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For an ethernet connection between 2 points which will be used as point to point communication (for embedded devices). Is internet connection, hubs or switches are really necessary? Or can we still send and receive data from one MCU to another one by using ethernet without using any internet connection, hubs or switches?
There's certainly no need for an Internet connection.
If you want to connect two computers together directly, then you will need to use a crossover cable rather than a patch cable unless the devices you are using support auto MDI-X.
Putting a cheap hub between them will probably be simpler.
No, they are not necessary. We ofen do this between either two of "product board", "FPGA board", and "PC" when debugging ethernet Tx/Rx issues.
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Closed 1 year ago.
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I have made a simple relay board using a 12vdc Bosch automotive relay.
The relay works great, Comm/NO being successfully controlled with RPi GPIO(25) using a 3+ RPi.
However, the only wire from RPi to relay board is the GPIO (initiated as GPIO.out) with no ground from RPi to relay board. So, is the grounding necessary?
I have researched and found multiple threads saying GPIO's do not need a ground return; others saying the opposite.
Here is the diagram:
Relay board diagram
Probably it needs to be grounded. At least nothing bad will happen.
The grounding happens indirectly over the power supply of the RPi and the power supply of the relay. While this may work, it is dangerous and may fry either part.
As there is no guarantee that the two PSUs generate a common ground, you may have undesired current flowing through the GPIO wire. The resistor there gives some protection, but this might not be enough to prevent frying your Pi. You might get a more detailed answer on the possible problems on https://electronics.stackexchange.com.
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Closed 6 years ago.
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When I do socket programming, I found at least one computer has to have a public IP to make the connection (or reverse connection). I'm wondering if it is possible for 2 computers that are behind different routers to connect to each other (and they don't have port forwarding and don't use proxy)? If that's not possible, how bit torrent works for computers that are behind routers? Does it mean the computers that are behind different routers cannot share among each other?
Bittorent clients are using a protocol named uPNP, that tells router to redirect specified port in bittorrent client to computer that runs client.
Here is more information about protocol.
https://en.wikipedia.org/wiki/Universal_Plug_and_Play
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Closed 8 years ago.
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Can I store a program on a USB Ethernet/WIFI adapter and auto-run the program when the usb wifi adapter is plugged in? Is it scenario where it may be possible on some but not other USB wifi adapters?
Rees-pek!
In short, no.
However, most of the Huawei 3G/4G devices have a virtual CD-ROM drive built-in.
And yes, you can modify the firmware to run your own code (It's an ISO image).
On a regular WiFi USB adapter, best chance would be to add an USB hub chip and a Arduino Teensy to send commands, yet, would be very big to fit in the original casing.
Or, just plant some regular USB flash drive inside the USB Wifi plastic casing.
Out of curiosity, why would you want this ?
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Closed 8 years ago.
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so I am planning to make a network analyzer using Perl. But before I start I have to answer this question, can a Perl program actually sniff packets in multiple NICs simultaneously? a feature of the program im going to make is that it needs to sniff the packets in the whole LAN within a switch. Is this possible in Perl?
Sniffing packets in the whole lan is not possible. It is only possible if your switch supports it. Many swith has an option to copy all traffic to one of its port for monitoring/sniffing.
http://en.wikipedia.org/wiki/Port_mirroring
http://www.miarec.com/knowledge/switches-port-mirroring
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When I browse my home network with a bonjour browser, I see this _acp-sync._tcp bonjour service beeing advertised by all my AirPort base stations. Can anyone give me any insights on what this is for?
The only likely reference I can find for an ACP protocol is in the man page for natutil:
natutil uses the ACP protocol to detect, configure, and extract status information from Internet gate-way gateway way devices (IGDs) (such as AirPort Base Stations) on the local network.
I doubt you'll find out much further about it without firing up a packet sniffer as the dearth of information about it is a good indicator that Apple want to keep it proprietary.
Of course, I'd quite forgotten about that feature of Server. And Lion now contains the natutil(8) utility in the client, with more documentation (but inaccurate control of Airport base stations). _airport._tcp uses same port number (5009). Sadly, the IANA registry contains very sparse information on the formats of the TXT records in either case, so we lose beyond this point. :-(