schlieren on a stick

schlieren imaging (wiki, mit and nasa)

Schlieren photography is similar to the shadowgraph (an optical method 

that reveals non-uniformities in transparent media like air, water, or glass)

and relies on the the fact that light rays are bent whenever they encounter changes

shadowgraph (bullet in flight - wiki)

how it works

what you need 

*spherical / parabolic / concave mirror (the biggest, lightest,

cheapest you can get) acrylic?

rigid selfie stick (length depends on the mirror focal length)

cellphone (video mode with led powered on)

*spherical mirror will achieve better uniform results

how to adjust

glue the mirror to the far end of the selfie stick

hang the phone on the selfie stick handle

extract the selfie stick to the point which the reflection of the led

seems to be smallest (about twice the focal length of the mirror) 

and that the led reflection covers the phone camera lens

zoom in, adjust the contrast and enjoy your new toy :-)

photo of the wanted (selfie stick) setup

and a video

some more videos

some notes

selfie stick was too flexible to get solid results
need to find a robust selfie stick (carbon fiber?) and make another video
auto exposure of the cellphone app drive me nuts need to find
proper video app with fixed exposure 

further reading:

Raffel, M. & Heineck, James & Schairer, Edward & Leopold, Friedrich & Kindler, Kolja. (2012). Background Oriented Schlieren techniques for helicopter related large scale and flight testing. 38th European Rotorcraft Forum 2012, ERF 2012. 2. 1-9. 

https://sciencedemonstrations.fas.harvard.edu/presentations/schlieren-optics

https://epjtechniquesandinstrumentation.springeropen.com/articles/10.1140/epjti/s40485-018-0045-1

monochromator stepper motor upgrade

upgrading a manual monochromator to scanning monochromator
using a small piece of alu some drill holes 

some screws stepper motor and shaft adapter 

some photos

poor man's smd tweezers

quick hack to use tweezers or chopsticks

as a smd tweezers
because what is more comfortable to catch a small thing then a tweezers

parts used for this hack:

short two wire cable

cheap tweezer
two banana plugs

heat shrink the wires to the tweezers

 testing

and testing

semi automated multimeter

build a poor mans semi automated multi-meter
in a couple of minuets
saving the hassle of switching the plug from voltage to amps
and lowering the torque required to adjust the meter dial  

parts used for this build:
arduino (code servo mood indicator)
switch
pot
some cables
small black build box

 

and a short proof of concept video with an irritating music

resistance short test

 

 resistance added switch and plugs test

using the servo was far from a good solution 

having just 180 degrees of rotation so might switch the servo
with another type of servo or a stepper motor or something else

switching the knob with buttons or voice commands
direct connection of the box to the meter
adding multiple meters to a single hub (kfir idea)
modding the probes is the next step
adding small switches and leds on the probes
something similar to a logic probe maybe  

usb power meter hack

using the usb power meter for just power meter
on the module its written 3.5-7v 0-3A
inside theres a HOLTEK HT46R064b (enhanced a/d type 8-bit otp mcu)
link for the datasheet is here

tested using 1 cell lipo battery

all you need to do is just get a usb extender cut it in half and use its power wire
(green and white are usually data wires)

diy bicycle auto led switch

having a trouble of forgetting 
to turn on or off your bicycle tail light?

well no more just build an automatic
 powering switch for the light whenever you riding 

for start i had a led shower-head 

that i got from my father that switches 
colors according to the water temperature
throughout a thermistor (resistor who change
 its resistance according to the temp)       

so i needed to hack the thermistor (temperature sensor) 
in order to control the different led colors
 (blue, green, red)  
to do so i used a 22kohm variable resistor
 for checking the resistance of each color
and then i could control the led with simple resistor

the last one was blinking red which was a great thing 
as it save me the use of another component 

so i just needed to hook it to a battery and a switch 
and figure a way to mount it to the seat 

the end result