Hardware/CubeSat Gumstix/Test/ADC

The ADC controller design reads the 8 ADC channels together with the temperature value and sends the values to the serial port.

The UART baud rate is 115˙200. The ADC sampling rate is 100 Hz, due to the slow UART text transmission. The ADC's SPI connection runs at 12.5 MHz (100 MHz / 4 / 2).

FPGA

The FPGA has to be configured with the procController-adc.bit file.

Alternatively, the procController-adc.mcs can be loaded into the M25P64 SPI flash (data width is 1 bit). Booting from the flash takes about 12 seconds.

SPI

The ADC's SPI interface is mirrored on the peripheral 2 connector:

• CS_n pin 5
• SCLK pin 6
• MOSI pin 7
• MISO pin 8
• RST_N pin 9
• BUSY pin 10

Serial port

The serial data out is provided on the serial port to the Gumstix. It is mirrored on the peripheral 2 connector:

• GND pin 2
• TxD pin 3 (not used)
• RxD pin 4

The FTDI serial-USB adapter uses:

• GND: black
• TxD: orange
• RxD: yellow

Measurements

With a 5 V voltage reference, the reading should be:

• FFF_h for the 5 V on channel 0
• A8F_h for the 3.3 V on channels 1 to 3
• 800_h for the 2.5 V on channel 1
• 5C2_h for the 1.8 V on channel 2
• 3D7_h for the 1.2 V on channel 4

Gumstix

Log-in to the Gumstix via the USB serial console. Make sure you belong to the group dialout.

List the possible serial ports:

ls -l /dev/tty*

With Yocto Linux, the device is ttyO0.

Change the baud rate:

FPGA_UART='/dev/ttyO0'
stty -F $FPGA_UART 115200

Display the ADC data:

cat $FPGA_UART

The output should look like:

0: FFF  1: CD7  2: 70F  3: D00  4: 4C0  5: 000  6: 000  7: 000  8: E9C
0: FFF  1: CE7  2: 712  3: CF9  4: 4BC  5: 000  6: 000  7: 000  8: E8E
0: FEF  1: CC9  2: 713  3: D10  4: 4B9  5: 000  6: 000  7: 000  8: E82
0: FF5  1: CD2  2: 71E  3: D07  4: 4B4  5: 000  6: 000  7: 000  8: EB0
0: FF0  1: CD6  2: 71C  3: D11  4: 4B5  5: 000  6: 000  7: 000  8: E9D
0: FEF  1: CCB  2: 712  3: D08  4: 4BB  5: 000  6: 000  7: 000  8: E8E
0: FFF  1: CDC  2: 719  3: CFF  4: 4B3  5: 000  6: 000  7: 000  8: EB1
0: FFF  1: CD7  2: 710  3: CFE  4: 4C0  5: 000  6: 000  7: 000  8: EA9
0: FFF  1: CD3  2: 70E  3: D00  4: 4C0  5: 000  6: 000  7: 000  8: EA5
0: FF8  1: CD6  2: 71E  3: D07  4: 4B4  5: 000  6: 000  7: 000  8: EB9