Building a Simple USB Flashlight

Overview

This tutorial walks you through building a compact USB-powered flashlight using tscircuit. The circuit takes 5 V from a USB-C connector, passes it through a push button and a current-limiting resistor, and lights a red LED.

Objectives

• Understand how to bring 5 V USB power onto a PCB with a USB-C connector
• Wire a pushbutton as a momentary switch in series with the load
• Calculate and place a current-limiting resistor for an LED
• Place and connect all components inside a small 12 × 30 mm board

Requirements

• The board must draw power from a USB-C connector (VBUS = 5 V, GND)
• A momentary pushbutton must interrupt the circuit so the LED is off when released
• A 1 kΩ resistor must limit the LED current to a safe level (~4 mA at 5 V)
• All components must fit on a 12 × 30 mm two-layer PCB

Components

Reference	Component	Footprint	Notes
J1	SMD USB-C connector	@tsci/seveibar.smd-usb-c	VBUS (5 V) + GND
SW1	Pushbutton	pushbutton	Momentary normally-open
R1	Resistor 1 kΩ	0603	Current limiter for LED
LED	Red LED	0603	Forward voltage ~2 V

Resistor calculation

With VBUS = 5 V and a red LED forward voltage V_f ≈ 2 V:

I = (V_supply - V_f) / R = (5 - 2) / 1000 = 3 mA

3 mA is well within the safe operating range for a standard 0603 LED (typically 20 mA max).

Step-by-step build

Step 1 — USB-C connector

Start with the USB-C connector. It exposes VBUS1, VBUS2 (both 5 V) and GND1, GND2. Tie both VBUS pins to net.VBUS and both GND pins to net.GND.

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}
    />
  </board>
)
}

Step 2 — Push button

Add a momentary push button (SW1). When pressed, pin2 (connected to net.VBUS) passes current through to pin1. pin1 connects forward to the positive terminal of the resistor .R1 > .pos — tscircuit resolves this reference once R1 is declared in the next step.

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: ".R1 > .pos", pin2: "net.VBUS" }}
      pcbX={0}
      pcbY={-1}
    />
  </board>
)
}

Step 3 — Current-limiting resistor and LED

Add resistor R1 (1 kΩ) and the red LED. Connect them in series:

• R1.neg → LED.pos (resistor output to LED anode)
• LED.neg → net.GND (LED cathode to ground)

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: ".R1 > .pos", pin2: "net.VBUS" }}
      pcbX={0}
      pcbY={-1}
    />
    <led name="LED" color="red" footprint="0603" pcbY={12} />
    <resistor name="R1" footprint="0603" resistance="1k" pcbY={7} />
    <trace from=".R1 .neg" to=".LED .pos" />
    <trace from=".LED .neg" to="net.GND" />
  </board>
)
}

Final circuit

The completed circuit on the PCB. All four components fit within the 12 × 30 mm board outline. The USB-C connector sits at the bottom edge, the push button in the middle, and the resistor and LED stack toward the top.