One Transistor FM Radio Receiver Circuit

Here’s simple FM receiver circuit for a simple superregenerative FM radio. It is sensitive, selective, and has enough audio drive for an earphone. These designs generally have low component counts, however the design or my construction have been far from simple.

FM Receiver Schematic

FM Radio Receiver Circuit Layout
Because this is a superregenerative design, component layout can be very important. The tuning capacitor, C3, has three leads. Only the outer two leads are used; the middle lead of C3 is not connected. Arrange L1 fairly close to C3, but keep it away from where your hand will be. If your hand is too close to L1 while you tune the radio, it will make tuning very difficult.

Winding L1
L1 sets the frequency of the radio, acts as the antenna, and is the primary adjustment for super-regeneration. Although it has many important jobs, it is easy to construct. Get any cylindrical object that is just under 1/2 inch (13 mm) in diameter. I used a thick pencil from my son’s grade school class, but a magic marker or large drill bit work just fine. #20 bare solid wire works the best, but any wire that holds its shape will do. Wind 6 turns tightly, side-by-side, on the cylinder, then slip the wire off. Spread the windings apart from each other so the whole coil is just under an inch (2.5 cm) long. Find the midpoint and solder a small wire for C2 there. Mount the ends of the wire on your circuit board keeping some clearance between the coil and the circuit board.

A tuning knob for C3

C3 does not come with a knob and I have not found a source. A knob is important to keep your hand away from the capacitor and coil when you tune in stations. The solution is to use a #4 nylon screw. Twist the nylon screw into the threads of the C3 tuning handle. The #4 screw is the wrong thread pitch and will jam (bind) in the threads. This is what you want to happen. Tighten the screw just enough so it stays put as you tune the capacitor. The resulting arrangement works quite well.

FM Radio Receiver Circuit Adjustment
If the radio is wired correctly, there are three possible things you can hear when you turn it on: 1) a radio station, 2) a rushing noise, 3) a squeal, and 4) nothing. If you got a radio station, you are in good shape. Use another FM radio to see where you are on the FM band. You can change the tuning range of C3 by squeezing L1 or change C1. If you hear a rushing noise, you will probably be able to tune in a station.

Try the tuning control and see what you get. If you hear a squeal or hear nothing, then the circuit is oscillating too little or too much. Try spreading or compressing L1. Double check your connections. If you don’t make any progress, then you need to change R4. Replace R4 with a 20K or larger potentiometer (up to 50K). A trimmer potentiometer is best. Adjust R4 until you can reliably tune in stations. Once the circuit is working, you can remove the potentiometer, measure its value, and replace it with a fixed resistor. Some people might want to build the set from the start with a trimmer potentiometer in place (e.g., Mouser 569-72PM-25K).

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Ultrasonic Wave Receiver Circuit

Ultrasonic Wave Receiver

Ultrasonic recipients will receive an ultrasonic signal emitted by an ultrasonic transmitter in accordance with the characteristic frequency. Received signal is going through the process of filtering using the frequency band pass filter circuit, with a frequency value that is passed has been determined.


Then the output signal will be amplified and passed to the comparator circuit (comparator) with a reference voltage determined based on the amplifier output voltage when the distance between the sensor mini vehicles with bulkhead / retaining walls to reach the minimum distance for the turn direction. Comparator output can be considered under these conditions is high (logic 1 ), while longer distances are low (logica0). Binary logics are then forwarded to the circuit controller (microcontroller).

The working principle of ultrasonic wave receiver circuit are as follows:

• First - the first received signal will be strengthened first by the circuit transistor amplifier Q2.
• Then the signal will be filtered using a high pass filter at a frequency of> 40kHz by a series of transistor Q1.
• After the signal is amplified and filtered, then the signal will be rectified by diode D1 and D2 series.
• Then the signal through a filter circuit low pass filter at a frequency <40kHz through the filter circuit C4 and R4.
• After that the signal will go through the Op-Amp comparator U3.
• So when there is an ultrasonic signal into the circuit, then the comparator will issue a logic low (0V), which will then be processed by the microcontroller to calculate the distance.

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