Fast digital to analog converter

[prisacari]

I’m a PhD student working in a mechanics laboratory in France (LMT Cachan) and one of the goals of my thesis is to control a hydraulic testing machine using digital image correlation techniques. In order to do this, I need to take a photo of a sample, process it, extract 4 parameters and send them to the testing machine. This process needs to be repeated at a frequency of approximately 80Hz. We need a device to send these values from a Linux computer to the 4 analog entries of the machine (0-10V, 0.5 mA) by coaxial BNC cable. We managed to do this for one channel using an USB  connected oscilloscope by sending a continuous current by changing the offset using C++. The problem is that this solution is too slow and has only one channel.

 

 

 

For this we would need a device that has a viable and fast connection (Ethernet, PCI, even USB if recommended) that can send data from a Linux computer (ideally using C++) with a latency of around 1ms, frequency of at least 100Hz, precision of 0.1% and on 4 synchronized analog outputs.  Given that I am not particularly specialized in the field of electronics, researching such a device among the large quantity of items produced by your firm proves to be a difficult task.

 

 

 

I would like to know if you have a product that fits our needs and if similar purpose programming has already been done (or could easily be done) to send data from a linux computer to analog outputs (using C++ ideally).

 

 

 

Best regards,

 

Ionut Prisacari         

 

 

[mwingerson]

Sorry for the delay, I didn't get an email notifying me that you replied to my post.

Unfortunately, we do not have any off of the shelf devices that can do a 0-10V signal.  This is a pretty high voltage for general microcontroller boards so you may have a hard time finding a board that will fit your needs without going to a specialized motor driving microcontroller which can be expensive.  Getting a DAC with 0.1% accuracy from 0-10V might be a bit difficult to find but more electrical engineering approach would be to use a transistor with an RC circuit to smooth a PWM signal from a microcontroller or FPGA.

All of the other specs are really easily done with any of our microcontrollers or FPGAs.  

The way that I would approach the problem is to buy SPI/I2C/UART DAC that meets the voltage constraints or use a transistor and RC circuit.  Then I would buy a UC32 use MPIDE to facilitate the serial communication with the linux machine and/or DAC.  If using the transistor RC circuit then I configure the PIC32 Output Compare module into 32-bit mode with direct register writes to get the resolution you need.

Details on the Output Compare module are here:

http://ww1.microchip.com/downloads/en/DeviceDoc/61111E.pdf

Hope this helps.

Marshall

[JColvin]

Hi Ionut Priscari,

I've contacted a person with a little more experience than I to help you find the ideal product for your needs.

Thanks,
JColvin

[mwingerson]

Hello prisacari,

To get this correct, you have a linux machine that is taking an image, doing some computation on it.  Then you need to send the data to an external controller that manipulates 4 analog channels from 0-10V @ 0.5mA to control the hydraulic testing machine?

The external controller needs:

 - have a voltage range of 0-10V

 - to update in less than 1ms from being sent data

 - update frequency of greater than 100Hz

 - with an accuracy of 10mV

 - and update on all 4 channels at the same time?

I want to confirm these stats before I start suggesting products otherwise, I might suggest the incorrect product.

Thanks,

Marshall

 

[prisacari]

Hello prisacari,

To get this correct, you have a linux machine that is taking an image, doing some computation on it.  Then you need to send the data to an external controller that manipulates 4 analog channels from 0-10V @ 0.5mA to control the hydraulic testing machine?

The external controller needs:

 - have a voltage range of 0-10V

 - to update in less than 1ms from being sent data

 - update frequency of greater than 100Hz

 - with an accuracy of 10mV

 - and update on all 4 channels at the same time?

I want to confirm these stats before I start suggesting products otherwise, I might suggest the incorrect product.

Thanks,

Marshall

 

Hello Marshall,

Thank you for the quick response. These are indeed our main requirements. Hope to hear from you soon with a solution.

Thank you in advance,

Ionut Prisacari