[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 !

[LASMO] External clocks, and XLR architectures

For the two processors STM32F7 and the STM32F1, we need to use externals clocks. Indeed, for the STM32f7, the processor can use a 16MHz internal clocks, but in order to have the best performance STM32F7 can provide, we will add an external clock of 26 MHz. We will do the same for the STM32F1, but with an external clock of 16 MHz.

Also, we will use two XLR connections in order to have a sound signal wich the animation will be synchronize with. After find out about XLR connection and signals, I understood that a connector XLR has 3 pins, carry at 24 V, and receive two symetrics signals but out-of-phase. So, we have to desymetrize the sygnal. To this end, we will use an instrumentation amplifier: 

with

[LASMO] Specifications

We have redefined the differents specifications of our project. To resume, LASMO is a displayer of a laser show. It will be able to display 2D ans 3D ILDA animations. All ILDA formats are supported. LASMO can display until 30 Kpps/s (at +/- 20° otpical) with a resolution of 4096 * 4096.  We use a RGB LASER in order to display until 16 millions colors.

Moreover, 3D animations are projected so that it looks 3D form from a certain point of view. This way, ILDA animations can be streamed either from internal memory (SD card) of from a PC via Wi-Fi or Ethernet.
Also, LASMO implement Art-NET protocoL in order to be controled by a standart light show controler thanks to Ethernet. So, it will be possible to synchronize on beat from stereo XLR input.

Furthermore, thanks to a picture, LASMO will be able to correct a deformed animation on a surface depending on the picture’s point of view and project a new one corrected always depending on this point of view.

[LASMO] LASER specification, Ethernet and Wi-Fi rate

For the LASER, we need to know which power we have to use, in order to know the LASER’s class. It was a difficult question which I had to think and reflect on. Actually, the class 3B is a higher level of LASER, but more dangerous. On another way, I thought that a 3R LASER couldn’t be powerful enough.  Finally, after some researches, we decided to take a 3R LASER of 5mW, which would be sufficient for projecting animations. Furthermore, the LASER will be in green colour (520 nm) , thus points will be more apparent and distinguishable.

There are 2types of LASER that we can use: The LASER diode, that can be used like a simpleLED or the LASER Diode Pumped Solid Stage. We will use the first one.

With those informations, we can now specified some characteristics like the tension : 2.8 – 6.5V/ DC

We will control our LASER with the TTL modulation and not a analogic one. We can also shade the beam’s brightness with PWM mode.

Now, we also know that in order to show an animation, we need 300KB/s = 2.4 Mbits/s.

Also, 10BASE-T Ethernet can provide us 10Mbits/s which is enough. We can also take another specification of Ethernet that will be widely enough like 100BASE-T .

For the Wi-Fi, norms are differents by the range and the rate. We can use almost every norm, but we prefer to have a considerable range in order to do the LASMO’s configuration everywhere in a site.  So,we will use the 802.11n norm Wi-Fi.

Now, we have to identified the micro-processor we will use

[LASMO] LASER choice



For our project, we need to define the LASER type we can use. So, I did researches about the different classes. There are 5 classes of LASER, and we can use only 3 of them without a specific licence. However, we need to have enough energy to properly see the projection. So, we will use a 3R LASER class, which can not be looking during more than 0.25 s. We need to program in hard a control module in order to avoid a potential risk.

Now, we have to precisely define the LASER’s colour, its power, its voltage, its diameter, and its control speed required for our project