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ECET-402 Week 2 Lab – Acquiring Temperature & Signal Conditioning This lab actually consists of two separate but related labs. They will be presented in Parts A and B.

Objective:
The objective of this lab is to use an LM34 temperature sensor to acquire temperature and display it in an 8-bit binary number using LEDs and designing simple signal conditioning circuits using op-amps.

Parts Needed:

1. Multisim 8 (or higher) 2. LM34 Temperature Sensor 3. ADC0809 4. 8 LEDs 5. Wires, wire cutter, and wire stripper 6. Adjustable DC Power Supply 7. Function Generator and DMM

Part A – Temperature Sensor

We will use an LM34 temperature sensor IC to measure temperature in Fahrenheit degrees. We will then convert the analog output voltage of the sensor to an 8-bit digital signal using the Analog to Digital converter ADC0809. Finally we will use 8 LEDs to display an 8-bit binary number representing the temperature.
LM34:
The LM34 series are precision integrated-circuit temperature sensors. The output voltage is directly proportional to temperature in Fahrenheit degrees. Output voltage increases by 10 mV for every one degree Fahrenheit. For example, an output voltage of 720 mV (0.72 V) indicates a temperature of 72 F. LM34 has a range of -50 to +300° F and can be operated with a voltage supply of 5 to 30 VDC. It draws only 75 µA from its supply.
ADC0809:
This analog to digital converter was discussed in your digital courses. The output is an 8-bit digital signal.
Calibrating the ADC: The 8-bit output of ADC translates into 256 possible readings. We will select a reference of 5.12 volts for our system (instead of typical 5 volts). This number works well with 256 as indicated in the formula below: Analog in (from LM34) Digital out ---------------------------- = ---------------- Reference Voltage 256
For example, at 72 F, LM34 produces 720 mV (0.72 V). Using the formula given above: = 36 (Digital output), or in Binary: 00100100, which is half of 72.
Therefore: The Temperature = (Output Reading of ADC in Decimal) 2
Procedure:
Part A1 – A Simple Thermometer: You can use an LM34 temperature sensor, a power supply, and a DMM to measure the temperature. Wire up the circuit shown in Figure 1. Multiply the reading of the DMM by 100 (depending on the setting of your DMM). That will be the temperature in your room. Hold the LM34 sensor between your fingers and notice that the temperature will increase. Isn’t this cool?!

Figure 1
Part A2 – Wiring up the ADC0809:

1. Place ADC0809 on a breadboard and connect all wires as shown in Figure 3. Connect the output from the LM34 temperature sensor to Input (0), IN0 of ADC. The address A2A1A0 is set to 000 to select IN0.

2. ADC0809 requires a clock. Use a 20 kHz square-wave signal from the SYNC or TTL output of a function generator. Make sure to connect the ground of the function generator to the common ground of your system. If you would like to build your own clock circuit, an optional 20 kHz oscillator circuit is provided in Figure 4 below.

3. Connect the eight outputs of ADC0809 to eight LEDs. Place the 8 LEDs in a row next to each other to represent an 8-bit binary number as shown in Figure 2. Note the LSB and MSB LEDs. Connect the output pins of ADC0809 to Anodes of LEDs. The Cathodes are connected to the ground.

Figure 2

4. Make sure all wires are connected. Turn on the function generator and power supply. Adjust the power supply to 5.12 V DC for the reason described on page 1. Note the temperature reading on DMM as described in Part 1. Convert the 8-bit binary number displayed by the LEDs into decimal. This number should be half of the actual temperature. For example if the actual temperature is 72F, the LEDs should display 001001002, which is 36 in decimal.

Figure 3

5. Complete Table 1 on week 2 lab worksheet and answer the questions.

A simple Oscillator circuit

The circuit shown below is an optional oscillator circuit that could be used with ADC0809 analog to digital converter. It will produce a square wave of about 20 kHz.

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Figure 4
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Part B – Signal Conditioning Circuits

Procedure:

1. Design an operational amplifier circuit that can be used to produce an output that ranges from 0 to -5 V when the input goes from 0 to 100 mV. Build the circuit in Multisim and show the voltmeter reading for an input of 100m V. Paste a copy of the circuit from Multisim on the worksheet.

2. An operational amplifier circuit has an input resistance of 2 kΩ. Determine the feedback resistance needed for a voltage gain of +50. Design and build the circuit in Multisim and verify operation. Paste a copy of the circuit from Multisim on the worksheet.

3. Build the circuit shown in Figure 5 in Multisim. When Switch S is open (no load), voltage V1 is 5V. However when switch S is closed, load voltage VL will drop considerably and load current may not be sufficient for the load. Determine load current IL and voltage VL when switch S is closed.

Figure 5

IL = 454.525uA VL = 454.47mV

Enter the same values on the worksheet.

Next, build the circuit shown in Figure 6 in Multisim. Determine load current IL and voltage VL and describe the advantage of the voltage follower circuit.

Figure 6

IL = 4.651mA VL = 4.651V

Enter the same values on the worksheet.