Buzzer-Employed Timer Circuit With Optional Optocoupler

The circuit was designed to formulate a timer that can provide an alert method with the use of a buzzer while the presence of the optocoupler will make it possible to drive an external circuit.

• 4060 – a 14-bit ripple counter with internal oscillator that has glitches which may occur in any logic gate systems connected to its outputs due to the slight delay before the later counter outputs respond to a clock pulse
• 4N25 – a general purpose optocoupler that consists of a gallium arsenide infrared emitting diode driving a silicon phototransistor in a 6-pin dual in-line package used in microprocessor inputs, digital logic inputs, and power supply regulators due to its features such as high isolation voltage between input and output, operating temperature up to +110ºC, and available in wide-lead spacing
• Optocoupler – a solid state component that uses a light emitting diode to transmit light through an optically transparent barrier between two isolated circuit wherein the barrier allows light to pass but not current

The main function of the circuit is performed by the IC1 4060 which inhibits a 14-stage binary divider and an oscillator. The optocoupler is denoted as IC2 using the model 4N25 where any external circuit can be connected across the points A and B. The RC circuit connected to the IC1 pins 9, 10, & 11, are responsible for determining the frequency of oscillation.

The circuit will be supplied by the start of action of switch S1. The pulse input will be present in pin 12 or the RESET pin, through capacitor C1 and resistor R3. This will null or void the counter and will require the measurement of to start from zero. As the 14th digit of the count is reached, a HIGH logic level is acquired at the pin 3 of Q14 output which will drive the base of Q1 & Q2. This voltage will the transistors ON and will produce sound on the buzzer BZ1. Also, the A & B contacts of optocoupler IC2 will be ready to drive any suitable external circuit. The presence of 500K ohms potentiometer RV1 is for the regulation of the time delay that would start from 1 minute up to 2 hours. The delay will depend on the combination of the values of RV1 and C2.

The supply of the circuit may originate form a 9 V battery source or an external power supply. The LED D1 and R4 will provide a visual indication that the circuit is working but they can be eliminated if not required, since it will not affect the operation of the circuit. In keeping these two components, it will only consume less current of approximately 1 mA unlike when the output of Q14 is activated which will require large amount of current boost. With the components D1, BZ1, & IC1 being activated, the current of the circuit will reach approximately 40 mA.

With regards to the operation of the circuit, it is best utilized in time measurement applications. They are widely seen in quiz and game shows using buzzers. In computer applications, they can be used as watchdog timers which can monitor the internal temperature, power supply, and generation of alarm to initiate corrective action.

Source:users.otenet.gr/~athsam/timer_with_buzzer_and_optocupler.htm