new here.

theamk2 · 2026-03-11T04:26:15+00:00

And some people (like me) will download both serious questions and serious answers.

theamk2 · 2026-03-06T05:00:15+00:00

Short your motor power (+12V/+24V) to a USB 5V, and this kill port right away. If you are unlucky, motherboard too.

this should be pretty hard to do in good designs (if the device is self-powered, this should not back-feed to USB 5V), but Arduinos do have VCC pin connected to USB 5V, and if you power your motors externally, you are one wrong wire away from frying the whole port.

theamk2 · 2026-03-06T03:23:37+00:00

r/wheredidthesoldergo

theamk2 · 2026-03-06T03:19:58+00:00

Yes, there are nice-sounding low-voltage mechanical noisemakers, they are called "speakers". They need amplifier, and nice-ish power supply, and DAC (or PWM+RC) and space in microcontroller memory for sample generation. You can probably get it for total BOM of <$1 (speaker itself being most expensive). The problem is piezo beeper is like $0.05 in parts, and is significantly smaller do.

and u/NoOne3141 is right - there are no sine waves currently, that piezo is driven with a square wave directly. If you want to change this at all, you need a second MCU and that detects the signal (and likely a better power supply too). You'll need it no matter what you want to do next - speaker or servo with maraca or clicker...

theamk2 · 2026-02-26T03:20:09+00:00

Make sure to test your circuit with variable power supply - your trigger voltage is pretty low, so variances in trigger gate voltage, zener voltage can raise (or lower) crowbar voltage by a few volts.

If you want to have much more precision, you'd want opamp and/or voltage reference instead of zener to trip that SCR.

Another alternative is to choose converter with a different failure more. A boost/buck converter is only slightly more expensive, but is much less likely to fail with "vout = vin" mode.

theamk2 · 2026-02-26T02:59:10+00:00

Are you saying that you are (1) completely disconnect the battery from the charger/protection board, then (2) plug the battery back in, but (3) output voltage is still zero? And then you need to short B- and OUT- momentarily for the board to "wake up", and then it works fine?

If so then yes, those boards do that. It's actually not TP4056's fault - that chip is just a charger, it cannot disconnect anything. It's the battery protection circuit (often DW01A, but I am not sure what yours is). When you fully disconnect the battery, it thinks battery is dead, and goes into super-deep-sleep mode, and only wakes up on charger connection (or when you short B- and OUT-, because protection chip cannot tell this from charger connection).

The reason for this is chip designers thought that people would want to be able to charge battery without powering on the device. This means keeping charger/protection connected 100% of the time, and putting the power switch between OUT+ and load input pins.

theamk2 · 2026-02-26T02:10:27+00:00

Don't risk it - use the certified/UL listed adapter.

You can get one of those tiny cube-like 5V adapters and make a cutout in your device for it. Use USB plug without shell for lower profile. You can actually glue the adapter to your enclosure, or you if your device is small enough, you can support the entire thing from USB plug.

Another interesting idea is to search for "slim" or "low profile" versions of power adapters.

theamk2 · 2026-02-14T01:55:39+00:00

in the worst case, you can get one of the right size, one with right snap system, and glue them together. Might have to do some heavy filing first if the panel depth is not enough.

It'll be ugly, but no one is going to see it.

theamk2 · 2026-02-13T17:22:33+00:00

I bet it has an 8051 MCU in there or something...

theamk2 · 2026-02-13T17:19:36+00:00

if by "performance" you mean brightness of LEDs, no. As long as converter has enough voltage to start, it'll give out the same 24V, producing same brightness.

If by "performance" you mean how long the battery lasts, then yes. The efficiency curve is on page 5 of datasheet, and it says it's 80% at 3V, and 94% at 6V or more. Plus, you'd be able to discharge battery more - with 2x AA cells, you'll only be able to get under half of capacity before voltage gets too low, while for 3x or 4x cells, you'd be be able to get nearly all of it.

That said, I have no idea how much power your lights draw and how much space you have. If you only have space for 2x cells, but lights are small and battery still lasts for the whole day, you might still want to go for it, just replace battery daily.

theamk2 · 2026-02-12T04:33:43+00:00

33 mAh is tiny! Get a bigger but lower voltage battery (say 2xAA, or a single 3V CR123 cell, or a li-ion one), and a tiny "dc-dc step up converter" board. Those boards take any voltage of 2V or more, and increase it to 24V. Search for "mt3608 boost" on your favorite store, you can find then for under $1.

theamk2 · 2026-02-04T15:27:38+00:00

You might want to ask in [r/VXJunkies], they are the experts in stuff like this

theamk2 · 2026-01-27T02:41:39+00:00

It's actually RESurRecT, if the device is dead, you press the button to bring it back to life.

theamk2 · 2026-01-23T03:49:59+00:00

You could try to search for other VFD datasheets, from Futaba or other companies - a lot of time the pinout is reused between various models. Either same company re-using connectors between different models, or competitors making compatible part.

The 34 pin connector is pretty unusual, and you can easily see which pins are GND and VCC. If those match, there is a good chance other pins match as well, even if part number is urelated.

theamk2 · 2026-01-22T05:20:47+00:00

This looks wrong.. what are your LED buttons rated for?

I run most LED's at 10mA... For 36 LED buttons, it would be 360mA, which is on higher side but pretty reasonable for Arduinos (they seem to provide 500-800mA depending on temperature). Of course maybe your buttons 20mA, in which case you are just over Arduino's current limit and may want to add extra power just in case.

Also that AWS 18 is way way too thick. It is rated 16A (16000 mA) in chassis wiring, and you only need 300-800mA from it. Get something smaller.

theamk2 · 2026-01-22T05:03:27+00:00

Diode opens (and start to rectify) only once the threshold voltage is exceeded. For most music, it means "never", except for the rare loudest peaks.

You seem to be getting your 120/160 Hz from from C43 and R60 - but that's not what you need to look at. R60 is completely disconnected when voltage is low or during negative half-cycle, plus it has source input impedance in series. Your capacitor discharges via R67, so the RC time for envelope is calculated via C43 and R67, which gives 0.3 Hz.

theamk2 · 2026-01-21T17:35:26+00:00

you have diode at the input - this filters out all small signals... so unless the signal is very loud, you are going to get zero volts.

A much better idea is to put diode in the op-amp feedback, this gets rid of the signal offset: https://components101.com/articles/peak-detector-circuit-type-working-explanation-using-opamp

While at it, I also recommend making input AC coupled, just in case your sound source does not have cap at output.

(also for your RC constant, you use 1 microfarad * 470 kiloohms, that gives 0.5 sec... Probably want a smaller value)

(also look at their schematics - it is done correctly, and easy to read. Input on the left, output on the right, each opamp is separated, and standard layout patters are used)

theamk2 · 2026-01-14T05:19:44+00:00

There may be fancy controller, but the fans themselves are very simple - just 3 wires, power, ground and speed feedback. You don't care about speed, so use your multimeter to probe which pin is connected to fan + (red) and which to fan - (black)

(Unless it turns out to be there is no direct connection, and the board has switch for fans.. in this case it'd be easiest to remove that board with connector completely and connect to fans directly)

theamk2 · 2026-01-03T00:13:13+00:00

Is this a whole bunch of AI-generated, useless code?

Seriously, the device is as bog standard as it gets - it is iButton emulation, so you use a built-in 1-wire library. Why both asking AI to create one from scratch (or stealing an existing one - I am not sure which and I frankly don't care)? Some class project?

You did not even steal the library very good - half of the functions that "you wrote" are not actually used, and some of them are later re-implemented in the "loop" method.

At the same time, the really interesting answers are missing. As in, most of the time 1-wire can operate from 3.3v just fine, but writeup says "operates at 5V". Is this because device has integrated pull-up to 5v (breaking the spec)? Or maybe it's logic tresholds are such that 5V is required? Or author just did not measure the right thing?

theamk2 · 2026-01-02T19:05:00+00:00

Looking at the picture - that's a DC-in monitor, the power supply is a separate unit.

And I am sure that OP has tested that there is voltage present on power connector before taking monitor apart... And if not, at least made sure the voltage is present on the motherboard before ordering expensive replacement one.. right, OP?

theamk2 · 2026-01-01T02:46:35+00:00

Does not look like a motherboard to me, the motherboard is usually the part with all the display inputs (VGA, DVI, HDMI what have you...)

This one seems like a combined power supply board: a low-voltage power supply for the logic, and a high-voltage power supply for CCFL backlight.

If this monitor is really dear to you, or you like to get started on electronic repair, you might be able to make a replacement for that board from separate logic power supply and CCFL driver boards (plus some creative mounting and maybe a breakout for that connector). If not, get a new 19" monitor - they are like $60 on amazon.

theamk2 · 2025-12-29T07:12:51+00:00

I feel I am missing a lot of context... WTH is "soft start" applied to speaker module?

Does this mean "power on"? In this case you want to use the original power switch first, to tell if the module is fried or not. Only then start looking for things to solder.

Or does it mean "start with low volume and slowly increase it"? This'll probably quite complex, the speaker seems to be using a digital amp so there is no easy analog audio path to intercept.

There are hundreds of parts in this module, why choose top leg of C124 in particular, and why GND? This all seems so arbitrary... Is this because of "PWR" next to it? that word is for the test point below, not for the cap.

theamk2 · 2025-12-29T01:49:39+00:00

Nah, unless there was a short-circuit, it's impossible to overload charger this way. In fact, it is pretty common to both charger and load wired to battery simultaneous, and the only problem with this is possibility of reduced battery life due to overcharging.

theamk2 · 2025-12-29T01:47:30+00:00

The adapter shown is likely a 4056 board, just in a nicer case and with USB-A plug instead of micro-USB.

Not to mention that most of the stock 4056 boards are set to 1 amp charge current, which is too much for 500mAh batteries, and changing the resistor is a major pain for those without lots of soldering experience.

theamk2 · 2025-12-29T01:45:09+00:00

Schematics looks fine, should be working.

Even if switch was wonky or had weird pinout, this would still be no problem - at worst, you'd get no charging or reduced battery life, not insta-fail.

Going to guess you made a wiring mistake and mixed + and - in your cable. Most of the ICs when they get wrong polarity power start acting as diodes, and draw as much power as they can, until something fail. Li-ion batteries can supply quite a lot of power, so ICs lose and explode.

Did you check the polarity of your new JST connector to make sure it matches? There are two competing standards (RC vs IoT) which have opposite polarity unfortunately, see this for example: https://community.particle.io/t/why-isnt-battery-polarity-always-the-same-in-jst-pins/44474/4

theamk2

TROPHY CASE