FM Radio add-on for Raspberry Pi

The QN8035 is a stereo FM radio receiver launched by the Quintic Corporation. Compared to other popular digital FM tuners (RDA5807, TEA5767, etc.), this tuner does not seem to be as popular among the DIY community. As we have seen, the biggest problem with this IC is the lack of information. During our initial search, we came across some details about this IC. Much of that information was confined to a product datasheet and a few undocumented GIT repositories.

Based on the information we found on the internet, we concluded that Quintic was no longer in business. According to the NXP website, it stated that Quintic Corporation was acquired by NXP in 2015.

Although the Quintic is no longer in business, the QN8035 IC can still be purchase at a low price from online stores. In addition, we found several FM radio kits manufactured using this IC in online stores.

Due to the lack of information, I decided to explore this IC to understand its functionality and limitations. In this article, I will describe my test setup and software applications built around this IC. After a few days of testing, I construct a fully functioning Raspberry Pi 3 based FM radio receiver using this IC.

The core components of this radio receiver are the QN8035 tuner and 32.768kHz oscillator. This entire radio design is to be powered by a 3.3V power supply. In our prototype, we drive this radio receiver using 3.3V supply terminals provided on the Raspberry Pi board.

QN8035 Tuner PCB.

The I²C bus has been used to interface the Raspberry Pi and QN8035 tuner IC. On Raspberry Pi, the I²C pull-ups are not necessary with this module. For other development boards, please check the pull-up resistor requirement from the documentation/schematic.

QN8035 and Raspberry Pi 3 connection diagram.

Initially, we developed a simple console application to test this tuner. This application and its source code are available at github.com/dilshan/qn8035-rpi-fm-radio. Binary executable compiled for the 32-bit Raspberry Pi operating system can also be downloaded in the release section of the above repository.

The terminal application is written using GCC and WiringPi library. Be sure to enable I²C support on Raspberry Pi using the "raspi-config" tool before testing this application.

GTK FM Tuner application.

After testing the QN8035 with the above application, we developed a GUI tuner application using GTK. This application provides all the features provided in the console application and which includes:

Manual and automatic station scanning.
Decode RDS PS (program service) data.
Volume control.
Display RSSI and SNR readings receive from the tuner.

Both these GUI and terminal applications have the RDS PS decoder to display the program/service name. As we have observed, the QN8035 RDS registers populate if it receives strong signals only. In some weak points, we observed that the RDS buffer received lots of incorrect data.

In setting up our tests, we used a 30cm long wire antenna with this radio receiver and received extremely stable reception. With a proper FM antenna, we got all the stations in the FM broadcast spectrum and were able to capture almost 95% of the channels and RDS data without any problems.

QN8035 tuner board with Raspberry Pi 3.

One of the significant shortcomings we saw in the QN8035 compared to the RDS5807M was its poor sensitivity to RDS data. Compared to the RDS5807M, this receiver does not decode RDS data in many weak stations.

The second significant drawback is the software complexity of the automated scanner (CCA) function. Compared to other digital tuners, we need to maintain a few states and values to perform the automatic scanning process on the QN8035.

We designed this receiver on a single-side PCB to minimize soldering inconvenience. The dimensions of the PCB are 58mm × 26.75mm.

The complete construction and configuration steps of this tuner are shown in the video presented in this article.

This is an open-source hardware project. All schematics, design files, and PCB layouts have been released under the Creative Commons Attribution 4.0 International license. Both test application and GTK FM Tuner application are released under the terms of the MIT License.

CD2003 - yet another simple FM radio receiver

In the last few days, we are looking for some simple FM radio receiver to integrate into one of our ongoing projects. For that, we try several FM radio receiver ICs including TDA7000, CD2003/TA2003/TA8164, CXA1019, and KA22429. Out of all those chips we select CD2003 (or TA2003/TA8164) based receiver for our project because of its simplicity and outstanding performance. Except to CD2003, Sony CXA1019 also perform well but we drop it because of its higher component count. We design our receiver based on Toshiba TA2003 datasheet and later we try TA8164 and CD2003 with the same circuit. Either CD2003 or TA8164 can directly replace TA2003 IC, and as per our observations, TA8164 gives excellent results out of those 3 chips. A prototype version of CD2003 FM radio receiver The PCB design and schematic which we used in our prototype project are available to download at google drive (including pin-outs of crystal filters and inductors ). Except for CD2003 IC, this receiver consist

Arduino superheterodyne receiver

In this project, we extend the shortwave superheterodyne receiver we developed a few years ago . Like the previous design, this receiver operates on the traditional superheterodyne principle. In this upgrade, we enhanced the local oscillator with Si5351 clock generator module and Arduino control circuit. Compared to the old design, this new receiver uses an improved version of an intermediate frequency amplifier with 3 I.F transformers. In this new design, we divide this receiver into several blocks, which include, mixer with a detector, a local oscillator, and an I.F amplifier. The I.F amplifier builds into one PCB. The filter stage, mixer, and detector stages place in another PCB. Prototype version of 455kHz I.F amplifier. In this prototype build, the Si5351 clock generator drives using an Arduino Uno board. With the given sketch, the user can tune and switch the shortwave meter bands using a rotary encoder. The supplied sketch support clock generation from 5205kHz (tuner frequ

Calculator for audio output transformers

Audio output transformers are heavily used in a vacuum tube and some (older) transistor base audio power amplifiers, but these days output transformer are quite hard to find and expensive item. For homebrew projects, the best option is to construct those transformers by ourselves and this script helps to calculate winding parameters for those transformers. This " AF output transformer calculator " script is written using Python and it works with most of the commonly available Python interpreters . The script is available to download at google drive under the terms of GNU General Public License version 3.0 . Homebrewed 25k: 4 output transformer Once supplied the input parameters this script provides a winding ratio, the number of turns required for primary and secondary winding and required copper wire gauges for both primary and secondary windings, etc. We construct several AF output transformers based on results of this script, which including transformers for M