Custom Teaching Board - Page 1
Forum section: electronics / projects

author: pedro10vitor
author_rank: Newbie
timestamp: May 08, 2019, 10:46:45 pm
content: Hello my friends, I would like to ask you guys for some input on a project I am working for a while. First off some background.I am a student making my undergraduate thesis which consists of a teaching board aimed at universities and companies. I have been working on this project for about two and a half years. Of course when I am done I will be publishing everything as open source.While I have prety much everything chosen and in good places I would like to know from you if you have any sugestions regarding positioning of devices, general layout, if you would rather see some peripheral instead of another and anything you like and disliked about the project. Just be aware that this is a working in progress, so some minor changes will be done and some symbols added, like ESD sensitve, not disposable, some texts etc.A bit about the project:The finished project will look like the first image and PDF attached (Project.png).The project consists of 4 main boards. Motherboard, microcontroller board, LCD and supply. The motherboard and the microcontroller board are 4 layers with standart layer stack. While all others are 2 layers.The aim of this project is communication protocols and advanced peripherals, digital stuff. Analog was not a focus!Each board could not have more than 2000 pins, I am using Diptrace.Supply board:Because limitation of the numbers of pins, this forced me to put the power supply on another board and also I think it looks quite nice to have a fixed power supply you can use somewhere else. The +3.3V and +5V rails are generated using two L7980 from STMicro to generate +3.3V and +5V, a bit overkill but keep in mind that this supply will be universal for all future projects.LCD board:The conection from this board to the motherboard was made in such a way that a lot of different screens could be used, be it TFT, characters, dots and e-paper. This one is using a conector for a TFT. On the back you can slect the type of interface as well as cut conection to some pins using the dipswitches. The size of this board was designed to fit a 3.5" from buydisplay with not much room to spare.PS.: The lcd on the image is NOT a 3.5" lcdMicrocontroller board:The microcontroller is a STM32F777BIT, there were a lot of reasons behind the selection of this component, but ultimately I am not happy with this choice. It is too expensive, but because it was chosen a lot of time ago, to change this would mean changing basically the whole project. The connection is made through two 2x50 mezzanine connectors there are some leds on the board and that is it. I didn't went for a normal pin header style because I figured taking out and puting back in 200 pins would apply a lot of stress on both boards, especially on the motherboard, and would make the microcontroller board extremely big.Motherboard:This is the main board, in here there several modules and external connectors to further increase the connection capabilities.The built in modules are:555-TimerRS-232RS-485Real Time Clock4x7 Segment display3 Potentiometers3 Grove connectorsSDRAMFlashEEPROM2 Axis joystickEncoderUSB HOST2 CansSD-CardEthernetUART-USB HIDUART-USB VCOM2 thermometers32 Leds32 ButtonsBesides that there are 3 BUG sockets, LCD connectors, supply connector, breadboard and debug connector. The BUG sockets have SPI, UART, I²C, some GPIOs, +3.3V and +5V rails. The debug interface is SWD, I will be using probably a J-Link. I wont copper fill the top and bottom layers because I have read that in some cases it can warp the board because of unbalanced amounts of copper on each side.Some peripherals share pins with others so you have to choose which one to use, but I tried my best to make sure the peripherals you could use in a sigle momment made sense, so for example the LCD can be used with the external SDRAM, the 7 segment display can be used with the encoder, etc. I will spare you with the bus layout, but if you want more detail feel free to ask.If you guys want to schematic and PCB layout just let me know, just remmember I am not done! There are is some pins to connect and better organize the schematic. Well that is it, please feel free to tell me what you liked and didn't like it.PS.: the quality in some images aren't very good because I am taking screen shots of the 3D view. Diptrace has no "Photo Shoot" mode.

author: OM222O
author_rank: Frequent Contributor
timestamp: May 08, 2019, 11:23:34 pm
content: what happens if switch for 3v3 is turned on at the same time as 5v switch being on?This will cause bad things if the outputs are connected together!you can use a on/off button to turn on the board, then another switch to switch between the two voltages.It's just good practice to make the circuit idiot proof.

author: pedro10vitor
author_rank: Newbie
timestamp: May 09, 2019, 12:01:19 am
content: Quote from: OM222O on May 08, 2019, 11:23:34 pmNo man, they are not connected... they are two completly different rails used in different circuits.