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On/Off switch using momentary push button
On/Off switch using momentary push button
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Old 6th December 2017, 04:35 AM   #11
reedcat is offline reedcat  United States
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I have mistakenly purchased a push button (link below) instead of a switch for my preamp project:
ULV4F2B11544 E-Switch | Switches | DigiKey

Is there an easy way to make a switch out of it?

I don't want to change the button (I like it and I already made a proper cutout in the front panel) or add auxiliary power supply to drive a denouncing circuit (this would be an overkill for the small project I have). Something simple that can run off of the mains AC would be great.

Edit: will something like attached work (given I use main AC rated relay and supply 120VAC instead of 12DC as pictured)?
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File Type: jpg make-latching-relay-with-a-dpst-relay.jpg (8.7 KB, 269 views)

Last edited by reedcat; 6th December 2017 at 04:43 AM.
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Old 6th December 2017, 05:34 AM   #12
mondogenerator is offline mondogenerator  England
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Default Best I can think of...

Why not try a latching relay/contactor for switching the power input? Or a latching circuit for a conventional relay/contactor?

I can't think of an easier solution other than using the correct switch!
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Old 6th December 2017, 10:13 AM   #13
AndrewT is offline AndrewT  Scotland
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I think Digikey data shows the 12V is for the illumination only.

The SPDT switch is mechanical. That part is mains rated for 3A 250Vac.
Have you downloaded the manufacturer's datasheet?

The switching you have in the sketch is double pole single throw (DPST).
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Old 6th December 2017, 10:33 AM   #14
jcarr is offline jcarr  United States
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https://www.edn.com/design/power-man...ary-pushbutton
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Old 6th December 2017, 02:25 PM   #15
reedcat is offline reedcat  United States
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Now that I look at my sketch I see that it requires double pole single throw. My button is single pole single throw, so it will not work. Does anyone know of an alternative schematic? I am hearing something about using 3 relays but I cannot find anything.

I don't mind getting a different push button switch (that will offer on/off latching action) but so far I cannot find one that fits my cutout (19.2mm diameter) and is black color (my front panel is black). This one looks nice but it is silver:
Electronic Components and Parts Search | DigiKey Electronics

jcarr, can the circuits you linked be adopted to work off of mains directly? I want to try to avoid adding another transformer in the chassis.
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Old 6th December 2017, 03:01 PM   #16
jcarr is offline jcarr  United States
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Reedcat, unfortunately those circuits are intended for use with a DC power supply.
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Old 6th December 2017, 03:20 PM   #17
CharlieLaub is offline CharlieLaub  United States
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On/Off switch using momentary push button
Quote:
Originally Posted by reedcat View Post
Now that I look at my sketch I see that it requires double pole single throw. My button is single pole single throw, so it will not work. Does anyone know of an alternative schematic? I am hearing something about using 3 relays but I cannot find anything.

I don't mind getting a different push button switch (that will offer on/off latching action) but so far I cannot find one that fits my cutout (19.2mm diameter) and is black color (my front panel is black). This one looks nice but it is silver:
Electronic Components and Parts Search | DigiKey Electronics

jcarr, can the circuits you linked be adopted to work off of mains directly? I want to try to avoid adding another transformer in the chassis.
You can create a latching relay with the addition of a single DPDT relay with a main AC rated coil (e.g. 115VAC coil) and another momentary button.

WIRING:
You wire one momentary pushbutton (for "ON" operation) in series with the relay coil. When you push the button the relay will operate (let's call this "ON"). But when you release the button the relay will return to its original "OFF" position. To prevent the return to OFF what you do is wire both DPDT contacts to the AC mains (before either of the momentary buttons). One of these contact pairs is then wired in parallel with the momentary button that you used to turn on the relay. Once the relay contacts close (e.g. when you push the ON button), even if you release the ON momentary button there is still AC power applied to the coil and it will stay on. Forever! So you also need a way to turn it OFF again. This is where the second momentary button (let's call it the "OFF" button) comes in. This is inserted into the AC mains before any of the other connections. When you push the OFF button all AC power is removed, the relay returns to its OFF position, and you are back where you started.

If you can live with two buttons, one for ON and one for OFF, or even a momentary ON-OFF-ON(2) type button, you can create this type of control. Instead of the button (or switch) taking the stress of making and breaking the current, it is the relay that is doing that job and the button has very little current to switch. This means you can use just about any button that is rated for mains AC voltage.

Anyway, it's kind of putting lipstick on a pig, but it'll work.

P.S. This is for switching one pole of the mains that leads to your amplifiers. If you need to switch live and neutral, you will need to use a 3PDT relay.
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Old 6th December 2017, 03:39 PM   #18
reedcat is offline reedcat  United States
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Quote:
Originally Posted by CharlieLaub View Post
You can create a latching relay with the addition of a single DPDT relay with a main AC rated coil (e.g. 115VAC coil) and another momentary button.
Thank you. I have a cutout only for one button so two buttons is not an option.
It appears my only practical option is to try to find a latching Off-On push button diameter that fits my front panel cutout. Adding an extra circuit with DC power supply is an overkill.
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Old 6th December 2017, 07:09 PM   #19
AndrewT is offline AndrewT  Scotland
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You can use the contacts of your existing push push switch to control another relay. That is the start of your relay latching circuit.
It can work from a low voltage DC supply.
Long twisted pair carrying DC cannot emit interference.
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Old 7th December 2017, 02:55 AM   #20
Bobsone is offline Bobsone  Germany
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Hi
If you are thinking about a flipflop option, there are a lot of these switch circuits and boards available online.

I have made the following circuit to switch an ATX power supply and it works well. Because it was powered by 5V DC from the ATX supply I didnít need to include a small step down transformer and because it is switching the ATX 5V trigger I didnít include the relay.
Toggle on / off switch
Toggle ON / OFF Switch - Electronics-Lab

However, in your case I am guessing you will need to include a mains stepdown circuit in the flipflop design so I have added two options that I have explored. I have a HLK-PM01 AC-DC on a delayed flipflop that I made, it works well and from the tests I have seen online people are happy with its construction and operation.
HLK-PM01 AC - dc 220v bis 5V Step-Down Netzteil Modul
1 Stuck HLK-PM01 AC - dc 220v bis 5V Step-Down Netzteil Modul | eBay

Details zu Print Trafo 230V / 12V 2,1VA 175mA BV EI 304 2082
Print Trafo 230V / 12V 2,1VA 175mA BV EI 304 2082 1Stuck | eBay

As has been mentioned, debouncing the mechanical switch ďmayĒ be necessary, if you are like me (a novice) and donít have any way to measure/see whatís happening in the circuit then although switch bounce generally isnít overly difficult to resolve (and if it is actually an issue) it may require a little research and testing.
As for the load side relay selection and any needed inrush control, hopefully others in the forum can help solve any issues.

Just for reference, here are some other examples (including an ebay special) I have seen;
Softstart Module
Hypex Electronics webshop

SST01 Softstart for toroidal transformers
SST01 Softstart for toroidal transformers - Sjostrom Audio

Soft Starter Start-up For Power Amplifier,W/ Thermal Dectector,Protect
https://www.ebay.com/itm/Assembled-S...AAAOxyKsZRxVtY

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