Disclosure: This note is published by the UnoProject brand account. UnoProject sells a starter kit for first breadboard circuits. The single link in this note goes to our own site. This is a bench procedure, not a shop listing.
A first circuit dies in a boring way. The board never shows a port, the LED never lights, or a jumper sits one row off and the pin is shorted to the rail beside it. This note is the check we want finished before any sketch is uploaded. It is written for someone building a first circuit on a solderless breadboard with a UNO-style board. It is not a catalogue, and it does not ask you to buy anything in the middle of the steps.
Who this is for
You have a computer, the official Arduino IDE, a USB cable, a UNO-style board, a breadboard, a few jumper wires, one small indicator LED, and one resistor to put in series with that LED. You have not yet proved that the board enumerates, and you have not yet proved that the breadboard wiring is safe to power. If you already have a working Blink and you are moving on to a display or a motor, this note is behind you. Stay with it if the board is still a new object on the desk.
UnoProject is the brand account behind these notes. The account shares practical bench notes for people building their first circuits. The person reading this is the builder. We are not writing as a named engineer with a job history, and we are not filling in a biography. The only commercial relationship to disclose is the one in the first paragraph.
What this check is trying to catch
Three failures look the same from the chair. The LED is dark. You do not know which one you have.
The first failure is the computer. The USB cable is charge-only, the board uses a USB chip the computer has never seen, or the IDE is pointed at the wrong board name. No port appears, so no sketch can leave the laptop.
The second failure is the breadboard. A jumper that was meant for a signal pin lands in the power rail. Two bare legs touch. The board is then asked to power a short. That is the failure this note refuses to "fix" by uploading again.
The third failure is the load itself. An LED with no series resistor, or a resistor in the wrong place, or the LED turned around so the flat side is on the wrong leg. The board may be fine. The load is not.
The order below separates those three. Do not start at the upload button.
Put only the first circuit on the bench
Clear the modules you are not using yet. A display, a servo, a motor driver, and a sensor can all wait. They are useful later. On the first power-up they hide the short. Leave them in the box.
Keep the board, the USB cable, the breadboard, jumpers, one LED, and one resistor. The official getting-started sequence for this kind of kit is short: install the Arduino IDE, connect the board with the USB cable, put parts into the breadboard with jumpers, choose Arduino UNO, then upload. This note inserts an inspection between "parts are in the breadboard" and "upload".
Work on a clear desk. A loose jumper under the board is enough to confuse the next ten minutes.
Install the IDE and name the board before you wire the LED
Download the Arduino IDE from the Arduino project and install it on the computer you will actually use. Windows, Mac, and Linux are all fine. Open it once so you know it starts. Do not install a random "driver pack" from a search ad. If the board needs a USB driver, you want the driver for the chip on that board, not a bundle.
The UNO-style board these notes assume is a UNO R3 with a CH340 USB chip. In the Arduino IDE the board menu entry you select is Arduino UNO. The name on the chip and the name in the menu are not the same string. Selecting a different board, because the chip name looked more specific, is a common way to get a port that never accepts an upload.
You do not need a soldered shield for this check. The first circuit stays on the breadboard. Push parts in. Do not start this note by building a motor circuit "to see if the board works". A motor tells you almost nothing when the LED test is still dark, and a stalled motor is a worse short than a dark LED.
Connect USB, then stop
Use the USB cable that came with the board. A cable that only charges a phone will power a light on some boards and still carry no data. If the computer never sees a port, swap to a cable you have already used for a data device before you reinstall the IDE.
Plug the board in. Watch the computer, not the breadboard. In the IDE, open the board list and select Arduino UNO. Then open the port list. You want a new port that appears when the board is plugged in and disappears when it is unplugged. That is the whole USB test. Unplug once and plug once so you have seen both states.
If a port appears and vanishes with the cable, the computer can see the board. Leave the cable plugged in for the rest of the note. Do not upload yet. The breadboard is still empty on purpose.
If no port appears, stay in this section. Do not paper over it with wiring. Try the cable, try another USB socket, and confirm you are not looking at a stale port that belonged to a phone. A CH340 board on a machine that has never seen that chip will need the matching USB driver before a port exists. Install that driver from a source you can name, then repeat the unplug test. Still no port means you stop. A sketch cannot prove a board the computer cannot see.
Read the breadboard before you trust a rail
An 830-point breadboard is two halves, with power rails along the sides. The holes in a numbered row are tied together across a short strip. The power rail is a long strip. Those two facts cause the usual short: a leg that you meant to seat in a signal row is actually in the rail, or a jumper leaves a row and lands one column further into the rail.
Look at the red and blue lines. Confirm which rail you will call 5 V and which you will call ground. On many breadboards the rail is broken in the middle, so the top half and the bottom half are not connected until you bridge them. If you assume they are one strip, the LED will be dark and you will blame the sketch.
Do not connect the board's 5 V and GND pins to those rails until you have looked at every other wire. The rails are the last connection, not the first.
One LED, one series resistor
The load for this check is one small indicator LED and one resistor in series with it. The resistor is what limits current. An LED across a supply with no resistor is not a "brighter test". It is a way to pull a pin or a rail harder than the LED can survive.
A resistor in the few-hundred-ohm range is the usual starting point for a small indicator LED on a 5 V rail. That is general practice for this kind of first circuit, not a claim about a particular part number in a box. If the LED in your hand has its own note for current, follow that note. If you do not know, use a series resistor and do not parallel the LED across the rails to "see it once".
Direction matters. The flat side of a typical LED marks the cathode, the side that goes toward ground. If you reverse it, the LED stays dark and the board is not at fault. Seat the LED in a free row, not in the power rail. Seat the resistor so it continues the series path. One end of the series chain will go to a digital pin. The other end will go to ground.
Use two jumpers you can see from above. One from the board pin you intend to drive, commonly the pin next to the on-board LED on a UNO-style board, to the resistor or the LED. One from the other end of the series chain to ground. Do not also tie that same row to 5 V. A pin and a rail fighting each other is the short this note is about.
Leave 5 V unconnected until the two signal jumpers are in the holes you can point at. Then connect 5 V only if this circuit actually needs the rail. A single LED on a pin and ground does not need the 5 V rail at all. Skipping the rail removes a whole class of mistakes. Prefer that.
The look you do with the cable unplugged
Unplug USB before the visual check. You are about to put your eyes close to the legs.
Trace the series path with a finger above the board, not on the legs. Pin, jumper, resistor, LED, jumper, ground. Every leg should sit in the row you think it sits in. No leg should lean into the next row. No spare jumper should still be attached from an earlier experiment.
Look down the power rails. They should be empty for this first test. If a stray jumper is parked in the red rail, pull it out now, while the board is unplugged.
Then plug USB back in. Do not upload for another moment. Look and smell. Nothing should get hot in the first few seconds of a single LED test. If a part heats at once, unplug. Do not upload a "fix". Find the wire that joins a pin to a rail or joins the two rails.
A sketch that only blinks one pin
When the visual check is clean and a port is present, the first sketch should do one thing. Drive one pin high, wait, drive it low, wait. The official IDE can create a new sketch. Replace the body with a program you can read out loud:
The pin number is a constant. setup sets that pin as an output. loop writes it high, waits half a second, writes it low, and waits half a second. There is no sensor read, no library, and no motor pulse.
Here is the whole program:
const int ledPin = 13;
void setup() {
pinMode(ledPin, OUTPUT);
}
void loop() {
digitalWrite(ledPin, HIGH);
delay(500);
digitalWrite(ledPin, LOW);
delay(500);
}
Pin 13 is the usual first pin on a UNO-style board because the board already has a small LED on that pin. If your series LED is wired to a different pin, change the constant and only the constant. Do not add a second blink "for luck".
Select Arduino UNO again. Select the port you proved with the unplug test. Then upload once. Wait until the IDE reports that the upload finished. Uploading twice because you were impatient does not create a port that was never there.
Read the result as one of three outcomes
Outcome one: the on-board LED blinks, and the breadboard LED blinks with it. The computer, the board, the pin, the resistor, and the LED path are all doing the same thing. Stop here for today. Add the next module in a later session, one module at a time, with the same visual check before you power it.
Outcome two: the on-board LED blinks and the breadboard LED stays dark. The board and the sketch are fine. The fault is in the series path. Reverse the LED. Confirm the resistor is actually in series and not sitting in a row by itself. Confirm the ground jumper goes to a ground pin, not to the pin next to it. Change one thing, then look again. Do not rewrite the sketch.
Outcome three: nothing blinks, and the IDE did not finish the upload. Go back to the port test. A failed upload with a missing port is still a USB problem. A failed upload with a present port and an angry red message is a board-menu problem or a cable problem. It is not a reason to add a motor so the project "does something".
If the port never returns
Unplug every other board. Close any serial monitor that is holding the port. Repeat the unplug test. If the port is gone only after you connect the breadboard, the breadboard is loading the board hard enough to drop it off USB. Unplug, remove every jumper, and repeat the port test with an empty breadboard. When the port returns, the wiring you just removed is where you look. Add the LED path back one wire at a time.
Do not keep a hot part connected while you search menus.
What to write down
Write four lines before you put the parts away. Which port name appeared. Which board name you selected. Which pin the LED path used. Whether the breadboard LED blinked, only the on-board LED blinked, or nothing blinked. The next session starts from those four lines. It does not start from a guess.
The next note can be a display or a sensor. It should still begin with the port test and a look at the rails. A new module does not retire this check.
Further getting-started notes for this account live on the UnoProject site at https://unoproject.co.uk/.
This account will keep posting bench notes of this kind: one check, one circuit, no product sheet in the middle of the steps.
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