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Registered Member #65
Joined: Thu Feb 09 2006, 06:43AM
Location:
Posts: 1155
A high-speed phototransistor has a higher gain and may inject less switching noise since this is a relatively low-speed isolated communication application where photoconductors may be unnecessary.
Note too, irda transceiver optics (4Mbit/s to 16Mbit/s) can be reclaimed from old cellphones, old laptops, and USB adapters
Registered Member #74
Joined: Thu Feb 09 2006, 09:17AM
Location: Nottingham UK
Posts: 99
CR, Although getting IrDA optics is easy (I can buy a trancever for £1) geting them to fire into a fibre effeciently would be a difficualt task.
I had thought about scrapping the fibre completly and using just the IdDA in free space, but I suspect the range would be worse and then I definatly can't use full duplex.
Interesting your point about photo transistors being less noisy, but I'd still need an amp. The limitation I have with my current circuit is that it has no automatic gain control, so I need to tweek it to each fibre length, another reason for scrapping it.
I have a bit to go on the TX level as I'm only just over the continious rating of the LED and of course I can now go higher up into the LED's pulse ratings now I'm using an encoder with 1/16th Mark/Space.
Ill get the calculator out and go for more power. see if that improves my BER.
Registered Member #74
Joined: Thu Feb 09 2006, 09:17AM
Location: Nottingham UK
Posts: 99
Ive seen the toslink modules, but the UK suppliers that I have tried appear to have them at 10 times that price, thats why I've avoided them, unless anyone here knows of a good UK supplier.
Registered Member #30
Joined: Fri Feb 03 2006, 10:52AM
Location: Glasgow, Scotland
Posts: 6706
Hey EE
You can get the Toslink transmitters and receivers from Farnell, I think they're about £2-3 each.
Beware the low frequency limit, many of the Toslink receivers are AC coupled with AGC, so they emit random data in the absence of an input signal. This has ruined a few 4hv members' days in the past. Search the forum for discussion on this, and read the small print on the datasheet carefully!
Registered Member #74
Joined: Thu Feb 09 2006, 09:17AM
Location: Nottingham UK
Posts: 99
Steve, Thanks Ill take a look at Farnell.
Id heard of the limitations of the toslink optostuff before in a thread, thanks for reminding me.
Luckily as Im probably going down the route of a blank frame keep alive every 500mS this may allow the toslink's to stay somewhere near their operating point.
Why is nothing in electronics simple, even the simplifications get complicated !
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RS232 Fireoptic Link (was FSK...)
