Logic latch circuits for relay drivers?

[Brian C]

Re: Logic latch circuits for relay drivers?

Please add "Free Wheeling Diode" across the relay's coil for protection. 1N4148 would be just fine.

[starfury1]

Re: Logic latch circuits for relay drivers?

yes shadow I know what you mean, sounds simple till you start trying to work the logic out With gates and can get complicated.

just going to post the pdf links on the above circuit Maxxarcade posted for reference.

74LS374 3-STATE Octal D-Type Transparent latches flip flop HERE

74LS27 Triple 3-input Positive NOR Gates HERE or HERE


74LS10 TRIPLE 3-INPUT NAND GATE HERE or HERE


Since BC550 may be a bit harder to find in the US (2N whatever use to be the main stay) and it may depend on the relay I'll include the pdf for it too.

BC550 (549~550) NPN SILICON AF SMALL SIGNAL TRANSISTORS HERE


This should make it a little easier to understand and put it all in one place for you maxxarcade.

(er yeah take back a little on what I said on the trannie relay thing did show resistor but true no diode)

cheers

[starfury1]

Re: Logic latch circuits for relay drivers?

I think this is the original source page HERE

Note the "fixed" on it, still looking to see what that means but it is drawn a little different.

So the original link thread did ask this question would it work as it was drawn? EDIT NO!!!!
So maybe there is an error in the diagram as posted.

THERE IS!!!!!

The 74LS374 on the diagram is showing the outputs as inputs and visa versa with the pin numbers



So do not follow the Diagram in this thread

grab the one from the link above.

Any other errors if the exist I haven't found yet.
If in doubt refer back to the PDF's

Cheers

[Maxxarcade]

Re: Logic latch circuits for relay drivers?

Thanks, I didn't notice that it was backwards. I would have gone to build it and said wtf...

As for the missing kickback diodes on the relay coils, I would have added some. I work on pinball machines for a living, and I know all too well about inductive kickback

I'm hoping to dig up my breadboard soon, I think I already have the parts laying around. I'll probably use lighted switches that I'll have to buy, along with some nice matching relays.

How much current should the relays be rated for? I think I have a whole bunch of 2A relays from a phone system in my parts collection.

[starfury1]

Re: Logic latch circuits for relay drivers?

well the heaver the better I think and possibly gold contact
(try the surplus places you might pick up a bargain)
2A you could try for proto type...(but no guru on relays an audio currents)
maybe they will be fine. Id try them anyway
I suppose it depends on if you listen like the Grateful Dead or shopping music

The circuit does have indicators on it for the relays but light up switches would be a good idea.
possibly 2 colours so you know whats input and output quickly

Are you going to use just one setup or two ?

Iam sure I don't have the ic's needed so I can't build it to have a look at what going on.

anyway keep us posted

Cheers

[shadow]

Re: Logic latch circuits for relay drivers?



This is the circuit that I have thought of. I know it is a little bit late now, however I could not be bothered drawing a circuit with 8 switches. It is a tedious method for 8 switches. However it is perfect if you want to switch up to about 4 switches.

The basic logic follows like this:

The buttons are attached to the clock signal of a Flip-Flop. Every time a button is pressed, the output will be the logic value '1' (this is because the JK flip-flop is setup to output a logic '1' on a clock edge. A D flip-flop can also be used easily). The button attached to one particular flip-flop is attached to all the other flip-flops 'reset' signal through an OR gate (the more switches you have, the more inputs the OR gate needs to have, no OR gate is required if you are switching between two switches). Therefore when a button is pressed, the output of that particular button will be a '1' and all the others will get reset to '0'. If two or more buttons are pressed at the same time, all the buttons are reset to '0'.

From there you attach the output of the flip-flops to your relay driving circuit or connect it directly to the relay if you are using compatible Solid State Relays.

The main limitation of the circuit is that when the flip-flops are first powered on, their output's are undefined until a button is pressed. This may potentially cause a problem. The solution is to somehow reset the switches when it first powers on. Or use a different solution.