Beaglebone cape with 24-bit sigma-delta A/D, VCXO, and split power supplies for a Yuma force-balance vertical seismometer
- Substitute LT1761IS5-SD for U8 ADP7118, due to availability. Lift pin 4 and add 10.5K and 10K feedback divider for 2.5V output.
- Change R21 from 115K to 162K. Change R24 from 7.15K to 10K.
- Change R31 from 255K to 170K (162K). R26 from 15K to 10K.
- Change R23 from 100K to 17.7K to set +15V correctly.
- Change C6,C9,C12 to film caps.
- FIXME - add divider resistors to R2 and R4 to set +/-10V input span.
- Jumper JP16 to select P915 GPIO48 as CAPE_EN
- Add UBlox Neo-6M GPS receiver. 47 nH + 15 ohm bias-T, 1K+LED on PPS. Connected to UART4.
- Added LEDs on 3.3V power and LED[1:0]
- FIXME - change ADR445ARMZ to ADR441ARMZ 2.5V ref, or ADR444ARMZ 4.096V ref. 5V is too close to AVDD span.
- Remove R9 and connect AD7175 CS# to PRU9_28/CS0
- Increase soft start time: add 1 uF in parallel to both C43 and C44. Change C23 to 200 nF.
CS <--> P9_28 PRU0_3 / CS0 (CS was tied low through resistor R9)
SCLK <--> P9_31 PRU0_0 / SCK
DIN <--> P9_30 PRU0_2 / MOSI
DOUT/RDY <--> P9_29 PRU0_1 / MISO
SYNC <--> P9_27 PRU0_5 (not used by code yet)
CAPE_EN <--> P9_15 GPIO_48
PPS <--> P8_7 TIMER4 and (not jumpered yet)
P9_16 PRU0_16 and
P8_16 EQEP2_INDEX
VCXO <--> P9_41 TCLKIN and (not jumpered yet)
P8_12 EQEP2A_IN
LED0 <--> P8_12 PRU0_14
LED1 <--> P8_11 PRU0_15