Wiring two lamps so that the one disables the other

Question

If we have two lamps, two switches and two batteries, how do we wire them up in a way that switching one of the switches makes it impossible for the other to work? I am experimenting in tinkercad, but so far no luck.

Edit: I was allowed to edit the question in order to clarify that switch A should not affect lamp B and switch B should not affect lamp A. In other words: Switch A should be off for circuit B to work and Switch B should be off for the circuit A to work. The first switch to be on, makes its lamp on and disconnects the other circuit. This is used as a way to measure who turns the switch faster without using digital logic or complicated/expensive electronics i.e it's noob-friendly.

Answer 1

^{simulate this circuit – Schematic created using CircuitLab}

Figure 1. The two-lamp priority circuit.

Thyristors have the odd characteristic that once switched on they remain on until the current through them falls below the holding current. We can use this to turn on the lamp of the first button to be pressed and inhibit the other.

How it works:

• Initially both lamps are off. LAMP1 provides battery voltage to SW2 and LAMP2 provides battery voltage to SW1.
• Pressing SW1 will trigger SCR1 causing it to turn on. LAMP1 will light.
• When SCR1 turns on the voltage at the lower terminal of LAMP1 will drop from V+ to a voltage close to ground. This means that if SW2 is now pressed that SCR2 will not be triggered (because the gate voltage is too low) and LAMP2 will not turn on.

Pressing the RESET button will reduce the current through either SCR to zero ready for the next round.

Answer 2

All these circuits fulfill the requested condition. Closing an odd numbered switch prohibits, that closing the even numbered switch has any effect on the lamps.
The first circuit may be useful, but don't try the others with real world components, batteries and switches will be destroyed.

^{simulate this circuit – Schematic created using CircuitLab}

EDIT: This circuit meets more detailed requirements mentioned in comments.

^{simulate this circuit}

Answer 3

You have \$N=2\$ switches (inputs), meaning that there are \$2^N=4\$ possible combinations of switch positions.

Before proceeding to tinker, it's best to formally define the lamp states that would result for each input condition, in a table:

Switch 1	Switch 2	Lamp 1	Lamp 2
Open	Open
Open	Closed
Closed	Open
Closed	Closed

Fill in columns 3 and 4, and then you can proceed.

As it stands, we are being asked to guess what "one lamp disables the other" actually means. This implies some symmetry to the problem, but if you think about it, one of the lamps will need priority in the case where both switches are on. Otherwise the system would have to have some form of "memory" of prior states. This suggests a fundamental asymmetry entirely absent from your description of it, which would become immediately clear if you formally described behaviour in the truth table.

What also becomes clear when you write out a truth table, is if the problem even has a solution using simple passive and combinatorial elements. It's unlikely to be an issue in this case, but the argument for a formal statement of input vs. output requirements is still strong. By forcing yourself to imagine the state of affairs for every single input condition, you must necessarily become aware of practical logical flaws.

Also, you say you want to use two batteries, implying that there is some independence between each set of "battery+switch+lamp", but almost every case in that table is possible to implement with a single voltage source. It's therefore also necessary for you to explain to us the reason for having two independent power sources. Without this information it is impossible to guess how they should interact, whether it's OK for one single battery to power both lamps, and so on.

You have not stated if it's OK to use relays, or transistors in the solution. Perhaps you wish to use purely passive elements, namely switches, lamps and batteries, or perhaps you are willing to consider active parts.

In short, your question is vague, and can't be answered in its current state.

Answer 4

^{simulate this circuit – Schematic created using CircuitLab}

I think this will work to detect the first button press. I forgot to add lamps across the relay coils.

Answer 5

Version 1

Version 1 does not satisfy the requirement (Refer PStechPaul's comment)

Version 2

Using two DPDT Ratchet relays

Operation:

1. Actuating S1 latches K1, turns on H1 and disables H2 circuit.

2. Actuating S1 again resets K1, turns off H1 and enables H2 circuit.

3. Now actuating S2 latches K2, turns on H2 and disables H1 circuit.

4. Actuating S2 again resets K2, turns off H2 and enables H1 circuit.