Half Duplex SPI allows all units to send to each other using MISO or MOSI. The challenge is that if 2 units try sending one might pull high and another low so you get a short-cut. The same goes if more than one tries to become Master and run the clock. The diagram above solves that by introducing small resistors on SPI. And this is recommended for Half Duplex SPI. This is one of the changes I will need to add to all my Hat’s.
Doing a review of your Jown work is a bit of a challenge, but it is possible. The trick I use it to complete the work and then let it rest 1-2 weeks before I pick it up and update documentation. This technique has in the past proven quite efficient, but I would recommend using colleges to double check your work if possible.
Checking SW work is very complicated because the work is often thousands of lines of cryptic text. It basically becomes very time-consuming and expensive to check everything, so we end up only scratching the surface. This is also whyJ it always should be a traceable path from specification to design to code to test coverage. Once you get this path into your fingers you will discover that it actually speeds up the life-cycle of development over time.
Electronics is easier. We Jhave automatics to check PCB’s, but schematics are drawings and very easy to check and discuss with colleges. These reviews raises discussions that make you question your own work. At the end it is not your colleges that make the changes, it is you who find improvements and execute them as a result of the discussions.
My previous schematics eJrror could have been discovered if I had done a simple exercise of annotating the electronics. But, lets be honest – I say could have – at the end neither all the checks, reviews and automation in the world will prevent mistakes and non-working PCB’s from happen. At some point you just need to make the PCB, assemble it and let theory meet the reality and unexpected.
I have seen electronic engiJneers do both. Some check their work forever and still end up with errors. Others just push forward, end up with errors, correct them and push forward again. You have to find your own balance.
J7 above is the USB connector on my Hat’s and 44/45 at right is the connection to the MCU. This is all you need to do to have a working USB connected to an STM32.
Software is even easier if you just want a serial port. You just install STM32 Virtual Serial port driver for Windows 10 and check out middleware setting in CubeMX – once the code is downloaded the serial port will just come up. Actually using it is a minimal amount of coding on both sides, but it could hardly have been easier from schematics to working SW. I have not tested other USB classes, but I assume they are equally easy.
The screen above is from CubeMX. To have USB driver included you just wire the pins in the model, select Middleware and enable the USB_Device library and set up parameters to what you want.
This is the PSU used on the LoRa/GPS Hat to allow switching the units on/off. The signal EnGPS connects to a GPIO pin and the MCU must pull it high for GPS to switch on – very simple.
One of the functions of a modern EDA is to check schematics and PCB. This works excellent and have saved me lot of work in the past, but I guess it would work even better if I remembered to switch in on. In this case I have somehow managed to switch checking for signal Logic off.
The error here is that I have forgotten to connect these signals on the PCB, so the PSU’s are constantly off. The automatic check would have warned me about this, but as I somehow have switched “signal logic” check off it did not. I made and ordered a lot of PCB’s at the same time and was obviously in a bit of a hurry. The cost of the PCB’s is no worry, but it takes 6 weeks to get them. I obviously need to double check this before ordering PCB’s, but as I have said before – I always expect 2-3 rounds with corrections.
I want to make a larger plane using drone technology and the drawing above illustrate a generic control system with 4 thrusters. In this case I suggest 4 main motors because I want to lift a large drone in a simple frame to test thrusters and control logic. But, the illustration is generic in nature.
Control System consist of a Raspberry PI A+ and a LoRa + NB-IoT Hat + XPortHub. I will connect to the remote control using Wifi, LoRa or NB-IoT in that sequence. NB-IoT require subscription, but has nation wide range. This means we can send the drone on long distance flights. In this case I use the powerfully Raspberry PI for AI logic while I leave motors and actuators to specialized MCU’s in a distributed control system. This is an excellent test case for all the projects I have done on this site.
To communicate with actuators and sensors I can basically scale up as per need. The plan is to use CAN (or RS485) for a wired telemetry interface. In fact I might need 2 for redundancy. Camera(s) will be a Raspberry PI Zero W with Camera attached. I will need to find or make a solution here to attach camera and a wired or wireless connection. I try to avoid wireless connections inside the drone due to noise and radio density.
2 separate battery banks with a battery charger and PSU’s are needed. Motor batteries and motor power feed is kept separate from control system and sensor PSU.
BLDC Controlles will be the 3KW 3-phase ones. I can use the Steam Punk Controller as well, but I think we need the smaller space on this one. We need a separate BLDC Controller per thruster.
3D Sensors are basically a variety of 3 axis sensors that is used to detect the drones position in 3D. This together with the GPS can locate the drone in 2D as well.
The advantage with this control system is that I can scale up/down as I please. Compared to a All-In-One system this adds a few concerns and complexity, but I am not targeting ultra small drones.
My first objective is a frame like the one below. This is just an early test to get a few meters above ground and get the vertical take off and landing working.
The sketch below is of the actual drone. I add a 5th forward thruster and ordinary wings. The objective is to get more flight distance and time than I can achieve with a classic drone and still have vertical take off and landing. I will build this mainly with 50cm carbon fiber rods jointed to get som size. The thruster will need to be some 3-Phase motor with a frame I need to make. The motors and batteries are probably the cost driver here. These drawing are also only illustrations. I am not an expert in aero-dynamics, and I have some concerns. But, well – that is where reality hits in + I am armed with a forrest of friends that can assist me.
The main concern I have is (1) mechanical design and (2) cost. The show-stopper for the project is however battery capacity that will limit flight time and usability. But, that will improve in the years to follow.
UDP is an excellent protocol for sending messages between nodes in a system with Ethernet or Wifi. It’s speed and behavior on a modern PC’s allows in the region of 100,000 messages per sec, which should be sufficient for most applications.To make a Connection you only need two end-Points of which one need to have a known (fixed) address so the other cand send to it. The receiver get the sender address so it can send back. Sending is also fire & forget as UDP will send regardless wherever the receiver is there or not.
To create a client/server is equally simple. You simple create one client on a fixed address and the the others can contact this.
The true power of UDP is however that it is a “mail-box” on Ethernet that anyone can send to. You can send to any UDP port and receive from any UDP port. UDP bind to the local ip-address and port you use for sending, but it is connectionless so it’s not affected if the receiver drops down, reconnect or simply is not there.
easyUDP is only a thin wrapper on top of UDP to provide a standard, easy, event driven interface. To use the interface you need to do 3 Things
UDP is very lightweight and you need to add you own protocol to maintain sequence and ack messages etc. But, UDP will maintain message integrity since the packet you send is 1:1 with what is received on the other side. The lower interface of easyUDP is different from platform to platform. I currently use a test implementation in C# on Windows that obviously will have only design and interface in common with one in C++ or one on a STM32. UDP/TCP already have a “standard” socket interface, but easyUDP uses a simpler approach of Open(), Close(), Send() and OnMessage().
UDP packets consist of UDP + IP Header + payload. easyUDP will in addition add it’s own little header to support streams. Basically we pack multiple easyIPC messages into the same UDP packet using the standard easyIPC format per Message.
easyIPC is the protocol and collection libraries I use to communicate cross various networks. easyIPC is not bound to a special technology as it provides universal device to device access through a variety of technologies including Ethernet/Wife, RS485, CAN, and SPI and in time others.
UDP, SPI, UART and CAN are examples of technologies I use and they all require a different lower protocol to take advantage of the underlying bus architecture. This is dealt with in AL (Abstraction Layer). UDP (as an example) will have a generic UDP interface, but the one I am interested in here is easyUDP and accordingly easySPI, easySerial and easyCAN. These layers are specially adapted to the easyIPC concept and each module has an identical interface so we don’t need to care about the underlying bus/stack complexity.
The concept is simple – we connect, send and receive messages as if everything is local using a common addressing scheme. Only the sender and receiver need to understand the messages. Message sequences are dealt with in easyIPC or user modules. Lets briefly discuss the technologies and why they are on this list.
| easySPI | We use a control system composed of Raspberry PI and multiple STM32F405 MCU using high speed Half Duplex SPI as the backbone bus. This gives a speed of 30-42Mbps which in reality makes it very comparable to a 100Mbps Ethernet. |
| easyI2C | This is the same as easySPI using I2C bus. This is currently not supported. |
| easySerial | Using RS485 or RS232 as bus. RS485 implement the TDM bus. Specially RS485 is well suited for distributed control systems as it covers up to 1km wired and as such allows a none-wireless interface to fixed locations. |
| easyCAN | Using CAN as bus. |
| easyUDP | Allows Ethernet and Wifi using the UDP protocol as carrier. |
| easyBluetooth | Allows IPC over Bluetooth. |
| easyLoRa | Allows IPC over LoRa Technologies. Long Range radio allowing up to 12km coverage. |
| easyNBIoT | Allows IPC over NB IoT Technologies. This is basically a low cost phone line allowing you to communicate in all areas With GSM,3G,4G, 5G etc. |
| easyShockburst | Allows 2.4Ghz Shockburst as IPC. Max range is 100 meters, but it is an awesome Wireless protocol With bandwidth up to 2Mbps. |
First 3D draft of the RS485 Hub. I have moved all connectors to left and top because it will be attractive to use this together with RPI 3B+ that have Ethernet/USB at right. As mentioned I could have used XPortHub for this, but I often need exactly RS485/Ethernet in higher density because RS485 is very attractive connecting to small, remote sensors/actuators. The drawback With what I do here is lack of galvanic isolation, but I will add a separate Hat for that purpose later. In an ideal world we would add galvanic isolation everywhere, but it comes at a huge size and performance cost (slower Serials), so it makes more sense to add isolation between nodes or then connecting to long wires or special Equipment.
The actual board will probably change a bit. I like doing these mock-up’s placing connectors and components, but as I start routing I also end up changing things to adapt. Schematics is done, so it will take me a few mornings to get routing done. I find PCB routing to be a relaxing mind game – so yes – this is my form for relaxing.
You probably feel the site have slowed down a bit, and yes it has. To much happening Real Life at the moment so it will be a bit like this for a while. It is also a consequence of me digging deeper into SW as I have an large backlog of things I need to code up.
XPortHub is great if you need a combination of ports, but I often need a high density of one port type so I made RS485Hub with 6 x RS485 ports, 2 x CAN ports and 1 x USB.
This is basically a simple Hat where I take advantage of the high number of RS485 ports on F405. The 2xCAN is added because they are available.
The main objective with an Abstraction Layer is to protect user modules from changes between platforms. Code on user level should be portable and plug & play after you done a 10 minute task of soft-wiring. I decided on the name “Abtraction Layer” because HAL (Hardware Abstraction Layer) is missued to much and was not a good fit.
The figure above illustrate what I want to achieve. The interface on AL should be identical, while we know that each AL module will need to be specially adapted to the technology in usage. In this case I will point out that easyIPC’s version of SPI is not a generic SPI interface. The easyIPC version is a TDM protocol that needs to be tightly integrated with hardware.