/r/AskElectronics
A subreddit for practical questions about component-level electronic circuits: design, repair, component buying, test gear and tools.
A subreddit for practical questions about component-level electronic circuits: design, repair, component buying, test gear and tools.
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/r/AskElectronics
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Component choice and/or circuit advice for open emitter circuit
I need to create an open emitter circuit to drive a line called `INH` (for inhibit) high (+5V) when needed, but to not create any shorts when other devices/circuits on the same line `INH` themselves try to assert the line high. The line is otherwise pulled low by a 4.7K resister. I do not have the option of changing how this `INH` line operates. The open emitter needs to operate in a 8 MHz clock with minimal latency (i.e., if it takes a significant fraction of 1/2 of the clock cycle to propagate the signal, that would not be good)
I tried using a BS250, but it turns off time was too slowly due to the gate capacitance. I tried using a BAT-43 diode but that was too slow too. What is driving the signal is some 74HC logic which I can make active high or low as needed to drive this open emitter.
Any advice on what options I have here would be appreciated. Thanks!
23:49 UTC
Help needed with this, should i have voltage at the red and black (the board that has the charge protection on the battery) individual batteries do show 2.9v and 3.3v but zero at the red and black spot
22:11 UTC
Crimp took for Molex KK 254?
Does anyone know the name of the crimp tool I need for Molex KK 254 connectors? A link would be even better. Thank you!
21:56 UTC
MSI MS-17F41 - Motherboard component identification
Hi all,
I spilled coffee on my running laptop and cleaned it thoroughly after opening it up. Before cleaning, I took pictures and later noticed that a small component is missing (highlighted with red arrows in the attached image). The board labels it as C759 or EL11—it doesn’t seem like a capacitor or transistor, more likely a diode.
Now, the laptop works on battery but not on charger (charger won’t charge the battery, and it won’t power up without the battery). I’m reading 19V at the charging port and capacitor near the battery connector.
Could the missing component be the cause? Any help identifying or sourcing it would be much appreciated!
20:53 UTC
How To Choose A Supercap?
Hello,
I am trying to see if I can use a supercap which I charge then it will power the circuit to read the sensors and display on e-ink, planning to use 3.3v pro mini for this. How does one know how to size the supercap? Is it like batteries that if you get a volt in the ballpark like 3.7v, you can kind of get any mAh since that just determines how long the battery will last before it needs charge? Is that the same thing with the capacitance since that will determine how long it will charge and discharge?
21:39 UTC
Which is preferable trace routing?
21:33 UTC
Explanation of HF schematic
Could someone explain me a bit deeper how this schematic works? Why are some components on it’s place and how the signal amplifies on different stages i will be very gratefull
20:17 UTC
How Would I Go About Creating Schematics for Unkown Cards?
Hey !! just wondering if anyone has any previous experiences, or knows of any resources and equipment needed to "create" schematics where schematics are not readily available. I have have a “known good" right now but I want to be able to have schematics to be able to troubleshoot other systems once l eventually lose this one. Just wondering what you guys think would be the best course of action?
19:32 UTC
Help identify Replacement Cap for DAN14CMB6EO REV e motherboard
19:03 UTC
Is this an real and working AM Transmitter Circuit?
18:56 UTC
What makes the Rigol DHO804 oscilloscope stand out?
Recently been looking for a good scope, I found MANY Reddit posts and YouTube videos online that the Rigol DHO804 is a very good choice (or any from that series). I'm wondering what makes this scope so good? What makes them stand out compared to others? (of course taking the price in consideration).
(I first wanted to go for an Alibaba scope, but figured I'd rather spend a bit more money and just have a good scope for many many years. But I don't really see what makes this scope stand out compared to others in this price range, but that's because I probably don't know too much about oscilloscopes specs, other than the basics. The bandwidth of 70MHz is good enough for me I assume, but usually around this price you'll find 100MHz bandwidth).
18:40 UTC
FT232RL based adapter is not recognized when under load
I'm working on updating ESP8266 firmware on an S31 smart plug. With the DSD tech FT232RL adapter just plugged into a PC, it is recognized as "Ltd FT232 Serial".
But when I connect adapter 3.3v and gnd to the S31 device, the adapter is no longer seen by the PC. When this connection is made, the vcc value goes from 3.3v to 3.225v
Is there a know issue with FT232RL based adapters? Has anyone found a fix for this type of issue?
I just ordered a different brand FT232RL based adapter to try. Now I wonder if an alternate adapter chip like CP2102N would be more reliable?
18:24 UTC
How do I communicate with K line ISO9141 using UART?
I’m hoping this sub could help me understand and fix a circuit please. I am trying to convert a K line OBD2 car signal (12V) to a UART signal for an MCU(STM32). K line is a single wire signal for both TX and RX. The image I have posted from GitHub shows a circuit. In this circuit wouldn’t RX0 always be high unless TX0 is specifically set to low? Most cheap MCUs have UART idle at high instead of low with no inverse option. So unless I force TX0 to low, RX will always be high at idle regardless of what K Line is doing? This is what I am witnessing when I built the circuit too. The circuit is very similar to ELM327 circuit on page 73 (https://cdn.sparkfun.com/assets/learn_tutorials/8/3/ELM327DS.pdf). I don’t have great knowledge of electronics and I need some help getting my mcu to talk to my car.
For the help in explaining to the mods I am asking how to make this circuit work, how do I communicate with K Line using UART because right now the RX0 is always high. Hope that explanation works and clears things up a bit.
18:04 UTC
Why does the voltage keep ramping?
I'm trying to design a boost converter with a discrete feedback loop. Currently everything in the simulation seems to work besides the output voltage. The PWM coming from the comparator isn't too high of a duty cycle, the voltage coming from the feedback is between the rails, and if the voltage coming from the feedback is too high the jfet should regulate the feedback path until it sufficiently lowered. However, with all this the voltage keeps increasing into the 40-70V range.
I'm wondering if it's a simulation issue or if anyone can spot where the problem is coming from. The green trace is the value from the feedback being fed into the comparator, and the pink trace is the jfet signal.
17:23 UTC
Logitech G29 STM32 Flash files
I have an G29 where the stm32 is burnt and trying to replace it. I have found the exact model to replace, own an st-link and also traced the correct pins on the PCB. Do any of you have the necessary files to flash the stm32 or know how to obtain them?
17:03 UTC
Help with Shift Register Issue in Logisim Circuit
I’ve built a circuit in Logisim with 4 registers connected in serial. A keypad is connected to a decoder, which sends signals to the registers to store numbers. The first register stores the numbers correctly and passes them to the second register.
The problem: For certain numbers, the wires from the 1st register to the 2nd turn red. However, the output from the 1st register itself is fine, and all other registers after the first work properly. The issue seems to be with the connection between the 1st and 2nd registers, specifically the input to the 2nd register.
I've added some screenshots of random attempts that either work or not.
Any ideas on what might be causing this? Thanks!
15:44 UTC
Buck Efficiency abnormally fluctuating with output current
*Long Post Warning* Hi, I am new to power electronics and this is the circuit I am working on. Instead of the supply directly, I am using Variac for safer testing. Also, ignore the current and voltage-sensing components from the circuit; I have not connected them yet. I have chosen my components so that the circuit can supply 60V and 20A in output. But before going to a 1200W application straight away, I have gradually increased the power at the output side using a programmable dc source as the load. While doing it, I have observed this bizarre behaviour from the circuit that I cannot logically make sense of. Before 1.5A, for a 20% duty cycle, the input current maintains an almost 1/5 ratio with the o/p current, which is expected. But after that, I have observed an abrupt change in the i/p current as it exponentially increases with the Variac and eventually becomes greater than the o/p current!! But if I keep increasing the Variac, the o/p current gradually supasses the i/p current, and efficiency slowly rises. Also, at 100W, while at 9.6A, the IGBT got blown, whereas it is rated for 1200V, 60A. My switching frequency is 7.8 kHz, the capacitors I have used are polarized big box capacitors of 10 mF, and the inductor is of gapped ferrite core. Any suggestion or explanation will be greatly appreciated. Thanks!
16:20 UTC
Weird value resistor
If i put this resistor in a website, should i put the first gold line as yellow? (Red red yellow gold Black) Because the slot for the third band dosent accept gold
15:42 UTC
I am trying to build this schematic, but it keeps failing (some gates fail upon pushing the button). I've built it on [Tinkercad](https://shorturl.at/bQCHT), I would appreciate any help. Also, what do the symbols on pin 1 and pin 14 of the 7439a mean?
15:34 UTC
Component selection in TPS55288 buckboost converter
Hey,
I am designing a buck boost converter using the i2c interface of the TPS55288 converter ic chip for a project in school. My part of the project is designing the hardware and the pcb of the project while the others are in charge of the software. My question is now:
- I have found a schematic from the WEBENCH TI Designer that will definetely work. BUT: The component values are waaay to specific and the switching mosfets are quite expensive if you buy them in a small quantity. How can I make sure my project works but without all the expensive and rather rare parts?
15:17 UTC
How to lower amperage for itrons ( VFD tubes ) supply?
I'm deeply sorry for posting 6 Times, I had loads of specific words, should be ok now
So, for the third and I Hope last time, I'm here with another post About VFD tubes. Weeks ago, I bought ELKA 50 calculator, and looked inside. I'm planning on Getting all of the components out, because I need the for some next projects, and it would be shame to Just throw out.
Now for the problem.
Since I want to use the tubes, I looked into the datasheet ( thanks to someone in my previous post ). I was bamboozled to see 0.5ma per tube...
In the calculator, there is one transformer converting 230 to I20 Volts and then, There is load of resistors to ( I guess ) get on 0.5ma and About 25 Volts.
So, since I want to learn how to make things and how do they work, what options do I have, and how am I supposed to get from About 100ma the 0.5ma ?
My working voltage is 25-30V or 45-50V if needed.
Thanks in davance!
15:09 UTC
Can someone identify this PD IC?
*NOTE: PD IC refers to USB Power Delivery IC
Used in one of those Aliexpress boards, but has no marks other than pin1:
The schematic is very simple:
Not sure (until i desolder it) is if there is a ground pad and what pin 10 does (there is no continuity to GND).
The output voltage is selected bringing PD_X pins high/low.
Thanks for any hint.
14:48 UTC
I’m looking for dimensions of vacuum tube bases
Specifically a “medium base 5 pin” for a 24 tube. All the references I have found show a schematic or at most a side “outline” drawing (RCA manual). I need the drawing of the pin sizes and locations. Thanks!
14:37 UTC