Building a Simple USB Flashlight

In this tutorial we will design a USB-powered LED flashlight as a printed circuit board (PCB). By the end you will have a complete, working schematic and PCB layout that you can send straight to a board house.

This is a great first project because it uses only three components and introduces the core tscircuit elements you will use in almost every design: a connector, a resistor, and an LED.

What You Will Build

A tiny PCB that plugs into any USB-A port. The 5 V supply from the USB bus powers a white LED through a current-limiting resistor. No firmware, no microcontroller — just light.

Components

Part	Value / Part	tscircuit element
USB-A connector (male)	USB-A through-hole	`<connector />`
Current-limiting resistor	68 Ω, 0402	`<resistor />`
White LED	Generic 0402 white	`<led />`

How the Circuit Works

USB supplies 5 V on pin 1 (VBUS) and ground on pin 4 (GND).

A white LED typically has a forward voltage (V_f) of about 3.0 V–3.4 V and wants roughly 20 mA of current. We choose R so that:

R = (V_supply − V_f) / I_led
R = (5 V − 3.2 V) / 0.020 A
R ≈ 90 Ω  →  use standard value 68 Ω (gives ~26 mA, fine for a bright flash)

The circuit is simply: VBUS → R1 → LED anode → LED cathode → GND.

Step 1 — Create a New Project

If you haven't installed tscircuit yet, follow the Quickstart CLI guide or use the online editor to follow along in your browser.

tsci init usb-flashlight
cd usb-flashlight
tsci dev

Open lib/MyCircuit.tsx in your editor. You will see a blank board template.

Step 2 — Add the USB Connector

A USB-A male connector exposes four pins. We only need pin 1 (VBUS, +5 V) and pin 4 (GND). In tscircuit we declare it with <connector /> and assign net labels to the pins we care about:

import { connector, resistor, led, board, trace } from "@tscircuit/core"
 
export default () => (
  <board width="20mm" height="15mm">
    <connector
      name="J1"
      footprint="usb_a_male_th"
      pinLabels={{
        pin1: "VBUS",
        pin4: "GND",
      }}
      pcbX={-7}
      pcbY={0}
    />
  </board>
)

Tip: footprint="usb_a_male_th" selects a through-hole USB-A male footprint from the built-in footprint library. You can browse available footprints at tscircuit.com/footprints.

After saving, you should see the connector appear on the PCB preview in your browser.

Step 3 — Add the Current-Limiting Resistor

Place a 68 Ω 0402 resistor to the right of the connector. Its left pin (pin1) will connect to VBUS, and its right pin (pin2) will go to the LED:

    <resistor
      name="R1"
      resistance="68"
      footprint="0402"
      pcbX={0}
      pcbY={0}
    />

Step 4 — Add the LED

Place a 0402 white LED to the right of the resistor. The anode (pin1) connects to R1, and the cathode (pin2) connects to GND:

    <led
      name="LED1"
      color="white"
      footprint="0402"
      pcbX={7}
      pcbY={0}
    />

Step 5 — Connect the Components with Traces

Now wire everything together. tscircuit traces are declared by listing the net path using dot notation ComponentName.pinLabel:

    {/* VBUS from USB connector pin 1 to resistor pin 1 */}
    <trace from="J1.VBUS" to="R1.pin1" />
 
    {/* R1 pin 2 to LED anode */}
    <trace from="R1.pin2" to="LED1.pin1" />
 
    {/* LED cathode back to GND on USB connector pin 4 */}
    <trace from="LED1.pin2" to="J1.GND" />

Full Circuit Code

Putting it all together:

import { connector, resistor, led, board, trace } from "@tscircuit/core"
 
export default () => (
  <board width="20mm" height="15mm">
    {/* USB-A Male Connector */}
    <connector
      name="J1"
      footprint="usb_a_male_th"
      pinLabels={{
        pin1: "VBUS",
        pin4: "GND",
      }}
      pcbX={-7}
      pcbY={0}
    />
 
    {/* 68 Ω current-limiting resistor */}
    <resistor
      name="R1"
      resistance="68"
      footprint="0402"
      pcbX={0}
      pcbY={0}
    />
 
    {/* White LED */}
    <led
      name="LED1"
      color="white"
      footprint="0402"
      pcbX={7}
      pcbY={0}
    />
 
    {/* Traces */}
    <trace from="J1.VBUS" to="R1.pin1" />
    <trace from="R1.pin2" to="LED1.pin1" />
    <trace from="LED1.pin2" to="J1.GND" />
  </board>
)

Step 6 — Preview and Verify

The tsci dev server shows three tabs: Schematic, PCB, and 3D.

Check the following:

Schematic: The net from J1 pin 1 flows through R1 and then through LED1 to GND. No unconnected pins ("ratsnest" lines) should remain.
PCB: All three components fit within the 20 × 15 mm board outline. All traces are routed (no airwires).
3D: The USB connector overhangs the board edge slightly — this is normal for a plug-style connector. If you see any ratsnest (unrouted) lines, double-check the from / to pin names in your <trace /> elements.

Step 7 — Export and Order

When you are happy with the design, export Gerber files for fabrication:

tsci export --format gerber

The files land in ./output/gerbers/. Zip the folder and upload it to your preferred PCB manufacturer (JLCPCB, PCBWay, OSH Park, etc.). A standard 5-board run of this simple design typically costs under $5 including shipping.

What's Next?

Add a push-button switch between VBUS and R1 to turn the light on and off (<pushbutton /> element).
Swap the single LED for three LEDs in parallel (each with its own 100 Ω resistor) for a brighter beam.
Try the Building a 3×5 LED Matrix tutorial to scale up to a full dot-matrix display.

What You Will Build​

How the Circuit Works​

Step 1 — Create a New Project​

Step 2 — Add the USB Connector​

Step 3 — Add the Current-Limiting Resistor​

Step 4 — Add the LED​

Step 5 — Connect the Components with Traces​

Full Circuit Code​

Step 6 — Preview and Verify​

Step 7 — Export and Order​

What's Next?​