Your first circuit: blink an LED
Welcome to ExoSynk. This is the classic "hello world" of electronics — and it's three components.
What you need
- 9V battery — the source
- 330Ω resistor — the current limiter
- LED — the output
That's it. The companion lab is @exosynk/blink.
Why the resistor?
An LED is not a regular bulb. It has a forward voltage (usually around 2V for red LEDs) — below that voltage it's off, above it the current rises fast, and above its max current (~20 mA for standard through-hole LEDs) it burns out.
Connecting a 9V battery straight to an LED would push something like 1 amp through it. It would glow for about 0.2 seconds, then go dark forever.
The resistor "eats" the extra voltage. Ohm's law:
I = (V_battery − V_led) / R
I = (9V − 2V) / 330Ω
I = 21 mA
Right in the happy range. LED glows brightly, nothing burns.
Try it
- Open @exosynk/blink
- Click Fork in the top-right — now it's your lab
- Change the battery to 3V. Does the LED still light? (It might not — 3V − 2V = 1V across a 330Ω resistor is only 3 mA, which is barely visible.)
- Change the resistor to 100Ω with the 9V battery. Watch the LED go
orange, then 💥
BURNT— we've exceeded max current.
What you learned
- LEDs need current-limiting resistors.
- Ohm's law picks the resistor value.
- In ExoSynk the simulation is honest — burn-outs are real.
Next up: voltage dividers.