Visit the me here on Github
Added parabolic musings 10/16/19, see below
…On using motioneye video clients on Pi Zeros & Raspbian over a BATMAN-adv Ad-Hoc network
link: motioneyeos
link: motioneye Daemon
link: Pi Zero W Tx/Rx data sheet:
link: BATMAN Open Mesh
This implementation of motioneye is running on Raspbian Buster (opposed to motioneyeos).
Calculating Mesh Effectiveness w/ Python:
Please take a look at dBmLoss.py- the idea here is one should be able to estimate the maximum plausible distance between mesh nodes before setting anything up. It can be run with no arguments-
python3 dBmLoss.py
…with no arguments, it should use default values (Tx = 20 dBm, Rx = |-40| dBm) to print this:
you can add (default) Rx Tx arguments using the following syntax:
python3 dBmLoss.py 20 40
python3 dBmLoss.py <Rx> <Tx>
57.74559999999994 ft = max. mesh node spacing, @
Rx = 40
Tx = 20
Regarding the Pi:
The Pi Zero uses an onboard BCM43143 wifi module. See above for the data sheet. We can expect around a ~19 dBm Tx signal from a BCM43143 if we are optimistic. Unfortunately, "usable" Rx gain is unclear in the context of the Pi.
Added 10/16/19:
Notes on generating an accurate parabolic antenna shape with FreeCAD’s Python CLI:
For whatever reason, (likely my own ignorance) I have been having trouble generating an accurate parabolic dish shape in Fusion 360 (AFAICT, Autodesk is literally drenching Fusion 360 in funds right now, I feel obligated to at least try). Bezier, spline, etc curves are not suitable!
If you are not familiar with FreeCAD, the general approach- geometry is formed through fully constraining sketches and objects- is quite different from Sketchup / Tinkercad / Inventor / etc, as most proprietary 3d software does the “constraining” of your drawings behind the scenes. From this perspective, you can see how the following script never actually defines or changes the curve / depth of the parabola; all we need to do is change how much curve to include. A wide, shallow dish can be made by only using the very bottom of the curve, or a deep / narrow dish by including more of the ever steepening parabolic shape.
import Part, math
# musings derived from:
# https://forum.freecadweb.org/viewtopic.php?t=4430
# thinking about units here:
tu = FreeCAD.Units.parseQuantity
def mm(value):
return tu('{} mm'.format(value))
rs = mm(1.9)
thicken = -(rs / mm(15))
# defer to scale during fitting / fillet elsewhere
m=App.Matrix()
m.rotateY(math.radians(-90))
# create a parabola with the symmetry axis (0,0,1)
parabola=Part.Parabola()
parabola.transform(m)
# get only the right part of the curve
edge=parabola.toShape(0,rs)
pt=parabola.value(rs)
line=Part.makeLine(pt,App.Vector(0,0,pt.z))
wire=Part.Wire([edge,line])
shell=wire.revolve(App.Vector(0,0,0),App.Vector(0,0,1),360)
# make a solid
solid=Part.Solid(shell)
# apply a thickness
thick=solid.makeThickness([solid.Faces[1]],thicken,0.001)
Part.show(thick)
Gui.SendMsgToActiveView("ViewFit")
"""
# Fill screen:
Gui.SendMsgToActiveView("ViewFit")
# Remove Part in default env:
App.getDocument("Unnamed1").removeObject("Shape")
"""
FWIW, here is my Python implimentation of a Tx/Rx "Free Space" distance calulator-
dBmLoss.py:
from math import log10
from sys import argv
'''
# estimate free space dBm attenuation:
# ...using wfi module BCM43143:
Tx = 19~20 dBm
Rx = not clear how low we can go here
d = distance Tx --> Rx
f = frequency
c = attenuation constant: meters / MHz = -27.55; see here for more info:
https://en.wikipedia.org/wiki/Free-space_path_loss
'''
f = 2400 # MHz
c = 27.55 # RF attenuation constant (in meters / MHz)
def_Tx = 20 # expected dBm transmit
def_Rx = 40 # (absolute value) of negative dBm thesh
def logdBm(num):
return 20 * log10(num)
def maxDist(Rx, Tx):
dBm = 0
d = .1 # meters!
while dBm < Tx + Rx:
dBm = logdBm(d) + logdBm(f) - Tx - Rx + c
d += .1 # meters!
return d
# Why not use this with arguments Tx + Rx from shell if we want:
def useargs():
use = bool
try:
if len(argv) == 3:
use = True
elif len(argv) == 1:
print('\n\nyou can add (default) Rx Tx arguments using the following syntax: \n \
python3 dBmLoss.py 20 40 \n \
python3 dBmLoss.py <Rx> <Tx> \
\n')
use = False
else:
print('you must use both Rx & Tx arguments or no arguments')
raise SystemExit
except:
print('you must use both Rx & Tx arguments or no arguments')
raise SystemExit
return use
def main():
if useargs() == True:
arg = [int(argv[1]), int(argv[2])]
else:
arg = [def_Rx, def_Tx]
print(str('\n ' + str(maxDist(arg[0], arg[1])*3.281) + \
' ft = max. mesh node spacing, @ \n' + \
' Rx = ' + str(arg[0]) + '\n' + \
' Tx = ' + str(arg[1])))
main()
