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Project Notes

#516 ZX2031 FM Radio Kit

Building an FM radio kit based on the Silan SC1088 FM receiver chip.


Here’s a quick demo..



I’m a sucker for radio kits. This time I’ve picked up a small FM kit that has an attractively small circuit board with primarily SMD components.

Most of the heavy lifting is performed by a single chip - the SC1088 in a SOP-16 package.


Ref Description checked installed
IC1 SC1088
V3 9014
V4 9012
V1 BB910
V2 LED 3mm red
L1 inductor bead
L2 choke
L3 78nH, 8 turns air core
L4 70nH, 5 turns air core
EJ headset
R1 153 15KΩ
R2 154 150kΩ
R3 122 1.2kΩ
R4 562 5.6kΩ
R5 681 680Ω TH
RP 51K
C1 222
C2 104
C12 104
C16 104
C10 104
C3 221
C5 221
C4 331 v
C6 332 v
C7 181
C8 681
C9 683
C11 223
C13 471
C14 33
C15 82pF
C17 332 ceramic
C18 100µF electrolytic
C19 223 ceramic





The heart of the circuit is the Silan SC1088 FM receiver chip.

Pin Function Description
1 Mute Mute output. Pull down to mute?
2 Voaf Audio out
3 Loop AF loop filter
4 Vp Power 1.8-5.0V
5 Osc VCO control input
6 IF Fb IF feedback
7 Clp1 Low-pass capacitor of 1dB amplifier
8 Voif IF output to external coupling capacitor(high-pass)
9 Vif IF input to limiter amplifier
10 Clp2 Low-pass capacitor of IF limiter amplifier
11 Virf signal input 1
12 Virf signal input 2
13 Cilm Limiter offset voltage capacitor
14 Gnd Ground
16 Cap All-pass filter capacitor. Pull-down for tuning search
16 Tune Electrical tuning/AFC. Pull-down to reset tuning



The BB910 is a varactor diode, supplied in TO92 package. I couldn’t find a corresponding datasheet for that package, but tests as follows:

  • anode: pin on the left of flat front
  • cathode: pin on the right of flat front


The circuit is very similar to “Fig. 4 Application circuit with AFC for mechanical tuning” from the SC1088 datasheet.



Construction Process




Credits and References

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

LEAP is just my personal collection of projects. Two main themes have emerged in recent years, sometimes combined:

  • electronics - 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
  • scale modelling - I caught the bug after deciding to build a Harrier during covid to demonstrate an electronic jet engine simulation. Let the fun begin..
To be honest, I haven't quite figured out if these two interests belong in the same GitHub repo or not. But for now - they are all here!

Projects are often inspired by things found wild on the net, or ideas from the many great electronics and scale modelling podcasts and YouTube channels. Feel free to borrow liberally, and if you spot any issues do let me know (or send a PR!). See the individual projects for credits where due.