Epitaxial vs 1N4002 Diodes

• SP3002 0.85pF, 12kV, Low Capacitance Diode Array for ESD Protection  should work for ESD protection...

Clem

Many thanks, Clem.

In the meantime after a reasonable investigation on the use I had in mind it seems that it is not the better solution. I was exploring the possibility to have a passive hub but it is not so reliable and - worst of all - it seems that with the LAN works only in half-duplex. The best usage seems to be with TV signals integration but it is not my case.

Just buy a small 5-8 port switch and stay at a nice 100Mbps and find your are much aster because most switches will switch at near line speed and you wont have any  collisions as such as you have more control of collision domains

More to the point who would want  to use the RPI for low latency switching when the USB to Ethernet  is so notoriously slow and fickle anyway !?!

Now you have explained what you want to do and referenced the basic circuit it is possible to answer your questions.

1) The whole idea is pretty dreadful since it relies on undocumented and unintended behavior of of the 10baseT or 100baseT hardware - however it obviously could work in some setups.

2) The diodes will need to be fast - 1N4002 would not work, 1N4148s probably would.

3) You can buy a 5 port switch from Amazon for £5.86 - you won't be able to buy one switch chip and the connectors for this price so building your own switch would be mad.

Your best bet (by far) is to buy a cheap switch and build the works of it into your system.

But pay attention to John's last remark - if you care about Ethernet performance the RPI is the wrong platform.

IMO you can remove the condition from that last sentence

What is your project - we might be able to suggest some alternatives to allow three processors to have a low latency network.

MK

Agree with you on all points there.

Need to know what sort of project he is taking on to give some idea of required speed and acceptable latency!

Sorry for the delay in my answers, I have read all your last comments on the mobile that is not very good to write decent responses.

John, the problem is not the cost as I already have one to make tests. The speed of 10/100 is more than sufficient. Your answer and the other guys before already gives me the correct vision, despite the project itself, that the choice now is between ISP (that is the less valuable I think) and the LAN connection that it is very probably I will decide for.

Michael, as you wrote

1) The whole idea is pretty dreadful since it relies on undocumented and unintended behavior of of the 10baseT or 100baseT hardware - however it obviously could work in some setups.

2) The diodes will need to be fast - 1N4002 would not work, 1N4148s probably would.

3) You can buy a 5 port switch from Amazon for £5.86 - you won't be able to buy one switch chip and the connectors for this price so building your own switch would be mad.

1) That's ok, I have explored again the of the passive hub (mostly for the power consumption but it is unreliable for too much aspects, so it is excluded apriori

2) This is anyway an information that I need at least for curiosity; following simply the logic, if there are specific high speed diodes there would be a reason, and this is another point that address me to exclude the solution.

3) That's ok for the mini switch and the problem is not the price itself

The project is - in general - metitech_project (this is the tag, you can find all the already wrote posts in the SiFi your Raspberry-Pi challenge blog). In this moment I am focusing all the obscure points, ad this is one of them, to define the complete architecture of the system.

For several reasons I have to use more than one RPI and I should have them exchanging data together in a private internal connection. Then at least two units will be in the same "box" or container. The system in general will be modular so some complex probes - better group of probes - will be external pluggable components driven by another RPI. The same mobile lightweight box will be also available in  a non-portable version with the devices connected together via a network. The "main controller" RPI will include a wifi for the main interface (Android based) so with these premises I think that the LAN is revealing to be the right solution.

The doubt that I already have is about the suggestion os clem57 about the possibility to use for the internal connections the SPI protocol. As I wrote in a precedent post, if by one side the SPI protocol on RPI has the limitation that doesn't support the slave mode by the other there is the master to master connection that - as for what I have read - seems to use only one channel instead of the traditional two bidirectional wire lines MISO and MOSI.

Anyway a t the moment I am strongly prepending for the LAN also for the internal connections.

Hello Enrico,

Now I know about your project I would definitely use LAN for communications. The advantages of SPI would not be available to you in this context. The implementation of Ethernet on the Pi is far from ideal but will probably be OK (I'm assuming that the earlier reliability issues have been sorted out  - some RPI expert may have  a comment here.)

One big advantage of using Ethernet is that the integration with Linux is far better than for any other reasonable bandwidth communications available to you on a PI.

MK

The spi can work if each RPI is a master and say an Arduino is the slave. One extra line is needed to send interrupt from Arduino back to a  particular RPI to request he master the bus high for a transfer back to him. Also before a master uses the bus, he must interrogate the bus in use because the select is already high (someone else using).

Clem

balearicdynamics Ciao Enrico whats up? I have been working hard to have a new tidbit to show off at Cockpit-Fest at the end of the month.

I Finally got the damn Pearl translated and updated in C. I spread it out over 6 modules... with the six header files a well. The update is to fix

the Pearl global variables ie make them local and use C structures to hold the data. makes life better. and my buddy Paul to stop bitching about Pearl.

No food to brag about but I just make some "Home Fries". Take some reds and nuke them for about 6min. cut them up to about 1"/30mmSQ Then toss them

into a nice frying pan, add Green Peppers, Onions, Course Ground Black Pepper, and a *** Load of Garlic, and Chives optional .  Can also do in oven.

cook medium heat, the object is to brown the spuds., then of course some bacon and eggs..

hey its me again, yes but no, your wired ethernet LAN is Full Duplex, with a switch, yes you can force it in to a HD mode but why?

What Is Half-Duplex And Full-Duplex Operation, And How Does It Affect Your Router?

Later

Cris

hey its me again, yes but no, your wired ethernet LAN is Full Duplex, with a switch, yes you can force it in to a HD mode but why?

What Is Half-Duplex And Full-Duplex Operation, And How Does It Affect Your Router?

Later

Cris