From the section 4.5 Powering Pico of the official Raspberry Pi Datasheet. I have decided to use the first method which is suggest to use a schottky diode with the VSYS pin.
I have used 1N5819 Schottky diode.which has
VRRM = 40V,
Maximum average forward rectified current IF(AV) = 1A
The schottky diode and the diode on the Pico PCB makes a power OR-ring. In this system the pico will take power which is greater. So if the power is greater from USB it will take power from USB. and if the voltage is greater from the power supply it will take power from it. Because of the use of schottky diode there will be a diode drop. To reduce it you can use a P-MOS as suggested in the datasheet. But for simpler circuits the Schottky diode works.
Using the suggestion from the datasheet. I made a schematic in KiCad.
The 1N5819 schottky connects to a custom switching step down voltage regulator made using the MC34063A IC.
This is the micropython program code that i used
import machine
import time
# Set up the button on GPIO22 with external pull-up resistor
button = machine.Pin(22, machine.Pin.IN, machine.Pin.PULL_UP)
# Set up the LED
LED = machine.Pin(4, machine.Pin.OUT)
# Set up debounce delay
debounce_delay = 50
# Initialize previous button value
prev_button = 1
# Loop forever
while True:
# Read the current button value
curr_button = button.value()
# If the button is pressed, print a message
if curr_button == 0 and prev_button == 1:
print("Button pressed!")
# Wait for a short delay to debounce
time.sleep_ms(debounce_delay)
#toggle the LED
LED.value(not LED.value())
# Update the previous button value
prev_button = curr_button
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