ELECINF344/381

Partie interactive du site pédagogique ELECINF344/ELECINF381 de Télécom ParisTech (occurrence 2011).

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TSV Safe Express: remote controlling is possible!

We have yesterday worked on the control of our circuit from a remote server, and we finally could remotely control all lights on the circuit. We could also run our train in both directions, corresponding to the remote program commands.

As we send information about the car position (sensor information), the remote program controls our circuit continuously.

After that, we were facing the problem that the railroad switches weren’t decoding our DCC commands. So we have reprogrammed them. After that some of the railroad switches. Unless the railroad switches aren’t included in our work specification, we try to control them all in order to make a free circulation of our train. Vaibhav and Theodor are concentrating on this part while I am doing the presentation for tomorrow.

TSV Safe Express: Big time troubleshooting.

Today we have faced numerous problems. The ethernet module causes a crash in our central station and we still haven’t figured out the solution. We also tried to connect all card’s (6 captor-6 traffic lights cards) to our main station and they failed to join our the network. As Alexis consulted us to do, we lowered the baud rate of the CAN bus so that problem is solved. All cards join the network and  CAN baud rate now is configured at 125kbp/s.

Regarding the communication of the server with the train we were able to track the position of the train and send it to the server. Our goal now is to remotely control lights and train, and we are working on it.

TSV Safe Express: Demystifying Conundrums

During the last two days, we have faced a lot of problems with the sensors of the track. We had two types of interrupts that were causing us problems:-
1. Debouncing Interrupts
2. Fake Interrupts

Problem: We have configured STM32 GPIO ports to Internal Pull-Up. All our sensors cards are powered by the Central Station Card through the CAN bus. We observed that there is some kind of parasitic signal that comes from the booster towards our Central Station which produces a glitch in the power towards the Nodes (Sensors card in this case). Due to this glitch in power, the GPIO ports which were pulled high become low and thus Fake Interrupts are produced. Thanks to Alexis who stayed till 5 in the morning to help us debug the problem.

The first one was solved by making sure that the any interrupts (that is not fake) from the sensors is processed only if there is atleast a gap of 100ms since the last time it was called. For the second one, which is more tricky, we use a simple method (a FreeRTOS task) which checks for glitches. This method was proposed by Samuel and we thank him for assisting with our software.

Right now, we are trying to do all the mapping of Reed Sensors and Lights to the XML Layout of the track. This is required as the central station needs to talk to server giving him with sensor input.

TSV Safe Express: Traffic lights set up and ready to go.

After stabilizing the NMRAnet  CAN bus , at least to what concerns the traffic lights, we connected all the traffic lights of the circuit to the cards and verified that indeed this part of the project has been finalized. 6 traffic light cards successfully respond to the assigned by the central station events, and glow led’s accordingly. Now what remains, concerning this part of the project is, their mechanical placement and installment.

Currently we are focusing mainly on the development of the sensor cards and we hope that won’t take much time. We got our first interrupts from the train passing over the reed sensors. Hopefully by the end of the week end we will be able to wrap everything up and start communicating with Samuel’s application.

Here comes a video of Siwar explaining our work up to this moment.








 

 

TSV Safe Express: progressing

As we we have foccussed on stabilizing our CAN protocol. We have tested glowing lights through CAN

with the central station and four light cards.

We have finished the ethernet part that takes bytes from a remote computer and translates them to DCC commands.

We have written a program for the sensor card.

Then we started moving some cables and old cards from our train circuit. We are now testing the controlling of six light cards.
After finilizing our software, what should take with testing two days, we will solder our sensors on our sensor cards and fix all cards on the train circuit.

TSV Safe Express: Sensors Card Development and Ethernet

Today, we received our 7 sensors card (which will track the position of the train and feed it to the central station), thanks to alexis who worked until very late in the night for soldering all the cards. So we wrote the code for the Sensor card which has a « producer » module who generates events on the CAN bus to indicate a sensor activity.

Also, Siwar is trying to do the communication protocol between ethernet and the server (setup by Samuel which controls the rail layout).

On the stabilisation of CAN, we are now filtering out events in CAN RX Queue 1(STM32 micro controller has 2 FIFIOs) and have left messages for network management on queue 0. This is done to avoid over-utilisation of queues due to either type of messages. Here is brief video of our project.

TSV Safe Express: Timing issues.

Today Alexis delivered us the whole set of the train light circuit. Initially we tried to add another light card to our current testing configuration. We managed to get 2 light cards configured , so up to this point the central station has been able to control 2 light cards, the train and an ethernet connection  in total.

Currently we are working on stabilizing the  NMRAnet CAN bus protocol. We encountered problems  of what we think mainly concern,  a difference between the CAN bus bandwidth  and the processing bandwidth of the central station. For example, as we observed, during programming the events of a node,  within an environment of multiple CAN packets exhange, the central station missed acknowledgement frames sent by the node after  the configuration file. This prevented the central station from successfully programming a node. After inserting a delay between sending the data of the configuration file and the ACK we observed that the node got successfully programmed. This led us to assume a mismatch in processing and CAN bus bandwidth.

In order to face these kind of problems which have appeared, we will adjust the CAN bus bandwidth, use one buffer for event processing and another one for network-management purposes, and additionally install event filters on the fly accordingly for each node.

 

TSV Safe Express:Going ahead with Ethernet part

we have started today making some tests on the DCC part. As we have seen the good results with the oscilloscope, we moved to testing on a rail part by placing the train and sending the DCC commands through the rails. In fact we could command our train in both directions in different speeds.

Then, we started to implement a small module that takes Ethernet commands following a simple protocol. This module is translating the Ethernet commands to appropriate DCC and CAN commands in order to command different parts of our train model.

In parallel we still test the stability of our CAN module. Despite the good results there are very rare cases where our cards become unstable. We are making some modifications and we are going tomorrow to test on multiple light cards.

Our next PSSC is the initialization of Ethernet (what is already done) and control of our circuit from an extern program.

RoseWheel: tests preparation

This week we tried to put together our developments and make them interact with each other. It includes sensors communication, kalman filter, control feedback, motors control, CAN communication protocol. We were dogged by bad luck as we realized the heatsink of our mainboard was too big to fit in the Zzaag… A few millimeters required us to order for a new one with a more suitable shape. Fortunately Alexis and Samuel helped us to find a new one. Because of that we were not able to validate the following « feedback control tuning » PSSC for Saturday as planned. Adviced by Samuel we also decided to postpone the « encoders drivers » PSSC as it wasn’t really in our first order priorities.

 

We tried to make profit of this situation and decided to prepare everything for the first tests. Alexis helped us defining our tests procedure to be as safe as possible for both hardware and people. Motors need special attention as they can be broken with unsuitable commands. Because of the wheels and the weight of the chassis they have a really high inertia. Asking them sharply to reverse their direction of rotation when they are rotating fast can seriously damage them and the H-bridges. If we damage them we wouldn’t be able to order new ones before the end of the course, it would be fatal for our project. Therefore we need at first to make some testing at low speed so as to define the maximum acceptable speed at which we can run the motors before they get damaged. To this extent we need an interpreter running on the mainboard and communicating using RS232 to be able to give motors various commands and define this maximum speed. Then we need to limit our commands to this maximum speed using software limitations. Finally the interpreter should be able to change the feedback control values for our testing to be more flexible. We implemented such an interpreter and made a video. The motors commands in the video are given between 0 and 1000 such as:

  • ml0 = 0%:  max negative speed
  • ml500 = 50%: stop
  • ml1000 = 100%: max positive speed

 

Before trying the Zzaag motors we do some testings on other DC motors with less inertia that we cannot damage as easily as the Zzaag’s ones. Putting all the pieces together we were able to shoot a video which shows the motors reacting appropriately to the inclination of the sensorboard. As for the Kalman filter, we implemented a lighter version than the one of RoseWheel as it works best when tested on the real system. This version was only able to track the gyroscope drift and correct it. As far as we could see during the testing, it did it well. Concerning the PID, we tried to test the version that we are going to use in the RoseWheel but it still needs to be improved during the next tests.

 

Tomorrow we will be able to work on the Zzaag motors using our safe procedure and the tools developped. We look forward to it as it is a major step further for our project…

TSV Safe Express: DCC Signals and Ethernet

Our journey has continued from CAN to LAN passing through DCC in its way. During the last two days, we tried to write the dcc encoder for our card which will act as the central station. In brief, I will try to explain DCC for all those who are not already aware of it. DCC (Digital Command Control) is a standard which permits us to operate model railways by sending modulated pulse wave(amplified with the help of a booster) to the rail tracks. Thereby, we can control any locomotive or accessory (like Traffic lights) if they have the dcc decoder. DCC is standard provided by NMRA.
We have done the following encodings for bit 0 and 1 as per NMRA DCC Standard.
(i) bit ’0′ – 232 microseconds (half high and half low)
(ii) bit ’1′ – 116 microseconds (half cycle is low)
On the implementation part, to generate such type of signal on the STM32 GPIO port, we use PWM module(using Internal Timer of STM32) with 50% duty cycle. This was setup in Output Compare Mode. Through the help of oscilloscope, we verified that we got the expected results. We created a dcc packet simulator(coded as a task of FreeRTOS) and we tried sending Messages to the port as per DCC Communication Packet format.

On the Ethernet part, we have chosen LwIP Stack as the TCP/IP Stack. We have chosen LwIP primarily as it has features like DHCP, UDP, IPv6 which we may need as the project matures further. So, we integrated the LwIP stack with STM32F107(which has in-built MAC Controller) and DP83848P Phy Controller taking help of a similar example provided by ST on their website. We were able to make a telnet connection to our Central Station and correponding exchange messages through telnet.

On the stabilisation of NMRA CAN protocol, we added a watchdog module within all the nodes including the central station. This was required because if the software hangs in one of the nodes, it should have the ability to re-join the network. The timeout of the watchdog module has been kept to 3 seconds(Typically because we want our nodes to rejoin the network as soon as possible and at the same time give Central Station enough time to remove this node from the node table and event table). Also, the command to reset the nodes sent by the network manager at the start of his execution as a broadcast message to all the nodes will have a deeper impact. Instead of doing a cache reset at the nodes, we are now doing an actual software reset to the node. This is just to simulate an actual reset. All these changes done to stabilisation are open for discussions and all remarks/critics/ideas are heartily welcomed.