fritz42_male
Senior Member
I'm also looking for a video player with serial control - Tenda don't do one and my Googling has been fruitless. Has anyone out there come across one?
mp3 playback module
- Thread starter Haku
- Start date
There are video players with RS232, just a case of finding one secondhand or still in production, and having pockets deep enough -
http://www.d-mpro.com/users/folder.asp?FolderID=1551
http://www.amazon.co.uk/TASCAM-DV-D01U-PLAYER-RS-232-PORT/dp/B000TUEWC8
http://www.bcdusa.com/content/view/28//
http://www.arcam.co.uk/advice-and-support/discontinued-products/DV79DVDPlayer
I reckon your Google search terms must have been wide of the mark as there's quite a a lot of other hits which turned up.
The cheapest solution is to simply get a PICAXE to control a player's remote or bypass that and inject the IR signal directly. Or interface directly to the front panel buttons.
The most flexible solution is probably to get a PC set up for Visual Basic playing back video full-screen and control the VB program via serial.
http://www.d-mpro.com/users/folder.asp?FolderID=1551
http://www.amazon.co.uk/TASCAM-DV-D01U-PLAYER-RS-232-PORT/dp/B000TUEWC8
http://www.bcdusa.com/content/view/28//
http://www.arcam.co.uk/advice-and-support/discontinued-products/DV79DVDPlayer
I reckon your Google search terms must have been wide of the mark as there's quite a a lot of other hits which turned up.
The cheapest solution is to simply get a PICAXE to control a player's remote or bypass that and inject the IR signal directly. Or interface directly to the front panel buttons.
The most flexible solution is probably to get a PC set up for Visual Basic playing back video full-screen and control the VB program via serial.
fritz42_male
Senior Member
Thanks for the suggestions but I was looking for a small footprint solution based on sd-card card or USB flash storage. I already have a Tenda VGA/composite video player that I can control via ir or link into the buttons but I was looking for something that did what the mp3 player did but for video as well e.g. Command set that allows you to play specific files.
4dsystems do a serial VGA unit that almost fits the bill (picaso) but the command set seems to be missing a video play feature
Second edit. A visit to the support forum shows that it will play video. Looks like this will do the job and at only $50. Oz based company as well!
4dsystems do a serial VGA unit that almost fits the bill (picaso) but the command set seems to be missing a video play feature
Second edit. A visit to the support forum shows that it will play video. Looks like this will do the job and at only $50. Oz based company as well!
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1968neil
Senior Member
are you using a preamp after the module ?
If the module is set at max vol it clicks as the output comes on.
With a preamp and the volume set mid way there is no click on mine.
Hope this helps
a cheap and low cost solutions is the maplin low noise stereo preamp kit at about £5 gbp.
Regards
Neil
If the module is set at max vol it clicks as the output comes on.
With a preamp and the volume set mid way there is no click on mine.
Hope this helps
a cheap and low cost solutions is the maplin low noise stereo preamp kit at about £5 gbp.
Regards
Neil
Have you tried adding DC-blocking capacitors ? Might not work / not be needed but just a thought. What are the characteristics of the 'click' on the scope; time, magnitude, shape - that might help give some pointer to what the cause is and what a solution may be.
I didn't hear any clicks but then I didn't use a 50W amp. Could it just be the particular MP3's ?
I didn't hear any clicks but then I didn't use a 50W amp. Could it just be the particular MP3's ?
1968neil
Senior Member
Hippy may have hit the nail on the head,
removed dc block caps from mine and it also has a click on the beginning of the file.
So would seem that the caps are needed, i put them in as a matter of course so never noticed the click.
i also used a preamp to give the module a little help, the output volume only needs to be at level 4 to give quite a nice clean level.
I used the Maplin low noise stereo preamp
It was only £5.99 GBP and not worth the effort of a self design/build for a prototype
The click does seem more prominent at higher levels without the caps. Can't see any caps on the mp3 board so one would have to assume that decoupling is down to the end user.
Hope the caps solve the problem for you.
1uF non polarised seems to be the magic value.
Regards
Neil
removed dc block caps from mine and it also has a click on the beginning of the file.
So would seem that the caps are needed, i put them in as a matter of course so never noticed the click.
i also used a preamp to give the module a little help, the output volume only needs to be at level 4 to give quite a nice clean level.
I used the Maplin low noise stereo preamp
It was only £5.99 GBP and not worth the effort of a self design/build for a prototype
The click does seem more prominent at higher levels without the caps. Can't see any caps on the mp3 board so one would have to assume that decoupling is down to the end user.
Hope the caps solve the problem for you.
1uF non polarised seems to be the magic value.
Regards
Neil
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The caps go in-line / in series with the signals ...
http://www.nrgrecording.de/html/opamps_2.html
A lot of audio equipment will come with blocking caps on the inputs and outputs so it's not usually necessary to add your own.
http://www.nrgrecording.de/html/opamps_2.html
A lot of audio equipment will come with blocking caps on the inputs and outputs so it's not usually necessary to add your own.
1968neil
Senior Member
As Hippy states, in series with the output of the MP3 Module and the input of your preamp/Amp.
This will remove DC disturbance at the input to the amp, as we dont know your amp hook up and if it actually has any such coupling then adding a cap in both left and right channels wont go a miss.
Regards
Neil
This will remove DC disturbance at the input to the amp, as we dont know your amp hook up and if it actually has any such coupling then adding a cap in both left and right channels wont go a miss.
Regards
Neil
Just as a wee reminder on the op-amp concept and the clicking on the audio, you really MUST have a preamp between the MP3 player module, and any stereo line-in.
The output from the module is only 200mV or so, which is roughly 25% of the input signal level that most line-in's are looking for.
So, you turn the wick right up on the amp, and you can then hear noises such as decoder noise and the pops at the start and end of songs.
If you use a simple LM833 or equivalent stereo pre-amp with a gain of about 6dB or so, this will lift the level into the amplifier up much closer to the 1V or so that they expect.
In my case, the preamp totally removed the pops, as with the extra gain of the pre-amp, you can't hear them anymore, nor can you hear any decoder noise. Results may differ with different pre-amp modules, but the one I used and posted photos of earlier, worked a treat.
One other thing to note, and that is that most IC amplifiers have programmable gain(or at least adjustable), and so generally don't need a pre-amp. Amps such as TDA7056 don't need a pre-amp, as they have enough internal gain to get around the problem, but home stereos or domestic amplifiers expect more input so will be under-driven most of the time without a pre-amp.
The output from the module is only 200mV or so, which is roughly 25% of the input signal level that most line-in's are looking for.
So, you turn the wick right up on the amp, and you can then hear noises such as decoder noise and the pops at the start and end of songs.
If you use a simple LM833 or equivalent stereo pre-amp with a gain of about 6dB or so, this will lift the level into the amplifier up much closer to the 1V or so that they expect.
In my case, the preamp totally removed the pops, as with the extra gain of the pre-amp, you can't hear them anymore, nor can you hear any decoder noise. Results may differ with different pre-amp modules, but the one I used and posted photos of earlier, worked a treat.
One other thing to note, and that is that most IC amplifiers have programmable gain(or at least adjustable), and so generally don't need a pre-amp. Amps such as TDA7056 don't need a pre-amp, as they have enough internal gain to get around the problem, but home stereos or domestic amplifiers expect more input so will be under-driven most of the time without a pre-amp.
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Finally; have got round to connecting things back up, plumbing the module into the Hi-Fi and I must say it's a pretty impressive module, and excellent for the price.
As in Python's Life of Brian, "My legs are grey. My ears are gnarled. My eyes are old and bent", but it sounded absolutely marvellous to me with 320kbps tracks. Have yet to load up tracks I'm familiar with and do a decent 'cranked-up' headphone test.
No pre-amp but as my amp is 250mVpp ( CD is 1Vpp ) it's not a problem. No DC-blocking capacitors needed, no thumps or clicks at start of track noticed.
Have got it scanning for albums and tracks, playing albums at random on button push and a stop, status LED's and album/track number display, so 90% of an MP3 player done.
Now all I need is a car boot Virgin Media STB to strip and fit it in, passed up many, then when you actually need one. ...
http://www.samsung.com/global/system/business/telecommunications/product/2007/6/26/219462m_smt2110c.jpg
As in Python's Life of Brian, "My legs are grey. My ears are gnarled. My eyes are old and bent", but it sounded absolutely marvellous to me with 320kbps tracks. Have yet to load up tracks I'm familiar with and do a decent 'cranked-up' headphone test.
No pre-amp but as my amp is 250mVpp ( CD is 1Vpp ) it's not a problem. No DC-blocking capacitors needed, no thumps or clicks at start of track noticed.
Have got it scanning for albums and tracks, playing albums at random on button push and a stop, status LED's and album/track number display, so 90% of an MP3 player done.
Now all I need is a car boot Virgin Media STB to strip and fit it in, passed up many, then when you actually need one. ...
http://www.samsung.com/global/system/business/telecommunications/product/2007/6/26/219462m_smt2110c.jpg
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Hmm, I'm still having trouble with noise inteference from the processor on the mp3 module.
I got given some cheap 2.1 Tesco speakers at christmas, one of the outputs was screwed so I took it apart and thought it might be the TDA2822M amp, ordered a replacement off eBay but a month later and the tracking system is still saying "we have your package", the seller sent replacements which I put one in the speakers a week ago and it fixed it.
Now I've just hooked an mp3 module up to the speakers, the module being powered from a battery pack, it actually sounds pretty good (except they put the bass volume too high on the 2.1 speakers), no inteference whatsoever.
But I hooked a couple of wires into the speakers to get voltage from it after the 4 bridge diodes, about 11-12v, then that voltage into the mp3 module, it works but now there's noticable 'processing' inteference coming from the mp3 module. The same when I switched the mains off to the speakers and powered them + the mp3 module from the same 8xAA battery pack.
How can I power an amplifier with speakers and the mp3 module from the same source and not get any inteference coming from the mp3 module? Is this the time I need to start learning about RF chokes?
I got given some cheap 2.1 Tesco speakers at christmas, one of the outputs was screwed so I took it apart and thought it might be the TDA2822M amp, ordered a replacement off eBay but a month later and the tracking system is still saying "we have your package", the seller sent replacements which I put one in the speakers a week ago and it fixed it.
Now I've just hooked an mp3 module up to the speakers, the module being powered from a battery pack, it actually sounds pretty good (except they put the bass volume too high on the 2.1 speakers), no inteference whatsoever.
But I hooked a couple of wires into the speakers to get voltage from it after the 4 bridge diodes, about 11-12v, then that voltage into the mp3 module, it works but now there's noticable 'processing' inteference coming from the mp3 module. The same when I switched the mains off to the speakers and powered them + the mp3 module from the same 8xAA battery pack.
How can I power an amplifier with speakers and the mp3 module from the same source and not get any inteference coming from the mp3 module? Is this the time I need to start learning about RF chokes?
As it seems to be that interference only appeared when you ran power from the speakers it seems reasonble to say that this is the cause of that interference. Though I'm not sure I understand why that remained when you went back to battery power. Perhaps it's pickup rather than processing noise ?
One thing which can get complicated in any multi-unit system is what's actually 0V and how things connect, are floating or even connected to mains ground. If the amp supply is meant to be floating, 0V comes via the audio common, then connecting power to 0V may cause problems. You'd really need a circuit of the amp to fully know what's going on.
I've burned some decent test tracks and tried headphones and I couldn't hear any interference but did detect a slight click on track starting. Must add a 'next track' button next
One thing which can get complicated in any multi-unit system is what's actually 0V and how things connect, are floating or even connected to mains ground. If the amp supply is meant to be floating, 0V comes via the audio common, then connecting power to 0V may cause problems. You'd really need a circuit of the amp to fully know what's going on.
I've burned some decent test tracks and tried headphones and I couldn't hear any interference but did detect a slight click on track starting. Must add a 'next track' button next
It seems to be when the amplifier (any amplifier from what I can tell) is powered from the same DC +V source as the mp3 module then there's noticable audio interference which appears to be coming from the microcontroller on the mp3 module (sounds like it's when it accesses the SD card), even when the mp3 module has it's power dropped down to 5v with a 78L05 which has 0.1uf caps on it's input & output lines.
But separate power sources for the amp & mp3 module means no audio interference.
I'm going to do more testing to try and get round this problem because it's seriously irking me.
edit: I wonder if an isolated DC-DC converter would fix the problem.
But separate power sources for the amp & mp3 module means no audio interference.
I'm going to do more testing to try and get round this problem because it's seriously irking me.
edit: I wonder if an isolated DC-DC converter would fix the problem.
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That is possible, any noise being put on the power rails can propagate into other power rails ( and via 0v ). It might be solved with capacitors ( larger reservoir and/or smaller decoupling ) around the place, or by moving the supplies apart; incoming PSU split then diode fed to the two separate PICAXE/MP3 and Amplifier modules, RF beads may also help.
Ideally one wants the fault condition and a good scope, to see what's happening and how things are affected when the PICAXE/MP3 and Amplifier are used in conjunction and separate. That should reveal what the problem actually is and point to the best way to solve things.
It might be an idea to draw a block diagram or give a circuit so we're entirely clear on how your supply sharing is implemented; "same DC source" could be interpreted in a number of ways.
I've tried that setup with two different amplifiers, a 5v one and a 9v-12v one, first running off a single battery pack and then separate battery packs.
If I had an oscilloscope I'd definitely be looking at the power lines to try and see what's going on.
In the meantime I'm going to order an isolated DC-DC converter to power the mp3 module as one of those isn't very much and it's worth a shot to eliminate this frustrating problem.
Ooh, look ma ... sparks!
I'm tending to agree there are odd things happening relating to power supplies using the MP3 module. I have my PICAXE, MP3 module and all else powered from a bench supply, +5V.
I am using a DS1307 RTC and that would occasionally lock itself out, return $FF's. I also saw sparks when connecting the 0V of another PICAXE board which had a download cable connected. Not big sparks but noticeable!
I thought it was related to the amp, not having DC-blocking capacitors, as turn everything off, turn PICAXE+MP3 on with amp off and DS1307 would recover, keep working when amp turned on.
Just tried a standalone DS1307 test program and that failed, $FF's, repeatedly. No amp connected. Disconnected the MP3 VIN from +5V, powered-up and it recovered. An earlier DS1307 fail had come with power off and just moving the MP3 VIN and 0V connectors on breadboard, and I recall sparks then - should have made that correlation earlier.
Will have to investigate further.
I'm tending to agree there are odd things happening relating to power supplies using the MP3 module. I have my PICAXE, MP3 module and all else powered from a bench supply, +5V.
I am using a DS1307 RTC and that would occasionally lock itself out, return $FF's. I also saw sparks when connecting the 0V of another PICAXE board which had a download cable connected. Not big sparks but noticeable!
I thought it was related to the amp, not having DC-blocking capacitors, as turn everything off, turn PICAXE+MP3 on with amp off and DS1307 would recover, keep working when amp turned on.
Just tried a standalone DS1307 test program and that failed, $FF's, repeatedly. No amp connected. Disconnected the MP3 VIN from +5V, powered-up and it recovered. An earlier DS1307 fail had come with power off and just moving the MP3 VIN and 0V connectors on breadboard, and I recall sparks then - should have made that correlation earlier.
Will have to investigate further.
@ 1968neil : Got the PM, will be in touch. Thanks. I'll be honest though; if you've got one my opinion is keep it, or one day regret not doing so. It's a nice looking box, 7-segs, buttons and IR sensor, would make a nice box for any PICAXE project. And I've been looking at a lot of boxes to repurpose.
Well it seems to have 'all gone Pete Tong' as they say, but not sure why. Though it has had some abuse like those sparks earlier it was stll working until late tonight then the MP3 module started putting start of track clicks out, but only on one channel. Swapped modules and the other is fine so definitely a module issue.
Just as a little addition to the PSU issues with the module, I have never used the module on anything less the 12v. The module has it's own on-board 317 regulator, which supplies the core with 3v3, so I don't really see the need or use of any pre-regulator in front of it. I would be dubious of using 5v to power the module, as the typical in-out voltage of a 317 regulator has to be at least Vcc + 2.5v, meaning that the core will be powered from 2.5v(under-voltage) if run from a 5v supply, assuming that the regulator does not start dropping out, which it probably would...
As far as noise is concerned, most of this can be eliminated by making sure you don't have any ground-loops in your audio circuit.
If you have the ability to make PCB's, use a ground-plane and connect all your audio and DC grounds to it, so that they are kept all at the same potential.
I did tinker with the MP3 module on a breadboard first though, and I made the module GND pin the common for all other ground connections - IE: DC GND connected to this pin, and all audio grounds, and any/all other grounds run back to this common point - do not daisy-chain ground connections from one device to the other.
Using the TDA7056 power amp, you don't need any preamp, as it has a very healthy maximum gain ability of about 70dB! In this case, I powered both 7056 IC's and the MP3 module from a common 12v supply.
EDIT: Page 2 of the datasheet for the module says minimum supply voltage should be 6v - even though it also says 5v in the features on the previous page... Typical supply voltage is 12v according to the datasheet.
As far as noise is concerned, most of this can be eliminated by making sure you don't have any ground-loops in your audio circuit.
If you have the ability to make PCB's, use a ground-plane and connect all your audio and DC grounds to it, so that they are kept all at the same potential.
I did tinker with the MP3 module on a breadboard first though, and I made the module GND pin the common for all other ground connections - IE: DC GND connected to this pin, and all audio grounds, and any/all other grounds run back to this common point - do not daisy-chain ground connections from one device to the other.
Using the TDA7056 power amp, you don't need any preamp, as it has a very healthy maximum gain ability of about 70dB! In this case, I powered both 7056 IC's and the MP3 module from a common 12v supply.
EDIT: Page 2 of the datasheet for the module says minimum supply voltage should be 6v - even though it also says 5v in the features on the previous page... Typical supply voltage is 12v according to the datasheet.
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I have successfully eliminated almost all of the 'processing' noise coming from the mp3 module when it's sharing the same +V line with the audio amplifier, with this little box:
Yeah I know it's overkill at being able to handle 3A but it only cost me £3, which is a bargain for such a high power isolated DC-DC converter.
The sound quality is now excellent again, no more having to faff around with two different battery packs etc., I've spotted some isolated 5v-5v 1cm square ones that look perfect for powering the mp3 module.
Yeah I know it's overkill at being able to handle 3A but it only cost me £3, which is a bargain for such a high power isolated DC-DC converter.
The sound quality is now excellent again, no more having to faff around with two different battery packs etc., I've spotted some isolated 5v-5v 1cm square ones that look perfect for powering the mp3 module.
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The Alfatronix DC-DC converter I got off eBay, it retails for a lot more and I was very suprised to get it for so little, I only really needed it for testing wether using an isolated DC-DC converter would stop the unwanted noise (which I'm so glad it does).
The converters I'm actually looking at getting for driving the mp3 modules are these since I haven't had any problems powering it from 5v - http://cgi.ebay.co.uk/370480694313
I have yet to test wether powering a controlling Picaxe from the same isolated voltage as the mp3 module causes any interference, or wether the Picaxe needs to be powered from the pre-isolated voltage. I get the feeling the Picaxe won't cause any inteference either way.
The converters I'm actually looking at getting for driving the mp3 modules are these since I haven't had any problems powering it from 5v - http://cgi.ebay.co.uk/370480694313
I have yet to test wether powering a controlling Picaxe from the same isolated voltage as the mp3 module causes any interference, or wether the Picaxe needs to be powered from the pre-isolated voltage. I get the feeling the Picaxe won't cause any inteference either way.
Thanks for the link I bookmarked the ebay page. I'm embarrassed to ask but why would you need the DC to DC converter that has an input that matches the output, sort of a misnomer. I'm guessing it somehow filters the noise from the incoming power supply. I've always used a capacitor or some sort of an RC network.
I just hooked up my battery powered module with a 20X2 to my stereo and so far no noise.
I am running it from a 2 cell LiPo which puts out around 8 volts and is regulated down to 5v by a 7805 and that feeds both the picaxe and the module. I realize that the module has a 3.3 volt regulator and I'm thinking the next version I build I want to make it really portable and solder to the regulator on the module to power the 20x2, I found a nice amplifier from Sure electronics that needs less then 4 volts. Also considering bypassing the regulator and powering everything with 2 C size batteries. On the current version of my build I have an IR receiver and I need to find an IR receiver that works at 3.3 volts.
I just hooked up my battery powered module with a 20X2 to my stereo and so far no noise.
I am running it from a 2 cell LiPo which puts out around 8 volts and is regulated down to 5v by a 7805 and that feeds both the picaxe and the module. I realize that the module has a 3.3 volt regulator and I'm thinking the next version I build I want to make it really portable and solder to the regulator on the module to power the 20x2, I found a nice amplifier from Sure electronics that needs less then 4 volts. Also considering bypassing the regulator and powering everything with 2 C size batteries. On the current version of my build I have an IR receiver and I need to find an IR receiver that works at 3.3 volts.
If you look back at the recent posts of mine in this thread you'll see I've had problems with unwanted noise coming from the mp3 module when it shares the same +5v or +12v line as the audio amplifier it's 'driving'.
When the audio amp and mp3 module have different power sources so they're only connected by gnd / left / right the noise is quiet enough to not be barely noticable.
I've tried various capacitors & also powering the +V to the amp & mp3 module through separate diodes but they haven't helped, nor has trying switching & linear regulators to power the mp3 module from the +V line used to power the amp, so I got the isolated DC-DC converter to test powering the mp3 module separately and found it works great.
The 5v-5v isolated DC converter is on my to-get list because it's small, cheap and the mp3 module + (most) Picaxes run off 5v.
When the audio amp and mp3 module have different power sources so they're only connected by gnd / left / right the noise is quiet enough to not be barely noticable.
I've tried various capacitors & also powering the +V to the amp & mp3 module through separate diodes but they haven't helped, nor has trying switching & linear regulators to power the mp3 module from the +V line used to power the amp, so I got the isolated DC-DC converter to test powering the mp3 module separately and found it works great.
The 5v-5v isolated DC converter is on my to-get list because it's small, cheap and the mp3 module + (most) Picaxes run off 5v.
Received 5 of these miniature 1w 5v-5v isolated DC-DC modules today and they work great with the mp3 playback module, price worked out at £2.88 per module for 5 + 3 weeks postage, cheaper than on Farnell if you're not in a hurry.
Like the high-power isolated DC-DC converter I tested with the module, they don't eliminate the background "dit-dit-dit-dit" processing sounds 100% when both the audio amp and mp3 module are sharing the same DC power supply, but it eliminates it enough that I'm happy with it that I can use the module's own digital volume control to make the output quieter without the "dit-dit-dit" sound in the background ruining the audio.
The voltage output I measured at 5.44v and am running it off a 78L05 which is getting warm and so is the DC-DC module but it hasn't shut down or gone bang yet
Like the high-power isolated DC-DC converter I tested with the module, they don't eliminate the background "dit-dit-dit-dit" processing sounds 100% when both the audio amp and mp3 module are sharing the same DC power supply, but it eliminates it enough that I'm happy with it that I can use the module's own digital volume control to make the output quieter without the "dit-dit-dit" sound in the background ruining the audio.
The voltage output I measured at 5.44v and am running it off a 78L05 which is getting warm and so is the DC-DC module but it hasn't shut down or gone bang yet
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It becomes an audio coupling transformer, or isolating transformer in other words.
It isolates and creates two distinctly seperate earth references - a termination for the input side, and a brand new ground reference for the output side.
Assuming this is a 1:1 transformer in a box, both sides of the transformer are electrically isolated from each other and share no common connection between primary and secondary, so no hum or other line noise gets through.
I have used audio matching transformers quite a bit to get rid of mains hum and other noise in microphone pre-amp circuits, when everything else fails. HiFi coupling transformers are havable, but they tend to be exceedingly expensive, whereas bog-standard ones with performance somewhere in the vocal range are cheap as chips.
I still don't know why Haku has been having these hum problems - it was never an issue for me, and I did have the module coupled to both a stereo pre-amp and directly to a power-amp IC, all running from the same 12v supply, and there was never any humming.
One of life's mysteries...
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I wish I knew why I was having these problems when nobody else is complaining and I've been occasionally watching MdFly's stock level on the sales page - they're still selling like hotcakes - either everyone else is tone deaf or I got the only 5 faulty boards they madeI still don't know why Haku has been having these hum problems - it was never an issue for me, and I did have the module coupled to both a stereo pre-amp and directly to a power-amp IC, all running from the same 12v supply, and there was never any humming.
One of life's mysteries...
But I'm extremely pleased to find an easy and cheap solution to the problem, the circuit is now thusly and I can barely hear any "dit-dit-dit-dit" interference on the audio now when without the DC-DC converter it was very prominent:
I'm still really impressed with the audio quality for these things considering their price!
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I too hear a bit of noise but i can live with it, probably because the modules are so affordable. i too will probably get the converter.either everyone else is tone deaf or I got the only 5 faulty boards they made
Grogster- thanks for the explanation.
I can't say this enough - PREAMP PREAMP PREAMP!!!
Naturally, this does depend somewhat on the native gain of the power amplifier in question, but if you are feeding into a common home stereo system, you really need the preamp, or you have to wind the wick right up on the stereo to get a decent volume, and that makes the decoder noise very audible.
@ Haku - are you still using the 2822's or are you using something else now?
I have had great sucess with the TDA7056 amps mentioned earlier, and I think I also posted the PDF datasheet too. They have an impressive gain of about 70dB so no need for any preamp at all on these. Mono amps though, so two needed, but they are cheap and pretty good performers.
@ julianE - My assumption was that Haku was using it as an audio coupling transformer, but he is not. If you were to imagine the matching transformer between the mp3 module and the amp, that was how I thought things were hooked up, but I see from the diagram Haku posted...
BTW - 20 pages!!! Popular thread...
Naturally, this does depend somewhat on the native gain of the power amplifier in question, but if you are feeding into a common home stereo system, you really need the preamp, or you have to wind the wick right up on the stereo to get a decent volume, and that makes the decoder noise very audible.
@ Haku - are you still using the 2822's or are you using something else now?
I have had great sucess with the TDA7056 amps mentioned earlier, and I think I also posted the PDF datasheet too. They have an impressive gain of about 70dB so no need for any preamp at all on these. Mono amps though, so two needed, but they are cheap and pretty good performers.
@ julianE - My assumption was that Haku was using it as an audio coupling transformer, but he is not.
If you were to imagine the matching transformer between the mp3 module and the amp, that was how I thought things were hooked up, but I see from the diagram Haku posted...BTW - 20 pages!!!
Popular thread...
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I have made the following observations about the noise on the mp3 module:
The problem is a constant clicking sound when playing - particularly noticeable on quiet tracks. It comes out with the sound and so cannot be filtered, but is a constant volume.
It does not occur when module is connected to a 9V battery but is loud and clear on mains through a 9v regulator. It changes pitch if a 5v regulator is attached to the same supply to drive the Picaxe.
If it does not appear with the battery connected but it does appear on the mains is this something to do with excess current being discharged by the in-built regulator?
I inserted a resistor on the supply to reduce the current flow (I am at work at the moment and cannot remember the size - but it was below 100 ohm) and the noise is considerably reduced. I also put a voltage divider on the output so that the output of the mp3 module is running on a high level to drown out any remaining sound. The combination of these makes the sound virtually indiscernible.
My problem would be how big a resistor to use and how to protect it from burning out. Also, is this a sensible conclusion or am I barking up the wrong tree??
The problem is a constant clicking sound when playing - particularly noticeable on quiet tracks. It comes out with the sound and so cannot be filtered, but is a constant volume.
It does not occur when module is connected to a 9V battery but is loud and clear on mains through a 9v regulator. It changes pitch if a 5v regulator is attached to the same supply to drive the Picaxe.
If it does not appear with the battery connected but it does appear on the mains is this something to do with excess current being discharged by the in-built regulator?
I inserted a resistor on the supply to reduce the current flow (I am at work at the moment and cannot remember the size - but it was below 100 ohm) and the noise is considerably reduced. I also put a voltage divider on the output so that the output of the mp3 module is running on a high level to drown out any remaining sound. The combination of these makes the sound virtually indiscernible.
My problem would be how big a resistor to use and how to protect it from burning out. Also, is this a sensible conclusion or am I barking up the wrong tree??
It's hard to tell what's going on without putting a scope on things and seeing what's happening, so hard to guess what's best for fixing things. It could be over-drawing current from a regulator / supply but the module by itself draws less than 100mA from recollection, a transistor-sized 5V LDO for 100mA may struggle but a TO-style 7805 should be good for up to 1A ( may require heatsinking, but likely not for 100mA ). I recall the module is specified for 6V-12V so perhaps supplying 5V is an issue for some. Maybe use a 7809 or 7812. It could also be an issue of reservoir caps though the module has quite a large cap fitted - That may be a clue that this is important.
Most of the effort seems to have been put in to disguising the problem or working round an unknown problem rather than investigating what the problem is. Unfortunately those who aren't having problems cannot really help in saying what's causing any problems.
Most of the effort seems to have been put in to disguising the problem or working round an unknown problem rather than investigating what the problem is. Unfortunately those who aren't having problems cannot really help in saying what's causing any problems.
Andrew Cowan
Senior Member
Have you tried fitting a bunch of low-ESR caps around the power lines? My module is still sitting in a drawer unplayed with, but often audio does need a bit of a boost...