Radio stations broadcast on medium wave bands and send a signal into the air. To receive these AM waves, just a few elements are needed: some electronic components, some electric wire, a paper tube and a loudspeaker. Assembly is simple and requires no soldering. A homemade radio of this type is capable of receiving the signal within 50 km of the broadcasting station.
Steps
Part 1 of 3: Preassemble the Required Components
Step 1. Gather the materials
You may already have a lot of items you need for this project, except some electrical components that you can buy at most hardware stores, DIY stores, and electronics stores. You will need:
- 1 1 Megaohm resistor
- 1 Capacitor of 10 nF
- Insulated electric cable, red (37-50 cm)
- Insulated power cable, black (37-50 cm)
- Enameled copper cable (section 0, 4 mm) for the coils - about 20 m
- 200 pF compensator (160 pF is fine as well - up to 500 pF)
- 1 22μF electrolytic capacitor (at least 10V)
- 1 33 pF capacitor
- Insulated electric cable (15-30 m of any color, used for the antenna)
- One 9 volt battery
- Experimental base
- Insulating tape
- 1 Operational amplifier (type µ741 or equivalent)
- Small cylinder of non-conductive material (glass bottle, plastic tube or cardboard, etc.)
- Speaker
- Wire stripping pliers (or similar tool such as a sharp pair of scissors or a knife)
- Small knife or medium-grit sandpaper
Step 2. Build an antenna
This is one of the simplest components of the handcrafted radio, the only thing you need is a long electric cable; In theory, you need a 15m segment, but if you can't get one that long, 4.5-6m wire may be enough.
- When choosing your antenna cable, opt for an insulated model with a small diameter (e.g. 20 or 22 gauge), as this is the most suitable.
- Improve antenna reception by wrapping it in a coil; you can prevent it from unrolling by fixing it with zip ties or insulating tape.
Step 3. Cut and strip the jumpers
These are the electrical wires that connect the components that you will later install on the experimental base; cut a segment of black cable and one of red cable about 13 cm long.
- Use wire stripping pliers or a sharp knife to remove 2 to 3 cm of insulation from both ends of each segment.
- If you find that they are too long, you can always cut them to size later; it is therefore worthwhile to prepare some rather long segments at the beginning.
Step 4. Prepare a coil that serves as an inductor
When you wrap the wire around the barrel without leaving any space between the coils, you allow the wire to receive radio waves as electromagnetic energy. This process may seem complex, but making a reel is pretty easy; just wrap the wire tightly around the cylinder.
- Start making the inductor at one end of the cylinder. Leave a 12-13 cm long segment at the end of the wire where you secure the cable to the edge of the cylinder with electrical tape; wind the rest of the cable without leaving any space between the coils.
- Get a cylinder with a diameter of about 5-8 cm, but make sure it is not metal, otherwise it will eliminate the signal.
Step 5. Cover the barrel completely to finish the inductor
The greater the number of turns, the higher the inductance value and the lower the tuning frequency; continue wrapping the wire until the core is fully coated and secure the end with electrical tape. At the end of the bobbin leave another free segment of 12-13 cm and cut the thread.
- Since the copper wire is enameled, you will need to scrape off the patina covering the ends with a small knife or sandpaper so that you can connect the bare copper parts to the circuit.
- You can keep the coils still with a few dots of hot glue or similar adhesive.
Part 2 of 3: Wire the Electrical Components
Step 1. Place the experimental board
Place it on the table so that the long side is facing you; it does not matter which face is facing up. The components of the circuit (such as capacitors and resistors) are connected by inserting them into the holes of the adjacent columns of the header.
- These bases have a difference from the classic ones: the long upper and lower rows create a horizontal connection (from left to right) and not in columns as happens for the other models.
- There are usually two lines on the top and two on the bottom; we will only use one line at the top and one at the bottom.
Step 2. Place the op-amp on the board
The ICs have a border on one edge, often semicircular in shape, so that they can be oriented in the right way (allows you to count the pins correctly). Arrange the IC so that you have the demarcation on the left. Logo, numbers and letters printed on the component will thus be on the right side when you look at them.
- Most breadboards have a long depression in the center that separates it into two identical halves. Place the amplifier in the center so that the four pins are on one side of the depression and the other four on the opposite side.
- This way, you can assemble a neat circuit with the antenna on one side of the board and the output (the speaker and compensator) on the opposite side.
- The integrated pins are numbered. Pin 1 is the one below the demarcation point (the first from the left of the bottom row). The pins are numbered consecutively starting with the first on the bottom row and continuing counterclockwise on the other side of the component.
- Confirm the numbering of the legs of the amplifier once installed on the breadboard as follows: on the bottom row, from left to right, we will have 1, 2, 3 and 4. On the opposite side, from right to left, we will have 5, 6, 7 and 8.
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The pins we will use to make this radio are:
- pin 2 = inverting input
- pin 4 = V-
- pin 6 = output
- pin 7 = V +
- Make sure not to reverse the polarity of the op amp, you will damage it irreparably.
- The op-amp is now oriented so that the top and bottom match the polarity of the V + and V- pins once the battery is connected to the circuit. This arrangement makes it possible to avoid possible "crossings" of the connecting cables causing a possible short circuit.
Step 3. Put the 1 Megaohm resistor on top of the op amp
Current flows into the resistor in both directions, so you don't have to worry about its orientation on the board. Place a lead directly above pin "6" of the op-amp; the other must be connected to pin "2".
Step 4. Place the 10 nF capacitor
Insert the short lead into the hole just below that of the 1 Megaohm resistor, in the bottom row of the amplifier pins; place the long one in the hole four columns away to the left.
Step 5. Connect the 22 μF electrolytic capacitor
Insert the shorter (negative) lead into the hole just above the resistor above the top row of amplifier pins; the short one should be connected four rows apart to the right of the long one.
Electrolytic capacitors only pass current in one direction. The current must enter from the shorter lead. Applying voltage the wrong way can literally cause the capacitor to explode
Step 6. Add the connecting cables
Use the red one to connect the hole above pin "7" of the amplifier to the first free and closest one in the top row (the one that generates a horizontal connection); the black cable connects pin "4" to the first free hole closest to the bottom row.
Step 7. Place the 33 pF capacitor
Insert a lead into the free hole above the 10 nF capacitor; the other lead should be connected to another empty slot which is four rows away to the left.
This capacitor is not polarized, just like the first one you assembled, the current can therefore flow in both directions and the orientation of the piece is not important
Part 3 of 3: Complete the Radio
Step 1. Connect the antenna
This element has not been used so far, but at this point you can link it. Insert one end into the hole above the lead of the 22 pF capacitor; this is the same lead that you placed four rows to the left.
You can improve reception by distributing the antenna cable in the room as far as possible or by wrapping it securely on a coil as described above
Step 2. Connect the compensator
Insert one end into the hole to the right of the 33 pF capacitor lead; the other end must be connected to the black wire in the long bottom row.
Step 3. Connect the inductor coil
Attach it to the compensator and the black wire along the bottom row using one of the two 12-13cm segments you left at the ends. The other end must be connected to the 10 nF capacitor and the 33 pf capacitor.
Step 4. Connect the speaker
Place it on the table to the right of the compensator. The red cable must be inserted in the upper row of the base to connect to the jumper cable of the same color; the black one fits directly into the hole above the short lead of the 22 μF electrolytic capacitor.
It is often necessary to untangle the red and black lead wires connected to the speaker, so that they can be joined to the radio circuit
Step 5. Connect the battery
Once the circuit is finished, all you need is electricity; use electrical tape to secure the cables to the positive and negative pole of the 9V battery and then:
- Plug the positive wire into any hole in the top row of the header to connect the speaker and red wire.
- Connect the negative wire to any hole in the bottom row of the header to power the black lead and compensator.
Step 6. Pay attention if the speaker is making noise
Once the circuit is live, electricity starts flowing into the amplifier and speaker; the latter should emit sounds, however faint or similar to interference. This is a good sign that the components are connected correctly.
Step 7. Rotate the compensator to change the frequency
Proceed slowly to vary the frequency the radio can pick up and find audible stations; the farther the broadcasting station is, the weaker the signal will be.
Be patient and slowly turn the knob; with a little patience you are likely to be able to tune into an AM station
Step 8. Resolve any problems
The circuits are delicate and may need some repairs, especially if this is your first try. All leads must be well inserted into the base and each element must be hooked in the correct way in order to function.
- Sometimes you may have fully inserted the lead into the housing without getting a good electrical connection.
- Review the links on the breadboard to make sure all leads are connected to the same column according to the diagram.
- Same thing goes for the connecting cables from one side of the breadboard to the other.
- Some breadboards have a different layout, as well as having a top and bottom, they also have a left and right side (useful when a circuit is powered by different voltages). If you're using such a breadboard, make sure the links are handled accordingly.
- Adjust the connections until you can hear the radio when you power the circuit; if nothing happens, you have to rebuild the circuit from scratch.
Advice
- Don't be discouraged if the circuit doesn't work on the first try. The design of these elements is extremely unstable, and it may take several trials before you get one working.
- Inspect the circuit for damaged parts; if you believe it has been assembled correctly and all connections are secure, it is possible that some element is malfunctioning. Capacitors, resistors and operational amplifiers are built in large quantities and at very low cost, so it is possible to find some damaged units in the package.
- Purchase a voltmeter to check connections; this instrument checks the current flowing through the components at any point in the circuit. It is not very expensive and allows you to understand if some pieces are not working or are not well connected, in which case the energy is not flowing.
Warnings
- Do not overload the circuit with a high voltage; applying more than 9 volts can damage components or start a fire.
- Do not touch bare cables when they are crossed by electricity; you would take the shock but it is not serious thanks to the low voltage applied to a circuit of this type.
- Do not connect the short lead of the capacitor to the positive pole of the power source; the condenser "burns out" generally emitting a puff of smoke. In the worst case, the components catch fire.
