Note! This only works on the early BeagleBone demo images, where the TPS device wasn't in use by the new cpufreq and tps drivers. 1. setting the TPS for SYS_VOLT: root@beaglebone:~# i2cset -y 1 0x24 9 5 root@beaglebone:~# cat /sys/devices/platform/tsc/ain8; echo "" 1557 1557/4096 * 1.8 = 0.684V Scaling this by 7.08 (2x for the voltage divider at the output of the TPS, and 3.54 for R1/R1+R2) SYS_VOLT=4.87 2. setting the TPS for SYS_5V: root@beaglebone:~# i2cset -y 1 0x24 9 2 root@beaglebone:~# cat /sys/devices/platform/tsc/ain8; echo "" 1858 1858/4096 * 1.8V = 0.82V Scaling this by 6 (2x for the voltage divider at the output of the TPS, and 3x for internal divider) SYS_5V=4.90 3. The voltage difference across the 0.1ohm resistor (R3) is 0.03V, so the current is 0.3A or 300mA. Power usage in Watts is P = V * A = 4.90 V * 0.3 A = .47 W TPS reference: TPS chip is at base address 0x24. The MUX register is at sub-address 9:
The values are (three lower bits): Analog multiplexer selection
(some parts copied from here: https://groups.google.com/forum/#!msg/beagleboard/cFBUxgsrZYA/sZ3FIQgDysMJ) |
Using the BeagleBone >