Legacy Circuit Mockups

GitHubOfficialFirst committed by jhaugaDistributed by GitHub

Skill
Content generator
Design and creative
MIT
No issues found

From the author

Generate breadboard circuit mockups and visual diagrams using HTML5 Canvas drawing techniques. Use when asked to create circuit layouts, visualize electronic component placements, draw breadboard diagrams, mockup 6502 builds, generate retro computer schematics, or design vintage electronics projects. Supports 555 timers, W65C02S microprocessors, 28C256 EEPROMs, W65C22 VIA chips, 7400-series logic gates, LEDs, resistors, capacitors, switches, buttons, crystals, and wires.

— the description by jhauga

AutoGineer summary

Written by AutoGineer from the skill’s own files, not by the author

Legacy Circuit Mockups is a specialized tool for creating visual representations of electronic circuits. It uses HTML5 Canvas to render breadboard layouts, making it ideal for documenting retro computing builds like 6502 systems, 555 timer circuits, and various logic gate configurations. The skill provides a structured approach to component placement, wiring, and labeling, ensuring that complex electronics projects can be visualized clearly for educational or documentation purposes.

What it does

Generates breadboard circuit mockups using HTML5 Canvas.
Supports a wide range of vintage components including 6502 microprocessors, 555 timers, and 7400-series logic.
Provides a grid-based system for precise component placement.
Allows for the visualization of wire connections with color-coded conventions.
Includes reference data for component pinouts and electrical formulas.
Facilitates the creation of educational visuals for electronics and retro computing.

When to use it

When you need to create a visual breadboard layout for a circuit design.
When documenting 6502 microprocessor or retro computer builds.
When you need to visualize component placement and wiring for educational purposes.
When designing or troubleshooting 555 timer or logic gate circuits.
When you require a clear diagram to explain electronic connections.

Advantages

Standardizes circuit visualization using a consistent grid system.
Simplifies the documentation of complex retro computing hardware.
Provides built-in support for common vintage ICs and passive components.
Enables clear communication of wiring and pinout configurations.
Reduces ambiguity in circuit assembly through visual guides.

Usage examples

“Create a breadboard mockup for a 555 timer astable blinker circuit.”: The agent generates a visual diagram showing the 555 timer IC, resistors, capacitor, and LED correctly wired on a breadboard grid.
“Show me how to wire a W65C02S microprocessor on a breadboard.”: The agent produces a layout diagram illustrating the placement of the CPU, power connections, and essential address/data bus wiring.

Install

Download the skill as a ZIP:
https://autogineer.com/agent-skills/github/legacy-circuit-mockups/download

Unzip it into the cross-client skills folder of your project:

mkdir -p .agents/skills && unzip legacy-circuit-mockups.zip -d .agents/skills

Documentation by jhauga

Legacy Circuit Mockups

A skill for creating breadboard circuit mockups and visual diagrams for retro computing and electronics projects. This skill leverages HTML5 Canvas drawing mechanisms to render interactive circuit layouts featuring vintage components like the 6502 microprocessor, 555 timer ICs, EEPROMs, and 7400-series logic gates.

When to Use This Skill

User asks to "create a breadboard layout" or "mockup a circuit"
User wants to visualize component placement on a breadboard
User needs a visual reference for building a 6502 computer
User asks to "draw a circuit" or "diagram electronics"
User wants to create educational electronics visuals
User mentions Ben Eater tutorials or retro computing projects
User asks to mockup 555 timer circuits or LED projects
User needs to visualize wire connections between components

Prerequisites

Understanding of component pinouts from bundled reference files
Knowledge of breadboard layout conventions (rows, columns, power rails)

Supported Components

Microprocessors & Memory

Component	Pins	Description
W65C02S	40-pin DIP	8-bit microprocessor with 16-bit address bus
28C256	28-pin DIP	32KB parallel EEPROM
W65C22	40-pin DIP	Versatile Interface Adapter (VIA)
62256	28-pin DIP	32KB static RAM

Logic & Timer ICs

Component	Pins	Description
NE555	8-pin DIP	Timer IC for timing and oscillation
7400	14-pin DIP	Quad 2-input NAND gate
7402	14-pin DIP	Quad 2-input NOR gate
7404	14-pin DIP	Hex inverter (NOT gate)
7408	14-pin DIP	Quad 2-input AND gate
7432	14-pin DIP	Quad 2-input OR gate

Passive & Active Components

Component	Description
LED	Light emitting diode (various colors)
Resistor	Current limiting (configurable values)
Capacitor	Filtering and timing (ceramic/electrolytic)
Crystal	Clock oscillator
Switch	Toggle switch (latching)
Button	Momentary push button
Potentiometer	Variable resistor
Photoresistor	Light-dependent resistor

Grid System

// Standard breadboard grid: 20px spacing
const gridSize = 20;
const cellX = Math.floor(x / gridSize) * gridSize;
const cellY = Math.floor(y / gridSize) * gridSize;

Component Rendering Pattern

// All components follow this structure:
{
  type: 'component-type',
  x: gridX,
  y: gridY,
  width: componentWidth,
  height: componentHeight,
  rotation: 0,  // 0, 90, 180, 270
  properties: { /* component-specific data */ }
}

Wire Connections

// Wire connection format:
{
  start: { x: startX, y: startY },
  end: { x: endX, y: endY },
  color: '#ff0000'  // Wire color coding
}

Step-by-Step Workflows

Creating a Basic LED Circuit Mockup

Define breadboard dimensions and grid
Place power rail connections (+5V and GND)
Add LED component with anode/cathode orientation
Place current-limiting resistor
Draw wire connections between components
Add labels and annotations

Creating a 555 Timer Circuit

Place NE555 IC on breadboard (pins 1-4 left, 5-8 right)
Connect pin 1 (GND) to ground rail
Connect pin 8 (Vcc) to power rail
Add timing resistors and capacitors
Wire trigger and threshold connections
Connect output to LED or other load

Creating a 6502 Microprocessor Layout

Place W65C02S centered on breadboard
Add 28C256 EEPROM for program storage
Place W65C22 VIA for I/O
Add 7400-series logic for address decoding
Wire address bus (A0-A15)
Wire data bus (D0-D7)
Connect control signals (R/W, PHI2, RESB)
Add reset button and clock crystal

Component Pinout Quick Reference

555 Timer (8-pin DIP)

Pin	Name	Function
1	GND	Ground (0V)
2	TRIG	Trigger (< 1/3 Vcc starts timing)
3	OUT	Output (source/sink 200mA)
4	RESET	Active-low reset
5	CTRL	Control voltage (bypass with 10nF)
6	THR	Threshold (> 2/3 Vcc resets)
7	DIS	Discharge (open collector)
8	Vcc	Supply (+4.5V to +16V)

W65C02S (40-pin DIP) - Key Pins

Pin	Name	Function
8	VDD	Power supply
21	VSS	Ground
37	PHI2	System clock input
40	RESB	Active-low reset
34	RWB	Read/Write signal
9-25	A0-A15	Address bus
26-33	D0-D7	Data bus

28C256 EEPROM (28-pin DIP) - Key Pins

Pin	Name	Function
14	GND	Ground
28	VCC	Power supply
20	CE	Chip enable (active-low)
22	OE	Output enable (active-low)
27	WE	Write enable (active-low)
1-10, 21-26	A0-A14	Address inputs
11-19	I/O0-I/O7	Data bus

Formulas Reference

Resistor Calculations

Ohm's Law: V = I × R
LED Current: R = (Vcc - Vled) / Iled
Power: P = V × I = I² × R

555 Timer Formulas

Astable Mode:

Frequency: f = 1.44 / ((R1 + 2×R2) × C)
High time: t₁ = 0.693 × (R1 + R2) × C
Low time: t₂ = 0.693 × R2 × C
Duty cycle: D = (R1 + R2) / (R1 + 2×R2) × 100%

Monostable Mode:

Pulse width: T = 1.1 × R × C

Capacitor Calculations

Capacitive reactance: Xc = 1 / (2πfC)
Energy stored: E = ½ × C × V²

Color Coding Conventions

Wire Colors

Color	Purpose
Red	+5V / Power
Black	Ground
Yellow	Clock / Timing
Blue	Address bus
Green	Data bus
Orange	Control signals
White	General purpose

LED Colors

Color	Forward Voltage
Red	1.8V - 2.2V
Green	2.0V - 2.2V
Yellow	2.0V - 2.2V
Blue	3.0V - 3.5V
White	3.0V - 3.5V

Build Examples

Build 1 — Single LED

Components: Red LED, 220Ω resistor, jumper wires, power source

Steps:

Insert black jumper wire from power GND to row A5
Insert red jumper wire from power +5V to row J5
Place LED with cathode (short leg) in row aligned with GND
Place 220Ω resistor between power and LED anode

Build 2 — 555 Astable Blinker

Components: NE555, LED, resistors (10kΩ, 100kΩ), capacitor (10µF)

Steps:

Place 555 IC straddling center channel
Connect pin 1 to GND, pin 8 to +5V
Connect pin 4 to pin 8 (disable reset)
Wire 10kΩ between pin 7 and +5V
Wire 100kΩ between pins 6 and 7
Wire 10µF between pin 6 and GND
Connect pin 3 (output) to LED circuit

Troubleshooting

Issue	Solution
LED doesn't light	Check polarity (anode to +, cathode to -)
Circuit doesn't power	Verify power rail connections
IC not working	Check VCC and GND pin connections
555 not oscillating	Verify threshold/trigger capacitor wiring
Microprocessor stuck	Check RESB is HIGH after reset pulse

References

Detailed component specifications are available in the bundled reference files:

555.md - Complete 555 timer IC specification
6502.md - MOS 6502 microprocessor details
6522.md - W65C22 VIA interface adapter
28256-eeprom.md - AT28C256 EEPROM specification
6C62256.md - 62256 SRAM details
7400-series.md - TTL logic gate pinouts
assembly-compiler.md - Assembly compiler specification
assembly-language.md - Assembly language specification
basic-electronic-components.md - Resistors, capacitors, switches
breadboard.md - Breadboard specifications
common-breadboard-components.md - Comprehensive component reference
connecting-electronic-components.md - Step-by-step build guides
emulator-28256-eeprom.md - Emulating 28256-eeprom specification
emulator-6502.md - Emulating 6502 specification
emulator-6522.md - Emulating 6522 specification
emulator-6C62256.md - Emulating 6C62256 specification
emulator-lcd.md - Emulating a LCD specification
lcd.md - LCD display interfacing
minipro.md - EEPROM programmer usage
t48eeprom-programmer.md - T48 programmer reference

Files

ATTRIBUTION.mdAdded by AutoGineer873 B
LICENSELicence file added by AutoGineer1.0 KiB
SKILL.md9.0 KiB
references/28256-eeprom.md4.6 KiB
references/555.md32.3 KiB
references/6502.md5.7 KiB
references/6522.md5.7 KiB
references/6C62256.md4.1 KiB
references/7400-series.md4.6 KiB
references/assembly-compiler.md4.7 KiB
references/assembly-language.md5.2 KiB
references/basic-electronic-components.md2.7 KiB
references/breadboard.md4.9 KiB
references/common-breadboard-components.md6.4 KiB
references/connecting-electronic-components.md14.9 KiB
references/emulator-28256-eeprom.md5.1 KiB
references/emulator-6502.md5.7 KiB
references/emulator-6522.md6.5 KiB
references/emulator-6C62256.md4.8 KiB
references/emulator-lcd.md5.0 KiB
references/lcd.md5.2 KiB
references/minipro.md4.0 KiB
references/t48eeprom-programmer.md4.3 KiB

references/555.md

555

www.fairchildsemi.com

The LM555/NE555/SA555 is a highly stable controller capable of producing accurate timing pulses. With a monostable operation, the time delay is controlled by one external resistor and one capacitor. With an astable operation, the frequency and duty cycle are accurately controlled by two external resistors and one capacitor.

Features

High Current Drive Capability (200mA)
Adjustable Duty Cycle
Temperature Stability of 0.005%/°C
Timing From μSec to Hours
Turn off Time Less Than 2μSec

Applications

Precision Timing
Pulse Generation
Time Delay Generation
Sequential Timing

Internal Block Diagram

flowchart TB
    subgraph IC["555 Timer IC"]
        direction TB
        
        subgraph DIVIDER["Voltage Divider"]
            R1["R (5kΩ)"]
            R2["R (5kΩ)"]
            R3["R (5kΩ)"]
            R1 --- R2 --- R3
        end
        
        COMP1["Comparator 1<br/>(Threshold)"]
        COMP2["Comparator 2<br/>(Trigger)"]
        FF["Flip-Flop<br/>S-R"]
        OUT_STAGE["Output<br/>Stage"]
        DISCH_TR["Discharge<br/>Transistor"]
        VREF["Vref"]
    end
    
    PIN8["Pin 8<br/>Vcc"] --> R1
    R3 --> PIN1["Pin 1<br/>GND"]
    
    R1 -.->|"2/3 Vcc"| COMP1
    R2 -.->|"1/3 Vcc"| COMP2
    
    PIN6["Pin 6<br/>Threshold"] --> COMP1
    PIN2["Pin 2<br/>Trigger"] --> COMP2
    
    COMP1 -->|R| FF
    COMP2 -->|S| FF
    
    FF --> OUT_STAGE
    FF --> DISCH_TR
    
    OUT_STAGE --> PIN3["Pin 3<br/>Output"]
    DISCH_TR --> PIN7["Pin 7<br/>Discharge"]
    
    PIN4["Pin 4<br/>Reset"] --> FF
    PIN5["Pin 5<br/>Control Voltage"] -.-> R2
    
    style PIN1 fill:#000,color:#fff
    style PIN2 fill:#f96,color:#000
    style PIN3 fill:#6f6,color:#000
    style PIN4 fill:#f66,color:#000
    style PIN5 fill:#ff6,color:#000
    style PIN6 fill:#6ff,color:#000
    style PIN7 fill:#f6f,color:#000
    style PIN8 fill:#f00,color:#fff

Pin Configuration:

Pin	Name	Function
1	GND	Ground reference
2	TRIG	Trigger input (< 1/3 Vcc starts timing)
3	OUT	Output (high or low)
4	RESET	Active low reset
5	CONT	Control voltage (2/3 Vcc reference)
6	THRES	Threshold input (> 2/3 Vcc ends timing)
7	DISCH	Discharge (open collector)
8	Vcc	Supply voltage (+4.5V to +16V)

Absolute Maximum Ratings (Ta = 25°C)

Parameter	Symbol	Value	Unit
Supply Voltage	Vcc	16	V
Lead temperature (soldering 10 sec)	Tled	300	°C
Power Dissipation	PD	600	mW
Operating Temperature Range<br>LM555/NE555<br>SA555	Topr	- 65 ~ + 150	°C

Electrical Characteristics

(TA = 250C, vcc = 5 15V, unless otherwise specified)

Parameter	Symbol	Conditions	Min.	Typ.	Max.	Unit
Supply Voltage	vcc	-	4.5	-	16	V
Supply Current (Low Stable) (Note 1)	Icc	Vcc = 5V, Rl = ∞<hr>Vcc = 15V, Rl = ∞	-<hr>-	3<hr>7.5	6<hr>15	mA<hr>mA
Timing Error (Monostable)<br>Initial Accuracy (Note2)<br>Drift with Temperature (Note4)<br>Drift with Supply Voltage (Note4)<br>	ACCUR<br>Δt/ΔT<br>Δt/ΔVcc	Ra = 1kΩ to100kΩ<br>C = 0.1μF	-	1.0<br>50<br>0.1	3.0<br><br>0.5	%<br>ppm/°C<br>%/V
Timing Error (Astable)<br>Initial Accuracy (Note2)<br>Drift with Temperature (Note4)<br>Drift with Supply Voltage (Note4)	ACCUR<br>Δt/ΔT<br>Δt/ΔVcc	Ra = 1kΩ to 100kΩ<br> C = 0.1μF	-	2.25<br>150<br>0.3	-	%<br>ppm/°C<br>%/V
Control Voltage	Vc	Vcc = 15V<hr> Vcc = 5V	9.0<hr>2.6	10.0<hr>3.33	11.0<hr>4.0	V<hr>V
Threshold Voltage	VTH	VCC = 15V<hr>VCC = 5V	-<hr>-	10.0<hr>3.33	-<hr>-	V<hr>V
Threshold Current (Note3)	Ith	-	-	0.1	0.25	μA
Trigger Voltage	VTR	VCC = 5V<hr>VCC = 15V	1.1<hr>4.5	1.67<hr>5	2.2<hr>5.6	V<hr>V
Trigger Current	ITR	VTR = 0V	0.01	2.0	μA
Reset Voltage	VRST	-	0.4	0.7	1.0	V
Reset Current	IRST	-	0.1	0.4	mA
Low Output Voltage	VOL	VCC = 15V<br>ISINK = 10mA<br>ISINK = 50mA<hr>VCC = 5V<br>ISINK = 5mA	-<hr>-	0.06<br>0.3<hr>0.05	0.25<br>0.75<hr>0.35	V<br>V<hr>V
High Output Voltage	VOH	VCC = 15V<br>ISOURCE = 200mA<br>ISOURCE = 100mA<hr>VCC = 5V<br>ISOURCE = 100mA	12.75<hr>2.75	12.5<br>13.3<hr>3.3	-<hr>-	V<br>V<hr>V
Rise Time of Output (Note4)	tR	-	-	100	-	ns
Fall Time of Output (Note4)	tF	-	-	100	-	ns
Discharge Leakage Current	ILKG	-	-	20	100	nA

Notes:

When the output is high. the supply current is typically 1mA less than at VCC = 5V.
Tested at VCC = 5.0V and VCC = 15V.
This will determine the maximum value of RA + RB for 15V operation, the max- total R = 20MQ. and for 5V operation, the max/
- total R 8.7MΩ
These parameters, although guaranteed. are not 100% tested in production.

Application Information

Table 1 below is the basic operating table of 555 timer:

Threshold Voltage<br>(Vth)(PIN 6)	Trigger Voltage<br>(Vtr)(PIN 2)	Reset(PIN 4)	Output(PIN 3)	Discharging Tr.<br>(PIN 7)
Don't care	Don't care	Low	Low	ON
Vth > 2Vcc / 3	Vth > 2Vcc / 3	High	Low	ON
Vcc / 3 < Vth < 2 Vcc / 3	Vcc / 3 < Vth < 2 Vcc / 3	High	-	-
Vth < Vcc / 3	Vth < Vcc / 3	High	High	OFF

When the low signal input is applied to the reset terminal, the timer output remains low regardless of the threshold voltage or the trigger voltage. Only when the high signal is applied to the reset terminal, the timer's output changes according to threshold voltage and trigger voltage. When the threshold voltage exceeds 2/3 of the supply voltage while the timer output is high, the timer's internal discharge Tr. turns on, lowering the threshold voltage to below 1/3 of the supply voltage. During this time, the timer output is maintained low. Later, if a low signal is applied to the trigger voltage so that it becomes 1/3 of the supply voltage, the timer's internal discharge Tr. turns off, increasing the threshold voltage and driving the timer output again at high.

1. Monostable Operation

Figure 1. Monostable Circuit

flowchart LR
    subgraph CIRCUIT["Monostable Configuration"]
        VCC["+Vcc"]
        
        subgraph TIMER["555 Timer"]
            P4["4<br/>RESET"]
            P8["8<br/>Vcc"]
            P7["7<br/>DISCH"]
            P2["2<br/>TRIG"]
            P6["6<br/>THRES"]
            P3["3<br/>OUT"]
            P5["5<br/>CONT"]
            P1["1<br/>GND"]
        end
        
        RA["RA"]
        C1["C1"]
        C2["C2<br/>0.01μF"]
        RL["RL"]
        GND["GND"]
    end
    
    VCC --> P4
    VCC --> P8
    VCC --> RA
    RA --> P7
    P7 --> P6
    P6 --> C1
    C1 --> GND
    
    TRIG_IN["Trigger<br/>Input"] --> P2
    
    P3 --> RL
    RL --> OUTPUT["Output"]
    
    P5 --> C2
    C2 --> GND
    P1 --> GND
    
    style VCC fill:#f00,color:#fff
    style GND fill:#000,color:#fff
    style TRIG_IN fill:#f96
    style OUTPUT fill:#6f6

Component Values:

RA: Timing resistor (1kΩ to 10MΩ typical)
C1: Timing capacitor
C2: Bypass capacitor (0.01μF recommended)
RL: Load resistor

Time Delay Formula: $$t_d = 1.1 \times R_A \times C_1$$

Figure 2. Resistance and Capacitance vs. Time Delay (td)

%%{init: {'theme': 'base', 'themeVariables': { 'primaryColor': '#fff', 'lineColor': '#333'}}}%%
xychart-beta
    title "Time Delay vs Capacitance (Log Scale)"
    x-axis "Time Delay (seconds)" [0.00001, 0.0001, 0.001, 0.01, 0.1, 1, 10, 100]
    y-axis "Capacitance (μF)" 0.001 --> 1000
    line "R=1kΩ" [0.001, 0.01, 0.1, 1, 10, 100, 1000, 10000]
    line "R=10kΩ" [0.0001, 0.001, 0.01, 0.1, 1, 10, 100, 1000]
    line "R=100kΩ" [0.00001, 0.0001, 0.001, 0.01, 0.1, 1, 10, 100]
    line "R=1MΩ" [0.000001, 0.00001, 0.0001, 0.001, 0.01, 0.1, 1, 10]

RA	C1	Time Delay (td)
1 kΩ	0.1 μF	110 μs
10 kΩ	0.1 μF	1.1 ms
100 kΩ	0.1 μF	11 ms
1 MΩ	1 μF	1.1 s
10 MΩ	10 μF	110 s

Figure 3. Waveforms of Monostable Operation

%%{init: {'theme': 'base'}}%%
gantt
    title Monostable Waveforms (Normal Operation)
    dateFormat X
    axisFormat %s
    
    section Trigger
    High (Vcc)    :a1, 0, 2
    Low (<Vcc/3)  :crit, a2, 2, 3
    High (Vcc)    :a3, 3, 10
    
    section Output
    Low (0V)      :b1, 0, 2
    High (Vcc)    :active, b2, 2, 8
    Low (0V)      :b3, 8, 10
    
    section Threshold (Vc1)
    Charging      :c1, 2, 8

    Trigger ─────┐     ┌─────────────────────
    (Pin 2)      └─────┘  
                    ↓ Trigger pulse
                    
    Output  ─────────┐          ┌───────────
    (Pin 3)         └──────────┘
                    |←── td ───→|
                    
    Threshold        /‾‾‾‾‾‾‾‾\
    (Pin 6)    ─────/          \────────────
               0V  ↗            ↘  
                  Vcc/3      2Vcc/3
                  
    td = 1.1 × RA × C1

Figure 1 illustrates a monostable circuit. In this mode, the timer generates a fixed pulse whenever the trigger voltage falls below Vcc/3. When the trigger pulse voltage applied to the #2 pin falls below Vcc/3 while the timer output is low, the timer's internal flip-flop turns the discharging Tr. off and causes the timer output to become high by charging the external capacitor C1 and setting the flip-flop output at the same time. The voltage across the external capacitor C1, VC1 increases exponentially with the time constant t=RAC and reaches 2Vcc/3 at td=1.1RAC. Hence, capacitor C1 is charged through resistor RA. The greater the time constant RAC, the longer it takes for the VC1 to reach 2Vcc/3. In other words, the time constant RAC controls the output pulse width. When the applied voltage to the capacitor C1 reaches 2Vcc/3, the comparator on the trigger terminal resets the flip-flop, turning the discharging Tr. on. At this time, C1 begins to discharge and the timer output converts to low. In this way, the timer operating in the monostable repeats the above process. Figure 2 shows the time constant relationship based on RA and C. Figure 3 shows the general waveforms during the monostable operation. It must be noted that, for a normal operation, the trigger pulse voltage needs to maintain a minimum of Vcc/3 before the timer output turns low. That is, although the output remains unaffected even if a different trigger pulse is applied while the output is high, it may be affected and the waveform does not operate properly if the trigger pulse voltage at the end of the output pulse remains at below Vcc/3. Figure 4 shows such a timer output abnormality.

Figure 4. Waveforms of Monostable Operation (abnormal)

    Trigger ─────┐  ┌──┐  ┌─────────────────
    (Pin 2)      └──┘  └──┘  
                 ↓     ↓ Retriggering during output high
                    
    Output  ─────────┐                ┌─────
    (Pin 3)         └────────────────┘
                    |←── extended td ──→|
                    
    Threshold        /‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾\
    (Pin 6)    ─────/                  \────
               0V  ↗                    ↘  
                  Vcc/3              2Vcc/3

    ⚠️ ABNORMAL: Trigger held low extends output pulse!
    Trigger must return high before output goes low.

Note: For normal operation, the trigger pulse voltage must return above Vcc/3 before the timer output goes low. If the trigger remains below Vcc/3, the output pulse will be extended abnormally.

2. Astable Operation

Figure 5. Astable Circuit

flowchart LR
    subgraph CIRCUIT["Astable Configuration"]
        VCC["+Vcc"]
        
        subgraph TIMER["555 Timer"]
            P4["4<br/>RESET"]
            P8["8<br/>Vcc"]
            P7["7<br/>DISCH"]
            P2["2<br/>TRIG"]
            P6["6<br/>THRES"]
            P3["3<br/>OUT"]
            P5["5<br/>CONT"]
            P1["1<br/>GND"]
        end
        
        RA["RA"]
        RB["RB"]
        C1["C1"]
        C2["C2<br/>0.01μF"]
        GND["GND"]
    end
    
    VCC --> P4
    VCC --> P8
    VCC --> RA
    RA --> P7
    P7 --> RB
    RB --> P6
    RB --> P2
    P6 --> C1
    C1 --> GND
    
    P3 --> OUTPUT["Output"]
    
    P5 --> C2
    C2 --> GND
    P1 --> GND
    
    MOD["Modulation<br/>(optional)"] -.-> P5
    
    style VCC fill:#f00,color:#fff
    style GND fill:#000,color:#fff
    style OUTPUT fill:#6f6
    style MOD fill:#ff6

Component Values:

RA: Charge resistor (controls HIGH time)
RB: Charge/discharge resistor (affects both HIGH and LOW times)
C1: Timing capacitor
C2: Bypass capacitor (0.01μF recommended)

Timing Formulas:

High time: $t_H = 0.693 \times (R_A + R_B) \times C_1$
Low time: $t_L = 0.693 \times R_B \times C_1$
Period: $T = t_H + t_L = 0.693 \times (R_A + 2R_B) \times C_1$
Frequency: $f = \frac{1.44}{(R_A + 2R_B) \times C_1}$
Duty Cycle: $D = \frac{R_A + R_B}{R_A + 2R_B}$

Figure 6. Capacitance and Resistance vs. Frequency

%%{init: {'theme': 'base'}}%%
xychart-beta
    title "Free Running Frequency vs Capacitance"
    x-axis "Frequency (Hz)" [0.1, 1, 10, 100, 1000, 10000, 100000]
    y-axis "Capacitance (μF)" 0.001 --> 100

(RA + 2RB)	C1	Frequency
1.44 kΩ	1 μF	1 kHz
14.4 kΩ	1 μF	100 Hz
144 kΩ	1 μF	10 Hz
14.4 kΩ	0.1 μF	1 kHz
14.4 kΩ	0.01 μF	10 kHz

Figure 7. Waveforms of Astable Operation

    Output  ────┐     ┌─────┐     ┌─────┐     ┌────
    (Pin 3)    └─────┘     └─────┘     └─────┘
               |←tL→|←─tH─→|←tL→|←─tH─→|
               
    Threshold       /\        /\        /\
    (Pin 6)   ─────/  \──────/  \──────/  \──────
              Vcc/3    2Vcc/3
              
              ├────── T ──────┤
              T = tH + tL = 0.693(RA + 2RB)C1
              
    Charging:   C1 charges through RA + RB
    Discharging: C1 discharges through RB only

Typical Values: RA = 1kΩ, RB = 1kΩ, C1 = 1μF, Vcc = 5V

An astable timer operation is achieved by adding resistor RB to Figure 1 and configuring as shown on Figure 5. In the astable operation, the trigger terminal and the threshold terminal are connected so that a self-trigger is formed, operating as a multi vibrator. When the timer output is high, its internal discharging Tr. turns off and the VC1 increases by exponential function with the time constant (RA+RB)*C. When the VC1, or the threshold voltage, reaches 2Vcc/3, the comparator output on the trigger terminal becomes high, resetting the F/F and causing the timer output to become low. This in turn turns on the discharging Tr. and the C1 discharges through the discharging channel formed by RB and the discharging Tr. When the VC1 falls below Vcc/3, the comparator output on the trigger terminal becomes high and the timer output becomes high again. The discharging Tr. turns off and the VC1 rises again. In the above process, the section where the timer output is high is the time it takes for the VC1 to rise from Vcc/3 to 2Vcc/3, and the section where the timer output is low is the time it takes for the VC1 to drop from 2Vcc/3 to Vcc/3. When timer output is high, the equivalent circuit for charging capacitor C1 is as follows:

Equation 1: Charging Circuit Equivalent

flowchart LR
    VCC["Vcc"] --> RA_RB["RA + RB"]
    RA_RB --> C1["C1<br/>Vc1(0-)=Vcc/3"]
    C1 --> GND["GND"]

Charging Equation: $$C_1 \frac{dV_{C1}}{dt} = \frac{V_{CC} - V_{(0-)}}{R_A + R_B} \quad (1)$$

$$V_{C1}(0^+) = \frac{V_{CC}}{3} \quad (2)$$

$$V_{C1}(t) = V_{CC} \left[ 1 - \frac{2}{3} e^{-\frac{t}{(R_A + R_B)C_1}} \right] \quad (3)$$

Since the duration of the timer output high state (tH) is the amount of time it takes for the VC1(t) to reach 2Vcc/3,

Equation 2: High Time Calculation

$$\frac{2}{3}V_{CC} = V_{CC} \left[ 1 - \frac{2}{3} e^{-\frac{t_H}{(R_A + R_B)C_1}} \right] \quad (4)$$

$$t_H = C_1(R_A + R_B) \ln 2 = 0.693(R_A + R_B)C_1 \quad (5)$$

The equivalent circuit for discharging capacitor C1, when timer output is low is, as follows:

Equation 3: Discharging Circuit Equivalent

flowchart LR
    C1["C1<br/>Vc1(0-)=2Vcc/3"] --> RB["RB"]
    RB --> RD["RD<br/>(discharge Tr.)"]
    RD --> GND["GND"]

Discharging Equation: $$C_1 \frac{dV_{C1}}{dt} + \frac{1}{R_A + R_B} V_{C1} = 0 \quad (6)$$

$$V_{C1}(t) = \frac{2}{3} V_{CC} e^{-\frac{t}{(R_A + R_B)C_1}} \quad (7)$$

Since the duration of the timer output low state (tL) is the amount of time it takes for the VC1(t) to reach Vcc/3,

Equation 4: Low Time Calculation

$$\frac{1}{3}V_{CC} = \frac{2}{3}V_{CC} e^{-\frac{t_L}{(R_B + R_D)C_1}} \quad (8)$$

$$t_L = C_1(R_B + R_D) \ln 2 = 0.693(R_A + R_B)C_1 \quad (9)$$

Since RD is normally RB>>RD although related to the size of discharging Tr., tL=0.693RBC1 (10) Consequently, if the timer operates in astable, the period is the same with 'T=tH+tL=0.693(RA+RB)C1+0.693RBC1=0.693(RA+2RB)C1' because the period is the sum of the charge time and discharge time. And since frequency is the reciprocal of the period, the following applies.

Equation 5: Frequency Formula

$$f = \frac{1}{T} = \frac{1.44}{(R_A + 2R_B)C_1} \quad (11)$$

3. Frequency divider

By adjusting the length of the timing cycle, the basic circuit of Figure 1 can be made to operate as a frequency divider. Figure 8. illustrates a divide-by-three circuit that makes use of the fact that retriggering cannot occur during the timing cycle.

Figure 8. Waveforms of Frequency Divider Operation

    Trigger ─┐ ┌─┐ ┌─┐ ┌─┐ ┌─┐ ┌─┐ ┌─┐ ┌─┐ ┌─┐ ┌─┐ ┌─
    (Input)  └─┘ └─┘ └─┘ └─┘ └─┘ └─┘ └─┘ └─┘ └─┘ └─┘
             1   2   3   1   2   3   1   2   3
             
    Output  ─┐        ┌──┐        ┌──┐        ┌──────
    (÷3)     └────────┘  └────────┘  └────────┘
             |← skip →|  |← skip →|  |← skip →|
                2,3          2,3         2,3
                
    Threshold      /‾‾‾‾\        /‾‾‾‾\        /‾‾‾‾\
    (Vc1)    ─────/      \──────/      \──────/
             
    RA = 9.1kΩ, RB = 1kΩ, C1 = 0.01μF, Vcc = 5V
    
    ⚙️ Divide-by-N: Set timing so output ignores (N-1) trigger pulses

4. Pulse Width Modulation

The timer output waveform may be changed by modulating the control voltage applied to the timer's pin 5 and changing the reference of the timer's internal comparators. Figure 9 illustrates the pulse width modulation circuit. When the continuous trigger pulse train is applied in the monostable mode, the timer output width is modulated according to the signal applied to the control terminal. Sine wave as well as other waveforms may be applied as a signal to the control terminal. Figure 10 shows the example of pulse width modulation waveform.

Figure 9. Circuit for Pulse Width Modulation

flowchart LR
    subgraph CIRCUIT["PWM Configuration"]
        VCC["+Vcc"]
        
        subgraph TIMER["555 Timer"]
            P4["4<br/>RESET"]
            P8["8<br/>Vcc"]
            P7["7<br/>DISCH"]
            P2["2<br/>TRIG"]
            P6["6<br/>THRES"]
            P3["3<br/>OUT"]
            P5["5<br/>CONT"]
            P1["1<br/>GND"]
        end
        
        RA["RA"]
        C1["C1"]
        C2["C2"]
        GND["GND"]
    end
    
    VCC --> P4
    VCC --> P8
    VCC --> RA
    RA --> P7
    P7 --> P6
    P6 --> C1
    C1 --> GND
    
    TRIG_IN["Trigger<br/>Pulse Train"] --> P2
    MOD["Modulation<br/>Signal"] --> P5
    P5 --> C2
    C2 --> GND
    
    P3 --> OUTPUT["PWM<br/>Output"]
    P1 --> GND
    
    style VCC fill:#f00,color:#fff
    style GND fill:#000,color:#fff
    style TRIG_IN fill:#f96
    style MOD fill:#ff6
    style OUTPUT fill:#6f6

Figure 10. Waveforms of Pulse Width Modulation

    Control  ╭──────╮      ╭──────╮      ╭──────╮
    (Pin 5)  │      │      │      │      │      │
          ───╯      ╰──────╯      ╰──────╯      ╰───
             |← Modulation Signal (e.g., Sine) →|
                    
    Trigger ─┐ ┌─┐ ┌─┐ ┌─┐ ┌─┐ ┌─┐ ┌─┐ ┌─┐ ┌─┐ ┌─┐
             └─┘ └─┘ └─┘ └─┘ └─┘ └─┘ └─┘ └─┘ └─┘ └─┘
             
    Output  ─┐  ┌─┐   ┌───┐   ┌─┐  ┌─┐   ┌───┐   ┌─
    (PWM)    └──┘ └───┘   └───┘ └──┘ └───┘   └───┘
             |←w1→|←w2─→|←w3──→|
             
    Pulse width varies with control voltage:
    - Higher control voltage → Longer pulse width
    - Lower control voltage → Shorter pulse width
    
    RA = 3.9kΩ, RB = 1kΩ, RL = 1kΩ, C1 = 0.01μF, Vcc = 5V

5. Pulse Position Modulation

If the modulating signal is applied to the control terminal while the timer is connected for the astable operation as in Figure 11, the timer becomes a pulse position modulator. In the pulse position modulator, the reference of the timer's internal comparators is modulated which in turn modulates the timer output according to the modulation signal applied to the control terminal. Figure 12 illustrates a sine wave for modulation signal and the resulting output pulse position modulation : however, any wave shape could be used.

Figure 11. Circuit for Pulse Position Modulation

flowchart LR
    subgraph CIRCUIT["PPM Configuration"]
        VCC["+Vcc"]
        
        subgraph TIMER["555 Timer"]
            P4["4<br/>RESET"]
            P8["8<br/>Vcc"]
            P7["7<br/>DISCH"]
            P2["2<br/>TRIG"]
            P6["6<br/>THRES"]
            P3["3<br/>OUT"]
            P5["5<br/>CONT"]
            P1["1<br/>GND"]
        end
        
        RA["RA"]
        RB["RB"]
        C1["C1"]
        GND["GND"]
    end
    
    VCC --> P4
    VCC --> P8
    VCC --> RA
    RA --> P7
    P7 --> RB
    RB --> P6
    RB --> P2
    P6 --> C1
    C1 --> GND
    
    MOD["Modulation<br/>Signal"] --> P5
    
    P3 --> OUTPUT["PPM<br/>Output"]
    P1 --> GND
    
    style VCC fill:#f00,color:#fff
    style GND fill:#000,color:#fff
    style MOD fill:#ff6
    style OUTPUT fill:#6f6

Figure 12. Waveforms of Pulse Position Modulation

    Control  ╭────────────╮          ╭────────────╮
    (Pin 5)  │            │          │            │
          ───╯            ╰──────────╯            ╰───
                Modulation Signal (Sine Wave)
                    
    Threshold     /\    /\      /\      /\    /\
    (Pin 6)  ────/  \──/  \────/  \────/  \──/  \────
                        
    Output  ─┐ ┌─┐  ┌──┐    ┌────┐    ┌──┐  ┌─┐ ┌─
    (PPM)    └─┘ └──┘  └────┘    └────┘  └──┘ └─┘
             |←t1→|←t2─→|←─t3──→|←t4─→|←t5→|
             
    Pulse spacing varies with control voltage:
    - Higher control voltage → Longer period
    - Lower control voltage → Shorter period
    
    RA = 1kΩ, RB = 1kΩ, C1 = 1nF, Vcc = 5V

6. Linear Ramp

When the pull-up resistor RA in the monostable circuit shown in Figure 1 is replaced with constant current source, the VC1 increases linearly, generating a linear ramp. Figure 13 shows the linear ramp generating circuit and Figure 14 illustrates the generated linear ramp waveforms.

Figure 13. Circuit for Linear Ramp

flowchart TB
    subgraph CIRCUIT["Linear Ramp Generator"]
        VCC["+Vcc"]
        
        subgraph CURRENT_SOURCE["Constant Current Source"]
            RE["RE"]
            Q1["Q1<br/>PNP"]
            R1["R1"]
            R2["R2"]
        end
        
        subgraph TIMER["555 Timer"]
            P4["4<br/>RESET"]
            P8["8<br/>Vcc"]
            P7["7<br/>DISCH"]
            P2["2<br/>TRIG"]
            P6["6<br/>THRES"]
            P3["3<br/>OUT"]
            P5["5<br/>CONT"]
            P1["1<br/>GND"]
        end
        
        C1["C1"]
        C2["C2"]
        GND["GND"]
    end
    
    VCC --> P4
    VCC --> P8
    VCC --> RE
    VCC --> R1
    
    RE --> Q1
    R1 --> Q1
    Q1 --> R2
    R2 --> GND
    
    Q1 -->|Ic| P7
    P7 --> P6
    P6 --> C1
    C1 --> GND
    
    TRIG_IN["Trigger"] --> P2
    
    P3 --> OUTPUT["Output"]
    P5 --> C2
    C2 --> GND
    P1 --> GND
    
    style VCC fill:#f00,color:#fff
    style GND fill:#000,color:#fff
    style Q1 fill:#fcf,color:#000
    style OUTPUT fill:#6f6

Figure 14. Waveforms of Linear Ramp

    Trigger ─────┐     ┌───────────────────────────
    (Pin 2)      └─────┘  
                    ↓ Trigger pulse
                    
    Output  ─────────┐              ┌───────────────
    (Pin 3)         └──────────────┘
                    |←──── td ────→|
                    
    Threshold        ╱              Linear ramp (not exponential)
    (Pin 6)    ─────╱               
               0V  ↗                 
                  Vcc/3           2Vcc/3
                  
    Linear ramp: Vc1 = (Ic/C1) × t
    Slope S = Ic/C1
    
    R1 = 47kΩ, R2 = 100kΩ, RE = 2.7kΩ, RL = 1kΩ, C1 = 0.01μF, Vcc = 5V

In Figure 13, current source is created by PNP transistor Q1 and resistor R1, R2, and RE.

Equation 6: Current Source Calculation

$$I_C = \frac{V_{CC} - V_E}{R_E} \quad (12)$$

Here, VE is:

$$V_E = V_{BE} + \frac{R_2}{R_1 + R_2} V_{CC} \quad (13)$$

For example, if Vcc=15V, RE=20kΩ, R1=5kW, R2=10kΩ, and VBE=0.7V, VE=0.7V+10V=10.7V Ic=(15-10.7)/20k=0.215mA

When the trigger starts in a timer configured as shown in Figure 13, the current flowing through capacitor C1 becomes a constant current generated by PNP transistor and resistors. Hence, the VC is a linear ramp function as shown in Figure 14. The gradient S of the linear ramp function is defined as follows:

Equation 7: Ramp Slope

$$S = \frac{V_{P-P}}{T} \quad (14)$$

Here the Vp-p is the peak-to-peak voltage. If the electric charge amount accumulated in the capacitor is divided by the capacitance, the VC comes out as follows:

V = Q/C (15)

The above equation divided on both sides by T gives us

Equation 8: Simplified Ramp Slope

$$\frac{V}{T} = \frac{Q/T}{C} \quad (16)$$

and may be simplified into the following equation.

S = I/C (17)

In other words, the gradient of the linear ramp function appearing across the capacitor can be obtained by using the constant current flowing through the capacitor. If the constant current flow through the capacitor is 0.215mA and the capacitance is 0.02μF, the gradient of the ramp function at both ends of the capacitor is S = 0.215m/0.022μ = 9.77V/ms.

Mechanical Dimensions

Package

8-DIP (Dual In-line Package)

    ┌─────────────────────────────────────┐
    │  ●                                  │
    │  #1                             #8  │
    │  ┌──┐                         ┌──┐  │
    │  │  │                         │  │  │
    │  └──┘                         └──┘  │
    │  #2                             #7  │
    │  ┌──┐       555 TIMER         ┌──┐  │
    │  │  │                         │  │  │
    │  └──┘                         └──┘  │
    │  #3                             #6  │
    │  ┌──┐                         ┌──┐  │
    │  │  │                         │  │  │
    │  └──┘                         └──┘  │
    │  #4                             #5  │
    │  ┌──┐                         ┌──┐  │
    │  │  │                         │  │  │
    │  └──┘                         └──┘  │
    └─────────────────────────────────────┘

8-DIP Dimensions (in millimeters):

Parameter	Min	Nom	Max
Package Length	-	9.60	-
Package Width	6.20	6.40	6.60
Package Height	-	5.08	-
Lead Pitch	-	2.54	-
Lead Width	0.36	0.46	0.56
Lead Thickness	-	0.33	-
Lead Length	2.92	3.30	3.68
Standoff	0.51	-	-

              6.40 ± 0.20
         ┌────────────────┐
         │                │
    ┌────┤                ├────┐
    │    │                │    │  9.60
    │    │                │    │  MAX
    │    │                │    │
    └────┤                ├────┘
         │                │
         └────────────────┘
              ↕ 2.54 (pin pitch)
         
    Side View:
         ┌────────────────┐
    5.08 │                │
    MAX  └──┬──┬──┬──┬──┬─┘
            │  │  │  │  │   3.30 ± 0.30
            │  │  │  │  │   (lead length)
         ═══╧══╧══╧══╧══╧═══
                ↕ 0.33 MIN

8-SOP (Small Outline Package)

    ┌───────────────────────────────┐
    │  ●                            │
    │  #1                       #8  │
    │  ─┐                       ┌─  │
    │   │                       │   │
    ├───┴───────────────────────┴───┤
    │           555 TIMER           │
    ├───┬───────────────────────┬───┤
    │   │                       │   │
    │  ─┘                       └─  │
    │  #4                       #5  │
    └───────────────────────────────┘

8-SOP Dimensions (in millimeters):

Parameter	Min	Nom	Max
Package Length	4.72	4.92	5.12
Package Width	5.70	6.00	6.30
Package Height	-	1.55	1.75
Lead Pitch	-	1.27	-
Lead Width	0.31	0.41	0.51
Lead Length (toe)	0.40	0.80	1.27
Standoff	0.05	0.15	0.25
Overall Width (with leads)	-	6.00	-

              6.00 ± 0.30
         ┌────────────────┐
    ─┐   │                │   ┌─
     │   │                │   │   4.92 ± 0.20
    ─┘   │                │   └─
         └────────────────┘
              ↕ 1.27 (pin pitch)
         
    Side View:
              1.55 ± 0.20
         ┌────────────────┐
    MAX  │                │
         └──┬──┬──┬──┬──┬─┘
            └──┴──┴──┴──┴── 0.10~0.25 standoff

Pin Assignment Summary

Pin	Symbol	8-DIP	8-SOP	Description
1	GND	●	●	Ground (0V)
2	TRIG	●	●	Trigger input
3	OUT	●	●	Output
4	RESET	●	●	Reset (active low)
5	CONT	●	●	Control voltage
6	THRES	●	●	Threshold input
7	DISCH	●	●	Discharge
8	Vcc	●	●	Supply voltage

Requirements and compatibility

Written for: GitHub Copilot

Works with: Claude Code, Claude apps, OpenAI Codex, GitHub Copilot, Cursor, Gemini CLI, Kiro, OpenCode, Goose, Amp, Roo Code, JetBrains Junie, Factory Droid, Devin (ex-Windsurf), Mistral Vibe, OpenHands, Letta

“Works with” means the tool reads the open Agent Skills format; a skill written for one tool may use features others lack.