The Magic of Mock Relays 7/11/2013 Return to Article View Comments: Newest First | Oldest First | Threaded View <<   <   Page 5 / 5 User Rank Author Re: Ladder logic should work 7/12/2013 7:16:08 PM NO RATINGSLogin to Rate You can do a very nice XOR using just two of those Mock Relays.  First a ladder diagram: `|---[ A]----[/B]--+--( )----|` `|---[/A]----[ B]--+` We get conduction if A & !B or !A & B.  Next, we use the fact that the relay can conduct in either direction through the NO and NC connections and use one set of SPDT contacts for both A and !A (connect COM to the terminal on the left) and one set of SPDT contacts for B and !B (connect COM to the relay coil on the right).  Then you just wire the NO/NC contacts of the two relays to each other.  You can swap the NO/NC wires to get XNOR. This is the same switching you use for an electric light that's controlled from two locations.  If you want more than two locations, you need DPDT switches for the middle switches which require pairs of the Mock Relays.  This gives you the odd or even parity function, depending on how you hook it up. Gates?  Pfui.  Relay networks are a lot more fun. User Rank Author Re: Ladder logic should work 7/12/2013 6:44:45 PM NO RATINGSLogin to Rate So, what does this rung do? |---[/]---------( )---|      /K1          K1 "Buzz, buzz", as Hamlet would say? User Rank Author Ladder logic should work 7/12/2013 6:01:54 PM NO RATINGSLogin to Rate +(supply)                 -(return) |---[ ]----[ ]----( )----| |     A       B      K1    | |---[ ]---- . . .           | |    K1  = A & B          | |---[/]---- . . .           | |    K1 = /(A & B)       | |                              | |---[ ]------------( )---|   |     A    |           K1   | |---[ ]---|                 | |     B                       | |---[ ]---- . . .           | |    K1   = A + B        | |---[/]---- . . .           | |    K1   = /(A + B)    |   Contacts in series implement the "and" function. Contacts in parallel implement the "or" function. When relays are energized they close their normally-open contacts (and open their normally-closed contacts).   http://en.wikipedia.org/wiki/Ladder_logic   So, what does this rung do? |---[/]---------( )---|      /K1          K1         User Rank Author FYI 7/12/2013 5:21:36 PM NO RATINGSLogin to Rate Harry Porter's Relay Computer Awfully new relays, but we don't all have a Mock Electronics handy :-) User Rank Author Re: I'm sorry... 7/12/2013 5:03:33 PM @studleylee: I find this relay interesting in the mechanical implemantion. When I was a student I'm afraid to say that I was more interested in the electronics and I paid little attention to the mechanical side of things. As the years have gone by, I have developed a much greater appreciation for the way in which things are put together -- and I love looking at a well-made assembly like the one shown in this relay... User Rank Author Re: I'm sorry... 7/12/2013 4:56:05 PM I find this relay interesting in the mechanical implemantion. The relay contacts and arm tension are adjustable. By taking things apart you can get into the mindset of the item's designer. My early electronics career was in repair. I would not trade the design style inspection experience I got from that era. You see many good and bad practices that you can improve upon or avoid. So I say HackAway :-) -Lee Studley User Rank Author Re: Claude Shannon explains it all to you 7/12/2013 3:07:30 PM NO RATINGSLogin to Rate @betajet: If anyone wants to cheat... The reasers of my columns aren't like that -- these are the people who scoff ("Ha!") at instruction manuals and prefer to work it out for themselves (no matter HOW long it takes :-) User Rank Author Claude Shannon explains it all to you 7/12/2013 2:48:53 PM NO RATINGSLogin to Rate You can get the functionality of the relay with a 2:1 bus switch such as the Fairchild Semi NC7SB3257.  Like the relay, you get bidirectional flow between the common terminal Y and the NC/NO terminals A and B. I remember playing with relay boxes in high school.  Lots of noise, loads of fun.  I took another look at relay logic when I studied VLSI design, since pass transistors let you do things like the controlling a single light from any number of DPDT switches instead of a bunch of TTL gates.  If anyone wants to cheat, the theory behind relay logic is contained in Claude Shannon's 1937 Master's Thesis A Symbolic Analysis of Relay and Switching Circuits, also published in a 1938 issue of Transactions of the AIEE.   User Rank Author I'm sorry... 7/12/2013 10:18:35 AM NO RATINGSLogin to Rate I must admit to feeling bad ever since I posted this, because I have to confess to being deliberately misleading. The reason I used quotes when talking about "input" A and "input" B and "output" Y is that the whole concept of inputs and outputs is a bit nebulous (or perhaps we should say "subjective") when it comes to working with relays. There, you see, I'm not being too mean... 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