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Help with simple logic

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jansjobe

New Member
Hi all!

I need help with constructing a 2 pole 16 way switch using relays, push buttons and indicator leds. Only one input/relay active at once.
As simple as possible. See attached image.
Any genious ideas out there?

Best Regards,
Jan Sjöberg
SWEDEN16 WAY SWITCH.jpg
 

MikeMl

Well-Known Member
Most Helpful Member
Are you looking for a "priority" or "lockout" circuit where if two or more buttons are pushed simultaneously, only one relay is energized?

Otherwise, sixteen buttons, sixteen relays, sixteen Leds and resistors, and the wiring is trivial and straight forward.
 

AnalogKid

Well-Known Member
Most Helpful Member
What you want is called a "radio button" circuit, after the interlocked pushbutton radio tuners in cars. Lotsa ways to do this (you can google for schematics). One of the most simple is to use DPDT relays, with one pole to control the switching and one pole to switch the signals (or whatever is being switched).

What are the specs for the relays you have chosen? Voltage / current / wattage?

Are you looking for electronic control or all electromechanical?

ak
 

crutschow

Well-Known Member
Most Helpful Member
Is this homework?
What is this to be used for?

There are numerous circuits out there that can do the "Radio Button" circuit.
My favorite uses a two NAND-gate latch (1/2 package), two resistors, and one diode per button.
 
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jansjobe

New Member
Only one releay must be active at any one time, so I assume this means "lockout".
The object is to switch midi signals that uses 2 wires, so both contacts in the relay must be used.

The Radio-button circuit seems promising. Could anyone show me?

Sorry if I posted this in the wrong area, what do you mean by "homework"?
 

Inquisitive

Super Moderator
Is this an assignment from a educational instructor?
 

eTech

Active Member
Hi

I believe midi signals are 5ma current loop.

Could use a push button to clock a couple of 1of 8 decoders to drive relays each having form C contacts

eT
 

AnalogKid

Well-Known Member
Most Helpful Member
So - 16 small relays? Look into DPST or DPDT reed relays. The contacts are hermetically sealed; excellent long-term reliability and perfect for low voltage signals.

What voltages are available to power the control circuit and the relay coils?

ak
 

AnalogKid

Well-Known Member
Most Helpful Member
First pass. This is a modified version of a circuit I've used for years. Each output can drive a small relay coil (<100 mA). Because this uses resistors to form a giant OR gate, the circuit can be fooled. If multiple buttons are pressed and held during the first 30 milliseconds (the switch debounce period), they all will be latched. More complex circuits (called game show or college bowl circuits) prevent this.

ak
RadioButtons-16-1.gif
 

AnalogKid

Well-Known Member
Most Helpful Member
After any button press. When any button is pressed, it triggers a monostable set to 30 milliseconds. The trailing edge of that pulse clocks the latches, and any buttons pressed at that time are latched as ones and drive relays. Once a button is held down and the 30 ms has passed, al buttons are ignored until all buttons are released and the monostable resets for the next event. To shorten the recovery time there should be a small diode added in parallel with R1. I'll update the schematic.

While there is a chance, technically, of a non-unique output, the odds are extremely low. There is another version of this circuit without the full monostable, just a transistor as an edge former, and it works just fine.

Note - the parts values and IC part numbers are suggestions, parts in my schematic library. Feel free to use different gates and latches. I like resistor networks but that's just me; individual resistors will work just as well.

ak
 

crutschow

Well-Known Member
Most Helpful Member
Here's an LTspice simulation of the NAND gate circuit with write-up here.
Only the output with the last pressed switch is active.
Each output, with an added transistor driver, or a driver IC such as the ULN2803, can control a relay.
The circuit can be extended to 16 outputs by duplicating the right portion of the circuit consisting of a diode, two resistors, and two NAND gates.


 

crutschow

Well-Known Member
Most Helpful Member
Would the CD4043/44 cut the body count in half?
Good thought.
Yes, it would.
So it would require 4 ICs instead of 8 for the 16 outputs.

But availability may be a consideration.
Jameco says they are discontinuing the device.
 
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