Sun Sensor

[Mainestar]

Anyone working on a low cost sun sensor solution or have any thoughts on how one could be made?

[maholli]

Hey @Mainestar great question.

Below illustrates what I did for sun sensing on the NASA V-R3x mission, but I'd love to hear what folks are doing!

TSL2561 sun sensors on each face (6 total).

[Mainestar]

Thanks Max!
I see that the TSL2561 is now listed as an obsolete part, do you think that the TSL25721 would work?

[maholli]

@Mainestar it looks like the TSL25721 doesn't have an "address select." This was one of the key features of the TSL2561 since it allowed having multiple sensors on the same I2C bus. Maybe I missed something in the new TSL25721 datasheet? If not, I'd do some more searching for similar sensors that have the ability to set the I2C address.

Another option would be to use an I2C mux, but I don't know of any off the top of my head with radiation data and flight heritage. So this would take some research as well.

Let me know what you find! I'll try and do some digging as well.

[maholli]

So I did some digging and I was surprised to see most manufacturers discontinuing their multi-address I2C ambient sensors. No idea why...

Here's what I found:

1. VEML6030 - can select from 2 slave addresses
2. BH1749/BH1746 - can select from 2 slave addresses
3. MAX44007 (discontinued?) - can select from 2 slave addresses

Pretty slim pickings... With only 2 addresses, it'd take 3 separate I2C buses to cover all six faces of a cubesat. You could probably get by with 4 cleverly placed sensors, but I'm hoping we can do better.

Couple other options I can think of:

• some address-configurable I2C ADC + photodiode on each face
• I2C mux
• use a combination of two (or more?) sensor types to avoid address conflicts on the bus

[polygnomial]

We're using OPT3001 and have a semi-working CircuitPython driver! It can do 4 different addresses.

[maholli]

Thanks @polygnomial that's a great alternative! Hopefully they'll be in stock soon.

You say semi-working CircuitPython driver? I noticed there are a few examples online.

Maybe you spot something in:

• this arduino library
• or this vanilla python library

that helps clear things up? If not, feel free to create a discussion and we can work thru it 😄

[Mainestar]

Thanks Max and Flynn,
I'm very interested in seeing how you progress with these approaches.
I've obtained some TSL2561s to experiment with.

[Mainestar]

Hi Max,
Do you have any code that I can use to test the TL2561s with the Pycubed?
Ideally would like to output the TL2561 level to the telemetry radio.
Tnx!

[maholli]

Sure! Below is a simple test script I put together for some summer students a year or two ago. It exercises TL2561 sun sensors and drv8830 h-bridge drivers (for torque coils) across two I2C buses.

Adafruit has a TL2561 library link, but I think I wrote the hbridge library so I just attached both (zipped). tsl2561_drv8830.zip

"""
PyCubed Torque Coil Test
"""

import time
from pycubed import cubesat
import adafruit_tsl2561 # sun sensor library
import drv8830          # h-bridge library

# initialize the second I2C bus if it hasn't been done in pycubed.py
if not hasattr(cubesat,'i2c2'):
    import board, busio
    cubesat.i2c2 = busio.I2C(board.SCL2,board.SDA2)


# Initialize sun sensors
sun_xp = adafruit_tsl2561.TSL2561(cubesat.i2c2,address=0x29)
sun_yn = adafruit_tsl2561.TSL2561(cubesat.i2c1,address=0x39)
sun_sensors = [sun_xp,sun_yn]

# Initialize h-bridges
hb_xp = drv8830.DRV8830(cubesat.i2c2,0x66)
hb_xp.panel = '+X'
hb_yn = drv8830.DRV8830(cubesat.i2c1,0x64)
hb_yn.panel = '-Y'
hbridges = [hb_xp,hb_yn]

imu_data = {
        'accel':0,
        'mag':  0,
        'gyro': 0,
    }
while True:
    cubesat.RGB = (0,255,0) # green LED
    # cache IMU data
    imu_data.update({
        'accel':cubesat.acceleration,
        'mag':  cubesat.magnetic,
        'gyro': cubesat.gyro})

    # print IMU data
    print('[IMU]')
    for imu_type in imu_data:
        print('{:>8} x: {:.6f},\ty: {:.6f},\tz: {:.6f}'.format(imu_type,*imu_data[imu_type]))
    # print sun sensor data
    print('[Sun] +X: {}, -Y: {}'.format(sun_sensors[0].lux,sun_sensors[1].lux))

    # exercise h-bridges
    print('[Torque Coils]')
    for h in hbridges:
        # set output voltage to max (VDD)
        # in our case, VDD=3.3V
        h.vout = 0x3F
        print('{:>5} Forward (2 sec)'.format(h.panel))
        h.mode = drv8830.FORWARD
        time.sleep(2)
        print('{:>5} Reverse (2 sec)'.format(h.panel))
        h.mode = drv8830.REVERSE
        time.sleep(2)
        print('{:>5} Off'.format(h.panel))
        h.mode = drv8830.COAST
        h.vout = 0
    print('-'*50)
    cubesat.RGB = (0,0,0) # LED off
    time.sleep(1)

For more details on the payload connector (where you can grab the second I2C bus) see here. This is the easiest bus to access.

Let me know how it goes.

[polygnomial]

@maholli are you using the CedarGrove CircuitPython driver for the DRV8830 or something home-brewed?