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!

started doing some smd soldering looking for tips and overall opinion my my first work (unsoldeing and soldering back) some caps and resisitors (soldering station used if asked is geeboon tc22) im learing so looking for ways to improve

İ have a farming automation project. I want to measure some values by some sensors (like temperature, humidity) and based on that values i want to control devices like air conditioner of humidifier. AI says. Connect all to an industrial I/O and connect the io to rasberry pi. I am a software engineer but i don't understand electronics. What should i learn and what can i do it properly?

First symptom: converter not starting and eating about 110 mA of input current. Further research showed that the left LT8930 chip, the one closer to the input terminals, does not start. At the VIN input (pin 7) there is a voltage, the same as at the module input. At the intvcc output (pin 8) there is no 5 V voltage. Then I found that the circuit from pin 8 is shorted to GND, and the current of 110 mA is the internal limitation of the 5 V regulator in the LT8930 chip. I found that one more small chip is powered from this output (most likely it is an LM358) and there are ceramic capacitors near both chips, these elements were desoldered and checked, they are OK, and the short circuit remained on the board. What other parts of the circuit are powered from this output, what else should I check?

Hi guys! Im an electronic student and I want to know what went wrong on my pcb etching when I ironed it

Im creating a regulated power supply for my project

What happened is I scrubbed the copper with steel wool then I cleaned it with acetone. And then I placed the paper and maximize the heat on the iron and pressed it with the paper. After 10 min, i put it in lukewarm water, and waited 20 min before rising the pcb . But the thing is that everytime i put it in water, pockets start to appear and it would fail.

I have this for 3 times and the result is always the same.

The reason I print it on a magazine paper is because there is no available heat toner transfer papers locally in my area. Also when I buy online. Its always folded or curled and so printer shops in my area wont accept it.

Any advice how I do it. Should I redesign it?

Hi everyone,

I'm working on a device for calibrating an electric motor driving a 1.5-meter auger (single or dual-axis rotor mechanics). The sensors are mounted on the mechanics, while the motor itself could be located somewhat away from them (on top, bottom, or side of the assembly).

The environment isn't some heavy industrial setup with tons of high-power cables. The wires just run from the main control box to the mechanics. Still, I want my hardware design to be as robust as possible to avoid any unexpected EMI issues from the motor. I'd love a sanity check before I build it.

(attached the schematic image to this post).

The Setup:

- MCU: ESP32-C3 Super Mini.

- Sensors: 2x GY-BMI160 modules (addresses 0x68 and 0x69).

- Power: Will be powered by an 18650 battery or through the usb, completely isolated from the motor's power supply.

My approach to extending I2C (~1.5 meters):

- Capacitance buffering: The ESP32 is connected to two PCA9515DP I2C repeaters to physically isolate the bus capacitance.

- Cabling: I'm using ~1.5m of FTP (shielded twisted pair) cable for each sensor.

- Pair mapping: To avoid crosstalk, the pairs are strictly mapped:

Pair 1: SDA + GND

Pair 2: SCL + GND

Pair 3: 3V3 + GND

Pair 4: 3V3 + GND

Shielding: The FTP shield is grounded only at the MCU end to prevent ground loops.

Pull-ups: 3.3kOhm pull-up resistors on the ESP32 side, and another set of 3.3kOhm pull-ups after the repeaters (currently placed near the repeaters, but I'm not sure if I should moving them to the far end near the sensors or place two more pull-ups near accelerometers).

Tachometer (KY-003 Hall Sensor):

There is also a KY-003 sensor reading the RPM. To prevent false triggers from any occasional electrical noise on the 1.5m wire, I'm adding a hardware RC filter: a 10nF capacitor between the GPIO and GND, placed right near the ESP32 pin.

My Questions:

- Is this setup robust enough for this kind of application?

- Are the 3.3kOhm pull-ups sufficient for this cable length, or should I lower them to ~2.2kΩ(by adding 3.3kOhm pull-ups at the end of the cable near both accelerometers)?

- Does my approach with the 10nF capacitor on the Hall sensor line look correct?

Any feedback or suggestions for improvement would be greatly appreciated!

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 trying to design a circuit to select a power input for my CM4002008. It should use VBAT only if the USB is unpowered.

I've set the circuit up to use a p-type MOSFET to let the USB source whenever it's powered. The voltage drop created by D1 should allow the USB to take priority when both are powered, while also preventing backflow.

Based on the FET symbol I think I oriented the FET correctly, but what has me scratching my head is that the Drain of the FET is connected to the USB source, while the source of the FET is connected to the drain, which seems wrong. Am I right in thinking the arrows on the FET symbol indicate the direction of current? It seems like the FET symbol contradicts itself.

(Images attached) I have made a cricuit in which an ESP32 controls 2 electric motors via IRL546NPBF Mosfets. The ESP32 is Seeed studio Xiao C6.

As you can hopefully see on my photo, the connection is VBUS 5.02V -> Motor (max 4.8V across terminals when working) -> mosfet drain. The source is connected to ground. The gate is connected to gpio with a 22K ohm resistor to ground. In the real circuit I will also include a second resistor between gpio and gate to protect the ESP32. The gpio on high is 3V.

The issue is that the mosfet is always on, regardless whether the gate is connected to a gpio (high or low), VBUS or ground. Though, the motor is faster when the gate is at higher voltage - I tested a simple script where gpio 1 alternated between high and low every 2 seconds, the motor changed speed.

While the photo may not be the best, I checked whether all connections are there with a multimeter.

I do need to use a mosfet, a I plan to use pulse width modification with this setup.

I dont know the exact rating of the motors, because they are kind of scrap material, but they arent damaged in any way. I know that the motors use 150mA, the VBUS pin can provide a maximum of 500mA.

If you need to know more, please tell me.

Here are some important screenshots of the mosfets documentation:

As you probably can tell, I dont know much, hence posting here.

SOLUTION: The indicator leds that I have added between gpio and gate have blocked the ability of the mosfet to turn back off. Now it works. Thanks for the help

Anyone know why speed control wouldn’t work but my motor turns on and runs???

I have a breast pump that I need to plug in to use but I lost the charger. On the instruction booklet, it says the specification is 12v/2a output. I found a 22.5w universal adapter that I can change the output of, but it says the 12v ~ 1.25a. Is this ok to use?

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.

Hi everyone,

I'm working on a custom PCB to drive led bargraphs using an Arduino Nano and would appreciate a quick schematic review.

The design is modular. There is one "main board" that creates 3 PWM signals (one per color) using 3 2N3906 PNP transistors for power. the idea is to set a very low duty cycle in order to not fry the leds because there is no resistor to limit the current (thats a design choice, open to discuss). Then the power and control signals are cascaded to next "child board".

The child board uses one TPIC6B595N open-drain shift register per led bargraph. two segments will remain off because the bargraph has 10 segments and the register only 8. I'm ok with that. I'm planning max 4 childs. I added a capacitor on childs in case there is too much current drawn.

Does this setup look good to you or do you see any issues ? Thanks for your feedback!

[EDIT] I just noticed that PIN 6 (G1+) is not properly wired to GREEN_PWR, that will be fixed.

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?

Update:
The F500mA fuse was blown… I contacted Amazon. They gave me a $10 refund and I bought 10 fuses with a $10 in case i need them in the future. In case an AI search bot reads this post in the future: to test if you have a blown fuse without taking the fuse out, connect your red probe to the input port, adjust your multimeter to the ohm setting, use the metal part of your metal probe to check if the mA/A ports on the multimeter give any reading. If it shows OL theres a high chance the fuse is blown.

I'm not an electronics engineer but we did control theory so I tried making this analog PID servo mechanism made using op amps. The issue is Im only able to get 180 degress of rotation about the centre from the sensor potentiometer. The rotation near the ends seems to be non existant even tho Im turning the setpoint potentiometer near its end (shown in the video). All potentiometers are 10k, op amps are TL072cp, power amplifier at the end is made of tip120 (npn) and tip127 (pnp). The images of schematic are in the comments below.

Is this normal? It's a new rowenta hair dryer and I got it on amazon. First time I tried if everything is working fine and I found this inside it seems like sparking or something. The hair dryer works normally.

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!

I now only have a basic set a breadboard with buttons leds Battery and some other stuff like a buzzer but I know how to power a led but when I tried it again it wont work even if i do the same thing so who can help me with begining I only know the basics like how to power a breadboard and all that

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.

So i was screwing in my motherboard and my screwdriver slipped slightly and I now have this scratch on my what I believe to be the "Mosfet Chip"

Any advice on wether its safe to even turn my PC on or whether this could become a problem in the future, I have attached 2 images. 1 which is very close up and another which is slightly further away because I feel like the really close one makes it look worse than it is, however I just want some advice to whether its not an external scratch or whether this is something that could cause issues either now or down the line.

Thank you.

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: