Raspberry Pi Production Delayed By Factory's Assembly Flub 132
nk497 writes "The first shipment of Raspberry Pi devices has been delayed, after the factory manufacturing the cheap educational computer used non-magnetic jacks instead of ones with integrated magnetics. The problem is already nearly fixed, but new jacks need to be sourced for subsequent shipments, so those could be delayed slightly. 'It's inevitable, isn't it — you're freewheeling along perfectly happily and then you get a puncture,' said spokeswoman Liz Upton, apologizing for the delay."
Magnetics (Score:5, Informative)
From the Raspi forums :
"It doesn’t mean no network connection at all on all devices, but this board has been designed for a magnetic jack. The magnetic bits mean better signal integrity, better filtering and shorter transmission distances for data."
"Magnetics refers to the presence of transformers and chokes which are used to isolate the Ethernet wires from the RaspPi’s power supply. and each other and probably to reduce high-frequency noise. Without them you would effectively tie the RX and TX signals together and probably turn the entire network into an aerial for Radio 2 reception."
Before anyone makes any silly comments... (Score:5, Informative)
The magnetics in question aren't to hold the connector in like those in a Mac power cord, but rather the tiny transformers [molex.com] that are required for Ethernet differential signal isolation/transformation.
Re:Why the magnetics? (Score:5, Informative)
I had the exact same thought and googled magnetic jacks:
Molex Magnetic Modular Jacks incorporate wire-wound components (magnetics) in standard RJ45 jacks. These integrated magnetics, resistors and/or capacitors filter common-mode noise to provide signal integrity, protect PHY chips, provide DC isolation and offer low-mode conversion.
I'm assuming that's the case here, and the magnets are providing filtering (given the cable's got a predominantly plastic and copper end it's not going to do much to hold it in place).
Re:Why the magnetics? (Score:5, Informative)
As I stated in the other, non-annointed article and posted here [slashdot.org], the magnetics are actually tiny transformers used to convert from differential to single-ended signals and to isolate. Additionally center taps can be used for PoE.
"The magnetics in question aren't to hold the connector in like those in a Mac power cord, but rather the tiny transformers that are required for Ethernet differential signal isolation/transformation."
Re:Why the magnetics? (Score:5, Informative)
I'm assuming that's the case here, and the magnets are providing filtering (given the cable's got a predominantly plastic and copper end it's not going to do much to hold it in place).
They're not magnets. They're tiny transformers and inductors that magnetically couple the signals while providing 1.5 kV DC isolation and some filtering against common-mode disturbances.
Re:Why the magnetics? (Score:3, Informative)
also see http://www.molex.com/mx_upload/family/magnetic_modular_jacks/hypejak.pdf [molex.com]
Re:Magnetics (Score:5, Informative)
Without the intervening transformer, the TX- and RX- lines would be tied together at ground on the device. In the diagram below, the differential RX+/- and TX+/- signals are turned into single-ended RX and TX by the transformers. Removing the transformers connects RX- and TX- to ground, which is a Bad Thing(tm).
RX+_____3 E_______RX
3 E
3 E
RX-_____3 E_____GND
TX+_____3 E_______TX
3 E
3 E
TX-_____3 E_____GND
Re:So much for opensource hardware taking off... (Score:4, Informative)
Actually, no. This is what happens when you outsource manufacturing to vendors in countries like China where it is common practice for them to quietly substitute parts between the reference design stage and when the device hits production. Sometimes, you get lucky and they even tell you in advance that they're doing this and you have a chance to evaluate impact on the design. Most times, they simply do it and pocket the difference in cost while hoping not to get caught.
Re:Magnetics (Score:3, Informative)
Radio 2: UK radio station broadcasting crap music for housewives.
Re:Seems reasonable enough (Score:4, Informative)
Quotesdfrom the forum
''Jamesh is right – they sent us test units which *did* have the right part on before they moved to a larger batch. "
Re:Seems reasonable enough (Score:2, Informative)
I hate to stereotype, but this is quite typical for China. You need to watch them closely or they will cut corners whenever possible.