Ask Electronics

Does anyone have any advice on routing some high speed signals on flex PCBs? I'm looking at jlcpcb because of the low cost but I'm having difficulty getting impedances to be decent.

My requirements are:

• 45 ohm single ended impedance (maybe? Def doable)
• 90 ohm differential impedance (usb spec)
• 5A current on power pins

But if we look at the capabilities: https://jlcpcb.com/capabilities/flex-pcb-capabilities

• 2 layer
• substrate thickness (PI) = 25 um
• 1 oz pour thickness = 35 um
• min trace width/spacing = 4/4 mil = 0.101/0.101 mm
• ε = 3.3

Is this feasible with this stackup? I'd like to do a 1 oz pour because of power traces, but there's also 0.5 oz (18um) and 0.33 oz (12um).

For the differential signals, when I'm doing impedance calculations, I can get to roughly 70 ohms using W=100um, S=200um. I don't think this is good enough. I think I can get away using a 0.33 oz pour but then I'm worried about the power pins.

And for the power traces, I'm needing 2.2mm, which is reasonable for the pins on a USB-C connector. But if I try using the 0.5 oz or 0.33 oz pour, it gets to be 4.2 mm and 6.3 mm, which seems impossible given the pins are tiny and very closely spaced together. Even with vias to the bottom layer, this seems problematic.

Anyone have any advice here? This is just for a hobby project, so I'm really not looking to change fabs because of costs.

Hy I bought a cheap Yagi wifi antenna need some help cause the previous owner broke it and tried to fix it red neck style... It didn't work ... I hope I would be able to add a picture here is a breaf description anyway it's the cheapest brand you can find online the main element is formed into an oval shaped metal ring and here comes my question where should I solder the middle wire ? On one end ? On the other ? Should I pass it throu the (hollow) metal ring and weld it back to himself ? I have seen people build Yagies with similar ovaly shaped rings and they made the cable pass through half the ring and weld it there the problem is that my ring is shaped exactly like a C it doesn't have a second gap in the middle of the left part ... (Here=>C) English is not my first language hope it's good enough to be understood ask if not 👍🏻

I'm trying to use it as a water pump for my aquarium. I'm using a 6V 4.5AH battery with a DC step up convertor to power the pump. After about 5 minutes it gets really hot. Is this expected?

Hello, and thank you in advance.

I'm making a privacy friendly "ring" cam/doorbell following this guide: https://tristam.ie/2023/758/ which has been great, but requires running a micro-usb cable down to the doorbell for power. I'm hoping to improve on this by using the existing doorbell power instead.

The problem is that I'm a DIY electronics noob and I can't create a mental model for how it should all work. The picture I attached is my existing doorbell wiring scheme, which is as simple as it comes. I totally get how this works. Pressing the doorbell completes the circuit and makes the bingbongs. But this will have to change so the new door cam gets power full time. Ideally without the chime bingbonging full time.

In addition to the ESP-32CAM, button, ring lights, etc., I also bought these: https://www.amazon.com/dp/B079FJSYGY which I thought might be needed to complete the circuit?

I measured the voltage after the transformer and it was around 18 volts, but maybe this is AC and I want DC?

Generally I don't know where in "the loop" to put things. Also, all the existing components are very far apart from each other, so I would love a solution that doesn't involve running any new wires through the walls.

Any help is appreciated. Thank you!!

xoJimbabwe

So I used something like these some years ago to recover data off a phone, but I was wondering if the reverse is possible in having a bga soldered adapter with a microsd slot on top. Or if PCBs can even be soldered together like that. I've never actually checked if bga chips have raised pads or something. The purpose would be for rapidly testing custom firmware for shitty old devices that were designed to be replaced without removing the emmc to flash it separately.

This was a switch that got its wires pulled out. I learned how to desolder today in order to remove it from the little switch board and now there's three holes where this used to be. Does this component have a name, because I'm wondering whether I can just get a replacement one like this. There are lots of tools and supplies at the makerspace I used, but I need to know what I'd be looking for.

Alternatively, what else might I be able to use to do this? I suppose I could just trim and strip the wires and shove those through and solder, but that seems...crude? I don't know. I'd prefer something with pins because I practiced soldering and desoldering using some broken electronics I had, and I'm more confident with pins than something so freeform.

Thanks for your time.

I am looking for some sort of big programmable buttons. Not sure if something simple exists.

Basically, this is to enhance flow through clinic, looking for a relatively simple solution.

I just want some big battery-powered bluetooth buttons that I can give custom commands in tasker to text tell people to assist with tasks or bring me certain things. I'm not sure if something simple like this exists. (Thinking of like three or four different colored "easy" buttons).

I haven't found anything quite as specific as this, but it's been something nerdy I've been thinking about that would save me time.

LEDs will conduct more current when they get warmer and differences between individual LEDs mean you cannot easily put them in parallel. A constant current DC supply will be good enough for part of the LEDs but will overload some others. To normalize current a series resistor is used with each individual LED.

Now, those resistors waste a bit of power. Are they really necessary? If you put several LEDs in series the individual differences become negligible at some point and a constant current supply will suffice for several strips of series LEDs in parallel.

How many LEDs would this require? Another possibility would be to have the resistor in series with a strip of LEDs.

I got some LED strips off AliExpress that run on 12V and each individual LED has a resistor in series with it. I believe this to be quite wasteful and it would be better to have several LEDs in series with a current regulator instead. The LEDs will end up in an autonomous greenhouse where power efficiency is important.

Hello Lemmings, Hope you guys are doing well.

Objective: Open the door automatically through HomeAssistant

My Plan:

1. Use an ESP32 and flash ESPhome. Wire up Servo Motor (SG90) with ESP32. Tie a thread on between the Servo Motor Arm and the physical latch (physical latch that I can pull to unlock the door) such that when the servo motor turns from -100 to +100, the latch is being pulled to cause the door to be unlocked.

2. I am planning to power this using AA Cells + DC DC Boost convertor.

Issue:

1. How do I mount the Servo Motor on the door?
2. Is there any other (read better) way to achieve the same result?
3. Would you recommend any power source other than AA Cells?

Image for reference:

The latch has a keychain-like loop where the thread is tied. To unlock the door manually, I pull the latch towards right (---->) . This action is planned to be automated by Servo Motor.

This is an idea that entered my mind. The traditional way is applying some etch resist like toner or dry film, etching away the copper and then adding solder mask before populating the board with components.

Can the solder mask be used as etch resist instead? It feels like skipping an unnecessary step in the process. Why isn´t this more common? This way you won´t need the step of removing etch resist only to replace it with a slightly different compound.

Ever since I've gotten into Retro Computing, I've been confronted about things like soldering, Circuits and Electrics in general... and it has made me want to try experimenting with my own ideas!

That does however mean that im still pretty inexperienced and thusly don't have anything to actually experiment with either.

So what kind of Breadboard Kit will give me the best and most things to start getting into this Hobby?

It appears to me that UV resin, used for SLA printers should be quite convenient for making PCBs with a laser etcher. You can spread a thin layer of resin on the board and quickly expose it using a laser engraver. It should be most convenient for silkscreen layers that are otherwise difficult to apply.

I think the common method of applying UV mask and spreading it using a piece of plastic sheet is messy and I can never guess how much resin to apply. It's always too much or too little and it's always unevenly spread. And then the UV light exposure is another guessing game.

I have a 500mw 405nm laser module attached to my 3D printer and could easily 'print' some PCB layouts on a thin layer of SLA resin.

Does anyone have experience with this?

Hello,

I'm creating a BoM for a youth group project. We're planning on building the Electromagnetic Ring Accelerator from Hyperspace Pirate. He's provided the 3d print files, but not the finer details on wire gauge, enamel wire gauge and ball size. I also want to confirm the photoresistor. Are there different photoresistors with with different sensitivities or ranges?

I've included the wip of the BoM.

Hey guys i cant find any usefull guide on how USB c charging works in depth. In particular i have bought a pair of Sony headphones which i would like to make wireless change so I also bought a crappy wireless coil meant to convert a phone into wireless charging. i opened the headphones, located the ground and 5v pin coming from the USB connected the circuit and surprise the charging led doesn't light ... The charging board is separated from the main board so I checked the flat cable that connects them, found the 5v and gnd ,spliced into it, and the led light lit as if it was charging. the next morning the led was of signaling the headphones are full, unfortunately after powering them on the battery status indicated was still 20% as the evening before ... Have I done anything wrong ? What about that phase when they negotiate the power output with a magic resistor ? What should I try next? Thanks in advance 👍🏻

Greetings again! Yesterday I posted the schematic for this circuit, and today I have routed it as a 2 layer PCB. The intent of this board is for it to be a playground to build autonomous LED animations with the LP5812 ICs from TI, which seem pretty neat.

I'm hoping to get feedback on this design and sanity checks to make sure I haven't missed something when routing this out. I couldn't figure out how to upload multiple photos, so I'll add some more views in the comments. Cheers!

If you're interested in the KiCad files or other related things, I've got it on GitHub.

Seriously, what sadist saw a flat PCB surface, flat pick and place machine heads, and said "lets create a round component"?

Joking aside I am genuinely curious what advantage the MELF design actually offers. I know they're a pain to get a machine to place properly, they have more solder flow issues than components with flat leads, and they seem like they would be harder to manufacture too. So why a round component? Anyone here have any insight on why they even exist?

Greetings! I've been throwing this schematic together as I want to experiment with the TI LP5812 IC which is an i2c controlled autonomous matrix LED driver. I am a novice when it comes to electronics so I'm looking to see if I've missed anything in this demo board schematic.

The intended purpose of this circuit will be to provide a playground to experiment with different lighting patterns by allowing the user to interact with two of these LP5812 ICs over i2c as each can only drive 4 RGB leds each.

My main points of concern: Making sure that I haven't missed anything critical in the rather dense TI datasheet https://www.ti.com/lit/ds/symlink/lp5812.pdf?ts=1710689049125 as well as making sure that my schematic makes sense.

I chose not to include i2c pullups on this dev board as I felt that was best left for the host to configure, but I'm happy to learn. Thank you!

Here's a link to the KiCad project if you'd like to see more https://github.com/scytherswings/Starlight-LP5812-Dev-Board/tree/main

Besides putting too many devices on a single wall socket, that draw too much power, what is supposed to happen?

Like say I chain ten dividers and put a single vacuum cleaner at the end. Is that more dangerous than plugging it directly into the wall?

I have a Mission MS 200 Subwoofer where the power supply has stopped working. I was quite happy with it, and would like to try to fix it, also I don't have the money for another. I have taken it apart and have narrowed the fault down to the PSU. I have visually inspected the solderings and components, and nothing obvious is wrong. I am not good enough to be able to reverse engineer the board, and was hoping there might be someone here with access to a schematic? Failing that, any pointers on where to maybe do some in-circuit measurements to narrow down which part(s) might be broken, would be very highly appreciated!

I'm trying to understand what's happening in this circuit:

I------------------T1 (+333V)
I                 I
I                 R1(10K)
(pos)             I
1000V             I------------gnd (0V)
(neg)             I
I                 R2(10K)
I                 I
I                 IT2(-333V)
I                 I
I                 R3(10K)
I                 I
I-----------------IT3 (-666.7V)

I am learning basic DC theory from reading and sometimes I come across something I'd like to ask a question about, so:

1. In the above circuit, without the ground, the voltage across all components would begin at 10V and finish at 0V. By adding a ground, I'm basically saying "here is 0V" and everything gets redefined in reference to that point and I end up with a 10 volt circuit with +3.33 as it's highest voltage and -6.667 as it's lowest.

2. The electrons could care less, they still flow from the anode to the cathode of the battery under normal conditions, going from the highest potential to the lowest.

3. This example was only used to demonstrate voltage dividers. It revolved around worker protection present in aluminum processing. Each machine is in series and mobile grounds are used nearest the machine a worker is using. I assume that this allows the worker to have the least exposure to electrical shock as they are also at ground potential?

I actually think working though these questions has cleared everything up, but please, comment on anything I got wrong.

Also, sorry about the crappy drawing, the autowrap in this editor really made things tough to format

Thanks!

I want to build a linux(yes i want linux specifically or a deritive of it) smartwatch as a prototype that lasts ~24 hours. Ive been looking for chips that are small and power effient enough but most of them cant run linux. If i have a 400mah battery that gives me a power budget of about 60mw... I know its possibly because there are wearos(basically android) watches that last 3-4 days. I dont know what kind of sorcery that is but that means it consumes about 15mw??? I really do feel like im miscalculating something but i checked multiple times. Do they hibernate linux/android and run it off of another chip. I also dont know how to excecute that properly and its kind of off topic of my question. So point is linux on a ~60mw budget in s smartwatch. I want to use a mip display as i really like the look and it uses little power but if ever want a heart rate sensor in it thats even more power consumpotion. Thanks in advance i guess if a saint answers this shitstorm of a question.

It happens rarely, but I will notice either my phone or the charger getting pretty toasty randomly. What could be causing this?