12V logic control of 3 LEDs

Question

I am building a circuit and am stumped without using many relays to achieve the result. I would appreciate any help I can get.

Basically I have 3 different colour LED's in a (push button) some of these push buttons are momentary, and some are latching. The LED's are common ground. Therefore I will be switching the power side. They are built into the pushbutton and have a resistor, so they are rated at 12 V.

I have a relay controlling if I supply red or blue, so its an either logic based on another latching pushbutton. Blue for day, red for night. I use DPDT 12V relays for this. this is globally applied to all the pushbutton led colours. I.e. all blue or all red. (There are 30 switches with 3 LEDs each)

What I need to resolve is that if I push one of the 30 buttons, it needs to turn off the red and the blue input to that button indicator, and turn on the green only for that button indicator light.

I prefer to use 12V (10 - 15V) as it is supplied by a 12V battery. was thinking it can be solved with MOSFET or similar.

Sadly the pushbuttons are only SPST latching or momentary, no spare contacts

Thanks for anyone's kind help.

Apologies for the crappily written first attempt. When I read it back I confused myself.

On the picture, the 12V is not actually 12V, it is reduced due to the dimming setting. Just put 12V for the purposes of the diagram.

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Truth table for OP to edit [added by @Transistor].

Relay  Button  R G B
--------------------
Off    Off     0 0 1
On     Off     1 0 0
Off    On      0 1 0
On     On      0 1 0

Thanks all for your information and taking the time to reply. I took a look at the cmos option 4000 series as suggested by Jasen. I have no experience in using such components. I simulated the circuit and seems I need XOR gates. This simulation works. I simplified the input selection which is via a relay.

My only concern is the 4070 shows it has a limitation of 10ma per gate (i assume). i put the led onto the power supply and it flickers between.000 and .001a which should be ok.

I removed the resistors as the LED's have their own resistors, is that ok?

the only part i have left to understand and fix is the sensing of the pushbutton switch. as you can see on the schematic it is used to switch a relay. Currently when the Pushbutton is off, the transistor allows the green LED to illuminate. I need the opposite. I need when the Pushbutton is open, the green led to be off. thanks

Answer 1

^{simulate this circuit – Schematic created using CircuitLab}

Figure 1. A possible solution. (LEDs are 12 V and have built-in current limiting.)

How it works:

• RLY1 switches between day (blue) and night (red).
• If the individual switch or button is off Q1 or Q2 is turned on depending on the day/night setting.
• If SW1 is pressed D7 and 8 conduct pulling the bases of Q1 and Q2 high and shutting them off. A Schottky diode is used here so that its lower V_F will pull higher than the BE turn-on voltage of the transistor. (I haven't tested this. You should. The simulation in Figure 2 indicates that it's good.) The result should be that green turns on and the day/night LEDs turn off.
• The primary purpose of the Schottkys (hmm - Schottkies? I don't think so) is to prevent illumination of D1 and D4 through the bases of Q1, etc.
• You could half the number of Schottkys and use a common one for Q1 and Q2 but you'll end up wasting current in the the base resistor of the unpowered transistor.

You'll need 60 PNP transistors and bias resistors and 60 Schottky diodes! You'll need to decide if it's worth the trouble.

^{simulate this circuit}

Figure 2. Simulation results for the circuit indicate good control. Left: switch / button off. Right: switch / button on.

Answer 2

this is the sort of thin that cauld be solves using 12V capable logic and a few resistors.

Old-school CMOS logic is good to 15V or more so use CD4001 or HEF4001 - you'll need one chip for every two illuminatred switches.

^{simulate this circuit – Schematic created using CircuitLab}