u/Relevant_Pumpkin9190

For those professional in fire alarm - who have witnessed a lithium-ion battery fire, is it a bit like a candle burning under an inverted glass in water? The flame goes out, but comes back when exposed to air again.

Or is a battery fire completely different because the battery keeps generating heat internally?

What did you observe firsthand?

I’m trying to make two Arduinos talk over the same two wires, with the slave getting its power from the master.

Master → Slave:

24 V = 1, 12 V = 0. A buck gives the slave 5 V from these supply line but it varies 24/12 also a voltage divider scales down voltage variation and decode bits.

Slave → Master:

50 mA = 0, 70 mA = 1 for 0.5 sec. A Hall sensor detects the current change in master, created by a constant load grounded for 20 ma to make data communication

So the same two wires carry power + two-way data. Is this practical, or is there a simpler way or references?

For example, Will what I’m doing right now help me, if I become jobless in the future, struggle financially, or when I’m old.

Will what I’m doing right now help me or my family when we’re going through a difficult time—financially, emotionally, mentally, or with our health?

I’m trying to build a very simple spread-spectrum experiment with basic components like a 555, MOSFETs, and a microcontroller. I’m mainly doing this to understand what is actually happening rather than to build a practical RF system.

My idea is to start with a 555 oscillator and use the microcontroller to switch between several resistors, so the 555 jumps between different frequencies.

For example, I might have 10 resistors giving 10 different frequencies, and use a pseudo-random sequence to control the hopping.

Would this be a reasonable simple demonstration of FHSS, or am I misunderstanding the concept?

I’m also trying to understand the receiver side. If the transmitter hops through those frequencies, what is the simplest way to decode the signal? Could the receiver use a microcontroller to measure the incoming frequency, identify which of the 10 frequencies it is, and then follow the same pseudo-random hopping sequence?

I’m also experimenting with OOK, where a MOSFET switches a 12 V signal at around 10 kHz according to the data. On a DSO I can see the waveform, but on a spectrum analyzer I should see the 10 kHz fundamental and its harmonics/sidebands.

For learning purposes, would using a DSO + logic analyzer + spectrum analyzer be a good way to understand the difference between the time-domain signal, the digital data, and the frequency spectrum?

Basically, I’m trying to build the simplest possible experiment that lets me actually see and decode FHSS and DSSS. Does this approach make sense, and how would you recommend simplifying the receiver/decoder?

If I power the same circuit from a battery, the noise almost disappears, but when I use a mains adapter, I get buzzing/whining.

Does that mean it’s probably not a typical ground-loop problem?

Could the noise be switching harmonics or other high-frequency noise from the power supply finding its way through the common ground?

Also when used isolation transformer it disappears,means it's AC components causing it?

::

I’m a beginner trying to understand something.

Suppose I generate a low-frequency square wave (below 1 kHz) using a 555 timer or a microcontroller, and use a MOSFET to switch/chop a power supply.

Now I want to take a small amount of DC power from that same switched output, but I don’t want to change the original square-wave signal.

What would be the simplest way to do this?

Would a diode + capacitor work, or would the capacitor load the MOSFET too much and change the square wave?

If more power is needed, would a small transformer or some other method be better?

Just looking for a simple practical explanation.

Edit - I have a project that is now in the final stage, and I just need to power a small LED. I only need a little power, but pulling an additional cable is not practical at this stage and would add extra cost.

The only available option is the existing 24 V DC power-over-data line. There are also some microcontrollers communicating over this line, so I’m wondering if there’s a simple way to extract a small amount of power from it without disturbing the communication.

Beforehand trying to make a safer simulations with 555 or microcontroller before connected in live

I’m a beginner, so maybe I’m missing something simple.

I have a DVR/audio source connected to an LM386 amplifier. If I power both from the same adapter, I get a lot of noise from the speaker.

But if I use a separate adapter for the amplifier, the noise almost disappears.

The confusing part is that I still connect the ground/negative of both together.

So what exactly is changing here? If the grounds are connected anyway, why does using a separate power supply make the noise go away?

I’ve also seen another thing. Sometimes, if I connect the amplifier negative/ground to 230 V earth, the noise becomes much lower. In some cases, even connecting the negative side of the big filter capacitor to earth seems to help.

Why does touching or connecting the ground to earth sometimes make the noise disappear?

How can I tell if this is power-supply noise, a ground loop, or noise being picked up by the circuit?

I’m mainly trying to understand what is actually happening, not just find a quick fix.

I’m looking for a good book or resource to properly understand grounding and earthing in microcontroller projects.

Not just basic GND connections, but things like:

\- Analog vs digital ground

\- RF ground

\- Chassis/shield ground

\- Different grounding topologies

\- Star grounding

\- Ground loops

\- Ground planes

\- Noise and EMI suppression

\- When to connect or separate different grounds

I keep seeing these terms in different projects, but I’d like to understand why and when each approach is actually used, rather than just memorizing rules.

Is there a book that explains this from a practical embedded-systems perspective, preferably with real PCB examples?

Like looking at a tree and asking, “How deep is the green of its leaves?” instead of asking a thousand questions about whether it was watered, how often it was maintained, what fertilizer was used, and so on.

What’s that one question for you for life, work and mind well-being?

I was thinking about something and wanted to know if it’s actually possible.

Could you transmit some kind of coded signal in the normal FM radio range and have the car’s existing radio pick it up, without installing a separate RF receiver?

Basically, I’m imagining the car radio receiving something that sounds like nothing useful to a person, but some small decoder could recognize the pattern and treat it like a command.

So instead of adding a completely separate wireless receiver, could you somehow make use of the antenna + FM tuner + existing audio system already in the car?

Has anyone tried something like this? Or is there something in the normal FM radio system that would make this impractical?

I’m building a small photo frame with an ESP32. The idea is pretty simple: touch the photo and it randomly plays an MP3.

I’m planning to put a large piece of aluminum foil behind the photo and use it as the capacitive touch sensor.

My concern is false triggering. The frame will also have LED lights, and I’m worried the foil might pick up noise from the LEDs, their wiring, or the power supply and randomly trigger the MP3.

Has anyone dealt with this kind of problem with ESP32 capacitive touch?

Would adding a grounded shield behind the foil, using a guard, filtering the readings, or simply changing the foil size help?

I want it to be sensitive enough to detect a finger through the photo, but not so sensitive that switching an LED makes it think someone touched the frame.

I’m worried the foil might pick up noise from the LEDs, their wiring, or the power supply and randomly trigger the MP3.

Has anyone dealt with this kind of problem with ESP32 capacitive touch?

Would adding a grounded shield behind the foil, using a guard, filtering the readings, or simply changing the foil size help?

I want it to be sensitive enough to detect a finger through the photo, but not so sensitive that switching an LED makes it think someone touched the frame.

I was reading about SIL and IEC 61508 and started wondering about fire alarm systems.

We deal with life safety in fire alarm, but we normally follow NFPA 72, EN 54, UL, etc. We don't usually say the system is SIL 2 or SIL 3.

So what is the actual difference?

Is SIL considered a higher level of safety than something like NFPA 72, or is that simply the wrong way to compare them?

If SIL is about how reliably a safety function performs when something goes wrong, don't fire alarm systems have a similar requirement through supervision, fault monitoring, redundancy, testing, etc.?

Would be interested to hear how experienced fire safety engineers look at this.

I’m trying to understand how safety is handled when you design a product around a microcontroller.

Is SIL (Safety Integrity Level) the main/critical rating for operational safety? For example, what would actually be different in the design of a SIL 1, SIL 2, SIL 3, or SIL 4 system?

If I’m designing a microcontroller-based product and want it to eventually meet a particular SIL level, where do I start?

Things I’m trying to understand are:

- How do you decide what level of redundancy is required?

- When do you need dual/independent controllers, monitoring, watchdogs, diagnostics, etc.?

- How do you design the circuit so that a single component failure doesn't create a dangerous condition?

- What standards or guidelines actually explain these design principles?

- Is SIL the only thing I should be looking at, or are there other safety standards/ratings involved?

Basically, I’m looking for the roadmap from a normal embedded design → safety-related design → SIL-rated product.

What standards, books, or guidelines should I read first?

I wanted to get started smd soldering from dip packages which is good and wanted learn this art.

How to start minimally.

I’m a beginner and want to experiment with sending data over the same two wires that carry 24 VAC from an isolated transformer.

I want to use the AC zero crossing as a timing reference, then briefly inject a high-frequency signal, similar to the basic idea of other protocols

What would be the easiest circuit to:

- Detect the 24 VAC zero crossing?

- Generate a short high-frequency pulse with an Arduino/ESP32?

- Couple that pulse onto the 24 VAC line?

- Detect the pulse at the other end?

- Decode it back into "1" and "0"?

I’m looking for the simplest beginner circuit and explanation, including the TX and RX sides with microcontroller without dsp

’m trying to send both power and data over the same two wires.

Instead of voltage modulation and capacitor coupling, I’m thinking of using a constant-current source:

- 200 mA → bit 1

- 400 mA → bit 0

The transmitter switches between these current levels based on the data. At the other end, an Arduino measures the current and decodes the two levels.

The idea is that current stays relatively constant even when the load changes, while the voltage adjusts according to the load.

Is this approach feasible? What would be the simplest beginner-friendly circuit to generate the two current levels and detect them with another Arduino?

I’m looking for a simple proof of concept for beginners to experiment.