Feedback on Audio Source switching in motorbike helmet - Page 1
Forum section: electronics / projects

author: chrisHem
author_rank: Newbie
timestamp: July 11, 2025, 02:53:10 am
content: Hey all,I have a motorbike helmet which has a Bluetooth receiver and camera unit integrated. I also have a secondary Bluetooth intercom unit. They each have their own stereo speakers and my goal is to integrate them into ONE stereo speaker. So ill end up having 2 audio inputs to one audio output going to the speakers.I initially wanted to use an audio ducking circuit shown herehttps://sound-au.com/project183.htmhowever the fact it runs on 12v put me off. I do have access to a single cell Li-ion battery in the helmet itself, but I don't have access to any higher voltage or source.I did change the schematics with my limited knowledge and what I thought I could get to work however I have not completely tested this. One thing I don't like is how I'm mixing the audio signals and then outputting them. For instance, the audio signal on the helmet is approx. 7v peak to peak on full volume. My limited understanding meant that I would need careful consideration on the supply voltage to get near lossless audio output. Upon testing this on a breadboard with the exact schematic from the website, using a 12v supply my output does work, however its slightly distorted and not the same levels as the input.I have since decided against that and have altered it slightly to use an analog switching circuit to just switch the inputs to the output depending on the Bluetooth intercom having audio.So my helmet audio will be playing as default, and switch to the Bluetooth intercom when audio is passed into the module. Looking to run this off a 3.2v coin cell battery. I am using an envelope detector to a comparitor to actually turn the power on/off to the TLV9152 because I want as long as possible battery life.I have the ability to alter the reference voltage on the TLV3011 comparator to ensure it triggers the SI2301 mosfet and powers up the TLV9152 circuit from Rods original design.I am however then using the output of the TLV9152 to drive the input pin either low or high of the TS3A5018 analog switch to switch between the inputs.I can adjust with a trim pot the sensitivity of the gain on the first half of the TLV9152 and also the delay time for the IRLML2502 mosfet to turn off using variable resistor trimmers.I have also found that the TLV3011 comparitor will use around 6 µA in general so when the unit is not receiving audio, the battery will last a very long time.Can anybody see issues with this design? I have a first revision board being made now, but would like to have this as compact as possible.I have since found out the TS3A5018 can only pass voltage within its input voltage, So 0-3.2v in this case, if my audio source is -3.5 to +3.5 this is obviously going to cause issues and will not work properly.I can bias the voltage up to be within 0-3.2v but on full volume it would obviously be outside the range allowed.I have already input the boards for manufacture, but its ok, i can always use them for testing and experiments.Can anybody think of a better way to achieve what I am trying to do? Basically have 2 stereo audio inputs, that are currently meant for 32ohm headphone/speakers (40mm speakers, small drivers), and have one stereo output, either switching between A and B inputs, or ducking one input lower when the other input is active. Running off a coin cell or single cell li-ion battery, (coin cell preferred to keep the module separate from the helmets power supply).basically trying to have 8 relays, but in a very small form factor, and preferably not physical relays so no sound when switching.