Author Topic: Another logic/footswitching question  (Read 4345 times)

DocHeavy

Another logic/footswitching question
« on: June 06, 2007, 12:48:39 AM »
I am trying to build a switcher where I can exclusively enable one of a group of relays. Switching one on should automatically switch off any other that may be on.

Each relay with be controlled by a NAND latch:



Both inputs are normally high.

Each switch will be a DPDT footswitch - one half of each switch will be wired in series:




The other half of each DPDT will be wired as shown:



The plan is...  When ANY switch is pressed, the "break" of the "a" side of the switch will fire a oneshot that sends a low to the RESET of all latches - turning off all relays.. The pulse needs to be shorter than the length of time it takes for the switch to "make" again. And it needs to be long enough to toggle the latch. Once the pressed switch "makes", the "b" side of the switch triggers another oneshot that sends a low to the SET of it's corresponding latch - turning on that particular relay.

My question is... is there any particular logic family that would be better suited for this. There seems to be plenty to choose from: 74LSxx, 74Cxx, 74HCxx, CDxxxx, etc. Supply voltage is not an issue as I will build the PS to suit.

The Tone God

Re: Another logic/footswitching question
« Reply #1 on: June 06, 2007, 01:40:29 PM »
Hmm...quite frankly I would probably use a shift register that can parallel load data and have each footswitch ground a matrix of pull ups on the register input along with clocking the load so the necessary pins are active.

As for logic families it depends on your power supply and perhaps your relay drive circuit. Need more information if you want to get specific but I would say the CD4xxx series is a safe bet.

Andrew

pjwhite

Re: Another logic/footswitching question
« Reply #2 on: June 06, 2007, 07:31:03 PM »
Are your switches momentary or do they toggle?

DocHeavy

Re: Another logic/footswitching question
« Reply #3 on: June 06, 2007, 09:05:08 PM »
PJ:
The switches toggle.

Tone God:
Interesting idea with the shift-register - I'll have to think that one through. The relay drivers will be straight from the GeoFex footswitcher - relays tied to Vcc and grounded by a transistor to activate.

soulsonic

Re: Another logic/footswitching question
« Reply #4 on: June 12, 2007, 06:11:10 PM »
It seems to me it would be much easier to do this with a 4044. Something like this could do it:



It works with momentary switches, and when one is selected the others are switched off via the AND gates. It's very simple. The DIP switches I have on the output are so it can be "programmed" to switch between four different combinations of what relays are on or off, but it would be easy to mod the basic circuit to suit whatever you plan on doing.
Check out my NEW DIY site - http://solgrind.wordpress.com

DocHeavy

Re: Another logic/footswitching question
« Reply #5 on: June 12, 2007, 07:34:13 PM »
A perfect solution. That will be much smaller and cheaper than the monstrosity I concocted. (and accomplish the same thing)


Thanks Sonic

soulsonic

Re: Another logic/footswitching question
« Reply #6 on: June 13, 2007, 01:14:11 AM »
No problem - I'd been bothered about how to tackle this kind of switching thing for awhile - then I saw a similar circuit to this on an amp forum for switching three channels - but what I needed was to be able to switch four or more and be able to potentially "program" it. So I found a good book on digital logic circuits and learned all the basics of how they work, then I went back to the original schematic I found and figured out how to get it to do more complex switching. I just ordered a handful of the CD4044 chips and they were only $.26 each, so it's definately an economical way of switching all kinds of stuff. For the MOSFETs, I'm going to use 2N7000 (BS170), but I'm sure you could use whatever is appropriate for the current you need to switch.

As I said, logic circuits are kind of a new thing to me, but I'm really glad I took the time to learn it, because it's been a huge help with my amp designs. The next thing I want to try and tackle is how to store presets in RAM, so I don't have to fool around with banks of DIP switches. If anyone could point me in a direction to look, it would be a big help.
Check out my NEW DIY site - http://solgrind.wordpress.com

CGDARK

Re: Another logic/footswitching question
« Reply #7 on: June 13, 2007, 07:15:14 AM »
Once you have understand the logic thing the next step is the microcontroller world, like the PIC and ATMEL. I personally use PIC microcontrollers. At first is a little complicated, but there are a lot of info and examples on the web which you can use to start building a good base knowledge. First read this:

http://en.wikipedia.org/wiki/Microcontrollers

CG