Are you sick of costly voice recorders?
This article explains how to construct a simple one for yourself!
It allows to record short messages for loved ones.
To record and play it back one needs to simply press two buttons.
Note: Compared to other projects this particular project is probably more challenging.
What is a Voice Recorder and Playback Circuit:
The purpose of a voice recorder and playback circuit is to record and store audio messages for replay at a later time.
Voice messaging systems, doorbells, announcements and other cases require the recording and replay of quick audio messages are just a few of the various uses which frequently depend on this kind of circuit.
A recording and playback integrated circuit (IC) a microphone for input, a speaker for output and additional supporting components are commonly included in the circuit.
Circuit Working:
Parts List:
| Component | Quantity |
|---|---|
| Resistors (All resistors are 1/4 watt) | |
| 52k | 1 |
| 1k | 1 |
| 100k | 1 |
| 10k | 1 |
| 10k to 30k adjustable resistor | 1 |
| 1k to 10k 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 |
| Record push button | 1 |
| Play push button | 1 |
| Electret MIC | 1 |
| Speaker 16Ω | 1 |
A recording and playback device is the heart of this voice recorder and playback system which allows for 16–30 seconds of clear sound recording.
It is used in automatic telephone answering machines, doorbells and train announcement systems.
The circuit includes the transistor 2N3904, 16 ohm speaker, electret microphone (MIC), voice recording and playback integrated circuit (IC APR9301) and other parts.
An excellent sound recording and playback integrated circuit is the APR9301 V2.
The external 52k resistor connected to pin 7 controls how long the message is recorded.
Mode of Recording:
The LED flashes to indicate that recording has begun when the switch record button is pressed.
To record a message users can talk into an electret microphone.
As long as pin 27 of IC1 is grounded and the record button is pressed IC1 stays in recording mode.
When the 52k resistor detects for 20 seconds the recording stops and pin 25 of IC1 goes high and the LED stops blinking.
The resistor 52k is used to modify the recording duration:
38k ohms for 16 seconds
52k ohms for 20 seconds
67k ohms for 24 seconds
75k ohms for 30 seconds
Mode of Playback:
Pressing the switch play button for just a few seconds plays the recorded message through the speaker.
In standby mode:
In order to go back to standby mode when recording and playback are finished pin 6 of IC1 is kept low.
Power down mode which limits recording or playback with a current usage of less than 1µA is triggered if pin 6 is high.
The circuit works simply by recording a message by holding down the switch record button for the amount of time indicated by the 52k resistor and then playing it again by slightly pushing the switch play button.
Assembling the PCB and looking for mistakes are part of the construction and testing process.
Be sure the power supply is set at +6V relative to 0V ground and seeing the LED light up then click the record button which can easily verify that IC1 is operating properly.
Formulas:
When building a circuit for a voice recorder and playback one must correctly arrange the components to ensure that the APR9301 IC operates as designed.
The formula to build your own circuit is as follows:
Voltage Divider (for Adaptable Resistors):
Adjustable resistors allow for the setting up of various thresholds and bias points.
With an adjustable resistor a certain voltage could possibly be generated using the voltage divider formula:
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 required Vout adjust R2.
LED Current Limiting Resistor:
To calculate the value of the LEDs current limiting resistor:
RLED = Vcc − VLED / ILED
where,
- The supply voltage is represented by Vcc which is 6V
- The forward voltage of the LED is represented by VLED which is usually 2V for a normal LED
- The required current is represented by ILED which is 20mA.
This design provides the simple construction of a voice recorder and playback circuit using the APR9301 IC with the components that are supplied.
Depending on the components features and particular requirements make the required adjustments.
How to Build:
For building a Simple Voice Recorder and Playback Circuit following are the connection steps one should follow:
Put the parts on the PCB:
- Using the circuit schematic as a guide place each component on the PCB.
- Start by connecting parts to the PCB including the IC1, 2N3904, speaker, MIC, resistors, capacitors, LEDs and switches.
Components of Solder:
- Make sure the solder junctions are tight and clean before connecting each component to the PCB.
- Take care when it comes to the polarity of parts like capacitors, LEDs and ICs.
Connect the wires:
- For cutting cables for connecting different components use a wire cutter or stripper.
- Connect the components using the proper wires by following the circuit schematic.
Adjustable Parts:
- Make adjustments to resistors and other components based on the recording time one need.
- Select resistor values using presets such as 38, 52, 67 or 75 kilo ohms depending on ones preferences.
Verify Connections:
- Verify every connection on the PCB one more time to make sure there are no soldering mistakes or missing parts.
Testing:
- Ensure that the voltage is within the required range before connecting the constructed circuit to the power source.
- Verify that the power supply at pins 14, 15 and 28 is correct.
- Check to see if the LED illuminates indicating that IC1 is operating properly after pressing the switch record button.
Test of Recording and Playback:
- Press the switch record button then use the microphone (MIC) to record a message.
- Once the correct recording period has passed release the switch record button.
- To play the recorded message back through the speaker press the switch play button.
Last Verification:
- Make sure that after recording and playing back the circuit switches back to standby mode.
- Check to make sure all recording, playback and standby modes are operating as planned.
Conclusion:
Voice recorder and playback circuits are useful for occasions when audio message requires a simple and affordable solution.
They are used in messaging apps, security systems and other technological devices where voice communication is important.