A single switch to control two circuits

Thread Starter

Thenextman

Joined Feb 3, 2017
42
Hi!

I am designing a circuit where a single On / Off button must control input to two circuits. I am wondering what type of circuit I require between the push button and inputs.

In what I think are simple terms, the circuit would work like this:

Push button is depressed - Circuit A is closed and Circuit B is open.

Push button is let go - Circuit A is open and Circuit B is closed.

The push button has two leads coming off it, the device I am controlling has 2 inputs (Circuit A and Circuit B) and a ground. It is a 5 V device.

What type of circuit would I need between the button and device to operate as described above?

Thanks all!
 

DickCappels

Joined Aug 21, 2008
6,463
Based on the information you provided I would use a circuit like this:
upload_2017-2-3_18-19-46.png
But I would really use CMOS instead of TTL. Instead of the LEDs you can connect your circuit.
 

Thread Starter

Thenextman

Joined Feb 3, 2017
42
Based on the information you provided I would use a circuit like this:
View attachment 119834
But I would really use CMOS instead of TTL. Instead of the LEDs you can connect your circuit.
Thanks so much for the speedy replies guys.

Wow! More complex than I thought it would be! (I have barely any experience with electronics - more simple electrical) I was thinking of using an arduino, but am worried about latency. This should act instantaneously?
 

Thread Starter

Thenextman

Joined Feb 3, 2017
42
A simple momentary type SPDT push button switch would do it with way less parts.

It would be basically Dicks circuit minus everything but the bottom left hand corner switch set.
Thanks TCM - unfortunately the switch is a floor sensing pad so I am limited in type.

Thanks again.
 

AnalogKid

Joined Aug 1, 2013
8,493
An arduino is massive overkill. What outputs to the circuit do you want when the switch is pressed? A +5Vdc signal, a pull down to ground? Does the output from the switch processing circuit need to supply any power to run the external circuit, or just a signal? Can you give us any more information about the two circuits being controlled? Depending on the answers, this might cook down to one transistor and a couple of resistors.

Note that all mechanical switches "bounce". That is, the contacts bounce on and off each other briefly each time the switch opens and closes. For a 5 V logic system, this can look like a burst of 1-0-1-0 transitions for a few milliseconds before things settle down. Depending on the circuits receiving the switch signals, this can be anything from ignored to a medium-sized annoyance than needs a few more parts to solve.

Do you have a maximum latency limit?

ak
 

#12

Joined Nov 30, 2010
18,210
To sum this up, you have a signal that might be any amount of current and any frequency, but the voltage is probably less than 5V, but it might not. You want a box that receives the condition of a switch and connects one or the other of two signals of unknown current, unknown frequency, and unknown impedance.

This isn't going to end well if you don't tell the conditions present.
 

AnalogKid

Joined Aug 1, 2013
8,493
What power is available for the switch interface circuit? For what I'm thinking you need 5 V at about 10 mA.

Also, if you already have the switch device. it would help greatly to know the voltage on the control input pins with nothing else connected.
1. Voltage from IN1 to G.
2. Voltage from IN2 to G.
3. Voltage from G to the shell or body of the DC power input jack with the DC power connected and unit unit turned on. The idea here is to determine the relationship between the power input ground and the control input ground. Hopefully, they are 0 V apart.

ak
 

Thread Starter

Thenextman

Joined Feb 3, 2017
42
Hmm sorry - I don't know more than the specs provided. Speaking with a rep at Kramer - the manufacturer of the video input switch - the physical switch should not require power. It is a 5v device from the specs on the website. He suggested a contact closure type button, but the pressure sensing mat is not expendable.
 

Thread Starter

Thenextman

Joined Feb 3, 2017
42
What power is available for the switch interface circuit? For what I'm thinking you need 5 V at about 10 mA.

Also, if you already have the switch device. it would help greatly to know the voltage on the control input pins with nothing else connected.
1. Voltage from IN1 to G.
2. Voltage from IN2 to G.
3. Voltage from G to the shell or body of the DC power input jack with the DC power connected and unit unit turned on. The idea here is to determine the relationship between the power input ground and the control input ground. Hopefully, they are 0 V apart.

ak
PS - I don't have the equipment yet for testing. Thanks!
 

ScottWang

Joined Aug 23, 2012
6,913
A single touch pad ON/OFF toggle switch, you could choose two sets of relay contacts. (6 pins)

Only needs a small touch pad and no need the push switch, or connects the input pin to +V with a push switch.

You can reduce R4 to match the current of your relay needed.

 

Thread Starter

Thenextman

Joined Feb 3, 2017
42
Then use the floor pad to activate a simple SPDT relay.
This seems workable with my limited knowledge of assembling circuits. Would of like to avoid any batteries / extra power supplies though - seems like the relay would need its own power source though.
 

AnalogKid

Joined Aug 1, 2013
8,493
Posts 2, 6, 7, 9, 12, and 13: Anything that inverts an electrical signal will need a power source. With the right parts it can last years, but still.

ak
 

AnalogKid

Joined Aug 1, 2013
8,493
That is the basic relay approach. Low-power relays with a 9V rated coil are rare, but a low-power 12 V relay probably will pull in reliably with a 9 V battery.

ak
 

Thread Starter

Thenextman

Joined Feb 3, 2017
42
Amazing. Thanks so much for all replies and major shout outs to @tcmtech and @AnalogKid. I feel great about this solution - low part count, and seems very reliable!

Hopefully the client is on board with project and I can let you know how it goes!

Thanks again,

Paul
 

Thread Starter

Thenextman

Joined Feb 3, 2017
42
Is this a single part / switch I can buy? The reason I want to use the mat specified is that it needs to reliably trigger over a decent surface area - i.e. The participant should be able to stand on a floor mat ~ 18" x 18" without having to look for a button.

Or I guess you are proposing the circuit downstream from the switch in your diagram be attached to my mat? I feel like I would screw this up - too many parts and connections :p

I tried to wire my own micro amp audio amp once with basically 1 IC and a few resistors / connectors and manages to totally bungle that.
 
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