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Project Notes

#131 AM/FM Radio Kit

Build notes for an AM/FM radio kit using the CD7642 AM, CD9088 FM and TDA2822 amp chips.

The Build

Notes

AM/FM radios are pretty rare these days but I wanted one for checking the behaviour of some RF circuits. So I got this kit from a seller on aliexpress. It’s a pretty nice kit - good PCB and no problem with the components - and the finished product works fine.

The kit is designed around 3 core integrated circuits:

  • CD7642 one-chip AM radio amp - pretty amazing, seems like all the guts of a 6-transistor superheterodyne stuffed into a TO-92 package.
  • CD9088 Monolithic Power FM radio tuner circuit in a 16 pin SMD
  • TDA2822 One Watt Stereo Amp IC - although marked as such, the circuit uses an 8-pin DIP which I’m guessing is one half of the chip i.e. mono. But I can’t find that datasheet.

AMFMRadioKit_parts

Construction

Some clarifications/intepretations of the instructions. Yes, its’s all in simplified Chinese;-)

  • battery leads are connected to pads marked GB+/GB-
  • the inductor with ferrite core fits in a plastic mount that slides/clips to the PCB. The leads are soldered to the two pads marked AM. This is the medium wave/AM antenna
  • the LED needs to stand-off the PCB to peep through the front casing properly. To get the measurements correct, it’s best to solder the LED in place with the PCB resting in the case in its final position.
  • I used a bit of flux to first solder the CD9088 SMD in place and avoid bridging the pins, but the PCB is well prepared and all the other components went in without trouble and without any flux assist.

The Schematic

The Build - PCB front

The Build - PCB rear

Credits and References

About LEAP#131 RadioAMFM

This page is a web-friendly rendering of my project notes shared in the LEAP GitHub repository.

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About LEAP

LEAP is my personal collection of electronics projects - usually involving an Arduino or other microprocessor in one way or another. Some are full-blown projects, while many are trivial breadboard experiments, intended to learn and explore something interesting.

Projects are often inspired by things found wild on the net, or ideas from the many great electronics podcasts and YouTube channels. Feel free to borrow liberally, and if you spot any issues do let me know or send a pull-request.

NOTE: For a while I included various scale modelling projects here too, but I've now split them off into a new repository: check out LittleModelArt if you are looking for these projects.

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