Ebay and Aliexpress are saturated by those illegal Chinese transmitters. While the small ones are less dangerous compared to their big 15 Watt brothers, their output power still exceeds what car FM modulators can create.
Today we concentrate on a particular design based Quintic QN8027 chip as the centerpiece. Together with a micro-controller and a special LCD (both mass produced), it is possible to put together a relatively standard commodity product with pirate FM capabilities at 0.1-0.2W power level. The twin receivers of an extremely similar exterior are produced .. likely with the intent to fool the poor customs officials at Western countries 🙂
About the QN8027 chip, these are available for sale at all major sites. Technical data:
- QN8027 datasheet (a 29 pages PDF)
- QN8027 hardware Application Note (17 pages PDF)
- QN8027 product brief (2 pages PDF)
- Operational Description (a weird PDF)
Below is a short overview of some related (toy) products. Common characteristics among these boards are, they can output a decent FM signal heard within 100m region. Some of the models are provided with buttons to regulate the frequency and volume. Some of the models have USB sound capability. Beware with the USB sockets, for model C only +5V is connected, thus no USB sound. It seems, all the devices retain their the last emitting frequency in memory.
The price of these modules tend to be around 4..10 USD and sellers seem to be wise enough to mark these as “product samples” thus no problems with customs.
Regarding this model, a brilliant review is available at the gough’s tech zone. Look at the spectrograms, it seems the chip itself should be capable to produce signals of much higher quality than implemented in these cheap toys:
Some people have not succeeded to launch this module as an USB modulated sound source:
This model seems to be the most current and polished one. A 3D printed case is available for it at Thingiverse. The USB cord can be used for the power or, after being able to install the sound driver (the device manifests itself as a sound device CD002), to also transmit music from the computer. If neither the USB sound nor 3.5mm jack carries the signal, the microphone starts transmitting and the device start acting as a little FM bug (aren’t they still out of fashion?).
A giveaway element of this model is a quartz crystal near the LCD and also the soldering areas on the back side. The label at the P4 is deceiving, it is not for USB, the contacts are R(ight), L(eft), G(round) and F or E. The intent of P3 is unclear. I really like the “pause” button – this is probably the one a victim is expected to push after discovering the bug 🙂
Big warning – model C does not support the USB data (and thus USB sound). Look at the PCB, the tracks to the most USB pads are missing. If you need USB sound, buy another board.
P5 with Tx/Rx/G(round) contacts is a TTL level serial interface permitting to issue some AT commands this PDF document is describing . For pure RS232, a level converter is needed. It is not clear whether AT commands can be used to task some RDS messages (the chip itself has some RDS support). The purpose of the contact F at P4 is unclear but it goes straight to the micro controller.
Model D is not a self-contained module but designed as a shield to a master board. All the usual contacts are clearly marked and available. Antenna filter seems to be the best among other models. This model too seems to permit to issue some AT commands described in this PDF document .
Model “E” (just for comparison)
Model E represents a previous generation of chinese FM toys.
The most interesting question is about the RDS. Are some of the soldering contacts giving the access to RDS? The datasheet of the QN8027 claims: RDS is there. There is an Arduino lib (1, 2) available for QN8027 with “limited RDS functionality” and Russians have produced a nice program code for Bascom-AVR.
The twin receivers of an extremely similar exterior are produced … likely with the intent to fool the poor customs officials at Western countries 🙂
The keywords to find all these toys at Google are: “DSP PLL 87-108MHz LCD FM board”
Extra links (in various languages):
- https://e-gizmo.net/oc/kits documents/FM Broadcaster kit/FM II.pdf