Toggle switch to push button switch conversion (Arduino or IC logic)

Hi Silviu,

An easy method to produce pulses is to get a 'quad XOR gate' ic.

Connecting one input of a gate to 0V makes a simple buffer which does nothing except delay a signal slightly. Do this with three of the gates so that you have 3 buffers. Connect them up in series. Lets call them gates #1,2,3.

Feed the final output from the third buffer (gate #3) into an input on the fourth gate. Connect your switch to 0V and (say) a 47k resistor to your supply rail. Connect the switch/resistor junction to the input of the fourth gate and the remaining input on gate#1.

The end result is that you get a brief pulse (a few tens of nanosec) whenever the switch is opened or closed.

But, I'm not sure this is what you really want. If (say) the power is off, and someone changes the toggle position and then powers on, then your software will have no idea what the initial toggle position is. Or, if the software is polling instead of using an interrupt, then it may skip some pulses (Maybe this is acceptable - depends on the actual application).

For these reasons it would be best to try to design it so you can accept a normal toggle input, rather than a pulse if possible.

Thank you for your answer Shabaz,

I have to say, i did tough of using a logic gate to produce the signal, tho, when you have 40 toggles you need to wire, it becomes inefficient. A tenth of a nanosecond wouldn't be enough, i'd need something like a half second pulse to trigger the command correctly.

Now, is there a way of doing this with an MCU? preferably an Arduino, (something like, if toggle on, then turn on led for one second, then if toggle off, do the same) I'd test it out with an LED, then replace it with an optocoupler. I have done the reverse, making a push button toggle a motor ON and OFF, but even then, i needed help with the code regarding the buffer of the Arduino. (i think using a delay without a loop would work, wouldn't it? the LED would turn on, and then stay off?)

Thank you for your answer Shabaz,

I have to say, i did tough of using a logic gate to produce the signal, tho, when you have 40 toggles you need to wire, it becomes inefficient. A tenth of a nanosecond wouldn't be enough, i'd need something like a half second pulse to trigger the command correctly.

Now, is there a way of doing this with an MCU? preferably an Arduino, (something like, if toggle on, then turn on led for one second, then if toggle off, do the same) I'd test it out with an LED, then replace it with an optocoupler. I have done the reverse, making a push button toggle a motor ON and OFF, but even then, i needed help with the code regarding the buffer of the Arduino. (i think using a delay without a loop would work, wouldn't it? the LED would turn on, and then stay off?)

Hi Silviu,

If you want to do it using an Arduino alone, you will need 80 pins for 40 switches and 40 outputs, so that may be unfeasible.

Anyway, below is some pseudocode that will do it for (say) 4 switches and 4 outputs. It is pseudocode since I'm not totally

familiar with Arduino and won't compile, but it should give you ideas on how to arrange your code. It's not particularly efficient

code, but was a quick thing. The logic should hopefully make sense, so that you can translate it into code.

// assume inputs are numbered 0-3
// assume outputs are numbered 4-7

set_outputs_low()
{
    // this function sets all four outputs low
    int k;
    for (k=4; k<8; k++)
    {
      digitalWrite(k, LOW);
    }
}

main()
{
    int i;
    char newval;
    char togglestate[4];
   
     // set all outputs initially low
     set_outputs_low();

    // read the initial state of the 4 toggle switches connected to
    // inputs 0-3
    for (i=0; i<4; i++)
    {
      togglestate[i]=digitalRead[i];
    }
   
    while(1) // loop forever
    {
      // For all inputs, set an output high if a corresponding input has flipped
      for (i=0; i<4; i++)
        {
          newval=digitalRead[i];
          if (togglestate[i] <> newval) // has the state changed?
          {
              togglestate[i]=newval;
            digitalWrite(i+4, HIGH); // set the corresponding output high
          }
        }
       
        // now sleep for half a second
        sleep(0.5);
       
        // now just set all outputs low
        set_outputs_low();
    } // loop forever
       
}

It sets an output high if it thinks the corresponding toggle input has changed from the previous value, and blindly sets all outputs low every half second, which has the desired end effect.

If you want to scale to 40 inputs and 40 outputs with an Arduino then some form of I/O expansion is needed. This makes the circuit more complex and larger of course - things like PCF8574 can each handle 8 I/O, but there are surface mount devices that can do 16 I/O, or maybe higher.

Thank you very much Shabaz,

I will sure check out and modify the code you gave, if usage of the Arduino I/O turns out too inefficient, i will research to find some kind of "special" momentary toggle switches, i know some old cars and planes use those kind of switches for ignition or other purposes. Thank you for your time, your answer was really helpful! (;

Hi Silviu,

I see that you have marked this question closed but I thought I would throw an old fashioned idea at you anyway. If you are able to use DPDT toggles you could hook them up to reverse the polarity of a capacitor. In this way each time the switch is toggled the capacitor would discharge and recharge creating a current of duration depending on the size of the capacitor. I prototyped a small circuit and was able to get an LED to turn on for one second each time the switch was toggled. If this idea fits your need you could save lots of hardware and programming. If you would like a schematic for the little prototype I put together let me know.

John

Hi John,

Indeed, I am very interested in your prototype, it would fulfill my purposes pretty well. I can always mark your answer as correct, no prob (;

The less programming and hardware the better, I'll await your response.

Thank you!

Hi Silviu;

I have drawn a schematic and added some notes. . Don't worry about right

answers as everyone contributes good ideas. If you have clarifying questions let me know.

John

You could also just use a MOM-OFF-MOM toggle. That is a Momentary toggle ON and OFF that returns to a center position. DPDT would work but it only needs to be a SPDT and therefore a bit cheaper. If you use the center pin as your output, you could send a positive for ON and a ground for OFF (as an example) or both positive or both ground.

Thank you very much for your diagram John, I will sure test it out!

Now, what do you mean by a NON-Polarized Capacitor? as I have never seen one before, all seem to have a polarization indication on them.

Thank you.