EK022 Electret Microphone Amplifier
Part.no: 41017402
EK022 is an amplifier board for electret microphones. A suitable microphone is included and can be soldered directly to the board.
The kit contains all parts required for powering the microphone and amplify the signal to a level suitable for use with a microcontroller or audio equipment.
The included microphone has a sensitivity of -50dBu, which can be translated to 3.16mV/Pa. To provide any useful signal, the microphone output have to be amplified greatly.
If the capacitor C5 is mounted, the output will be AC coupled and works with audio equipment. If the amplifier is to be used with a microcontroller or similar, the signal has to be DC coupled and instead of mounting C5, simply short the two pins with a component lead.
The amplification is set to 100x, but can be increased or decreased by changing the feedback resistor (R3). The amplification can be calculated using the formula G=R2/R3 (1k/100k = 100x amplification).
The included OP amplififer TLC271 works with a wide supply range and can be powered with voltages from 3V to 12V. Please note that loud sounds can be clipped when using lower voltages and R3 should be changed to a lower resistance.
The board has an unused space for an additional capacitor (C6), which is not required or included in the kit. A capacitor in the range of 100 - 1000pF↗ can be placed here to reduce high frequency noise.
- Supply voltage: 3 - 15VDC
- Current draw: 2.2mA (12V)
- Dimensions: 38 x 25mm
- Mounting holes: c-c 33 x 20mm, ø2.5mm
Component list
| RefDes | Value | Qty. | Part.no. | Marking |
|---|---|---|---|---|
| A1 | Electret microphone | 1 | 40290007 | |
| C1 | Ceramic capacitor 1uF | 1 | 41017671 | 105 |
| C2 | Ceramic capacitor 100nF | 1 | 41003038 | |
| C3, C4, C5 | El.lyt capacitor 10uF | 3 | 41017674 | 10uF |
| C6 | Not used | 0 | ||
| D1 | LED 3mm red | 1 | 40307000 | |
| P3 | Pin header 2.54mm 3-pin | 1 | 41001167 | |
| R1, R4, R5, R6, R7 | Resistor 10kohm | 5 | 40811410 | |
| R2 | Resistor 1kohm | 1 | 40811310 | |
| R3 | Resistor 100kohm | 1 | 40811510 | |
| U1 | OP amp TLC271 | 1 | 40350271 | TL271CP |
Assembly guide
Before starting the assembly, check that the PCB is free from damage and scratches. Verify that you have all the components to be assembled, compare with the component list!
It is easiest to start by mounting the lowest components and work upwards in size. Begin by soldering the IC socket in place, then continue with the resistors.
Once the IC socket and resistors are soldered, continue with the LED and the ceramic capacitors.
Finish with the electrolytic capacitors and the microphone. The microphone can be soldered either flat against the PCB or angled out from the board edge. Please note the polarity! The pin with three dashes goes in the hole marked "-".
When all components are in place and connectors or wires have been soldered, the amplifier IC can be mounted in the IC socket. Make sure all pins are aligned correctly with the socket and are not bent. Also pay attention to the orientation! Compare the marking on the PCB with the IC.
Interactive assembly guide ↗
Circuit description
How an Electret Microphone Works
The first stage of the circuit is the electret microphone A1. Electret microphones are sometimes called condenser microphones because they function similarly to a capacitor. They consist of two plates, one fixed and one movable. The movable plate is the diaphragm that captures sound waves and together with the other plate, generates a small voltage. This signal is extremely weak and high impedance, requiring buffering before further processing. Therefore, the microphone includes a built-in amplifier, powered through a resistor (R1) connected to the supply voltage.
The audio signal at the point where R1, C1, and the microphone’s positive terminal meet now has a DC offset, as the power voltage and the audio signal are combined. The capacitor C1 ensures that only the AC (audio) signal passes through, preventing the operational amplifier (op-amp) from amplifying unwanted DC voltage.
Amplification of the Signal
After C1, the signal is sent to the inverting input of the operational amplifier (U1). The gain is determined by resistors R2 and R3 according to the formula: Vout = R2 / R3. For example, if R2 = 100 kΩ and R3 = 1 kΩ, the gain is 100x, meaning the signal is amplified 100 times, making it strong enough for use with audio equipment.
Reference Voltage and Stabilization
Since an op-amp requires a reference voltage to properly handle audio signals, R4 and R5 form a voltage divider, setting the reference voltage to half of the supply voltage. This allows the signal to swing both positively and negatively relative to the reference voltage. When no sound is present, the audio signal will match the reference voltage.
To reduce noise and ripple in the reference voltage, capacitor C3 is used for stabilization. Capacitor C6, connected between the op-amp’s output and its inverting input, helps maintain amplifier stability and filters out high frequencies beyond the audible range. C6 is not required for normal use.
Signal Adaptation
For use with audio equipment, the signal should not swing between 0V and V+, but instead be centered around 0V. C5 and R7 form a high-pass filter that removes DC offset, which is important to prevent clicking noises and to protect audio equipment.
If the amplifier is instead used with a microcontroller or ADC (Analog-to-Digital Converter), C5 can be bypassed with a wire, and R7 can be omitted. This retains the DC offset, allowing the signal to swing between 0V and V+.
Power Supply and Indicators
To ensure a stable supply voltage, C2 and C4 help filter out noise from the power source. D1 and R6 form an LED indicator with a current-limiting resistor, which lights up when the amplifier is powered on.
Schematic
Drawing
