--- title: "Digital device applications; frequency counter" subject: "Digital Logic" chapter: 11 key: "semester_3/digital_logic:digital-devices-frequency-counter" source: https://www.bctengineer.com/q/semester_3/digital_logic/digital-devices-frequency-counter site: BCT Engineering --- # Digital device applications; frequency counter Digital Logic · Chapter 11: Applications - Asked in: 2076 Chaitra, 1+4 marks - Answer checked by Claude Opus 5.5 (high effort) on 2026-10-14 - Page: https://www.bctengineer.com/q/semester_3/digital_logic/digital-devices-frequency-counter - Whole chapter: https://www.bctengineer.com/md/semester_3/digital_logic/chapter-11 ## Question What are the applications of digital devices? Explain frequency counter. ## Short answer Digital devices are used in computers, instruments (frequency counter, DVM), clocks, communication, control systems, and consumer electronics. A frequency counter uses a crystal time-base to open a gate for Tg, counting shaped input pulses on decade counters, latching and displaying N, with f = N / Tg (1 s gate gives Hz). ## Answer #### Applications of digital devices Digital ICs (gates, flip-flops, counters, registers, decoders, multiplexers) are used wherever information is processed as binary signals: - **Computers and microprocessors** – arithmetic, memory, control units. - **Digital instruments** – frequency counters, digital voltmeters and multimeters, time-interval meters. - **Digital clocks and timers**, stopwatches, multiplexed displays. - **Communication** – multiplexing, encoding/decoding, error detection (parity), digital switching. - **Control systems** – traffic light controllers, vending machines, industrial PLCs. - **Consumer products** – calculators, mobile phones, digital TV and cameras. #### Frequency counter A **frequency counter** counts the number of cycles of an input signal during a precise gate time $T_g$; then $f = N / T_g$. With $T_g = 1$ s the count equals the frequency in Hz. ```text Input ─> Schmitt ─> ┌─────┐ ┌─────────┐ trigger │ AND │─> │ Decade │ └─────┘ │counters │ ^ └────┬────┘ Crystal ─> Divider ─> gate v (1 s gate, latch/reset) Latch ─> Decoder ─> Display ``` **Operation** 1. The Schmitt trigger shapes the input into one clean pulse per cycle. 2. A crystal oscillator and divider chain give an accurate gate pulse (e.g. 1 s). 3. The AND gate lets input pulses reach the decade counters only during the gate time. 4. At the end of the gate, the count is transferred to the latch and shown through BCD-to-7-segment decoders; the counters are then reset for the next reading. **Example:** 50,000 pulses counted in a 1 s gate means $f = 50$ kHz. ## Check yourself The answer's key points as multiple-choice questions, with the correct option and why. 1. Which is an application of digital devices listed in the answer? A. Traffic light controllers and vending machines (control systems) B. Analog audio amplifiers only C. Power transmission lines D. Radio antennas Answer: A. Digital ICs are used in control systems such as traffic light controllers, vending machines and PLCs, besides computers, instruments, clocks and communication. (Key point: Applications) 2. Why is an AND gate used in the frequency counter? A. To let input pulses reach the counters only during the gate time B. To invert the pulses C. To drive the display D. To shape the input Answer: A. One AND input is the shaped signal and the other the gate pulse, so counting happens only during T_g. (Key point: Gate AND role) 3. 50,000 pulses are counted in a 1 s gate. What is the frequency? A. 5 kHz B. 50 kHz C. 500 kHz D. 50 Hz Answer: B. f = N / T_g = 50,000 / 1 = 50 kHz. (Key point: Frequency formula) 4. What is done with the count at the end of the gate? A. It is transferred to the latch and shown through BCD-to-7-segment decoders, then the counters are reset B. It is discarded C. It is fed back to the Schmitt trigger D. It is multiplied by the crystal frequency Answer: A. The latch holds the reading for the display while the counters are reset for the next reading. 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