I have a Gateway - Node application using the LoRa module but I don't know whether to choose the LoRa module to interface UART or SPI.
Can someone help me distinguish the difference when using these two types? Example: when I have 5 Nodes connected to Gatewway, which one should I use? and same when I have 50 Nodes.
Thanks!
A UART converts the signals to RS232 signaling(NOT VOLTAGES, You will need an additional adapter chip like the FTDI 232H) to hook up to a serial port on a computer. Speeds are usually limited to less than 400 Kilobits per second(varies based on distance and devices)
If you are connecting multiple devices to the same micro-controller(Arduino), use SPI. The connection speeds are not limited by standards. It is a bus arrangement with 4 pins (clock SCLK, input MISO, output MOSI and Slave select SS) The SCLK, MISO, MOSI are connected to all devices.To chain additional devices it requires an additional SS pin per device.
SPI is going to be faster(several (<5?)Megabits per second is not uncommon (depends on length(not greater than .3 meters), wire quality, environmental noise and device specifications) and requires less discrete components.
Since LoRa speeds max out around 300kbps, a single SPI connected gateway could theoretically handle 15 LoRa transceivers on a single gateway.
Doing 15 devices may violate local RF duty cycle restrictions resulting in fines and/or imprisonment.
Please check with your regulatory institutions prior to implementation of any solution.
I would suggest using four transceivers with external antennas each pointing in a different cardinal direction(possibly offset) at each gateway. This configuration should permit 400+(depending on usage patterns) client devices per gateway.
Related
I'm learning embedded development, and I'm trying to communicate with the accelerometer (LIS3DSH) on the discovery board using the SPI protocol. I'm only using CMSIS headers so that I'm forced to interact directly with the registers.
According to the schematics, these are the pins being used by the board for communication with the accelerometer:
PA5: SPI1_SCK
PA7: SPI1_MOSI
PA6: SPI1_MISO
PE3: CS_I2C/SPI
From my theoretical understanding of the SPI protocol, whenever I want to receive or transmit data between the master and the slave, I first need to pull the CS pin (PE3) down and then start the communication. This seems to be confirmed by the LIS3DSH user manual as well.
But now I'm confused about what the meaning of SSM is. According to the board's user manual, this is what the software slave management bit does:
When the SSM bit is set, the NSS pin input is replaced with the value from the SSI bit.
The NSS pin is nothing but the slave select pin, right? Which means it is PE3 in this case.
The SSI bit is bit 8 on the SPI_CR1 register. Does this mean I should instead toggle this SSI bit instead of PE3? That doesn't make sense because how would board know that the PE3 is the relevant CS pin?
So how are the CS pin/line and the SSM bit related, if at all?
If they're not related, do I need to configure the PE3 pin with alternate function mode and and as a pull-up, and then pull it low every time I need to communicate using SPI with the accelerometer?
The NSS pin is an input used as a CS by some other device when the SPI peripheral is in slave mode, or can be used as an output to support multi-master configurations.
If you are operating the SPI in single-master mode, the pin is not used at all.
Moreover SPI1_NSS is an alternate function of PA4 or PA15 so not related to the CS GPIO on PE3 in your case. In master mode, any number of available GPIO pins may be used as CS lines for each peripheral on the same SPI bus, and is driven in software - it is not an "alternate function", and not part of, or controlled by, the SPI peripheral.
I'm controlling a couple of i2c slaves (PCA9505) using the I2C module of National Instruments LabVIEW. I need to improve the project so I can add new slaves to the bus without manually adjusting the address of the slaves. (pins A0 A1 A2 on PCA9505). As a consequence, hardcoding the addresses is not a option.
Also, PCA has only 3 pins, so I can add max 8 slaves. I need to go for 16.
How can I give the slaves dynamic addresses?
How can I expand to 16 slaves?
Thanks for your help!
PS: PCA9505 = 40-bit parallel input/output (I/O) port expansion for I2C-bus applications
Personally, I like to use a configuration file to set the parameters needed for an application. In this case, it would define the addresses for each device you need to talk to. Arrays also help a lot here for expandability.
As far as extending your I2C bus, you can use something like a PCA9544A I2C mux. This chip allows for controlling 4 different buses. You will have to control the mux as part of your addressing of the individual chips.
From a brief read of the PCA9505 datasheet it doesn't look as if there's any way of selecting the device's address other than using those address lines. You are either going to have to multiplex the bus as crossrulz suggests, so that each device is at the same address on a different I2C bus, and add code to control which one you talk to at any one time, or add some hardware that sets the address lines differently for each device.
Will the devices be added to the bus via some sort of connector? If so could you include the address lines in the connector, so that each connector on the master adapter sets a different address for the device that's plugged in to it? Or if you connect devices in a daisy chain, each device could add 1 to the address on its upstream connector and output the new address on its downstream connector?
I am new to Wireshark and capturing packets and all Stuff. Let me get it to the straight.
I have a hardware which outputs its data over Ethernet using a UDP Broadcast. I Can directly plug a Ethernet Cable to a In-line RJ-45 Coupler (attached to the hardware) and my PC Running Wireshark.
REQUIREMENTS : I need to Capture RAW Data which my hardware is broadcasting so that it can be given to other team so as to know the format in which it is providing for further post processing.
What I Did : Initially , I connected the Ethernet Cable from my home and Started capturing the packets which didn't make any sense to me.
Can you please point out if I am going in correct direction ? Sorry if its a very basic question, but raw data from the hardware is important for my further tasks....
As far as any software can understand a wire you will always get a packet. Between you (in front of a computer) and the cable in the in the RJ-45 jack sits a NIC (network interface controller, i.e. your network card).
Your Ethernet NIC will read the current on the cable (in manchester encoding for ethernet) and synchronize itself to any Ehternet traffic on that cable. What does "synchronizing" mane in there? In front of any Ehternet traffic come 64 alternate bits of 0s and 1s which are meant to synchronize the clocks on both communicating NICs. Without proper clock synchronization some data may be misinterpreted.
But why I am talking about clock synchronization? Because if you want the data as RAW as it is on the cable you will not get it. A NIC will never send any synchronization bit to the rest of the computer, therefore it is absolutely impossible to read exactly what is on the cable by using software.
On the other hand I find hard to believe you want the RAW data as RAW as that. After the synchronization bits come an Ethernet encapsulated packed. Yup, Ethernet uses packets. They're link layer packets (layer 2 in OSI).
And wireshark gives you exactly that (in most cases, see note at the end for two exceptions to this rule): every Ehternet packet that the NIC understands, manages to sync, and manages to read without collision is sent to the kernel and then read by wireshark. A cable has electrical interference and has no provision against collisions (it's just a piece of cooper!) therefore the NIC abstracts things like interferences and collisions.
I'll repeat it once more: After abstracting the synchronization bits, sender collisions (which turn the cable into one huge interference) and plain interferences; all that remains is a stream of packets, one after the other.
Extra Notes
NICs sometimes do ignore some Ethernet packets: packets that are not directed to their MAC. This can be changed by enabling promiscuous mode (available in most NICs). This is irrelevant for broadcast packets.
There are exception to the rule of wireshark getting all the traffic coming from the NIC:
If the traffic comes incredibly quick, wireshark may drop out of kernel schedule and not see some packets. It happens, nothign can be done about it.
If you listen on all interfaces (as opposed to selecting a single interface to listen at), wireshark will strip the Ethernet (or Wifi) headers. This is a wireshark hack needed to make output files uniform (and possible to be read by other applications).
TL;DR, wireshark output (pcap) is pretty much just the stream of packets that it got from the NIC, one after the other. That is as RAW as you can get with software.
I have an old hub that sucks, so I converted it to a USB-tripler by soldering all of the input 4 wires to the corresponding wires on the output connectors. I had to do this because modern devices require 2.0 or 2.8 volts on d+, and refuse to charge if d+ is shortened or not connected. It works well charging three devices from a 1a wall adapter.
But if someone accidentally connects this to a PC port, what will happen? Well if there is only one device, it would be detected no problem. But if two devices are wired to the same port, how dangerous is that?
I would prefer the first connected device to be identified in the system, while the second connected devices just get the power.
One of the first steps in USB enumeration is to send a reset signal by driving D+ and D- low. All the devices plugged in will see the reset and think it was intended for them. After the reset they will each think they have address 0 and respond to requests to that address. The result will be multiple devices trying to drive the bus at the same time, for a brief period before the host gives up.
I think it wouldn't damage anything, but you will be causing a short circuit for a few microseconds which is bad.
I am using several XBee Zigbee with some Arduino modules (or microcontrollers, Arduino is not mandatory). I configured my XBees in AT/transparent mode.
I need to broadcast information: when one module is touched, every other module must react at the same time and immediately.
Unfortunately, if I have good speed results in unicast mode, there are lots of latencies in broadcast mode. It is something known and documented, see XBee ZigBee Addressing.
No data is lost, but they are sometimes buffered for a few seconds by an XBee before being sent again or delivered to my Arduino.
It seems it is not a configuration problem, it is the way the broadcast protocol work. Any idea on how I could speed-up the process?
The only one I have would be to use the API mode, to make each Arduino keep a list of the XBee addresses, and unicast information to the list of these addresses... but I lose the comfort of the broadcasting method, and I cannot easily add a new module without updating every Arduino.
Transmitting data using broadcast addressing with XBee ZB modules will generally give you much, much less performance than transmitting an individual unicast to each node you want to talk to. This is because broadcasting works very differently on the XBee ZB modules than with the XBee 802.15.4 modules.
When you send a broadcast with the XBee 802.15.4 modules, a single 802.15.4 frame is transmitted to the network and all the nodes that can hear the transmission pick it up and send the information out of their serial UARTs. The 802.15.4 network is a simple star network and no implicit repeating of the broadcast is performed by any of the nodes on the network. With XBee ZB, this is different. The XBee ZB modules are acting in a mesh topology and need to repeat the information to the other nodes that are out of range of the original transmission.
When you send a broadcast with the XBee ZB modules, each node that receives the broadcast will re-broadcast it 3 times, causing a lot of data to be transmitted between nodes. Additionally, there can only be a certain number of broadcasts which are "live" on a network at any given time. This often surprises people into thinking that the network is dropping their data when in fact the XBee is rejecting the transmission request.
Unless you are sending data very infrequently--perhaps a broadcast once per minute or more slowly--it is often better to follow this procedure:
Built a list of all nodes by performing a network discovery or collecting route record packets by enabling the AR feature
Send a unicast to each node you wish to transmit to
If you're sending information to a nodes on a large ZB network (i.e. greater than 30 notes) you may want to read this article: Large Networks and Source Routing
I don't think you can optimize it much more, unless only some of the modules need to receive the message. In this case you could use a multicast (might only be available with Xbee 2) instead of a broadcast, which would bring some very minor improvement on the overall speed of your network when it grows big enough (greater than 16 nodes, i.e. the basic routing table).
Have you tried a comparison between unicast, multicast and broadcast? It may be that making a dozen unicasts is on average faster or at least more reliable, especially if you have many hops in your specific network (ex: a 12-node network with 8 hops).
With unicast you can get a confirmation or ack so you know the overall time and success of the operation, and whether you need to retry or not.