Insoluble Conundrum? (switching relays)...

C

Cursitor Doom

Guest
Gentlemen,

I can\'t come up with a straightforward solution to what ought to be a
simple problem so I\'m posting this in the hope that intellects greater
than mine can crack it.
I\'ve acquired an HP RF attenuator, but it wasn\'t the one I wanted. I
wanted the manually-switched version with a knob you can twist to
select the degree of attenuation required, but I\'ve ended up with the
electronic one instead. Anyway, even the plugs for these things are
made of pure unobtainium, so I\'m going to have to re-work the damn
thing from scratch.
So here\'s the problem. The attenuator provides from 10db to 70db
attenuation depending on which resistances are selected by sending a
short pulse to the relay for that particular resistance card.
Sequential pulses toggle the relevant resistance in and out of
circuit. You only have to momentarily ground one end of the relay to
flip it from one state to the other - and therein lies the problem.
I\'d like some LEDs as status indicators to show which resistances are
\'in\', but in a system such as this, I can\'t figure out how to readily
implement that. Any ideas?
Here\'s the internals of the attenuator:

https://disk.yandex.com/i/YNlfjGMfCe6FMA
 
On 2023-01-14 16:21, Cursitor Doom wrote:
Gentlemen,

I can\'t come up with a straightforward solution to what ought to be a
simple problem so I\'m posting this in the hope that intellects greater
than mine can crack it.
I\'ve acquired an HP RF attenuator, but it wasn\'t the one I wanted. I
wanted the manually-switched version with a knob you can twist to
select the degree of attenuation required, but I\'ve ended up with the
electronic one instead. Anyway, even the plugs for these things are
made of pure unobtainium, so I\'m going to have to re-work the damn
thing from scratch.
So here\'s the problem. The attenuator provides from 10db to 70db
attenuation depending on which resistances are selected by sending a
short pulse to the relay for that particular resistance card.
Sequential pulses toggle the relevant resistance in and out of
circuit. You only have to momentarily ground one end of the relay to
flip it from one state to the other - and therein lies the problem.
I\'d like some LEDs as status indicators to show which resistances are
\'in\', but in a system such as this, I can\'t figure out how to readily
implement that. Any ideas?
Here\'s the internals of the attenuator:

https://disk.yandex.com/i/YNlfjGMfCe6FMA
Click to expand...

From the schematics, it appears to have a \'set\' contact and a \'reset\'
contact. It will only take a brief current pulse to change state,
but there is nothing that prevents you from leaving the coil
contacts energized. You can control it with four spdt switches
and the same switches can drive your status LEDs too. Easy.

Jeroen Belleman
 
On Sat, 14 Jan 2023 15:21:37 +0000, Cursitor Doom <cd@notformail.com>
wrote:

Gentlemen,

I can\'t come up with a straightforward solution to what ought to be a
simple problem so I\'m posting this in the hope that intellects greater
than mine can crack it.
I\'ve acquired an HP RF attenuator, but it wasn\'t the one I wanted. I
wanted the manually-switched version with a knob you can twist to
select the degree of attenuation required, but I\'ve ended up with the
electronic one instead. Anyway, even the plugs for these things are
made of pure unobtainium, so I\'m going to have to re-work the damn
thing from scratch.
So here\'s the problem. The attenuator provides from 10db to 70db
attenuation depending on which resistances are selected by sending a
short pulse to the relay for that particular resistance card.
Sequential pulses toggle the relevant resistance in and out of
circuit. You only have to momentarily ground one end of the relay to
flip it from one state to the other - and therein lies the problem.
I\'d like some LEDs as status indicators to show which resistances are
\'in\', but in a system such as this, I can\'t figure out how to readily
implement that. Any ideas?
Here\'s the internals of the attenuator:

https://disk.yandex.com/i/YNlfjGMfCe6FMA
Click to expand...

A relay coil has one end that will be +24 volts when the solenoid is
in the \"in\" position; the opposite side from the one that you just
blipped to ground. So a resistor+LED to ground will indicate the
position.

You can verify that with a DVM.

1 mA, 22K resistor, would be plenty bright but not influence the
solenoid.
 
Okay, well, I don\'t understand how I missed that. After that
conspicuous display of ignorance, I shall bow out ungracefully.
Thanks, chaps.
 
On Saturday, January 14, 2023 at 12:45:31 PM UTC-4, Jeroen Belleman wrote:
On 2023-01-14 16:21, Cursitor Doom wrote:

Gentlemen,

I can\'t come up with a straightforward solution to what ought to be a
simple problem so I\'m posting this in the hope that intellects greater
than mine can crack it.
I\'ve acquired an HP RF attenuator, but it wasn\'t the one I wanted. I
wanted the manually-switched version with a knob you can twist to
select the degree of attenuation required, but I\'ve ended up with the
electronic one instead. Anyway, even the plugs for these things are
made of pure unobtainium, so I\'m going to have to re-work the damn
thing from scratch.
So here\'s the problem. The attenuator provides from 10db to 70db
attenuation depending on which resistances are selected by sending a
short pulse to the relay for that particular resistance card.
Sequential pulses toggle the relevant resistance in and out of
circuit. You only have to momentarily ground one end of the relay to
flip it from one state to the other - and therein lies the problem.
I\'d like some LEDs as status indicators to show which resistances are
\'in\', but in a system such as this, I can\'t figure out how to readily
implement that. Any ideas?
Here\'s the internals of the attenuator:

https://disk.yandex.com/i/YNlfjGMfCe6FMA

From the schematics, it appears to have a \'set\' contact and a \'reset\'
contact. It will only take a brief current pulse to change state,
but there is nothing that prevents you from leaving the coil
contacts energized. You can control it with four spdt switches
and the same switches can drive your status LEDs too. Easy.
Click to expand...

I like this circuit and the way the relay disconnects itself once it has flipped. As you say, that lets you ground the active input continuously. If that is an option, then yes, you can put an LED across the two inputs and 24V. The activated input will pull the LED to ground as well lighting it.

But, if the control signal is only a momentary for whatever reason, an LED can be connected from ground, to the input that is now connected to 24V. As Larkin has said, you need to size the LED resistor so it draws very little current compared to the pull in current of relay. I don\'t recall about latching relays, but I expect they don\'t have drop out current ratings. The LED current should be less that this if they specify it. If the relay current is anywhere near a mA, it would require a transistor to drive the LED.

--

Rick C.

- Get 1,000 miles of free Supercharging
- Tesla referral code - https://ts.la/richard11209
 
On Saturday, January 14, 2023 at 1:37:42 PM UTC-5, John Larkin wrote:
On Sat, 14 Jan 2023 15:21:37 +0000, Cursitor Doom <c...@notformail.com
wrote:

Gentlemen,

I can\'t come up with a straightforward solution to what ought to be a
simple problem so I\'m posting this in the hope that intellects greater
than mine can crack it.
I\'ve acquired an HP RF attenuator, but it wasn\'t the one I wanted. I
wanted the manually-switched version with a knob you can twist to
select the degree of attenuation required, but I\'ve ended up with the
electronic one instead. Anyway, even the plugs for these things are
made of pure unobtainium, so I\'m going to have to re-work the damn
thing from scratch.
So here\'s the problem. The attenuator provides from 10db to 70db
attenuation depending on which resistances are selected by sending a
short pulse to the relay for that particular resistance card.
Sequential pulses toggle the relevant resistance in and out of
circuit. You only have to momentarily ground one end of the relay to
flip it from one state to the other - and therein lies the problem.
I\'d like some LEDs as status indicators to show which resistances are
\'in\', but in a system such as this, I can\'t figure out how to readily
implement that. Any ideas?
Here\'s the internals of the attenuator:

https://disk.yandex.com/i/YNlfjGMfCe6FMA
A relay coil has one end that will be +24 volts when the solenoid is
in the \"in\" position; the opposite side from the one that you just
blipped to ground. So a resistor+LED to ground will indicate the
position.

You can verify that with a DVM.

1 mA, 22K resistor, would be plenty bright but not influence the
solenoid.
Click to expand...

Just 2x LEDs and a single resistor. LED anodes to each contact terminal, LED cathodes joined together and wired to GND thru common current limiting resistor. Unfortunately when you open that actuation circuit, the 125 mA in the coil wants to go somewhere and there aren\'t a lot of alternative paths other than thru the LED on that contact terminal. So you may need a flyback diode from the contact terminal to the 24 V.
 
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