These are the insides of a witch’s broom toy that’s supposed to make noise and spin around. It isn’t working, even though we checked the batteries multiple times.

I’m thinking it’s the red wire attached to the motor that’s burned, but I’m not sure. Would yall be able to tell if somethings wrong based on these images? Sorry if they’re not clear.

I’m trying to pre amp an 8MHz signal and it’s not working.

I've got an original Elektor "MatchBox BASIC Computer" board from 1995 (8051-based, EEPROM program storage, published as a magazine project series). Finally decided to bring it back to life after years in storage.

The good news: after a lot of hands-on diagnostics (multimeter, then an 8CH logic analyzer + PulseView), I've fully confirmed the board is electrically healthy — serial UART works, I²C bus to the external EEPROM works perfectly, clean address/ACK/data on every transaction. I even erased and rewrote the EEPROM via an ESP8266 test rig to rule out a dead chip.

The blocker: the onboard monitor keeps throwing "IIC ERROR adr:xx" at boot. I'm pretty convinced it's checking for a specific config/signature at the start of the EEPROM that a real compiled MBL program (via the original MBC.EXE compiler) would normally write there — bytes I don't have, since I never owned the companion diskette (Elektor order code 956009-1).

Does anyone have a copy of the original MBC.EXE compiler, or even just one compiled .MBL program I could pull the hex bytes from? Searched archive.org, worldradiohistory.com, vintage computing forums — this seems to be one of the rare Elektor projects whose software never got archived online.

Happy to document/share everything once (if) I get it running. TL;DR: hardware's fine, need 30-year-old DOS software or its byte format.

Hi Guys,

Previously I have posted a question but due to the circuit diagram in the post, it deviated from the original question. If you haven't seen the previous post, it's fine. I'll explain everything clearly below.

I'm working on a project where I need to control a diesel injector. This is an academic project, if it goes well it shall get into industry level, so looking for a standard Good approach.

The diesel injector is activated by an Arduino(this is the initial setup, and will soon switch over to stm32). The diesel injector is outside the engine in a separate setup which gets supplied by a constant pressure fuel pump driven by an ac motor(const speed). I'm using a MOSFET to control the injector. The MOSFET I'm using is IRLZ44N. The drain of the MOSFET is connected to negative terminal of the injector and source of the MOSFET is connected to the negative terminal of the injector's power supply (i have added flyback diode for safety circuit for injector). The Arduino controls the injector via the gate pin of the MOSFET. The power supply for injector is 12v SMPS.

The Arduino gets signal from the injector's supply and control wires, we tapped these 2 wires and gave them to an optocoupler pc817. This optocoupler's output is given to the digital pin of Arduino. Arduino mirrors this signal to the gate pin of the MOSFET. You might wonder why I'm using Arduino, if the setup goes well, I will alter the pulse in future. So that's why I'm using it.

Issues faced:

1) this setup worked as intended, but after sometime, that is, after 2-3 weeks of testing this setup, the injector has gone. We didn't notice any smoke or smell, but the injector stopped actuating. We lost 2 injectors in this journey.

2) we started the engine and maintained in idling for 60seconds and started our injector setup, we collected around 90ml of fuel at idling, which feels abnormal.

Now, I need a reliable approach for this project. It would be really helpful if someone can come up with some idea for this.

Thank you in advance

Hi there, I'm basically working in a project where we are building a dual fuel injection system. For prototyping we are tapping the injection pulse of a fuel injector of a running engine and reading it via optocoupler and actuating another injector by pulse read by a microcontroller. We used Arduino for first stage of prototype, where the Arduino gets digital input from the optocoupler and adjusts the pulse width and gives out as output in a digital pin, which is connected to a MOSFET's gate pin. The drain and source pin of the MOSFET are connected between the injector's control line. 

But we need a more reliable approach, since the injector we are using is peak and hold diesel injector. Currently we referred few sources and built a circuit, which resembles something like in the image. But is there any better way to read the signal and controlling the injector pulses using a microcontroller? 

My goals:

• Set can be momentary or held
• Reset can't reset if Set is held
• RF shouldn't set or reset (my last circuit was very sensitive to my finger touching the mid point of the set and reset switches.

I'm just not sure how to select my resistors. 100K seems like it would make the circuit be more susceptible to noise, but then if I lower the values, I either get too much wasted current, or the circuit stop functioning.

https://www.falstad.com/s.php?s=qNHMeq

Hi all,

I'm trying to troubleshoot a Tectrol TC91S-1465 power supply (48V, used in some industrial/telecom equipment) and I'm running into a DC failure on it. It's a discontinued unit, so I'm having a hard time finding any documentation.

Does anyone happen to have a schematic diagram for this specific model, or know where I might be able to find one? Any help pointing me in the right direction would be appreciated.

Thanks!

555 Astable as a Capacitive Water-Level Sensor

I’ve been looking at a simple approach where the capacitive liquid-level sensor itself replaces the timing capacitor in a 555 astable circuit.

As the water level rises, the effective capacitance increases, which slows the RC cycle and lowers the 555’s output frequency. An ESP32 or Arduino can then measure the frequency and map it to the liquid level.

The interesting part is how practical this is in a real tank. Things like stray capacitance, electrical noise, long sensor wires, and water movement could potentially affect the frequency measurement.

Hey all, I wanted to see if anyone is interested in helping me in my efforts to add the ability to create technical schematics (such as circuit diagrams) into an open source framework that I have been working on.

The project is similar to PlantUML and MermaidJS - being a text based solution to "describe" a diagram, and have the drawing and layout handled automatically. But I was also interested in making it easier to extend so that it would support (just about) any type of visualization.

One of the areas I felt was missing from other solutions was the ability to handle technical schematics. That is something I am still in the process of working on, but there is some basic support :)

For anyone interested, you can read more at https://docs.runiq.org

I’m trying to understand how a 2-wire pinned circuit can provide both power and data to multiple client units.

1. Multiple client units sharing the same two wires for both power and data.

2. Purpose and function of D1 in the circuit.

3. Effect of D1 on the data signal during client transmission.

4. D1 creating a logical AND effect when multiple clients are connected.

5. Combining signals from several clients on the same two-wire bus.

6. Bus behavior when Client 1 sends HIGH while Client 2 sends LOW.

7. Each client distinguishing its own data from data generated by other clients.

8. Physical connection of additional client units to the two-wire bus.

9. Practical limit on the number of clients connected to the bus.

10. Factors determining maximum cable length, power capacity, and data speed.

Hi everyone ,

I am currently trying to interface the ADC and DAC with the eclypse z7 board , but I am facing issue in finding the resources to do so , can anyone guide me on how to do the interfacing. To mention , I have already tried out following the hackster.io tutorials but all the tutorials seem to use the outdated IP for the ADC and DAC and the IPs have been modified by Digilent.

Also I tried to implement the example designs by digilent , but wanted to make sure how the connection with ADC and DAC actually works.

Please help me if anyone has any idea to achieve this

I have a circuit that is supposed to latch when one of 4 inputs is low. Then if you take the DONE line and touch the +3.3V it unlatches. (The four inputs and the DONE line will eventually be connected to the GPIO of an MCU. The 10K resistors are recommended for the MCU's GPIO).

When I build it with two generic MOSFETs, it works, but the DONE wire is so sensitive that if I touch it, it relatches.

https://www.falstad.com/s.php?s=hFwWZO

What am I doing wrong?

Hello everybody, I am looking for some help creating a circuit that can translate button presses into a morse code letter.

The morse code alphabet can be displayed in a binary tree, with states branching from a short or long press. The other two button options to track are the space between letters and the space between words. Timing is as follows:

Short press (dit) - base unit of measure

Long press (dah) - 3x dit time

Space between characters - 3x dit time

Space between words - 7x dit time

The first part of the circuit would be to time and track these different options. The attached image is what I have so far. I know there are only three timings, but is the idea solid? Just RC timing circuits with an op-amp comparator on the voltage divider?

I worked with analog circuits in college, but that was some time ago. A good design review and some feedback would be much appreciated.

I used circuitjs to simulate the circuit, the below code block can be saved in a .txt file and uploaded to the circuitjs website to view and simulate the circuit

<cir f="1" ts="0.000005" ic="382.76258214399064" cb="59" pb="43" vr="5" mts="5e-11">
  <c x="-192 128 -144 128" f="0" c="1e-8" iv="0.001" sr="0.1" vd="-0.00009389816900907154"/>
  <r x="0 128 48 128" f="0" r="100000"/>
  <w x="-112 128 -128 128" f="0"/>
  <g x="-192 128 -192 144" f="0"/>
  <w x="-128 128 -144 128" f="0"/>
  <OpAmpReal x="-192 256 -272 256" f="3" slr="0.6" cl="0.023100000000000002" mt="0" vd="-0.3314506481694839"/>
  <R x="-224 288 -224 320" f="16" wf="0" maxv="0" ir="0.001"/>
  <R x="-224 224 -224 192" f="16" wf="0" maxv="5" ir="0.001"/>
  <w x="-128 240 -128 128" f="0"/>
  <w x="-192 240 -128 240" f="2"/>
  <R x="-32 208 0 208" f="16" wf="0" maxv="5"/>
  <r x="-48 208 -48 256" f="0" r="10000"/>
  <r x="-48 288 -48 336" f="0" r="10000"/>
  <w x="-32 208 -48 208" f="0"/>
  <w x="-48 272 -48 256" f="0"/>
  <w x="-48 272 -192 272" f="2"/>
  <w x="-48 288 -48 272" f="0"/>
  <w x="-48 336 -48 400" f="0"/>
  <w x="-352 256 -272 256" f="2"/>
  <g x="-48 608 -48 624" f="0"/>
  <r x="-48 416 -48 464" f="0" r="100000"/>
  <w x="-352 384 -272 384" f="2"/>
  <w x="-48 400 -192 400" f="2"/>
  <w x="-192 368 -128 368" f="2"/>
  <R x="-224 352 -224 320" f="16" wf="0" maxv="5" ir="0.001"/>
  <R x="-224 416 -224 448" f="16" wf="0" maxv="0" ir="0.001"/>
  <OpAmpReal x="-192 384 -272 384" f="3" slr="0.6" cl="0.023100000000000002" mt="0" vd="-0.3314506639423478"/>
  <w x="-48 400 -48 416" f="0"/>
  <w x="-128 368 -128 240" f="0"/>
  <OpAmpReal x="-192 512 -272 512" f="1" slr="0.6" cl="0.023100000000000002" mt="0" vd="-4.76290601338709"/>
  <R x="-224 544 -224 576" f="16" wf="0" maxv="0" ir="0.001"/>
  <w x="-192 496 144 496" f="2"/>
  <w x="-48 528 -192 528" f="2"/>
  <w x="-352 512 -272 512" f="2"/>
  <w x="144 496 144 320" f="0"/>
  <w x="144 320 128 320" f="0"/>
  <w x="256 320 144 320" f="1"/>
  <r x="256 320 304 320" f="0" r="100000"/>
  <c x="80 320 128 320" f="0" c="1e-8" iv="0.001" sr="0.1" vd="4.999999478361566"/>
  <R x="80 320 48 320" f="16" wf="0" maxv="5" ir="0.001"/>
  <R x="-224 480 -224 448" f="16" wf="0" maxv="5" ir="0.001"/>
  <r x="-48 544 -48 592" f="0" r="10000"/>
  <w x="-48 592 -48 608" f="0"/>
  <w x="-48 544 -48 528" f="0"/>
  <w x="-48 464 -48 528" f="0"/>
  <R x="304 128 304 96" f="16" wf="0" maxv="5"/>
  <R x="304 320 304 288" f="16" wf="0" maxv="0"/>
  <R x="48 128 48 96" f="16" wf="0" maxv="5"/>
  <R x="304 48 304 16" f="16" wf="0" maxv="0"/>
  <dpdt x="224 64 288 64" f="0" p="1" po="2"/>
  <w x="304 48 288 48" f="0"/>
  <w x="224 64 -128 64" f="1"/>
  <w x="-128 64 -128 128" f="0"/>
  <w x="144 112 144 320" f="0"/>
  <w x="304 128 288 128" f="0"/>
  <w x="0 128 -112 128" f="1"/>
  <x x="-420 263 -367 266" f="0" si="24" te="Long"/>
  <x x="-426 392 -369 395" f="0" si="24" te="Short"/>
  <x x="-436 514 -368 517" f="0" si="24" te="Space"/>
  <x x="207 26 276 29" f="0" si="24" te="Button"/>
  <b x="176 -16 376 164" f="0"/>
  <w x="224 112 144 112" f="1"/>
  <b x="79 81 -343 165" f="0"/>
  <x x="-332 109 -215 139" f="0" si="24" te="Long/Short\nRC Timer"/>
  <b x="454 269 32 353" f="0"/>
  <x x="340 307 441 337" f="0" si="24" te="Space\nRC Timer"/>
  <b x="-82 194 30 654" f="0"/>
  <x x="38 621 124 651" f="0" si="24" te="Voltage \nDivider"/>
</cir>

Thanks

This configuration saves battery power by reactivating the LoRa circuit only when necessary. When the door or flap opens, the switch triggers the 5V supply to the board; GPIO33 then goes high (logic 1) to maintain power to the circuit. It sends a "Mail received" message to the receiver, after which GPIO33 returns to the low state (logic 0), cutting off the 5V supply via the MOSFET until the next activation. I would appreciate any feedback regarding the capacitor value or other components.

My understanding is that you don't always need a direct conductive connection to get a small shock/tingling sensation from an AC source. Even with a floating source, capacitive coupling can provide a small AC current path, and a high-impedance meter can show phantom voltage.

I want to build a safe, low-voltage educational experiment using a microcontroller to demonstrate:

\- Floating AC source

\- Capacitive coupling to earth

\- Phantom voltage measured with a high-impedance input

\- How a load behaves differently from a high-impedance measurement

Difference between a floating inverter output and a floating isolation-transformer secondary

What would be a good safe low-voltage circuit to demonstrate these effects and measure the tiny currents with a microcontroller?

Hi everyone,

I would like to recreate a Philips PM 5133 function generator from scratch, as closely as possible to the original — essentially trying to build a replica of the actual instrument.

I really like this particular Philips generator and especially its analog design. I have the service manual with the schematics and circuit descriptions, so I would like to use the original design as the basis for the project.

The reason I'm considering building one myself is simply that I don't have enough money to buy a PM 5133, either new or used. Instead, I would like to see whether I can recover and reuse components from old electronics and build the instrument myself.

I know this is probably a difficult project, but I would really like to try it.

What would be the best way to approach this if my goal is to reproduce the PM 5133 itself, rather than design a different or modern function generator?

Has anyone ever attempted something similar, or worked on recreating old Philips test equipment from its original schematics?

Any advice about how to start, what to pay particular attention to, and whether it is realistically possible would be greatly appreciated.

Thanks!

Hi all,

I have three remote zoom controllers for a camera, each with a different pot that all aren't working correctly. I want to replace the pots but I'm having issues matching them.

The first (two pics) is a B20K, PCB mount, flattened shaft, which is all fine, but it has only about 100° rotation and has a spring return to centre. It also has this white support on the front. I can get close, but can't find anything with the return spring and support.

The second (two pics) is very similar to the first just with a shorter shaft. Though this one is a PCB mount it obviously doesn't have to be as it's chassis mounted here. All other attributes are the same. I figure if I can find the first one I can make something work for this as well.

Lastly, this one (two pics) I've come close (I think) but can't find the exact right value. I found a datasheet on Mouser that I used to partially crack the code as best I could... https://au.mouser.com/datasheet/3/531/1/Potentiometer_251_datasheet.pdf

As far as I can tell it's a 10K, 10% tolerance, Linear, no centre tap. But given this is unlikely to be a CTS brand (pot doesn't appear to have any branding on it) I can't be sure of everything. Mouser has a 100K version of this, but can't find anything 10K for sale anywhere, and I'm having trouble finding any other brand with this form factor (no idea what it's called).

I would like to find good quality replacements pots as I've had these units replaced under warranty several times already and seems I have no other option than to repair them when they crap out again and again.

Any info would be super helpful, TIA

Hey everyone,
I'm working on a custom electronic control unit for my motorcycle's turn signals and I'm about to pull the trigger on the PCB production. Before I do, I wanted to run the circuit by you guys and get some honest opinions on long-term reliability.
The project:
It reads the stock 12V handlebar switches, processes everything via a custom ATmega/Arduino setup, and drives the indicators using a P-MOSFET (AO4407A) switched by an NPN transistor (2N3904).
I have two main things I'm stressing about:
Arduino on a motorcycle: We all know bikes are brutal environments-massive temperature swings, vibrations, and nasty voltage spikes/noise from the electrical system. Is a DIY Arduino board actually viable for road use long-term, or am I asking for it to freeze or fry after a few months? What are the absolute must-haves for protection here?
l've attached my schematic and PCB layout for the MOSFET driver stage. Does it look solid, or are there any hidden landmines that'll let the magic smoke out?
Any tips, tweaks, or reality checks would be awesome.
Cheers!

Hi everyone,

I work in electronic component sourcing, and one thing I’ve noticed is that finding a difficult part is often more complicated than it looks.

When a component becomes hard to source, what do you usually prioritize?

1. Authorized distributors
2. Independent distributors
3. Excess inventory from other manufacturers
4. Alternative / replacement parts
5. Other options

I’m especially interested in how purchasing teams handle EOL parts and urgent shortages without taking unnecessary quality risks.

Would be great to hear how others in the industry approach this.

About 3 days ago I made a post here about a constant current driver to see if it was fine to use. Apparently I made alot of mistakes so I went ahead and did the research and tooks y'alls advice (thanks btw). Hopefully this revision should manage properly.

Here's what I did:
- Swapped the 1V2 zener for a LM4040 2V5 shunt regulator.
- Swapped the N-MOSFET for a 200 hfe BJT.
- Made sure the sense resistor is seeing ~250mV at ~140mA (maximum).
- Removed any components I deemed not needed.

So far the difference between the non-inverting and inverting inputs of the op amp is 18uV ~ 22uV

If you wanna mess with the circuit, here's the link to it.

Also here is the link to the original post.

Running an ESP32-WROOM-32 with a PN532 RFID reader (SPI), a status LED, and a buzzer, all on the same 3.3V rail. When WiFi is actively connecting/transmitting and the RFID reader is polling/generating its RF field at the same time, I see WiFi connection delays and general flakiness bad enough that I've had to disable the brownout detector just to stop reboot loops, which obviously isn't a real fix.

My guess is combined peak current draw (WiFi TX bursts + PN532's RF field generation) is causing enough voltage sag to disrupt things, even though nothing's crashing outright.

Has anyone dealt with this specific combo (WiFi + active RFID/NFC peripheral) on ESP32? Looking for:

Realistic peak current numbers for WiFi TX + PN532 active scanning together

Decoupling cap sizing / regulator recommendations that actually fixed this for you

Whether staggering/throttling RFID polling during WiFi activity is a common workaround, or if it's purely a hardware fix

made with nano banana and instructions from claude

Hi everyone,

I'm currently scribbling around for a new project and I ran into an issue.

I have 2 voltage supplies as input, where both could be at a different voltage levels. Hence I (to my understanding) I should protect the two sources from each other. Additionally, depending on the voltage level I may need to first put it through a DC-DC converter.

I've come up with the below concept to said things.I used PMOS as high side switches and added a second one to protect against reverse current. To be sure that I don't short anything by accident, I added a small logic such that only one path could be active.

I'm currently not sure whether this concept will work or if there is a better approach to achieve my issue. Any feedback would be greatly appreciated.

Thanks for your help

Hello! I'm currently working on a laser project and was wondering if this circuit was perfectly fine to use, or if I should tweak a few things. The circuit in question is based off of this driver's schematic.