Welcome to our site! Electro Tech is an online community (with over 170,000 members) who enjoy talking about and building electronic circuits, projects and gadgets. To participate you need to register. Registration is free. Click here to register now.
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?
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?
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.
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.
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.