Transducer and Signal Processing

A transducer, for all practical purposes, is a devise that converts one kind of energy (or signal) to another. Here’s a thermocouple converted a radiant heat signal into an electric voltage for input into an amplifier. This is the figure that shows about principle of transducer;

The thermocouple used for sensing temperature was the AD590L manufactured by Analog Devices (See Appendix C). Basically the AD590 is a two-terminal integrated circuit temperature transducer which produces an output current proportional to absolute temperature. When wired as a voltage divider in series with a 1kW resistor, the transducer is capable of producing a change of 1mV / °C. This is far too small a change to be adequately sampled. Therefore it was necessary to process the signal by means of amplification. A 741 operational amplifier was employed to enhance the signal by a scaling factor(See Appendix K).

Zero Crossing Detector Circuit for Magnetic Transducer

This is a circuit that can be used to detects zero crossing in the output of a magnetic transducer within a fraction of 1 mV. Here’s the figure of the circuit;

 

The resistive divider, R1 and R2, biases the inputs 0.5 V above ground, within the common-mode range of the LM111. The output will drive DTL or TTL directly. Because the output must drive any capacitive loading for positive-going output signals, the value of R5 determines circuit speed (a lower value increases speed). An optional offset-balancing circuit using R3 and R4 is included in the schematic. [Circuit diagram source: National Semiconductor Application Notes]

Ultrasonic Electrostatic Transducer for Ultrasonic Measurement

This is a complete design circuit for a complete ultrasonic transceiver used in a variety of pulse/echo-ranging applications. Here’s the figure of the circuit;

In this circuit, the LM1812 transmits a burst of oscillations with transducer X1. Then, using the same X1, listens for a return echo. If an echo of sufficient amplitude is received, the LM1812 detector produces a pulse (pin 16) of about the same width as the original burst. The closer the reflecting object, the earlier the return echo. Using the values and parts shown, the circuit has a range of about 4 inches to 30 feet. L6 resonates at 50 to 60 kHz, with the 500-pF capacitance of X1. L1 is tuned to this frequency by watching for maximum echo sensitivity with a scope at pin 1. [Circuit diagram source: National Semiconductor Application Notes and Seekic.com]

Transducer Amplifier Circuit

This is a design circuit for transducer amplifier circuit diagram. Here’s the figure of the circuit;

In this circuit, Pins 9 and 15 are not connected. Connect the other pins as shown. Capacitors on the supply (470uF and 0.1uF) need to be close to the IC. Keep in mind that the electrolitic capacitors have polarity (see top one). Although the amp outputs and speakers have polarity as well, it does not make a difference how you connect them, as transducers are on separate areas anyway, so do not cancel. The 1uF input coupling capacitors make a high-pass filter with the output amplifier’s 30k input resistance at about 5Hz.

Gamma Correction Circuit

Transducers is used in video system to convert optical signal to electrical signal in the acquisition. In the display, transducer is used to convert electrical signal back to light. Transducers often have a transfer function (the ratio of signal in to light out) that is unacceptably nonlinear. This is the figure of the circuit;

The newer technology of video camera transducers (the improved versions of vidicon-like tubes and CCDs) are adequately linear, however, picture monitor CRTs are not. The following equation shows the transfer functions of most CRTs follow a power law:

Light Out = k • VSIG?

where gamma (?) is the exponent of the power law (gamma ranges from 2.0 to 2.4) and k is a constant of proportionality.  This deviation from nonlinearity is usually called just gamma and is reported as the exponent of the power law. Gamma value of 1 results in a linear transfer function. The typical CRT will have a transfer function with a gamma from about 2.0 to 2.4. Such values of gamma give a nonlinear response which compresses the blacks and stretches the whites. Cameras usually contain a circuit to correct this nonlinearity. Such a circuit is a gamma corrector or simply a gamma circuit. [Circuit diagram source: Linear Technologies Application Notes]

Differential Capacitive Transducers

Transducers with greater sensitivity and immunity to changes in other variables can be obtained by way of differential design, much like the concept behind the LVDT (Linear Variable Differential Transformer). Here’s the design of the differential capacitive transducer circuit;

Capacitive transducers provide relatively small capacitances for a measurement circuit to operate with, typically in the picofarad range. Because of this, high power supply frequencies (in the megahertz range!) are usually required to reduce these capacitive reactance to reasonable levels. Given the small capacitances provided by typical capacitive transducers, stray capacitances have the potential of being major sources of measurement error.

AC Instrumentation Transducers Circuit

This is a simple of design AC device instrument transducer circuit. Here’s the figure of the circuit;

Just as devices have been made to measure certain physical quantities and repeat that information in the form of DC electrical signals (thermocouples, strain gauges, pH probes, etc.), special devices have been made that do the same with AC. It is often necessary to be able to detect and transmit the physical position of mechanical parts via electrical signals. This is especially true in the fields of automated machine tool control and robotics. A simple and easy way to do this is with a potentiometer.

Obstacle Detection Sensor Circuit

The robot requires means of detecting an obstacle (or another robot) without making physical contact. This allows the robot to decide whether to avoid or to confront and investigate the obstacle depending on its programming. This is one solution and the design of obstacle detection circuit. Here’s the figure of the circuit;

 

In this circuit, ultrasonic transducers were chosen for this because they are more reliable and have a greater range than IR sensors (effectiveness of IR sensors varies with ambient light level). The IC U1 is a 555 timer in astable configuration to oscillate at 40 KHz. Instead of using exact values for the two resistors that is placed between pin 6 and 7, a 10K ohm potentiometer (VR1) was used. This also allows for some fine tuning of the output frequency. The output (pin 3) is then attached to a 40 KHz ultrasonic transmitter (UTR1).

The receiving circuit is a dual LM358N (U2) op-amp. An ultrasonic receiver (UTR2) is connected to pin 3, the non-inverting input of U2a which is a non-inverting amplifier with a gain of 220. The output of U2a is put through a low pass filter via D1, C3 and R4 to produce a somewhat stable DC voltage. This DC voltage is fed into the non-inverting input of U2b configured as a non-inverting comparator. Sensitivity of U2b is controlled by VR2 to set the threshold trigger value. The output of U2b is connected through R5 to the base of a bipolar 2N2222 transistor (Q1) acting as an inverter with a LED (LED1) to indicate if an obstacle has been detected. Finally, the collector of Q1 goes to the Handy Board's digital port (Handy Board uses inverted logic levels, 0V is a logic 1 and +5V is a logic 0).

Interfacing Pressure Transducer Circuit

This is a design circuit of 3 kΩ pressure transducer bridge circuit that is powered from 5 V. This circuit is based on the AD620 that is especially suitable for higher resistance pressure. Here’s the figure of the circuit; 

 

In such a circuit, the bridge consumes only 1.7 mA. Adding the AD620 and a buffered voltage divider allows the signal to be conditioned for only 3.8 mA of total supply current. Small size and low cost make the AD620 especially attractive for voltage output pressure transducers.

Hearbeat Sensor (Tranducer) Circuit

This is a design circuit of a simple heart-beat transducer. Here’s the figure of the circuit;

 

This circuit made from an infrared phototransistor and infrared LED.  This transducer works with the principle of light reflection, in this case the light is infrared.  The skin is used as a reflective surface for infrared light. The density of blood in the skin will affect on the IR reflectivity. The pumping action of heart causes the blood density rises and falls. So that we can calculate the heart rate based on the rise and fall of intensity of infrared that reflected by skin.

CMOS Piezo Transducer Buzzer Driver

Here’s figure shows a design circuit for CMOS piezo transducer buzzer circuit;

A CMOS gate and transistor buffer can be used as an effective driver for a piezoelectric or piezoceramic transducer. This circuit is powered by 5 VDC. You can change piezoelectric transducer sound changing R2 and C1 values. PIN A connected to +5V and PIN B connected to Q1 collector.

PARTS LIST
R1 1MΩ
R2 560kΩ
R3 18kΩ
R4 1kΩ
C1 1000pF
Q1 2N2222
ICa And ICb CD4011
S1 Single Pole Double Throw
Switch PIEZO Piezo Element

AD586/597 Temperature Transducer (Sensor)

That is a design circuit for a stand alone temperature transducer/sensor circuit. This device uses The AD596/AD597, employing its internal junction compensation temperature sensor inside. Here’s the figure of the circuit;

This device can be used as temperature sensor by omitting the thermocouple and connecting the inputs (Pins 1 and 2) to common. The output will reflect the compensation voltage and the AD596/AD597 temperature will be indicated by the output. the AD596/AD597 will be operated over the full extended –55°C to +125°C temperature range. This device has output scaling of 10.1 mV per°C with the AD597 and 9.6 mV per °C with the AD596. When AD596 is used in temperature sensing mode, it will read slightly high, because there is 42mV offset.

Differential Instrumentation Amplifier Circuit Using Bridge Transducer

This is a design circuit for a simple differential instrumentation amplifier that has a resistive transducer (Rt).  A resistive transducer is a device whose resistance changes when a certain physical energy applied to it changes. Common examples include transducers with resistances that vary with temperature, pressure, and light shining on it. Here’s the figure of the circuit;

As in most bridge circuits, the components in this circuit's bridge network (consisting of Ra, Rb, Rc, and Rt) are chosen so that the bridge is balanced at a certain reference condition, i.e., Rc/Rb = Rt/Ra.  One way to do this is to make Ra=Rb=Rc=Rt=R at the chosen reference point. 
  
When the bridge above is balanced, Va = Vb, causing the input voltages to A3 to be equal and the output of A3 to be zero.  When the resistance of Rt changes, however, the bridge becomes unbalanced, causing a non-zero voltage Vab to appear across the inputs of A3. This, in turn, results in an output voltage Vo that is proportional to the change in resistance of Rt, i.e., Vo = (RF/R1)(ΔR/4R) Vdc where ΔR is the change in Rt's resistance. By attaching an indicating meter to the output of A3 and calibrating this accordingly, this circuit may be used to measure various physical quantities with the appropriate transducer.