Computer Engineering Department

Faculty of Engineering, Khon Kaen University

EN842003 Digital Electronics

Practice Session 1: Basic electronic circuits

1. Objectives

• To practice construction of electronic circuits • To learn how to use electronic workbench tools

2. Apparatus

- Digital experiment box - Digital multimeter - 1 x 390 Ohm resistor - 1 x 680 Ohm resistor - 1 x 1K Ohm resistor - 1 x LED

3. Digital multimeter

Digital multimeter is an electronics measuring instrument that has ability to measure several electrical parameters for example: voltage (V), current (A), resistance (Ohm).

Fig. 1 Digital multimeter

Operation of multimeter

- Turn selector knob to desire measuring parameter - Connect black probe to common jack (labeled COM) on the meter - If measuring voltage and resistance, connect red probe to the jack labeled V, Ω. - If measuring current, connect red probe to the jack labeled A

Resistance measuring

- Make sure that the resistor to be measured is not connected to any power supply. - Turn selector knob to Ω. - Probes must be connected at COM and V, Ω jacks. - Touch probe tips on both ends of the resistor. - Read resistance on the display. Notice the unit of measurement carefully.

Fig. 2 Resistance measuring

Voltage measuring

- Turn selector knob to VDC (indicated by ). - Probes must be connected at COM and V, Ω jacks. - Touch probe tips on points where potential difference is to be measured. - Read voltage on the display. Notice the unit of measurement carefully.

Fig. 3 Voltage measuring

Current measuring

- Turn selector knob to DCA (indicated by ). - Probes must be connected at COM and A jack. - Cut the circuit to be measured and insert probes as shown in fig. 4 in order to allow current

to flow through the meter. - Read current on the display. Notice the unit of measurement carefully.

Fig. 4 Current measuing

4. Digital experiment box

Digital experiment box is an instrument that is used for prototyping or building digital circuits. It contains built-in peripherals which support circuits testing for example: power supply, breadboard, logic probes, 7-segment LED display and etc.

Fig. 5 Digital experimental box

Power supply

There are two types of power supply on digital experiment box: fixed and variable voltage supply. Fixed voltage supplies are provided as connectors above breadboard. They are labeled -5V, +5V, 0V, +12V and -12V. Variable voltage supply is located on the right of breadboard and has a knob for choosing output voltage, which can be varied from 0-10V or 0-5V. Variable voltage supply is used for generating reference voltage only, not for power up circuit.

Breadboard

Breadboard is the area on the digital experiment box for constructing circuit. It is a board with holes for holding electronics components. Breadboard is pre-wired as shown in fig. 6.

Power rail area connection Component area connection

Fig. 6 Breadboard pre-wired connection pattern

Pre-wired connection simplifies circuit construction because connection point is expanded to several points and therefore less wiring is needed.

5. Procedures

5.1 Construct the following circuit on the breadboard

5.2 Measure voltage across 390 Ohm resistor (VR390 = ……………………V)

5.3 Measure voltage across 680 Ohm resistor (VR680 = ……………………V)

5.4 Measure voltage across 1K Ohm resistor (VR1K = ……………………V)

5.5 Measure current flowing in the circuit (I = ……………………..A)

5.6 Change supply voltage to 12V

5.7 Measure voltage across 390 Ohm resistor (VR390 = ……………………V)

5.8 Measure voltage across 680 Ohm resistor (VR680 = ……………………V)

5.9 Measure voltage across 1K Ohm resistor (VR1K = ……………………V)

5.10 Measure current flowing in the circuit (I = ……………………..A)

5.11 Turn off the power and measure actual resistance of each resistor

5.12 Discuss whether the result satisfies Ohm’s Law, V = I*R, or not.

(in our case R = R1+R2+R3).

5.13 Construct the following circuit:

5.14 Measure current and voltage across resistor when R is as follows:

Resistor value Voltage across resistor (V) Current (A) Voltage across LED (V)

390 Ohm

680 Ohm

1K Ohm

5.15 Discuss whether the result obtained in previous step satisfies Ohm’s Law or not.