480 Seconds Voice Record/Playback Circuit with PCB Layout Using ISD17240 IC

Project has been designed for record & playback multi voice massages applications using nuvton ISD17240 IC.  Messages are stored in flash memories made in unique Multilevel Storage Technology (MLS).  Circuit  provides high quality audio recording and simple operations.  Circuit operates in dual mode standalone or micro-controller SPI mode.  Onboard tactile switches for standalone mode and 10 (2×5) pin box header connector for SPI mode.  160-480 Seconds voice massage recording capacity.

ISD1700 product is recommend for new designs in the 20 to 480 seconds storage duration (See Table1 below for cross reference parts) because of its simpler interface automatic power-down and new features such automatic message management, PWM speaker driver, volume control, vAlert, Erase operation, and configurable current (AUD) or voltage (AuxOut) output to drive external power amplifier.

NOTE : The PCB board can accommodate following ICs ISD1730, ISD1740, ISD1760, ISD17120 and ISD17240.






  • Supply 2.4 to 5 VDC (5 VDC @ 100 mA)
  • 26 to 80 Seconds selectable voice recording capacity
  • Selectable sampling rates 4KhZ To 12Khz
  • Directly drive 8 Ohms speaker or typical buzzer
  • Analog audio out to driver external audio amplifier
  • Digital volume control via onboard tactile switch
  • Dual mode operation stand alone or micro-controller
  • SPI Interface (4 wire serial interface)
  • 10 (2×5) Pin box header for SPI interface
  • Full control on memory and analog path configuration audio input, output and mix in SPI mode
  • Automatic power-down after each operations cycle (standalone mode)
  • Onboard tactile switch for Record, Play, Erase, FWD, Volume control, Reset and Feed-Through
  • Onboard power indication, record play indication
  • Voice message fed in via microphone or analog signal in
  • ISD1740 provides a PWM class D speaker driver and speaker output simultaneously
  • 100 Years message retention
  • 100,000 Record cycles
  • Four mounting holes of 3.2 mm each
  • PCB dimensions 80 mm x 76 mm




SW1 (Recording)

Push switch for triggering REC function Recording initialized by HL edge of this signal, continues when it stays at L and stops when LH edge occurs or memory is full.  In standalone mode, massages are recorded sequentially until end of memory.  The location where recording of individual message starts is determine by the internal record pointer. Addressable record and playback operations are accessible only in SPI mode.

SW2 (Reset)

Push switch for triggering reset function – device enter into the initial state and initializes all pointers to the default state without erasing recording massages.

SW3 (Play)

Push switch for triggering the Play function – playback of current massage in memory.  Beginning of current massage determined by the internal playback pointer.  Short Low pulse start the playback of this massage and next pulse low stop this operation.

SW4 (Erase)

Push switch for triggering the erase function – Erasing the first or last message in memory or global erasing the all message (whole memory).  Short Low pulse erases the current message.  Holding this input for more then 3Seconds initiates the global erase operations.


Push switch for triggering the FWD function – Forward operations, advance to the next massage.  Short pulse causes. In standby mode advance from current message to the next message (one message forward) and setting the pointer the playback pointer on it.  During the playback-halting this process, advancing to the next massage and restarting the playback from beginning.

SW6 (Volume)

Push switch for triggering Volume – Control of audio volume on speaker output, Analog audio output and Aux/Audio output.  There are 8 steps of volume control.  Default value after power on is maximum.  Repeated low pulses decrease the level by 1 step until the minimum value reached and then increase the volume by one step until maximum value reached and so on.

SW7 (FT)

Push switch for triggering the FT function – In stand alone mode, it configures the analog path as feed-through path from ANA IN audio input to Speakers output and Aux Audio output.






PCB Top Silk Screen


PCB Top layer


PCB Bottom Layer


Bill Of Material


The Nuvoton ISD1700 ChipCorder Series is a high quality, fully integrated, single-chip multi-message voice record and playback device ideally suited to a variety of electronic systems. The message duration is user selectable in ranges from 26 to 120 seconds, depending on the specific device. The sampling frequency of each device can also be adjusted from 4 kHz to 12 kHz with an external resistor, giving the user greater flexibility in duration versus recording quality for each application. Operating voltage spans a range from 2.4 V to 5.5 V to ensure that the ISD1700 devices are optimized for a wide range of battery or line-powered applications.

The ISD1700 is designed for operation in either stand-alone or micro-controller (SPI) mode. The device incorporates a proprietary message management system that allows the chip to self-manage address locations for multiple messages. This unique feature provides sophisticated messaging flexibility in a simple, push-button environment. The devices include an on-chip oscillator (with external resistor control) , microphone preamplifier with Automatic Gain Control (AGC) , an auxiliary analog input, anti-aliasing filter, Multi-Level Storage (MLS) array, smoothing filter, volume control, Pulse Width Modulation (PWM) Class D speaker driver, and current output.




A project has been designed around Holtek,s HT8970 voice echo IC.  Project can be used in various audio systems karaoke, toys, Animatronics, shows, displays, exhibitions, and sound equipment’s. The HT8970 is an echo/surround effect processor. It is designed for various audio systems including karaoke, television, sound equipment’s, etc. The chip consists of a built-in pre-amplifier, VCO or Voltage Control OSC, 20Kb SRAM, A/D and D/A converters as well as delay time control logic. The HT8970 chip echo processor IC utilizing CMOS technology. Which accept analog audio input signal, a high sample rate ADC transfer the analog signal into a bit stream then storage to internal  RAM, after processing the bit stream will de-modulate by DAC and low pass filter. Overall delay time is determined by internal VCO clock frequency, and user can easy to change the VCO frequency by trimmer pot. Jumper J1 provided to select the Microphone input or External audio signal input, CN1 Audio Signal input, PR1 Audio signal level adjust, PR2 output audio signal adjust, PR3 sound delay adjust,




  • Supply Input 5V DC
  • Onboard MIKE and Aux audio input ( Dual Option Selecting using Jumper)
  • MIKE and Aux  Selection via jumper
  • Input/MIKE signal level adjustable using Trimmer Potentiometer
  • It works in two modes – echo or surround
  • On Board Output signal level adjust Trimmer Pot
  • Onboard Trimmer Pot  for Sound Delay Adjust
  • Onboard LED for Power Supply Indicator
  • Four mounting holes of 3.2 mm
  • PCB dimensions 79 mm x 70 mm







Tiny Metronome Using 555 Timer and Buzzer

A metronome is a device that produces an audible click  sound at a regular interval that can be set by the Trimmer Potentiometer , typically in beats per minute (BPM). Musicians use the device to practice playing to a regular pulse.

Musicians practice with metronomes to improve their timing, especially the ability to stick to a tempo. Metronome practice helps internalize a clear sense of timing and tempo. Composers often use a metronome as a standard tempo reference—and may play or sing their work to the metronome to derive beats per minute if they want to indicate that in a composition.

555 Timer IC is a heart of the project, Buzzer used as sound generator, Trimmer Potentiometer provided to set the tempo of sound. circuit works with wide range 5V to 12V and its consumes 30-50mA current. Frequency range adjustable 1Hz to 20Hz. other frequency output possible altering the C3 and PR1.






About 555 Timer

These devices are precision timing circuits capable of producing accurate time delays or oscillation. In the time-delay or mono-stable mode of operation, the timed interval is controlled by a single external resistor and capacitor network. In the a-stable mode of operation, the frequency and duty cycle can be controlled independently with two external resistors and a single external capacitor.

The threshold and trigger levels normally are two-thirds and one-third, respectively, of VCC. These levels can be altered by use of the control-voltage terminal. When the trigger input falls below the trigger level, the flip-flop is set, and the output goes high. If the trigger input is above the trigger level and the threshold input is above the threshold level, the flip-flop is reset and the output is low. The reset (RESET) input can override all other inputs and can be used to initiate a new timing cycle. When RESET goes low, the flip-flop is reset, and the output goes low. When the output is low, a low-impedance path is provided between discharge (DISCH) and ground.

The output circuit is capable of sinking or sourcing current up to 200 mA. Operation is specified for supplies of 5 V to 15 V. With a 5-V supply, output levels are compatible with TTL inputs.


Multiple-Message Record/Playback Module Using ISD1932/ISD1964

This Module has been designed around Nuvoton’s ISD1932 ChipCorder® is the newest single-chip multiple-message record/playback series with dual operating modes (address trigger and direct trigger) and wider operating voltage ranging from 2.4V to 5.5V. The sampling frequency can be selected from 4 to 12 kHz via an external resistor, which also determines the duration from 10.6 to 32 seconds. These ICs are designed mostly for standalone applications, and of course, it can be used in conjunction with a microcontroller, if necessary.


The two operating modes are address trigger and direct trigger. While in address trigger mode, both record and playback operations are manipulated according to the start address and end address specified through the start address and end address pins. However, in direct trigger mode, the device can configure the memory up to as many as eight equal messages, pending upon the fixed message configuration settings. With the record or playback feature being pre-selected, each message can be randomly accessed via its message control pin.

The device has a selectable differential microphone input with AGC feature or single-ended analog input, analog in, under feed-through mode. Its differential Class D PWM speaker driver can directly drive a typical speaker or buzzer.


Sampling Rate or Recording Time Selection

  • R5: 53.3K 12 KHz sampling frequency 21.3 Seconds Voice Recording
  • R5: 80K    8 KHz sampling frequency 32 Seconds Voice Recording
  • R5: 100K 6.4 KHz sampling frequency 40 Seconds Voice Recording
  • R5: 120K 5.3 KHz sampling frequency 48 Seconds Voice Recording
  • R5: 160   4 KHz sampling frequency 64 Seconds Voice Recording



  • Wider operating voltage from 2.4 to 5.5V
  • Higher sampling frequency from 4kHz to 12kHz
  • Voice Recording Time 21 Seconds to 64 Seconds depend on sampling rate selection ( R5-OSC Resistor )
  • FT: converts MIC+ to ANAIN & feeds it to the speakers
  • R/P: record/playback switch
  • REC: level or edge recording
  • PLAYE: edge-trigger, toggle on/off
  • PLAYL: level playback or looping playback
  • LED: LED output for recording
  • LED Blinks for while at end of the message in play mode
  • NORM (Address Trigger) : variable message duration
  • MODE: (Direct Trigger) : fixed message duration









Example Circuit for Multiple switch connections


Sound To Light Effects Using LM358 Op-Amp LEDs & Microphone

Sound to Light Effects Using OP-Amp LED and Microphone (1)

This PROJECTS  will turn your favorite music into light effects, a microphone picks up the sound and gives  light effects with 6 Red LEDs, ideal for creating fun atmosphere at parties & discos. Supply 9V-12V DC.



  • Supply 9V-12V DC (PP3 9V Battery)
  • On Board Preset for Gain Adjust
  • 6 On Board LEDs
  • On Board Condenser Microphone
  • SMD based small Board
  • PCB Dimension 45.72 X 28.58 MM
  • CN1 Supply Input
  • PR1 Sensitivity Adjust


Sound to Light Effects Using OP-Amp LED and Microphone (3)

Sound to Light Effects Using OP-Amp LED and Microphone (2)

Sound to Light Effects Using OP-Amp LED and Microphone (1)

Moisture Sensitive Alarm Circuit Using BC547 Transistor and PCB Based Sensor


Circuit here is moisture sensor sounds an alarm when water reaches its sensor or moisture level is very high in the air. This project is a simple and a cost effective project for use in home or industrial purpose.


  •  Power Supply Input – 6 VDC @ 25 mA
  •  Output – Buzzer
  •  Onboard On/Off Switch
  •  Sensor PCB included
  •  Terminal pins for connecting power supply
  •  Four mounting holes of 3.2 mm each
  •  PCB dimensions 63 mm x 42 mm




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