1 megaohm resistor (x1) 10nF capacitor (x1) 15–20 inches (38–51 cm) of red insulated wire 15–20 inches (38–51 cm) of black insulated wire 45–60 feet (14–18 m) of 26 AWG (0. 4 mm) enamelled wire (for the inductor) 200pF variable tuning capacitor (160pF will do. Up to 500pF works) 22uF electrolytic capacitor, (10v or higher) (x1) 33pF capacitor (x1) 50–100 ft (15–30 m) insulated wire (any color; for the antenna) 9-volt battery (x1) Electronics breadboard Electrical tape Operational amplifier, type 741 or equivalent (also called an op-amp[1] X Research source ; x1) Toilet paper tube, or small, non-conductive cylinder, 1. 75–2 inches (44–51 mm) in diameter (glass bottle, cardboard/plastic tube, etc. ) Speaker Wire strippers (or a similar item, like sharp scissors or a knife) Small knife or medium grit sandpaper
When choosing wire for your antenna, prioritize small diameter insulated wire (like ones in the 20- or 22-gauge), as these work best. Boost the reception of your antenna by looping its insulated wire into a coiled circle. You can keep the coil from unraveling with zip ties or electrical tape. Loop 50 feet (15. 2 m) of wire about 5 times.
Use wire strippers (or a sharp knife) to remove about 0. 5 inches (1. 3 cm) of insulation from both ends of each piece of wire. Jumper wires can always be cut down to size if they turn out to be too long, so you may want to cut these a little on the long side at first.
Start winding your inductor at one end of the cylinder. Leave about 5 inches (12. 7 cm) of slack where you fasten the wire with electrical tape to the lip of the cylinder. Wrap leaving no gaps in the windings. Aim for cylinders 1. 75 to 2 inches (44 to 51 mm) in diameter. Avoid metal cylinders, because metal will throw off your signal.
Since the wire is covered with enamel, scrape the ends with a small knife to reveal 0. 5 inches (1. 3 cm) of bare copper so that we can connect it to the circuit. Alternatively, use medium sandpaper to sand the ends. The windings of your inductor can also be held in place with a liberal application of hot glue or a similar adhesive. [6] X Research source
There is one exception to the connections on a typical breadboard: the long, connected rows at the top and bottom of it connect left-to right, not up-and-down like the rest of it. There are usually two rows on the top and two on the bottom, we will use only one row on the top and one row on the bottom.
Most breadboards have a long trough running across the middle, separating the board into two equal halves. Place your op-amp (with the divot on the left) centrally on the board so that four pins are on one side of the trough and four are on the other. This will allow an uncluttered layout, with the input (the antenna and tuning capacitor) on one side of the breadboard and the output (the speaker) on the opposite side. [8] X Research source The pins of amplifiers are numbered. To identify the pin numbers, place the divot the left of you, pin 1 is the first pin on the left of the bottom row. Sometimes in addition to, or instead of, the divot, pin 1 has a circular depression or dot above it. The pins are numbered consecutively from 1 starting on the bottom row and continue counter-clockwise on the other side of the device. Confirm the numbering of the legs of the amplifier after installation is as follows: on the bottom row, moving left to right: 1, 2, 3, 4. From the leg opposite 4, moving right to left: 5, 6, 7, 8. [9] X Research source The only pins used in this radio are: pin 2 = inverting input pin 4 = V- pin 6 = output pin 7 = V+ It is important not to reverse the polarity to the op-amp as it will destroy it. The op-amp is now oriented so that the top and bottom row match the polarity of the V+ and V- pins, when they are connected to the battery later. This layout avoids crossing the jumper wires and possibly causing a short circuit.
Electrolytic capacitors only accept voltage going in one direction. Electricity must enter in through the shorter lead. Applying voltage incorrectly can cause the capacitor to fail in a puff of smoke. [13] X Research source
This capacitor, like the first one you placed, isn’t polarized, so current can pass through it in both directions. It won’t matter which lead goes in which spot.
You can improve reception by spooling the wire of your antenna across the room as far as possible, or by winding it into a coil as described in the step on making the antenna.
In many situations, you’ll need to untwist the wires for the black and red leads attached to your speaker so they can be tied in to the radio circuit.
Add the positive wire (usually red) to any hole on the topmost row of the breadboard so it connects the speaker and the red jumper wire. Add the negative wire (usually black) to any hole on the bottommost row of the breadboard to supply the black jumper and variable capacitor with current. [17] X Research source
Be patient and turn the knob slowly. With a little patience, it’s likely you’ll be able to pick up an AM radio station.
Sometimes you may have thought that you’ve pushed the lead all the way in to the board without it actually making a good connection. Inspect your connections on the breadboard to see if you have not connected a component in an adjacent column. The adjacent columns are not connected, therefore that component will not be connected to the others and may even be connected to the wrong item. The rows at the top and bottom on the breadboard are separate, make sure that the holes where the jumper wires are plugged in belong to the same row, not adjacent rows. Some breadboards have the top and bottom rows split into a left side and a right side. [18] X Research source This is used when there are 2 different voltages in a circuit. In this radio, there is only one voltage is used. If the jumper wires are connected such that one is in the left side of a row and one is in the right side of a row, the radio will not work. The solution is to connect the jumpers in the same group of 5 holes of the same row, or to bridge the two rows with a small jumper wire at the middle of the rows. Adjust connections until you can hear audio when power is supplied. If this fails to work, you may need to rebuild the circuit from scratch. [19] X Research source
