555 timer

555 Timer Astable PCB

Overview

This PCB is a simple 555 timer circuit configured in astable mode, designed to blink an LED. It is powered by a 9V battery and includes a single LED with a current-limiting resistor.

This was a project done under IEEE at UC Irvine. The PCB was designed using KiCad.

Key features:

• Uses NE555 or equivalent timer IC
• Astable configuration for continuous oscillation
• Battery-powered (9V)
• LED indicator with current-limiting resistor
• LTSpice simulation file included for testing and verification

Components

• Timer IC: 555 timer (NE555)
• Capacitor: 1µF between TRIG/THRES and GND
• Resistors:
  • R1 = 1kΩ series resistor with LED
  • R2 = 470kΩ between DISCH and TRIG/THRES
  • R3 = 1kΩ between DISCH and VCC node (also RESET tied to VCC)
• LED: Indicator for output
• Power supply: 9V battery

Wiring & Connections

The LED includes a built-in 1kΩ current-limiting resistor.
Note: The battery connector is where you connect the 9V battery; observe LED polarity.

Usage

1. Connect a 9V battery to the PCB.
2. The 555 timer begins oscillating in astable mode.
3. The LED will blink according to the calculated frequency.
4. You can simulate the circuit using the included LTSpice file to verify timing and LED behavior.

Calculations

For a 555 timer in astable mode:

T_high = 0.693 * (R2 + R3) * C
T_low  = 0.693 * R2 * C
T_total = T_high + T_low = 0.693 * (R3 + 2*R2) * C
f = 1 / T_total
Duty cycle = T_high / T_total

Using component values:

• R2 = 470kΩ
• R3 = 1kΩ
• C = 1µF

Step 1: Total period

T_total = 0.693 * (R3 + 2*R2) * C
T_total = 0.693 * (1,000 + 2*470,000) * 0.000001
T_total ≈ 0.651 seconds

Step 2: Frequency

f = 1 / T_total ≈ 1 / 0.651 ≈ 1.54 Hz

Step 3: Duty cycle

T_high = 0.693 * (R2 + R3) * C
T_high = 0.693 * (470,000 + 1,000) * 0.000001 ≈ 0.326 s
Duty cycle ≈ T_high / T_total ≈ 0.326 / 0.651 ≈ 50%

R1 (LED resistor) does not affect timing.

Simulation

• You can simulate the circuit using the included LTSpice file.
• The OUT pin waveform will correspond to the LED blink pattern.
• Adjust R2, R3, or C to change the frequency and duty cycle as needed.

Images

Schematic

PCB Layout

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