Transducer is a device capable of being actuated by an an energizing input from one or more transmission media and in turn generating a related signal to one or more transmission systems. It provides a usable output in response to specified input  measurand , which may be in the form physical, chemical, Mechanical or  optical....

For eg. temperature transducer transduces temp. changes to equivalent resistance changes which can further converted into electrical signal (voltage) for measurements.                                                                                                                                 

TEMPERATURE                                     

1. LM35 Precision temperature sensor                                                     

• LM34 series are precision integration-circuit temperature sensors whose output voltage is linearly proportional to the Fahrenheit temperature.
• LM35 series are precision integration-circuit temperature sensors whose output voltage is linearly proportional to the Celsius temperature.

 I am using LM35DT package to operate over a 0° to +100°C temperature range

    R5 and C3 are used for capacitive load compensation.

INTERFACING TO MICROCONTROLLER USING ADC804

• The ADC804 has 8-bit resolution with a maximum of 256 steps and the LM35  produces 10mV for every degree of temperature change.

•We will do calibration such that ,

for temperature range of  0 to 100°C , voltage in at the input of ADC will be 0 to 2.56 v.

•we need to set Vref/2 = 1.28V

so step size will be 2560mv/256 = 10mv

also for every degree change in temp. LM35 output changes by 10mv ,so  every degree change in temp. will produce 1 unit change in digital out of ADC

•Thus resolution of our system will be 1deg C , which is Smallest temp. that we can measure with this system.
 

Although our theoretical design is correct , operational amplifiers are often needed to to be calibrated practically , what i mean to say is that you need to adjust gain of amp. (Adjusting pot -R2)  so that we get designed output at various temperature. That is if current temp. is 25°C , LM35 output will be 250mv and amp. output should be 250x2.56 =0.64v . if it is not,  adjust R2.

2. P100 Platinum resistance temp. detector .

PT 1 00 - platinum resistance temp. detector (PRTD) . PT 1 00 has a resistance of 100 W at zero deg. Celsius .

• Linear

• Sensitivity-a0 =0.00385W/ deg. Celsius

• Response time - 0.5 to 5 s or more.

• DESIGN (0 to 85 deg. cel.)
 
1)    R1*R4 = R2*R3  -----BRIDGE BALANCE CONDITION      
2)    Rt = Ro [ 1 + a T]  ----- RESISTANCE VARIATION FOR RTD
3)    Vab =  V*R3 / ( R1 + R3 )  -  VR4 /( R2 + R4 ) --- BRIDGE OUTPUT    (V=5v)  
4) Vo = R2 / R1 ( Va – Vb )---- GAIN OF INSTRUMENTATION AMPLIFIER
 
1. At 0oC

R1=R2=R3 =R4(100 W RTD )=100 ohms.

so bridge is balance -o/p vtg 0v

    
 2.At 85 oC                          

R85  = 100 ( 1 + 0.00385 [ 85 ] )
            =  132.72 ohms 
Bridge output
        Vab = 0.35V.     (FOR R1=R2=R3=100ohms)
    
         
3.Gain of Amplifier    

Vo = R2 / R1 ( Va – Vb )

           For Vab = 0.351  &        Vo  = 0.351 V at 85 deg. Cel.

         A = R2 / R1  = 14.62

           For R1 = 1 k ohm ;     We let R2 = 14.62 K ohm  approx. R2 = 15 k ohm(use preset).

Since the change in resistance of RTD w.r.t. temp.is linear , the change in bridge output is also linear w.r.t. temp. i.e. change in temp. from 0 to 85 deg. Cel. causes bridge output to change from 0 to 0.351 V.

I have given Ref voltage of 5.12 v to ADC chip so step size will be ,5120mV/256 (8 bit ADC) =20 mV.

So bridge output voltage in the range  0 to 0.351 V corresponding to 0 to 85oC change in temperature is converted in to 0 to 5.12V using Amplifier  having gain of 14.62 . Interfacing is same as that I have shown in ADC-DAC page .
 

PROGRAM LOGIC: 

Output of an ADC is from 00 TO FFH for  an input voltage variation of 0 to 5.12V. I used lookup table method to display the proper temperature. For this,I prepare a lookup table of 256 values(00 to FF)i.e output of ADC.. An small example of a lookup table has been shown below. Values corresponding to output of ADC are selected  from lookup table and displayed. 

CONCEPT FOR LOOK- UP  TABLE:

SONAR MODULE
Sonar's are basically a device that puts out an inaudible pulse, and counts the time it takes to get an echo. The Polaroid 6500 series sonar ranging module has a range of 6" to 35 feet.

INTERFACING TO  8051

Polaroid makes the 6500 series sonar ranging module. Basically the init line is brought high and a timer is started, when the echo line goes high the time counted is run through a simple formula of 0.9 ms per foot to calculate the distance traveled to an object detected. An additional line may be brought to the MCU if object detection of distances less than 18 inches is desired.

                              +5v
                 +---------+   |
          init   |         |---+
   to MCU -------|  sonar  |
          echo   |  module |    /
          -------|         |===| transducer
                 |         |    \
             +---|         |
             |   +---------+
            gnd