Turn on LED when manual switch ON only

Question

The circuit consists of a 12V DC supply, there is a GPIO to turn on the solenoid rated at 12V 500mA. Also, a manual switch is there to turn on the solenoid when needed.

The placement of LED and 1K resistor is such that LED would turn ON whenever Solenoid is turned on, be it either due to GPIO high OR by manual switch. My requirement is to Turn on a LED if Manual Switch is ON irrespective of GPIO level.

• Manual ON , GPIO ON : LED ON
• Manual ON, GPIO OFF : LED ON
• Manual OFF, GPIO ON : LED OFF
• Manual OFF, GPIO OFF : LED OFF

How can it be accomplished?

NOTE: TIP122 is transistor used. The diode is flyback diode

Answer 1

Adding a diode like in the following picture will do the job:

Answer 2

^{simulate this circuit – Schematic created using CircuitLab}

There's a million ways to do most anything. What Paul drew is clever and would work. So would this one.

Mine has 1 more component, but Pauls has two minor tricks you should be aware of...

One is that diode has to be able to handle all the solenoid current (500mA)... not all diodes can do this. What I wrote uses 2 small-signal diodes --- 1N4148's can't handle 500mA (not even close). So these 2 diodes would be cheaper, but there's 2 of them. Pauls circuit, you'll need a power diode like 1N4001.

Another catch with his circuit, all the current flows through the switch so it also has to handle 500mA (and the associated spark that occurs when a coil is interrupted), with mine the current in the switch is a trickle and not inductive i.e. you can use a smaller switch, or if using the same switch, it would likely last MUCH longer.

BTW, The 270 resistor is presuming a 5V I/O. If it's only 3.3V, that resistor should be made smaller.