[LASMO] PCB progress

Externals Clocks

In my previous article, I talk about the STM32F7’s and the STM32F1’s clock.  However, according to the STM32CubeMX and after talked with Alexis, we will use for each controller a 8MHz external clock (for consumption questions) and rise the frequency using the PLL until 216 MHz for the STM32F7 and 72MHz for the STM32F103. According the oscillator design guide for STM32, we have 

with CL the load capacity of the clock wich is 18pF here and Cs the stray capacitance of the printed circuit board and connections wich is 10pF here. So, we have the construction for each controller : 

Also, we have a ESP32devKitC which don’t must to have an external clock because the ESP32 WROOM integrated has one.

XLR connection

We also work an the XLR connection but due to the phantom and the symetrisation we had some problem with the architerture, so we decided to use a jack connector. We talked about an architecture but we change again for RCA connectors which Pierre will talk about.   

DAC to LASER 

The drivers of the laser work with a balanced analog input ranging from 0 to 5V. Since the DAC of the MAX outputs a single-ended signal ranging from 0 to 3.3V , this is an issue we had to resolve. 

We basically had to convert an analog single-ended signal to a other one, and amplify it with a 5/3.3 ratio. We achieved this by using an ADA4500-2 amplifier with two resistances, as represented below.

This circuit is composed of a non-inverting amplifier (taking the out of the MAX5105 as entry), which, with the resistances of 1kΩ and 1.96 kΩ, multiplies the signal by 1+1/1.96 = 1.51 = 5/3.3 (approximately). Then an inverting amplifier with a gain of 1, create aa signal which is going to the input of the laser

After talking with Sam, we decided to delete the DAC_OUT signals from the MAX5101  to the F103 microcontroller because their are not essential. So, we configure the HREF of the MAX5101 at 5V, and not at 3.3 V. So, we don’t need this architecture for the lasers’ inputs.

Project architecture

We also decided about the architecture of our project and about the workflow. I put the configurations files of the STM32F4 controller that we use in TP in order to begin to code with the board that we have. Let’s begin !

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