Building a Simple USB Flashlight (Complete Guide)

Overview

This tutorial walks you through building a simple USB-powered flashlight using tscircuit. You'll learn how to design a circuit that takes 5V from a USB-C connector, uses a push button for on/off control, drives an LED through a current-limiting resistor, and lays it out as a manufacturable PCB.

Components

Ref	Part	Description	Footprint
J1	USB-C Receptacle	USB Type-C connector for 5V power	`smd-usb-c`
SW1	Tactile Push Button	Momentary SPST switch for on/off	`pushbutton`
LED1	Red LED	0603 surface-mount indicator LED	`0603`
R1	150Ω Resistor	Current limiting resistor for LED	`0603`

Circuit Theory

The circuit is straightforward:

USB-C Power: The USB-C connector provides 5V on VBUS and a ground reference on GND
Push Button: Acts as a switch between VBUS and the LED circuit
Current Limiting: The 150Ω resistor limits LED current to approximately 20mA
LED Indicator: The red LED illuminates when the button is pressed

Current Calculation

Using Ohm's Law: I = (V_source - V_LED) / R

For a red LED with forward voltage ~2.0V: I = (5.0V - 2.0V) / 150Ω = 20mA

This is the typical operating current for a standard 0603 indicator LED.

Step 1: USB-C Connector

Start with the USB-C receptacle. We use the community-sourced @tsci/seveibar.smd-usb-c component:

import { SmdUsbC } from "@tsci/seveibar.smd-usb-c"

<SmdUsbC
  name="J1"
  connections={{
    GND1: "net.GND",
    GND2: "net.GND",
    VBUS1: "net.VBUS",
    VBUS2: "net.VBUS",
  }}
  pcbY={-10}
  schX={-4}
/>

Key points:

Both GND pins are tied to the ground net
Both VBUS pins are tied to the power net
pcbY={-10} places it at the board edge for connector access
schX={-4} positions it on the left side of the schematic

Step 2: Push Button Switch

The push button connects between VBUS and the rest of the circuit:

<pushbutton
  name="SW1"
  footprint="pushbutton"
  layer="top"
  connections={{
    pin1: "net.VBUS",
    pin2: ".R1 > .pos",
  }}
  pcbX={0}
  pcbY={-1}
/>

When pressed, pin1 connects to pin2, completing the circuit from VBUS through the LED.

Step 3: LED and Current-Limiting Resistor

<led name="LED1" color="red" footprint="0603" pcbY={12} />

<resistor
  name="R1"
  footprint="0603"
  resistance="150"
  pcbY={7}
  connections={{
    pos: ".SW1 > .pin2",
    neg: ".LED1 > .pos",
  }}
/>

The resistor is placed in series with the LED to limit current. Without it, the LED would draw excessive current and burn out.

Step 4: Ground Return Path

<trace from=".LED1 > .neg" to="net.GND" />

The LED's cathode connects to ground, completing the circuit.

Step 5: Complete Circuit

Here's the full circuit file:

import { SmdUsbC } from "@tsci/seveibar.smd-usb-c"

export default () => {
  return (
    <board width="12mm" height="30mm">
      <SmdUsbC
        name="J1"
        connections={{
          GND1: "net.GND",
          GND2: "net.GND",
          VBUS1: "net.VBUS",
          VBUS2: "net.VBUS",
        }}
        pcbY={-10}
        schX={-4}
      />
      <pushbutton
        name="SW1"
        footprint="pushbutton"
        layer="top"
        connections={{
          pin1: "net.VBUS",
          pin2: ".R1 > .pos",
        }}
        pcbX={0}
        pcbY={-1}
      />
      <resistor
        name="R1"
        footprint="0603"
        resistance="150"
        pcbY={7}
        connections={{
          pos: ".SW1 > .pin2",
          neg: ".LED1 > .pos",
        }}
      />
      <led
        name="LED1"
        color="red"
        footprint="0603"
        pcbY={12}
        connections={{
          neg: "net.GND",
        }}
      />
    </board>
  )
}

PCB Layout Considerations

Board Dimensions

Width: 12mm — narrow enough to fit in a pen-sized housing
Height: 30mm — provides enough space for all components with good spacing

Component Placement

USB-C at the bottom edge (-10mm) for external access
Push button in the middle for easy pressing
LED at the top (12mm) as the light source
Resistor between button and LED in the current path

Trace Routing

The tscircuit autorouter handles the connections, but you can also manually route traces:

<trace from=".R1 .neg" to=".LED1 .pos" width="0.3mm" />
<trace from=".LED1 .neg" to="net.GND" width="0.3mm" />
<trace from="J1 .VBUS1" to=".SW1 > .pin1" width="0.5mm" />

Use wider traces (0.5mm) for power connections and standard width (0.3mm) for signal lines.

Schematic View

The schematic shows the circuit topology clearly:

USB-C VBUS ──┬── SW1 ── R1 ── LED1 ── GND
             │
USB-C GND ───┴────────────────────────

Current flows from VBUS through the button when pressed
The resistor limits current to the LED
The return path goes through ground

Building and Testing

Local Development

# Create a new tscircuit project
mkdir usb-flashlight && cd usb-flashlight
tsci init

# Save the circuit file
# (copy the circuit code into index.circuit.tsx)

# Build the project
tsci build

# View in browser
tsci preview

Generate Manufacturing Files

# Generate Gerber files for PCB fabrication
tsci build --gerber

# Generate BOM (Bill of Materials)
tsci build --bom

# Generate pick-and-place file
tsci build --pick-and-place

Cost Estimate

Component	Unit Cost	Quantity	Total
USB-C Receptacle	$0.15	1	$0.15
Tactile Push Button	$0.05	1	$0.05
Red LED 0603	$0.02	1	$0.02
Resistor 150Ω 0603	$0.01	1	$0.01
PCB (2-layer)	$0.50	1	$0.50
Total			$0.73

At scale (1000+ units), the per-unit cost drops below $0.30.

Extensions

Once you have the basic flashlight working, try these modifications:

Multiple LEDs

<led name="LED1" color="red" footprint="0603" pcbY={10} pcbX={-3} />
<led name="LED2" color="red" footprint="0603" pcbY={10} pcbX={3} />
<resistor name="R1" resistance="300" footprint="0603" />
<resistor name="R2" resistance="300" footprint="0603" />

Different LED Colors

<led name="LED1" color="blue" footprint="0603" />
<led name="LED2" color="green" footprint="0603" />
<led name="LED3" color="white" footprint="0603" />

Add a Capacitor for Persistence

Add a small capacitor to keep the LED lit briefly after releasing the button:

<capacitor
  name="C1"
  footprint="0603"
  capacitance="100uF"
  pcbY={5}
  connections={{
    pos: "net.VBUS",
    neg: "net.GND",
  }}
/>

Summary

You've built a complete USB-powered flashlight circuit using tscircuit, covering:

Component selection and specification
Circuit theory and current calculations
Complete circuit implementation in TSX
PCB layout with proper component placement
Manufacturing file generation
Cost analysis
Extension ideas for more advanced versions

This project demonstrates tscircuit's ability to handle everything from simple LED circuits to complex multi-layer PCB designs.

Overview​

Components​

Circuit Theory​

Current Calculation​

Step 1: USB-C Connector​

Step 2: Push Button Switch​

Step 3: LED and Current-Limiting Resistor​

Step 4: Ground Return Path​

Step 5: Complete Circuit​

PCB Layout Considerations​

Board Dimensions​

Component Placement​

Trace Routing​

Schematic View​

Building and Testing​

Local Development​

Generate Manufacturing Files​

Cost Estimate​

Extensions​

Multiple LEDs​

Different LED Colors​

Add a Capacitor for Persistence​

Summary​