This NE555 timer intregrated circuit based module generates an adjustable square-wave PWM signal with a frequency range of 7 Hz to 1.4 kHz. The output pulse can be used for motor speed control, LED brightness adjustment, signal testing, and other applications.
The NE555 IC is configured in the circuit board as an astable mode where it continuously oscillates between HIGH and LOW states, producing a square wave output with no stable state. The output frequency (f) of this module is calculated using the formula: f = 1.44 / (R2 + 2 x RP1) x C3.
Schematic of the ne555 frequency adjustable pulse generator module circuit is shown below.
When DC power (ranging from +5V to +12V) is supplied, capacitors (C1, C2) filter out input noise, and LED D1 indicates the power-on status (protected by the current-limiting resistor R1).
At startup, capacitor C3 is uncharged state and causing the trigger pin (pin 2) voltage to drop to around 0.1V. This activates the integrated comparator-B of U1 which helps to setting the flip-flop and making the output HIGH (about Vcc – 1.5V) for 70 ms. The integrated discharge NPN transistor turns off, allowing C3 to charge through resistors R1 and PR1 from 1/3 Vcc to 2/3 Vcc.
When C3 voltage exceeds 2/3 Vcc, integrated comparator-B of U1 resets the flip-flop which making the output LOW for 69.3 ms. The integrated transistor turns on, and C3 discharges through PR1 from 2/3 Vcc down to 1/3 Vcc. The cycle repeats and producing a continuous square wave.
The potentiometer PR1 adjusts the output frequency. The output frequency is about 7 Hz with a 50% duty cycle at maximum resistance where the frequency reaches 1.4 kHz with a 98% duty cycle at minimum resistance.
A capacitor (C4) connected to pin-5 filters noise and prevents false triggering for stable operation.
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