App note from Texas Instruments on isolating DC and high frequency noise in audio using their automotive op amps. Link here (PDF)
Phone calls, emergency alerts, and music are just a few of the reasons that a high quality audio system is vital in automotive infotainment and clusters. Operational amplifiers (op amps) are one of the most common building blocks of automotive audio circuits. Many designers choose to incorporate op amps into their automotive audio circuits in order to increase audio performance. Higher order filters, which can be created through a combination of second order filters, attenuate noise more aggressively than lower order filters. Additionally, active filters remove the chance of unwanted interference with the audio signal.
Vasily Ivanenko @ QRPHB writes, “I sought a low distortion, single supply, AF power amplifier for my transistor radios. I’ll present my experiments, some musings, test equipment and a reference to some wonderful books & their wise author. Sadly, some amateur radio receiver builders diligently craft their RF stages, but skimp on the PA audio stage. Actually — many commercial radio designers also do this.”
If you are an audio enthusiast and if you have multiple audio systems and speakers, you may definitely need to have a speaker selector switch. These switches allow you to route a audio signal through a switching system and distribute it to various speakers. Using this listener can select single amplifier – speaker combination through the switch. We mainly design this switch to share our speaker system with multiple audio amplifiers. We design this switch to handle 6 stereo audio channels.
See the full post on his blog here. Project files are available at Github.
For some time, on different chinese webstores (for example Banggood) there is a module called JQ6500 for sale:
it’s often described as a voice sound module or as an MP3 player sound module.
Actually JQ6500 is the name of the main chip hosted on the module:
The chip is manufactured by a Chinese company named JQ. A datasheetfor the chip is also available, unfortunately only in Chinese (but Google Translate can help to understand what it contains).
On the other side of the PCB, the module houses two additional integrated circuits:
a 16Mbit flash memory (25L1606E)
a 3W audio amplifier (HXJ 8002)
When you connect the module to your computer via USB, it is detected as a CDROM drive. If you browse the content of the CD, you can find the MusicDownload.exe application that allows to upload audio files in the flash memory:
The software is in Chinese but its use is very simple: by moving to the second tab you can select the MP3 files to be uploaded. If you now move back to the initial tab, you can start the upload process clicking on the only available button. In the video at the end of this post you can see how it works…
You can control the JQ6500 chip in different ways. The easiest one is using external buttons connected to pins K1-2-3-4-5:
When you press a button, the chip plays the corresponding audio file. For example if you press the button connected to pin K1, the chip plays the audio file named 001.mp3.
The onboard amplifier (HXJ 8002) is a mono IC and its output is connected to pin SPK+ and SPK-. You can therefore connect to those pins a small speaker. If you want a stereo audio, you can instead use pins ADL_L (left channel) and ADC_R (right channel) and connect them to an external amplifier.
This module is an excellent and inexpensive solution to add audio to your projects. The use of an internal flash memory has the advantage of not requiring SD cards or other media to store your audio files; in contrast its capacity (16Mbit = 2MByte) makes it more suitable to reproduce sound effects / guide voices than to make a music player.
In the next articles I will show you how to interface the module with Arduino … meanwhile here is a video showing my first tests:
Following up on Part 2, it’s time to talk about the output stage.
This output stage is the brainchild of my friend Kostas, all I did was lay out the PCB.
It is a fully discreet single-ended class-A output stage, outputting ~2.4V RMS.
I have been working on some games for the ESP32 and needed some decent quality audio with a minimum number of additional components. I was bouncing between using the DAC and using the I2S bus. The DAC requires less external parts, so I went that way. I ended up creating a very simple library for use in he Arduino IDE. (Note: This only works with ESP32)
This article is the first of a series detailing the design and build process of an Arduino controlled Dual Mono AK4490 DAC by DimDim:
The design goal was to do a dual mono design so as to maximize SNR and channel separation. A 4-layer PCB design was chosen so as to have a very solid, low impedance ground plane as well as proper power and signal planes. The I2S, audio signals and power after the local LDO regulators are routed on the top layer, the 2 middle layers are ground and power planes, and the bottom layer serves to route I2C signals and some power lines.
Holtek’s App note about their audio to digital signal converter chip BH45F0031 that together with an phone app, communication via audio phone jack is possible. Link here (PDF)
The BH45F0031 is a Flash type 8-bit high performance RISC architecture microcontroller, which is designed for smart phone headset interface applications that can directly transmit data and communicate with the microcontroller using their audio earphone interface.
The BH45F0031 can convert the analog audio signals from mobile phones into digital data and transmit them to a master external MCU. The device can also convert the digital data from the master MCU into analog audio signals and transmit them to mobile phones.
One of the problems that has accompanied the advent of ever more complex home entertainment systems is the complexity of the burgeoning stack of remote controls that manifest themselves alongside your system. It doesn’t matter if you have a fancy does-the-lot universal remote, you are still left with a slew of functions to perform before you can sit down to enjoy the music.
[Robert Cowan] had this problem with his whole-house audio system. Playing music required a fiddle with the remote, and the moment was gone. What was needed was an automatic system that simply issued the relevant commands to the stereo without all the fuss.
His solution was to have everything happen when an audio output was detected from his Sonos Connect streaming media player. He tried rectifying its line output to detect music but hit problems, so instead used a SparkFun audio detector module. This in turn speaks to an Arduino, which then talks via a level shifter to the stereo’s RS232 port. [Robert] included all the relevant parts, schematic, and software is links in the video description. It’s a project that should almost be a feature built into a decent stereo, yet the manufacturers prefer the awful interfaces of their remote controls.
We can’t help wondering if his spotless bench and suspiciously tidy workshop is a scene of real hardware hacking or a TV studio, but we’ll forgive him that for his good result.