Tired of expensive voice recorders?
This post shows you how to build your own simple one!
You can use it to record short messages for your family or friends.
Just press a button to record and another button to play it back.
Note: This project might be more complex than some others.
What is a Voice Recorder and Playback Circuit:
A Voice Recorder and Playback Circuit is an electronic system designed to capture and store audio messages for later playback.
This type of circuit is commonly used in various applications such as voice messaging systems, doorbells, announcements and other scenarios where the recording and playback of short audio messages are required.
The circuit typically involves components like a recording and playback IC, a microphone for input, a speaker for output and other supporting components.
Circuit Working:
Parts List:
| Component | Description | Quantity |
|---|---|---|
| Resistors (1/4 watt) | ||
| 52k | 1 | |
| 1k | 1 | |
| 100k | 1 | |
| 10k | 1 | |
| 10k to 30k adjustable | Adjustable resistor | 1 |
| 1k to 10k adjustable | Adjustable resistor | 1 |
| Capacitors | ||
| Ceramic 0.1μF | 2 | |
| Ceramic 0.01μF | 1 | |
| Electrolytic 22μF 25V | 2 | |
| Semiconductors | ||
| Transistor 2N9304 | 1 | |
| IC1 APR9301 | 1 | |
| LED (any 5mm, 20 mA) | 1 | |
| Other Components | ||
| Record push button | 1 | |
| Play push button | 1 | |
| Electret MIC | 1 | |
| Speaker 16Ω | 1 |
This voice recorder and playback system centers around a recording and playback chip supporting voice recording for 16 to 30 seconds with clear reproduction.
It finds applications in doorbells, railway announcement systems, and automatic telephone answering devices.
The circuit incorporates the voice recording and playback IC APR9301, transistor 2N3904, 16 ohm speaker, electret microphone MIC and other components.
The APR9301 V2 is a high quality voice recording and playback IC.
The duration of message recording is determined by the external resistor 52k connected to pin 7.
Recording Mode:
Pressing switch record button initiates recording indicated by the glowing LED.
Users can speak into microphone electret MIC to record a message.
IC1 remains in recording mode as long as record button is pressed and pin 27 of IC1 is grounded.
Recording halts after 20 seconds determined by the 52 kilo ohm resistor, pin 25 of IC1 goes ‘high, and LED ceases to glow.
Recording duration can be adjusted based on resistor 52k:
- 38 kilo-ohms for 16 seconds
- 52 kilo-ohms for 20 seconds
- 67 kilo-ohms for 24 seconds
- 75 kilo-ohms for 30 seconds
Playback Mode:
Momentarily pressing switch play button plays the recorded message from the beginning through speaker.
Standby Mode:
Pin 6 of IC1 is kept ‘low’ for a return to standby mode after recording and playback completion.
If pin 6 is high power down mode is activated, prohibiting recording or playback, with a current consumption of less than 1µA.
The circuits operation is simple record a message by holding down switch record button for the duration set by resistor 52k and play it back by briefly pressing switch play button.
Construction and testing involve assembling the PCB and checking for errors.
A simple check involves verifying correct power supply at +6V relative to 0V ground and observing LED glow upon pressing record button, indicating IC1 proper functioning.
Formulas:
In order to guarantee that the APR9301 IC functions as intended, you must properly set the components when designing a circuit for a voice recorder and playback.
Below is the formula to create your own circuit:
Divider of Voltage (for Adjustable Resistors):
Different thresholds and bias points can be established with adjustable resistors.
The voltage divider formula may be used to establish a certain voltage using an adjustable resistor:
Vout = Vin × R2 / R1 + R2
where,
- R1 is the resistor connected in series with the movable resistor R2
- The supply voltage is represented by Vin.
- To get the intended Vout adjust R2.
Current Limiting Resistor for LEDs:
To get the LEDs current limiting resistor value, compute:
RLED = Vcc − VLED / ILED
where,
- The supply voltage is represented by Vcc 6V,
- The forward voltage of the LED is represented by VLED (usually 2V for a normal LED)
- The required current is represented by ILED (20mA).
With the included components, this configuration offers a simple implementation of a voice recorder and playback circuit utilizing the APR9301 IC.
Adapt as necessary depending on the features of the component and your unique requirements.
How to Build:
Building the voice recorder and playback circuit involves assembling the circuit on a PCB.
Place Components on PCB:
- Identify each components location on the PCB according to the circuit diagram.
- Begin by placing and securing components such as IC1, 2N3904, Speaker, MIC, resistors, capacitors, LED and switches onto the PCB.
Solder Components:
- Solder each component onto the PCB, making sure the solder joints are clean and secure.
- Be cautious with the polarity of components such as capacitors, LED and IC.
Connect Wires:
- Use the wire cutter or stripper to prepare wires for connecting various components.
- Follow the circuit diagram to connect the components using the appropriate wires.
Adjustable Components:
- For components like resistors, adjust them according to the desired recording time.
- Use preset to set resistors to values such as 38 kilo ohms, 52 kilo ohms, 67 kilo ohms, or 75 kilo ohms based on your preference.
Check Connections:
- Double check all connections on the PCB to ensure there are no soldering errors or misplaced components.
Testing:
- Connect the assembled circuit to the power supply ensuring the voltage is within the specified range.
- Check for correct power supply at pin no 14,15 and 28.
- Press switch record button and verify that LED glows indicating that IC1 is functioning correctly.
Recording and Playback Test:
- Press switch record button and record a message using the microphone MIC.
- Release switch record button after the desired recording time.
- Press switch play button momentarily to play back the recorded message through speaker.
Final Check:
- Ensure that the circuit returns to standby mode after recording and playback.
- Verify that all modes (recording, playback and standby) are working as intended.
Conclusion:
Voice Recorder and Playback Circuits are valuable in applications where a simple and cost effective solution for audio messaging is needed.
They find use in security systems, messaging devices and various electronic gadgets where voice communication is essential.