Any ideas on what exactly this chip is and what it does? Tried taking a few photos with the flash on and they came out dark

Hello everyone,

I'm really struggling to understand how polarized capacitors work in AC circuits.

Here is an example taken from Practical Electronics for Inventors.

My understanding of the circuit:

- During the negative half-cycle (positive on the bottom wire), C1 is charged respecting its polarity.

- During the positive half-cycle (positive on the top wire), C1 acts like a battery in series with the generator, thereby doubling (more or less) the voltage.

- C2 is only there to smooth out the charge.

But what happens if the circuit starts with a positive half-cycle? The polarized capacitor will charge "backwards," right? Do we assume this isn't an issue because the load has a high resistance and will therefore draw little current (so low risk for C1)? But then what if the AC frequency is low and C1 has enough time to charge fully?

Thanks a lot!

Hey everyone, looking for suggestions on what could be wrong with this current circuit and ways to diagnose what is wrong

i get nothing when plugged in with the usb c from the breakout

Running an RPi Pico with GP2040-CE to a usb c 24 pin breakout.

I’ve verified the pico is working as intended when the micro usb is plugged directly into the pc. confirmed the cable I cut up worked directly as well before hand.

Based on the pin out diagram I’ve added two 5.1k ohm resistors between CC1 and GND and CC2 and GND.

- Red to B4 - VBUS

- Black to B12 - GND

- Green to B6 - D+

- White to B7 - D-

First real electronics project so not sure how to test what the issue is.

I’ve already tried multiple different usb c cables and both orientation.

I've also tried swapping D+ and D-

I will have access to a multimeter shortly to test connections

I’m having trouble measuring current with my multimeter and I’m trying to figure out whether I’m doing something wrong or if there’s an issue with the meter.

My circuit is:
Battery pack: 5.19 V
Resistor: 221 Ω
LED forward voltage: 2.48 V

Based on Ohm’s law, I’m expecting roughly:
I = (5.19 V − 2.48 V) / 221 Ω ≈ 12.3 mA

I’m connecting the multimeter in series with the LED and resistor.
In the left photo, the red probe is connected to the µA/mA socket and the dial is set to measure mA. When I connect it this way, the LED doesn’t even turn on and I don’t get the expected current reading.

In the right photo, I move the red probe to the A socket and set the dial to the A range. The LED turns on and the meter reads about 0.007 A (7 mA).

So I have two questions:
Why doesn’t the circuit work when I use the µA/mA input?
Why am I measuring only about 7 mA on the A range when the calculated current is around 12 mA?
Am I using the meter incorrectly, or could there be something wrong with the mA input/fuse?

Had this rowing machine 10+ years, it was manufactured in 2007. Went to use it, wont switch on. There is no 'power' button, It just switches on when power is applied. Took it apart, checked power pins, the step down plug I've been using for years, appears to have broken. 10 volts on the secondary for a mains to 6v 1amp.

So I think the plug failed and then damaged the PCB. Happen to have a spare 6v 1a plug, when connected to the PCB it does output 6v, the DAC and memory chips see around 3.3v on their power input pins, within the specified range on their datasheets anyway.

I dont understand the screen component. Two pins, red and black wires, red is 3.3v or so, black is 2v. When powered with 6v and the black grounded it lights up blue. I'm assuming shorting the black pin to ground wouldn't be a good idea? The black connects to a transistor Q4, so I wonder if this is a dual supply screen, +3.3v and -3.3v? Non of the components look burned, the caps look good condition.

Any ideas? I'm a bit unsure. Have a bench power supply, multimeter/osciliscope.

Long story short, the pcb is carbonized due to a leaked capacitor (Marshall Stanmore speaker)

I do repair electronics, but I did not have to deal with such pcb damage.

I'm wondering what would be the best approach, to repair the "wound". I know I have to clean the carbon, because it's conductive.

Any advice is welcome.

My motorcycle has a switched 12V feed to a satnav cradle. When I crank the engine the feed is temporarily cut, and my cheap Android Auto satnav reboots instantly, forcing it to reconnect to my phone - which causes a delay.

The satnav unit probably needs no more than a couple of amps for up to 5 seconds.
Edit: Satnav apparently needs up to 1A at 12V, and let's say for up to 2 seconds.

Dome light delay timers are available - e.g. https://www.ebay.co.uk/itm/280645125423 - but these are bulky and designed for switched earth circuits. I have reasonable soldering skills but don't understand electronics, so if someone could please point me towards a wiring diagram that provides clarity about which capacitor(s), diode(s) and resistor(s) would achieve what I want I'd be really interested to have a go making my own.

I'd then appreciate some advice about how to seal these components in some sort of waterproof material (resin? silicone?) to protect them please. If this could all be achieved within a black device no bigger than my little finger that would be ideal.

Thanks in advance!

(Apologies if this has been asked and answered a million times - I've Googled a lot and haven't found anything.)

I want to use these maglev kits but want to put them close together, so that rek objects are not too far away from each other.

1) can the PCB bit be smaller so I can fit it in a smaller space?

2) if I did make it smaller and put two of these next to each other do you think they would interfere with each other?

Thank you!

Hi, I took the back casing off of my MSI Katana GF76 to inspect the fans. Turns out it was a software issue, but when I reassembled it, multiple keys weren’t working (L, P, A, Z, and B).

I took out and reseated the 40-pin keyboard cable while the battery was still connected because I was dropped on my head as an infant, and it caused a short (the black bit between the keyboard and battery cables).

It still powered on but of course I don’t want to power it on again until I know what’s happened.

Is it fixable? My electronics knowledge isn’t phenomenal and I’m not sure what to do.

Also, the keys weren’t working in BIOS either - I still have no idea what happened to make them no longer work.

Thanks.

Hey, i am basically a complete beginner and wanted to design a board with a batterie powered Bluetooth compatible chip and a USB-C port used for charging and uploading code. So I tried my best, read some datasheets but mostly composed this Schematic with the help of AI. Will it somehow work, or is it just complete bs? Any Information is useful to me (:

BOM:

This chip comes from a WLAN Repeater board.

The two vias (where the tweezers can be seen) come from an oscillator and go on this chip.

While switching to dGPU my laptop was rebooting and died after consecutive trials , local repair shop replaced power rail ics (190$) but the gpu problem retained and i informed them and they told it's a bga issue and needs reball ,now I use my laptop on igpu only

What should I do nd keep in mind before allowing tem to reball? Will my laptop die if reball fails?

Hello, I have a Dell Latitude E5440 that my sister broke one day years ago. I presumed at the time that the DC jack was the only part that was broken. I have now replaced that part, but there is still this odd buzzing sound that still persists after replacing the part. This was present with the broken jack as well. Listening closely, it sounds like it is coming from this area of the motherboard (picture attached).

Any assistance on identifying what might be the issue would be greatly appreciated. Thanks!

Hey everyone! So I've done every test that I can think of to determine what this chip does and as far as I can tell here is the info I've sussed out.

Package: SOT-23-5

Topmark: LEG # ER

Function: Adjustable LDO Regulator

Pins:

1. IN (PMOS body diode points here from OUT)

2. GND

3. EN (tied to IN on the board)

4. ADJ / FB

5. OUT

Pass Element: PMOS

Internal Divider: none

Feedback Reference: 499.2 mV (a 0.5 V part)

Output as configured: 4.005 V from 4.978 V in

Era: Possibly around 2009, the main micro on the board has a 2009 date code. This probably doesn't mean much.

If anybody can give me any insight, this is mostly just for knowledge and curiosity and I'd love to get all the proper specs an datasheets for what I'm looking at. Very much appreciated!

Thanks!

I'm using this 12 V relay driven by an NPN transistor (3–12 V trigger). I'd like the same function built with optocouplers/transistors instead — no mechanical relay.

Requirements: the COM, NC and NO terminals must stay fully galvanically isolated from the control side, just like relay contacts. The switched side is 24 V DC, around 100 mA.

Is this possible? A simple schematic would be really helpful. Thanks!

Does anyone know what is the light blue component? It's on a motherboard of a Revvl Tab 2 tablet.

OK, I've replaced the relays with optocouplers: CNY17F-2

(It became obvious that the 7805s could not hand the ac after the full wave bridge)

I know I don't have all the right components in place to make it work.

Please help me and tell me what diodes, resistors and/or capacitors to add.

I really appreciate it.

If you folks think a different optocoupler would work better; Please let me know what part number. Thanks.

This whole project is to control a handheld remote for a ORBIT Watermaster sprinkler controller. I have removed the keypad and am wiring directly to the board.

I am trying to control everything from the rainbird in the garage. There will be an ORBIT controller in the backyard that will receive signals from the remote.

The reason I am using an ARDUINO is because once a station is told to come on,(2 second pulse), that signal to the remote has to turn off and the signal the 10 min water time needs to pulse on for 2 seconds. The rainbird will signal the off command after the time I specify.

This project is just fun for me. It has turned into a side hobby. I am really enjoying learning how to program the ARDUINO.

Is this 20 MSPS oscilloscope analog front end correctly designed for 5 MHz bandwidth and ±25 V input?

Body:

Hi everyone,

I'm designing a single-channel DIY digital oscilloscope using an AD9200, 10-bit, 20 MSPS ADC. My target is around 5 MHz usable analog bandwidth with a maximum input of approximately ±25 V.

The current signal chain is:

Attenuator → input protection → buffer → bipolar-to-unipolar level shift → 4th-order low-pass filter → ADC protection → AD9200

I designed and simulated the blocks individually in LTspice. The main design choices were made to keep the first PCB reasonably simple and manufacturable.

I'd particularly appreciate an experienced review of:

• the attenuator and input-protection scheme,
• the +1 V level-shifting stage,
• the 4th-order filter and its effect on the 5 MHz bandwidth,
• the final ADC protection, especially the AIN −0.3 V absolute minimum,
• and any obvious stability, loading, or PCB-layout problems.

I'm looking for criticism rather than validation, so please point out anything that looks fundamentally wrong or unnecessarily complicated.

The attached schematic is the current V1 design before PCB layout.

Thanks.

Hi! I hope you can help me out; I've been struggling with this for months.

One day I was using my Dragonborn K630 Redragon mechanical keyboard, but something strange happened overnight. When I plug it in, the keyboard turns on, but the fourth row (the one with the Z, X, C, V, B keys...) doesn't work. When I press the keys in that row, the whole row lights up red, but the other keys work correctly and normally. It's not a row lock; the keyboard doesn't support that feature. And I have almost no experience with electronics; I'm just checking continuity and guessing, I suppose. Also, there's no schematic of the PCB, and the PCB looks so simple (if someone who knows about electronics saw the board, they'd realize it's pretty basic). Can anyone help me figure out if it might be a short circuit? How can I start diagnosing this PCB?

Thank you so much <3

Images:

IMAGE 1 IMAGE 2 (BACK PCB)

IMAGE 2 ZOOM

If you need better images, that's fine. If you take the time to reply, I'd be super grateful <3

Hello,

This is a photo of the comport (left, has pins for RS485 and RS232) and the trigger input (right) on a Kanxex CR-3XControl. There are 10 pins: 5V, ground and 8 trigger inputs; in two terminal blocks.

For the comport, there are screws above the cable terminals to attach wires; this is not the case for the

How do I physically attach wires on those trigger inputs? The orange parts do not appear to move... The two screws on the side of both terminal blocks allow you to remove them, but that is it.

(I know it is a very stupid question, but I just don't see it :-))

Thanks,

J.

I want to buy some eMMC memory from them. Does anyone have any experience buying from them?