Electrical circuit guru's in here, please

[nanotech]

Many years ago when I went through electronics school, I knew how to make the circuit I'm looking for, but now that memory is fading......  

What I'm looking for is the ability for a relay to be controlled by a momentary contact switch, but for the relay to stay on.

In other words, a pulse hits the circuit which turns a relay on, then the relay's own output keeps it energized.

Then another pulse will turn the relay off and the relay's "off" output keeps it in the de-energized state.

Everyone catching my drift?  If not, don't feel bad.  I forgot my ADHD meds this morning, so there's a distinct chance I'm babbling incoherently and don't even realize it!!  

Any help would be greatly appreciated.  Thanks in advance.

[Random Guy]

How about buying a push-on/push-off switch and using that to control a relay? It will reduce wiring complexity.

[Drives]

First time posting a pic.  

This is a basic motor control circuit.  We use a normally closed push button for our stop, a normally open push buton for the start, and a set of "dry" (not connected to anything else) relay contacts as the "seal in or aux" contacts.  

When you push the start button power flows to the relay coil and energizes it.  When the relay "picks up" it closes the normally open set of dry contacts, and takes the place of the momentary start button...holding the circuit energized.  When the stop button is pushed, it breaks the circuit, and everything becomes denergized.  

You can substitute any type of momentary switches in place of the push buttons, just be sure to observe the type of contacts...normally open or closed.

[wdyasq]

Gee Dean,

I think one could draw up a lot more complicated circuit than that.  

With electronic latching sometimes one does need to provide a diode or two for protection of a semi-conductor.  Things can get over-engineered very quickly.

Ron

[Norm]

  Is this what you want?

 one tap of the key turns it on...another turns it off...it's called an RTL inverter ..





  I found it in my 200 in One Electronics

Project Lab book...how about that ?

and I'm not even an electronic guru...

   Hope you can figure what resistors and stuff

if not I'm sure a real Guru can !

                   ( :>) Norm.

[Nando]

THOUGH you could use a SPDT (Single Pole Double Throw) switch, there are cases due to the distance that a relay is needed.

There are, as well, small relay that are latch-able by design, one push for ON, then another PUSH for OFF.

The schematic that I have uploaded here, gives the same effect and can be used with very large size relays and some relays are designed with a set of smaller current contacts for such purpose.

There are 2 circuits, the first may need a small capacitor for proper operation ( like 0.3 to 1 UF at with a breakdown voltage to at least 1.3 times the volts supply.

Regards

Nando

[Drives]

Ron:

Interesting point, and you already know the answer....the "KISS" philosophy. :-)

Yes, we could design this circuit using transistors, or digital gates, even op amps could be used to create this circuit.  Heck, I even seen some people mix all types of components to create some crazy final monsterousity.  

Yet, after having worked on so many of these over complicated systems over the years, and admiring the best (simplest), longest lasting designs....I have developed a "KISS" (Keep It Simple Stupid) methodology.

It is amazing how many of these kids coming out of college were never taught this!

PS. I like black, rubber, P215/60R15, Michelin Tires...because my car is Red, of course! Ha Ha.

Nanotech:

If you have more specifics on what you are using the circuit for, how much you want to spend, what voltages, and currents, I'll be happy to throw something together for you.

[tinker]

Like this?

http://www.uoguelph.ca/~antoon/circ/relay8.html

[John II]

It can be done Nanotech: Back about 30 yrs ago when I was a kid, I got in a bet with my dad. He lost haha...

I made relays count in a binary fashion without any additional components such as delay capacitors or diodes etc. Purely relays alone.

I don't know if I can find that schematic or not... but I think it's what you are looking for.... Just one push button to switch it locked on or locked off.

Push your momentary switch once and your light is on. Push it again and the relays drop out and your light goes out.

I know it can be done... because I done it... I'll look for the schematics when I find a little time.

It's ultra simple if I recall and not subject to static... highly reliable over some of the solid state stuff.

John II

[nanotech]

Well, I'm wiring my garage up as 12VDC for lighting (in preparation for RE) and wanted to have a system where when I walked in the lights went on by themselves (optical circuit I already have) and then turn off automatically when I leave again.

The only problem I had was that the circuit I have produces a closed circuit when there is a break in the optical path, and an open circuit when there's nothing blocking it.

So I needed some way to turn the lighting relay on with a pulse (closed circuit) and remain on until another pulse came through.  I guess I could try and scavenge a rear-window defogger circuit out of a car as they are ready-made 12V high current capable, huh?

I was also going to put in one of those light sensing circuits so that the lights were only operational at night.  Just put it in line with the optics so that thier "pulse" only got through when the light sensor detected it was nighttime and lights were required.

[nanotech]

That's it exactly!!

I'd be mucho appreciated if you can find it!!

[Epower]

Here is a simple circuit that works... Epower

[kell]

Here's a thread on Google Groups about this subject

http://groups.google.com/group/sci.electronics.design/browse_frm/thread/84052532398fd280/aee4a0638db
b7491?lnk=st&q=momentary+on+off&rnum=4&hl=en#aee4a0638dbb7491

I would probably just buy a latching relay; it has a mechanical action like a push on push off switch.  When you energize the coil briefly, the relay changes its postion and latches there.

[stop4stuff]

Hi Nanotech,

I hope this may be useful to you.

I found an electronic circuit a while back.

http://www.edn.com/article/CA472837.html

the pdf circuit diagram is here;

http://www.edn.com/contents/images/472837f1.pdf

my version, using seriesed resistors to make up the larger values.



All of switch circuit components were liberated from various dead equipment.

In the piccy above, the circuit switches 3 LEDs on/off, the power supply is 4 5.5v 1F capacitors. Charged to 5v the caps provide about 55 mins of power for the LEDS. Using one of my hand driven gennies, the caps take about 4 mins to charge.

In the circuit, different values for R9 can be used to limit the current allowed through by Q4.

paul

[kell]

It's called an alternating relay, not a latching relay.  My bad.

[dinges]

Hi Nanotech,

I think I know what you mean:

A momentary push on a button energizes the relay and it holds itsself energized (self-latching). Another push de-enegizes the relay.

I have the schematic somewhere, it's pretty simple and only uses one resistor and one capacitor (electrolytic) if I remember correctly. Found it years ago in an old book, made a quick copy on it on a scrap piece of paper and have filed it somewhere. Will look it up for you :-)

IIRC, you had to 'tweak' the resistor and capacitor value for optimum performance with your specific relay. If that's a problem, I'd go with the electronic variants of which plenty have already been posted & can be found on the net. If it's a quick & dirty solution that you need, go with 'my' solution.

Grtz,

Peter,

The Netherlands

[dinges]

Hi Nano,

Found it pretty quickly (2minutes); was amazed...

Okay, here goes in ASCII:

                          ---------

                    -----|  R2   |------ +9V

                    |K1   |-------|

                    |

 -----------------   -------------

 |     |      |            |        |

 |     |      |            |       ( )

---    -       ---   *----        ( ) Relay coil

---   | |          ---             ( )

 |C1  | |R1      pushbutton         |

 |     -           switch          GND

 |     |

GND   GND

My first every try at an ASCII schematic...

Not bad eh?

My other notes:

C1=2200uF

R1=100 ohm

R2=150

K1= contact of the relay ('output' or switched contact)

With all the other contacts of the relay (K2,K3,etc) being used to switch useful things, i.e. the other contacts can be used for what you need to switch on/off.

With the pushbutton switch, you can energize AND de-energize the relay; has to do with the energy stored in the capacitor. They said it worked but you might need to tweak the various resistances and capacitor.

I have never used this schematic before, but it should work.

Hope this is of help,

Peter Dingemans,

The Netherlands

[dinges]

OMG!

It looked so nice in the editor I was typing it in, but it shows all messed up in the list!

If it's not clear enough, let me know and I'll scan it or do it in Autocad. That'll not be today, though.

Peter,

The Netherlands.

[Drives]

nanotech:

It appears a bunch of folks helped you before I could. Thanks everybody.  

Kell's link below brings you to 2 different circuits that will work.  

http://beradio.com/news/radio_pushonpushoff_switch_2/

Is the relay circuit I think Dinges may be talking about, and will require some minor experimentation with capacitor and resistor sizes depending on the relay you use.  I'm sure the car guys can recommend a cheap, high current type relay.

http://www.terrypin.dial.pipex.com/Images/Momentary1.gif

http://www.terrypin.dial.pipex.com/Images/MomentaryScan1.jpg

This is a schmitt trigger circuit, and is also effective.

I recommend the first circuit because of it's simplicity & durability.

Good Luck!

[dinges]

Hi again,

My first try at inserting pictures, so hope it works.

Have re-drawn my original schematic for clarity and added a few comments to make it more clear.

When you momentarily push the switch, +12V (or +9, whatever you chose) goes to the relay coil; it energizes. The left capacitor (which was at +12V) then gets discharged through the left 100ohm resistor. When you push again, the capacitor gets charged (draws a current), which lowers the voltage available to the relay-coil (which is fed via the 150ohm resistor). The relay de-energizes, going back to the original situation; you push again and it swiches on.

drawbacks:

1. you need to experiment with the resistors and capacitors for reliable switching.
   
2. the circuit always draws power: +12V/(100+150)= 48 mA... This may be an issue in R.E. applications.
   
   

Hope this helps,

Peter,

The Netherlands.

[Ungrounded Lightning Rod]

You can use an extra pole to get rid of the drain during "off".  It also gets rid of the need to twiddle the resistor values to get good operation.

 - Remove the connection between the cap and the left hand contact of the current setup.

 - Unhook the left-hand resistor from ground and hook it to the arm of the new pole.

 - Hook the new pole's NO contact to ground, its NC contact to power.

 - (Increase the value of the left-hand resistor to something much larger than the right one - maybe to 1K or so.  It must be big enough that, if you were to hook the relay coil to the power supply through it alone, the relay would not pull in.)

Now the left-hand resistor is in charge solely of limiting the current pushing the cap to its new voltage when the relay switches (and not providing enough current to let the relay pull back in), and the right-hand one solely of giving the cap a chance to overwhelm it and force the relay to the open state (while providing enough current to hold the relay in).

Once the capacitor has come to its new voltage after a change, the only current flowing is any capacitor leakage (minute) and the coil current (if on).

[John II]

Hello Again Nanotech:

I found this circuit on the net.. go to the very bottom of this web page...

This guy draws his relays differently, and I'd have to re-draw them in my fashion to follow the logic.

I'm certain this is the way I did mine... but I have not located my own schematics yet.. have been to busy at other things for the time being.

John II

http://www.the12volt.com/installbay/forum_posts.asp?TID=57075&PN=1

[deloiter]

This circuit has one momentary pushbutton to energize the circuit and another to shut it down.