If you’re looking to do this project without a microcontroller – it’s an exercise that every SW engineer should consider doing at least once – then the venerable 555 timer may be of aid here:

https://elonics.org/light-sensor-circuit-using-ldr-555-timer-adjustable/

This isn’t quite an ELI5, but ARRL has a 2004 article on FM fundamentals; it’s five pages intended for a beginner ham radio operator, but applicable to all FM applications nevertheless. It also discusses four different ways to receive FM.

But to answer your question directly:

The frequency of the FM signal at any instant in time is called the instantaneous frequency. The variations back and forth around the carrier frequency are known as deviation

FM can also be detected by a PLL. As shown in Figure 6, the PLL’s natural function of tracking a changing input frequency can be employed to generate a voltage that varies as the input frequency change

In a nutshell, FM only ever has one instantaneous frequency at a time, which dances around the nominal center frequency (aka carrier). So the receiver has to detect the instantaneous frequency, relative to the carrier.

To actually recover the original signal, the receiver must also account for the modulation index used by the transmitter, which describes how much the output will deviate for a given input frequency. The modulation index is usually standardized for the application, such as FM broadcasting, amateur radio FM, walkie talkie FM, etc.

Because a larger modulation index means the same input signal will result in wider deviations, more RF bandwidth is used, spreading the signal wider and generally improving noise immunity.

When it comes to what insurance does or doesn’t cover, the best answer will come from the text of the policy itself. This is, unfortunately, very dry reading and most people – although instructed to keep a copy handy – don’t have the full text nearby. That said, because of the regulated nature of insurance in the USA, standardized forms of policies exist, and homeowner policies are no exception.

The common homeowner policies are numbered HO-1 to HO-8. HO-1 only pays out only for the ten listened “perils”, and is thus the most barren policy available. Not all HO-1 policies are verbatim identical, but the gist usually matches.

We can look at this sample text from a random HO-1 (issued by American Family Insurance). Page 5 shows that “fire or lightning” is covered, so that’s a good start.

On page 6, we find the exceptions to the coverage, so if any of these apply, the policy will not pay out. Nothing in Part A would seem to apply to a DIY LED project, unless you tell me your LEDs are radioactive. Part B also doesn’t apply, unless you’re somehow perpetuating a fraud using LEDs.

Part C reads like it could apply, because it mentions “construction”, “design, workmanship or specification”, and “maintenance”, but this section only applies to the dwelling and so refers to those things which are permanently affixed to the house. That would include things like ceiling fans and light fixtures, but wouldn’t include stuff that is attached to the walls using thumbtacks or 3M Command strips. It even says that:

However, we do cover any resulting loss to property described in Coverage A - Dwelling and Dwelling Extension not excluded or excepted in this policy.

This clause basically means the exceptions on Page 6 should be interpreted narrowly, not broadly.

The point is, in the entire policy, there isn’t a clause that requires listed equipment, and remember that this is the most bare bones policy commonly available. If such a requirement did exist, then building your own PC wouldn’t be possible, since the standards bodies do not test individual computer parts – except the PSU, because that plugs into the mains.

If a fire that damages the house does occur, the most probable causes would be due to: 1) an unlisted power supply or power brick feeding the ESP32 or the LEDs, or 2) no current limiting (eg a fuse) to cut out the power supply. Other failures like a shorted LED are unlikely to actually cause a house fire, and the insurance companies and UL know this; they’re more focused on preventing arc-faults that contribute to an estimated 50% of electrical house fires every year.

Good design and clean installation on your part, and using properly listed low-voltage power supplies, will mitigate the major fire risks, leaving just software bugs and lighting snafus for you to deal with.

As a matter of completeness, if there is an unlikely fire, be it from an LED project or from a candle falling over, the insurance company will still pay. But big or small, the claim will be recorded in the CLUE database along with the payout amount. This often reflects negatively on homeowners, so future rate increases may occur. But that varies by state. In any case, though, the insurance policy has still done its job: cover a non-intentional loss.

I would nevertheless advise you to have a look at what sort of homeowner policy your dwelling is covered under. Everything beyond HO-1 is nicer, and some even include limited claim forgiveness of some kind (for a price). Also consider talking to your insurance agent, who should be able to help interpret how the policy applies.

My first thought for a compact, air-blower would be the inflater for air mattresses. They’re already fairly small, have a high flow rate, and exist in forms which accept 12 VDC.

Another option is a small tank of compressed air, but that option is either heavy (steel tank) or stores air at inefficient, low pressures (plastic tank).

I suppose a third option is to rig a can of air-duster so that it blows through the whistle. That would be mechanically simple to implement a solenoid to press the valve, although there is a small environmental cost to using cans of air-duster regularly.

The 74AHCT125N appears to be a 3v to 5v level shifter, which I wouldn’t expect to be drawing a lot of current. So if just the adapter’s presence is causing 0.2v drop, then yeah, that would suggest the output current of the port’s voltage rail isn’t very high, causing substantial sag.

To be abundantly clear, is the Blueretro meant to work when only powered by the console? It certainly wouldn’t be as convenient – an extra cable and power block to deal with – but everything is functional when externally powered by USB, yes?

Do I understand that your original post is debugging why the console isn’t sufficient to power the Blueretro?

I don’t have specific experience with game consoles, but the erratic behavior when powered by the console suggests that the port’s voltage is sagging when the Blueretro is attached, possibly lower than what the AMS1117 can tolerate.

A quick search seems to show that the AMS1117 has a minimum dropout voltage of 1v. So for 3.3v output, the input must not drop below 4.3v. Other Low Dropout (LDO) regulators could have a smaller dropout voltage, but that might not be the root-cause.

It’s possible that without load, the port provides 4.6-5v. But when loaded, it dips below 4.3v, producing the behavior you see. The problem then becomes: is it the NES that’s not providing sufficient current on the voltage bus, or is it the Blueretro trying to draw too much current?

Are you able to measure the port’s voltage bus when the Blueretro is attached? That would help prove if the bus is sagging. Does the Blueretro allow you to use USB power when plugged into the console?

TIL. Although to be fair, the removable part of that Orange Pi is a modular PCB that happens to have only an eMMC chip mounted on it. It’s still very clever as it offers the user a choice in memory size, but it’s apparently not standardized by any industry body, at least that I’m aware of.

Plus, if we allow that the loading if a normally embedded chip onto a PCB makes it removable, there’s a Ship of Theseus quandary that arises lol

If there are pads that break out the pins to the eMMC, then manually soldering very tiny wires is usually doable with steady hands. If test pads, then a jig/PCB with pogo pins can work.

For really fine pads, then it’ll be quite the uphill battle, bordering on whether to even attempt it. I personally miss the days when devices had a MicroDrive or ConpactFlash card hidden inside.

From some chats a few years ago with EEs in the industry, eMMC chips – as the “e” would suggest – are embedded on the board and aren’t meant to be removed once placed. To program these devices after-the-fact, the prototype units will usually load a header with maybe 6-8 pins, that breaks out the SPI lines and power. Then an ISP device would be used against that header – with appropriate breakout board – to load the flash image. Once the image passes final verification, it’s given to the manufacturing line to load prior to being soldered down. The SPI lines usually suffice, trading off performance.

In one instance, I have seen a USB-to-SD card adapter that was rewired in a pinch, so that it could read out the image from an installed eMMC chip.

I will note that I’m not an expert in the plethora of USB charging standards. Quite frankly, USB C is almost like black magic to me. With that said, finding the D+ and D- lines might be tough unless you’ve got a USB C charging cable you’re willing to cannibalize.

That is, what you can do is carefully splice into such a cable, then connect it to the board and a USB charging block. By probing the wires, you can rule out the power wires, which should leave you with the D+ and D- wires. You would want to do this with a cable that’s meant only for changing, such as USB C to USB A. That way, there would only be four wires inside. If you cut open a USB C to C cable, you’ll have a lot more wires that you have to check.

Once you identify the D+ and D- this way, you can then do continuity checks from those wires to various pads on the board. In this way, you’ll eventually find your D+ and D- pads, and can then add your temporary resistors, to see if that works.

As for identifying the USB charging spec in use, that’s going to be tougher. I think there are test devices that take the place of a USB charger and can display or change the spec, but I’ve never used such a thing.

You might try the resistors first, although in such a way that it could be removed if that doesn’t work. If you have correctly found the D+ and D- lines broken out from the USB C connector, and added resistors to those, I can’t see how that would cause an issue with the wireless charging; they should be mostly independent, since if there’s no USB power supply attached, the resistors won’t be sensed anyway.

Two things come to mind with USB C charging that’s usually different than micro USB or prior standards. First is that some USB C circuits are tightly coupled to battery charger circuitry. The idea is that if the pack voltage is higher than standard 5v, then it may be advantageous for USB C to request one of the higher voltages from the wall-power block. But I think this is unlikely, if the photo you’ve included is of the board in question; there would usually be the leads for the battery pack attached to the same board.

Second, USB C – unlike every other USB spec preceding it, I think – requires the sense resistors on the consume side before any power is supplied, even low-current 5v that we would otherwise expect. What’s probably happening with the LED becoming lit is that it’s probably indicating a data connection, as if you connected to a computer.

Before getting to the meat of the question, I think it will be instructive to clarify on what exactly a voltage is. Voltage is the difference in electrical potential. That is, it is always a relative measurement, taken between two points. Colloquially, you’ll hear engineers and electricians say things like “this wire is at 12v”, but they’re implying a specific reference point. There must always be two points to take a measurement; a multimeter must always have two leads.

Often, that reference point is “ground” (aka GND, aka protective earth, aka COM) but the choice of designating a particular point as ground is always arbitrary. Even the physical soil of the earth is not at the same voltage level all over, which means a ground rod is only a valid reference within a certain proximate area. Instead, ground is often chosen by whatever is most convenient and reaches everything that needs it.

But as you’ve found, having a ground reference is not mandatory for electricity to flow in a circuit. Instead, a ground connection serves ancillary goals, like personnel or equipment safety, or avoidance of objectionable currents.

Comparing floating and grounded circuits, a single loose wire in a floating circuit will not cause a diversion of current to somewhere, because a second wire would need to be the return path. With two loose wires, there can be a second loop for current to flow. A grounded circuit intentionally ties some part of the existing circuit to ground, meaning you are now just one loose wire away from a possible diversion of energy, which could be fatal.

This sounds like grounded circuits would be bad, and would imply that grounding the aluminum conveyor belts in your example would be insane. But this is actually the personnel safety from earlier, if we add the right protective devices to the circuit: a circuit breaker, fuse, a GFCI, or some combination. Those devices will cut out the power source upon a fault condition, and they require a sturdy ground connection to operate effectively. We improve overall safety by having protective devices, and having a robust ground connection.

Finally, I want to offer a piece of advice as you proceed in your studies. The rule that “electricity wants to return to ground” is hogwash. It’s so hideously flawed compared to the true rule, which is universally valid: electricity returns to its source, in inverse proportion to resistance

From a conceptual perspective, very low quiescent current (aka idle/standby current) when unactivated is entirely achievable. What your design will need to do is assess how much each component will draw at idle, and if it’s too high, then you may need to have gates which turn off those high-draw components when idling.

From a cursory Google Search, the DFPlayer Mini datasheet shows a standby power of 20 mA, which far too high. A forum post shows that if the sleep mode is enabled using the serial interface, current drops to 0.4 uA. This is much better.

For the 555 itself, you mention an astable oscillating configuration, although I’m wondering what your intention for the 555 is. Ostensibly, the DFPlayer either needs a brief pulse to start playing (roughly “edge triggered”) or needs to be kept active for as long as the music should be playing (roughly “level triggered”). In either case, a 555 in a one-shot configuration would make sense, since an astable oscillator would imply the music would restart on its own every so often.

If you’re insisting on the 555, then you may not be able to access the sleep mode in the DFPlayer Mini. So your option might be to gate the DFPlayer so that it only gets Vcc power when the 555 supplies it, probably using a MOSFET. Alternatively, using a cheap microcontroller would let you control the DFPlayer Mini via serial. Your microcontroller could then also receive the signal from the vibration switch and come out of deep sleep to issue commands to the DDPlayer.

The ATTiny uC and MSP430 uC families can draw as low as microamps or even nanoamps in some low-power modes. So that neatly addresses the standby current.

What you’ll also have to assess is the active current, or how much the music player draws when it runs for however long. This should give you an idea of the total lifetime for your application on a single battery charge.

If your coil was oscillating, then perhaps an iron core moving through it would cause perturbations which are detectable. But that would require extra logic to compare the expected oscillation frequency with what the coil is actually oscillating at.

Since you say that tilt switches are not an option – for reasons I’m not entirely sure I understand – another option is to have a linear Hall effect sensor mounted nearby a small magnet. If the magnet moves relative to the sensor, then that is a change which can be acted upon. A linear sensor makes it possible to use a trim pot to tune the sensitivity.