suitable microphone to trigger an adjustable level

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You need to rectify it, then use the resulant DC to feed a comparitor, the output of that will be a nice switching signal, which you could use to drive a switching transistor.
 
ahh i see, excellent.

so i guess i could use a standard type bridge rectifier?

as for the comparitor im not really familiar with them. What are the characteristics to look for?

Im running the RF module through a encoder chipset, it has four inputs so i guess I could switch one on with a transistor?
Would there be enough power to do that without having to amplify the signal further?

thanks again
 
danrogers said:
so i guess i could use a standard type bridge rectifier?
Click to expand...
A single diode and a capacitor converts audio AC to DC.

as for the comparitor im not really familiar with them. What are the characteristics to look for?
Click to expand...
Maybe a comparator is not necessary. What is the sound that will be used as a control signal? Will there be much background noise?

Im running the RF module through a encoder chipset, it has four inputs so i guess I could switch one on with a transistor?
Click to expand...
The encoder's datasheet will tell you how to turn the inputs on and off.

Would there be enough power to do that without having to amplify the signal further?
Click to expand...
Probably but it depends on how much power the switch needs.
 
Please forgive my lack of electronic knowledge, Ive only started getting a bit deeper with it in the last year so please bear with me

In the past ive only used bridge recifiers to rectify ac from the mains, how would one use a cap and diode to do it?

There should be minimal background noise as it will be used indoors. The sound that I hope to use to trigger the device will be the buzzer/ timer on microwaves or ovens so should be fairly loud.

On the datasheet it shows the inputs with switches between vcc and the pins, and looking at the supply i think it will run from 2-6v.

is it possible to get transistors that can be operated at voltages less than 3v from the microphone circuit you kindly shared?

thanks again!
 
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danrogers said:
In the past ive only used bridge recifiers to rectify ac from the mains, how would one use a cap and diode to do it?
Click to expand...
A coupling capacitor from the output of the opamp in series with a diode then the cathode of the diode feeds a filter capacitor with its negative wire connected to ground. The junction of the cathode of the diode and the positive wire of the filter capacitor will be a positive voltage that fluctuates with the loudness of the audio.

There should be minimal background noise as it will be used indoors. The sound that I hope to use to trigger the device will be the buzzer/ timer on microwaves or ovens so should be fairly loud.
Click to expand...
Then a comparator will not be needed. The DC voltage from the diode circuit will turn on a transistor that activates an input on your encoder.

is it possible to get transistors that can be operated at voltages less than 3v from the microphone circuit you kindly shared?
Click to expand...
A transistor turns on with an input of 0.7V.
 
The microphone you selected will be fine.
I use electret mics from broken phones and toys.
 
danrogers said:
thats great i will order one of those then.

With regards to the TL071, there appears to be many different types, some with slightly different properties. some look like they have different clock rates, 3 or 4mhz?
Click to expand...

Opamps don't have clock rates?.

For example would this one be suitable with 3mhz clock? TEXAS INSTRUMENTS|TL071ACP|OP AMP, JFET | Farnell United Kingdom

thanks again for all your help and advice
Click to expand...

That looks absolutely fine - it's even a PDIP (it's SO easy to order a surface mount chip by mistake!).
 
Hi Nigel, thinking about it of course they dont have clock rates!

haha yeah I dont want a surface mount package yet untill ive made a PCB.

Cant thank you both enough for helping me through this so far, looking foward to getting the bits and building it now
 
Nigel Goodwin
Everyone and every thing uses an electret mike - nice and small as well.
Click to expand...



They do? For two-way communications my favorite pick is an Astatic crystal mike. For demanding audio I use either Sure, AKG or Beyer dynamics. For quality voice recordings I use an RCA ribbon mic. For a Big Ear listening device I use an electret.
 
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Farnell sells the TL071ACP for 0.73 pounds each and sells the TL071CN for 0.23 pounds each. They are both almost the same and you will hear no difference.
 

One other thing I'm unsure of is what value caps to use, and also what type of diode?
 
danrogers said:
One other thing I'm unsure of is what value caps to use, and also what type of diode?
Click to expand...
You need to decide on how low a frequency the coupling capacitor must pass then calculate its value with the resistance it feeds.
You must decide on a suitable resistance.
You must calculate the value of a suitable filter capacitor depending on how long you want its voltage to remain and on the lowest frequency it will work at.

I use 1N914 and 1N4148 little signal diodes that are both the same.
 
Ok thank you for that, I'm slightly daunted by all those calculations I will need to make!
What would you suggest as the first step?
 
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