Building a Switch Panel - On/Off Buttons, Turn One Switch off if Another is Turned On

Discussion in 'The Projects Forum' started by uberstyle, Jan 22, 2016.

  1. uberstyle

    Thread Starter New Member

    Jan 22, 2016
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    Hello, I am looking at building a switch panel for the bay meters in my self serve car wash. It will have 12 on/off buttons and I would like the panel to work such that if one switch is on (say the high pressure rinse switch) and a customer selects a different button switch (say the low pressure engine degreaser), the original button (rinse) will turn off and the new button (degreaser) will activate.

    I am trying to avoid having two switches on at once.

    Can anyone kick me in the right direction?

    By way of background, I have done some minor things around the wash electronics related, mostly PLC and sensor stuff. My theory is not great but not afraid to get my hands dirty...

    Here's an example of what the panel might look like, if it's any help.
    http://www.cpcarwash.com/meterboxes.htm

    Thank you.
     
  2. dl324

    Distinguished Member

    Mar 30, 2015
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    Something like this (from a STM datasheet) driving some decode logic?
    upload_2016-1-22_19-7-55.png
     
    Last edited: Jan 22, 2016
  3. uberstyle

    Thread Starter New Member

    Jan 22, 2016
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    Maybe so! Thanks for the reply and the guidance. I will start doing some research to see if I can piece it together. Thanks again.
     
  4. dl324

    Distinguished Member

    Mar 30, 2015
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    The decoding can be done with a 74HC154. And welcome to AAC!
     
  5. AnalogKid

    Distinguished Member

    Aug 1, 2013
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    This sounds a lot like another thread where a guy wants three buttons to switch speakers to his stereo, mutually exclusive. Also know as a version of a game show circuit. What do the buttons ultimately control? Logic level inputs to a controller? Relays that turn motors on and off? In other words, once the switches make an output, where does the output go?

    ak
     
    Last edited: Jan 22, 2016
  6. uberstyle

    Thread Starter New Member

    Jan 22, 2016
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    Thanks to both of you, and thanks for the welcome!

    Right now the meter box is set up on a rotary switch, such that only one option can be made at a time. I think that's the foolproof way but I like the upgraded look of the push button panel. The rotary switch in place today just directs power to the appropriate motor or pump via a terminal strip, depending upon the option selected. Power becomes available once the correct number of coins have been entered.

    Right now, there are no relays in the box. I was looking at potentially an arduino with a relay board setup to run the 12 options, because I thought that way I could build logic in the arduino to turn off a switch before turning another one on, but was hoping there was a simpler/smaller/cheaper way - which it seems there is based on your input, dl324. I will explore the 74HC154 and the speaker circuit you each reference.

    And I think this is probably blasphemous, but if it's already been done and it's for sale, I would be interested in that as well (aside from buying the $4,000 panel in my link).
     
  7. crutschow

    Expert

    Mar 14, 2008
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    What you want is a Radio Push-button type of circuit.
    Here's my take on that which uses four ICs (read text) for up to 16 momentary buttons.
    It actually dl324's post #2 circuit with a 4514 to do the decoding since it has a latch to retain the reading, which the 74HC154 decoder doesn't have.
     
    Last edited: Jan 23, 2016
  8. uberstyle

    Thread Starter New Member

    Jan 22, 2016
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    Right on! I was actually already reading your page when I got the notification that you had responded to the thread (found from the speaker thread). Great stuff - I am going to give it a shot!
     
  9. crutschow

    Expert

    Mar 14, 2008
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    To control the pumps/motors you will need relays, either mechanical or solid-state type. The mechanicals are likely cheaper but the SSRs are more reliable, take less power, and won't be affected by any possible water/humidity that may be present at their location in the car wash.

    In either case you will need BJT or MOSFET drivers on the 4514 outputs to control the relays.
     
    Last edited: Jan 23, 2016
  10. tkng211

    Well-Known Member

    Jan 4, 2008
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  11. AnalogKid

    Distinguished Member

    Aug 1, 2013
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    Another option is a set of switches that are interlocked mechanically, like the buttons in an old car radio. Pressing any switch forces all others to release, no electronics required. If you need only one set, these are reqularly available in surplus shops. A gang of 12 might be rare, but the approach is something to consider.

    With an electronic circuit you have choices. If two switches are pressed almost simultaneously, the circuit in post #10 locks out all other switches the instant (as in 20 nanoseconds) the first one is pressed. Excellent security, but difficult to expand. Wally's circuit captures the higher valued switch, not quite the same thing. There is a circuit I've used for years that relies on the user not pressing multiple switches at once, something that can be addressed with switch spacing. It is less complex and much easier to expand to a large number of switches, but it is slightly possible to capture multiple switches and have multiple outputs in the on state.

    ak
     
  12. Alec_t

    AAC Fanatic!

    Sep 17, 2013
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    Something based on this perhaps? Three stages are shown, but by adding further stages (each as shown in the dotted box) unlimited extension is possible.
    LatchingSwitches.PNG
     
    uberstyle likes this.
  13. uberstyle

    Thread Starter New Member

    Jan 22, 2016
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    You guys are great! Never had a forum experience like this. I am ordering some parts and will report back in two weeks.

    Andy
     
  14. uberstyle

    Thread Starter New Member

    Jan 22, 2016
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    Hello - I wondered if you could guide me on both the MOSFET and the SSRs that I will need? I have 24 volts coming in, I was going to step it down to 5 volts, run it through the switches/encoder/decoder. I am not positive where to go from there.

    Because I have 12 switches, I assume I will need 12 solid state relays?

    I was looking at something like this for the relays: http://www.ebay.com/itm/24V-380V-40...937205?hash=item2ee5440a75:g:0MoAAOSwD0lUduWt

    I definitely need to do some research on MOSFETs... I am not sure if I want N or P or how to spec the right values.

    Thoughts? Thank you.
     
  15. crutschow

    Expert

    Mar 14, 2008
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    Yes, you will need 12 relays.

    My circuit will work from 5V to 15V so anything in that range is okay.

    That SSR looks satisfactory. It's a very cheap price for that size SSR, so there's the usual caveat about that, but for that price it's probably worth a shot.

    The SSR takes 40mA-20mA to turn on so the cheapest way to drive that would likely be an NPN BJT such as the 2N3904 or 2N2222.

    You could also use an N-MOSFET but they're generally more expensive and have no particular advantage in this application except they don't require a resistor at their (gate) input.
    I indicate the MOSFET connections in parentheses.

    Connect the positive SSR input to your circuit plus supply and the negative SSR input to the transistor collector (drain).
    Connect the transistor emitter (source) to ground.
    Connect one end of a 10k resistor to the transistor base (gate) and the other end to the desired circuit control output (MOSFET doesn't require the resistor).
     
    Last edited: Jan 26, 2016
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