[LASMO] Started PCB design

This week, I start to draw the design of the PCB.
I start to add the main components of the PCB, and decide the exact references we need :

  • For the STM32F7, all references available on the ST website are suitable, so I choose the one that was already in the Xpedition PCB library, the STM32F767vit6
  • For the ESP32, Luc choose the ESP32-WROOM-32: it has an embedded Wi-Fi antenna, an RMII interface for the ethernet, and an SPI interface to communicate with the STM32F7
  • For the security microcontroller, I choose the STM32F103RE. This MCU has to integrate 5 ADCs, one GPIO and an SPI interface. So, a very small STM32 MCU is enough.
  • For the triple 8bits-DACs, I change the MAX512 to a MAX5105 because the MAX512 don’t integrate three equal DACs. Moreover, the MAX5105 has an asynchronous MUTE input, which is convenient for the stop of the LASERs by the security MCU

Then, I work on the Ethernet connection. I add a LAN8742A and an RJ45 connector to make the physical layer. I never made design PCB, so I spent a lot of time to find and understand the different components to add to the design.

After finishing the Ethernet design, I work on the MAX5105 connections. This part was easy to make, but I’m not sure about the direct connection (cf figure 1) between the DACs’ outputs and the inputs of LASER drivers. I don’t have the LASER documentation yet, so it’s confusing for me to know how correctly connect these two parts.

(figure 1) MAX5105 connections

This is the newest version of our main components implementation :

[LASMO] Main components architecture

The LASER and the scanner were chosen : a LASER RGB of 1W and a scanner with a speed of 30 Kpps. They came from laboutiquelaser.fr, a French website. We are waiting for the technician’s answer for the availability of the LASER and a real documentation of each component. 

The choice of these two components allow us to define the main architecture of the project :

Main components’ architecture

The main controller is a STM32F7 family. On this micro-controller we will :

  • Use two DAC of 12 bits to control the scanner
  • Use two ADC of 12 bits to get a stereo input line ( in order to synchronize the animation with a sound beat )
  • Communicate with a SD card 
  • Communicate with ESP32, STM32F3 and MAX512 with SPI protocol

The network controller is an ESP32. It will allow us to communicate with LASMO over Ethernet or Wi-Fi. It will integrate a HTTP server to provide us a web app in order to control LASMO.

The MAX512 is a triple 8 bits DAC. It will be able to control the LASER with 3 analog inputs (RGB). This information have to be confirmed, we don’t have yet the documentation of the LASER. In case the input is not analog, the MAX512 component will be removed.

The STM32F3 is a micro-controller whose solely role is to comply with security norms : indeed, the LASER can’t be turn on more than 25 ms on the same position. The security controller monitors the return position signal of the galvanometers and force the laser inputs signals to zero if the galvanometers don’t move enough.