Hello.
To my understanding there is still no proper electrical datasheet of the RPi. Nevertheless, does someone have information on the 3.5 mm audio jack? In particular: what is the voltage range of the signal, and what is the minimum load impedance? I have no doubt that the jack is compatible with most devices one would like to plug in, but it would be nice to have concrete specs to rely on.
Thanks,
Lauri
Normally sound chips are about 1v peak to peak (350mV RMS) and IIRC either a couple of K impedance wise or low enough to reasonably drive headphones.
You should aim to have at least 10K input impedance and can safely assume not much more than the above voltage on the output pins and ring.
You could always read the schematic - it was published well over a year ago. The bit you need is on page 2, bottom right.
There are no amplifiers - it's the 3.3v GPIO output via a simple low pass filter and reducing resistors to take it to ~1v pp.
Any little amplified PC speakers work well with it, I'm told. I've only used it once and plugged it into my monitors speakers (Which have an on-board amp.)
Gordon
But RPi doesn't have a sound chip, it has some shonky 11 bit PWM output that pops and crackles. If you want to do audio with the RPI you really need to use a USB card or add a proper codec to the PCM header.
El 04/07/2013 3:00, Lauri Alanko escribió:
With the values shown in the schematic of the 2.0 revision, for a 1 kHz sinewave you can expect about 1.07 V pp (0.75 V RMS), with an output impedance of about 120 ohms (supposing that the IO pin impedance is about 25 ohms).
The cutoff frequency is about 40 kHz, a bit high for me.
Or use HDMI sound
I meant to add that, HDMI->VGA+audio-line-out adapters from about £15 delivered on eBay, the ones with digital and optical audio-out cost rather more, presumably because they're aimed at home-cinema / "audiophile" use.
As a matter of curiosity, do any of the semi-economical VGA/XGA projectors use something with better life than a projector bulb? Some kind of high-intensity-discharge device (like a BMW headlight, IIRC), which presumably has a long life.
Yesterday I passed a small ground floor flat in which someone was watching a really huge picture; after a moment I realised it was a projection onto a wall screen, and suddenly lusted after the same for myself. But such a projector would need to have very high resolution, good brightness, and a price much lower than a 60" or 70" LCD or plasma.
It would be amusing to generate a huge image from a tiny Pi.
£700 for a 1080p DLP projector with 3000 lumen lamp, 4000 hour life, £200 replacement. 3000 lumen is about the dimmest you can get away with not blacking out a room, you will need a proper projection surface (not just a white wall) to get good results. Also the fan can be quite noisy - ideally you want a "projection booth" (e.g. double-glazed window through to the next room) to put it in. AFAIK HID units last 3000 hours depending on use - like many electrical things they don't like power cycling, particularly in a short space of time.
There are some 'pocket' projectors with LEDs. Obviously not as bright as bulbs, but not too bad. Very long life, and came be much smaller and cheaper as no need to have a hot bulb, means to change it, fans, etc etc.
Theo
Amusing? Boring more like. 1920 pixels x 1080 is not too shabby and Pi's do that every day.
Or then there's this:
Gordon
there are LED projectors, (presumably LED illuminated DLP or liquid crystal - I don't think OLED is quite there yet)
Casio do a LED projector, 2000 lumens, 25000 hours "lamp" life. However, the LED runs just as hot as a lamp, so the fans make a similar amount of noise. Price 2 years ago was around £700. I'd expect other makes/models to appear, and the price to drop, but now I've retired, I'm not watching the market.
Discharge-based lamps have been used in video projectors at least since about 2004. I repaired a Panasonic projector a few years ago that had been in use in April, 2005 and perhaps some years before that. Its lamp was a high-intensity-discharge rather than incandescent filament. The ignitor board produced around 300-400 volts for the lamp. IIRC, it had a lifespan of about 1500-1800 hours.
Too expensive for me, unfortunately.
Might not be suitable for a 60" or 90" display then. But otherwise good.
I wonder how they managed to get good resolution. Presumably you'd need something like 16384 x 9216 resolution for each wall, which would also be good for a single largish display. Is there a way to get one or more Pis to each handle a small part of the whole display?
Not too boring, I think.
I suppose you'd need about 100 watts of lighting, roughly speaking, with discharge lamps of some type at the moment being still ahead of LEDs
The life sounds good; it's getting all the various factors right that's difficult.
Exactly. And the "incoming" resolution is split up among the displays, so they are not HD individually.
-michael - NadaNet 3.1 and AppleCrate II:
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