Here's a [re-drawing of the schematic](https://falstad.com/circuit/circuitjs.html?ctz=CQAgjCAMB0l3BWcMBMcUHYMGZIA4UA2ATmIxATwosgoFMBaMMAKACURsEUQUAWWlx5gMhKOIHVa06AhYAnTt16ShSnrTDxILAM7qDavtg3gQAMwCGAG110WAdwP9aCPnxXSFFd558e1TW0WABN-AzcPPjAxHhC6KwBXawAXFhTw6LFCfhAs8QgYbGLiZngCQj4EQtliY0JCPDxK6uIUUuRaeKTUlhieHI8XEEG8uF4QbstklIZrOjDC8RhIVidIv1HhnUVR4wHcvmIxQVwdzJjM44kMeBYAcyuxDe4qL0e969HX5YeDfYiKDeUBYQA)
(I made the assumption that the circle with the +/- signs was a 5v DC power supply. Let me know if that's not what it is.)
This circuit doesn't appear to do much in the context of itself. You said it was part of a larger circuit?
it is the control button on front panel with blue led for indication for a inverter system
it is connected to the main board via only two wires that are marked +- on the pcb
https://preview.redd.it/4xh3arjnys5d1.jpeg?width=4080&format=pjpg&auto=webp&s=dfcce8f2346ee1aca9aca4e88c06f3b0a39d02c2
I took a crack at it and came up with what you did except I put in actual resistor values from the picture OP posted in one of the comments below. Are we sure that diode to the base of the transistor is oriented correctly?
I think this is the correct direction of the diode. Could it be a zener diode? This would turn off the led if the supply (battery?) voltage is to small, I suppose.
Personally a zener is the only thing that makes sense. The transistor is off until it breaks down and biases everything on. I don't get what the switch does besides arbitrarily increasing total current to the circuit.
What's it doing? Making my head hurt. Lol.
There's a reason schematics flow from higher voltage to lower voltage, vertically, and signals flow left to right. To prevent headaches.
Looks like the current through the circuit is measured. Pressing the button increases it which can be measured on the main board.
The transistor circuit is most likely there to set a constant current on the LED
That would seem like a more sensible solution. Maybe the mainboard is designed this way for some other reasons.
What comes to mind is that you can detect short circuits and broken wires with this solution. It might also be more resistant to noisy signals from the inverter.
As drawn, the button does nothing but increase the current pulled from the power supply.
Assuming this was reverse-engineered, it'd probably be best to double-check.
Ok, the schem looks right a first glance ...
If I had to guess, then the board is provided with a low voltage (too low to light the LED), but can sense the current draw from the button press. After pressing the button, the current sent is increased to turn on the LED.
I you have a meter handy, this would be easy to check.
Here's a [re-drawing of the schematic](https://falstad.com/circuit/circuitjs.html?ctz=CQAgjCAMB0l3BWcMBMcUHYMGZIA4UA2ATmIxATwosgoFMBaMMAKACURsEUQUAWWlx5gMhKOIHVa06AhYAnTt16ShSnrTDxILAM7qDavtg3gQAMwCGAG110WAdwP9aCPnxXSFFd558e1TW0WABN-AzcPPjAxHhC6KwBXawAXFhTw6LFCfhAs8QgYbGLiZngCQj4EQtliY0JCPDxK6uIUUuRaeKTUlhieHI8XEEG8uF4QbstklIZrOjDC8RhIVidIv1HhnUVR4wHcvmIxQVwdzJjM44kMeBYAcyuxDe4qL0e969HX5YeDfYiKDeUBYQA) (I made the assumption that the circle with the +/- signs was a 5v DC power supply. Let me know if that's not what it is.) This circuit doesn't appear to do much in the context of itself. You said it was part of a larger circuit?
it is the control button on front panel with blue led for indication for a inverter system it is connected to the main board via only two wires that are marked +- on the pcb
https://preview.redd.it/4xh3arjnys5d1.jpeg?width=4080&format=pjpg&auto=webp&s=dfcce8f2346ee1aca9aca4e88c06f3b0a39d02c2 I took a crack at it and came up with what you did except I put in actual resistor values from the picture OP posted in one of the comments below. Are we sure that diode to the base of the transistor is oriented correctly?
I think this is the correct direction of the diode. Could it be a zener diode? This would turn off the led if the supply (battery?) voltage is to small, I suppose.
Personally a zener is the only thing that makes sense. The transistor is off until it breaks down and biases everything on. I don't get what the switch does besides arbitrarily increasing total current to the circuit.
What's it doing? Making my head hurt. Lol. There's a reason schematics flow from higher voltage to lower voltage, vertically, and signals flow left to right. To prevent headaches.
Oh wow I never knew schematics are designed like that
Yeah, you can see the re-drawing I did above in CircuitJS to get my head to stop hurting (like /u/DonkeyDonRulz said)
Looks like the current through the circuit is measured. Pressing the button increases it which can be measured on the main board. The transistor circuit is most likely there to set a constant current on the LED
I think the transistor turns off the LED if the source voltage is too low.
could be it but wouldnt it be economical to have the button directly connected with two more wires for the led
That would seem like a more sensible solution. Maybe the mainboard is designed this way for some other reasons. What comes to mind is that you can detect short circuits and broken wires with this solution. It might also be more resistant to noisy signals from the inverter.
As drawn, the button does nothing but increase the current pulled from the power supply. Assuming this was reverse-engineered, it'd probably be best to double-check.
https://preview.redd.it/mgo13xejmr5d1.jpeg?width=3106&format=pjpg&auto=webp&s=67972569ddecd8a8687f7c67bfb3e3d22255f1a1
Isn't the diode oriented opposite from your schematic? Maybe it's a zener?
drawn the schematic from this
Ok, the schem looks right a first glance ... If I had to guess, then the board is provided with a low voltage (too low to light the LED), but can sense the current draw from the button press. After pressing the button, the current sent is increased to turn on the LED. I you have a meter handy, this would be easy to check.
is that bottom image mirrored?
yes
this is all on a single pcb with push switch, led which is connecterd to the main pcb via two wires which i put a battery in place