Day 1: 1st Electronics Engineering

Project

NSF SPIRIT Workshop2007

Build Your Own Battery Tester

Build Your Skills

• OBJECTIVES:– Learn to Solder– Learn how the circuit components work in a

simple circuit used to test a battery.– Gain exposure to the fundamental law of

circuit design – Ohm’s Law.– Build the circuit in lab.– Take it with you!

Light Emitting Diodes(or LEDs)

• A diode is a semiconductor electronic device.

– Form numbers on digital clocks, – Transmit information from remote controls, – Tell you when appliances are turned on– Form images on a jumbo television screen or illuminate a traffic

light.

• A semiconductor is a material with varying ability to conduct electrical current

Reference: http://electronics.howstuffworks.com/led1.htm

Semiconductor Basics• Semiconductors are

made from a poor conductor that has had impurities (atoms of another

material) added to it. This process is called doping.

• When these two materials are joined, a P-N Junction is formed.

• A semiconductor with extra electrons is called N-type material, since it has extra negatively-charged particles.

• A semiconductor with extra holes is called P-type material, since it has extra positively-charged particles.

At a P-N Junction, electrons can jump from hole to hole, moving from a negatively-charged area to a positively-charged area. The holes appear to move in the opposite direction. This Flow of Charge is called Current!

A diode comprises a section of N-type material bonded to a section of P-type material, with electrodes on each end. This arrangement conducts electricity in only one direction. When no voltage is applied, to the diode, electrons from the N-type material fill holes from the P-type material along the junction between the layers, forming a depletion zone. In a depletion zone, the semiconductor material is returned to its original insulating state -- all of the holes are filled, so there are no free electrons or empty spaces for electrons, and charge can't flow.

The Diode: a tiny “P-N Junction”!

To get rid of the depletion zone, you have to get electrons moving from the N-type area to the P-type area and holes moving in the reverse direction. To do this, you connect the N-type side of the diode to the negative end of a circuit and the P-type side to the positive end. The free electrons in the N-type material are repelled by the negative electrode and drawn to the positive electrode. The holes in the P-type material move the other way. When the voltage difference between the electrodes is high enough, the electrons in the depletion zone are boosted out of their holes and begin moving freely again. The depletion zone disappears, and charge moves across the diode.

Ah-hah! Let’s put a Battery to it!

What happens if we Reverse it?

If you try to run current the other way, with the P-type side connected to the negative end of the circuit and the N-type side connected to the positive end, current will not flow. The negative electrons in the N-type material are attracted to the positive electrode. The positive holes in the P-type material are attracted to the negative electrode. No current flows across the junction because the holes and the electrons are each moving in the wrong direction. The depletion zone increases.

LED, You Light Up My Life!

The interaction between electrons and holes in this setup has an interesting

side effect -- it generates light!

HOW Does a Diode produce light?

Summary

• A Diode is a common component in many electronic applications.

• A Diode is a P-N junction that allows current to pass in only 1 direction, under the right conditions.

• Light-emitting diodes, or LED’s emit light when current is flowing across the diode.

Battery Tester • Use a LED to build a circuit that will show a

good battery from a bad battery.

• Connected Correctly, A Good Battery will Light up the LED!

+ DIODE -

Let’s Design the Circuit• OHM’s LAW will help guide how we design the

battery tester circuit.

• OHM’s LAW states: • Voltage = Current X Resistance V = I x R• Here,

• V = Voltage has units Volts• I = Current has units Amps• R = Resistance has units Ohms

•

Let’s Design the Circuit

• The conceptual design of the battery tester circuit (shown at right) will allow a very high (almost infinite) current to flow across the diode.

• To prevent exceeding the current spec of the diode, we will use Ohm’s Law to limit the current.

+ DIODE -

V=IR

Let’s Design the Circuit

• Rearranging V=IR, we see I = V/R.

• Choose a resistance R to achieve a current, I = V/R, that will be at a safe level for the diode, given the set value of V (e.g. 9 volt battery).

• Simply put, solve the equation!• (The components have been selected for you and

will be provided in the lab.)

V=IR

Battery Tester Circuit

BATTERY

++

--

RESISTOR Used to limit current.

How?

V = I x R

Thus using Ohm’s Law, we arrive at the final Battery Tester Circuit design shown in this schematic:

Build Battery Tester Circuit

• A fundamental skill needed to assemble electronic projects is that of soldering.

• The idea is simple: Join electrical parts together to form an electrical connection

• Use a molten mixture of lead and tin (solder) together with a soldering iron.

For more information, see: http://www.epemag.wimborne.co.uk/solderfaq.htm

Build Battery Tester Circuit in Lab

• Get components for battery tester circuit: – LED– Resistor– Battery Leads

• Attach these components on a circuit board & solder connections between them.

Photographs © 1996-2006 Alan Winstanley WORLD COPYRIGHT RESERVED

Build Battery Tester Circuit in Lab

• RESOURCES:

• Online Soldering Guide

• Engineering Staff

• Equipment in Rooms 305 & 311

Photographs © 1996-2006 Alan Winstanley WORLD COPYRIGHT RESERVED

References • Information & Photo Source – Slides 3 through 10

– How Stuff Works: http://electronics.howstuffworks.com/led1.htm

• Copyright Notice – Information on Slide 13 & Photos Slide 14– Everyday Practical Electronics Soldering Guide:

http://www.epemag.wimborne.co.uk/solderfaq.htm

– Text © 1996-2006 Wimborne Publishing Limited, Wimborne, Dorset, England. Everyday Practical Electronics Magazine has provided this document as a free web resource to help constructors, trainees and students. You are welcome to download it, print it and distribute it for personal or educational use. It may not be used in any commercial publication, mirrored on any commercial site nor may it be appended to or amended, or used or distributed for any commercial reason, without the prior permission of the Publishers.

– Photographs © 1996-2006 Alan Winstanley WORLD COPYRIGHT RESERVED

• Presentation Created by: Alisa N. Gilmore, P.E. Department of Computer and Electronics Engineering, University of Nebraska-Lincoln, July 2006; updated July 2007