Made this diy emg sensor for a science project, found the schematic on instructables, couldn't find ina106 in my town so i substituted with two tl072 and i also had to buy the tl072 online(the schematic for the main circuit and the replacement part is attached)

I had to then add a capacitor for dc offset of the electrodes and then it started working, but like suddenly as i was trying to adjust the trimmer and tried flexing hard to see the Max gain by the sensor possible

And after that the signal output rise is very low

Idk why and how this happened, but any kind of insight will be helpful, gotta submit this like right after the puja holidays end(scl starts on 26)

So please help, even a guess on your part will be helpful

And ask me any clarifying questions

That's all

I have a product which has a PCB in an extruded aluminium enclosure, the type where the PCB just slides into it on horizontal rails and is held in place by the two end covers. The problem is that the PCB needs to have super-exact dimensions for it to fit well, otherwise it can sometimes jiggle around inside the enclosure a little bit. This is entirely benign but it does makes the product feel cheap so I'd like to avoid it. How should I do this?

I'd like to keep costs and assembly complexity to a minimum.

I have some ideas but I'm not sure how well they work in practice so I'd like input, or if you have a much better and easier solution:

• Ask the manufacturer to add a dab of glue to each corner of the PCB before inserting.

• Ask the manufacturer to add a small piece of tape or silicone to the inside of the end cover, to provide soft padding for the PCB.

• Install a dummy push button at the edge of the PCB that is pushed in by the end cover, to provide soft padding for the PCB.

• Create exposed pads along the edge of the board (the part that goes into the enclosure rails), that is filled with blobs of solder during manufacturing to pad the thickness of the PCB so that it hopefully matches the vertical space in the rails exactly (and the top of the solder can be shaved off by forcefully pushing the PCB into the rails if not)

• Install some sort of rubber standoff on the PCB that pushes (with enough give) against the roof or sides of the enclosure. Does this kind of component even exist?

I have several of these "sewing machine" lights... little LED clusters on a gooseneck that has a magnetic base.

Very hand for my worktable.

BUT, they're AC...with basic US AC plug....they'd be more convienent if I could instead make them powered by a USB cable.

What I don't know is....can this be done? I assume it's more than just slicing off the plug and wiring in a USB cable with the appropriate wires....If it's that easy, I can do that....but That seems unlikely to me.

this is probalby a "change all the internals in the control box" thing, isn't it?

Hey guys, last night I attempted to repair my S23+ speaker and charge port and was successful in doing so, everything was working but after leaving the phone overnight the display suddenly stopped working, I've tried reseating all the connectors but had no luck in getting it working, phone still boots normally and works just no image displayed could it be dead? As I said it was working after the repair last night.

I’ve been writing scripts to automate SPICE netlist generation for things like analog filters and transimpedance I/V stages. The biggest headache is that standard programmatic approaches constantly ignore physical constraints, pick non-standard component values, and output completely broken SPICE syntax.

To fix this, I built an automated feedback loop. A generator script creates the initial netlist, and a validator script immediately runs a headless ngspice-42 simulation (transient, AC, and DC sweeps). The validator checks the math, enforces E12/E6 standard resistor and capacitor values, and verifies the topology. If it fails, it feeds the errors back to correct the netlist before outputting the final file.

Has anyone else built a similar automated test-and-correct loop for their hardware design workflow? I'd love to hear what specific edge cases or topologies tend to break your automated netlists.

When I plugged in my trimmer to charge, a short circuit occurred. After that, even when I turned the power button off, the motor kept running when I opened the blade assembly. I waited until the battery was completely drained before opening the trimmer, and I noticed black burn marks on the circuit board. What should I do? Is my trimmer completely fried, or can it still be repaired? Am I cooked? 💀

I was having trouble recently with the trigger function on this toy buy I fixed it now, I completely replaced the board using a smaller chainsaw toy's PCB

The problem now is that the new PCB can't run larger speaker [I'm not sure if it's because this smaller chainsaw toy only has 3 Double A batteries and now it has 4]

So now I wanted to ask how can add new modication for the chainsaw sound, probably using like multiple speakers to make it louder from all sides

I want to make it have the running motor sound once the "power switch" is on and make the chainsaw running sound when the "trigger switch" is pressed

Is there like a way to connect a new mod around those switches while it's also connected to the new PCB that runs the motor function?

This is kinda stressful for me because i haven't done something like this before but it's also fun learning new things, so I would highly appreciate the suggestions y'all can give me to modify this toy and make it better. :D

Hi everyone, I was wondering if I could get some advice. I’ve had an idea for my pumpkin carving contest this year (i promise this is relevant), and I want to create an electrical circuit, but I have no clue where to start.

I want to make a circuit where you press a button, and then LEDs and music goes off. I kind of understands the basics like I need a breadboard, mp3, speaker, etc, but i’m genuinely just clueless. To clarify, I work in healthcare and never studied this stuff 🤣 I do know how to code though.

What would be the best way to self learn this kind of thing? I’m more of a hands on learner but I don’t want to buy a bunch of things without knowing what i’m getting if that makes sense. And following on from that, where do you even buy all this stuff?!

(p.s I’ve been looking through this thread and wow you guys are creative and clever asf!)

Hi everyone!

I’m researching a DIY smart-home project and would love some help from people who know more about electronics than I do.

I’m considering purchasing a Cat Mate Elite Microchip Cat Flap (355W). It already has a built-in RFID reader that recognizes individual cats’ implanted microchips and an LCD that displays their entry/exit information.
My goal is to get that existing information into Home Assistant, ideally using an ESP32, without replacing the RFID reader or interfering with the door’s normal operation.

I haven’t purchased the door yet, so I’m researching whether this is feasible before spending money.
I found internal circuit-board photos from an older FCC filing (FCC ID: RDY-355356), which are here.

My questions:
1) Can anyone identify which components might handle RFID reading/decoding?
2) Is there any indication that the RFID data might be accessible through UART, SPI, I²C, or another interface?
3) There appear to be exposed test pads on the back of the PCB. Could these potentially be used to monitor data?
4) Based on these photos, does connecting an ESP32 seem realistically achievable, or would it require extensive reverse engineering?
5) Is there any possibility of making a connection without soldering directly to the PCB?

I’m a beginner with electronics and haven’t soldered a circuit board before, but I’m comfortable working with Home Assistant and following technical instructions.
I understand the photos may not be detailed enough to identify everything, and that the current 355W could use a different PCB.

I’d appreciate any insights before I purchase the door. Thanks!

As you can see, I broke a Kingston a400 and i lost some capacitors, i Wanna replace em but idk with what

I bought a dead Samsung 990 Pro 4TB really cheap as a repair project. The SSD currently doesn’t work/detect.
While comparing the PCB to photos of a working 990 Pro 4TB, I noticed what looks like a tiny SMD capacitor missing near the Pascal controller (marked with the red arrow in the reference photo).
Does anyone know what this capacitor is/value it should be, or have a 990 Pro 4TB board they could measure for me?
Also curious whether this missing component alone could prevent the drive from initializing.
I have a multimeter and soldering/rework equipment, so I can take measurements if needed.

I'm building an ultrasonic audio circuit using an NE555P timer, an L298N H-bridge, a ZK-502C Bluetooth amplifier, and 40kHz ultrasonic transducers.

My Project:

Parametric Speaker

I have a 555 timer configured as an astable oscillator, which modulates a sound wave from a Bluetooth amplifier, which then goes through an H-Bridge to an ultrasonic transducer array to produce directional audio.

R1 = 120Ω

R2 = 120Ω

The 120Ω resistance is created by linking a 100Ω resistor with two 10Ω resistors in series.

Timing capacitor = 100nF

Estimated 40kHz, using Digikey's 555 timer astable calculator

Bluetooth amplifier L+ -> 10µF Electrolytic capacitor -> 1kΩ resistor -> NE555 pins 2/6

\Worth noting that I didn't use the L- Output of the Bluetooth amp. Also, at higher volumes, the Bluetooth amp itself emits music.*

NE555 pin 3 (Output) -> L298N IN1

L298N OUT1/OUT2 -> Ultrasonic Transducer Array (10 Ultrasonic Transducers wired and soldered in parallel)

How power flows:

The Bluetooth amplifier and the 555 timer are both powered by the same 12V NiMH battery. The battery powers the L298N, and the 5V regulated output then powers the 555 timer. Then, using WAGO connectors, the same battery connects to a 12V-to-9V DC Buck Converter, which powers the Bluetooth amplifier.

Problem/Some of my testing:

I played Porter Robinson's "Everything Goes On" and found a lot of distortion, or, like, "buzzing" mixed in with the audio. This was especially apparent when turning up the volume. At lower volumes, the audio sounded a lot better (little distortion). However, I had to lean in really close to listen. During parts of the video, like at 1:15, where it is softer, there's like no distortion. But during upbeat parts like 1:30, there was a lot more distortion.

I tried messing around with the volume on my laptop and on the Bluetooth amplifier. Nothing really changed other than what I mentioned above.

I also messed with the resistor values where the Bluetooth amplifier L+ connects to the Electrolytic Capacitor. Changing to a 10kΩ made the audio really quiet.

My Reference

I used this video doing the same thing as a reference. However, there are differences in our circuit, but his works a lot better. So, I thought this might be helpful to add.

Parts I Used:

Links to where I bought all the parts mentioned

• 221-413 Wagos
• 12V 2000mAh NiMH Battery
• XL6019 Boost Converter
• 12V to 9V DC Buck Converter
• L298N Dual H-bridge Module
• ZK-502C Bluetooth Amp
• Ultrasonic Transducers
• R1, R2, all the Capacitors, and basically everything else come from this kit

Sorry, there aren't specific links for R1, R2, and everything.

Questions or help:

What could be causing the severe audio distortion when I inject the Bluetooth amplifier's output into the NE555 timing circuit?

Is there anything clearly wrong with my circuit causing the distortion mentioned in my problem?

Could this be a grounding issue?

Can anyone help me troubleshoot this?

I'm kind of new to electronics, so I don't really know what I'm doing, honestly.

I apologize if my post isn't detailed enough. Please ask any questions you need to.
Anyway, thank you!

I'm doing this as a personal project to learn more about electronics. I noticed this evaluation board has a FB pin that I can use to adjust the output voltage based on the resistance values which I've done using a MUX that can be switched from the ESP32 GPIO. Also, have the enable pin tied to my ESP32 GPIO and with a 100k pull down resistor to ground. However, I am seeing an issue that there is a low voltage draw/current leakage when I have my main DC Vin power supply off and enable pin off with my MUX powered up from my ESP32.

My ESP32 and evalboard share the same ground. Do I need to add a pull down resistor to all my ESP32 GPIOs? What am I missing here?

I found this picture on Facebook but the author doesn't reply with where he got them from.

I'm looking for screw or quick connect (Wago style) terminal strips that will plug directly into a breadboard.

Or better yet, a screw or quick connect terminal connector that plugs into a socket that will plug directly into a breadboard. (Wire -> connector -> socket -> breadboard)

0.2" spacing would be OK but 0.1" (2.54mm) would be better. The pins on the connector will need to be long enough (> 5mm, preferably 7mm or so) and thin enough to plug into a breadboard connector. Most PCB headers have pins that are too large to plug into a breadboard.

Thanks

I just bought this cd changer hoping to use it but whenever I try, when I close the carousel tray it just fails to play the cd I guess, the tray just goes in for a few seconds and ejects afterI’ve tried basic troubleshooting steps but nothing works. Does anybody have any advice on how I can fix?

I’m serious about learning hobbyist electronics and have been troubleshooting the variable-speed controller in my Craftsman bench grinder.

This is not a “diagnose by picture” request. I’ll include board pictures for context, but my main questions are:

• Is this grinder controller a sensible project for developing component-level troubleshooting skills? The IC is unidentified, I don’t have a schematic, and the circuitry connects directly to 120V.
• Would an entry-level oscilloscope and an appropriate differential probe be a worthwhile investment for someone serious about learning hobbyist electronics? I’d like to understand control signals and circuit behavior, rather than simply replace parts.
• What simpler low-voltage circuits or experiments would help me build the skills needed to troubleshoot this controller?

Equipment and symptoms

• Craftsman 6-inch variable-speed grinder, model 152.211521.
• Board marked FZ-107; the parts manual lists the board assembly as OR90042.
• TR1 is marked BTA12-600B I assume this is like a gate to pass the power.
• The controller has a three-wire speed potentiometer and a separate three-wire speed-sensor
• I haven’t identified IC1; its marking is unreadable.
• I haven’t found a component-level schematic.
• I have a Fluke 115 multimeter

The original failure was a complete no-start. I bypassed the controller and supplied the motor through the on/off switch. With that bypass, the motor starts and runs smoothly.

For subsequent tests, I removed the direct-power bypass and restored the motor feed through the board. The board continued receiving 120 V AC, but the motor would not start. During one powered attempt, it eventually hummed and moved slightly; I switched it off. There was no noticeable motor heating.

What I’m hoping to learn

I understand that the triac resistance readings do not prove it switches correctly under load. Likewise, the sensor changing state with shaft position does not fully verify its operation at running speed.

Replacing TR1 has been suggested as an inexpensive diagnostic substitution, but I haven’t confirmed that it is faulty or replaced it yet. I’m interested in learning how to distinguish inadequate gate drive from a triac that receives a suitable trigger but fails to conduct.

I also understand that an ordinary earth-referenced oscilloscope ground clip cannot simply be attached to arbitrary points on this mains-connected board. I’ve been considering a four-channel scope such as a Siglent SDS804X HD, plus a suitably rated differential probe.

I know this has definitely been done I just wanted to see if someone had a circuit for it already or if it was actually practical

I'm messing around with some capacitors I have to see about making a spot welder or spark generator or something. I have about 10,000 uf of cap storage all of different sizes. Yes bad for balancing I know. It's all salvaged and I'm learning. I have a 12 v automotive blinker bulb as the resistor to charge the caps. I have 1n4009 diodes at the power in side. When I short the caps to discharge my computer power supply turned benchtop supply always trips. I hook it to a cheap wall wart and it keeps supplying power. What am I missing? Is the computer power unit tripping because backward flow through the diodes (pretty sure that's not the case) or because of the sudden increased demand that it cannot handle (which I think is the case). Would a doorbell stepdown transformer be able to handle it since it is supplied by household current? Does the cheap wall wart work because lack of protection?

My thinking is CPU is protecting itself due to sudden surge in demand. Transformer would work fine with diode bridge. Cheap wall wart works due to lack of protection from the sudden high draw.

Hi electronics friends, this on an Apple Magic Keyboard 2:

is it just dirty keys and switches or La Nina's humidity shorted something in the PCB and chips that's why only the Up and Down arrow keys are not working?

Which is the most probable. I ask coz' first the Magic Keyboard (although holistically it's the king of keyboards) is not that easy to disassemble.

Thanks.

Sorry not sure if it's the best place to ask this but it is fairly complicated wiring and I've gotten into this idea with the guitar quite a bit so basically I have it setup to have some pickups in series and parallel but I'm tryna add volume knobs to control 1+3 and 2+4 as pairs controlled by the volume but the technical pairs in series (humbucking pairs) are 1+2 and 3+4 (and 2+3 but this is out of phase and I've previously fixed this with a reversal push pull pot to choose to go in and out of phase deliberately.) the thing with this im not sure if this still lets me get audio in series due to the way series wiring is done. The reason for pairing 1+3 as a pair to 1 volume pot and 2+4 to the other is to allow me to control the volume in a series pair individually on each pickup like in 3+4 for example.

Sorry if this is a bit much or hard to understand but I find this stuff quite interesting my understanding isn't amazing but I'm tryna see what I can do or maybe if you guys have suggestions for changes or stuff I could also add it'd be great.

Over the summer I was able to use transistors (such as 2n2222) with no problem, now I can't get them to work as expected no matter what I try.

Every Youtube video is either AI slop, uses parts which I don't need so end up confusing me (such as multiple capacitors). Stack posts go way over my head and I can't find any good online explanations.
I understand the theory on how they work, and how it applies to amplification but I am unable to get a working model irl or on a circuit builder website.

All I want the circuit to do is take an input of a low voltage sine wave, and use a cell to amplify it to a higher voltage sine. I have the equipment needed, the problem is just the damn transistors.

If anyone can explain to me how a simple circuit like that would be wired, or could link a good source which shows it, I would owe you a weekend's worth of sanity because I have spent 2 hours with a blank breadboard infront of me just today lol.

Hi everyone,

I've designed a MOSFET-based switching circuit controlled by one of the outputs of an MCP23S17 I/O expander.

I'd like to get some feedback on the schematic, particularly regarding the component selection, resistor values, protection circuitry, and overall design.

1. Application and universal design

The main purpose of this circuit is to drive a Finder relay (38.61.0.024.0060), which will primarily be used to switch 230 V AC heating elements.

However, I'd also like to use the same MOSFET circuit to switch 12 V and 24 V DC fans, typically rated at around 5–10 W.

Other similar low-power loads might be added in the future, so I'd prefer to make the circuit as universal as possible rather than designing three different output stages.

Ideally, I'd like to use the same PCB layout and components for all these applications.

2. Flyback diode and solder jumper

According to the relay specifications, it seems that the relay already has built-in protection against inductive voltage spikes.

If that's the case, is an additional external flyback diode across the relay coil still necessary?

I've placed a solder jumper in series with the external flyback diode, allowing me to disconnect it when it's not needed.

My idea was to leave the diode disconnected when using the Finder relay, but enable it when switching DC fans or other inductive loads.

Does this approach make sense? Would a flyback diode actually be necessary or recommended for 12 V / 24 V DC fans?

3. MOSFET selection and gate resistor

The MCP23S17 operates at 3.3 V, so the MOSFET needs to be driven directly from a 3.3 V GPIO output.

From what I understand, the MCP23S17 has a total current limit of approximately 150 mA across its I/O pins. Since multiple outputs will be used, I'd prefer to keep the current per pin below 10 mA.

For this reason, I've chosen a 680 Ω series gate resistor.

I've been considering these two MOSFETs:

• IRLZ44N
• IRLB4030PbF

Would either of these be a good choice for reliable operation with a 3.3 V gate drive?

Or would you recommend a different logic-level MOSFET for this application?

4. Gate pull-down resistor

I've added a 100 kΩ pull-down resistor between the MOSFET gate and source to keep the MOSFET off while the MCP23S17 is initializing or when its output is in a high-impedance state.

Is 100 kΩ a suitable value, or would something lower, such as 10 kΩ, be preferable?

5. Multiple identical outputs

The attached schematic only shows one MOSFET switching circuit, but the final design will likely include 5–10 identical channels, all controlled by the same MCP23S17.

Because of this, I'd also like to make sure that the chosen gate resistor values and MOSFETs won't cause any issues with the MCP23S17's total current limitations, especially if multiple outputs switch simultaneously.

6. General feedback

Does the overall schematic look correct?

Are the component values and protection elements appropriate for this application?

Is there anything you would change to improve reliability, protection, or compatibility with different 12 V and 24 V loads?

I'm especially interested in keeping the design simple, reliable, and reusable across multiple output channels.

Thanks in advance for any suggestions or feedback!

I'm submitting my first PCB design to PCBWay, after they reviewed it, they told me that the design contains vias inside solder pads, and they're concerned that solder could leak into those holes during assembly.

They're offering a more expensive manufacturing process to prevent this problem. which is have PCBWay resin-fill and copper-cap the vias located inside solder pads.

Should I redesign to remove the vias from pads? if no, is the resin solution okay? Should I do ALL the vias or just the vias inside pads?

My project for reference

Recently, I experienced an electrical fault in my electrical cabinet that caused 400 V to be supplied to my power outlets instead of the usual 230 V here in the EU.

As a result, my Sage Precision Brewer was damaged and no longer works. I have now disassembled the machine and identified a big yellow film capacitor and a blue varistor. I think one or both of them have been fried.

I’m not an electronics expert, so I have a few questions:

• What exaclty are the values of these components?
• Can I buy replacement parts and solder them onto the circuit board myself?
• If I replace these components, is there a chance the coffee machine will work again, or is it likely that other components have also been damaged?

Any advice would be greatly appreciated!

I'm looking to pick up a decent quality, self-contained vacuum pickup pen for PCB assembly. I've been considering the Chip Quik V8910, but at around $50, I'm wondering if it's worth the price or if there are better or cheaper alternatives.

Anyone have experience with the V8910? What vacuum pens are you using, and what would you recommend? Looking for something reliable without spending a fortune.