old press brake should have an example.

I'd check the yellow pages for a sheet metal or metal fab shop in your area with an old Wysong. They may let you look at the schems.

Rod
The (CNC dude)