Hi guys,
I have been using a pair of Sennheiser headphones for quite some time now (HDR 118). They offer good sound and sit comfortably, however they do work based on RF signals (863 - 865 MHz) and have been catching a lot of interference as of late.
Instead of just getting a new pair of headphones I decided to go ahead and try to mod this pair to work with Bluetooth instead of RF to get rid of the interference and lose the dependency of the RF transmission station which sends the signal to the headphones.
After taking them apart, I have identified one chip as FM/AM stereo radio chip (CXA1838N) and a stereo headphone opamp (PT2308). Both datasheets attached. The big silvery block on the PCB is some sort of antenna combined with tuner to bring the frequency down I think, but I'm not sure as there are no markings anywhere on the block. The two rotary dials are an FM tuner (3 connections) and volume knob (5 connections).
The entire thing is powered by 2 x AAA batteries of 1.2 V for 2.4 V of available voltage in total.
I've been looking around at off-the-shelve BT receiver circuits that I could easily plug in there with some minor soldering and severing some connections to the RF chip and possibly removing the antenna/tuner-thing, but they almost all come with the following;
1. A voltage requirement of at least 3 V, most often 5 V.
2. An included op amp
This is a problem because:
1. I only have 2.4 V at my disposal.
2. I'd like to keep the audio driver on the current circuit as it would be nice to keep the volume knob working without too much messing around.
Another option would of course be to just re-do the entire circuit. It has however been a looong time since I meddled with PCB's and I'm afraid to waste a lot of time and money on a crappy design that I need to rebuild 3 times to get it working.
Do you guys have any tips as to which off-the-shelve BT receiver circuits could be easily modded in here? Or do you perhaps have some other idea's about how I could achieve my goal? Any advice is welcome!
I have been using a pair of Sennheiser headphones for quite some time now (HDR 118). They offer good sound and sit comfortably, however they do work based on RF signals (863 - 865 MHz) and have been catching a lot of interference as of late.
Instead of just getting a new pair of headphones I decided to go ahead and try to mod this pair to work with Bluetooth instead of RF to get rid of the interference and lose the dependency of the RF transmission station which sends the signal to the headphones.
After taking them apart, I have identified one chip as FM/AM stereo radio chip (CXA1838N) and a stereo headphone opamp (PT2308). Both datasheets attached. The big silvery block on the PCB is some sort of antenna combined with tuner to bring the frequency down I think, but I'm not sure as there are no markings anywhere on the block. The two rotary dials are an FM tuner (3 connections) and volume knob (5 connections).
The entire thing is powered by 2 x AAA batteries of 1.2 V for 2.4 V of available voltage in total.
I've been looking around at off-the-shelve BT receiver circuits that I could easily plug in there with some minor soldering and severing some connections to the RF chip and possibly removing the antenna/tuner-thing, but they almost all come with the following;
1. A voltage requirement of at least 3 V, most often 5 V.
2. An included op amp
This is a problem because:
1. I only have 2.4 V at my disposal.
2. I'd like to keep the audio driver on the current circuit as it would be nice to keep the volume knob working without too much messing around.
Another option would of course be to just re-do the entire circuit. It has however been a looong time since I meddled with PCB's and I'm afraid to waste a lot of time and money on a crappy design that I need to rebuild 3 times to get it working.
Do you guys have any tips as to which off-the-shelve BT receiver circuits could be easily modded in here? Or do you perhaps have some other idea's about how I could achieve my goal? Any advice is welcome!
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