Low power cordless magnetic field digitizer with differential grid sensing and synchronous position demodulation

What is claimed is:

1. A digitizing system including a tablet and a cordless pointing device, comprising in combination:

(a) a plurality of pairs of position resolving conductors each of which forms one or more differential coil elements in the tablet, receiving a magnetic signal transmitted by the pointing device;

(b) first, second, third, and fourth carrier recovery conductors in the tablet receiving the magnetic signal;

(c) position resolving circuitry including

i. a differential amplifier,

ii. multiplexing circuitry selectively coupling various pairs of the position resolving conductors to a pair of inputs of the differential amplifier,

iii. synchronous demodulating circuitry coupled to an output of the differential amplifier, having a first input responsive to selected signals induced onto the differential coil elements and a second input responsive to a recovered pointing device carrier signal for producing position resolving information,

iv. an analog-to-digital converter having an input coupled to an output of the synchronous demodulating circuitry to produce digital position resolving information;

(d) a computerized control system having a plurality of inputs coupled to a plurality of outputs, respectively, of the analog-to-digital converter, and a plurality of outputs conductors coupled to selection inputs of the multiplexing circuitry;

(e) carrier recovery circuitry including

i. a first controllable gain differential amplifier having a pair of inputs coupled to the first and second carrier recovery conductors, respectively, and a second controllable gain differential amplifier having a pair of inputs coupled to the third and fourth carrier recovery conductors, respectively,

ii. a first frequency doubler circuit having an input responsive to an output of the first controllable gain amplifier and a second frequency doubler circuit having an input responsive to an output of the second controllable gain amplifier,

iii. signal combining circuitry having first and second inputs coupled to outputs of the first and second frequency doubler circuits, respectively,

iv. a threshold generating circuit having an input coupled to the output of the signal combining circuit and an output coupled by an error amplifier circuit to gain control inputs of the first and second controllable gain amplifiers,

v. a signal slicing, limiting circuit having a first input coupled to an output of the signal combining circuit and a second input coupled to an output of the threshold generating circuit,

vi. a phase-locked-loop circuit having an input coupled to the output of the signal slicing, limiting circuit and producing a double frequency output signal;

vii. a divide-by-two circuit having an input coupled to receive the double frequency output signal from the phase-locked-loop circuit to produce the recovered pointing device carrier signal; and

(f) means in the computerized control system for measuring and decoding the frequency of the magnetic signal and resolving the position of the pointing device in response to the analog-to-digital converter.

2. The digitizing system of claim 1 wherein the magnetic signal has a frequency in the range of approximately 300 to 550 kilohertz.

3. The digitizing system of claim 1 wherein the differential amplifier is a controllable gain differential amplifier, the computerized control system being coupled to the differential amplifier and operating to control the gain thereof.

4. The digitizing system of claim 1 wherein the multiplexing circuitry includes a first section having a first group of inputs coupled to a first group of the position resolving conductors, and a second section having a second group of inputs coupled to a second group of the position resolving conductors.

5. The digitizing system of claim 4 wherein the threshold generating circuit is implemented by means of a low-pass filter and the signal slicing, limiting circuit is implemented by means of a comparator.

6. The digitizing system of claim 5 wherein the first and second frequency doubler circuits are implemented by means of full-wave rectifiers having essentially zero switching thresholds.

7. The digitizing system of claim 1 including means for performing post detection signal integration using the analog-to-digital converter.

8. The digitizing system of claim 1, wherein the plurality of pairs of position resolving conductors recited in Paragraphs (a) and (b) extend generally in a first direction along a surface of the tablets and further including another plurality of similarly arranged and connected pairs of position resolving conductors that extend along the surface of the tablet generally in a second direction orthogonal to the first direction, and a plurality of similarly arranged and connected carrier recovery conductors that extend along the surface of the tablet generally in the second direction.

9. The digitizing system of claim 1, wherein the decoding means recited in Paragraph (f) further includes means for identifying the type of the pointing device.

10. The digitizing system of claim 9, wherein the position resolving means recited in Paragraph (f) resolves the position of the pointing device in accordance with the type of the pointing device.

11. In a digitizing system including a tablet and a pointing device, a carrier recovery circuit comprising in combination:

(a) a first controllable gain amplifier having an input coupled to a first carrier recovery conductor in the tablet, respectively, and a second controllable gain amplifier having an input coupled to a second carrier recovery conductor in the tablet, respectively;

(b) a first frequency doubler circuit having an input responsive to an output of the first controllable gain amplifier and a second frequency doubler circuit having an input responsive to an output of the second controllable gain amplifier;

(c) signal combining circuitry having first and second inputs coupled to outputs of the first and second frequency doubler circuits respectively;

(d) a threshold generating circuit having an input coupled to the output of the signal combining circuit and an output coupled by an error amplifier circuit to gain control inputs of the first and second controllable gain amplifiers;

(e) a signal slicing, limiting circuit having a first input coupled to an output of the signal combining circuit and a second input coupled to an output of the threshold generating circuit; and

(f) a phase-locked-loop circuit having an input coupled to the output of the comparator that is in a precise phase relationship to a carrier signal induced in the first and second carrier recovery conductors.

12. In a digitizing system, including a tablet and a pointing device, oscillator circuitry in the pointing device, comprising in combination:

(a) a power source having first and second terminals;

(b) an inductor having a center tap connected to a first terminal of the power source;

(c) first and second transistors, an emitter of the first transistor being coupled to an emitter of the second transistor and to a first terminal of a current source having a second terminal connected to the second terminal of the power source, a collector of the first transistor being coupled to a first terminal of the inductor, a collector of the second transistor being coupled to a second terminal of the inductor, a base of the first transistor being coupled by a first capacitor to the collector of the second transistor, a base of the second transistor being coupled by a second capacitor to the collector of the first transistor;

(d) a third capacitor coupled between the collectors of the first and second transistors; and

(e) a bias voltage source coupled to the bases of the first and second transistors by first and second resistors, the inductor and the third capacitor forming a tank circuit, the current source producing a predetermined current, the first and second transistors forming a current switch that alternately switches the predetermined current into different parts of the tank circuit,

whereby the power level of a magnetic signal transmitted from the inductor is substantially independent of the voltage of the power source and the inductor radiates maximum power at a self-resonant frequency of the tank circuit regardless of the capacitance coupled to the inductor.

13. In a digitizing system, the oscillator circuitry of claim 12 including a plurality of frequency shifting capacitors, each having a first terminal coupled to the collector of the first transistor and a second terminal coupled in response to a plurality of manual switches, respectively, to the collector of the second transistor.

14. In a digitizing system, the oscillator circuitry of claim 12 wherein the voltage of the power source, the inductance of the coil, the capacitance of the third capacitor, and the current supplied by the current source are such that neither of the first and second transistors saturate, whereby power loss of the oscillator circuitry is reduced so that the Q of the oscillator circuitry is increased.

15. In a digitizing system, the oscillator circuitry of claim 12 including a voltage variable capacitive device coupled between the first and second terminals of the inductor and means responsive to a transducer for controlling a voltage across the voltage variable capacitor in response to a signal produced by the transducer.

16. In a digitizing system including a tablet and a pointing device, an improvement in the pointing device comprising a self-resonant, current switched LC oscillator including:

(a) an inductor and a capacitive element coupled to form a self-resonant tank circuit, wherein the inductor radiates a magnetic signal to the tablet;

(b) current source means for supplying a measured amount of current; and

(c) current switching means coupled to the current source means and the tank circuit for alternately switching the measured amount of current into different sections of the tank circuit,

whereby the inductor radiates maximum power at the self-resonant frequency of the oscillator regardless of the capacitance of the capacitive element.

17. In a digitizing system, the improvement of claim 16 including a voltage variable capacitive device coupled across the inductor, and means responsive to a transducer for controlling a voltage across the voltage variable capacitor in response to a signal produced by the transducer.

18. A digitizing system including a tablet and a cordless pointing device, comprising in combination:

(a) a plurality of pairs of position resolving conductors each of which forms one or more differential coil elements in the tablet, receiving a magnetic signal transmitted by the pointing device;

(b) first and second pairs of carrier recovery conductors each including at least one differential coil element;

(c) synchronous demodulating circuitry having a first input responsive to selected signals induced onto the differential coil elements and a second input responsive to a recovered pointing device carrier signal 51 for producing position resolving information;

(d) carrier recovery circuitry including

i. a first controllable gain amplifier having a pair of inputs coupled to the first pair of carrier recovery conductors, respectively, and a second controllable gain amplifier having a pair of inputs coupled to the second pair of carrier recovery conductors,

ii. a first frequency doubler circuit having an input responsive to an output of the first controllable gain amplifier and a second frequency doubler circuit having an input responsive to an output of the second controllable gain amplifier,

iii. signal combining circuitry having first and second inputs coupled to outputs of the first and second frequency doubler circuits, respectively,

iv. a threshold generating circuit having an input coupled to the output of the signal combining circuit and an output coupled by an automatic gain control circuit to gain control inputs of the first and second controllable gain amplifiers,

v. a signal slicing circuit having a first input coupled to an output of the signal combining circuit and a second input coupled to an output of the threshold generating circuit,

vi. a phase-locked-loop circuit having an input coupled to the output of the signal slicing circuit and producing a double frequency output signal;

vii. a divide-by-two circuit having an input coupled to receive the double frequency output signal from the phase-locked-loop circuit to produce the recovered pointing device carrier signal; and

(e) means for resolving the position of the pointing device in response to digital output signals produced by the analog-to-digital converter.

19. A method of operating the digitizing system including a tablet and a pointing device, comprising the steps of:

(a) transmitting a magnetic signal from the pointing device to a plurality of pairs of position resolving conductors, each pair of position resolving conductors including one or more differential coil elements, and also transmitting the magnetic signal to first and second carrier recovery conductors in the tablet;

(b) differentially amplifying selected signals induced onto the position resolving conductors;

(c) applying the differentially amplified signals to a first input of a synchronous demodulating circuit having a second input responsive to a recovered pointing device carrier signal;

(d) essentially simultaneously with steps (b) and (c), differentially amplifying signals induced by the magnetic signal onto the carrier recovery conductors;

(e) doubling the frequency differentially amplified signals of Step (d);

(f) operating a phase-locked-loop circuit in response to the combination of the frequency doubled signals to produce the regenerated pointing device carrier signal 51 which bears one or more precise phase relationships with the magnetic signal;

(g) operating the synchronous demodulating circuitry in response to the differentially amplified signals of Step (b) and the regenerated pointing device carrier signal to produce position resolving information; and

(h) operating on the information resolving position to produce a coordinate representing the location of the pointing device.

20. In a digitizing system including a tablet and a pointing device, a method of regenerating a carrier signal transmitted by the pointing device for use in the tablet, comprising the steps of:

(a) transmitting a signal from the pointing device to first and second sets of carrier recovery conductors in the tablet;

(b) amplifying signals induced onto the carrier recovery conductors by the carrier signal;

(c) doubling the frequency of the amplified signals of Step (b);

(d) operating a phase locked-loop-circuit in response to the frequency doubled signals to produce a regenerated pointing device carrier signal which has a precise phase relationship with the magnetic signal.

21. In a digitizing system including a tablet and a pointing device, a method of regenerating a carrier signal transmitted by the pointing device for use in the tablet, comprising the steps of:

(a) transmitting a signal from the pointing device to first and second sets of carrier recovery conductors in the tablet;

(b) amplifying signals induced onto the carrier recovery conductors by the carrier signal;

(c) doubling the frequency of the amplified signals of Step (b); and

(d) producing a regenerated pointing device carrier signal in response to the frequency doubled signals, which regenerated pointing device carrier signal has a precise relationship with the magnetic signal.

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CROSS REFERENCE TO RELATED APPLICATIONS

This patent application is related to commonly assigned application entitled "POSITION RESOLVING SYSTEM", by Billy C. Fowler, Donald F. Gray, and James L. Rodgers, Ser. No. 769,447, filed on even date herewith, and incorporated herein by reference.

BACKGROUND OF THE INVENTION

Digitizing systems including cordless electric field, and also cordless magnetic field, coupled pointing device (including pens, cursors, mouses, etc.) are well known. Commonly assigned U.S. Pat. Nos. 4,859,814, 4,672,154, and 4,748,295, incorporated herein by reference, are generally indicative of the state of the art. Two types of digitizers, those with "electric field coupling" between the pointer and the digitizing grid and those with "magnetic field coupling" between the pointer and the digitizing grid have been widely used. It is known that such digitizing systems frequently must operate in environments with high electrical noise over a broad frequency spectrum. The major sources of such electrical noise are the fundamental and harmonic frequencies produced by a wide variety of common video monitors. In an office environment, computer monitors are the major source of electrical interference which would interfere with digitizing tablets, but there also are other noise sources, sources such as fluorescent lights and switching power supplies.

These noise sources all generate electric fields and electromagnetic fields that can interfere with the signal to be transmitted from the pointing device to the grid of a digitizer tablet. This is a particular problem in a cordless system. In general the spectrum of the fundamental frequencies of this interference is mostly under 100 KHz and the harmonics are mostly above KHz. In the frequency range from 300 KHz to 550 KHz most of the interference is harmonic in nature and subsequently the levels of interference are significantly less than at frequencies below 100 KHz. Operation in the frequency range from 300 KHz to 550 KHz is possible with a magnetic tablet or digitizer with the added benefit of increased transmission efficiency from the pointing device to the grid conductor due to the improved magnetic coupling at these higher frequencies. However, care must be taken in the design of the grid configuration to ensure that the self-resonance frequency of the grid is sufficiently above the operating frequency range so as to not to result in significant cross coupling between grid conductors so as to result in increased current flow that causes one line or loop to transmit a signal to other lines or loops. Major cross coupling of signals between grid conductors causes unpredictable errors in determining the pointing device position, and such errors are not amenable to usual correction techniques.

In contrast, operation of electric field coupled tablets or digitizers at frequencies much above 100 KHz is difficult or impractical due to the increased pointing device drive power required and the greater shunting effect that grid capacitance has on the "high source impedance"characteristic of an electric field induced grid signal.

Commonly assigned U.S. Pat. No. 4,859,814, entitled "NOISE CANCELLATION IN DIGITIZING SYSTEMS AND METHOD issued on Aug. 22, 1989, by Sciacero, et al. incorporated herein by reference, discloses use of a differential sensing technique in an electric field coupled system to cancel ambient noise.

It is generally accepted by those skilled in the art that digitizing systems based on magnetic field coupling between the pointing device and the digitizing grid are more "robust" than electric field coupling systems in the sense that they are less affected by the nearness of the user's hand, moisture, partial conductivity of materials put on the tablet surface such as certain inks or pencil leads, and conductive or dielectric effects of drawing instruments and other items in close proximity to the digitizing surface, and are generally more accurate and less affected by external environmental effects than electric field coupled digitizing systems.

In the past, magnetic field coupled tablets or digitizers have operated at carrier frequencies less than 100 KHz for several reasons. First, the grid configurations of prior magnetic field coupled tablets, especially those with repeating grid patterns, have had a low self-resonance frequency, and operation at any higher frequency results in uncorrectable positional errors. Second, the gain bandwidth product of the tablet carrier amplification/filtering stages of prior magnetic field coupled tablets has been limited due to the use of low frequency and low cost operational amplifier integrated circuits in these stages instead of discrete video type circuits. Third, the power consumed by the pointing devices of prior magnetic field coupled tablets has been less important because the pointing devices have been connected by a cable to the tablet, so the drive power could be as high as necessary to achieve an adequate induced grid signal-to-interference ratio.

In one prior art system, a cordless magnetic design utilizes a passive pointing device design. In this system a magnetic field is transmitted from the surface or grid and coupled into a high Q tuned circuit in the pointing device. The magnetic field then is turned off and the residual magnetic energy in the tuned circuit is received by the grid and used to resolve position of the pointing device until the residual energy is spent. This system has the advantage that the pointing device is essentially a passive device with minimum circuitry and without a need for additional power. However, this system requires periodic wait intervals when no detection of the pointing device signal is taking place and instead the "passive" pointing device is being "excited" by a magnetic signal being radiated from the tablet grid. This also means that the duty cycle of the received signal is greatly reduced, reducing the overall signal-to-noise ratio over time.

The above-described system also requires that the signal induced onto the grid by the pointing device be subjected to a two-way path loss. This two way loss generally leads to the requirement of more overall power for operation than the one-way loss to which the radiated signal of the present invention is subjected. While reducing circuitry in the pointing device, the foregoing technique requires added complexity to the grid structure since many lines or coils must be switched and driven with high power. This is particularly relevant in tablets used in portable or battery operated applications. Also, the foregoing approach requires that the grid be able to transmit as well as receive signals in order to operate. This requires that the grid conductors be of low resistance or impedance in order to obtain sufficient current and resulting magnetic field intensity to effectively transmit to the transducer coil. This leads to the requirement that the grid utilize low resistance wire or printed circuit elements in order to achieve sufficient power transmission. That prevents or limits the use of low cost and low-weight printed grids, such as those having silver ink printed on mylar film. The foregoing technique results in use of more power, generally lower proximity height for the pointing device, and reduced signal-to-noise ratio and increased susceptibility to noise, jitter, etc.

SUMMARY OF THE INVENTION

Accordingly, it is an object of the invention to provide a cordless magnetic field coupled digitizing system that provides highly accurate and reliable digitizing of the location of a pointing device while at the same time exhibiting high immunity to the noise produced by computers, monitors, switching power supplies, fluorescent lamps, etc. that is common in a digitizing environment.

It is another object of the invention to provide a magnetic field coupled cordless digitizing system that is capable of improved performance in operating with a wide range of pointing devices such as pens, cursors, pressure sensitive transducers, and devices with a high number of control switches, with automatic identification of such devices.

It is another object of the invention to provide a magnetic field coupled digitizing system that can operate with a pointing device located a substantial distance from the tablet surface.

It is another object of the invention to provide a magnetic field coupled digitizing system that requires only a very small amount of power to operate its pointing device.

It is another object of the invention to provide a digitizing system that can operate with sufficient bandwidth and speed to reproduce handwriting.

It is another object of the invention to provide a digitizing system with high immunity to noise generated by an LCD display or lamp noise such that the tablet and the display can be integrated into a single unit with the tablet grid directly in front of or behind the display.

It is another object of the invention to provide a digitizing system that allows a tablet grid implementation with either very low-cost printed silver or mylar conductors or very thin, nearly transparent indium-tin-oxide or equivalent conductors.

It is another object of the invention to provide improved operation with a cordless pointing device.

It is another object of this invention to provide improved operation and decoding of signals representing force applied on a pressure sensitive pen.

It is another object of the invention to provide a magnetically coupled digitizing system having a cordless pointing device with high accuracy despite appreciable "tilt" of the cordless pointing device.

It is another object of the invention to identify the pointing device to effectuate appropriate "s" curve correction for that pointing device.

Briefly described, and in accordance with one embodiment thereof, the invention provides a digitizing system including a cordless pointing device and tablet detection grid and electronics including a plurality of pairs of position resolving conductors each of which forms one or more differential coil elements in the tablet, each receiving a magnetic signal transmitted by the pointing device. First, second, third, and fourth carrier recovery conductors in the tablet also receive the magnetic signal. Position resolving circuitry includes a differential amplifier, multiplexing circuitry selectively coupling various pairs of the position resolving conductors to a pair of inputs of the differential amplifier, and synchronous demodulating circuitry coupled to an output of the differential amplifier. The synchronous demodulating circuitry includes a first input responsive to selected signals induced onto the differential coil elements and a second input responsive to a recovered pointing device carrier signal 51 to produce position resolving information. The system includes an analog-to-digital converter having an input coupled to an output of the synchronous demodulating circuitry to produce digital position resolving information. A computerized control system includes a plurality of inputs coupled to a plurality of outputs of the analog-to-digital converter. A plurality of outputs of the computerized control system are coupled to selection inputs of the multiplexing circuitry. The digitizing system includes carrier recovery circuitry including a first controllable gain differential amplifier having a pair of inputs coupled to the first and second carrier recovery conductors and a second controllable gain differential amplifier having a pair of inputs coupled to the third and fourth carrier recovery conductors. The carrier recovery circuitry also includes a first frequency doubler circuit having an input responsive to an output of the first controllable gain amplifier and a second frequency doubler circuit having an input responsive to an output of the second controllable gain amplifier. A signal combining circuit includes first and second inputs coupled to outputs of the first and second frequency doubler circuits, respectively. A threshold generating circuit includes an input coupled to the output of the signal combining circuit and an output coupled by an error amplifier circuit to gain control inputs of the first and second controllable gain amplifiers. A signal slicing, limiting circuit includes a first input coupled to an output of the signal combining circuit and a second input coupled to an output of the threshold generating circuit. A phase-locked-loop circuit includes an input coupled to the output of the comparator and produces a double frequency output signal that is deglitched and filtered. A divide-by-two circuit operates on the double frequency output signal from the phase-locked-loop circuit to produce the recovered pointing device carrier signal. The computerized control system measures the frequency of the magnetic signal and decodes the frequency of the magnetic signal, and at the same time resolves the position of the pointing device in response to the digital output of the analog-to-digital converter. The computer uses the decoded frequency information to determine status of switches of the pointing device, the type of the pointing device, and/or a value associated with a transducer output signal.

In the described embodiment, the magnetic signal has a frequency in the range of approximately 300 to 550 kilohertz. The multiplexing circuitry includes a first section having a first group of inputs coupled to a first group of the position resolving conductors, and a second section having a second group of inputs coupled to a second group of the position resolving conductors.

In the described embodiment, the pointing device includes a self-resonant, current switched LC oscillator including an inductor and a capacitive element coupled to form a self-resonant tank circuit, wherein the inductor radiates a magnetic signal to the tablet. The oscillator includes a current source supplying a measured amount of current, and a current switching circuit coupled to the current source and the tank circuit to alternately switch the measured amount of current into different sections of the tank circuit, wherein the inductor radiates maximum power at the self-resonant frequency of the oscillator regardless of the capacitance of the capacitive element, and wherein the power level of the magnetic signal transmitted from the inductor is substantially independent of the voltage of a power source energizing the pointing device. A plurality of frequency shifting capacitors are coupled across the tank by a plurality of manual switches to selectively shift the oscillation frequency. Alternatively, the capacitance of a voltage variable capacitive device coupled across the inductor is varied in response to a transducer to continuously shift the oscillation frequency in response to a signal produced by the transducer.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram of a presently preferred embodiment of the invention.

FIG. 2 is a diagram illustrating a basic detection grid for resolving pointing device position in the x direction and regenerating a carrier signal in accordance with the present invention.

FIG. 2A is a diagram useful in explaining the structure of the grid shown in FIG. 2.

FIG. 3 is a diagram showing a portion of the grid of FIG. 2 and a portion of the circuitry of FIG. 1 used for regenerating the carrier signal.

FIG. 3A is a diagram useful in describing signals induced onto the grid carrier recovery conductors of FIG. 2 as a function of pen position.

FIG. 3B is a diagram showing waveforms of signals produced by the carrier recovery circuitry shown in FIG. 3.

FIG. 4 is a schematic diagram useful in describing the differential detection of signals induced by a pointer onto a differential coil element in the grid of FIG. 2.

FIG. 4A contains graphs that show characteristics of the signals that are sensed by a differential coil element as a function of pointer position.

FIG. 5 is a schematic diagram of circuitry in the pointer shown in FIG. 1.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1 shows a magnetic field coupled digitizing system wherein signals are induced onto conductors of a grid 11 by a magnetic signal transmitted by a cordless pointing device 32 (although a corded pointing device also could be used). Such grid conductor signals are processed by a data channel including multiplexor circuitry 34 that switches grid conductor signals on conductors 35 and 52 into a selectable gain preamplifier 52. The variable gain control is useful when the cursor needs to be positioned a significant distance above the tablet surface so that more gain is needed, or when various pointing devices having different signal levels are to be used (pointing devices having larger diameter inductors to radiate the magnetic signal generally have more signal strength). Having variable gain control also reduces the need for gain calibration or alignment. The data channel also includes amplification/bandpass filtering circuit 38 having an input connected to the output of preamplifier 36 and an output connected to synchronous demodulator 41. The output of synchronous demodulator 41 is fed to an analog-to-digital converter 42, whose implementation also performs post detection signal integration of the synchronous demodulator 41 output.

The multiplexing circuitry 34, in response to grid selection signals 37 produced by a microprocessor system 26, selectively connects the two inputs of preamplifier 36 to various differential coil conductor pairs, by means of various conductors collectively designated by numerals 35 and 36, causing the data channel to amplify and sample the grid signals. Microcontroller 26 controls the gain of the data channel by means of outputs that connect to the gain select inputs of preamplifier 36. Microprocessor system 26 also controls analog-to-digital converter 42 by signals on conductor 45. The digital output of analog-to-digital converter 42 is read by microcontroller system 2