Mutually triggering relays with momentary pushbuttons

[salomonander]

Hey there,
Im super inexperienced regarding any switching and logic circuits. I need to come up with a design that allows me to trigger 4 relays with momentary buttons. Only one relay can be active at a time tough. I guess its called mutual triggering?
Say i push button1, relay1 is latched. When pushing any of the other buttons, i want relay1 to unlatch and the according (to the new button pressed) relay to latch instead.

Can anyone point me towards an easy solution or circuit? I did find the attached schematic, but im not certain, if it does exactly what i need. Its from this page: https://sound-au.com/project163.htm

 

[JohnRoberts]

There are a number of ways to skin this cat...

This might be a nice beginner project to do with a mcu. I have used a lot of PICs and some have active pull ups on multiple inputs so the input hardware could be as simple as switch closures to ground. You would need to use interrupts and software to recognize the switch hit, debounce, release the former latched state, output drive suitable for driving relays.

Backing up I could imaging some CMOS logic counter with a jam input so you can force an output state which by definition clears the former state. There are probably multiple combinations of parts to do this.

How easy or hard do you want to make this?

JR

 

[rogs]

Of the circuits on the page you linked to I've used variations on the circuit in figure 7 - which used a 4017 Johnson counter - on several occasions over the years ...... (Relatively) few components and a reliable, simple concept. You will probably need to add transistors to the outputs to drive the relays.... 2N7000 mosfets should work well for this task.
Don't forget to include the reverse bias protection diodes across the relay coils..... You'll blow up the transistors without them!

The 'minimum component' version for this task will be with a PIC, and almost everyone under the age of 50 will probably recommend that approach!
Don't forget to allow time for learning how to program them though, if you're a newcomer.
If you're looking to build just one then the single 4017 approach is hard to beat, IMHO

 

[salomonander]

Thanks guys!
Im under 50, but hell no programming for me please still, thanks for that suggestion. Rogs, will the attached circuit (figure 5 in the paper) achieve what it want it too as well? It seems to be a simpler build than figure 7.

Thanks!

 

[rogs]

Thanks guys!
Im under 50, but hell no programming for me please still, thanks for that suggestion. Rogs, will the attached circuit (figure 5 in the paper) achieve what it want it too as well? It seems to be a simpler build than figure 7.

Thanks!

I'm not sure why you think figure 5 is simpler? -- with all those diodes, resistors and capacitors it uses quite a few more components than fig 7 !
But yes, I think it should work OK You'll still need to add drive transistors and protection diodes though.....

 

[totoxraymond]

I vouch for the CD4017 solution, nice and easy to implement.

 

[JohnRoberts]

Back in the day I used lots of CMOS 4000 series, oddly I went over to the MCU side only in my later decades of design.

JR

 

[hillcrest4lb]

In your application, what is the consequence of multiple outputs being on simultaneously? This simple 40174 circuit in the schematic will not guarantee mutual exclusion of the outputs (Note that a 40174 is not the same as a 4017).

 

[Brian Roth]

In your application, what is the consequence of multiple outputs being on simultaneously? This simple 40174 circuit in the schematic will not guarantee mutual exclusion of the outputs (Note that a 40174 is not the same as a 4017).

Indeed. In Ye Olde Days with mechanical pushbuttons from Schadow, etc. you had two choices when specifying multi-position interlocking switch assemblies:

1. Interlocking, BUT NOT locked out. Press a button and any previously latched button will pop up and release. However, if you press two (or perhaps more) buttons at once, then both (all) will lock down until something else is pressed.

2. Interlocking AND locked out. One and only one button can be pressed and locked at the same time.

Bri

 

[Brian Roth]

In my experience with audio selector switching, NOT locked out has made sense.

Examples on a recording desk:

Selector for an audio source to the CR monitors. Yes, typically you want to listen to a single source at any given moment. But, in a "blue moon" it can be handy to listen to two different sources at once.

Selector for speakers in the control room. Again, usually only one set activated at the same time. Blue Moon times, it is nice to have that option.

Bri

 

[rogs]

Back in the day I used lots of CMOS 4000 series, oddly I went over to the MCU side only in my later decades of design.

JR

I remember the dreadful early days of Z.80 and 6502 projects.... lots of keen young engineers absolutely convinced that CMOS 4000 series would be disappearing virtually overnight ... and writing awful software that would make the project crash, if someone sneezed within half a mile ! ....

I think I would modify your comment -- 'went over to the MCU side' to 'went over to the dark side' !

 

[nsalis]

Hey there,
Im super inexperienced regarding any switching and logic circuits. I need to come up with a design that allows me to trigger 4 relays with momentary buttons. Only one relay can be active at a time tough. I guess its called mutual triggering?
Say i push button1, relay1 is latched. When pushing any of the other buttons, i want relay1 to unlatch and the according (to the new button pressed) relay to latch instead.

Can anyone point me towards an easy solution or circuit? I did find the attached schematic, but im not certain, if it does exactly what i need. Its from this page: https://sound-au.com/project163.htm

FSR IT-R4

Hey there,
Im super inexperienced regarding any switching and logic circuits. I need to come up with a design that allows me to trigger 4 relays with momentary buttons. Only one relay can be active at a time tough. I guess its called mutual triggering?
Say i push button1, relay1 is latched. When pushing any of the other buttons, i want relay1 to unlatch and the according (to the new button pressed) relay to latch instead.

Can anyone point me towards an easy solution or circuit? I did find the attached schematic, but im not certain, if it does exactly what i need. Its from this page: https://sound-au.com/project163.htm

FSR IT-R4

https://fsrinc.com/fsr-products-listing/product/it-r4-series

Dipswitch settings:

Nbr. 1 = 0

Nbr. 2 = 0

Nbr. 3 = 0

Nbr. 4 = 1 if you have four dry contact buttons that switch the control inputs A (B, C, D, E) against the earth symbol for at least 100 ms.

Nbr. 4 = 0, if you have an external voltage of 2 VDC to 24VDC, which you apply to inputs A (B, C, D, E) against the earth symbol for at least 100 ms.

Activating input E deletes any activated inputs 1 to 4.

A typical short button press by a normal person takes about 200 ms, enough to switch the FSR device's inputs.

For the sake of order: The FSR output contacts can only switch so-called low-level signals (max. 30 VDC, max. 3 A). If you want to switch mains voltages (lamps, motors, or similar), hire an electrician who will connect the low-level output contacts of the FSR device with other switching elements and fuses to the high-current loads in a safe and correct manner.

The required minimum load on the FSR output contacts must also be taken into account. This is 10 mA @ 5 VDC. This means that any switched load that is less than 10 mA or less than 5 VDC should not be switched directly from the FSR device's output contacts. If you do it anyway, it's not dangerous, but the silver-plated contacts of the FSR output relays will oxidize after a short time and no longer make reliable contact. If you are planning such an application, let us know and we can provide you with suitable relays that can be controlled by the FSR device and will function reliably for years. This (the use of additional relays) also applies if you want to switch balanced audio signals (the FSR device only has one 1-pin contact per output, but switching balanced audio signals requires 3 contacts).

Nick Salis

 

[salomonander]

Thanks guys!
I need his to be exclusive. Only one output active at a time. The last button pressed should always be the one with an activated output. Will the circuit work for his?

Another question - i dont want to open another thread:
When i want to trigger a bistable relay with a momentary switch, do i need to debounce the switch? If so, does anyone have a simple (ideally passive) circuit for this?

 

[Newmarket]

...I guess its called mutual triggering?
Say i push button1, relay1 is latched. When pushing any of the other buttons, i want relay1 to unlatch and the according (to the new button pressed) relay to latch instead.

Better described as "Mutually Exclusive".

 

[JohnRoberts]

Thanks guys!
I need his to be exclusive. Only one output active at a time. The last button pressed should always be the one with an activated output. Will the circuit work for his?

Another question - i dont want to open another thread:
When i want to trigger a bistable relay with a momentary switch, do i need to debounce the switch? If so, does anyone have a simple (ideally passive) circuit for this?

Crude but placing a small cap across the mechanical switch can suppress switch bounce. Using CMOS latches a classic problem is a single switch hit being interpreted as multiple hits.

In the embedded controller domain switch debouncing is done with short delays to lock out multiple hits.

JR

 

[rogs]

Thanks guys!
I need his to be exclusive. Only one output active at a time. The last button pressed should always be the one with an activated output. Will the circuit work for his?

Another question - i dont want to open another thread:
When i want to trigger a bistable relay with a momentary switch, do i need to debounce the switch? If so, does anyone have a simple (ideally passive) circuit for this?

As Newmarket says, the concept is best described as 'mutually exclusive'....... As I mentioned above, I still think the 4017 option (figure 7) is the best approach:

• Always mutually exclusive ( As hillcrest4lb mentions in post #8 above, the 40174 option from figure 5 is not necessarily mutually exclusive..... Hold 2 buttons together and they'll both latch on )
• No need for any switch de-bouncing
• Fewer components overall

 

[totoxraymond]

On both devices i've built using 4017, i had to debounce the switch with a 100nF cap. Just 2 cents (both the part and my experience ).

I think i even put a decoupling cap for the 4017 which is probably overkill. At least it's better to have the footprint on the pcb and not use it.

 

[Newmarket]

Crude but placing a small cap across the mechanical switch can suppress switch bounce. Using CMOS latches a classic problem is a single switch hit being interpreted as multiple hits.

In the embedded controller domain switch debouncing is done with short delays to lock out multiple hits.

JR

Yes. I like hardware denounce. Though obvs on a commercial basis if you're reading the switches with a micro then it's tempting to implement software denounce to save the components and PCB area.
From memory a cap, and possibly a resistor for an RC network, then a Schmitt input gate eg a gate on a 74HC14 to square it up nicely for the micro pin.

 

[moamps]

I made and used this circuit more than 20 years ago.

 

[nsalis]

"When i want to trigger a bistable relay with a momentary switch, do i need to debounce the switch?"

Bistable relays engage reliably after briefly pressing a button, without any bounce protection being needed. Most bistable relays are not suitable for audio signals because their contact material cannot reliably switch small voltages and currents.

Other disadvantages of bistable relays are:

a) Large coil current when activating and deactivating. This current requires the power supply and wiring to have the appropriate power capability.

b) Switching can lead to clicks in the audio signal if the momentary contacts are not spark protected with a resistor/capacitor combination.

c) When switching the contacts from open to closed and vice versa, a relatively strong mechanical clicking noise is produced. This may or may not be a problem.

Nick Salis

Bistable relays, on the other hand, are recommended for switching mains voltages, e.g. those for the rack mounted equipment in an audio system.

Please tell us what kind of signals you want to switch, then we can help better.

Nick Salis