signal turn on led

Thread Starter

guyromb

Joined May 5, 2009
28
hello,

I have a reciever that on his output i get 1khz sound (i can hear it using headphones) - I would like to turn on a simple led when this sound is heard. I also built a highpass\lowpass active filter.. I thought to use xor gate but not sure.

Please help me:)

thanks
 

Thread Starter

guyromb

Joined May 5, 2009
28
thanks.

I prefer bert's circuit (i have the components). The highpass\lowpass filter seems to work.. but the volume is low - should i amp. it again? (which resistors to use?) - i use lm324 (quad op.amp). This is the l\hpass circuit:
 

Thread Starter

guyromb

Joined May 5, 2009
28
Can the comparator be op.amp too ? but i am not sure about the voltages comparison (i get low voltage on the filter output)
 

bertus

Joined Apr 5, 2008
19,947
Hello,

Are you using a single powersupply voltage?
Then you can not connect the + input of the opamp to ground.
You can make a "virtual" ground by using two equal resistors (say 10K) with a capacitor of 10 uF from the midpoint to ground.
The top of the capacitor is your "virtual" ground.
This you can connect to the + input of the opamp.

Greetings,
Bertus
 

Thread Starter

guyromb

Joined May 5, 2009
28
Thanks!! so just tell me if i understood correct:
op.amp+ leg -> 10k resistor -> 10k resistor -> 10nf Capacitor -> ground.
 

Thread Starter

guyromb

Joined May 5, 2009
28
leg 11 ( op.amp gnd) and leg 4 (op.amp vcc) can be conntected as normal to the +\- right?
 

Thread Starter

guyromb

Joined May 5, 2009
28
bert .. i tried your circuit but i hear the 1khz very low again... Moreover, when I transmit the sound or not - i get the almost same output voltage.
However, by chance i got the sound very high (also i see on the voltmeter that there is a change in the output voltage).

What i did:
leg 3 (op.amp +) to 10kohm to 10kohm to 10microfarad to ground.... but not sure if it's good :D
 

Audioguru

Joined Dec 20, 2007
11,251
Pin3 should be at half the supply voltage. Maybe your input source is grounding the voltage at pin3.
Make the circuit like this and look in Google for Multiple-feedback Bandpass filter.
 

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Thread Starter

guyromb

Joined May 5, 2009
28
Pin3 should be at half the supply voltage. Maybe your input source is grounding the voltage at pin3.
Make the circuit like this and look in Google for Multiple-feedback Bandpass filter.
Is that bandpass filter circuit for 1khz pass? I forgot to mention that use ~5-6v power
 

Thread Starter

guyromb

Joined May 5, 2009
28
It's just killing me that i have done everything and it works.. and just the simple thing - turning on a led - doesnt work :(
 

Thread Starter

guyromb

Joined May 5, 2009
28
Please, somebody can help me?
I can hear the 1khz using headphones on the reciever output... I just need to convert this sound signal to '1' logic only when this it's heard.... I tried many things and I really don't know what to do :(:(
 

Thread Starter

guyromb

Joined May 5, 2009
28
I would expected that i would see a voltage differents - when i transmit or not
 
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