Need simplest circuit to convert momentary switches to latching "switches"

[[email protected]]

Hello,

I'm a volunteer in the exhibits department at the USS Midway museum in
San Diego (www.midway.org), and I'm working to make some old equipment
look operational. Among the things I need to achieve are to get a
series of buttons to turn on various embedded LEDs (probably four per
button).

The pushbuttons originally were push-on/push-off, but were very, very
specialized, with about 25 contacts each. The button faces were
backlit using bulbs, but we're converting to LED lighting. As a
result, I stripped out all of the actual switching mechanism, and I
now have a series of what could become momentary switches (I'm not
explaining it well -- sorry).

Anyway, I've found various latching circuits that might work, but I'd
have to have about 24 double-sided PCBs made, one for each copy of the
circuit. That's way above our budget (in fact, I've already blown the
budget and I'm now buying things out of my own pocket).

However, I found a circuit online that uses a 4017 CMOS that looks
like it might work if I build just three circuits. The only problem is
that the clearest reference I've found online is above my schematic
reading skills (my level of electronics knowledge is just high enough
to be dangerous). The circuit I found is at:

nov55.com/ther/latch.html

This one panel of pushbuttons is the one that's got me most concerned.
I was going to just attach push-on/push-off buttons to the back of
each button "facade," but I found that the push distance (stroke, I
guess) of the old buttons is shorter than the new buttons I bought, so
that when pressing the old button, it won't go in far enough to
activate or deactivate the new pushbuttons.

Can anyone out there help with clarifying the circuit? I'm not
familiar with some of the symbols, for instance. Free tickets or other
Midway stuff for the clearest answer... : )

Thanks in advance!

Dave

 

[Spehro Pefhany]

Hello,

I'm a volunteer in the exhibits department at the USS Midway museum in
San Diego (www.midway.org), and I'm working to make some old equipment
look operational. Among the things I need to achieve are to get a
series of buttons to turn on various embedded LEDs (probably four per
button).

The pushbuttons originally were push-on/push-off, but were very, very
specialized, with about 25 contacts each. The button faces were
backlit using bulbs, but we're converting to LED lighting. As a
result, I stripped out all of the actual switching mechanism, and I
now have a series of what could become momentary switches (I'm not
explaining it well -- sorry).

Anyway, I've found various latching circuits that might work, but I'd
have to have about 24 double-sided PCBs made, one for each copy of the
circuit. That's way above our budget (in fact, I've already blown the
budget and I'm now buying things out of my own pocket).

However, I found a circuit online that uses a 4017 CMOS that looks
like it might work if I build just three circuits. The only problem is
that the clearest reference I've found online is above my schematic
reading skills (my level of electronics knowledge is just high enough
to be dangerous). The circuit I found is at:

nov55.com/ther/latch.html

This one panel of pushbuttons is the one that's got me most concerned.
I was going to just attach push-on/push-off buttons to the back of
each button "facade," but I found that the push distance (stroke, I
guess) of the old buttons is shorter than the new buttons I bought, so
that when pressing the old button, it won't go in far enough to
activate or deactivate the new pushbuttons.

Can anyone out there help with clarifying the circuit? I'm not
familiar with some of the symbols, for instance. Free tickets or other
Midway stuff for the clearest answer... : )

Thanks in advance!

Dave

Do you know any programming? This is one of those rare occasions when
something like a BASIC Stamp might fit the bill.

The circuit is very simple and should work okay. If you just want the
indicators to turn on, ignore the AND gates and the OR gate, so you
would need (5V regulated supply required):

1 74HC4017 (pin numbers as given)
1 74HC4049 (or ULN2003 for up to 7 outputs) (ground unused inputs
on 4049 only, not necessary on ULN2003- leave 9 open on
ULN2003)
1 74HC14 (ground unused *inputs*)
1 MCP101-450HI/TO to replace the 2 resistors and capacitor on the
right. The output goes directly to pin 15 on the 4017.

2 resistors 30-100K (not critical)
1 resistor to determine LED current. The ULN2003 will allow
more current and will allow you to drive multiple LEDs up to
several hundred mA.
1 100pF capacitor (eg. ceramic)
2 0.1uF (100n) ceramic bypass caps (put from +5 to GN

Go to some place such as digikey.com and get the datasheets (I've
linked most of them below), and compare with the schematic. If
anything is not clear, you can ask here or in sci.electronics.basics
and someone will be able to help.

You can check it out on one of those socket breadboards and then
transfer it to a matching PCB available from hobby shops. Use DIP
sockets for the chips and buy spares.

ULN2003: http://focus.ti.com/lit/ds/symlink/uln2003a.pdf
MCP101-450HI/TO:
http://ww1.microchip.com/downloads/en/DeviceDoc/11187f.pdf
74HC14: http://www.fairchildsemi.com/ds/MM/MM74HC14.pdf
4017: http://www.st.com/stonline/books/pdf/docs/1960.pdf



Best regards,
Spehro Pefhany

 

[Donald]

Hello,

I'm a volunteer in the exhibits department at the USS Midway museum in
San Diego (www.midway.org), and I'm working to make some old equipment
look operational. Among the things I need to achieve are to get a
series of buttons to turn on various embedded LEDs (probably four per
button).

The pushbuttons originally were push-on/push-off, but were very, very
specialized, with about 25 contacts each. The button faces were
backlit using bulbs, but we're converting to LED lighting. As a
result, I stripped out all of the actual switching mechanism, and I
now have a series of what could become momentary switches (I'm not
explaining it well -- sorry).

Anyway, I've found various latching circuits that might work, but I'd
have to have about 24 double-sided PCBs made, one for each copy of the
circuit. That's way above our budget (in fact, I've already blown the
budget and I'm now buying things out of my own pocket).

However, I found a circuit online that uses a 4017 CMOS that looks
like it might work if I build just three circuits. The only problem is
that the clearest reference I've found online is above my schematic
reading skills (my level of electronics knowledge is just high enough
to be dangerous). The circuit I found is at:

nov55.com/ther/latch.html

This one panel of pushbuttons is the one that's got me most concerned.
I was going to just attach push-on/push-off buttons to the back of
each button "facade," but I found that the push distance (stroke, I
guess) of the old buttons is shorter than the new buttons I bought, so
that when pressing the old button, it won't go in far enough to
activate or deactivate the new pushbuttons.

Can anyone out there help with clarifying the circuit? I'm not
familiar with some of the symbols, for instance. Free tickets or other
Midway stuff for the clearest answer... : )

Thanks in advance!

Dave

Keeping it simple, you can use "latching relays".

Energize the coil once and the contacts stay closed, energize the coil
again the contacts are open.

Digikey has lots of them to chose from.

donald

 

[Fred Bloggs]

[...useless and irrelevant background non-information snipped...]

Among the things I need to achieve are to get a
series of buttons to turn on various embedded LEDs (probably four per
button).

No one can figure out what you want to "achieve" from that long winded
and confused description. Does a single pushbutton turn on all four LEDs
simultaneously or sequentially or in some kind of group patterns. I am
somewhat amazed that you can believe a web circuit will do the job when
you can't even understand how it works.

 

[Fred Bloggs]

Keeping it simple, you can use "latching relays".

Energize the coil once and the contacts stay closed, energize the coil
again the contacts are open.

Digikey has lots of them to chose from.

donald

That sounds like a unique style of latching relay. Perhaps you can link
us to a particular part number so we can know this gem???

 

[Spehro Pefhany]

That sounds like a unique style of latching relay. Perhaps you can link
us to a particular part number so we can know this gem???

Yes, please. IIRC the old X10 appliance modules had something like
that.. a solenoid-operated mechanism toggling a hefty microswitch, all
controlled by dodgy inadequately protected electronics, of course.


Best regards,
Spehro Pefhany

 

[neon]

one can try to biuld latches out of AND gates or actualy buying latches chip a CD4017 is not a latch BUT CD4016 IS. and you are right you did not explain your problem clearly a schematic would help. one push aand 25 switches open-close?try again leave the personal stuff aside.

 

[Robert Latest]

The pushbuttons originally were push-on/push-off,

So they were independent of each other, right? Push once, light on, push
once more, light goes off, right? This is called a "toggle" switch.

nov55.com/ther/latch.html

The circuit is cute and simple, altough it suffers from some terrible design
flaws that may or may not bite you when you build the thing. However, it has
the most convoluted and awkward description that I've ever seen. No wonder
you're confused. And then it doesn't even provide the functionality you
need.

Because what you need might look like this:


.. +12V
.. ,---------------------------------R1------, R1 = 12V-(N*UD)/ID
.. | | UD = LED fwd V
.. | spdt ,---------. R1 ID = LED fwd I
.. | microswitch | | |
.. | ,-----. | ,-----. | N LEDs
.. | ,o---+-----|4 | `-|12 9|-' |
.. '--o | | 1|----|11 | c
.. o---|--+--|6 | | 13|----4k7-b
.. | | `-----' `-----' e---gnd
.. 4k7 4k7 4013B
.. | | Pins 3, 5, 7, 8, 10 to gnd
.. | | Pin 14 to +12V
.. +--+--gnd

The venerable '13B is a dual D flipflop; one half is doing the
switch debouncing and the other one does the toggling. The transistor can be
any cheap TO92 npn part.

I found that the push distance (stroke, I
guess) of the old buttons is shorter than the new buttons I bought, so
that when pressing the old button, it won't go in far enough to
activate or deactivate the new pushbuttons.

You need to use "microswitches" that are tailored for tasks like this. They
have a flexible activation "tongue" and are easily mounted.

robert

 

[[email protected]]

Thanks for the answers everyone! Just to clarify, each button will
control multiple LEDs (probably four per button). The LEDs will be
incorporated into the old buttons, as they're backlit when activated.
I was thinking about trying something like a BASIC stamp, etc.,
although I've never worked in that area before. I've been looking over
Arduino (sp?) controllers for stepper motor control, and I think they
might work here too. As far as the latching relay solution, I've
looked into that but the cost is prohibitive as I have to do this for
about 24 buttons. And regarding latching microswitches, I think that
would be a good solution but I haven't been able to reliably identify
which ones on Digikey or Mouser are latching. Any suggested part
numbers?

Dave

 

[Fred Bloggs]

If all you want is to backlight the switches then this technique is low
parts count, the SW toggles with each press:

View in a fixed-width font such as Courier.

..
.. +-----------------------------------------------------------------+
.. | MAIN 100k |
.. | BOARD .-----/\/\/\-----------. .----. |
.. | | | | | |
.. | | CD4049 | | | |
.. | | |\ |\ | |- | |
.. | +-----| O----+----| O--+-|2n7000| |
.. | | |/ | |/ |- | |
.. | | / | | |
.. | | 1M --- | |
.. | | / /// | |
.. | | \ | |
.. | | | | |
.. | | .-----+ Vdd [RLIM] |
.. | | | |0.22U | | |
.. | | | === | | |
.. | | | | | | |
.. | | | --- | | |
.. | | | /// | | |
.. | | | | | |
.. | | | | | |
.. | | | | | |
.. +---------------+------+--------------+---------+-----------------+
.. | | | |
.. | | | |
.. x x x x
.. --------------------------------------------
.. | | | | | |
.. | | SW | SWITCH | | |
.. | | | | +-|>|-|>|-+ |
.. | | --- | | | |
.. | '-o o--' '-|>|-|>|-+ |
.. | |
.. | |
.. --------------------------------------------
..
..
..

 

[Donald]

That sounds like a unique style of latching relay. Perhaps you can link
us to a particular part number so we can know this gem???

Hmmm, Ancient technology unknown by modern engineers.

"Latching relay

A latching relay has two relaxed states (bistable). These are also
called 'keep' relays. When the current is switched off, the relay
remains in its last state. This is achieved with a solenoid operating a
ratchet and cam mechanism, or by having two opposing coils with an
over-center spring or permanent magnet to hold the armature and contacts
in position while the coil is relaxed, or with a remnant core. In the
ratchet and cam example, the first pulse to the coil turns the relay on
and the second pulse turns it off. In the two coil example, a pulse to
one coil turns the relay on and a pulse to the opposite coil turns the
relay off. This type of relay has the advantage that it consumes power
only for an instant, while it is being switched, and it retains its last
setting across a power outage.
"


As has been said so many time before, Google is your friend.

http://en.wikipedia.org/wiki/Relay#Latching_relay

 

[Donald]

Hmmm, Ancient technology unknown by modern engineers.

"Latching relay

A latching relay has two relaxed states (bistable). These are also
called 'keep' relays. When the current is switched off, the relay
remains in its last state. This is achieved with a solenoid operating a
ratchet and cam mechanism, or by having two opposing coils with an
over-center spring or permanent magnet to hold the armature and contacts
in position while the coil is relaxed, or with a remnant core. In the
ratchet and cam example, the first pulse to the coil turns the relay on
and the second pulse turns it off. In the two coil example, a pulse to
one coil turns the relay on and a pulse to the opposite coil turns the
relay off. This type of relay has the advantage that it consumes power
only for an instant, while it is being switched, and it retains its last
setting across a power outage.
"


As has been said so many time before, Google is your friend.

http://en.wikipedia.org/wiki/Relay#Latching_relay

Oh, I forgot. Digikey has 585 latching relays.

Not cheap, but easy to use.

donald

 

[MooseFET]

If all you want is to backlight the switches then this technique is low
parts count, the SW toggles with each press:

View in a fixed-width font such as Courier.

I have a small change. I will edit it in:


Modified

.
. +-----------------------------------------------------------------+
. | MAIN 100k |
. | BOARD .-----/\/\/\---------------+----. |
. | | | | |
. | | CD4049 | | |
. | | |\ |- | |
. | +-----| O----+--------- -|2n7000| |
. | | |/ | |- | |
. | | / | | |
. | | 1M --- | |
. | | / /// | |
. | | \ | |
. | | | | |
. | | .-----+ Vdd [RLIM] |
. | | | |0.22U | | |
. | | | === | | |
. | | | | | | |
. | | | --- | | |
. | | | /// | 10K | |
. | | | +--/\/\---+ |
. | | | | | |
. | | | | | |
. +---------------+------+--------------+---------+-----------------+
. | | | |
. | | | |
. x x x x
. --------------------------------------------
. | | | | | |
. | | SW | SWITCH | | |
. | | | | +-|>|-|>|-+ |
. | | --- | | | |
. | '-o o--' '-|>|-|>|-+ |
. | |
. | |
. --------------------------------------------
.
.
.

Using the 2n7000 as one of the inverters would make my friend Less
Partz happy because you now get 6 channels per CD4049

 

[Peter Bennett]

Hello,

I'm a volunteer in the exhibits department at the USS Midway museum in
San Diego (www.midway.org), and I'm working to make some old equipment
look operational. Among the things I need to achieve are to get a
series of buttons to turn on various embedded LEDs (probably four per
button).

The pushbuttons originally were push-on/push-off, but were very, very
specialized, with about 25 contacts each. The button faces were
backlit using bulbs, but we're converting to LED lighting. As a
result, I stripped out all of the actual switching mechanism, and I
now have a series of what could become momentary switches (I'm not
explaining it well -- sorry).

Is it possible to recover the original switching mechanisms? You
would likely be able to find contacts in them that would perform the
alternate action function that you require.


--
Peter Bennett, VE7CEI
peterbb4 (at) interchange.ubc.ca
new newsgroup users info : http://vancouver-webpages.com/nnq
GPS and NMEA info: http://vancouver-webpages.com/peter
Vancouver Power Squadron: http://vancouver.powersquadron.ca

 

[[email protected]]

Is it possible to recover the original switching mechanisms? You

would likely be able to find contacts in them that would perform the
alternate action function that you require.

Well, although I have the original mechanisms, they're not usable for
two reasons. First, they block access to the area I need to place the
LEDs, and second (most importantly), when the ship was put in
mothballs, various systems and such were "demilled" - demilitarized,
which means they took hammers and cutters to a variety of things to
make them inoperable. The switches are just one victim. The vintage
Univac computer (1961) was trashed, as well as the inertial navigation
system gyroscopes.

 

[Spehro Pefhany]

Oh, I forgot. Digikey has 585 latching relays.

Not cheap, but easy to use.

donald

Sure, I just spec'd some miniature latching relays last week, but they
were set/reset, not toggle. Most have two coils and a few work by
reversing the current in a single coil, but I've not seen a toggle
type in many years. They were some that were built in a similar
fashion to stepping switches (the "ratchet and cam") but that was
aeons ago.

Do you know of any contemporary types that toggle?


Best regards,
Spehro Pefhany

 

[Fred Bloggs]

If all you want is to backlight the switches then this technique is low
parts count, the SW toggles with each press:

View in a fixed-width font such as Courier.

I have a small change. I will edit it in:


Modified

.
. +-----------------------------------------------------------------+
. | MAIN 100k |
. | BOARD .-----/\/\/\---------------+----. |
. | | | | |
. | | CD4049 | | |
. | | |\ |- | |
. | +-----| O----+--------- -|2n7000| |
. | | |/ | |- | |
. | | / | | |
. | | 1M --- | |
. | | / /// | |
. | | \ | |
. | | | | |
. | | .-----+ Vdd [RLIM] |
. | | | |0.22U | | |
. | | | === | | |
. | | | | | | |
. | | | --- | | |
. | | | /// | 10K | |
. | | | +--/\/\---+ |
. | | | | | |
. | | | | | |
. +---------------+------+--------------+---------+-----------------+
. | | | |
. | | | |
. x x x x
. --------------------------------------------
. | | | | | |
. | | SW | SWITCH | | |
. | | | | +-|>|-|>|-+ |
. | | --- | | | |
. | '-o o--' '-|>|-|>|-+ |
. | |
. | |
. --------------------------------------------
.
.
.

Using the 2n7000 as one of the inverters would make my friend Less
Partz happy because you now get 6 channels per CD4049

LOL- good one. That's what I get for mindlessly cutting and pasting a
previous ASCII together...

 

[Spehro Pefhany]

Do you know of any contemporary types that toggle?

Best regards,
Spehro Pefhany

Okay, here's an old P&B design available in surplus:
http://www.herbach.com/Merchant2/me...AR&Product_Code=TM94RLY2590&Category_Code=RLY
Digikey has some similar ones in stock (11 pieces in stock) for $47.64
USD each.

Magnecraft's 711 series is still available from Allied for $15 each
(120VAC coil) or $23 (12VDC coil). DPDT.

Priced mostly for the maintenance man market, looks like.


Best regards,
Spehro Pefhany

 

[Rich Grise]

Well, although I have the original mechanisms, they're not usable for
two reasons. First, they block access to the area I need to place the
LEDs, and second (most importantly), when the ship was put in
mothballs, various systems and such were "demilled" - demilitarized,
which means they took hammers and cutters to a variety of things to
make them inoperable. The switches are just one victim. The vintage
Univac computer (1961) was trashed, as well as the inertial navigation
system gyroscopes.

This is quite sad, it's true - but if you can salvage even one contact
on each switch, with some electronics you should be able to pull it
off.

Did you say the switches are currently lit? You might have to do a
little creative hacking to replace the current bulbs with LEDs, but
it's not inconcievable that you could do so.

They're showing "Star Trek" reruns on Sunday nights here, and I get
a kick out of the flashing lights on the "computer" panel.

Good Luck!
Rich

 

[[email protected]]

Yep, but the switch module (monster is more like it) gets in the way
of where the LEDs would go (the plan is to use LEDs), and there
doesn't seem to be a way to incorporate LEDs into the modules. These
devices were built like tanks so you could continue to get navigation
data despite having a nuke go off next to the system. : )