2 layers92.6 × 46.8 mm Open555, the printed circuit board in 3D

Open555

An 555 circuit entirely made out of THT transistors

Size: 92.6 × 46.8 mm
Copper layers: 2
Thickness: 1.6 mm
Parts: 84
Nets: 31
Pads: 120
Tracks, vias: 235, 7
Pours: 1
Routed: Yes
KiCad: KiCad 9.0 (file 20241229)
Created: 20 Mar 2025
Updated: 22 Jan 2026

Overview

Open555 is an open-source printed circuit board by cheyao, from the cheyao/Open555 repository on GitHub, published under the Zlib licence. It is a 2-layer board of 92.6 × 46.8 mm with 84 parts on 31 nets, routed with 235 tracks and 7 vias.

Its parts include 22 transistors, 15 resistors, 1 capacitor, 1 diode and 1 connector.

README

README.md

Open555

Ever wondered how a 555 timer IC worked? Here you have it! A 555 IC, made entirely with THT transistors.

Schematic

PCB

Features

Low power design! 3V operating voltage
On board square wave generator
Selectable features through solder bridges
A Schematic on the back side!
Super cute cats on the front side - Kudos to @acornitum

How to build

Just order the PCB & components, open up the KiCAD file and build it accordingly.

BOM

1 Battery holder
1 10uF Capacitor
11 PNP Transistor
11 NPN Transistor
1 100k Resistor
1 10k Resistor
10 4.7k Resistor
3 220 Resistor
2 Potentiometer
1 Push Button

Made by @Cyao on slack :D

Made as a part of http://solder.hackclub.com/!

Parts

Qty	Value	Footprint	References
39	LOGO	LOGO	G*, G, G, G, G, G, G, G, G, G, G, G, G, G, G, G* +23
11	NPN	Package_TO_SOT_THT:TO-92L_HandSolder	Q8, Q9, Q10, Q11, Q12, Q15, Q16, Q19, Q20, Q21, Q22
11	PNP	Package_TO_SOT_THT:TO-92L_HandSolder	Q1, Q2, Q3, Q4, Q5, Q6, Q7, Q13, Q14, Q17, Q18
10	4.7k	Resistor_THT:R_Axial_DIN0207_L6.3mm_D2.5mm_P7.62mm_Horizontal	R2, R4, R5, R6, R10, R11, R12, R14, R17, R18
3	100	Resistor_THT:R_Axial_DIN0207_L6.3mm_D2.5mm_P7.62mm_Horizontal	R3, R7, R8
2	R_Potentiometer	Potentiometer_THT:Potentiometer_Runtron_RM-065_Vertical	RV1, RV2
1	100k	Resistor_THT:R_Axial_DIN0207_L6.3mm_D2.5mm_P7.62mm_Horizontal	R16
1	10k	Resistor_THT:R_Axial_DIN0207_L6.3mm_D2.5mm_P7.62mm_Horizontal	R13
1	10uF	Capacitor_THT:CP_Radial_D8.0mm_P5.00mm	C3
1	Battery_Cell	Battery:BatteryHolder_Multicomp_BC-2001_1x2032	BT1
1	Conn_01x05_Pin	Connector_PinHeader_2.54mm:PinHeader_1x05_P2.54mm_Vertical	J1
1	LED	LED_THT:LED_D5.0mm	D1
1	SW_Push	Button_Switch_THT:SW_PUSH_6mm	SW1
1	SolderJumper_2_Bridged	Jumper:SolderJumper-2_P1.3mm_Bridged2Bar_RoundedPad1.0x1.5mm	JP1

Questions

How big is the Open555 PCB?

It measures 92.6 × 46.8 mm and has 2 copper layers, 1.6 mm thick.

What parts does the Open555 use?

84 parts. The full list of its parts is on this page, with links to each part's symbol and footprint where PCBKit's library has them.

Where can I download the Open555 KiCad files?

From the cheyao/Open555 repository on GitHub, at the commit this page was made from: the board is src/Open555.kicad_pcb and its schematic src/Open555.kicad_sch. PCBKit opens the board in the browser, with nothing to install.

Can I use the Open555 design in my own project?

Its repository publishes it under the Zlib licence: you may reuse it on that licence's terms (keep the author's notice, and for a copyleft licence share your changes alike).

Topics

555 kicad pcb timer

Project files

Show this board on your page

A live frame, for any web page

<iframe src="https://pcbkit.io/embed/boards/cheyao-open555" title="Open555 in PCBKit" width="100%" height="480" style="border:0;border-radius:12px" allow="fullscreen" loading="lazy"></iframe>

A picture

<img src="https://pcbkit.io/embed/boards/cheyao-open555.jpg" alt="Open555" width="1200" height="900">

A picture that opens the board, for a README

[![Open555](https://pcbkit.io/embed/boards/cheyao-open555.jpg?size=s)](https://pcbkit.io/boards/cheyao-open555)

Source

Repository: cheyao/Open555
Board file: src/Open555.kicad_pcb
Commit: 61364e8
Homepage: solder.hackclub.com
Licence: Zlib

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