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TESA Open Knowledge

Breadboarding

Objectives

Section titled “Objectives”

By the end of this lesson you will:

  1. Correctly identify which rows and power rails are connected on a breadboard
  2. Build from a schematic using conventional wire colours, and check it with a multimeter before applying power

Before you start

Section titled “Before you start”
  • You can already use a multimeter’s continuity mode and diode mode (lesson Measuring voltage and continuity)
  • For the lab: a breadboard, several coloured jumper wires (red, black, and at least two other colours), three red LEDs, four 1 kΩ resistors, one 10 kΩ resistor, one push button, and a TESAIoT Dev Kit flashed with the QWA309 Header I/O Test example
  • If using the Eva Kit, wire the same circuit to spare pins on the board, and write a short program yourself that blinks the LEDs and reads the button

See it work first

Section titled “See it work first”

Turn the breadboard over and look at the back. If you can peel off the adhesive backing without damaging it (or look at a manufacturer’s diagram), you will see metal strips arranged under the holes — many short strips in the middle, and a couple of long strips along the top and bottom edges.

Before reading on, guess which pairs of holes connect to each other, then prove it with your multimeter’s continuity mode (plug two short jumper wires into the holes you want to test, then touch the meter’s leads to the ends of those wires). If you guess a pair wrong, that is good news — it means you have just avoided that mistake before wiring a real circuit.

Concepts

Section titled “Concepts”

1. Inside a breadboard

Section titled “1. Inside a breadboard”
+ − a b c d e f g h i j centre channel 1 4 7 10 power rails (long) 5 holes in a column = one node
The faint thick lines are the metal strips under the holes: the five holes a through e in the same column connect to one point; f through j connect to another. The centre channel keeps the two sides apart. The power rails at the top connect lengthwise (some models break in the middle).
  • Groups of five holes. In the middle of the breadboard, five holes in the same column (a through e) connect to a single point (one node); f through j form another point. Different breadboard brands label these “rows” or “columns” differently — remember the rule “five holes in line, not crossing the centre channel,” rather than a name.
  • The centre channel keeps the two sides apart, sized to fit a dual in-line (DIP) chip, so each of its pins lands on a different point.
  • Power rails. The long strips along the edges, usually marked with a red (+) line and a blue (−) line, used to distribute power and ground. On some long breadboards, the power rails break in the middle — always check with continuity mode before using any board for the first time.
  • The hole spacing is 2.54 mm (0.1 inch), matching a typical header pin.

The classic mistake is plugging a resistor’s two leads into the same group of five holes — the resistor is shorted out, and the circuit behaves as if it were not there at all. An LED wired this way will not light either, because there is no voltage across it.

2. Wire colour and layout

Section titled “2. Wire colour and layout”

Wire colour has no electrical effect, but it matters a great deal for checking. The common convention:

Colour Used for
Red The positive supply rail (if there are several voltages, use a different colour for each, e.g. red = 5 V, orange = 3.3 V, and label them)
Black (or blue) Ground
Other colours Signals, colour-coded by function, e.g. yellow = a pin driving an LED, green = a pin reading a button

Layout habits that make checking easy:

  • Wire the schematic one net at a time. Once a net is wired, mark it off on your printed schematic.
  • Keep wires short and flat against the breadboard, never arching over components; trim component leads to a matching length.
  • Place components following the schematic’s orientation (power at the top, ground at the bottom, signal flowing left to right) — this lets whoever checks it compare quickly against the drawing.
  • If a chip is present, add a 100 nF capacitor across the rails right next to each chip’s power pin (the reason is in the lesson Basic components).

A breadboard’s limits. The metal strips running parallel to each other have a few pF of capacitance between them, and the contacts have their own resistance and inductance. The result is that a breadboard does not suit fast signals in the multi-MHz range, high-resistance points, or high current.

5 pF of stray capacitance with a 100 kΩ signal source
f_c = 1 / (2π × R × C) = 1 / (2π × 100 kΩ × 5 pF) ≈ 318 kHz

Signals faster than about this get filtered into rounded edges. At 1 MΩ, this frequency drops to about 32 kHz. Contacts that have seen a lot of use grow loose, a common cause of a circuit that “sometimes works, sometimes doesn’t,” which is hard to diagnose.

3. Check before applying power

Section titled “3. Check before applying power”

Check in this order every time, while the breadboard is still disconnected from the board or any supply.

  1. Check by eye. Go net by net against the schematic. LEDs and capacitors are polarised. No component’s two leads should accidentally sit in the same group.
  2. The power rails and ground must never connect. Continuity between the + rail and the − rail must not beep.
  3. Resistance between the rails must make sense. Calculate in advance what resistance the circuit should show between the rails, then measure and compare.
  4. Test each LED in diode mode. Touch the red lead to the anode and the black lead to the cathode — you should read roughly V_f, and some LEDs will glow faintly.
  5. Apply power in order: GND first, then the supply, then signal wires. If your supply can limit current, set the limit low first (e.g. 50 mA), so a mistake burns nothing.

Worked example

Section titled “Worked example”

Problem: wire three LEDs to pins P13.3, P13.4, P13.5, and an active-low button to pin P13.0, on a TESAIoT Dev Kit, then test with the header test program’s GPIO Out and GPIO In buttons.

Schematic (written as a net list)

Net Connects to
GND The header’s GND pin, the − rail, LED1 through LED3’s cathodes, one side of the button
3V3 The header’s 3V3 pin, the + rail, one end of R_pu 10 kΩ
LED1 P13.3 → 1 kΩ → LED1’s anode (likewise LED2 at P13.4, LED3 at P13.5)
BTN_N R_pu’s other end, the button’s other side, and 1 kΩ to P13.0

Wire list

From To Colour
The header’s GND The − rail Black
The header’s 3V3 The + rail Red
P13.3, P13.4, P13.5 Each LED’s 1 kΩ resistor Yellow
P13.0 The 1 kΩ resistor connected to BTN_N Green

Calculate before wiring

Each LED's current while the pin is 1 (V_f ≈ 1.8 to 2.0 V): (3.3 − 2.0) / 1 kΩ ≈ 1.3 mA to (3.3 − 1.8) / 1 kΩ = 1.5 mA
Resistance between the + rail and the − rail, disconnected from the board:
  Button released → no current path → reads OL (open circuit)
  Button pressed   → through R_pu to ground → reads 10 kΩ

Check: the + and − rails do not beep, read OL, and read 10 kΩ when the button is pressed. Every LED passes diode mode. Then connect to the board, in order: GND, 3V3, signal wires.

Test: press GPIO Out — the three LEDs should light in sequence, one pin at a time, about 0.7 s each. Press GPIO In, then press the button — bit 0 of the mask must change with the button. The 1 kΩ resistor between BTN_N and P13.0 protects the pin: while GPIO Out drives P13.0 as an output, if someone presses the button, the current will never exceed 3.3 mA.

Practice

Section titled “Practice”
  1. On the breadboard in the figure, are holes a12 and e12 connected? What about e12 and f12? What about a12 and a13?
  2. A resistor is plugged in with one lead at b15 and the other at d15. What happens?
  3. With 5 pF of stray capacitance and a 10 kΩ signal source, at what frequency does filtering start?
  4. A breadboard carries both 5 V and 3.3 V. How should you arrange wire colours and labels?
  5. Before applying power, you measure 0.4 Ω between the + rail and the − rail. What should you do next?
  6. In the worked example, if you forget to add R_pu 10 kΩ, what will the resistance between the rails read while the button is pressed, and will the button still work in GPIO In mode?

Solution

Section titled “Solution”
  1. a12 and e12 are connected (the same group of five holes). e12 and f12 are not connected (separated by the centre channel). a12 and a13 are not connected (different groups).
  2. Both leads land in the same group, so the resistor is shorted out — it has no effect on the circuit.
  3. f_c = 1 / (2π × 10 kΩ × 5 pF) ≈ 3.18 MHz.
  4. Use a different colour for each voltage, e.g. red = 5 V, orange = 3.3 V; keep them on separate rails, and label the rails too — never make someone else guess.
  5. Never apply power. A value close to 0 Ω is a short circuit. Find the wire or component lead connecting the + and − rails, removing components one at a time and measuring again.
  6. It reads OL both pressed and released, because there is no path from the + rail to ground. The button can still pull the pin down to 0 while pressed, but while released the pin floats (GPIO In sets it as no-pull), so the reading is unreliable.

Check your understanding

Section titled “Check your understanding”

Answer at least 4 of the 5 questions in quiz.yaml correctly.

Lab

Section titled “Lab”
  1. Survey your own breadboard. Use continuity mode to check whether the power rails run the full length or break in the middle, and spot-check a couple of groups of five holes. Record the results.
  2. Draw the schematic of the worked example on paper using proper symbols (see the symbols in the lesson Reading a schematic if you are not familiar yet). Print it or photograph it, and keep it beside you.
  3. Wire one net at a time, following the wire list. Mark off each net on the schematic as soon as it is wired.
  4. Check before applying power. Complete all five steps in Concepts section 3. Record the resistance between the rails, both released and pressed.
  5. Apply power. Connect GND, then 3V3, then the signal wires. Measure the + rail’s voltage against the − rail with a multimeter.
  6. Test its behaviour. Does GPIO Out light the LEDs in the right order? Does GPIO In’s bit 0 follow the button?
  7. Have a classmate check it. Hand them the breadboard and the schematic without explaining anything, and time how many minutes it takes them to confirm every net is wired correctly. This time is your work’s tidiness score.
Check Result
Does the power rail break in the middle?
+ rail vs. − rail (button released) should be OL
+ rail vs. − rail (button pressed) should be about 10 kΩ
Every LED passes diode mode
+ rail voltage after applying power
GPIO Out lights in the right order
GPIO In’s bit 0 follows the button
Time your classmate took to check it

Going further

Section titled “Going further”

A breadboard suits experimentation, but a circuit that must survive real use needs soldering. The next lesson, Soldering safely, practises soldering one row of a connector well enough to pass a visual check and a multimeter check.

Reflect

Section titled “Reflect”

The last time a circuit on your breadboard did not work, what was the cause? If you had used this lesson’s pre-power checklist, how much sooner would you have found it?

References

Section titled “References”

Review questions

Answer on your own first, then open the answer.

  1. On a standard breadboard, are holes a10 and e10 (same side of the channel, same strip) connected? (Objective 1)

    1. ต่อกัน เป็นกลุ่มห้ารูเดียวกัน
    2. ไม่ต่อกัน
    3. ต่อกันเฉพาะเบรดบอร์ดยาว
    4. ต่อกันผ่านรางไฟ
    Show answer

    Answer: A. ต่อกัน เป็นกลุ่มห้ารูเดียวกัน

    รู a ถึง e ในแนวเดียวกันอยู่บนแถบโลหะแถบเดียว จึงเป็นจุดเดียวกันทางไฟฟ้า

  2. Are holes e10 and f10 connected? (Objective 1)

    1. ต่อกัน เพราะอยู่แนวเดียวกัน
    2. ไม่ต่อกัน เพราะร่องกลางแยกสองฝั่งออกจากกัน
    3. ต่อกันเมื่อเสียบชิปคร่อมร่อง
    4. ขึ้นกับสีของเส้นบนรางไฟ
    Show answer

    Answer: B. ไม่ต่อกัน เพราะร่องกลางแยกสองฝั่งออกจากกัน

    ร่องกลางออกแบบให้ขาสองแถวของชิป DIP อยู่คนละจุดกัน f ถึง j จึงเป็นอีกกลุ่มหนึ่ง

  3. A resistor is inserted with one leg in b15 and the other in d15. What happens? (Objective 1)

    1. ทำงานปกติ
    2. ตัวต้านทานถูกลัดทิ้ง เพราะทั้งสองขาอยู่ในกลุ่มห้ารูเดียวกัน
    3. ตัวต้านทานไหม้ทันที
    4. ค่าความต้านทานเพิ่มเป็นสองเท่า
    Show answer

    Answer: B. ตัวต้านทานถูกลัดทิ้ง เพราะทั้งสองขาอยู่ในกลุ่มห้ารูเดียวกัน

    ขาทั้งสองอยู่บนแถบโลหะเดียวกัน แรงดันคร่อมเป็นศูนย์ ไม่มีกระแสผ่าน วงจรทำงานเหมือนไม่มีตัวต้านทานตัวนั้น

  4. Before powering, you check continuity between the + and − rails. What result should you get? (Objective 2)

    1. เครื่องส่งเสียงดัง แสดงว่าต่อครบ
    2. เครื่องไม่ส่งเสียง และความต้านทานใกล้เคียงค่าที่คำนวณจากวงจร
    3. อ่านได้ 0 Ω
    4. ไม่ต้องตรวจ ถ้าต่อตามแผนผังแล้ว
    Show answer

    Answer: B. เครื่องไม่ส่งเสียง และความต้านทานใกล้เคียงค่าที่คำนวณจากวงจร

    ถ้าดังแปลว่าไฟเลี้ยงลัดลงกราวด์ ห้ามจ่ายไฟ ค่าที่ควรได้คือความต้านทานรวมของวงจรที่คำนวณไว้ล่วงหน้า หรือ OL ถ้าวงจรไม่มีทางเดินกระแสระหว่างราง

  5. Put the steps from a finished build to power-on in order. (Objective 2)

    1. ต่อไฟเลี้ยงและสายสัญญาณ แล้ววัดแรงดันราง
    2. ตรวจด้วยตาทีละ net เทียบกับแผนผัง
    3. ต่อสาย GND ระหว่างบอร์ดกับเบรดบอร์ด
    4. วัดความต่อเนื่องและความต้านทานระหว่างราง + กับราง −
    Show answer

    Correct order: B. ตรวจด้วยตาทีละ net เทียบกับแผนผัง → D. วัดความต่อเนื่องและความต้านทานระหว่างราง + กับราง − → C. ต่อสาย GND ระหว่างบอร์ดกับเบรดบอร์ด → A. ต่อไฟเลี้ยงและสายสัญญาณ แล้ววัดแรงดันราง

    ตรวจทั้งหมดขณะยังไม่มีไฟ ด้วยตาก่อนแล้วด้วยมิเตอร์ แล้วจึงต่อกราวด์เป็นเส้นแรก ตามด้วยไฟเลี้ยงและสัญญาณ

Cite this lesson

If you teach from this lesson or reuse it in slides or documents, credit it with the text below. If you changed it, add (adapted) after the title.

"Breadboarding" from TESA Open Knowledge by the Thai Embedded Systems Association (TESA), https://github.com/tesaiot/tesa-qualification-program, licensed under CC BY-NC 4.0

Thai attribution: "ต่อวงจรบนเบรดบอร์ด" จาก TESA Open Knowledge โดยสมาคมสมองกลฝังตัวไทย (Thai Embedded Systems Association: TESA) https://github.com/tesaiot/tesa-qualification-program สัญญาอนุญาต CC BY-NC 4.0

Lesson link: https://tesaiot.github.io/tesa-qualification-program/en/courses/electronics-and-instruments/m06-build-and-read/l01-breadboarding/

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TESA Open Knowledge · © 2026 สมาคมสมองกลฝังตัวไทย (TESA) · CC BY-NC 4.0

Content is licensed CC BY-NC 4.0. Reuse it non-commercially and credit the Thai Embedded Systems Association (TESA) every time. · How to cite TESA