ESSENTIAL INFORMATION BUILD INSTRUCTIONS CHECKING YOUR PCB & FAULT-FINDING MECHANICAL DETAILS HOW THE KIT WORKS GET IN TUNE WITH THIS FM RADIO KIT Version 2.
FM Radio Essentials www.kitronik.co.uk/2157 Build Instructions Before you start, take a look at the Printed Circuit Board (PCB). The components go in the side with the writing on and the solder goes on the side with the tracks and silver pads. 1 PLACE RESISTORS Start with the eleven resistors: The text on the PCB shows where R1, R2 etc go. Ensure that you put the resistors in the right place. PCB Ref R1 R2 & R9 R3 R5 & R11 R6 R8 R10 R12 R13 2 Value 100k 220k 56k 0Ω 6.8k 3.
FM Radio Essentials www.kitronik.co.uk/2157 4 SOLDER THE TIMING CRYSTAL This is a very small metal cylinder with two very thin legs protruding from one end. Gently place this component into the holes in the PCB where it is marked ’XTAL1’. The legs are fragile so care should be taken when putting them through the holes in the PCB. 5 SOLDER THE POTENTIOMETERS The two potentiometers are different so make sure that you check which is which before soldering them into position.
FM Radio Essentials www.kitronik.co.uk/2157 Checking Your FM Radio PCB Check the following before you connect any batteries to your radio. Check the bottom of the board to ensure that: All holes (except the four large mounting holes) are filled with the lead of a component. All these leads are soldered. Pins next to each other are not soldered together. Check the top of the board to ensure that: The negative markings on the electrolytic capacitors line up with the same markings on the PCB.
FM Radio Essentials www.kitronik.co.uk/2157 Designing the Enclosure (All measurements are in mm) Mounting the PCB to the enclosure The drawing to the left shows how a hex spacer can be used with two bolts to fix the PCB to the enclosure. Your PCB has four mounting holes designed to take M3 bolts.
FM Radio Essentials www.kitronik.co.uk/2157 Improving the Radio Tuning Tuning the radio using the potentiometer can be a tricky task. This is because one turn of the potentiometer covers the whole frequency range. This means that only very small adjustments of the potentiometer are required to tune into the different stations. Large Dial One way to improve the tuning mechanism is to attach a large dial to the end of the potentiometer. Look at the two dials below.
FM Radio Essentials www.kitronik.co.uk/2157 How the FM Radio Kit Works To aid the description of the circuit we have split it into two parts. The first deals with the decoding of the FM radio signal and the second deals with the audio amplification. Radio decoding For the radio circuit to work it needs a stable power supply. To provide the stable power supply a voltage regulator is used. This provides a 3.3V output for the circuit to run from.
FM Radio Essentials www.kitronik.co.uk/2157 Audio amplification The audio amplification is performed by another Integrated Circuit or IC called an NCP2890-D. Inside the NCP2890-D are lots of transistors, which are connected together to allow the small input signal to be amplified into a more powerful output that can drive a speaker. All amplifiers need to use feedback to ensure the amount of gain stays the same. This allows the output to be an exact copy of the input just bigger.
FM Radio Essentials www.kitronik.co.uk/2157 Audio amplification continued The output of the NCP2890-D uses two op-amps that are connected in a differential configuration. The second amplifier produced a 'mirror' (or reverse) of what the first op-amp produces. The output of one feeds OutA and the other feeds OutB. This configuration allows twice the power to be generated compared to amplifiers using a single op-amp configuration.
Online Information Two sets of information can be downloaded from the product page where the kit can also be reordered from. The ‘Essential Information’ contains all of the information that you need to get started with the kit and the ‘Teaching Resources’ contains more information on soldering, components used in the kit, educational schemes of work and so on and also includes the essentials. Download from: www.kitronik.co.
