MUTR Televisor

[Steve G8CYE]

NP.
I've now tried it with my MP3 player. Sync is not so steady, and takes a lot longer to lock. Anyway I've got a new player on order. Whilst I wait for that I'm going to try a better diffuser, brightness is absolutely fine. I've knocked up an inverter circuit and also a small audio amplifier/speaker box to sit alongside it. I might also convert a few video clips.

[Klaas Robers]

In most cases MP3 and all the other compressed digital audio systems are badly suitable for NBTV. The compression is optimized for sound, such that you almost don't HEAR the distortion. But NBTV is a video signal and MP3 is never designed to support that.

It is possible that the worst thing that happens is that sound is more or less mixed up with the picture. So if the sound channel is muted (silence) then the video signal (picture) might be not too bad. Experiment with it please.

On the other hand, quite some MP3 players play also pure .wav files. Try that any way. That has a much better chance of success. Then you can still use the player, small and portable. Then the playing duration is about 1/10 of the MP3 playing duration, but for experiments, who cares.

A circuit diagram of an inverting amplifier can be found in the NBTV handbook.

[Steve G8CYE]

CD Player arrived. First success the polarity of the output is correct, but the signal level is way too low. I'm building a combined inverter and amplifier with a variable 20dB gain, which I reckon will be large enough. The circuit is from somewhere on the forum, I forget where.

[Lowtone]

too low? it works with the line out

[Klaas Robers]

Remember that one of the two potentiometers on the PCB is a gain control. I experienced that the optimal setting is different for CD reproduction and the built in test picture.

[Steve G8CYE]

Unfortunately the cheapo cd player I got only has an earpiece out. I've got another possible solution to try over the next few days, time permitting. I have an old PC CD drive with an analogue output on the back, and a step button on the front. I'm going to look out an old PC PSU and wire it as a 5v & 12v supply (done it before for other projects now in my new shack in Portugal!). BTW having fiddled with the levels on my MP3 player and on the televisor I can get reasonably stable video and good audio.

[Steve G8CYE]

I've now had a go with my idea of an ex-pc cd-drive and PSU. Works perfectly, taking the analogue signal from the back of the drive. I even made a couple of video clips of Portuguese fado (my wife is Portuguese). She only made a couple of comments (I think she was secretly impressed) first was that the fadista (singer) looked a bit red, and the size of the picture. She reckoned that the fadista was perfectly recognisable!

[MarbleMad]

Hello.. I'm a newby to the forum, first post in fact. Just thought i'd chip in on the subject of mp3 audio.
i've messed around with the MUTR tv and have built an arduino mechanical tv recently. On both i've found mp3 work fine.. you may get even better results with more modern types like m4a though. I've been using m4a files off an apple device and wma from an android device as my broadcast signals. They work fine. I've been encoding them using 'audacity' which is free.. and it does a good job. I've re opened files after conversion and looked at the waves.. i don't see any problem with them.

One caveat though.. although i've got mp3 files working fine, I've also been experimenting with using them to send pulse width modulation to servo motors. The m4a and wma files still work fine but the mp3 files can cause problems so there may be something in what's being said about them corrupting things... in short.. try an m4a.

[Lowtone]

mp3 is only a low end costumer format, PCM wav or aiff is a production format, wich holds all the quality. Mp3 uses lossy compression wich is not desirable for what we are doing here. At least FLAC could be used since it doesn't butchers the signals.

Storage devices gets bigger and bigger, and nowadays internet is getting faster too; lossy formats like mp3 starts to become obsolete ( technology wise ) since there is ( or will be soon ) no point to use them anymore.