Astable Multivibrator (HIGH SPEED LOGIC ICs)

The image on the right is the schematic and pin layout of the IC that we will be using for this circuit. The MC74HC04 IC is a low cost CMOS Hex Inverter. I used this type mainly because, it is what I have, although you can use LS type but, with a little modification or exemptions

For 'HC' type:
Always connect unused inputs to an appropriate voltage level (e.g. GND, or V_CC), unused outputs can be left open.

For 'LS' type:
You can leave unused inputs open as well as unused outputs.

The figure below is the schematic layout for the circuit. The circuit makes use of passive components R1, R2 and capacitor C to make the oscillation. LED1 serves as the output indicator for the High to Low transition of the circuit.


Schematic diagram of the CMOS Oscillator

Based on the circuit above, the following conditions should be followed:

2(R1) ≤ R2 ≤ 10(R1)
C ≥ 100 ρF
1 kΩ ≤ R1 ≤ 1MΩ

The frequency of oscillation can be computed as follows:



BREAD BOARD LAYOUT

PARTS

• IC1 = MC74HC04 (1)
• R1 = 390kΩ (1)
• R2 = 680kΩ (1)
• R3 = 330Ω (1)
• C = 10uF/16V tantalum/electrolytic (1)
• LED1 = 5mm LED Diode any color (1 each)
• 9V Battery, 9V Battery Clip (1 each)

* All resistors are 1/4W 5% tol. carbon composition type unless specified.

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