Found on a cookie box. My guess is NFC or RFID inventory tracking, but not sure.

I purchased this 4 inch CRT online as a project to turn it into an oscilloscope. I hooked it up to 12V DC power as it called for and soldered in two pots for contrast and brightness, 1k and 50k ohms respectively (top left of board in blue). As far as I understand, turning on a CRT with no input should give some sort of visible raster lines or a dot in the center, but all I can manage is an extremely faint glow. I can hear the 15khz whine while it's on. What could this issue be? Is this normal and I'm tripping? The display is identical with the deflection coils both plugged into and unplugged from the board.

If there is a better subreddit to post this please let me know

I am trying to solder a LED on to this car instrument cluster. For this I need to disassemble the cluster first and I am stuck on disconnecting the LCD display from the board. As I am new to this can anybody tell me wether this is soldered directly to the board or is there a trick to disconnect these kinds of connections?

Any alternatives for them? I have custom power LEDs which I control with those (+transistors ofc) but I want to have the slave PCB much smaller. Ideas?

I'm replacing this pot and for the life of me I can't get solder to stick to this terminal. Tried flux, flux cored solder, filed slightly, alcohol clean... nothing. Any clues as to what I am doing wrong? Iron set to 400.

Hey everyone, I’m testing an optocoupler-controlled MOSFET circuit in Falstad, and I’m having trouble understanding the voltages I’m getting when it’s supposed to be off.

The control side uses 3.3 V, and the power side uses 8.4 V. When I turn off the optocoupler LEDs, I want the MOSFETs to disconnect power from the right-hand side of the circuit. I expected the voltmeters shown in the screenshot to read approximately 0 V.

However, with the controls off:

• The upper circuit reads about 2.031 V across the output terminals.
• The lower circuit reads about 21 mV.
• Probing the node after the diode also shows around 4–5 V.

These are simulation results; I haven’t built the circuit yet. There’s no load resistor across the output terminals in the screenshot, just the voltmeter. Also, the voltmeters measure between the two output terminals, rather than directly from an output to ground.

Could the outputs simply be floating, or have I made a mistake with the MOSFET source/drain connections or gate drive? Could a body diode be providing an unintended current path?

I’d really appreciate someone pointing out what I’m missing and how I should test whether the output is actually disconnected.

In the explanation videos i have seen they model the voltage across C2 during the positive half cycle as V_in + V_p (voltage over charged c1) = 2*V_in (assume no voltage drop across diodes and ofc no resistance). Does this happen because c1 cant deliver a constant voltage for c2 and c1 and c2 just equalize their charges?

I'm trying to build a multi-LED strip driver to replace a cheap one. I've figured out most details, but I'm stuck on a few and need some help.

The original LED driver unfortunately has issues (flickering in cameras) and I wasn't able to recover any useful part numbers from it, so I had to design my own. I also wanted to add a feature: variable color temperature over the day, so I needed an RTC for that.

My plan so far:

• Input: 24V, 2A, in a switched outlet. PSU came with the original LED strip.
• 24V => 5V via AP63357DV-7 (I already have this on hand)
• Pi Pico as MCU (I already have this on hand)
• For each temperature string, MCU -> Gate Driver -> 24V N-CH MOSFET -> 24V LEDs
• For the RTC to keep time when I turn the lights off, a PCF85363ATT/AJ RTC, and either a CR2032 or CR1632

These lights will be on ~8hr a day, and possibly off for up to 3 weeks at a time when I go on vacations, hence why I need the RTC + Battery.

I'm fairly confident of the RTC and MCU side of things, but the Gate Driver + N-CH MOSFTET is worrying me. Based on my reading, it seems like I need to be able to drive the LEDs via ~100kHz PWM to remove the flickering/banding in cameras, and I've never used a mosfet > 100Hz before, or a large power MOSFET either. Based on https://www.dmcinfo.com/blog/17021/mosfet-power-loss-calculator/, I found several MOSFETs that would have <0.5W loss, such as RQ3E120GN (~0.2W), RQ3E080GN(~0.3W), or IRLML0030TRPbF (~0.4W). I am concerned about power loss as this will be in a small box near the ceiling, hence oversizing for the current requirements. However, I'm entirely unsure how to go about picking a gate driver for this situation. I've read a number of guides and calculators, but they seemingly don't agree with each other, and all left me with more questions than answers; clearly I do not yet understand what I need to search for.

How can I figure out the current and other requirements for picking a gate driver for this application, and would any of those then influence the MOSFET selection? Is it better to have a 5V/3.3V gate driver, or a full 24V gate driver?

Thanks!

Note: I prefer non-BGA components as I'm hand-soldering these with solder paste. The AP63357DV-7 is about the limit of my skills so far.

Hello electrons,

I'm trying to come back to hobby electronics after a very long time and would love some help.

I want to build the simple circuit that can detect how close 2 wires are to each other. Ideally the closer they get the louder a buzzer will be or the brighter a LED will get. The wires will be separated by up to 1cm of insulating material, probably silicone.

If not way more complicated, some indication that the wires have physically touched would also be great.

Appreciate any help

The Sunbeam WiFi heated mattress pad has an annoying safety feature that requires you to physically press a button within 45 minutes after adjusting settings over WiFi, so I would like to add a small circuit to pull the button signal to ground periodically. I only want to wire up 3.3V, GND, and an open drain output on a single chip/module, and it needs to be low power since I don't want to overload the regulator. I can't think of anything simpler than a small microcontroller. I have JTAG, SPI and UART programming cables and don't want to invest in any proprietary cables. What do you suggest? Thanks!

Hi everyone,

over the past few weeks I've been iterating on this PCB design for a simple board that would allow me to use one keyboard with two devices.
I know switches like this exist commercially, but I wanted to try making one myself because it seems like an interesting and simple first-time PCB project.

I have planned the design around 0805-sized components where possible, as I will be handsoldering the board and from my research that is in the "doable" range. How well I'll fare with the connectors, the tvs diodes and the USB3740B IC in the center I'm not too sure.

In terms of tools I have a temperature-controlled soldering iron with a fine tip, a big magnifying glass on a stand, ESD tweezers, a regular hardware-store hot air gun and syringes of no-clean solder paste and flux.

The holes in the corners are for securing it in a 3D printed case that I'll design after I receive the boards.

Please lmk if there are any glaring issues with this and if there's anything I can improve :)

Thanks!

Hello,

I have been trying to build a cnc machine using two dvd drives and an arduino.

I saw that there was already tin on the coils of the stepper motors so I decided to solder dupont cables without adding more. But for some reason I could not solder all the cables, it seems the tin quantity was not sufficient to allow the cables to stay put.

Should I add more tin?

EDIT: Thanks to everyone who commented. I have what I need now. You people are amazing!!!

I’m looking to replace this cap (the back has cracked apart). I need to locate a suitable replacement but am not sure about the specs. Any assistance is much appreciated. Below is my best shot at it

Type: Polyester film capacitor? Can any other type be substituted?
Value: 0.0047uF ?
Tolerance: 20% +/- ?
Voltage: ?

Dear community,

I desoldered 27 capacitors as I want to do a full recap. I did a good job on 24 of them, while three solder pads under the desoldered capacitors are a bit problematic. Two do them are just a tiny bit loose on one end.

1) Do you think I can still use them to attach a new capacitor?

2) One of the three problematic pads is probably damaged for good. I attached a photo for this solder pad. Would you assess that this solder pad is more or less gone and I need to attach a jumper wire?

Thank you for your expertise!

I'm finding it really hard to properly satisfied with the explanations I get through YouTube videos . Is there any book or any other resource which might help me?

This is a inverter ac slipt unit pcb.

Something happend, i called maintenance - they told me the IPM module is burned. I asked the board back to take a look.

I'm a newbie, so i thought i would just play around.

I found some videos on how to test that module, it seems fine, after that i notice a blown capacitor - i have successfully changed some caps, before.

I also tested this tension regulator.

While mounted, it showed a short.

I desoldered it and tested.

Only kind of weird is that the high difference between pins 1 and 2(around 630), to pins 2 and 3(around 1150) - using the continuity mode, on my multimeter.

Then i tested the pcb pads. I got a short between both the pads to pin 1 and 2, and the big pad that woulbe pin2 (Gnd i guess).

After all that, i noticed that tiny little thingy identified as C413.

I tested for continuity and the multimeter buzed both way.

Its that thing bad? What else should i check, and how?

Is it possible to replace that micro tiny thing?

I only have a cheap soldering iron.

Hello,

I making a command for a personnal project and I need a BJT547 transistor but when searching for it got several results with different declination of the same transistor like CBK, BBK, CTA, BTA, B and i don't know how i need to choose between all of these.

I know it's maybe just packaging but i saw different parameters between them like the hfe changing from 450 to 800. And if it's just packaging how do you choose the right one what make a good packaging.

Maybe the answer is just choose the cheapest if i don't need special requirement but if somoene can help i would appreciate.

Thanks

I have this tread mill and the control panel to engage it has quit working. I have this crazy idea by just looking at this that there has to be a way to take power from the wall, and add 2 seperate switches that control the speed for the drive motor, and the posidtion for the incline motor. Obviously I can just wait for a marketplace deal but I like this tread mill, I also like making things work and trying to figure weird shit out like this lol.

Anybody here have experience with something relative to this?

I was looking for STM32G431 alternatives as the lead times have increased to 52 weeks! And the G4 series prices rose by almost 2-3x!

Any suggestions? Looking for uC with a good supply chain in India

The belt is new. I cleaned all of the pots and switches, as well as the the speed control pot. I'm wondering if this is somehow related to POWER? The speed seems somewhat consistent when it's laying flat on the desk, but you need to be able to walk with your Walkman, man!

Hi all-

I have a flood light that I don't necessarily need. It's battery powered by 3 C batteries. The issue is this: the timer sucks. I was going to use it in a shed that doesn't have power going to it, for the rare occasions I need light in there. But, the timer only lasts 30 seconds on. That doesn't work at all for me.

I'd prefer either a longer timer or no timer at all and just operate it via the on/off switch. I'm familiar with electronics and pcb's, ic's,etc.

Admittedly, I maybe over thinking this. My first instinct was to disconnect (desolder) the ic for the timer. Then, after some time to think about it, I also thought to just bypass the pcb altogether and wire the on/off switch to the unit directly. I'd still be interested in knowing which ic to desolder and if that route is even feasible.

I'm including a pic of the pcb along with the stampings on the ic's.

TL;DR: Is it possible/recommended to remove the ic controlling a timer for a flood light to have the light stay on longer or is it better to just rewire the on/off switch and bypass the pcb altogether?

The thing with the pins came with the ADS1115 but it’s a loose fit. After a couple days of debugging I discarded that the issue isn’t a programming one and I’ve confirmed that the ADS1115 does indeed work, cables are connected where they need to be and I measured the voltage on each pin, everything is right in that regard too.

In my engineering degree I learned the basics electrical stuff but no real formation with electronics; so I know enough to tell when an idea might be stupid but not how to not do something stupid.

I am making a prop camera for a project and I need to know how to make a circuit which creates a quick burst of light when you press the button, like a camera flash. I searched online but a lot of the results were either not what I was looking for or were over complicated. Thanks!

Component is on the top left in the first picture. Bottom left on the second. It’s a slide switch. I got my iron very hot, using a small piece of braid. And tons of flux. Mixing in some regular solder in before trying to wick off. Do I need to clip the pins to get it clean? I’m just trying to get the dang thing out.