One more once

[Don Foreman]

I did a simulation. There was a glitch on one output if the relays
close faster than they open -- which is often the case, particularly
with DC relays snubbed with diodes.

The minor modification fixes that without requiring any more relays.
Relay count now is:

2 DPDT
1 SPST

If your relay coils aren't the same voltage as your load, then you may
need to add a couple of SPST load relays.

This was fun. I haven't designed relay logic for decades!

 

[Joerg]

Hello Don,

This was fun. I haven't designed relay logic for decades!

And now on to tube logic

 

[Don Foreman]

Hello Don,



And now on to tube logic

Cross-coupled 6146's comprising Eccles-Jordan flops -- yeah!

Why use 3 relays when one can put together a microcontroller, write
and debug software, do signal conditioning of input, add relay
drivers and output relays or load switches, find a power supply, and
put it all in a box -- or buy a PLC, hook that up and program it with
(ta dahhh) RELAY LADDER LOGIC?

I see some elegance in a rugged 2-bit state machine with a speed of
....uh...Hertz, that goes clackity clack and does the job, and can be
built in an hour with 3 relays, some wire, a bag of crimp terminals
and a crimper.

 

[Joerg]

Hello Don,

Cross-coupled 6146's comprising Eccles-Jordan flops -- yeah!

Why use 3 relays when one can put together a microcontroller, write
and debug software, do signal conditioning of input, add relay
drivers and output relays or load switches, find a power supply, and
put it all in a box -- or buy a PLC, hook that up and program it with
(ta dahhh) RELAY LADDER LOGIC?

I see some elegance in a rugged 2-bit state machine with a speed of
...uh...Hertz, that goes clackity clack and does the job, and can be
built in an hour with 3 relays, some wire, a bag of crimp terminals
and a crimper.

Don't forget that can of contact spray ;-)

 

[ehsjr]

I did a simulation. There was a glitch on one output if the relays
close faster than they open -- which is often the case, particularly
with DC relays snubbed with diodes.

The minor modification fixes that without requiring any more relays.
Relay count now is:

2 DPDT
1 SPST

If your relay coils aren't the same voltage as your load, then you may
need to add a couple of SPST load relays.

This was fun. I haven't designed relay logic for decades!

How about a one-shot?
<== big evil grin (having made one already)

Ed

 

[Don Foreman]

How about a one-shot?
<== big evil grin (having made one already)

Ed

What's the delay mechanism? Capacitor,or just actuation delay time
of one or more relays?

 

[Joerg]

Hello Don,

What's the delay mechanism? Capacitor,or just actuation delay time
of one or more relays?

The one in our heat pump had a transistor, some resistors and an
electrolytic (which, of course, failed after 10 years or so).

The weirdest relay one-shot I ever saw had a cam that was lifted onto a
notched wheel. Upon triggering it would start a little gearmotor.
Rat-tat-tat-rrrrrrrrrrrrrrr-KLUNK.

You can still find similar schemes in washing machine timers. Those are
probably "the" epitome of electromechanical control.

 

[ehsjr]

What's the delay mechanism? Capacitor,or just actuation delay time
of one or more relays?

Capacitor.

 

[Joerg]

Capacitor.

Nah, in them days they were called condenser

 

[ehsjr]

How about a one-shot?
<== big evil grin (having made one already)

Ed

Ok - no takers. Here it is: relay one-shot
(view in courier font)

+ Vcc ------+-------+-----------------+
| | |
o | |
S1 \ | |
o | Ry1 |
| | N/C |
[Ry1] N/O|> |<-----+ | +---> Out
| |+ | Ry2| |
| [C1] [Ry2] N/O|> |<---+
| | | |
Gnd --------+----------+------+------[R1]-----+

Output high when S1 opens, until *condensor* C1
(thanks Joerg )
discharges sufficiently for Ry2 to drop. A VR
across C1 can be used to adjust duration.

(Anticipating objection) ... so debounce the output.

Ed

 

[Charlie Edmondson]

Hello Don,




Don't forget that can of contact spray ;-)

And Tweakers! don't forget your contact tweakers!

I used to do SxS maintenance...

Charlie