data logging to USB and SD card

There is a vast difference between SD Card and a USB memory stick. The former can be written with an SPI port and fairly simple software. The USB Stick requires USB host or On-the-Go capability and the hardware and software are much more complex.

4 channels of 12 to 16 bits at 75KHz is going to require writing 600KBytes/second to your device.

75KHz is not really a fast ADC. Fast ADCs sample in the MHz range. You might look at the Analog Devices AD7606-4. It does the simultaneous sampling in hardware and has both parallel and SPI serial data interfaces. I think you're going to need something faster than an 8051....One of the ARM cortex chips would be my first choice.

Mark Borgerson

. =A0Fast ADCs sample in the MHz

RM cortex chips

Thanks very much. I saw the datasheet of 7606 and it is sufficient for me. And any other alternatives for the ARM processors?

Thanks in advance. Willy.

cortex chips

Sorry, but I can't be much help there. My last ARM design used an Atmel AT91SAM7S chip and that was several years ago. I've looked at the Cortex chips and have a couple of Dev Kits, but I haven't yet had the time to work with them enough to give good advice. I'm considering a design using the AD7606 and an MSP430 chip, but the overall data rate is much lower and I don't have to save the data to an SD card.

Mark Borgerson

Thanks very much. I saw the datasheet of 7606 and it is sufficient for me. And any other alternatives for the ARM processors?

Thanks in advance. Willy.

Pick an ARM Cortex M3 with a proper SD card interface (SPI is a poor second for SD cards). There are several in ST's STM32F1XX series which will do. Another processor route you might like is the Atmel AVR32 which is supported by free software tools. If you want to write FAT32 compliant files to an SD card at 600kByte/s you will need serious data buffering and much cleverer code than the ususal freebie stuff for managing the file writing. Unless you have a really good reason for making this yourself why not just use a cheapo PC and a ready made DAQ system ?

Michael Kellett

Yes, a full SD card interface will certainly speed things up.

I ran into that problem at lower rates with the SPI interface. It required implementing caching for FAT and directory sectors.

Power consumption and size are the first two things that might get in the way of this approach.

Mark Borgerson