Logic latch circuits for relay drivers?

[Maxxarcade]

I want to build a source/output selector box, like they use at department stores, that you press a button to pick which stereo or set of speakers you want to listen to.

I was planning on using several SPDT relays, connected to a logic circuit with momentary pushbuttons, that would activate and hold whichever relay corresponds to that switch.

Are there any pre-made buffer/driver IC's that would serve this function? Or am I going to have to use individual IC's wired together? It can't be too hard to do this.

Another way would be to use ganged rotary switches, but those are a pain to work with.

[Maxxarcade]

Re: Logic latch circuits for relay drivers?

Well, I found this:

http://www.aaroncake.net/forum/topic.asp?TOPIC_ID=6356

Looks like what I need... Any ideas?

[shadow]

Re: Logic latch circuits for relay drivers?

What you are trying to do is to have a bunch of switches and depending on the switch that you press, the appropriate output device is chosen. In other words, you have one input and multiple outputs. Is this correct?

If so, then the job sounds easy with an electronic device known as a De-Multiplexer. There are heaps of these things around for probably fairly small prices. You will probably need a few Flip-Flops if you want to use momentary push buttons rather than the permanent type. Flip-Flops would be needed to latch the logic value from a particular switch. Then you will probably need a small logic gate circuit connecting all the buttons with the appropriate select signal needed on the De-Multiplexer.

Does that give you any good ideas? I just realised that the main problem with this approach is that this is a digital circuit. It really is not designed to work with analogue signals like sound from a radio or cd-player. The way to fix this up is to not use a De-Multiplexer but use either a Relay or a Solid State Relay. The rest of the circuit would largely be unchanged.

[Maxxarcade]

Re: Logic latch circuits for relay drivers?

What you are trying to do is to have a bunch of switches and depending on the switch that you press, the appropriate output device is chosen. In other words, you have one input and multiple outputs. Is this correct?

Correct, mostly. I'll be using relays to couple the signals, I just don't know how to make the circuit to drive the relays.

There will probably be several inputs and outputs. Basically I have several different receivers, and several pairs of speakers. I want to be able to pick between a combination to listen to without patching cables around.

The rules for operation are, only one input (receiver/amp) can be on at a time, but up to two outputs (speakers) can be on at a time.

I'll worry about the output side of things myself, I just need help making a logic circuit that takes a momentary input, turns on its respective output, and latches it on until another switch is pressed. I will use switching transistors to allow the logic circuit to drive the relay coils.

[shadow]

Re: Logic latch circuits for relay drivers?

I will work something out for you, however what I am thinking about at the moment is to use D type Flip-Flops to act as a suitable latch for the buttons.

EDIT: I wish I had a circuit drawing program!

[andrew77]

Re: Logic latch circuits for relay drivers?

EDIT: I wish I had a circuit drawing program!

Try this program out that I found. Probably be pretty decent to work out some logic circuits with.

http://sol.gfxile.net/atanua.html

It's someone's project for school. He's been updating it daily, also. I think he wants feedback so he can make a good grade.

[starfury1]

Re: Logic latch circuits for relay drivers?

Well your still probably going to have to do some sort of circuit work

but I found these to give you an idea

http://www.maxim-ic.com/appnotes.cfm...te_number/3224

https://cdn.badcaps-static.com/pdfs/...c1b601a718.pdf




By the sounds of it you want one Input selected only but the possibility of 2 outputs.

I take it you actually switching the power amp outputs of the receivers to separate speaker pairs


The ic's them selfs maybe pricey and perhaps as shadow said using some cheap type flip flops with an *"interface "for the relay switching might be a cheaper way to go.
(* transistor etc on coil)

what would add to the complexity is if you want to make it "idiot proof" by only have 2 output relays connected at one time.
especially if you are switching power amp outputs
(which may introduce another set of problems)

Side point
If your were talking about line level type signals there are things known as bilateral switchers
(they do have some resistance and I don't think they are great for audio, thought I do vaguely remember them bing used in this application but not totally sure on that)





I suppose something like this maybe commercially available but would probably cost...I guess Hi Fi stores would have this type of thing.

I know there use to be switch box things available from places like radio shite but I think they were just a big switch anyway.

hers a simple AB switch I found over at RE's ESP site

http://sound.westhost.com/absw.htm

Main page

http://sound.westhost.com/index.html


its a doable thing just a matter of working out or finding a suitable circuit that can be adapted

Anyway hope this helps, I'll have a look around some more

Cheers

[Maxxarcade]

Re: Logic latch circuits for relay drivers?

Great info, thanks!

I'm going to start drawing up some basic diagrams this weekend, to get an idea of layout and operation. I think I'm going to have 8 different receivers, and 3 or 4 pairs of speakers to choose from. I'm going to need a big shelving unit

[Brian C]

Re: Logic latch circuits for relay drivers?

I want to build a source/output selector box, like they use at department stores, that you press a button to pick which stereo or set of speakers you want to listen to.

I was planning on using several SPDT relays, connected to a logic circuit with momentary pushbuttons, that would activate and hold whichever relay corresponds to that switch.

Are there any pre-made buffer/driver IC's that would serve this function? Or am I going to have to use individual IC's wired together? It can't be too hard to do this.

Another way would be to use ganged rotary switches, but those are a pain to work with.

Are u familiar with assembly language.... get a basic micro-controller like the atmel at89c2051, some tact switches, transistors and DPDT relays. Else u need some logic ICs like demultiplexer and switch debouncing circuit.

[shadow]

Re: Logic latch circuits for relay drivers?

A cheapo micro-controller will also do the trick and it would be done more easily than an electronic circuit. Although most micro-controllers (at least I think) can be programmed in C as well as assembly (some even support C++). It would not be a very big program, so even an assembly program won't be very big and won't take very long to write.

[starfury1]

Re: Logic latch circuits for relay drivers?

Are u familiar with assembly language.... get a basic micro-controller like the atmel at89c2051, some tact switches, transistors and DPDT relays. Else u need some logic ICs like demultiplexer and switch debouncing circuit.

And yours too shadow

I actually thought something like that would probably be a better idea but I know stuff all on them. (last time I played with asm was on a Z80 cpu years ago)

but for someone who knows there stuff it shouldn't be that hard I imagine

I was thinking along the lines of a single I/P selector switch, momentary push on
so you just step through the I/P relays (like a counter with 1 of 8 decode)
A "common" relay common to both sides
Then 8 relays each individually selectable for the output side

A "sense circuit" to detect if more then 2 relays are on
if you try and switch on a third one it kicks out the common relay.

So you have to switch one output relay off before switching on another.
(the idea is to save the amps from seeing to low a load)

(yes switch debounce is important too)

Anyway thats a very rough "form" of an idea.

cheers

[starfury1]

Re: Logic latch circuits for relay drivers?

ok another few links

relay driver pdf basics

relay driver tutorial

A touch activated relay driver for automotive use

relay driver

another thought (and yeah why did it cross my mind before) you can get driver board for pc's

like the following here

But I an think you probably got a stack of relays just itching to put to work

So you want to do it without it costing you a Kings ransom of $$$

I guess the crude simplest way to go is toggle switches and relays and a psu
(but it does have a risk factor)
(or multi gang type switches as you said a headache)

anyway the above as ref material for you really

hope its of some help


andrew77 thanks for the link to that little proggie ..interesting

Cheers

[Maxxarcade]

Re: Logic latch circuits for relay drivers?

I've got the part down on how to interface the relays with the control logic, I just don't know how to make the front end control.

Seems that since only one of the eight input relays can be on at once, it would be an 8 input XOR circuit, with 8 outputs.

The confusing stuff comes with the output side, that needs to allow for any two outputs to be on at once. I think I'll just use manual control for the outputs and forget the control logic.

Each input and output would have one DPST relay, which would mean one set of contacts for each left and right channel.

So basically forget all the complex stuff... I just need a circuit that would allow me to push a button to turn on a relay, and if a different button is pressed, would cancel the first. I'll control the output relays manually with a simple latching circuit (press on/press off).

[starfury1]

Re: Logic latch circuits for relay drivers?

humm well yeah simple is the best way to go.

I haven't thought in terms of digital gate logic in a long time so rather rusty on it all
which is why I didn't start suggesting the content of how you might do it, just a form.

but if I dream up something I'll post it

keep us posted on how you going with it Maxxarcade if you dont mind thanks

Cheers

[shadow]

Re: Logic latch circuits for relay drivers?

Hmm...I have thought about this for a little while and I like the idea of using Flip-Flops (such great useful things they are) however I have not figured out a good way for the 'reset' logic. That is, when one switch is pressed, all the others are turned off no matter what. This sounds like such an easy task, yet it has that one hairy part that is not so easy to get rid of.

That is why I have suggested using a micro-controller. It will probably end up being cheaper than making an electronic circuit and it can be 'upgraded' and further functionality can be implemented. Micro-controllers are fun things to play around with!

If worse comes to worse, I can write a small program in VHDL that solves the problem and I can use a 'compiler' (so to speak) and it can give me a electronic circuit for the solution of the problem.

[starfury1]

Re: Logic latch circuits for relay drivers?

mx is going the simple route

but now his got me thinking about it and so with reference to my rough idea this would be the input side.

the 4017 IC is the puppy I was trying to think of well that type of logic anyway

Ic families have moved on quite a bit since my days with CMOS and TTL

see this page here

the bit of text is under the 2nd schematic with the 4017 and relays

you would have to adapted it to work with a momentary push on switch, if memory serves a flip flop would provide de-bounce for it.

this would allow you to step through (which is a down side I suppose) each input relay.
The up side is only one (hopefully) will ever be on..so you don't have to receivers (amps) connected to each other.

Note the use of Leds too.

The output stage as you said shadow could be done with flip flops (and relay driver interface) and the (above type) switches.

(I did find a circuit that used a 556 timer and an M P type switch here )

The "safety stage" (which is not really necessary but might save the amps)
Conceptually would be to monitor the outputs of the
output switching flip flops (or possibly ic relay specific chips)
and have in between common to all "safety relay" which disconnects the inputs and outputs from each other

This would trigger when 3 logic highs appear
sure it would be connected for a finite time but that worse case would be in Milliseconds
(yeah I know, transistors can die in micro seconds)

The idea of the protection is to stop the amps inadvertently driving too low an impedance by having more then 2 sets of speakers paralleled.

As I said you don't really need it.
(to me its a good idea for (hopefully) protection from the DOH! factor)

Anyway I'll just go with the flow as you got some of these way rusty old cogs turning

Yep small uP's have taken over and as I said above probably easier if you know how.

anyway

Cheers

[starfury1]

Re: Logic latch circuits for relay drivers?

So basically forget all the complex stuff... I just need a circuit that would allow me to push a button to turn on a relay, and if a different button is pressed, would cancel the first.

A heavy duty one that could handle current for the relay coil (4way 6 way whatever) "rotary selector type" switch I guess would do this...you would probably want BREAK BEFORE MAKE contacts.

something like this here

or maybe you got a junked push button one of some kind

going the digital path I think you will still have a little complexity...but maybe there is an easier way.
the above is the simplest Ive thought of so far...but theres are always more then on way to skin a cat

i'll see what else I can find or dream up.

Cheers

[Maxxarcade]

Re: Logic latch circuits for relay drivers?

This diagram I posted earlier seems to be exactly what I need, I'll have to test it on a breadboard.

[starfury1]

Re: Logic latch circuits for relay drivers?

Sorry Maxxarcade this was your original question
(before I went off on spiel)

If it switches a bunch of relays on and off then yes it would do what you want.
I think as was posted the relay and trannie are more a representation of what should be there

LS is an old family

It won't have any DOH! factor protection but thats up to you anyway

I take it you were going to have some RLY's as I/P others as O/P

I'll have to have a better look at the finer details later got to run...

BTW the safety thing above I did scratch it got a better idea.

chers mate and yep do a bread board and see if it does the functions you need then go the whole hog.

[shadow]

Re: Logic latch circuits for relay drivers?

My mind finally clicked for a proper method of latching the value of a button and preventing two buttons being pressed at the same time. It is relatively simple solution (and it took me long enough to work it out dammit) but the number of connections increases a fair amount with every extra switch that is added to the circuit. There is probably a better way to solve the problem but it is a start. Now how to draw this circuit neatly with 8 switches. Hmmm