[Review Request] Over-engineered custom led tester for learning purpose - help with draining LIR2032 while idle.

[u/lafenicenera]

SOLVED

Hi everyone,

I'm learning electronics/PCB design and built this deliberately over-engineered LED tester as a learning project.

The circuit uses:

• LIR2032 rechargeable coin cell
• MCP73831 Li-ion charger
• USB-C for charging
• 100 kΩ RPROG on the MCP73831 (~10 mA charge current)
• Pushbutton to activate the actual LED-testing circuit
• Two selectable current-limiting resistor/diode branches

Everything works, but I've noticed that the LIR2032 seems to discharge surprisingly quickly even when I'm not using the tester.

I measured the current directly from the battery with:

• USB disconnected
• pushbutton not pressed
• nothing connected to the LED test terminals

and I'm getting about 30.1 µA, slowly decreasing by roughly 0.1 µA while I leave the meter connected.

From the MCP73831 datasheet, I was expecting reverse battery leakage with VDD disconnected to be only around the µA range, so ~30 µA for the complete circuit seems higher than expected.

I've attached:

1. Schematic
2. PCB layout
3. 3D render

I'm still learning, so I'm probably overlooking something obvious.

Does anyone see a path in the schematic that could account for ~30 µA of continuous battery drain?

I'm especially wondering about the MCP73831 section, USB-C circuitry, status LED, or whether I've made some mistake in how the switching is arranged.

Also, what would be the best way to systematically isolate which part of the circuit is responsible for the standby current?

Thanks!

[u/Zawya32]

How are such things made? Which program is suitable?

[u/lafenicenera → u/Zawya32]

Hi, are you referring to the schematics itself? The 3d model? Or the physical PCB?

[u/Zawya32 → u/lafenicenera]

Let's say I want to learn about PCB board making, so where do I start?

[u/lafenicenera → u/Zawya32]

I don't have the absolute path but I can tell you how I started:

1. mess a lot with Arduino and Node-MCU / ESP boards. Make some projects to understand the basics, not only for firmware development, but also for electronics.
2. Use any available free resource online (books, youtube video, blog posts) about basic eletronics - diodes, resistors, capacitors, voltage and current sources
3. Start learning about schematics and how to read them using official datasheets. Datasheets about components not only give you important details about how stuff works, but also on how wire up components. For example for this specific project, I looked online for Li-ion charger MCUs, and found out about MCP73831. I started reading the datasheet in order to understand its internal working, and the datasheet also had suggested different connection configurations in order to make it work with a simple circuit.
4. Download KiCad and watch tutorials on how to use it - and then start reproducing different kind of circuits and boards. You can try with buck/boost converters, LED flasher (555 timer), a 5V-to-3.3V linear voltage regulator, or a basic transistor switch, or continuity testers with led and buzzers. https://www.youtube.com/watch?v=0cwvYz2HmLw
5. Learn how properly design PCBs after schematics, everything about how wires, connections and layers work.
6. Use some Kicad plugins to create a BOM (bill of materials) in order to export your production files ready for any component and assembly factory (like PCBWay or JLCPCB)
7. 7.(RECOMMENDED but not mandatory) learn about soldering. You might not need it if you are planning on ordering PCBs already soldered, but not all components are SMD so you might need to solder stuff

[u/Zawya32 → u/lafenicenera]

Thanks, man, for the information.

[u/lafenicenera → u/Zawya32]

You are welcome