Hello,

I have an antenna that I designed with an envelope detector. In the sender side I have a touch sensor that I made and is working fine. In the receiver side I can see a change between 10 (no touch) and 11 V (when I touch the sensor) coming from the envelope detector. Now I need to change that pulse to give me a digital 0 (no touch) and 5 (touch). I have tried with a differentiator opamp circuit but the problem is that the current change is not that sharp so it does not get triggered. Can anyone help or point me in the right direction of how can I do this please? Thanks in advance.

 

Hello,

I have an antenna that I designed with an envelope detector. In the sender side I have a touch sensor that I made and is working fine. In the receiver side I can see a change between 10 (no touch) and 11 V (when I touch the sensor) coming from the envelope detector. Now I need to change that pulse to give me a digital 0 (no touch) and 5 (touch). I have tried with a differentiator opamp circuit but the problem is that the current change is not that sharp so it does not get triggered. Can anyone help or point me in the right direction of how can I do this please? Thanks in advance.

Are you using AM modulation with the transmitter? If so the modulation % seems low.

 

Hi k7elp60

Are you using AM modulation with the transmitter? If so the modulation % seems low.

Yes, I am using AM modulation. Unfortunately it is kind of low but the problem is that my sensor cannot give me a better response with the TFTs that I built. My big problem is that I cannot remove the DC offset in my receiver side so I haven't been able to produce a digital output.

 

Try a comparator, such as the LM339/393 to detect the difference between 10V and 11V.

 

Try a comparator, such as the LM339/393 to detect the difference between 10V and 11V.

Hi crutschow,

I think I will give it a try. I forgot about those. Maybe it will work if I use a comparator with a coupling capacitor and a virtual ground. BTW I need the v-ground because I don't have 10 V reference, I have to use 2 coin cell batteries at most here. Thanks!!

 

I don't have 10 V reference

Then what is generating the 11V signal?

But you can use two resistors in a voltage divider to reduce the signal voltage to what you have.

 

Then what is generating the 11V signal?

But you can use two resistors in a voltage divider to reduce the signal voltage to what you have.

The 11 V signal comes from the antenna, since the coil has a high Q the voltage after the envelope detector comes out between 10 and 11 V

 

Two coin cells should give about 6V.
Use a resistive divider to reduce the 10V to about 3V (say 100kΩ to ground and 232kΩ to the signal.
Connect the resistor's junction to the comparator (+) input.
Then you use a 100kΩ pot between the 6V and ground with the wiper tied to the comparator (-) input for the trigger reference.

 

Hi k7elp60


Yes, I am using AM modulation. Unfortunately it is kind of low but the problem is that my sensor cannot give me a better response with the TFTs that I built. My big problem is that I cannot remove the DC offset in my receiver side so I haven't been able to produce a digital output.

A comparator as crutschow suggests - just set Vref between the 2 voltages you want to discriminate.