Low Power Mode, Power computation

I see. So basically set the last two bits to 0 in the config register in order to get into power down mode. I'll see if I can muck about with the SDL_Pi_INA3221.py to that effect.
Maybe just like that : self._write_register_little_endian(INA3221_REG_CONFIG, 0) after reading the values ?

Well, at that point I have made my measurements and don't really care any more. When I next invoke the script it will re-configure the sensor anyway, right?

ina3221 = SDL_Pi_INA3221.SDL_Pi_INA3221(addr=0x43)

(I use 0x43 because the INA219 is sitting on 0x40)

I implemented low power mode for both INA3221 and INA219, so far without adverse impact. Thanks for the guidance!

#!/usr/bin/env python



# imports



import SDL_Pi_INA3221

import ina219

import time,json



# ina3221

ina3221 = SDL_Pi_INA3221.SDL_Pi_INA3221(addr=0x43)

time.sleep(1)

channel = [" ","battery","solarcell","output"]

print "{\"measurements\":{"

for f in range(1,4):

   shuntvoltage = 0

   busvoltage   = 0

   current_mA   = 0

   loadvoltage  = 0

   busvoltage = ina3221.getBusVoltage_V(f)

   shuntvoltage = ina3221.getShuntVoltage_mV(f)

   current_mA = ina3221.getCurrent_mA(f)

   loadvoltage = busvoltage + (shuntvoltage / 1000)

   g = " "

   if (f>1): g = ","

   print g+"\"%s\":{\"bus\":%3.2f,\"shunt\":%3.2f,\"load\":%3.2f,\"current\":%3.2f}" % (channel[f], busvoltage, shuntvoltage, loadvoltage, current_mA)

# ina219

ina219 = ina219.INA219(0.1)

ina219.configure()

print ",\"servo\":{\"load\":%3.2f,\"current\":%3.2f}" % (ina219.voltage(), ina219.current())

# blend in weather data

file = open("/home/pi/temphum.json","r")

j = json.loads(file.read())

print "},\"timestamp\":\""+time.strftime("%Y-%m-%d %H:%M:%S")+"\",\"temperature\":%.1f,\"humidity\":%.1f,\"pressure\":%.1f}" % (j['temperature'],j['humidity'],j['pressure_bme'])

# put ina3221 to sleep

ina3221._write_register_little_endian(0, 0)

# put ina219 to sleep

ina219.sleep()


Just to recap: The load circuit and the solar tracker/servo circuit are independent (with different batteries and different control boards), they only share a common ground, and the I2C bus.

Here is a sample output:
{"measurements":{
"battery":{"bus":3.82,"shunt":10.80,"load":3.83,"current":108.00}
,"solarcell":{"bus":4.91,"shunt":-3.80,"load":4.91,"current":-38.00}
,"output":{"bus":5.18,"shunt":10.20,"load":5.19,"current":102.00}
,"servo":{"load":4.18,"current":0.00}
},"timestamp":"2019-01-14 09:00:04","temperature":23.0,"humidity":76.5,"pressure":1018.5}

Note that the servo current is 0 - I use an USB boost/control circuit to only provide power to the servo when I actually want to rotate the panels (once an hour). This pretty much guarantees that there's always enough power available in the servo battery even though it is only charged by a very small stationary solar cell (300mW), and it makes the addition of the INA219 a purely academic exercise.

Just a simple servo - don't think I can afford a stepper motor or one of these fancy linear actuators (and I would need two for proper azimuth and elevation control ...)

Although I have to say that the servo is at times struggling to keep the panels in place. Quite amazing what wind can do to a flat pane. I positioned the servo rotation axis as close as possible to the center of gravity of the panel assembly to minimize that impact.

The nice thing about the servo is that I can directly input the calculated azimuth (from about 40 degrees to -40 degrees) into the PWM.


def Move(frm,to):

   #switch on servo

   GPIO.output(ctl, 1)

   pwm=GPIO.PWM(pin, 50)

   pwm.start(0)

   s=1

   if(frm>to): s= -1

   print "Rotating from %.0f to %.0f (%.2f to %.2f)" % (frm,to,center + frm/18.0 ,center + to/18.0)

   for d in range(int(frm),int(to),s):

       duty = float(d)/18.0 + center

       pwm.ChangeDutyCycle(duty)

       time.sleep(0.02)

   time.sleep(0.2)

   pwm.ChangeDutyCycle(0)

   pwm.stop()
   #switch off servo power

   GPIO.output(ctl, 0)
What I don't like is that I don't have a return signal of the servo's actual position. Using the above code I tried to smooth out the movement as much as possible but I still see the occasional  hiccup where the servo doesn't move because the change is not large enough. Not a big problem as it will then move the next time a bit more.  Short of using the camera to validate the solar array position there's not much I can do with the current setup, I think.

Adafruit offer an analog feedback servo but it has plastic gears, isn't waterproof and can't hold the weight of the solar panels.

Would that rotary encoder be waterproof?