IFD:Printing Acoustic Interfaces/acoustic sensing circuits: Difference between revisions

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 ==Printed Capacitive (Condenser) Microphone==
 However, the circuits where still capable of sensing vibrations, because of another effect that was not anticipated, but stronger in the actual circuit: The '''capacitive effect''' of the two opposing coils. This capacitive effect can be made larger by providing a bigger overlapping area of the two conductors that form the microphonic surface. That simplified our print designs a little, because we were not forced to print coils as two port devices, but could use two rectangular shapes with a single port each. Leading to lesser connections and no jumper wires on our paper printed microphones.
-[[File:receiving_circuit.png|1200px]]
+Our actual designs are sender-receiver type circuits, utilizing the radio frequency signal transmission as a means to get rid of mains hum and other interferences. At the same time, this provides the flexibility to detect different frequencies with a single receiving circuit. We will use a high frequency changing voltage (approx. 300Khz) on the sending capacitor plate, that we will receive on the other capacitor plate. When we change the distance between the plate, the capacitance changes and with it, the actual amplitude (volume) of this high frequency tone increases or decreases. To get the actual volume information of this high frequency tone, we use the half wave rectifier. This circuit is commonly used in radio signal receivers, where the amplitude of the frequency of a radio station is changing with the actual transmitted sound wave. This is called Amplitude Modulation (AM Radio).
-Our actual designs are sender-receiver type circuits, utilizing the radio frequency signal transmission as a means to get rid of mains hum and other interferences. At the same time, this provides the flexibility to detect different frequencies with a single receiving circuit.
+[[File:sender.png| thumb| left| triangle wave generator]]
+The sending circuit is a very simple triangle wave generator using parasitic effects of the circuit board to reach high frequencies and at the same time provide minimal component counts. The output of the sending circuit is putting and removing charge to one plate of the printed capacitor in the shape of a high frequency triangle wave.
+[[File:receiving_circuit.png| thumb| left| receiving circuit]]
+The receiving capacitor plate's capacity is modulated by the high frequency triangle wave from the first plate, as well as the distance from this first plate. The distance modulation in audio range (0-20kHz) is what we are interested in detecting. First we pre-amplify the modulated signal from the receiving capacitor plate with a charge mode amplifier, than we detect the envelope of the high frequency wave with a half wave rectifier and a low pass filter and finally amplify and buffer the resulting envelope. The output of this receiver circuit corresponds to the distance of the two capacitor plates in audio rate, the signal we were originally interested to detect.
+The following two diagrams show the breadboarded sending and receiving circuits using two TL072's or one TL074. Note that instead of four AA batteries we are using two 9V blocks two get a dual power supply of +-9V.
 [[File:microphone_amp_tl072_Steckplatine.png | thumb|left| TL072 Version ]]
 [[File:microphone_amp_tl074_Steckplatine.png | thumb|left| TL074 Version ]]
+==Falstad Circuit Simulations==
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