Learning Objectives

After this activity, students should be able to:

• Construct a working radio using a correct and efficient soldering technique.
• Identify the circuit components used to construct their radios, as well as explain how their radios function.

Materials List

For the entire class to share:

• wire strippers
• small screwdriver
• extra kit, for spare parts

Each group needs:

• Elenco^® 2 IC AM Radio Kit and Accessories, available for $16.99 at Amazon
• soldering Iron, available from Radio Shack
• solder (recommend silver bearing rosin core for high-tech projects; small diameter)
• safety glasses
• wire lead clippers, to clip leftover solder leads close to board
• 9V battery

(optional) For each student to use to practice soldering during the introduction to soldering:

• LED Flashing Kit, available for $2.25 at http://www.allelectronics.com/make-a-store/item/ledkit/led-flashing-kit/1.html

or

• 20 assorted extra resistors, available at Radio Shack
• 1 blank circuit board, available at Radio Shack

Worksheets and Attachments

Pre-Req Knowledge

• Students should be able to identify the value of a resistor based on its color bands, as taught in the associated circuits lesson. It may be a helpful resource for students to refer to a resistor color chart (such as this one: http://www.resistorguide.com/standards-and-codes/resistor-color-code/resistor_color_codes_chart/) when they determine the resistor values in their kits.
• Students should be able to identify diodes (including the directions they should be oriented), capacitors and inductors. During the associated lesson, refer to the kit components when teaching students about these circuit components so they know what the parts look like.
• It is helpful if students already have soldering experience, but as this is unlikely, good soldering tutorials are provided at https://learn.sparkfun.com/tutorials/how-to-solder---through-hole-soldering and http://www.aaroncake.net/electronics/solder.htm, and soldering is explained in activity Procedure section.
• Since the activity goal is not only for students to build working radios, but to also understand how they work and what each part of the radio does, a background in how radios function is also important.

Introduction/Motivation

Spark students' interest by explaining that many college students complete similar projects in their electrical engineering classes—yet they are conducting a similar activity in middle or high school!

It is likely, however, that explaining the goal of this activity (to solder components to a circuit board to create a working AM radio) will be enough to spark students' interest.

Procedure

Before the Activity

• It is helpful if the teacher builds a radio with the kit him/herself in advance of the activity. The diagram for the placement of circuit components can be confusing at times, so this ensures that the teacher fully understands the schematic before introducing it to students who will invariably need assistance.
• Since students need guidance for this project, especially younger students, it is helpful to have extra adult supervision available to ensure that the soldering is done safely and correctly. Also, it is best to keep desoldering to a minimum, so additional adult supervision ensures that students place circuit components in the correct place before they are soldered to the circuit board.
• Set up stations for each student pair with the following items: a radio kit, wire clippers, a soldering iron with a wet sponge to wipe the tip of the iron if solder gets on it (comes with the soldering iron), solder and goggles.
• When practicing soldering, provide each station with a practice breadboard and ~20 resistors.

With the Students

1. Present to the class an introduction to soldering. Good "how to solder" tutorials can be found at https://learn.sparkfun.com/tutorials/how-to-solder---through-hole-soldering and http://www.aaroncake.net/electronics/solder.htm. First explain that the components should be inserted into the side of the breadboard, which is plastic and has no metal, thus the leads stick out the metal side. So flip the board over to the metal side. The solder should be held at the base of where the lead emerges from the hole in the breadboard. Place the soldering iron on the lead as well, but at a position slightly above the solder, so that it is close, but not touching. When the tip of the soldering iron touches the solder, the solder melts, covering the tip; repetition of this occurrence can ruin the tip. If solder gets on the tip, have students clean off the tip with the wet sponge located on the soldering iron docking station.
2. As the iron is held just above the solder, the heat from the iron makes the solder melt around the base of the lead. Enough solder should be melted such that the entire base is covered, making a small "mound" of solder at the base of the lead. When practicing, have students experiment with using different amounts of solder so they can identify the correct amount to use; this entails finding a balance between using enough solder to create a good connection, yet not so much that the entire breadboard is one large network of solder. Once the base is covered, it is best if they follow a "less is more" soldering rule. After soldering is complete, cut the excess lead wire using the wire clippers provided at each station.
3. Explain soldering safety . Always wear goggles to prevent any eye injuries. The soldering iron is very hot and the metal on the back of the circuit board conducts this heat, so be careful when touching any metal pieces that have the potential to be hot. This is especially true for the soldering iron itself. Often, one student holds a component in place or holds the solder, while another holds the iron; if doing this, each student must pay careful attention to where the soldering iron is with respect to the placement of each person's hands. The potential for a student to get burnt is very high, so warning them against any misuse of the iron may help reduce the incidence of injury.
4. Once soldering has been explained and demonstrated to students, equip each group with a practice breadboard and several resistors or the LED Flashing Kits. Have students practice for at least 45 minutes and show samples of their final soldering technique to the teacher before moving on to their radio kits.
5. Upon opening the kit, have students identify every part and find it on the parts list located on the radio building instructions. Matching the parts to this list helps when placing each component on the circuit board, because they also match to the label the kit instructions give the component. The diagram showing where to place each component uses these labels, so matching the component to its corresponding label ensures that every component is placed correctly on the circuit board.
6. Once all of the components have been sorted, recommend that teams begin soldering the resistors first. It is easiest to build the radio using the flatter components first and then adding the taller or more complex components towards the end. Also, resistors are less heat sensitive, so if students are still taking a while to solder each component, it will not ruin the resistors like it may ruin other components. Thus, direct students to identify the resistor of the correct value (using the color bands) and solder it to the proper place on the circuit board following the kit diagram. Once the resistors have been added, solder the diodes as the next circuit component to add. It is important to note which direction the diode should be oriented, as a diode facing the wrong way causes radio malfunction; the black band on the diode specifies the positive side (the cathode). Next, add the capacitors, followed by the inductors and any other components requiring soldering. Attach the speaker last by using the wire specified in the Materials List section.
7. Continuously check on the teams to make sure all components are being soldered in the correct position in order to prevent having to debug the radio later by desoldering components.
8. Alert students to the fact that most components are heat sensitive, so it is advised that they place the soldering iron on the lead of the component for a minimal amount of time.
9. Once all components are soldered to the circuit board, use a 9V battery to power the radio. With the volume at its maximum setting, tune the signal slowly to find a radio station. It may be difficult to find a signal in a certain area, so conduct further investigation into tuner adjustment and antennae orientation before trying to debug the radio. If the radio still does not work, check all of the soldered components to ensure that they are both soldered correctly and in the right place. Comparing to a previously completed radio helps for quick checking.

Vocabulary/Definitions

amplitude: The height of the wave; in sound waves, large amplitudes correspond to loud noises.

capacitor: Stores energy in electric field, often for quick release (camera flash).

current: Flow of electrons in a circuit.

diode: One-way valve for current.

electric power : Rate of energy being used or generated.

frequency: Number of cycles per second for a signal - higher frequency signals travel farther generally than lower frequency signals, so AM radio waves which have a frequency in the range of a few hundred thousand cycles per second go farther than sound waves, which are in the 20-20,000 cycles per second range.

inductor: Temporarily store energy in magnetic field - coil antennas are big inductors.

integrated circuit: Inexpensive and tiny prefabricated circuit that is found in many common applications. Abbreviated as IC.

modulation: The process of embedding an information signal in a carrier signal so that it can be broadcast to another point.

resistor: Restricts flow of electrons (current).

transistor: Switches current on/off - controlled by voltage.

voltage: Electric potential energy measurement.

Assessment

Pre-Activity Assessment

• Correctly identify circuit components.
• Explain concepts of AM radio signal transmission.

Activity Embedded Assessment

• Correctly read the diagram found in the kit instructions, as well as match corresponding components to the symbols on the diagram.

Post-Activity Assessment

• Check to see if the radios work.
• Ask students to generally explain how their radios work.

Investigating Questions

• Why does it matter which way a diode faces? ( Answer: The diode acts like a one way flow valve. Conventional current flows from the anode to the cathode. If the orientation is reversed, it does not conduct current. The symbol for a diode is an arrow with a bar across the tip (see Figure 1).

The back side of the arrow is the anode (-) and the tip of the arrow is the cathode (+). The cathode on a diode is denoted with a black, white or silver stripe. As an example, if a light emitting diode (LED) is reversed when inserted into a circuit, it will not conduct and will not emit light. On an LED, the long wire lead is the anode and the short lead is the cathode.)

• Which component controls the volume? (Answer: The volume is controlled by a potentiometer. It controls the volume by attenuating the audio output, similar to a light dimmer control in a house - it also looks just like a light dimmer control!)
• What part of the signal changes when you change the volume? (Answer: The audio signal (voice/music) from the audio amplifier.)
• Which component controls the tuning? (Answer: The tuning is controlled by a variable capacitor or inductor.)
• Which part of the circuit demodulates the signal? (Answer: The radio signal is demodulated by a detector circuit using a diode.)
• Which part of the circuit filters the signal? (Answer: The intermediate frequency (IF) amplifier filters all unwanted signals from the antenna and the tuning circuit before being passed on to the demodulator circuit.)
• Why do you think some components are subject to over-heating? (Answer: When a component overheats from an excess current is flowing through it. Energy is dissipated in the form of heat.)

Safety Issues

• Soldering irons get extremely hot, as do any metal or conductor they touch. So carefully explain the use of these irons, including the dangers of getting burned. Assign an adult to oversee all use of the soldering irons to ensure that they are used safely and correctly. If a burn results from the irons, it will likely be very minor; run the affected skin area under cold water.
• To prevent eye injuries, have students wear safety glasses or goggles.

Troubleshooting Tips

If a radio does not work, ask the following questions:

• Are resistors of the correct value placed in the proper places?
• Are the diodes in the proper orientation (positive side corresponding to black band)?
• Are all of the soldering connections complete? That is, the entire hole that the leads emerge from covered?
• Has the wire connecting the speaker or 9V battery to the circuit board been stripped enough?
• Since the diodes, transistors and integrated circuit are very heat sensitive, have these parts been overheated?
• Additional troubleshooting tips are included in the kit instructions.

Activity Extensions

You are an engineer that designs radios. Using the AM radio you just built, design a shell to house your radio while meeting the following design constraints:

• The listener needs to easily hear the speaker.
• The listener needs to be able to access the tuning and volume knobs.
• The housing needs to be a protective yet attractive "housing" to the AM circuit you built.
• The listener needs a way to turn the radio on and off without having to disconnect the battery each time [Only use this bullet-point if you can obtain switches from RadioShack or elsewhere].

Have students share their designs with each other and discuss how well each design meets the constraints outlined above.

Activity Scaling

• The level of adult involvement affects the scaling a great deal; the more involved adults are in the radio completion, the less time it takes. While adult involvement conserves time, it also impedes students' full understanding of how the radios function, so be careful not to "do" the activity for the students.
• Make this activity more challenging by increasing the depth of material concerning how the radio signal is interpreted by the radio.

References

Copyright

Contributors

Supporting Program

Acknowledgements

This content was developed by the MUSIC (Math Understanding through Science Integrated with Curriculum) Program in the Pratt School of Engineering at Duke University under National Science Foundation GK-12 grant no. DGE 0338262. However, these contents do not necessarily represent the policies of the NSF, and you should not assume endorsement by the federal government.