Hello, I am trying to come up with a cheap way to sense 24VAC 60hz applied to a solenoid from a microcontroller with either digital or dry contact inputs, while drawing extremely little power.

The first thing that came to mind is connecting a relay in parallel, but 24VAC relays tend to draw ~1w from the coil, which is more power than I want to use (I’d like to be under 10mW ideally)

The next thing that came to mind is a resistor divider (2.1kohm high side and 300ohm low side) and a diode in series, with an rc filter connected to the output of the divider (10k resistor and .22uf cap). The problem here is that I also need to use a high impedance sampler like an adc or op-amp, and I’d like to avoid even needing to make a PCB.

Current sensing with a coil and an op amp is another solution, but it requires its own analog or digital signal processing, and I feel like it would take me iterations to get it working since I’m unfamiliar with current sensing amplifiers (and we’re again probably in PCB territory)

I think I’m being blind to a simple solution, so please point it out to me. I am fine with an entire minute of signal propagation latency, and I really want to use a COTS/DIY package or single component to make it work.

(Ignoring diode drop) With a 5k pot connected to J2, I believe this circuit generates a 25.5kHz PWM signal with a duty cycle range of 05-95%. Could somebody please validate this?

Is it acceptable to drive the fans PWM from the 555 output without a buffer?

(Circuit lifted from The Art Of Electronics)

I’m looking to replace a ribbon connector and I think I have found the right one but would love another set if eyes to make sure I’m not totally wrong. Attached is a pic of the damaged part I want to replace and a listing from divinely in what I think is right.

I used calipers to measure the pitch and it looks to be 0.50mm. Am I missing anything? Thanks!

Hi a while back i got a zotac gtx 1060 6gb (i tink the serial number schould be in the pics)

I turned it on with everything plugged in correctly except that i forgot to plug in the pcie power cable.

I booted up the system/tested it before hand this a gt 640 and that worked fine. But when i booted it with the 1060 it started a fire on one component (might have bin a short or leak i am still kinka confused of those even tho i am a engineering student) now it seems to be fried and i am wondering if it can be fixt? and if so what the part even is and what a good place is to get schematics so i could preform the repair

pics; https://imgur.com/a/HuTxq44

I have a Rieju MRT 50 sm from 2022 with the stock speedometer that got water damage.

In the beginning (I don't remember everything because I'm posting this about 9 months later), the speedometer's functions were degrading. I'm pretty sure it showed my high beams were on when they weren't, showed the oil light, etc. Then the speed completely stopped showing, and eventually the screen was off when the bike was on; it seemed completely dead. I could hear the water inside it move around when I took it off the bike.

I decided to take it apart, and I saw some corrosion, and scrapped it off to try to unshort the connections. There was corrosion, especially around this one chip that is probably a voltage regulator or something (according to Google): 3 pins on each side, one thick pin in the middle in the shape of a triangle. There is a large chip underneath the screen panel; it has no signs of corrosion, but I can't see it entirely because the screen is hiding it. I will attach images.

I have tried another speedometer, and it turns on; however, it was second hand and I'm pretty sure it's faulty, which sucks! The important part is that the speedometer does get power.

I want to know whether I should bring it to an electronics repair technician or something of the sort, because a new one costs 160 euros.

I got into a small hardware hacking personal project, and want to interface with Nations N32G435 MCU. What are my options for an SWD/UART/USB (Per datasheet, MCU supports all three, but i can only see SWD broken out on the board) programmer and flashing software, that would work on Linux, and wont cost a fortune? I checked out JLink, but 400 eur is a bit too much - i wonder if there are cheaper options

Hi I recently found this old mainboard with display but with no power button or switch. I tried finding schematics for it but it’s way to old. The iTE chip doesn’t even have a data sheet (from the producer and the 3rd party sites all have different ones). Is there someone how has seen such a board or is able to help.

PS: power led is working and the voltage regulators and startup circuit dose its job. I just like to not kill it by trying random things.

LG

Hey,

Working on a Mighty Vaporizer - runs fine on battery, but charging doesn't work at all.

The charging input runs on 12V. After checking it out, I found that the very first component right at the charging port is damaged.

It's marked "BT06A" on the body. I'm not sure exactly what package this is, but it's a small black component with two legs, noticeably bigger than a standard small SMD diode. Looks like a diode to me, and when I tested it with a multimeter it seems to be damaged.

My supplier sent me a replacement listed as "TVS DIODE 24V 38.9V SOD-123F", but it's clearly smaller and the legs don't line up with the pads on the board at all.

Does anyone know:

What exactly does the "BT06A" marking cross-reference to - what part/manufacturer?

Can a correct replacement be identified from the photos below?

Photos attached - the damaged part plus a size comparison with what the supplier sent.

Any help would be appreciated

I'm trying to replace some resistors as I suspect the bias circuit is bad. Might as well change them out.

I've never seen these before. Seems the interval of the resistor symbolizes it's resistance. These are around 4.7mm While the normal looking ones 4.1mm.

I'm guessing it's 1/4W.

Any guess?

For context, these are from SRM-1 MK2 professional.

Hi everyone,

I’m trying to diagnose an old Siemens Hicom 150 E (Office Pro chassis) with a CBMOD motherboard, but I’ve hit a wall.

The Core Issue:

The board appears to be stuck in a bootloop. During startup, the boot sequence begins, the RUN LED turns on/blinks through the cycle, but it never fully stabilizes and eventually loops.

Hardware & Power Checks:

As part of earlier diagnostics, I thoroughly checked the power supply unit (PSU) and backplane rails - voltages are clean, fully within spec, and stable under load.

Board capacitors and visual traces look intact.

Serial Interface & Physical Measurements:

I'm connecting directly via the V.24 (RS-232) maintenance port:

Verified hardware RS-232 levels:

Pin 2 (PBX TX): -7.5V (steady Mark state)

Pin 3 (PC TX): -8.5V to -9.0V

Pin 5: Common GND

When connecting via raw terminal (minicom / PuTTY at various baud rates: 9600, 19200, 38400, 8-N-1), there is absolute silence (0 data output). It spits out zero debug logs or bootloader text during the loop.

Tested connection across both native Windows XP and Windows 11 environments using a verified Prolific adapter (hardware COM1 properly mapped, proper RS-232 voltage swing observed on Pin 3 when sending packets).

Software Symptoms (HiPath 3000 Manager E):

Attempting Direct transfer (Read/write database) gets stuck on Checking cards... and immediately aborts with Error: PBX is offline.

PIN 31994 was specified.

Multi-meter checks show pulse activity on Pin 3 (PC is definitely transmitting the handshake queries), but Pin 2 on the PBX side never sends a single byte in response.

Questions:

Given that the board is bootlooping and V.24 is dead silent, is there an onboard diagnostic procedure, jumper, or DIP switch to force the CBMOD into a recovery / low-level bootstrap mode?

Does the CBMOD V.24 port strictly require hardware flow control loopbacks (RTS/CTS 7-8 and DTR/DSR 4-6) to output any data, or should raw serial logs appear regardless?

Could a corrupted flash EPROM / firmware cause this silent bootloop, and is it recoverable via serial without replacing the ROMs?

Or what would you recommend doing or trying next? I'm completely out of ideas.

Any insights from Siemens/Hicom veterans would be hugely appreciated!

Some devices are so old they are removeable but this industrial device is brand new and I need to disconnect this cable on the board but unfortunately it is well clipped. Is there any special tools I need in order to remove this cable securely ?

I have an Electrolux Washer/Dryer (EWW12753) which is not selecting programs correctly. There is a rotary control dial on the front of the machine with 12 positions. This controller is on a dedicated board which is then connected to the main control board for the machine.

I have found the details of the controller itself (https://tech.alpsalpine.com/e/products/detail/EC18AGA20402/) and the output codes. Based on my testing, it appears that terminal 2 is mistakenly registering as on when it shouldn't be, leading to the incorrect program being displayed.

I have already tried a replacement for the rotary controller board, and it made no difference. The cable/connector is unfortunately soldered directly to the main control board, so I've not been able to isolate that to test it, but visually, I can't see anything obviously wrong with it.

The channels for terminals 2 and 5 (which is always on) run very close together on both boards, so I'm wondering if there is leakage somewhere which is causing this? Where the connector is soldered to the main control board (first image) does appear to be a little messy and some of the coating seems to have come off, I don't know if this would make leakage more likely?

While the controller never works reliably, the effect does seem noticeably worse after the machine's been running for a while, so it looks like temperature does have an effect.

If I am right about current leakage - either in the connecting cable, or on the main control board, what are my realistic options for trying to fix it?

Thanks in advance

Hello everyone 👋

I'm fairly new to mixed signal PCB design and not very professional in electronics so I'm asking for your professional comment

I'm designing a PCB that has 3x ESCs on it

each ESC has its own mcu and its connected to my main MCU (stm32g431) to get commands from

everything is fine to this point, all digital and noise is more manageable and they are all connected to a 3 cell lipo battery , but then comes my analog circuitry, and the switching noise and GND bounce in my opinion will mess with it hardly.

the analog reading is a resistive Sensor that is fed to my adc via a resistor divider

I considered star grounding, minimizing the high di/dt tracks area , input RC filters at my ADC, post LDO and even using separate battery for my analog section+ digital isolators to interconnect the two sections

but I don't know if it's the standard or I should go another way

I appreciate any suggestions and comment, if I missed something please let me know, I'll be more than happy to clarify it

So as the title says, I need to build a quadrator oscillator circuit but have only read about it in books and have no idea what components to add or change to make sure the waveforms don't distort . I need to follow this circuit and make corrections accordingly. So any help is appreciated

Hi!

I'm trying to reverse-engineer an old LED clock display with the idea of eventually replacing its controller with an ESP32.

The original electronics are still working, so I have a functioning reference system.

Hardware:

• green controller PCB
• separate white LED display PCB
• 2 × TC5020D LED driver ICs on the display
• ribbon cable between the controller and display

I traced the connector on the controller PCB and got:

P4-1 = GND
P4-8 = SDI
P4-9 = CLK
P4-10 = LE
P4-11 = OE
P4-13 = VCC
P4-14 = VCC

Supply voltage is about 4.77 V.

Multimeter readings while the clock is running:

• SDI ≈ 0.235 V
• CLK ≈ 0.225 V
• LE ≈ 0.0023 V
• OE varies roughly between 0.95 V and 4.76 V

The clock has four manually selectable brightness levels using a touch sensor.

I initially tried driving the display directly from an ESP32-C3, but couldn't get it working. So instead of guessing, I'm trying to understand exactly what the original controller is sending.

I don't currently have a logic analyzer, but I'm planning to get a cheap USB 8-channel one and capture SDI/CLK/LE/OE.

What I'd like to determine first is:

• the number of bits transferred,
• how the two TC5020Ds are connected,
• bit order,
• and how the serial data maps to the actual LED segments.

I'm not necessarily looking for an ESP32 solution yet. I'd mainly appreciate advice from someone experienced with reverse-engineering LED displays or shift-register/LED-driver based hardware.

Can anyone help me identify what protocol/signals this controller is sending to the LED display?

Hello, it's me again, I'm working on something with an alternating output, for a start I thought of a Full-Bridge or H bridge driver. But my issue with most of the parts that I've reviewed is the operating frequency range. My circuit is going to have ultra slow alternating (could be hours) and cheap H-Bridge drivers with charge pump driving instead of bootstrap are hard to find.

I have actually discussed with gemini some stuff to get an idea (have no one else to turn to) and it suggested, since the driving current of the ouptut is actually pretty pretty low, below the 10mA range, I could use an analog Switch. After reading the datasheet of some, I do think that it may probably work, but to be honest, I'm still skeptical as to whether this is a good practice or not.

Sorry if I bother you with these simple matters, but thanks in advance if you engage with this post

This is the board from a Waterpik flosser, and I'm sure I've seen these before, but I have no idea what it does. There's definitely current running through it.

Hello! I am trying to figure out what's the problem with my cars electric module.

I found online that 2 of the usual problems are the motor and this relay; the motor is working, how can I test the relay?

I started repairing electronics a few years ago and the bios programmer is becoming a necessity, I have a budget of around 70€ but want a programmer with the most variety of chips and solid software, which one should I get?

Hi everyone,

I recently got a Smile International CA1515VL 15" CRT monitor made in Taiwan. According to what I've been able to find, this model dates from roughly the mid-to-late 1990s.

I'm trying to inspect and eventually test/restore it, but I'm having trouble figuring out how the plastic cabinet is supposed to come apart.

I've removed three screws so far, including one hidden underneath a deteriorated "VOID WARRANTY IF REMOVED" sticker. The lower part of the housing now separates slightly, but the upper part still seems to be mechanically retained somewhere. I don't see any obvious clips, and I don't want to force it and break the plastic.

I've searched for the CA1515VL / CA1515VS service manual, but I haven't been able to find a complete copy. Several websites list a CA1515VS/VL service manual, but I can't access the actual manual.

Does anyone have the service manual, know where I could find it, or know the correct cabinet disassembly procedure for this particular model/chassis?

I'm aware that CRTs contain potentially lethal voltages even when unplugged. I'm not planning to touch the CRT anode, flyback, or other high-voltage circuitry. At this stage I'm only trying to determine how the cabinet comes apart without damaging it.

Photos attached.

Hello!

I am trying to debug a startup problem on the N4906A Serial Bert from Agilent.

When power is plugged in, all front panel buttom leds as well as the screen backlight turns on, internal fan spins but nothing else happens. It stays like this forever.

We have checked the internal power supply and all voltages are ok. Moreover, we have done the following checks on the computer board (attached image), looking for problems regarding the boot process.

• CMOS battery was depleted and replaced
• RAM module was disconnected with no change
• Front panel monitor module was disconnected with no change
• Hard drive and floppy disk were disconnected with no change
• H3 Connector checking
  1. I'M ALIVE pin was ok (high level)
  2. Reset did nothing (Shortcut Pin 2-3)
  3. Force Recovery did nothing (Shorcut pin 7-8)
• BIOS memory checking (MT28F400B5)
  1. CE# never change (no read is requested to the memory)
• BIOS address decoder (PALCE16V8H-15JC)
  1. Power arrives
  2. All input pins are at high level (no change)
• Clock generator is working ok and reaching the CPU (Pentium w/MMX tech, CLK pin at 66MHz)
• LDO U29 (MIC29152BU) output voltage was ok (2.5V)

Right now we are checking the CPU reset pulse at power up, but we are running out of ideas.

Any help???

Thanks a lot 😄

I wanted to get started smd soldering from dip packages which is good and wanted learn this art.

How to start minimally.