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

Latest revision as of 20:03, 27 June 2019

Printed Transformer Type Microphone

In the first part of the course we explored the possibility of a transformer based microphone, involving printed coil structures on paper. Unfortunately the printed structures have shown a large resistance, making them unsuitable for inducing magnetic field. This is because the strength of the magnetic field is proportional to the amount of current flowing through the coil, which, in turn, is limited by the resistance of the coil. It was found, that by using our printed inkjet techniques, the resistance of coils was too large by approximately two orders of magnitude. Goal: 4-20 Ohms, Actual circuits: 500-1000 Ohms. You can find the explored circuits below

transformer microphone and 555 timer oscillator (outdated circuits)

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. 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).

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.

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.

TL072 Version

TL074 Version

Falstad Circuit Simulations

Receiving Circuit

Charge Mode Amplifier for Capacitive Microphone

275kHz Receiver

309 kHz Receiver

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+==Printed Transformer Type Microphone==
+In the first part of the course we explored the possibility of a transformer based microphone, involving printed coil structures on paper. Unfortunately the printed structures have shown a large resistance, making them unsuitable for inducing magnetic field. This is because the strength of the magnetic field is proportional to the amount of current flowing through the coil, which, in turn, is limited by the resistance of the coil. It was found, that by using our printed inkjet techniques, the resistance of coils was too large by approximately two orders of magnitude. Goal: 4-20 Ohms, Actual circuits: 500-1000 Ohms. You can find the explored circuits below
 [[/transformer microphone and 555 timer oscillator (outdated circuits)/]]
+==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.
+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).
+[[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.
-[[File:transformer_and_rectifier.gif|thumb|right|A Radio Signal Receiver [http://hyperphysics.phy-astr.gsu.edu/hbase/Electronic/amfmdet.html#c1 source] ]]
+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.
-To get rid of our big magnets, we build an electro magnet with the help a a sending coil that will build up a magnetic field. When the current though this sending coil changes, it will induce a magnetic field, that we can use to induce a current in the second (receiving) coil. Two coils that share their magnetic flux via the air are called an "air core transformer". Both coils will be printed on paper, but on different sheets, leaving a gap filled with air. If the sheets are close together the second coil induces more current and lesser when it is further away. It is important, that the currents change constantly, because only changing currents can induce magnetic fields. We will use a high frequency changing current (50Khz) on the sending coil, that we will receive on the other coil. When we change the distance between the coils, 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 the frequency of a radio station is changing with the actual transmitted sound wave. This is called Amplitude Modulation (AM Radio).
-====Sender: Square Wave Generator Circuit====
-[[File:555_Pinout_800px.png|thumb|left|555 Timer Chip Pinout [https://de.wikipedia.org/wiki/NE555      source] ]]
-To send the high frequency current, we will use the 555 Timer chip configured as a square wave generator. This circuit has little components and is comparably easy to build. It uses only one capacitor and one resistor to set the frequency of the square wave.
-You can find the circuit in the link below. Be sure to match the pinout in the circuit according to the figure on the left.
-[http://www.falstad.com/circuit/circuitjs.html?cct=$+1+0.000005+1.8479586061009856+50+5+43%0Ax+-411+-176+-251+-173+4+18+555%5CsTimer%5CsOscillator%0A165+-304+-48+-192+-48+6+14.99990131685941%0Ar+-416+-32+-416+64+0+100000%0Ac+-416+112+-416+176+0+1e-10+5.13158725767721%0Ag+-208+112+-208+144+0%0Aw+-304+48+-304+80+0%0Aw+-416+80+-320+80+0%0Ag+-416+176+-416+208+0%0Aw+-176+16+-112+16+0%0Aw+-112+16+-112+-112+0%0Aw+-112+-112+-416+-112+0%0Aw+-416+-112+-416+-32+0%0AR+-240+-80+-240+-144+0+0+40+15+0+0+0.5%0Aw+-176+-16+-176+-80+0%0Aw+-176+-80+-240+-80+0%0Aw+-320+80+-304+80+0%0Aw+-416+64+-416+80+0%0Aw+-416+80+-416+112+0%0Ao+9+1+0+5640+20+0.000390625+0+2+9+3%0A 555 Timer Oscillator]
-====Receiver: Half Wave Rectifier Circuit====
-When we change the distance between the coils in our paper built air core transformer, the actual amplitude (volume) of the high frequency tone increases or decreases. To get the actual volume information of this high frequency tone, we use the half wave rectifier. The circuit consists of a diode, a resistor and a capacitor. The diode lets only the positive current travel through it (in the direction implied by the arrow) and blocks the negative current, running against its direction. This leaves us with the positive half of the sending waveform. The final thing we need to do is average this positive half wave to get the average amplitude of this half wave. This averaging is achieved by the capacitor and the resistor. When the capacitor is charged, and there is no voltage on the right side of the diode, a discharge current will flow through the resistor to ground. The amount of discharge current is controlled by the resistor. The bigger the resistance the less discharge current will flow. We need to adapt  the value of this resistor to have the capacitor discharge just a little bit, before the next positive half wave arrives at the right side of the diode. Then, if we receive less current in the second coil, the average charge on the capacitor decreases, following the actual acoustic waveform between our two sheets of paper.
-[http://www.falstad.com/circuit/circuitjs.html?cct=$+1+6.25e-7+0.9891409633455756+50+5+43%0Ac+-208+-16+-208+32+0+1e-8+2.682978234748702%0Ag+-352+32+-352+64+0%0Ag+-496+32+-496+64+0%0AT+-496+-16+-352+32+0+4+1+0.0007569310440390104+-0.0009922610211878194+0.999%0Av+-496+-16+-496+32+0+1+50000+5+0+0+0.5%0Ar+-272+-16+-272+32+0+10000%0Ad+-352+-16+-272+-16+2+1N4148%0Aw+-352+32+-272+32+0%0Aw+-208+-16+-272+-16+0%0Aw+-272+32+-208+32+0%0Ax+-605+-91+-218+-88+4+24+Half%5CsWave%5CsRectifier%5Csand%5CsTransformer%0Ax+-612+114+-182+117+4+8+To%5Csget%5Csrid%5Csof%5Csour%5Csbig%5Csmagnets,%5Cswe%5Csbuild%5Csan%5Cselectro%5Csmagnet%5Cswith%5Csthe%5Cshelp%5Csa%5Csa%5Cssending%5Cscoil%5Csthat%5Cswill%5Csbuild%5Csup%5Csa%5Csmagnetic%5Csfield.%5Cs%5Cs%0Ax+-614+131+-94+134+4+8+When%5Csthe%5Cscurrent%5Csthough%5Csthis%5Cssending%5Cscoil%5Cschanges,%5Csit%5Cswill%5Csinduce%5Csa%5Csmagnetic%5Csfield,%5Csthat%5Cswe%5Cscan%5Csuse%5Csto%5Csinduce%5Csa%5Cscurrent%5Csin%5Csthe%5Cssecond%5Cs(receiving)%5Cscoil.%0Ax+-614+148+-60+151+4+8+Both%5Cswill%5Csbe%5Csprinted%5Cson%5Cspaper,%5Csbut%5Cson%5Csdifferent%5Cssheets.%5CsIf%5Csthe%5Cssheets%5Csare%5Csclose%5Cstogether%5Csthe%5Cssecond%5Cscoil%5Csinduces%5Csmore%5Cscurrent%5Csand%5Cslesser%5Cswhen%5Csit%5Csis%5Csfurther%5Csaway.%0Ax+-613+167+-219+170+4+8+It%5Csis%5Csimportant,%5Csthat%5Csthe%5Cscurrents%5Cschange%5Csconstantly,%5Csbecause%5Csonly%5Cschanging%5Cscurrents%5Cscan%5Csinduce%5Csmagnetic%5Csfields.%5Cs%0Ax+-614+186+-43+189+4+8+We%5Cswill%5Csuse%5Csa%5Cshigh%5Csfrequency%5Cschanging%5Cscurrent%5Cs(50Khz)%5Cson%5Csthe%5Cssending%5Cscoil,%5Csthat%5Cswe%5Cswill%5Csreceive%5Cson%5Csthe%5Csother%5Cscoil.%5CsWhen%5Cswe%5Cschange%5Csthe%5Csdistance%5Csbetween%5Csthe%5Cscoils,%0Ax+-615+203+9+206+4+8+the%5Csactual%5Csamplitude%5Cs(volume)%5Csof%5Csthis%5Cshigh%5Csfrequency%5Cstone%5Csincreases%5Csor%5Csdecreases.%5CsTo%5Csget%5Csthe%5Csactual%5Csvolume%5Csinformation%5Csof%5Csthis%5Cshigh%5Csfrequency%5Cstone,%5Cswe%5Csuse%5Csthe%5Cshalf%5Cswave%5Csrectifier.%0Ao+6+1+0+4099+20+0.0015625+0+2+6+3%0Ao+8+1+0+4099+5+0.003125+1+2+8+3%0A Half wave rectifier and Transformer Coils]
-====Full Circuit====
 [[File:microphone_amp_tl072_Steckplatine.png | thumb|left| TL072 Version ]]
 [[File:microphone_amp_tl074_Steckplatine.png | thumb|left| TL074 Version ]]
-[http://www.falstad.com/circuit/circuitjs.html?cct=$+1+6.25e-7+0.2500940013662129+50+5+43%0A165+-224+32+-192+32+6+14.912728026205588%0Ar+-336+128+-336+16+0+10000%0Aw+-224+128+-336+128+0%0Aw+-336+128+-336+160+0%0Aw+-336+160+-224+160+0%0Aw+-336+16+-336+-64+0%0Aw+-336+-64+-48+-64+0%0Aw+-48+-64+-48+96+0%0Aw+-48+96+-96+96+0%0Ac+-336+160+-336+208+0+1e-9+4.896848769281841%0Ag+-336+208+-336+224+0%0Aw+-96+64+-96+0+0%0Aw+-96+0+-160+0+0%0AR+-160+0+-160+-48+0+0+40+15+0+0+0.5%0Ag+-128+192+-128+224+0%0Ac+-160+192+-160+240+0+1.0000000000000001e-7+9.99999999999783%0Ag+-160+240+-160+272+0%0Aw+304+144+368+144+0%0Aw+368+96+304+96+0%0Aw+224+144+304+144+0%0Ad+224+96+304+96+2+1N4148%0Ar+304+96+304+144+0+10000%0AT+80+96+224+144+0+4+1+0.045662539372062244+-0.00046382702123317076+0.999%0Ac+368+96+368+144+0+1e-8+11.37069202361252%0Aw+80+96+-48+96+0%0Ag+80+144+80+176+0%0Ag+96+352+96+384+0%0Aw+96+304+-32+304+0%0Ac+384+304+384+352+0+1e-8+11.37069202361196%0AT+96+304+240+352+0+4+1+0.0406078464966577+-0.0004638270212340074+0.999%0Ar+320+304+320+352+0+10000%0Ad+240+304+320+304+2+1N4148%0Aw+240+352+320+352+0%0Aw+384+304+320+304+0%0Aw+320+352+384+352+0%0Aw+-48+96+-48+304+0%0Aw+-48+304+-32+304+0%0Ao+7+1+0+4098+20+0.003125+0+2+7+3%0Ao+23+1+0+4099+20+0.00625+1+2+23+3%0A One Sending and two Receiving Circuits]
+==Falstad Circuit Simulations==
+[http://www.falstad.com/circuit/circuitjs.html?cct=$+1+1.0416666666666667e-7+5.459815003314424+50+5+43%0Ag+-384+32+-384+48+0%0Av+-560+-48+-480+-48+0+6+300000+1+0+0+0.5%0Ax+-218+-233+-5+-230+4+24+Receiver%5Cs@%5Cs309kHz%0Aa+-384+16+-272+16+8+15+-15+1000000+-0.000004640178701983729+0+100000%0A207+336+-64+384+-64+4+output%0Aw+-272+16+-272+-48+0%0Aw+-384+-48+-384+0+0%0Ar+-368+-48+-288+-48+0+100000%0Aw+-368+-48+-384+-48+0%0Aw+-288+-48+-272+-48+0%0Ag+-560+-48+-560+-16+0%0Ac+-384+-48+-480+-48+0+1e-11+0.6583435098491084%0Ac+-384+-96+-272+-96+0+1e-11+-0.4640225103770748%0Aw+-384+-96+-384+-48+0%0Aw+-272+-96+-272+-48+0%0Aw+320+-128+336+-128+0%0Aw+240+-128+224+-128+0%0Ar+240+-128+320+-128+0+100000%0Aw+224+-128+224+-80+0%0Aw+336+-64+336+-128+0%0Aa+224+-64+336+-64+8+15+-15+1000000+0.06877102612285581+0.06877859093572933+100000%0Ar+144+-128+224+-128+0+10000%0Al+-176+-48+-176+16+0+0.00033+-0.00003235853297545487%0Ag+-176+16+-176+48+0%0Ac+-112+-48+-112+16+0+3.3e-10+-0.08826364906288835%0Aw+-176+-48+-112+-48+0%0Ad+-48+-48+48+-48+2+default%0Ac+48+-48+48+16+0+1e-9+0.06877929646277242%0Ar+112+-48+112+16+0+100000%0Ag+48+16+48+48+0%0Aw+48+16+112+16+0%0Aw+48+-48+112+-48+0%0Ac+112+-48+224+-48+0+1e-7+7.055270430933458e-7%0Ag+144+-128+144+-112+0%0Ar+-272+-48+-176+-48+0+1000%0Ac+-48+-48+-48+16+0+4.7e-10+-0.08826364906288835%0Aw+-112+-48+-48+-48+0%0Ag+-112+16+-112+48+0%0Ag+-48+16+-48+48+0%0Ab+-459+-176+-262+99+0%0Ab+-247+-176+-28+98+0%0Ab+-16+-177+130+98+0%0Ab+139+-177+349+97+0%0Ab+-482+-175+-594+99+0%0Ax+-566+-142+-518+-139+4+12+mic%5Csinput%0Ax+-423+-145+-283+-142+4+12+charge%5Csmode%5Cspre-amplifier%0Ax+-203+-145+-78+-142+4+12+309%5CskHz%5Csbandpass%5Csfilter%0Ax+3+-144+99+-141+4+12+half%5Cswave%5Csrectifier%5Cs%0Ax+3+-123+99+-120+4+12+and%5Cslow%5Cspass%5Csfilter%0Ax+200+21+282+24+4+12+output%5Csamplifier%0Ao+1+64+0+4098+1.25+0.1+0+2+1+3%0Ao+4+64+0+4099+2.5+0.00009765625+1+2+4+3%0Ao+25+4+0+5122+0.625+0.1+2+2+25+3%0A Receiving Circuit]
-===Printed Capacitive (Condenser) Microphone===
 [http://www.falstad.com/circuit/circuitjs.html?cct=$+1+0.000005+38.696464541249114+50+5+43%0Ag+-384+32+-384+48+0%0Av+-608+-48+-480+-48+0+1+100+1+0+0+0.5%0Ax+-605+-177+-207+-174+4+18+Charge%5CsMode%5CsAmplifier%5Csfor%5CsCapacitive%5CsMicrophone%0Aa+-384+16+-272+16+8+15+-15+1000000+1.0518728194493546e-7+0+100000%0A207+-48+32+0+32+4+output%0Aw+-272+16+-272+-48+0%0Aw+-384+-48+-384+0+0%0Ar+-368+-48+-288+-48+0+3300000%0Aw+-368+-48+-384+-48+0%0Aw+-288+-48+-272+-48+0%0Ag+-608+-48+-608+-32+0%0Ac+-384+-48+-480+-48+0+1e-11+0.8509954347565091%0Ac+-384+-96+-272+-96+0+1e-11+0.010518833381775491%0Aw+-384+-96+-384+-48+0%0Aw+-272+-96+-272+-48+0%0Aw+-64+-32+-48+-32+0%0Aw+-144+-32+-160+-32+0%0Ar+-144+-32+-64+-32+0+100000%0Aw+-160+-32+-160+16+0%0Aw+-48+32+-48+-32+0%0Aa+-160+32+-48+32+8+15+-15+1000000+-0.000010508114998345217+0+100000%0Ag+-160+48+-160+64+0%0Ar+-272+16+-160+16+0+1000%0Ao+1+64+0+4098+1.25+0.1+0+2+1+3%0Ao+4+64+0+4099+2.5+0.00009765625+1+2+4+3%0A Charge Mode Amplifier for Capacitive Microphone]