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Unanswered Questions

14,608 questions with no upvoted or accepted answers
12
votes
2answers
3k views

DRC tool for Gerber files

Do you know any tools which perform design rule checking for Gerber files of PCB and are suitable for using in batch mode on a remote server? Something similar to what BatchPCB or FreeDFM uses (I ...
11
votes
0answers
380 views

Switch from JTAG to SWD with bitbang sequence on STM32F103VB

I am trying to switch from JTAG to SWD without any external devices. Why? Because I would like to use the SWO pin to send a stream of logging information to another device. To accomplish this ...
9
votes
3answers
368 views

Digital Signal Cables Penetrating a RF Shielded Room

Disclaimer: I'm not a trained electrical engineer...I'm a recent Computer Science grad with about ten years experience as a RF test tech. I don't know everything, and to me, experience reigns supreme ...
8
votes
1answer
5k views

STM32F407 + LAN8720A + lwIP + FreeRTOS = No received Ethernet frames

I'm trying to bring up a PCB that uses an STM32F407 and LAN8720A Ethernet PHY, and I can't seem to receive any Ethernet frames — even though I have no problem transmitting frames. Hardware setup I ...
8
votes
2answers
181 views

Which part of some LED TV screens acts as two gratings crossed at non-straight angle?

Some modern LED TVs display the following diffraction pattern (photos taken from this question): In my answer to another question about the origin of this pattern I explained that this should be due ...
7
votes
1answer
107 views

Black Pad. Will heat remove the gold from an ENIG finish?

I have a batch of new PCBs with ENIG (electroless nickel / immersion gold) surface finish. My assembly house has had two unsuccessful attempts at populating the boards. We're trying to troubleshoot ...
7
votes
1answer
107 views

“Temporary boost” supercap

I have a 12VDC load (up to 10A) that functions correctly down to 8VDC. Sometimes (frequency: many seconds max, many minutes typical) the power source has a very brief (few milliseconds) drop to 7V. ...
7
votes
1answer
4k views

Stability factors of a voltage divider bias circuit

I am trying to derive the stability factors of a voltage divider bias circuit. I could derive S,S', however, I'm facing some problem with the derivation of S''. Please help me in this regard. How to ...
6
votes
0answers
60 views

Calculate sheet resistance in finite element method

I have a simulation with several polygonial mesh cells (Voronoi-mesh) and their centers of gravity \$P_i\$, each with its own electrical potential. Every cell has the same height \$h\$ all over. How ...
6
votes
1answer
117 views

Voltage Controlled Current Source - help needed

I am designing a voltage controlled current generator for the currents in a range from 0 - 2.5mA. The load resistance is within the range of 0 - 5k Ohms. I decided to go with difference amplifier ...
6
votes
1answer
257 views

What antenna is this?

I just disassembled an external FM antenna designed for an old Asus laptop. I expected to find some circuitry and a monopole or some other simple antenna. However, what I found was the antenna shown ...
6
votes
1answer
341 views

Design of cavity filter

I try to design a Chebyshev bandpass filter for 6 GHz as a coaxial cavity filter. I know that the filter can be designed with the aid of the coupling coefficients between the resonators and the loaded ...
6
votes
0answers
522 views

LM386 guitar practice amp circuit not working, need help finding mistake

I'm very new to electronics and I built this guitar amp circuit on a breadboard: and it was working really nicely. Now I've decided to put the circuit on a universal PCB which I'll use in the actual ...
6
votes
1answer
659 views

Interfacing FPGA to an external chip and timing constraints

I have designed a system using Artix-7 FPGA on a custom board. The goal is to transfer 32-bit data to an external onboard chip whose data bus is an inout port. ...
6
votes
2answers
1k views

Designing/Predicting Output from Permanent Magnet Motorcycle Stators

I'm hoping you can help me. I've long been into motorcycles, and have restored and customized many different bikes. While building custom motorcycles, I often add electrical accessories, and use high ...

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