AC Signal Amplitude converted to a 4-20mA Signal

[mondo8205]

I have a microphone picking up a certain frequency using a filter and I want to have this signal's amplitude converted somehow into a 4-20mA signal. I have a 24Vdc source I can use to create the 4-20mA signal but need some type of circuit to relate the two together.

Can anyone point me in the right direction to accomplish this or have any ideas?

 

[ericgibbs]

I have a microphone picking up a certain frequency using a filter and I want to have this signal's amplitude converted somehow into a 4-20mA signal. I have a 24Vdc source I can use to create the 4-20mA signal but need some type of circuit to relate the two together.

Can anyone point me in the right direction to accomplish this or have any ideas?

hi,
Get the datasheet for an AD694 IC, depending upon your AC signal you may need an amplifier.

 

[ronsimpson]

Almost understand:
Do you have the microphone amplifier working?
Is the filter designed?
Do you want a peak detector after the filter.
Do you have a 4-20mA driver?

Is the output (x mA) related to microphone level (at one frequency)? The output is DC.
Or do you want the output to have that frequency on it? The output is AC.

 

[ronsimpson]

Is the output linear or log (in db). This is audio so db might be best.

 

[mondo8205]

I am using this https://www.mouser.com/Search/ProductDetail.aspx?R=MIKROE-333virtualkey99990000virtualkey932-MIKROE-333 for my microphone/amp setup. I will be designing a custom filter for a frequency I dont know yet, which will be after the mic/amp.

Im not really sure if the output is linear or in db, this is the only datasheet for it https://www.mikroe.com/eng/downloads/get/1444/mic_amp_manual_v100.pdf.

 

[ronsimpson]

The amplifier will take a mic signal to headphone or small speaker level.
There are two outputs. One is 180 out of phase of the other.
You will make a filter that connects to one of the outputs.
I would add a diode & cap after the filter to get a DC level that relates to the level of the output of the filter. The detector time constant could be set to 0.1 second or shorter.


**broken link removed**

 

[mondo8205]

Thank you so much! This will definitely help me out!

 

[mondo8205]

Actually another question, how did you know that the two outputs were 180 out of phase and what is the purpose of that?

 

[ericgibbs]

Actually another question, how did you know that the two outputs were 180 out of phase and what is the purpose of that?

hi,
As Ron is not here at the moment, I will jump in.

The lower amp inside the LM4864 circuit diagram, shown in the datasheet, is an inverting amplifier, so the output from that will be 180deg phase shifted from the upper amp output.

The purpose of the 180deg is the that speaker is driven by a 'push pull' signal, ie: the output is effectively double drive

E.