Electrical Engineering Weekly Newsletter
Electrical Engineering Weekly Newsletter

Top new questions this week:

How can "purely" electrical circuits emit sound?

Moving membranes or piezoelectric materials obviously produce sound waves, but how can "purely" electrical circuits such as transformers or DCDC choppers (and others) often have an audible noise? Is …

transistors transformer noise sound speakers  
asked by Mister Mystère 29 votes
answered by Olin Lathrop 53 votes

What are those small metal bars going across a PCB for?

In quite a lot of PCBs that I have seen, they often have these small metal bars going across from one point to another. Here is an image of what I am talking about. In this example it is a charger: …

pcb identification  
asked by George H 15 votes
answered by Tut 33 votes

Is it bad if I held solder with my mouth?

When soldering, I have on a few occasions, used my teeth to hold a strand of solder while my hands were busy. I do not do this frequently, but sometimes I forget that solder is made of lead and I …

soldering  
asked by Nikzilla 15 votes
answered by placeholder 13 votes

AC to DC without transformer. How does this thing work?

I disassembled a Chinese-made flashlight and found they use just capacitors to bring down the voltage instead of a transformer. They are using it to charge small lead-acid battery. My question is how …

capacitor ac rectifier  
asked by Ryu_hayabusa 12 votes
answered by Andy aka 6 votes

PCB RF Layout Critique: Input on my radio-telescope PCB

I'm attempting to do the board layout for a radio-telescope we're building at one of my jobs. Here is the overall system topology: QRFH is for "Quad Ridged Feed Horn". It's a rather esoteric …

rf layout transmission-line  
asked by Connor Wolf 7 votes
answered by Dave 1 vote

Can I series windings of separate transformers to increase the voltage rating of the whole?

I need a 1:1 transformer, 25VA 600VAC. I'm not having much luck finding such a thing. It occurs to me that I could take five smaller 1:1 120VAC transformers (like this), series all the primary …

transformer series  
asked by Stephen Collings 6 votes
answered by Spehro Pefhany 3 votes

Wavelengths blocked by a certain metal mesh

Introduction: I've heard about a theory, according to which you can check if there is any leakage in your microwave oven by putting your mobile phone inside and call it. However, I gave it a try and …

gsm physics microwave  
asked by hryghr 6 votes
answered by Floris 3 votes

Greatest hits from previous weeks:

What would happen if I connect two different DC voltage sources in parallel?

I have a computer power supply that I'm hacking together as a bench supply. For this particular model to power on, I need a minimum load across both +5V and +12V. "Easy," I thought, "I'll just …

power-supply dc parallel  
asked by rascher 16 votes
answered by Adam Lawrence 21 votes

Difference between UART and RS232?

Most of the time RS232 and UART come together in serial communication theories. Are they both the same? From my readings I concluded UART is a hardware form of RS232 protocol. Am I correct?

serial communication uart rs232  
asked by tollin 17 votes
answered by Nick Alexeev 23 votes

Can you answer these?

How to calculate average delay time of circuit having several possible transition states

Is it possible to calculate average delay for all possible states directly without calculating them individually using Xilinx or with Cadence.

circuit xilinx delay time cadence  
asked by user1698787 1 vote

Weird bug in MPLAB X IDE

When using the RTCC module in the PIC24F, we need to use the secondary oscillator (by setting bit #2 of OSCCONL register) and disable the write lock on the RTCC registers. Now the write lock can be …

pic assembly mplabx  
asked by 3bdalla 1 vote

Antenna matching network topology

In tuning an antenna, there are multiple possible topologies that will take it to the middle of the smith chart. Some differences that I can see between them are: Component ESR (losses). Effect …

antenna component-selection impedance-matching tuner  
asked by apalopohapa 6 votes
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