Wiring guide for fanless 1S LiPo + USB power sink with automatic 3.3V cutoff, for capacity testing.

Components:
Variable Voltage USB Power Source (3.3V to 5.1V).
Stable 5V USB Power Source.
Six 220Ohm Resistors.
One S8050 NPN Transistor.
One LM393 Comparator IC.
One LD1117V33 Voltage Regulator.
Ceramic Capacitors: 0.1uF (100nF).
Base Resistor for S8050: Approximately 2.7kOhm.
Pull-Up Resistor for LM393: Between 4.7kOhm and 10kOhm.
Breadboard and Connecting Wires.

Wiring Guide:

Step 1: Setup Voltage Regulator for Reference Voltage
LD1117V33:
Input: Connect to the stable 5V USB power source.
Output: Provides a stable 3.3V reference.
Ground: Connect to the common ground.

Step 2: Setup the LM393 Comparator
Powering LM393:
VCC: Connect to the stable 5V USB power source.
GND: Connect to the common ground.
Comparator Inputs:
Non-Inverting Input (+): Connect to the 3.3V output of the LD1117V33.
Inverting Input (-): Connect to the positive terminal of the variable voltage USB power source.
Comparator Output:
Connect to the base of the S8050 through a 2.7kOhm base resistor.
Optionally, add a pull-up resistor (4.7kOhm to 10kOhm) between this output and the 5V supply if needed.

Step 3: Setup the S8050 Transistor
Collector: Connect to one end of the resistor network (six 220Ohm resistors in parallel).
Emitter: Connect to the common ground.
Base: Connect to the output of the LM393 through the 2.7kOhm base resistor.

Step 4: Resistor Network
Resistors in Parallel:
Connect one end of all six 220Ohm resistors together and to the collector of the S8050.
Connect the other end of all resistors together and to the positive terminal of the variable voltage USB power source.

Step 5: Decoupling Capacitors
Ceramic Capacitors:
Place a 0.1uF (100nF) capacitor near the power supply pins of both the LM393 and LD1117V33, between VCC and ground.

Step 6: Final Connections and Safety Checks
Common Ground:
Ensure all ground connections are common: the ground of the 5V source, the ground of the variable voltage source, and the grounds of the LM393, LD1117V33, and S8050.
Check Connections:
Double-check all connections against component datasheets. Ensure there are no shorts or incorrect connections.

Step 7: Testing
Initial Testing:
Before applying power, use a multimeter to check for shorts.
Verify the 3.3V reference voltage is correct.
Functional Testing:
Connect the variable voltage USB source.
Observe the circuit behavior as the voltage varies, ensuring the resistors heat when above 3.3V and turn off below this threshold.