![]() The audio is amplified/converted to differential signals using the transistor Q1. The audio can be adjusted for volume using the potentiometer VR2 shown on the left side of the circuit below. The circuit below forms the audio amplifier that connects to the audio output pin from the radio chip. The circuit diagram shown here forms the entire radio apart from the audio amplifier! It's impressive how few components are needed. The circuit is powered from 3V, so two AA or AAA batteries can be used. An antenna wire is soldered to pin 1 of connector J3. Tuning is achieved by adjusting the potentiometer VR1, and the audio appears on pin 16 of the IC. The circuit diagram and the circuit board are labeled with the wire jumper position to select the FM band for Europe or the USA region (for other regions, the SI4825 datasheet will need to be examined). In my case, I decided to not connect any switch there and I soldered a wire jumper to permanently select the FM broadcast band.īy changing the resistor values, or by moving the wire jumper or wiring a switch there, the SI4825 can be reconfigured to support AM broadcast and short-wave modes, or different region FM bands. There is a chain of resistors to select the frequency band, the idea being that a multi-way switch can be used to select a tap point between resistors. The right-side portion of the circuit consists of a string of resistors that are used to select the desired frequency band and mode. Pins 2 and 3 on that connector are for AM mode, which isn't implemented. The FM antenna input is pin 1 on connector J3 on the far left side of the circuit. The SI4825 accepts a variable resistor (potentiometer) to act as the tuning control. The radio circuit is based around a single integrated circuit (IC), Silicon Labs SI4825, and not much else. Working in pairs, it should be possible for one child to hold a surface-mount component in position with tweezers, while the other solders it. Of course, to solder surface-mount successfully they had to use a reasonably small soldering tip size (around 1 mm) and thin solder (0.38 mm diameter is great) and some of the components had to be taped into position, or Blu-Tack (repositionable putty) can come in handy. After watching sub-10-year-olds soldering a couple of surface-mount integrated circuits (see photos below), I was encouraged that surface-mount technology was not difficult for them! If anything, occasionally through-hole components posed more of a problem. Then the output of the power amplifier is applied to the speaker.I'm convinced that children could assemble this circuit. The demodulator circuit gives de-emphasizing signal as output.Īfter passing the de-emphasizing signal (which coming from the demodulator circuit) through the AF or Audio Frequency Voltage Amplifier we get the original audio signal which was sent from the sender station.Īt last the audio signal is fed to the power amplifier circuit to amplify it. The FM demodulator circuit recovers the actual modulated signal which comes from the transmitter circuit in the form of the radio signal. ![]() The FM Demodulator Circuit is used to demodulate the FM signal. The IF amplifier circuit takes the IF signal or Intermediate Frequency signal coming from the Mixer Circuit and amplifies it. By combining those two signals, the mixer circuit generates the IF signal. The mixer circuit takes two signals as input, one is the amplified RF signal coming from the RF amplifier and another is an oscillating signal coming from the local oscillator. The RF amplifier is also responsible for Noise-reducing, impedance matching, etc. The received RF signal is very weak that is why it needs to amplify. The RF amplifier is used to amplify the RF signal received by the antenna. The next block is Radio Frequency Amplifier or RF amplifier. The antenna is used to receive the radio signals and intercepted it. To easily understand the working principle of FM Receiver, see the block diagram.
0 Comments
Leave a Reply. |
AuthorWrite something about yourself. No need to be fancy, just an overview. ArchivesCategories |