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Tutorials

Building a Simple USB Flashlight

Overview​

This tutorial walks you through building a USB-powered flashlight using tscircuit. You'll connect a USB-C connector, a push button switch, a current-limiting resistor, and an LED on a small board. When the push button is pressed, the LED lights up — powered entirely over USB-C.

What You'll Learn​

  • How to import and use the USB-C connector component
  • How to wire a push button as a power switch
  • How to select and place a current-limiting resistor
  • How to connect an LED and understand polarity
  • How to route traces between components

Circuit Requirements​

The flashlight circuit must:

  • Be powered entirely from a USB-C port (5V)
  • Use a push button to turn the LED on and off
  • Include a current-limiting resistor to protect the LED
  • Fit on a small 12mm x 30mm board
  • Be manufacturable as a PCB

Understanding the Components​

USB-C Connector (SmdUsbC)​

The USB-C connector provides 5V power from a USB port. The SmdUsbC component has two VBUS pins (power, 5V) and two GND pins (ground). We connect each pair together to handle the current draw of the LED.

Push Button Switch​

A momentary push button acts as the power switch. When pressed, it connects VBUS to the rest of the circuit. The pushbutton component in tscircuit uses a standard pushbutton footprint suitable for PCB assembly.

Current-Limiting Resistor (1kΩ)​

An LED needs a resistor in series to limit current. Without it, the LED would draw too much current and burn out. At 5V (USB voltage), a 1kΩ resistor limits the current to roughly 3–5mA, which is safe for a standard indicator LED. The 0603 footprint is a common surface-mount size.

Red LED​

The LED (Light Emitting Diode) is the light source. LEDs are polarized — the positive side (anode, .pos) must connect toward the power source, and the negative side (cathode, .neg) must connect to ground. We use a red LED in a 0603 surface-mount package.

Building the Circuit Step by Step​

Step 1: Set up the Board and USB-C Connector​

Start by creating a board and placing the USB-C connector. The SmdUsbC component is imported from a published tscircuit package.

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

export default () => (
  <board width="12mm" height="30mm">
    <SmdUsbC name="J1" pcbY={-10} schX={-4} />
  </board>
)
Schematic Circuit Preview

The name prop gives the connector a reference designator (J1). The pcbY moves it toward the bottom of the board — this matches the physical layout where the USB connector is at the edge of the PCB.

Step 2: Add the Push Button​

Next, place the push button switch above the USB connector on the board.

Schematic Circuit Preview

The pushbutton is centered on the board (pcbX={0}) and sits just above the USB connector (pcbY={-1}). The layer="top" prop places it on the top copper layer.

Step 3: Add the Current-Limiting Resistor​

Add the 1kΩ resistor that will protect the LED from excessive current.

Schematic Circuit Preview

The resistor sits near the middle-top of the board at pcbY={7}. The 0603 footprint matches standard surface-mount resistor dimensions.

Step 4: Add the LED​

Place the LED at the top of the board, above the resistor.

Schematic Circuit Preview

The LED is positioned at pcbY={12} near the top edge of the board. The color prop sets the LED color for the schematic and 3D preview.

Step 5: Wire Everything Together​

Now connect all the components with traces and assign power nets.

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

export default () => (
<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}
  />
  <resistor name="R1" footprint="0603" resistance="1k" pcbY={7} />
  <led name="LED" color="red" footprint="0603" pcbY={12} />
  <trace from=".R1 .neg" to=".LED .pos" />
  <trace from=".LED .neg" to="net.GND" />
</board>
)
Schematic Circuit Preview

Here's how the circuit flows:

  1. USB-C connector (J1) — assigns VBUS pins to net.VBUS and GND pins to net.GND
  2. Push button (SW1) — one pin connects to net.VBUS, the other connects to the resistor's positive pad (.R1 > .pos). When pressed, power flows from VBUS through the switch to the resistor
  3. Resistor (R1) — limits current from the switch to the LED
  4. Resistor-to-LED trace — carries current from the resistor's negative pad to the LED's positive pad
  5. LED-to-GND trace — completes the circuit from the LED's negative pad back to ground

PCB Layout​

The component placement on the PCB follows a logical top-to-bottom flow:

  • USB-C connector at the bottom edge for easy cable access
  • Push button in the center for convenient pressing
  • Resistor above the switch, close to the LED
  • LED at the top edge as the light source
import { SmdUsbC } from "@tsci/seveibar.smd-usb-c"

export default () => (
<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}
  />
  <resistor name="R1" footprint="0603" resistance="1k" pcbY={7} />
  <led name="LED" color="red" footprint="0603" pcbY={12} />
  <trace from=".R1 .neg" to=".LED .pos" />
  <trace from=".LED .neg" to="net.GND" />
</board>
)
PCB Circuit Preview

You can adjust pcbX and pcbY values to fine-tune component placement for your specific enclosure or design preferences.

Ordering the PCB​

Once you're happy with the design, you can order PCBs from a manufacturer:

  1. Export the PCB fabrication files using the tscircuit CLI: 
    tsci export --format gerber my-flashlight.circuit.tsx
  2. Upload the generated Gerber files to a PCB manufacturer such as JLCPCB or PCBWay
  3. Select your board specifications (thickness, copper weight, solder mask color)
  4. Order the stencil if you plan to hand-assemble components

See Ordering Prototypes for a detailed walkthrough.

Next Steps​

  • Add a second LED with its own resistor for more brightness
  • Replace the push button with a slide switch for latching on/off
  • Add a capacitor across VBUS and GND to smooth out power
  • Try building the Simple Buzzer HAT to learn about Raspberry Pi add-on boards