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.

Unfortunately LAN is a half duplex protocol as you found out.  If you want full duplex, SPI is the way to go. But it is meant  as a limited distance. How far do you need to go?

Clem

Unfortunately LAN is a half duplex protocol as you found out.  If you want full duplex, SPI is the way to go. But it is meant  as a limited distance. How far do you need to go?

Clem

LAN has been full-duplex..  for some time now (*). For 10 and 100Mbps there is a pair of wires dedicated to each direction, and both can be active at the same time. For 1Gbps LAN over CAT5 cable, all four pairs are used. There can be datatransmission going on all pairs in EACH direction at the same time.

But I'm getting the impression that I'm missing some context.

(*) Remember the coax cables for 10mbps? If you got a terminator wrong, the whole network stopped working. (#)

(#) Anecdote: 1992-ish: I wanted to hook up an extra workstation in my room. So I hooked it up and walked over to the sysadmin to ask him if I'd done it correctly. But by the time I got there, his phone was red hot, so I saw that he was busy with more important things and I went back to work.... It hit me when 15 minutes later I saw him diving under my desk..... the last room he was checking for missing terminators and the like....

I am referring to the protocol at software level. Cannot send/receive at same time in software interface. But there is some acks under the cover that are overlapping.

Clem

That's a limitation of the application. Not the network stack or you would never be able to surf in multiple browsers and have a file transfer going and watch TV / my youtube videos at the same time  

I'm baffled now - are we seem to be talking about Ethernet but which protocol:

It's easy to send and receive UDPs simultaneously, TCP links usually look full duplex even to quite high level software - I'm obviously missing something but not sure what

MK

clem57 wrote

Unfortunately LAN is a half duplex protocol as you found out.  If you want full duplex, SPI is the way to go. But it is meant  as a limited distance. How far do you need to go?

Clem

I have replied from my mobile to this comment but now I see that it seems nothing happened, so I repeat. What I plan is to make a inter-network between 2-3 raspi in the same place (I mean almost the same box), so the distance is few centimetres less or about 20 cm every connection. Then for any networked external connection with the resulting device set I have to use a common switch or any other reliable network.

What do you intend as SPI ?

Why bother with the diodes then if this is so close together.

If you want them for some special reason you really need to state the environment  otherwise there is little benefit in the answer as every one is taking a guess at whet you are working towards.

Also yeah Ethernet is Bi-Directional Duplex

John

John, the - possibile - choice of the passive small hub with diodes only was to ensure data exchange between the processors using the Ethernet protocol (that simplifies a lot of things in kind of communication I am approaching) but I don't understand what do you mean with your suggestion, what kind of alternative is ?

I, and many others I guess, have no clue whatsoever what you think you can achieve with diodes on ethernet. To connect several pi's together you need a hub or switch. A hub will transmit on all outgoing links as soon as it recieves something on one of the incoming RX lines. A switch will quickly analyse the incoming transmission and transmit only on the appropriate port (with a time-delay of a few microseconds). In the past (say more than 15 years ago) you might chose a "hub" over a switch because of costs. As the price difference has dropped, I don't think hubs are in serious active production anymore.

So, besides your "four pi's" you'll need a small switch. 5port 5 Ports 10 100Mbps Fast Ethernet Network Switch Hub USB Cable Kable SY | eBay

Or you could connect the SPI ports together. The problem is that SPI is a master slave protocol, and the "pi as a slave" part has not been implemented yet. You'll need to do that yourself. Big job. Same goes for other options. Unless you have very specific needs, you're better off just putting a network switch near your 'pi's...

Roger,

the point is that I know very well both hub and switches roles and how do these devices works, collision problems and so on. Instead I have not a sufficiently wide visibility about the concept of "passive hub", that is, a unpowered hub to connect three different RaspPI. The thing is possible, and a circuit exists but the logic on it is based is not convincing me very well. (here is on link: http://www.diyelectronicsprojects.com/2012/07/building-passive-ethernet-hub.html and all the hundreds of others I have found are identical to this scheme, no matter of the site).

Instead frankly I had not considered the SPI connection that will be a good idea, excluding the problem you mention of the unimplemented slave mode.

I see that there is a master-to-master SPI connection solution but it seems having only one wire for data and this slowdown again the speed. The idea for a direct connection via ethernet has a lot of advantages in the SciFi project (tag: meditech_project) I am developing and the solution that has sense in a modular environment with the ability to connect the Raspberry-pi modules in the same place or remotely is just the ethernet way. As there will be two kind of networks, one barely local to exchange the data flow and one to the Internet via the WiFi dongle, I think that the final solution I will adopt is an internal hub.

I was exploring this part of the project also because this choice influences both the contained design of the portable device and the powering system.

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