hi,Originally Posted by mondo8205
Get the datasheet for an AD694 IC, depending upon your AC signal you may need an amplifier.
AC Signal Amplitude converted to a 4-20mA Signal
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2nd May 2012 02:16 PM #1mondo8205
AC Signal Amplitude converted to a 4-20mA Signal
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?
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2nd May 2012 03:00 PM #2ericgibbs
Super Moderator0Eric " Good enough is Perfect "
I will NOT answer PM's requesting technical help, please use the Forum
"Nigels Asm tutorials:" www.winpicprog.co.uk/
"Ian Rogers 'C' conversion of Nigels Asm tutorials:" http://www.electro-tech-online.com/c...torials-c.html
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2nd May 2012 03:02 PM #3ronsimpson
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.0
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2nd May 2012 03:04 PM #4ronsimpson
Is the output linear or log (in db). This is audio so db might be best.
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2nd May 2012 03:22 PM Thread Starter #5mondo8205
I am using this http://www.mouser.com/Search/Product...932-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 http://www.mikroe.com/eng/downloads/get/1444/mic_amp_manual_v100.pdf.0
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2nd May 2012 04:30 PM #6ronsimpson
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.
http://www.allaboutcircuits.com/vol_3/chpt_3/5.html
http://www.afrotechmods.com/videos/p...or_circuit.htm0
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2nd May 2012 04:59 PM Thread Starter #7mondo8205
Thank you so much! This will definitely help me out!
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3rd May 2012 12:53 PM Thread Starter #8mondo8205
Actually another question, how did you know that the two outputs were 180 out of phase and what is the purpose of that?
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3rd May 2012 01:02 PM #9ericgibbs
Super Moderatorhi, Originally Posted by mondo8205
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.0Last edited by ericgibbs; 3rd May 2012 at 01:03 PM.
Eric " Good enough is Perfect "
I will NOT answer PM's requesting technical help, please use the Forum
"Nigels Asm tutorials:" www.winpicprog.co.uk/
"Ian Rogers 'C' conversion of Nigels Asm tutorials:" http://www.electro-tech-online.com/c...torials-c.html
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