Five: TRF AM Radio Receiver in Software

Generator EAN / UCC - 13 in Software Five: TRF AM Radio Receiver

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the circuit board; when finished remember to trim the excess component leads The ZN414 or MK484 TRF module looks very much like a common three-lead transistor Carefully refer to the pin-out diagram for the MK484 before installing, in order to prevent damaging it upon power-up One lead is the input lead from the tuned circuit One lead is the ground lead and the remaining lead is the output lead which is directed to the actual circuit The AM radio project uses a single dual in-line integrated circuit, an LM471 We elected to use an IC socket as insurance against a possible circuit failure at some point in time Integrated circuit sockets are inexpensive and make life easier in the event of a circuit problem, since it is much easier to unplug an IC rather than attempting to unsolder a multi-pin integrated circuit Go ahead and solder-in a good quality IC socket for U2 Take a look at U2 and you will notice that at one end of the plastic package you will find a cut-out, notch or indented circle Pin 1 of the IC will be just to the left of the notch or cut-out Be sure to align pin of the IC to pin 1 of the IC socket, pin 1 of U2 is the null offset pin which is not used in this circuit Note that pin 2 of U2 is the inverting input which is connected to the junction of R6 and R8 Next locate the ferrite inductor coil or L1; you will notice that it is in parallel with the tuning capacitor C2 The parallel tuned circuit is placed between capacitor C1 and the input of U1, the MK484 TRF IC These components are best placed at one end of the PC board if possible, or can be placed off the PC board on the front of your enclosure Now, locate the volume control, the 10k ohm potentiometer; it is a chassis mounted control which can be mounted on the front panel of your enclosure Let s wrap up the project First you will want to solder the battery clip; note that the black wire of the battery clip will go to the circuit board minus or ground bus and the red battery clip wire will go in series with one post on the on-off switch at S1, the remaining post of the SPST toggle switch will connect to the Collector of Q1 Finally locate two 4 pieces of #22 ga insulated hookup wire Bare both ends of the two wires, solder one end of each wire to the speaker leads Now take one free wire end and solder it to the common ground of the circuit and then solder

the remaining free wire end to the minus end of capacitor C8 This completes the construction of the AM radio project Let s take a well deserved rest and when we return we will check the circuit board for possible cold solder joints and possible short circuits Pick up the circuit board with the foil side facing upwards toward you Look closely at the circuit board, first we will inspect the circuit board for possible cold solder joints The solder joints should all look clean, shiny and bright If any of the solder joints look dull, dark or blobby then you should remove the solder from that joint and re-solder the joint over again Now pick up the circuit board once again and we will look for possible short circuits Short circuits are usually caused from one of two reasons The first cause of short circuits are loose solder blobs or solder balls which can sometimes stick to the circuit board The second cause for short circuits is to have stray component leads stick to the foil side of the board Rosin core solder residue can often be sticky and often solder blobs or stray component leads can bridge across circuit traces causing a short circuit Look over the board and remove anything that looks like it might be bridging any circuit traces Once the circuit inspection has occurred, you can prepare the circuit for its first test Connect up a fresh 9 volt battery to the AM radio circuit Once the battery is connected to the circuit, you can flip the on-off switch to the on position and you should begin to hear some hiss from the speaker If you do not hear anything, turn up the volume control to mid-position At this point you should begin to hear some sounds from the speaker Move the tuning capacitor control across the AM radio band and if all goes well you should begin to hear some local stations Move the ferrite core coil or the circuit board around in a 360 pattern to see where the station is loudest Hopefully the radio works fine without any further adjustments In the event that the AM radio circuit does not work at all, you will have to remove the battery from the circuit and inspect the circuit board one more time, but this time you will be looking for components placed incorrectly Remember earlier, we talked about certain components have polarity such as diodes, electrolytic capacitors, transistors, etc Now, you will need to