Need circuit for mute the unwanted audio (Squelch control circuit)
This is a basically audio without squelch control.
I want to mute the speaker when there is no signal present. Is there any way to mute this audio?
Please share the schematic
Audio Noise-1.zip
This sounds like audio from a radio receiver.
There are two easy methods, assuming you don't want to go into software solutions:
1. If you have access to a point where signal strength can be read, use it to open or close an audio switch (mute).
2. operate a mute circuit based on the amplitude of the audio.
3. rely on the 'hiss' having a large high frequency content. Filter to remove lower frequencies and use the remainder to operate the mute switch.
Method 1. is by far the best to use because it doesn't rely on the audio itself but on whether a station is present. Method 2 works but makes the audio 'choppy', meaning it cuts in and out all the time, making it uncomfortable to hear. Method 3 is a compromise that works reasonably well. You need a filter to split the audio into two paths, the low frequencies go to the loudspeaker via the muting circuit, the high frequencies are rectified and used to operate the mute switch. The idea is that when the hiss drops, the switch turns the audio on, otherwise it stays off.
Exactly how you do the muting depends on the surrounding circuits. Usually it is done just before the volume control using an analog gate but many amplifiers already have a mute control you can utilize.
Brian.
Try this:
... just for info, Vfone's schematic uses method 3 I described. The small input capacitor and the inductor are the filter components.
Brian.
Thank you for your response
Can you please confirm capacitor value in schematic because some of the capacitor value is just mention like 005 and 002
005 means 5nF, 002 means 2nF, and 1 means 1uF.
The 1uF capacitors should be non-polar caps.
thanks vfone.
Is there any way to control squelch by software?
Note: I'm using 16 bit micro controller so it doesn't have audio processing capability.
There are some digitally controlled potentiometers available on the market that may help you:
http://ww1.microchip.com/downloads/e...Doc/21978c.pdf
http://www.analog.com/media/en/techn...ets/AD5227.pdf
https://datasheets.maximintegrated.c...60-MAX5161.pdf
1) I'd implemented the circuit but couldn't get the required output.
MPF103 and audio amplifier section not implemented as in my circuit i'm using LM4871 for amplification.
I'd just monitored the voltage at 560K resistor and collector pin at Q1 but output remain same in both cases when signal is present and without signal (HISHHH audio ouput).
2) Also I implemented the active high pass filter (with different cutoff frequency - 3KHz, 3.5 KHz) but could not achieve the required output.
Assumption: Squelch noise (HISHHHH sound) is above 3KHz frequency so I've set the cutoff frequency 3.5 KHz and amplify the noise so that it can be monitored.
How the other walkie talkie maker companies like Motorola, Kenwood,..etc are control the squelch?
Squelch of radio receivers is always controlled by RF level rather than audio.
Do you have any reference design or could you share more information?
The original post didn't mention any FM receiver involved. Was asking only for a noise suppressor squelch type of an audio signal.
For example, during a speech, to suppress the noise between spoken words.
This type of noise cannot be filtered because its frequency is broadband, and could have the same frequency with the desired signal.
Basically I'm using DRA818 module for walkie talkie application.
In this module squelch level are configurable from 1 - 8 level and 0 - is for continuous scan mode.
If I set 1 - 8 squelch level then during audio reception voice is breaking in between and it is not working properly but the same thing works properly with scan mode with just having one issue audio amplifier remain continuously ON and HISHHHH sound(attached in first post) is heard from speaker when signal is not present (No one is talking).
After this I'd decided to use this module in scan mode and implement separate squelch control circuit so that microcontroller can turn ON or OFF audio amplifier in absence of signal.
Note that in this module RSSI checking stop responding after voice is transmitted (TX switch is pressed) so i can not use this method.
@vfone
Do you know why this is not working?
Hi,
Single supply without DC input biasing.
Klaus
Not understood what you are trying to say
Compare specified OP input common mode range with the biasing applied in your circuit.
Hint:
Double the value of R2 then add a new resistor from pin 3 to VCC of the same value. For example change 4.7K to two 10K resistors so the overall frequency response isn't changed but the op-amp input is at half VCC.
That fixes the input voltage problem but the negative feedback still can't work properly. You need to isolate the DC path through R7 but still let it control the gain. To do that, add a capacitor in series with R7, it will fix the DC problem but also introduce a low frequency roll off. In your circuit that isn't very important as you are only interested in high frequencies anyway. The 6dB cut off will occur when the capacitor reactance is equal to the value of R7 so for example, if you use 1uF it will be ~34Hz.
Brian.
Don't know if OP07 is your actual device. It's no even specified for 5V supply, minimal supply voltage in datasheet is 6V.