[LASMO] Making progress in PCB, basic I/O functions

Hi! Last week has been mostly about PCB design. We’re still waiting for our galvanometers and lasers to arrive… Hopefully we’ll have them soon. In the meantime we can’t make much progress about the PCB itself but we corrected some problems.

About the input of the galvanometers, I made a mistake in the voltage adaptation circuit: when the scanner is at its maximum angle, it should be either at -5V/5V or 5V/-5V (positive input/negative input). So we had to adapt the system so that when the ADC outputs 0V, it outputs -5V/5V; when 3.1V (max) 5V/-5V; when 1.55V, 0/0. That means we have to change the resistors values: R1 = 1kΩ, R2 = 2.21kΩ. As Mr Polti pointed out, we also have an issue with the component used: the ADA4941-1 has an output voltage swing of +/-2.9V, which isn’t enough to generate the desired signal. So we decided to make our own adaptation circuit with two ampops that will have the good characteristics (for example, the ADA4666-2 works). The circuit is as follow:

Voltage amplification circuit for scanner input

Meanwhile, I also worked a bit on coding the basic I/O functions of the main controller: I started with connecting the SD slot, testing my code on the development boards we use in practical works this year, OLIMEX STM32-E407. I haven’t been able to test it though, as the only microSD card I have is the on in my smartphone, and I failed to get it out of the phone.  

Luc Moussiegt

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