Relay NAND and AND gates circuit

[John Newport]

I’ve just joined the Forum so hope that this is the right place to ask my question! It's a question about relays, not semiconductors.

I retired twenty years ago (so my knowledge of modern components is pretty vague) but worked all my life on relay logic circuit design (mainly 12v, 24v, 110v DC circuits), however, I’m more than a bit rusty.

I did, on occasion, work on semi-conductor design but the industry I was in wanted mainly relays.

My son has asked me to design and build a NAND gate and an AND gate using just relays, with lights or whatever, to demonstrate how they work. It’s for pupils in his Computer/Electronic classes at the local school.
I, of course, said “Yes” (!?) – then realised just how rusty I’d become but I don’t like to admit it!

Could anyone, please, give me designs for the two gates and give me details of relays (and anything else) suggestd? If I could build these gates, satisfactorily, I would lie to my son for a few days and, then, tell him the truth – someone designed it for me – but, for those few days ....Glory, just like the old days!

Thanks,

John

 

[ADWSystems]

To clarify, you want to show how to build NAND and AND gates from using only relays?

If so, you are talking old school relay ladder control system electronics.

 

[MikeMl]

Since the input(s) are likely to be toggle switches, you can just use the switches directly without any relays.

 

[Ian Rogers]

I think it's a good idea... It would certainly explain "visually" all about "Nand" and "And" and all the others for that matter.

I'll start the ball rolling

 

[AnalogKid]

Yup. Battery -> switches -> light bulb or LED.
Two switches in parallel = OR gate.
Two switches in series = AND gate.

Or, two switches can go individually to SPST relays.
Two contacts in parallel = OR gate.
etc.

ak

 

[granddad]

Excellent start , school has the right idea.

 

[dr pepper]

Hi John, welcome to the forum.

I wont get into relay logic, thats allready been done further up, however just to let you know there are still machines that use relay logic, I maintain a couple of industrial machines, one a milling machine and the other a paper processor, both are relay logic controlled and use hundreds of relays, the mill uses gpo style ones.
Every so often I have a heck of a time finding a stuck or burnt contact.

 

[John Newport]

The only word I can think of is ....blimey! Look at all the answers I've got! Thanks to you all. Yes, I can see now what I need to do, now. I'm surprised that I had forgotten something as simple as this - - but I genuinely had! Stupid! But it has been 25 years since I actually did any DC logic control design and I used to love it -- going to work was a pleasure.

But, at least, I think I've found a new hobby. I shall be back to this forum looking for ideas as to what to build next.

Brilliant! Thanks to all. I really am delighted.

John

 

[Wade Hassler]

I really am delighted.

I think I know what you mean...
In 1977 I built a relay-logic machine (200+ relays controlling 30 motors and 20+ hydraulic actuators) that chugged along happily, 10 hours a day, 6 days a week, until a relay(s) failure in 2005 revealed that my former employer had never delivered drawings.
All six of the control cabinets have been replaced with PLCs in the past ten years and it's been gobs o' fun

 

[John Newport]

Hi John, welcome to the forum.

I wont get into relay logic, thats already been done further up, however just to let you know there are still machines that use relay logic, I maintain a couple of industrial machines, one a milling machine and the other a paper processor, both are relay logic controlled and use hundreds of relays, the mill uses gpo style ones.
Every so often I have a heck of a time finding a stuck or burnt contact.

Thanks for your welcome! Thinking about it, there are probably many old machines, such as you mention, out there as, if they still do a good job, why go to the cost of replacing them?

My main work was on electrical generating sets. We built these machines for places as far apart as New Zealand, Norway, Saudi Arabia, Iraq, and the Indonesian islands (when the world was much more peaceful!). Most often they were designed as a power package of 3 machines - main power supply, standby, and emergency – for airports, telecommunications, and oil platforms. We designed and supplied all distribution and switchgear panels - and each system was different, as far as controls went - it was surprising what the customer could think of as regards, what he wanted the sets to do! But that was why I got paid - and I loved every minute of it! Anyway, we're into the ramblings of an old fella - "When I was a young man.......".

That’s why we continued to use relays (generally 24v DC) well after the coming of semiconductors - customer pressure – wherever you were in the world, they were relatively cheap to buy, relatively easy to locate, and very easy for the local engineers (of various abilities) to fault find and repair.

Thanks again,

John

 

[John Newport]

I think I know what you mean...
In 1977 I built a relay-logic machine (200+ relays controlling 30 motors and 20+ hydraulic actuators) that chugged along happily, 10 hours a day, 6 days a week, until a relay(s) failure in 2005 revealed that my former employer had never delivered drawings.
All six of the control cabinets have been replaced with PLCs in the past ten years and it's been gobs o' fun

Hi Wade,

Yes, you obviously know what I mean. That sounds like my cup of tea - it turns work into fun! I must say, having retired a long time ago - gardening, researcher for several local history groups, volunteer for a local museum are all very good and keep the brain active but they can't replace that feeling when, having a complicated designed a circuit that you're sure fits all the customer's requirements, seen it wired, switched on - and, then, work exactly as planned - well, it's that Sherlock Holmes moment when the case is solved against all the odds!

Hello? I've come over all unnecessary and am getting quite nostalgic for the good old days! I'm going to see if I can get an apprenticeship, somewhere.

Thanks Wade for your reply - am very grateful,

John

 

[MaxHeadRoom78]

That’s why we continued to use relays (generally 24v DC) well after the coming of semiconductors - customer pressure – wherever you were in the world, they were relatively cheap to buy, relatively easy to locate, and very easy for the local engineers (of various abilities) to fault find and repair.
John

On the subject of trouble shooting relay logic over PLC, I have trouble shot both and also converted many to PLC, IMO the PLC is far nicer for trouble shooting as the ladder and I/O logic (on/0ff) status can be displayed in boolean ladder logic on a PC screen hooked up to the PLC unit.
Max.

 

[John Newport]

Thanks MaxHeadRoom78,

I've no doubt you're right but back in the 1950s, 60s, 70s, and 80s, which was when I worked on control circuits, the situation was quite a bit different! PLCs didn't exist and weren't even dreamed of!

Cheers, John

 

[MaxHeadRoom78]

Yes it was at the behest of GM back in 1968 that Dick Morley came up with the first working concept.
GM wanted a system to replace the often troublesome relay logic control and replace with an electronic version that made Assy line trouble shooting easier.
I started with the PLC in the early '80's.
M.

 

[John Newport]

Thanks M,

I didn't know that. In the mid-80s, I had salesmen trying to sell me, what I suppose were the early versions of, PLCs but we built only one-offs and the circuitry design was always so different due to the customer. The best I could do was design and build PCBs, trying to save wiring time and costs but I still had to use plug-in relays.

Thanks M, I've had a nice trip down memory lane over the past few days and, if I can think of something to build, I think I've found another hobby! I remember, in the early days of transistors, the only project that seemed to be available for the amateur was building electronic egg-timers!

Cheers,

John

 

[dr pepper]

In the paper industry we use siemens plc's, I think they are amongst the most complex.
My point here is with siemens plc's if you werent the original designer of the system they can still be tricky to fault find.
That said the only faults on siemens plc's I've had is welded relay contacts on the o/p's, and thats probably down to the desginer overloading them.

 

[John Newport]

Just out of interest, I've drawn simple circuits using just switches. I thought, why use a switch to operate a relay which only closes or opens a contact when that's exactly what a double throw switch does. Making them DPDT switches I can use LEDs to indicate the switch positions.

I've been asked to do the same for the NOT, EXOR, and EXNOR gates and, thanks to all your help, I reckon I can do that myself. If I can't I will come back!

Anyway thanks again and cheers,

John