Hi, just some news about our project :
The PCB of the station and remote control are almost ready.
In the same time, Guillaume is working on the bootloader. Brice implements a NMRANet communication thread between can, ethernet and dcc. As for me, i tested if the remote control can be supply by 5V and i’m working on the conversion between Xpressnet (Remote -> Board) and DCC nmranet packet (Board -> Station -> Train).
Motor command :
This week-end I worked on the PCB will command the motor. It is now finished. We will use a AT90USB162 as micro controller.
Power problems :
We have finally solve our power management problem : indeed, in the propeller we need 1.2V, 1.8V, 2.5V, 3.3V, 5V(with almost 10A for 5V).
I thought about the internal architecture of our FPGA. My idea is the following :
I have coded the RAM controller part. I will realize a testbench to compare the timeline with the needed timeline.
As sensor, we will use a coding wheel. But, we have put on the propeller an halls sensor too, just in case …..
Using the simulation tool from Linear we got results about the behavior of our circuit to generate 3.3v and supply a current at least 1.2A with the LTC3113.
The circuit is ok, we should use an inductance which support more than 3A.
Considering the ESR of the input and output capacitance, the variation in the ripple changes but it is still is not significant.
You can find more tests here : Power-supply-3.3-data.
The motors we choose are 6V nominal but the documentation says they can be driven with 9V. The stall current is of 360mA.
I choose a driver IC we had on our mentor graphics library, the L6206. I have one uncertainty about it, it’s its over current protection. The datasheet gives information on how to calibrate the current threshold using a resistance between 5k and 40k. The problem is that the minimum threshold previewed (with a 40k resistance) is about 552 mA, which is above the stall current. I am not sure this is a big problem, if anyone has comments I’d appreciate =].
Meanwhile I am searching a voltage regulator for the motor. It has to generate the 9V with 800mA, from the voltage coming from the battery/usb system. This input voltage is not constant and may vary from 2.5 to 4.2 V. Looking for some options at Linear technologies, I found some ICs, and narrowing down to the simpler and most adapted ones I got these:
None are available in our library, so one of them needs to be added. I could not see important differences between them, but I think the 1872 is a little more powerful than we need. For now I am going with the 1370.
On Thursday, we finished out presentation about switched-mode power supply with both Guillaumes and then we presented it on Friday.
We hope that our presentation was clear enough for everybody and don’t hesitate to ask question about switched-mode power supply, we will be happy to help you.
On Friday afternoon and today, I continued working on the STM32 practical work.
Simulation about Ball-E should be made during next week.