Using CN0540 and ESP32-S3 to collect IEPE accelerometer data

Question

Hello! I recently acquired a CN0540 board and want to use it in my project to measure sensor data from PCB's 393A03 and 393B12 accelerometers. However, I'm using ESP32-S3 microcontrollers, which are not compatible with the board. 
 The thing is, I don't require much configuration of the board itself, I only wish to measure acceleration with a 200Hz maximum sampling frequency, convert using a 24 bit ADC and store the measurement values in an SD card, so I believe the default settings should do it, but I could be wrong. 
 Currently, I'm only connecting the ESP32 to the following pins on top of the board: -3.3V and GROUND -SPI interface (CS_ADC, DOUT, SDI and SCLK); -PIN_N/SPI -RESET_ADC All the remaining pins, including the ones at the bottom of the board, are disconnected. 
 
 I am capable of reading and writing register values from the AD7768-1, but attempting to read the 24 bit data register only results in the value 128.00, even after connecting the sensor via SMA to the CN0540 board, which indicates that it isn't working. Moreover, in the board itself, only two LEDs light up, the FAULT LED (red) and the CC LED (blue). I know that the POWER LED (green) should also be on, but it isn't. 
 With this in mind, my question is: can I use this method to interface with the CN0540 board and obtain sensor data with 24 bits resolution? If yes, what connections am I missing? If not, is my only alternative buying one of the supported boards? 
 I hope someone can help me out!

malcolm_kwok · Accepted Answer

Hi BananzSplit 
 To answer your main question: 
 With this in mind, my question is: can I use this method to interface with the CN0540 board and obtain sensor data with 24 bits resolution? If yes, what connections am I missing? If not, is my only alternative buying one of the supported boards? 
 The connections you have for SPI* are correct, so you will be able to communicate and collect data from the ADC. However, this reference design makes use of a level shifting DAC which subtracts the DC bias voltage of your sensor. Without this sort compensation algorithm which is loadable to the DE10Nano, the sensor signal would saturate the ADC, giving erroneous data. The algorithm itself is not very complicated (successive approximation model, like balancing a seesaw), so if you can have that and communicate with the DAC and ADC, then you get the intended performance. Still, note that the drivers working with the DE10nano controls other parts of the board, so it is still more convenient to have this platform. 
 *This notes that the 3V3 label you see on the board is actually the "IOREF" node on the schematic. This powers the ADC's SPI communication block, which allows you to communicate with it. But this also means that the actual "3V3" node powering the supply rails is not powered in your setup, which is the reason why the POWER LED is off.

Sorry about the confusion. To power all the supply rails, you can provide 3.3V to the AVDD2 test point or through the Arduino header (P2 pin 4) underneath.

Regards, 
 Malcolm)

14HDtube · Answer

Hi everyone, 
 I'm currently working on a similar project where I use the CN0540 board connected to an ESP32-S3 microcontroller to measure data from IEPE accelerometers . I connect the ESP32-S3 via the SPI interface (3.3V, GROUND, CS_ADC, DOUT, SDI, and SCLK) 
 I'm adapting the No-OS drivers to work with the ESP32-S3, but I&rsquo;m facing challenges in establishing proper communication between the board and the microcontroller. 
 Would you be able to share any sample code or advice on setting up SPI communication and configuring the ADC for accurate data collection? Any tips 
 or troubleshooting suggestions would be greatly appreciated! 
 Thank you for your help!

BananzSplit · Answer

Hi! 
 I have been hard at work trying to make this board work, and I think I've finally done it :D So first, I discovered that the pins IO5 and IO4 require soldering resistors in the actual board, so I followed your advice and started using the output of the ADC as a reference for the successive approximation algorithm. The 4.22V I got from the VREF test point using the oscilloscope, but that value might be off because the probes can be damaged, so I started using the 4.096V that is referred in the datasheet. Regarding the ADC, what I did to turn the codes into voltage was use the equation provided in the AD7768-1 datasheet: 
 
 However, I had a lot of trouble understanding the process of converting the codes from two's complement to straight binary, and honestly I still don't understand how it's done. For example, the datasheet indicates that the value 0x7FFFFF in table 12 should be turned into 0xFFFFFF, but how? I tried many methods to implement this equation into my code, and finally found a way to correctly transform codes into voltages: I just use the two's complement code coming from the ADC instead of converting to straight binary, and in the equation I don't subtract the Midscale code (8388608). As such, my equation looks like this: 
 Voltage = (Code x 2 x Vref)/2^24 
 Where Code is taken directly from the ADC and Vref =4.096V. 
 With this implementation, I was able to obtain the same values of voltage shown in Table 12. This means that the code 0x7FFFFF gives me +4.095999512V, 0x000001 gives +488nV, 0xFFFFFF gives -488nV and so on. Furthermore, my successive approximation algorithm can use the voltage to adjust the DAC value. On startup, with the accelerometer standing still on my desk, the algorithm can get to a voltage value of around -0.2V to -0.4V. Then, when the system is capturing data, if I start hitting the accelerometer, the voltage levels change accordingly and I get voltages between -4.096V and 4.096V. 
 Really happy that I'm finally getting something out of this blue board, but please tell me if I'm doing something wrong! I would like to thank you once again for the great help, and in case more questions appear, I'll post them here!

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Using CN0540 and ESP32-S3 to collect IEPE accelerometer data

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