Morning Overflowers,
For a specific in-house application for my company, I need to be able to make a Gigabit ethernet connection go through DB15 connectors, as seen bellow.
Here is what I'm trying to achieve:
For the first version, I just cut in half a cat 5e ethernet cable. I did not care too much about the pin-out from the cable to the DB15 connector and in the end I ended up having a 10MBit/s data rate, which is super low. Also my cable was super short, 2m in total.
For the second version I used a 5m cat 6 cable for one side, and the remain of the other cat 5e cable (resoldered) for the other side. I was more careful about the pinout and used the 4 left most pins to place the ethernet pairs as seen here:
The data rate is this time 100 MBits/s, but still not 1 GBits/s.
Before going through a 3rd version I thought I'd use my brain a little. I noticed while soldering that although inside a cat 5e/cat 6 cable there are 4 pairs, not all of them are side by side on the RJ45 socket as seen on figure bellow where blue and green wires are a bit mixed.
There is probably a reason for that arrangement and putting pairs together other that inside the cable itself is not probably a good idea, which leads to my question.
For version 3, should I just keep pin 1 to 8 in that order and solder them to the DB15 connector on adjacent pins?
More generally I am aware that unless the DB15 section is super short I won't be able to maintain Gibabit ethernet due to noise and other problems caused by unmatched pairs on that section.
I am open to any suggestion or tips or anything :)
Thanks in advance
After trial and errors, it turned out that it works fine if you arrange pairs to match a RJ45 connector (like on the figure "ethernet plug wiring"). The quality of the cable is probably not the one of a perfect 5e/6 cable but my computer can negociate a Gbits connection and transfer files over the network at speeds way above 10 MB/s reaching 50 MB/s. I always soldered more section with various connectors and it worked fine too.
Related
I really wanted at first an rs232 8-channel relay board that I could command devices to turn on/off with a command string.
All of the ones I found online have the same deficiency in functionality for me: you can't set a subset of relays at the exact time. I can set relay 1 on, and then relay 7 on afterwards, I can set all 8 relays at once, but there is no command structure to pick out the exact leds I would like to turn on/off.
In the past I have dealt with hardware that had a bit-map of the IO pins, and a bit-map of the states and would apply all 8 settings at once. here are some examples:
to set pins 1 and 7 to on and the other pins off (8-bit binary bit-mapping,) send the following byte: in binary: 0100 0001b
to set pins 1,2,3,6 to on and the other pins off (8-bit binary bit-mapping,) send the following byte: in binary: 0010 0111b
I couldn't find any such device to do this so I thought I could make one with a raspberry pi using a simple 8-channel relay board, something like this:
https://www.amazon.com/SainSmart-101-70-102-8-Channel-Relay-Module/dp/B0057OC5WK
but on a Raspberry Pi, I'm running into the same issue: I don't see a way to set the gpio pins as a block command, only individually setting them in a for loop. I looked all morning and can see things like gpioctl, and mmio, but I can't put it all together to a simple proof of concept program on a testboard, any help would be appreciated.
I would really like a solution in C or scripting,
Thanks,
jleslie
Let's say I am talking to a PHY chip via RGMII.
What is the relationship between the serial information transmitted on the RGMII to the signals that go out to the MDI?
I understood from the timing diagram of RGMII that the rising edge is 4 bits and the falling edge is 4 bits. So for each clock that gives 8 bits.
For 100Mbps, the clock required is 25MHz. So for every 25MHz clock cycle, 8 bits are transmitted.
Does the PHY chip simply send each 8 bits over the MDI immediately?
If that is the case, then how do I correctly package these serial 8 bits of data into a proper ethernet frame?
I a trying to troubleshoot a piece of hardware where the PHY does not work properly but the only way troubleshoot is if I can control the RGMII. However, I do not understand this relationship between the RGMII and how it affects the MDI.
I presume that if I look at wireshark, it will not show any packets of information unless I send a string of serialized data in a proper Ethernet frame.
The PHY should have some documentation and sample code. Without, finding out how exactly it works can be a very tedious task.
You can find the general RGMII description here: https://web.archive.org/web/20160303212629/http://www.hp.com/rnd/pdfs/RGMIIv1_3.pdf
I have a project that consisted of transmitting data wirelessly from 15 tractors to a station, the maximum distance between tractor and station is 13 miles. I used a raspberry pi 3 to collect data from tractors. with some research I found that there is no wifi or GSM coverage so the only solution is to use RF communication using VHF. so is that possible with raspberry pi or I must add a modem? if yes, what is the criterion for choosing a modem? and please if you have any other information tell me?
and thank you for your time.
I had a similar issue but possibly a little more complex. I needed to cover a maximum distance of 22 kilometres and I wanted to monitor over 100 resources ranging from breeding stock to fences and gates etc. I too had no GSM access plus no direct line of sight access as the area is hilly and the breeders like the deep valleys. The solution I used was to make my own radio network using cheap radio repeaters. Everything was battery operated and was driven by the receivers powering up the transmitters. This means that the units consume only 40 micro amps on standby and when the transmitters transmit, in my case they consume around 100 to 200 milliamps.
In the house I have a little program that transmits a poll to the receivers every so often and waits for the units to reply. This gives me a big advantage because I can, via the repeater trail (as each repeater, the signal goes through, adds its code to the returning message) actually determine were my stock are.
Now for the big issue, how long do the batteries last? Well each unit has a 18650 battery. For the fence and gate controls this is charged by a small 5 volt solar panel and after 2 years running time I have not changed any of them. For the cattle units the length of time between charges depends solely on how often you poll the units (note each unit has its own code) with one exception (a bull who wants to roam and is a real escape artist) I only poll them once or twice a day and I swap the battery every two weeks.
The frequency I use is 433Mhz and the radio transmitters and receivers are very cheap ( less then 10 cents a pair if you by them in Australia) with a very small Attiny (I think) arduino per unit (around 30 cents each) and a length on wire (34.6cm long as an aerial) for the cattle and 69.2cm for the repeaters. Note these calculations are based on the frequency used i.e. 433Mhz.
As I had to install lots of the repeaters I contacted an organisation in China (sorry they no longer exist) and they created a tiny waterproof and rugged capsule that contained everything, while also improving on the design (range wise while reducing power) at a cost of $220 for 100 units not including batterys. I bought one lot as a test and now between myself and my neighbours we bought another 2000 units for only $2750.
In my case this was paid for in less then three months when during calving season I knew exactly were they were calving and was on site to assist. The first time I used it we saved a mother who was having a real issue.
To end this long message I am not an expert but I had an idea and hired people who were and the repeater approach certainly works over long distances and large areas (42 square kilometres).
Following on from the comments above, I'm not sure where you are located but spectrum around the 400mhz range is licensed in many countries so it would be worth checking exactly what you can use.
If this is your target then this is UHF rather than VHF so if you search for 'Raspberry PI UHF shield' or 'Raspberry PI UHF module' you will find some examples of cheap hardware you can add to your raspberry pi to support communication over these frequencies. Most of the results should include some software examples also.
There are also articles on using the pins on the PI to transmit directly by modulating the voltage them - this is almost certainly going to interfere with other communications so I doubt it would meet your needs.
I have been following a tutorial that enables you to play around with the TXPOWER parameter of your wifi card / wifi adapter:
http://null-byte.wonderhowto.com/how-to/set-your-wi-fi-cards-tx-power-higher-than-30-dbm-0149606/
You can easily boost up your wifi range when increasing the TXPOWER.
Now, most people want to improve their wifi signal strength of their home router, right. But in my case, I would like my home router (which runs on a raspberry pi) to have a relative small wifi signal radius (say, a radius of 2 meters), so that you actually need to physically look for the pi home router when trying to connect to it.
I have learned that this tutorial does not do a thing with the wifi link quality and/or the wifi signal level and thus does not influence the wifi radius of my pi home router.
link quality & signal level
Do you guys have any ideas/thoughts about how to decrease link quality and/or wifi signal level (e.g Link Quality = 12/70 and Signal level =-10dBm) ? Is this even possible ?
I am using a Tp-Link TL-WN722N IEEE 802.11n USB - Wi-Fi Adapter.
WIRELESS LITE N ADAPTER 150M USB HIGH GAIN 1DETACHABLE ANTENNA WL-AP.
150 Mbps - External
First, I recommend reviewing this section from your link:
QUICK DECIBEL UNDERSTANDING:
Every 10 decibels is a 10X increase in power starting from 1 dBm equal
to 1mW... 10 dBm equals 10 mW, 20 dBm equals 100 mW, 30 dBm equals
1000 mW, and so on. Every 3 decibels is approximately double that of
the prior power, so 30 dBm is 1000 mW, if we add 3 dBm, then we can
double the power such that 33 dBm is about equal to 2000 mW.
It appears to me that you are able to modify the transmit power of your adapter as the tutorial states. Are you saying this is not working? If you set your transmit power to something extremely low (-30dBm, for example) you would effectively be turning off the transmitter. Keep increasing that value until you get your desired coverage radius.
If the transmit power parameter is not functioning as per the tutorial, then there are other means to achieve reduced coverage. The model you specified has a detachable antenna....so detach it. This would definitely reduce your coverage. However, if it reduces coverage too much, you could simply add an inline attenuator. Fortunately, your antenna uses an SMA connector which is very common. You can find many SMA attenuators on ebay with different attenuation values. Experiment with different values until you get the desired coverage.
And if that doesn't work, just wrap a bunch of aluminum foil around the thing lol.
Looking for some help to be honest, This is not my area of knoladge atall.
Ive read around the question of powering my Pi with a battery, now I nabbed one of these guys for my phone
http://www.amazon.co.uk/13000mAh-Portable-External-Technology-Motorola-Black/dp/B00BQ5KHJW/ref=sr_1_cc_1?s=aps&ie=UTF8&qid=1420826597&sr=1-1-catcorr&keywords=anker+astro+e4
Incase the link dies in the future;
Item model number: AK-79AN13K2-BA
Anker® 2nd Gen Astro E4 13000mAh 2-Port (3A Output) Fast
Max 3A Out
5V Out
Now, from what i've read there have been mixed notes of, don't use batterys, only use this battery, don't do this, don't exeed this magical number ( which was differant each time ). so any help would be grately needed. If i was to power my pi via this thing. im I going to get a poof of smoke and need to replace the poor pi :(
A raspberry Pi is powered via USB, which means that it simply takes the 5V supplied via USB to run. As long as your current source is stable (ie. it doesn't change when you draw current from it), no device will care whether it is a battery or a switching power supply. Now, a bare raspberry Pi B uses less than 2W of power, 2W/5V = 0.4A = 400mA, so if that battery pack lives up to its specification, you are going to be fine. The device is spec'ed to provide 13000mAh, so at a constant current of 400mA, this would last you more than 32 hours.
Now, most people attach something to the raspberry, and that something will also draw power, but just add that power to the calculations above, to see if it's going to work out.