Автор: Taushicage
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Extended resistance element 10' is in the form of a linear touch panel surface, so that resistance r1 is directly proportional to the distance between end or boundary 11' and any selected touch point 18'. When the user's finger F touches the extended resistance element 10' at point 18', a small current flows through his body impedance, which is schematically represented by a lumped impedance 17', to ground.
Operational amplifiers 20 and 21 maintain the ends 11' and 14', respectively, of the extended resistance element 10' at the same instantaneous potential as the a-c output of signal generator 24 by supplying currents through feedback resistors 22 and 23, respectively.
The current through feedback resistor 23, which is equal in magnitude and opposite in polarity to the current through r2, produces a voltage which is added to the output of signal generator 24 to give an instantaneous potential at the output of operational amplifier v. Subtractor 27 instantaneously removes the output voltage of signal generator 24 from v21, and rectifier 28 converts the a-c signal into a d-c level proportional to the average magnitude of current i2 : v.
It shows a pattern of conductive segments that is inlaid or overlaid as by silk screen printing on a uniform sheet of resistive material to produce what is termed a linearized resistive surface in my application Ser. When appropriate voltages are applied to corner terminations A, B, C, and D, a uniform electric field with controllable amplitude and direction is created on the surface. I have found that the structure of FIG.
If there currents are measured with the spot corresponding to selected touch point 18' at various locations, it can be shown that they are related to the X and Y coordinates of the spot by the equations: EQU4 wherein k1 is an offset, k2 is a scale factor, and iA, iB etc. In FIG. In actual practice the resistive layer may be trimmed or limited to the outermost conductive segments Similar results have been obtained with a rectangular linearized resistive surface possessing a non-square aspect ratio and fabricated with the construction shown in FIG.
In this case constants k1 and k2 differ for the X and Y equations. This embodiment is an extension to two dimensions of the principle embodied in FIG. When the linearized resistive surface is touched by the user, small currents flow through the four terminations A, B, C, and D. Voltages proportional to these currents are developed across the feedback resistors , , , and of the four input amplifiers , , and , respectively, as the amplifiers follow the output of oscillator The amplifier outputs are applied to four high-pass filters , , and respectively.
These filters are not essential to system operation, but were added to eliminate the 60 -Hz signals which may be picked up by the user's body from power wiring. Filters attenuate Hz signals while passing the oscillator frequency, which is typically 20 kHz. In a later-disclosed embodiment, the 60 Hz or any radiant ambient environmental energy field may be used as a source of position signal energy for the touch panel surface.
The resulting signals are rectified in rectifiers , , and , respectively, to provide d-c levels proportional to the amplitudes of the a-c signals. The levels corresponding to the top two terminations A and B of the linearized resistive surface are summed by the Y-axis summer , the levels corresponding to the right-hand two terminations B and C are summed by the X-axis summer , and all four levels A, B, C and D are summed by the all-channel summer to provide a denominator input for the two dividers and These dividers and then operate on the Y-axis and X-axis sums to perform the divisions of equation 10 above, and output amplifiers and with adjustable offset and and gain provide the desired X-axis and Y-axis outputs described by Equation A level detector monitors the all-channel summer output and switches state when the user's finger touches the linearized resistive surface It is not necessary for the user's finger to make ohmic contact with the linearized resistive surface; a thin insulating layer may be deposited over the resistance material for protection, and capacitive coupling through the insulating layer will still provide adequate current for system operation.
Termination A of the linearized resistive surface is connected to the inverting input of operational amplifier A1 through isolating resistor R2. The noninverting input is connected to Es, the output of a Wien-bridge oscillator operational amplifier A9 through a voltage divider, consisting of R35 and R37 all of which corresponds to oscillator shown in the block diagram of FIG.
The output of operational amplifier A1 goes through a filter comprising capactors C1 and C2 and resistors R3 and R The inverting input of operational amplifier A5 is used as a summing node and hence corresponds to adder of FIG. A phase shifter, operational amplifier A10 e. The amplitude and phase of Es are adjustable, so that the effect of the capacitance between the linearized resistive surface and ground can also be cancelled.
The circuit of operational amplifier A5 is a precision rectifier providing a d-c output for constant finger position, e. Identical circuitry is provided for the other three terminations B, C and D of the linearized resistive surface, using operational amplifiers A2, A3, A4, A6, A7 and A8.
Two ADJ analog multipliers and are connected to divide e. Operational amplifier A14 level detector of FIG. Diodes D12 and D13 and resistors R78 and R82 constitute a pull-down circuit to cause the X and Y outputs to go off-scale when the linearized resistive surface is not touched; removing a jumper disables this feature. It will be seen that many alternative techniques can be used to accomplish the same normalizing function as the dividers in FIGS. For instance, digital outputs can be easily obtained by applying the X and Y axis sums to voltage-to-frequency converters, and counting the output pulses for a period of time proportional to the output of the all-channel summer.
Analog normalization can be accomplished by controlling the gains of the input amplifiers with a feedback loop so as to maintain the output of the all-channel summer at a constant value. Another normalization technique is illustrated in FIG. The touch panel's linearized resistive surface 40 is deposited on, or bonded to, a rigid supporting plate 41, each corner of which rests on one of four piezoelectric elements.
Two of these, labeled 42 and 43, appear in FIG. One terminal of each of the four piezoelectric elements 42', 43', 44 and 45 is connected in common, with the same polarity being observed for all four elements.
The other terminals are connected to four inputs of voltage-summing circuit The voltage outputs of the four piezoelectric elements are summed by voltage-summing circuit 46 to provide a vertical axis output proportional to the net downward pressure exerted on the linearized resistive surface by the user's finger. The geometry of the conductive segments between each two corners is the same as the geometry of the conductive segments between adjacent corners in FIG.
A uniform electric field can also be established in this triangular surface in a manner analogous to that described for the rectangular surfaces as described in patent application Ser. In fact, it is possible to provide a uniform field, as disclosed in my above-identified patent application, in conjunction with the location-or position-detecting apparatus and method of the present invention. I have found that if all three terminals A', B', C' are held at the same potential and a spot or selected touch point on the linearized resistive surface is held at a different potential, the currents flowing through the terminations at corners A', B' and C' follow the relationship: EQU5 wherein dA is the perpendicular distance from the side opposite corner A' to the current source; iA, iB and iC are the currents through the corresponding terminations; and k1 and k2 are offset and scale constants.
It will be seen that, given any two of the three distances dA, dB and dC, the two-dimensional location of the selected touch point is determined. When the linearized resistive surface is touched by the user at any selected touch point , currents flow through the terminations at corners A', B' and C'.
Voltages proportional to these currents are developed across the feedback resistors , and of the three input amplifiers , and , respectively as the amplifiers follow the output of oscillator The amplifier outputs go to high-pass filters , and , and the outputs of these filters are supplied to adders , and which receive the Es signal from inverter to remove the oscillator signal component as described above for the embodiment illustrated in FIG. The resulting signals are rectified by rectifiers , and to produce d-c levels proportional to the currents through the three terminations A', B' and C' of the triangular linearized resistive surface An adder sums the three d-c levels.
In this implementation of my invention, the ratios required by Equation 11 are obtained by maintaining the sum of the three d-c levels at a constant amplitude with a feedback loop. As shown in FIG. The output of differential amplifier is used as an automatic gain control voltage to control the amplitude of the output of oscillator Each of the three d-c levels also goes to a digital track-and-hold circuit , and These circuits, the details of which are described in the literature See the article by Eugene L.
When these circuits switch from track to hold mode, a stored digital number maintains the output at its last value. The digital outputs of the track-and-hold circuits are connected to logarithmic attentuators , and Adder combines the outputs of the attenuators to produce the mixer output.
Switching of the operating mode of the track-and-hold circuits , and is controlled by a level detector analogous in function to the level detector of FIG. When the user touches the linearized resistive surface , the presence of his finger is sensed by the level detector and the track-and-hold circuits , and are switched to the track mode of operation.
When he removes his finger, the track-and-hold circuits , and switch to the hold mode and maintain the last attenuator settings until the user touches the touch panel again. It will be appreciated that besides use as an audio mixer this technique can be applied to various other arts where it is desired that a plurality of signal levels be provided at a single touch or input by the user. This technique has the advantage that it imposes no voltage on the body of the user.
Although the voltages and currents imposed on the user by the previously discussed embodiments are far below levels that can be felt, and even farther below levels that can do bodily harm, some corporations prefer that products they use impose no voltages or currents whatsoever on the user.
Touch panels made using this technique should also be less expensive, as fewer circuit elements are required. In the touch panel of FIG. These currents flow to virtual ground at ends 11" and 14" of the resistance element.
Ground potential is maintained at ends 11" and 14" by currents supplied through feedback resistors 22' and 23' by operational amplifiers 20' and 21'. Rectifiers 26' and 27' convert the output voltages of operational amplifiers 20' and 21' to d-c levels, which are summed by adder 29'. Divider 30' divides the amplitude of one level by the sum of both to produce an output proportional to the position of the point touched.
Applications are envisioned for a multiplicity of one-axis touch panels, each operated by a different finger of the user, and for combinations of one-, two- and three-dimensional touch panels. Two one-axis touch panels can be maintained orthogonally related to provide X and Y coordinate readouts for various manually controlled devices. The circuit of FIG. The circuit relies instead on impedance 29, the impedance of the user's body between the points 18''' and 18"", to simultaneously complete the circuits of FIG.
A suitable resistive surface for this purpose can be made by depositing indium tin oxide on transparent polyester film. The pattern of conductive segments is then silk-screened on the resistive surface with silver-filled expoxy paint. A slight modification of the pattern of FIG. Subtraction As subtraction is merely the addition of a negative number, we can implement subtraction in our ALU as long as we can add, and we can convert numbers to their negatives. Since finding the negative of a number requires flipping all the bits, we pass the bits of B through NOT gates.
To add 1, we set the carry bit of the rightmost bit, 20, equal to 1. This will yield our result A — B. We take the contents of register A, and feed it into the rows corresponding to our first number, and we take the contents of register B, and feed it into the rows corresponding to our second number. To allow for subtraction, we have an option to invert the bits of B and to add 1 to the sum effectively adding -B, as described above. Finally, we have the interface from the ALU to the bus, which requires tri-state buffers, allowing us to control whether we are outputting onto the bus or are disconnected from it.
Engineering Challenges The primary challenge I ran into this week when trying to test and debug the circuit was wiring everything. The image you see is the version after I had cleaned it up somewhat. As you can probably tell, this is not a very efficient way to do things, nor was it very robust, since I kept jostling other wires out of their slots.
The white wires allow the testing module to stay plugged in to the small bus section, which improved convenience a lot. Another challenge I encountered was miswiring the ports between the binary adders and to the tri-state buffers. The problem with wiring the connections neatly and flat to the breadboard is that, if you need to adjust the lengths on the wires such as if you need to correct the port connections , you have to redo the wires entirely, which is pretty costly in terms of time.
The final product from this week is the ALU, allowing for 8-bit addition and subtraction from the A and B registers.
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Electrical Engineering: Ch 5: Operational Amp (8 of 28) Summing Amplifier (Non-Inverting)
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