Low-resolution video camera with a lot of opened germanium transistors used as light-sensitive elements
For this project I've got a few flat lenses (Fresnel):
And largest one is 11x7.5 inches (not pictured here), so if one "open transistor cell" will occupy area 0.5x0.5 inches then I can achieve enormous image resolution 22x15 pixels!
Project got covered by hackaday.com!
Thank you editors of Hackaday! ;)
Now we can try to use it as phototransistor as per this soviet book from my childhood (1st schematics):
I took МП25А (MP25A) and built 1st stage of that circuit on the breadboard:
R1 and R2 were represented by single resistor 1M (and instead of R3 it was series of 2K resistors, because I didn't have 5.1K right away). Voltmeter showed slightly under 1V between emitter and ground (which should be positive for P-N-P transistors) in the dark and above 2V on the bright light.
Better transistors like МР42А (MP42A) could be used as solar cell to generate voltage directly!
Here you can see 0.15V between base (negative) and collector (similar results fro emitter).
P.S. I also remembered this trick from childhood - article about solar panel from transistors was published by one soviet magazine for kids in early 80s:
Soviet MP-transistors are relatively easy to open:
First of all you need pliers to hold a head of transistor like this to avoid damaging of semiconductor joints inside:
Then you need to squeeze the head to break it:
If it is not disconnected right away you can help it with screw driver:
After that it will look like this:
Now cover could be easily removed: