nilclass

EDIT: I believe I found the answer, it's something turned by this: https://ctatools.com/products/5065

Found some trash on the street that i'd like to take apart, but this screw is in my way.

It's like a hex bolt, but with 5 sides, and rounded (a bit like flower petals).

Here's another picture from the top:

I tried turning it with various tools (hard to get pliars in unfortunately), no success so far. The material is very soft, which doesn't help..

I can't recall a time when I wasn't lost in the inner solar system. Currently I'm stuck on the third dot - how do I proceed?

[A grayed-out sentence in the Times New Roman font reads "Optimistic aliens measure space typographically". The "O" in "Optimistic" is dark black and indicated as representing the Sun (not to scale). The dots of the letters "i" in the sentence are similarly dark black. The dot in the first "i" in "Optimistic" is indicated as representing Mercury; the dot in the second "i" represents Venus; the dot in the third "i" represents Earth. The dot in the "i" in "aliens" is indicated as representing Mars. The dot in the "i" in "typographically" is indicated as representing Jupiter. A measurement bar indicates that the distance between the "O" and the third "i" in "Optimistic" is equivalent to 1 AU (astronomical unit).]

[Caption below the panel:] 
Space tip: if you're ever lost in the inner Solar System, you can just type out the phrase "Optimistic aliens measure space typographically" in Times New Roman and use the dots as a map.

I am powering a 5V microcontroller (arduino clone, atmega328p) using a 9V block and a buck converter. Now I want to let the microcontroller occasionally measure the battery voltage, so I can get an idea of how full it is.

My first idea was to use a simple voltage divider:

I've chosen the resistor values so that:

• the voltage at the measure output is < 1.1V, to be able to use the 1.1V internal reference of the atmega's ADC
• R1 || R2 < 10kΩ, since the atmega datasheet says "The ADC is optimized for analog signals with an output impedance of approximately 10 kΩ or less"

This is great and all, but what bothers me is that this circuit will constantly draw ~100µA from the battery.

So, my next thought was to add a mosfet to the divider, to switch it on only while measuring:

This is obviously bad, because now when the mosfet is off, the ADC input sees the whole battery voltage.

To address that issue, I've added a second mosfet into the measure path:

This works, and it does not draw any current, except while measuring.

However, it's quite a few parts. So I'm curious if anyone has an idea how to do this with just a single mosfet. It seems to me like it should be possible, but I haven't figured out how.

Oh, and if I'm doing something stupid here, please tell me :)

I have a whole bunch of them. They are possibly a bit older (70s, 80s) judging by other contents of the junk box they are from.

There are no labels of any kind, but on the top they have stripes that look hand painted.

For at least some of them the resistance roughly corresponds to the color code.

So, I'm just curious why I can't find anything about these on the internet.

I'm taking apart a broken tape recorder produced in the 70s (a Tesla B57, made in Czechoslovakia), to harvest some parts (inductors, switches, ...) and maybe reuse the case for some project.

Which made me wonder: are there any dangers to protect myself against? I know about lead, so I'll take precautions when desoldering things. Is there anything else to be aware of? Some fumes, other toxic materials, ...?

I'm not planning to connect the device to power in any way, so from an electrical perspective there should be nothing to worry about (except for caps maybe). Am I wrong?