IN homemade we use LEDs for indication, it’s good when there is one LED in the circuit, but when several of them will have to be calculated by current-limiting resistors. But if the circuit allows, it is easier to use a driver.
How to make a DC source, issuing 20mA
(operating current of many LEDs) at the output. Or better known as an LED driver.
The driver input voltage is 5-15 volts DC.
The driver with these components of the circuit will pull up to 7 LEDs without resistors, while the LEDs are completely safe.
Minimum and affordable components
27 ohm resistor
10k resistor
KT3102 transistor or equivalent
Two diodes: 1N4007 or equivalent
We assemble according to the scheme
I think it is not possible to make a mistake in assembling this scheme.
The circuit works immediately and without problems. For the test, connect the LED, when the power is connected, it will light up.
You can connect from 1 to 7 LEDs per circuit.
Calculation example:
Input voltage = 9V
Circuit consumption = 0.7 V
voltage for example red LEDs = 1.8 V
0.7 + 1.8 + 1.8 + 1.8 + 1.8 = 7.9 in <9V Norm!
I think the principle of calculation is clear and not cause difficulties.
Good luck!