Practice. It takes a whole lot of practice to get better with any skill. To this end, projects should be aligned to learn or practice skills with each one. Case and point, is this small FM Radio Module kit readily available on a lot of online sites.
The module is built around the FM Radio in an IC, the HEX3653. It has a relatively small amount of components and the PCB is of a high quality considering it’s low price at around $2-3 depending on the site you get it from.
The reason I would recommend this for a beginner’s project list is the IC, it’s an surface mount (SMD) but it’s only that one IC which is SMD, all the other components are through hole which would make it an interesting kit to practice SMD soldering on.
Here’s my crack at assembling the kit.
The kit comes in a single plastic bag of loose parts. Not anything glamorous but gets the job done.
What is noticeable is the lack of paperwork. There’s no written instructions. Fortunately the board itself has the components indicated and their placement. All resistors also have the same value so you really can just pick up the kit and start going ham on it.
(And yeah, the IC is slightly soldered skewed, but we’re not here for perfection) I also decided to just add a JST connector for the battery connector instead of directly soldering the battery wires to the board, for personal convenience.
I also highly suggest that, just as any soldering job, to cleanup the board after. I used the drag soldering technique for the IC so I cleaned up all the flux before I proceeding with the through-hole parts. To learn more about drag soldering and soldering SMD parts in general, here’s a video about it:
What’s great about this kit is a quick search on Google and YouTube shows a great deal of documentation available, so assembly can be through the aid of one of the many videos that review the kit.
Also, a comprehensive Instruction Booklet/Datasheet is available: https://www.google.com/url?sa=t&rct=j&q=&esrc=s&source=web&cd=&cad=rja&uact=8&ved=2ahUKEwiMi-Psg4n2AhXZEXAKHdTLAmEQFnoECDEQAQ&url=https%3A%2F%2Fabra-electronics.com%2Findex.php%3Fdispatch%3Dattachments.getfile%26attachment_id%3D599&usg=AOvVaw19MC8nNriN2pu-s1nHtM2D
The IC is fairly simple to understand as all the lovely demodulation work is hidden in the IC, allowing for a simple pinout structure of the IC.
The input signal can be sourced from either and external antenna or the wire of the headset plugged into the audio jack, chosen using a provided jumper connection.
This input is passed through a passive LC filter formed by the 10uH inductor and 100nF capacitor. To likely the protect the input of the IC, the signal is clipped using the two 1N4148 diodes.
The UX is also very simple with just 4 buttons, 2 to auto-seek for FM radio stations, and 2 for volume control. A power switch is also available to set the module to a “sleep mode” whilst still remembering the last station it was tuned into.
An external 32kHz clock is supplied for the demodulation functionality of the IC.
An interesting implementation to show “power on” is found on the output side of the IC. The stereo output has a DC offset for the audio and is used by a transistor to drive a yellow LED to show when the IC is powered.
The audio can be sourced through the audio jack or through exposed hole pads on the board. Interestingly, the schematic implies that the right audio is broken up to that pad after the coupling capacitor, but the left audio is directly connected to the pad (DC offset and all). Upon inspection of the board however, it was determined this is a fault on the schematic but not on the board itself (the board itself has both exposed pads connected after the coupling capacitor).
What I like about this kit is that because of the simplicity, it’s easy to integrate and adapt into projects. Indeed, the module can easily be integrated into an enclosure and have the buttons extended beyond the board. The audio is also fairly easy to access and can be ran through an audio amplifier to have built-in speakers (which would necessitate an external antenna as the headset wire wouldn’t be present always).
As for the functionality, well, it’s not that bad. For the price, it’s definitely worth it to pick up just for the value of practice. Luckily I live in a place where FM radio is still a thing so I can realistically actively use this piece of kit.
I’ll definitely pick this kit up again and maybe create a small standalone radio with it and probably think up of something fun to do with the audio signal.
Over the Corner 