texts: Confusion between the necessity of maximum voltage and maximum power transfer

texts:
This is a conceptual question therefore I want to ask with an example.
I'm wondering in which cases impedance matching is used.

For example, if one has a sensor which can be modeled as voltage source call it Vs. Imagine it is outputting mV level voltage signals and it has 1k output resistance. And if we want to amplify it we would use an amplifier with a very big input impedance like 10Meg so that most of the Vs reach the amplifier input.

But for maximum power transfer the input impedance of the amplifier must be equal to 1k which would halve the Vs reaching to the amplifier input.

If we have a signal to be amplified why would we match the source output impedance to receiver's input impedance? In my example it was not a good idea. And I know that in radio transmission impedance matching is used. But again I'm stuck at the same point. There must be a difference in two cases where we need maximum voltage at the receiver or we need maximum power at the receiver.

Can this be explained by two examples for each case?


texts: Small bluetooth device (not off the shelf) which sends a single button input to a phone

texts:
What I need is some bluetooth device, that would accept a single button input and send it via blutooth to my android phone. Example commands might be - to stop playing music, forward to next track or etc.

I have made this illustration to make it more clear -

Just like those selfie stick remotes -
However, I would need to send a different command, than taking a photo and I need a custom self made button (which I will trigger with my toe)

I've tried googling around, and some solutions suggest using Arduino. However I need something smaller. Is there any solution you know of, that is easy to do for an electronic amateur?


texts: What happens when wire touches only negative battery terminal?

texts: Might be more of a physics question, but what happens when you connect a wire only to the negative (or positive) terminal of a battery, in terms of electron movement? Do electrons flow in/out of the wire until equilibrium is reached?


texts: How to measure uV voltages buried in noise?

texts:
I'm working on a project in which I am analogly processing ultra low signals. The phase, harmonics and signal shape are critical to circuit functions. The signal on the input comes from an antenna type device, so as you can guess, it picks up a ton of noise.

My minimum input voltage is 2uV AC ranging anywhere from 10-10kHz.

The circuit applies a gain of 1000 and does some other jazz to the signal. The problem is being able to measure the input signal and compare it with the output.

I'm even having trouble measuring the output properly as even my Tektronics scope does not go anywhere near that low. I'm  currently using a 6 1/2 digital bench DMM but I can only measure amplitude.

In noisy, low voltage situations like this, how do I go about measuring this signal?

If I amplify everything more I fear the noise to signal ratio will be so large I will only see noise anyway.

Would I need to use a band pass?


texts:
I was wondering how I could remove the silver (chip?) from the center of this PCB. It appears to be held down by that clear substance (epoxy?). The PCB is small, 2 cm sides (Not sure if relevant but thought I would add).

I've never done this before and was wondering if anyone else had experience with this.


texts: 5v power supply upgrade for an ESP chip and a couple dozen relays

texts:
I have remote setup of one ESP32 chip, with a couple of sensors on it and 3 relay boards (total 16 relays).
I currently power them with two separate phone usb chargers.
One charger for the ESP chip (which powers one 4-relay board through it 5v out) and one usb charger for the two other relay boards.
All have common ground to a small breadboard for the ESP to be able to control the relays.
Although this set up seems to be working ok for a year now, i would like to upgrade the PSU as i have the feeling that sometimes (randomly - i can't place it) there's not enough power to switch all 16 relays on.
I was thinking of buying a dedicated PSU to power all of this stuff.
Something like this, 5v 10A, or like this 5v 5a.
Unfortunately i have no clue how to go ahead and calculate my needs.
Could i have a small guidance as to how to select a PSU to power the following stuff adequately:

ESP32 Wroom something like this
Two (or perhaps three in the future) 4relay board. Sample
One 8relay board. Sample

Stuff plugged on the ESP chip:

DHT 22 temp/hum sensor. Sample
Simple buzzer. Sample
PIR Sensor HC-SR501. Sample

The website I'm shopping from also has Meanwell PSUs for 2 or 3 times the price, is it worth going for a better brand? (safety wise i guess)
Is there an issue if I go for a larger UPS i.e. 5v 14A?
And lastly what about power consumption, will a larger UPS only draw the Watts I need or do they work at full consumption?
Looking forward to some help and sorry a very basic question.
Thank you


texts: FSM implementation using single always block in Verilog?

texts: So while looking up for material on implementing high level state machines in Verilog I came upon this: I am also trying to implement a high level FSM in Verilog that has a number of nested conditional (if) statements and many inputs. Overall the design I am trying to implement is a synchronous design where the inputs and outputs are also available on clock edges. So my question is is there any pitfall in designing an FSM like this? Any help is appreciated.


texts: I am teaching electronics a few people as a hobby. I wanted to show them that as the frequency increases output voltage of low pass filter(simple first order RC filter) decreases. I don't have a signal generator to produce frequencies. I am using 555/556 timers for this purpose. But for correct filter output calculations I need to know what is the output impedence of these ICs. But those information is not present in the datasheet. How do I calculate this output impedence?


texts: Flooding GND plane in the top side has any problems?

texts:
Hope Everyone is doing well.
I got confused in the grounding of PCB.
I checked many open hardware boards I noticed they don't flood GND plane in the top side to connect SMD components( all components on top ) which is appeared to me the best way to minimize the number of vias
instead they use vias for each pad connected to GND PLANE IN THE bottom layer and they run only signal/power traces on the top.
Can anyone explain this to me please


texts: Moving code from an ARM M0+ to an ARM M4, what changes?

texts:
Say I have a very simple program that functions perfectly fine on a ARM Cortex M0+ processor.  How much will I need to change in order for it to work on an ARM Cortex M4 processor, assuming they are both made by the same company and I have imported the new cores header.

I just can't think of any reason it wouldn't work.  They use a similar instruction set.  I mean the M4 has a much more expanded Thumb-2 instruction set over the M0+. In my experience, companies keep the same naming scheme when they make their ARM device headers.


texts: How much current do I need for a 5050 RGB strip?

texts: I want to use 5 meters 5050 RGB Waterproof 300 LED Strip + 20 Key Music IR Remote Controller Sensor. Is it okay if I use a 12V 6A Power Supply?


texts: Tips on parts for a very low power LED blinker

texts:
I'm looking into designing a badge for a tech conference and we're thinking of creating a small PCB with one or more LEDs on it.

Requirements:

Less than $5 per unit for 2500 badges
The PCB has to be around the size of a 3.5" floppy with place to add a sticker with the participant's name of it
A silk layer would be nice to show of the parts and complete the "geek" feeling
Ideally it would run on a "button"/"cell" battery, but a AAA battery might be needed.
It would be nice if it would run for up to a year, but the conference is two days so anything that would run for at least three days is doable

Options we're thinking of:

Blinking a single red LED
One "glowing" RGB led that changes between the three different colors of the event's design
A strip of RGB LEDs making the whole badge "glow"
Using some kind of plastic to use less LEDs to illuminate more of the badge

The question is: what kind of architectures should I look into?

The LM3909 is supposed to be nice, but out of production. Are there any replacement components like that?

For stuff that glows I see two possibilities some MCU (MSP430 perhaps?) to do PWM between one or three colors or use a D/A to set the voltage of the LED to an appropriate level.


texts: multiple RGB LEDs with common resistors for each color

texts:
I am modifying a pcb with 9 RGB LEDs having three resistors each normally. I know that it is the proper way of doing it. However what is the disadvantage of connecting them as below?

Resistors being higher power rated compared to three resistor each setup.


texts: Analysis in a motor controll amplifier circuit

texts:
I've the schematic that is in the picture below:

simulate this circuit – Schematic created using CircuitLab

And I did the following analysis:

the opamp acts as a voltage follower, so when \$V_{in}\$ is between \$0\$ volts and \$10\$ volts the output of the opamp can only be as high as the voltage I apply to the positive \$V_+\$ of the opamp;
$$R_1=\beta_{min/T2}\cdot\frac{V_b-V_++(V_{sat}-V_{be/T1})}{I_{motor max}}$$
Where \$\beta_{min}\$ is the minimum of the current gain of transistor \$T_2\$, \$V_b\$ is the external voltage source voltage, \$V_+\$ is the positive voltage at the opamp rail, \$V_{sat}\$ is the saturation voltage of \$T_1\$, \$V_{be/T1}\$ is the base-emitter voltage of \$T_1\$ and \$I_{motor max}\$ is the maximum motor current.
$$R_2=\frac{V_+-V_{be/T1}-V_{be/T2}}{I_{motor max}}$$

  Question: Are my formulas to find \$R_1\$ and \$R_2\$ correct?


texts:
I've got a keypad hooked up to an ATMega168 and its supposed to play various tones depending on the button pressed while the respective key is held down. I'm generating these tones by alternating the state of the port the speaker is attached too at 2* the rate of its frequency (or close enough to it)

It works as intended save for the fact that every tone is the same. Is there a limitation to the frequency it can output this way? If so is there a better way of doing it?

I've tried it with an LED at a far lower frequencies so I know the keypad subroutine is working as intended.

if (keychar == '1'){
                    while (keypressed()){
                        PORTB |=(1<<PB1); //Set Port B to high
                        delay_ms(1000/524); //for note fequ *2 (50% duty cycle)
                        PORTB &= ~(1<<PB1); //Set Port B to low
                        delay_ms(1000/524); //for note fequ *2 (50% duty cycle)
                    }
                }
                if (keychar == '2'){
                    while (keypressed()){
                        PORTB |=(1<<PB1); //Set Port B to high
                        delay_ms(1000/588); //for note fequ *2 (50% duty cycle)
                        PORTB &= ~(1<<PB1); //Set Port B to low
                        delay_ms(1000/588); //for note fequ *2 (50% duty cycle)
                    }
                }
.....
                if (keychar == '7'){
                    while (keypressed()){
                        PORTB |=(1<<PB1); //Set Port B to high
                        delay_ms(1000/988); //for note fequ *2 (50% duty cycle)
                        PORTB &= ~(1<<PB1); //Set Port B to low
                        delay_ms(1000/988); //for note fequ *2 (50% duty cycle)
                    }
                }
.....


texts: Good way to pick up voices in a small room for speech recognition

texts:
I've written an app that's pseudo-intelligent and responds to voice commands. I'd like it to be able to pick up my speech from anywhere (initially just one room, but possibly many later on).

At present I'm using a bluetooth mic but it's annoying and frankly looks ridiculous.

The room I'm starting with is approx 4x7m. The floor is carpet and there's furniture against almost all the wall space. There are no obvious echoes (at least that I can hear).

Can anyone with some experience suggest how I should get started?

What sort of microphone should I be looking for? and do I need any processing equipment?


texts:
I decided I would like to start learning how electronics work, so I got myself The art of electronics.

I guess its trivial, but I cannot wrap my head around why is there a wire that I painted with red color. Doesn't it mean, that the LED has voltage all the time because of the red wire? And how would the circuit look as a whole, with battery? Do all the grounds go into the second terminal of battery?

I would understand the circuit without the red wire. If the temperature is higher that 30C, LED circuit gets voltage and starts working.

Could anyone help me with explaining how it works?

Thank you


texts: Draw the amplitude and phase diagram through the transfer function

texts:
My function in terms of s (Laplace variable) is:

$$G(s)=\frac{1000(s+200)}{(s+20)(s+2000)}$$

The calculations I've done so far:

$$G(s)=\frac{1000(s+200)}{(s+20)(s+2000)}=\frac{\frac{1000}{11}}{s+20}+\frac{\frac{10000}{11}}{s+2000}=\frac{\frac{1000}{11}}{20+1\omega j}+\frac{\frac{10000}{11}}{2000+1\omega j}=\frac{\frac{1000}{11\times 20}}{1+\frac{1}{20}\omega j}+\frac{\frac{10000}{11\times 2000}}{1+\frac{1}{2000}\omega j}=\frac{\frac{50}{11}}{1+\frac{1}{20}\omega j}+\frac{\frac{5}{11}}{1+\frac{1}{2000}\omega j}$$
$$G(s)\approx 4,55\frac{1}{\sqrt{1+\big(\frac{\omega}{20}\big)^2}}e^{-j\,arctan\big(\frac{\omega}{20}\big)}+0,45\frac{1}{\sqrt{1+\big(\frac{\omega}{2000}\big)^2}}e^{-j\,arctan\big(\frac{\omega}{2000}\big)}$$

Then,

$$\omega_1=20\,rad/s$$
$$\omega_2=2000\,rad/s$$

I simulated the Bode Plots in Scilab:

I know that:

$$1\,dB=20log\Big|\frac{u_0}{u_g}\Big|$$

My problem is that I do not know how to calculate the points of the Bode diagram through calculations, since I have a sum of two distinct individual transfer functions (one with \$\omega_1=20\$ rad/s and other \$\omega_2=2000\$ rad/s).
How can I apply the previous expression to calculate in dB the amplitude of the sum of the two functions?

My attempt:


texts: transformerless low-current power supply design

texts:
Hi Friends and Colleagues!

With one of my pupils we are designing a kind of LED light source. It is fed from 220 AC directly with basic diode rectifier - many strips of LED band are soldered sequentially.

Now we want to add some control logic to it (e.g. IR or acoustic switch). The trick is how to power this logic. I.e. how to create low-current 5V as we only have about 310 DC here.

My current idea is to use zener diode and powerful resistor: to draw 5 mA from about 300 V we need a resistor of 60 kOhm / 2 W.

The supposed schematics is below. I'm unsure whether it would be ok to use 5V zener and feed the logic from point A (i.e. without 78L05) or it is better to use 9V zener and take the voltage from point B? And do you believe it is safe design overall, provided that no one is going to touch anything when under voltage (and probably this is going to be used mainly for demo purposes anyway).

UPD: Dear Friends. Thanks a lot for that many hints and opinions. I'm sorry I was impatient and implemented the thing before waiting enough to collect all these answers. I dare to add a couple of words about...

About safety - thanks for your concerns, all this is pretty correct.

However this project is directly aimed to teach safe procedures while working with dangerous voltage. It is not that important to make production ready device (though I hope we'll be able to show it at school conference), but more important that pupils learn to apply proper safety measures.

The matter arose from the fact that several of them after soldering a few 5V schemes decide they are real gurus and started playing with power lines in their homes etc - which led to some hazardous situations. One of their "domestic experiments" included plugging 5V schematics into 220 directly - with enough sparks, smoke etc. When I learned about it, I decided we should cover the topic of working with home switches, bulbs, plugs etc, etc - and particularly about difference between 5 volts for logic, 12/24 for leds and 220 AC...


texts: How to search for a step-up transformer: 10V -> 90V

texts:
I'm working on something where I need to take ~10VAC @ 60hz and step it up to around 90VAC @ 60hz.  Ideally a small step-up transformer should be fine, but I'm having trouble identifying the part I need through any of the major components vendors.  Everybody seems to focus on listing parts that step down from 120VAC to some value... searching for something designed to go the other way has been an exercise in frustration.  Can any tell me if there's a secret to identifying these things?  Even the "parametric search" at places like Newark and Mouser don't let you do a simple thing like selecting the primary side and secondary side voltages.

And, FWIW, yes, I know I could use a step down transformer and just treat the secondary as my primary.  But then you run into limitations in regards to how much current the "cheat primary" can carry, etc.  I'd really like to find a part that's designed specifically to be a step-up, that has a ratio around 1:9.


texts: A recessed battery connector with curved contacts? 2.5mm pitch

texts:
I'm trying to find a battery connector with curved contacts like this, so that an OEM battery with recessed contacts can slide over it in both directions. The spec is 2.5mm pitch, gold plated.

I've created this example image with the contact block surface-mounted on the other side of the board. I've not seen this but time and again I would find it useful so that I could get the battery flat on the PCB.

Can anyone recommend a component with one of these characteristics, or perhaps a keyword which I'm missing to improve search results? Nothing in the AVX or Bournes catalogues seems to fit the bill.

Thanks


texts:
I'm currently trying to design a relay network for a piece of laboratory equipment (PPMS).  I would like to describe what the setup is, what I am doing now, what I hope to do, and how I hope to do it.  Skip ahead if you're bored!

The current setup and what I am doing now:

The machine has 12 pins which are accessible via a LEMO connector on the side.  Thus far, a colleague made a LEMO to DA-15 cable and I made a DA-15 to 15 BNC breakout box.  I have a voltmeter and a current source with BNC cables coming out for V+, V-, I+ and I-.  Right now, if I wanted to, say, change V+ from pin 1 to pin 2, I physically disconnect the BNC from pin 1 and attach it to pin 2.

What I hope to do:

I would like to be able to assign roles to these pins programmatically.   I have an Arduino Uno and a bunch of Magnecraft W171DIP-2 reed relays.

How I hope to do it

I am naively thinking of a scheme like this (simplified to a case of 3 pins (nodes here) and one source (CCCS1 here) rather than 12 pins and 2 "sources") (the switches "SW#" would be digital outputs of the Arduino):  (sorry for the mess--I'm not experienced drawing this kind of thing)

I would need to get some I/O expanders and/or a different microcontroller (Seeeduino Mega?) to have enough pins (I would need 48 relays to do 12 pins and 2 "sources" this way).

Now, here's my question:  Is there some awesome way I can simplify this circuit?  I'm not good with electronics so maybe I'm missing an obviously better approach?  Or maybe there exists some IC that would bundle the functionality of a bunch of relays into one cheap, tidy package?

Thanks a lot in advance!!  Criticize away! (so long as you then tell me how to do it right!)

Brian


texts: Is a solar panel clamped to a battery a drain on the battery at night time?

texts:
I noticed that in the night time (dark) the voltage measurement on the battery was lower than in the day time (sun), measured with my voltmeter. I'm new to electricity, but that made me assume it had lost charge.

Voltage in the day in bright sun: 12.56V

Voltage early the next morning: 12.42V

Did I lose charge over night by leaving it clamped?

I'm using a 12v solar trickle maintainer on a 12V sports-bike battery. I am trying to charge it up over several days, and don't want the voltage to drop. The instructions said the battery is done when it reaches 12.7V... I assume it'll take like 5 days.


texts:
I'm trying to actuate a solenoid lock with the following specifications from the vendor's page:

Working voltage: 12 Vdc
Starting current: 0.9 A
Steady current: 0.12 A

For this application, I'm using a circuit based on the answer to the question in this link: MOSFET to run 12 V, 0.5 A door lock
My circuit diagram is as follows, with the solenoid wires connected to the J2 borne connector:

However, the IRLML2502 MOSFET is not able to actuate the solenoid lock when a logic pulse is supplied to its gate. The original idea is to operate it using 3.3V, but I also tested it using 5V to no success.
From what I understood, the datasheet gives a maximum of  for , resulting in a voltage drop of 0.08 at 1 A.
Using a DMM, I measured the solenoid's current draw from activating the MOSFET gate using 5V logic on a protoboard. As soon as the 5V pin switches, the DMM shows the current of 9.9 mA, then goes out of the 200 mA range and settles at 182.1 mA for the rest of the pulse. The solenoid does not fully actuate in this setup, only when supplied 12.1 V (measured) directly from a 2.5 A DC power supply.
I'm suspecting here of the MOSFET not being able to handle the higher starting current. Am I missing any information here? What parameters should I consider in this case? Is it possible to use IRLML2502 MOSFET for this application? If not possible, any substitute parts reccomendations are greatly appreciated.


texts: Charging 8 LiIon 18650 cells in parallel

texts:
I'm working on project that is Powered with 8 LiIon batteries/cells connected in parallel. Everything Works fine until batteries run out of "juice".
For charging module I decided to use TP4056(@ 1A). Now, problem is - TP4056 module can charge only one LiIon cell at the time, so I need 8 modules for proper charging(one module per cell). There is two versions of TP4056 module, one with over discharge Protection(pins: B+, B-, OUT+, OUT-), one without Protection(pins: OUT+, OUT-), so I decided to go with module that has over discharge Protection(now I'm asking myself why I did that).
Next is scheme(I don't have it but I'll write it):

Pins OUT+ and OUT- are connected in parallel(between modules). Those pins are in use as VCC for project(let's say it's "power source").
One cell is connected on B+ and B- pins of one module. With that way one module charges only one cell(as it should).

But!
Yesterday I found that sometimes(since I buy from eBay) those Protection modules have problem/bug and they aren't reliable. Also later I found that cut-off voltage is 2.5V, while manufactuer recommends 3V(in most LiIon cells). I guess this design will fail so I decided to find another solution.

So my question is:
How to make this same "design" with TP4056 without over discharge Protection(only OUT+ and OUT- pins)? How I should connect batteries with modules so only one module charges one cell? Any advices?

I paid more than €50 for those 8 cells and last thing I want to do is to destroy them with wrong charging "design".

I'm not sure is my solution correct so I wrote this question.
My solution is:

Connect cell's positive pole to OUT+ pin of TP4056 and same thing with negativ pole(to OUT-).
Connect cells in parallel and that use as power souce.

So my thinking is:
While charging, current will flow where is less resistance(as river in nature), it will flow from OUT+ through cell then from negative pole to OUT-. Is that correct? But if cells are used as power souce then current will flow as normal in parallel connection. Am I right?

Thanks a lot!


texts: If I have a battery that provides a high current at almost constant voltage, how do I use it to power other components that require lower currents?

texts: I have a drone which is powered by a 2200mAh 11.1V 40C/80C LiPo Battery. I want to power a Raspberry Pi 3 B and a video transmitter (TS832) that is rated at 220mA at 12V. Do I need to add resistors or other components to ensure that the the transmitter and the Pi are protected from high current? If so, in what configuration?


texts:
I am trying to create a bloc with Xilinx system generator to detect the maximum of a sine wave. I used the strategy that:

$$ x(n-1)-x(n-2)>0$$

and

$$ x(n)-x(n-1)<0 $$

but I didn't find the maximum. The result is wrong, as shown in the image below:

What am I doing wrong? How can I detect the signal maximum?


texts:
I've the following analog amplifier:

simulate this circuit – Schematic created using CircuitLab

The Vin is the input voltage of the amplifier and the V- system and the V+ system are the two points where I can controll the motor with the amplifier.

The questions I've are:

Has this amplifier a specific name?;
I think that the resistor R1 is a resistor to limit the current, but how does it do that?;
I think that R2 is a resistor to controll the voltage at the input of the voltage follower, but I can I caluclate that volateg?


texts:
For an experimental thermo-electric generator (TEG), developed by a colleague for low-power energy harvesting, it is possible to achieve an output power of 400 uW at the maximum power point. The voltage is 20 mV and the current is 20 mA.

This voltage needs to be switched up to at least 1.2 V, preferably 3.3 V.

How would you choose to proceed to switch up such a low voltage, also considering a need for maximum power-point tracking (could be simply current-limiting the input)?
It might not be possible, but in that case, what would you consider the minimum voltage, and how would you answer question 1 with that minimum voltage?


texts:
I have taken this from the FGPA XIlinx documentation, it says that a single 6 input LUT can be configured to be 2 5 input LUTs. Does anyone know how this is implemented?
Does a single address signal essentially enabled different LUT masks or memory?


texts: How to build (from scratch) a GFCI Circuit?

texts:
I am looking to understand what is the circuit inside a Ground Fault Current Indicator (GFCi). What does the circuit look like?

Simple google search is not yielding good results about the guts of it.


texts: What happens when you nand the same input?

texts: I am trying to conceptually understand what happens to the output of the second nand gate when input into the 1st nand gate are combinations 00, 01, 10, 11.


texts: Implement an 8 input AND gate with least delay

texts:
I'm trying to implement an 8-input AND gate using CMOS technology with the best number of stages and least delay (I have attached the schematic in the link given).

Using logical effort I have so far figured out that I should try to create a 5 or 6 stage design. I'm not sure how to find out the different configurations for a stage.

Can you give me some hint or source from where I learn more about how to find the different design configurations?


texts:
So I've got a pretty simple circuit that doesn't seem to be behaving as expected. I am unfortunately on a computer with no schematic drawing software so I scrapped together a schematic in mspaint...

But yeah as I'm hoping you can tell, it is 2 anti-parallel LEDs being driving by 2 MOSFETs. When I connect that open wire to +5V, the NMOS should turn on and the PMOS should turn off. Turning off the PMOS should have the resistor on the right pulling one side of the LEDs to ground while having the NMOS turn on should pull the other towards +5V. Now, the LEDs have slightly different Vfs but I only wanted to use one voltage source so I made the resistors have different values. The NMOS I'm using is a fairchild 2N7000, and the PMOS I'm using is a BS250, not sure who makes it.

When I bring the Gates to +5V, for some reason neither of the LEDs turn on.

Any reason this circuit wouldn't work as I expected? Thanks

EDIT LED Datasheet: http://www.advancedphotonix.com/ap_products/pdfs/PDI-E832.pdf


texts:
I am reverting here for some advice on a LED panel circuit that I am trying to build as I cannot find any concrete answers anywhere else online. My apologies as my understanding of electronics is very limited and I lack some of the basic understanding around voltages and current and how this is consumed by components. This is why I am reaching out to the experts.

The complete circuit that I want to build will have 100 LEDs. The specs of the LEDs are as follows from the datasheet:

Forward Voltage (VF) - Typ: 3.30V - MAX: 3.80V

Forward Current (IF) - Typ: 20mA - MAX: 25mA

The datasheet can be found here if it helps at all:
http://www.luckylight.cn/UploadFiles/484WC1C-W5-3P.pdf

My source voltage is a 5V 7A power supply.

Im not sure if I have the right forward voltage value from the datasheet though. I built a test circuit with 10 of these led's in parallel and they all lit up quite brightly. The test circuit got its power from the 5V pin on a raspberry pi which outputs 5V at about 200mA. When I measured the output on these pins using a multimeter before the LEDs were connected I got a reading of 5.22 V and after I connected the 10 LEDs in parallel I received a voltage reading of 5.17V indicating a voltage drop of around 0.05V for 10 LEDs. This is where I am a bit uneducated as the way I understand it is that  if I have 5 volts, I will only be able to power to LEDs with a forward voltage of 2.5V each and it baffles me as to why a circuit with 10 LEDs with a 3.30V forward voltage will light up so brightly on a 5V power supply.

What I would like to accomplish is to split the 100 LEDs into 5 rows of 20 where each row runs in series on its own resistor (just one resistor) due to the fact that the space on the circuit that I have is very limited. I then take that one row of 20 LEDs in series and duplicate it 5 times which gives me the 100 LEDs. I guess you can then say I have 5 isolated LED circuits all connected to the same power supply.

I have tried calculating the resistor value that I need to run all 20 LEDs on online calculators but they all provide me with a parallel diagram where each individual LED has it's own resistor which is not what I want. I want to run all 20 LEDs on one resistor so I need to calculate which resistor I need to do that.

My questions basically sums up to this:

How can I calculate the resistor needed to drive the 20 LEDs in series with all 20 LEDs using only one resistor?
I have 5V 7Amp on the power supply available in my project and at 25mA the entire circuit should utilize 2500mA or 2.5 Amps which should be fine. Will the 5V be enough to drive the 100 LEDs at 3.5 to 3.8 forward voltage per LED though? This is where I lack a basic understanding of how it works. I do have access to a 12V 3A power supply in the same project if this is needed.
Will it be a problem if I build the 20 LED circuit, duplicate it 5 times and connect them all to the same power supply?
Is it necessary to use a resistor at all with all these LEDs running on the same supply?

Thanks for the assistance.


texts: Connecting different specification LEDs in series / parallel combinations

texts:
How would you consider connecting two different types of LEDs, a white (6 V @ 150mA) and red (2 V @ 350mA) in a series-parallel combination? (W W R W W R W W) << parallel multiple strings of 8 series connected LEDs.

Similar LEDs will share more or less the same characteristics within a series / parallel circuit using a constant current and a small current balancing circuit (mirror or similar).

If I use a CC driver for the LEDs, it will divide the current to each parral string for instance 150mA per string. But now I have a couple of 350mA LEDs within each series string. This will either cause the efficacy to be next to zero or they will not even light up. Driving all the strings at 350mA will probably create a small electrical fire.

Any insights?


texts: How to wire up a circuit with a button that cancels other circuits

texts:
What I really want to do is slightly more complex than this but I can distill it down to the following concept. Let's say I have 4 buttons and 4 LED lights. Each button turns on 1 LED light. If any other lights are on when a button is pressed then they will automatically shut off.

I'm pretty new to electronics so the following will not be using technical terms if you can provide any in the response so I can tell the electronics store what I need that would be appreciated.

Ideally the buttons should be single action buttons i.e. no "down state". Considering that I'm assuming the momentary press of the button will have to trigger some kind of switch to turn the circuit for the LED on so that the LED will stay on. Do these switches exist and if so what are they called? Also can the button press to turn one light on also simultaneously "cancel" the other three switches for the other lights?

EDIT: Alternatively could you explain a way to have two momentary press switches and an LED. Where one switch turns the LED on and another turns it off.


texts: Which chip to use for automation using Wifi?

texts: I am working on a project where I will be controlling a device using android mobile phone (WiFi as medium). Which is the chip at present in the market which is low cost and effective for my application. the size is of no concern (it can be big).


texts: Why could a UPS device need of a microprocessor?

texts:
I have read about some UPS devices that are microprocessor-controlled, and I would like to understand the fundamentals of needing such a microelectronical device like a CPU for what it just seem a current management machine.

Why do some (all?) UPS devices incorporate a microprocessor? What do my UPS loose if it has not one inside?
How complex/advanced is this microprocessor and what are the advantages of having a better microprocessor for a UPS?
What happens if this microprocessor is not good enough, and how may detect such flaw?


texts: Why does my new, primary side EMI filter capacitors explode?

texts:
I have a HP 8568A (+ HP 85662A display module) spectrum analyzer.
In the last 2 days, I had 3 caps that released the magic smoke.
On the following schematics there is a capacitor C1 that I marked. The original, 40 years old ones exploded in about a minute, which is no surprise. On the other hand, the new one I bought also exploded. Capacitance is the same, 100nF.

What could be the reason for that? What kind of capacitor should I use here?
Old one:

New one:


texts: Ammeter for 24V power that can be read by a Raspberry Pi?

texts:
I have a project I'm trying to design and build that involves a "more accurate/useful" battery gauge for an electric scooter. The scooter runs on 24V off of two AGM cells in series. The details of the project are pretty interesting, but the one part I am stuck on is how to actually get the current readings into a Raspberry Pi for recording.

Basically I have the following idea so far:

Use a current shunt ammeter to read the current the scooter is using. Also need to get the voltage too, for proper watt calculation. Sample this current/voltage value often (once per second?) and use this to compute the watt-hours used. This is the part I'm not sure how to approach.
Write code on the RasPi to drive a character LCD, read the current and read input switches, and to perform data logging and computation to determine the remaining battery capacity.
Wrap this whole thing up in some kind of project box, hook up all the wires, add in a 24V-to-5V buck converter to power the Pi, and enjoy.

I do currently have a current shunt ammeter on the scooter, but it's just one of those manual ones that displays to a dedicated screen. I've done calculations to figure out the minimum available battery capacity based on the scooter's maximum current draw and the battery's internal resistance during discharge. Then I currently do the calculation in my head to figure out the percentage remaining based on Wh used on the display. But with a RasPi driving this I could do all sorts of fun stuff - GPS tagging, battery "odometer" (total Wh used since battery was installed), and even a podcast/music player because why not.

The only thing holding me up is figuring out the best (and safest) way to get the current and voltage readings. The scooter's maximum possible current draw is around 20 A at 24 V, going up a steep hill at full speed. I'm not sure if the RasPi itself is sensitive enough to get decent voltage readings that can detect the miniscule changes a current shunt registers, and the only other device I have is a multimeter with a USB optical interface, but that seems way overkill and would require more work. Ideally I'd find some sort of ammeter like the one I currently have, but with a USB port (or an RS232, since I can convert that easily) so the RasPi can read the current ratings in real time.

Anyone have any insight? I'm guessing someone has to have done some sort of ammeter project around a RasPi before?

(PS: I actually want to develop this project even further, possibly working out algorithms to account for the varying current the scooter draws over time, and the battery's natural aging and capacity loss, and also to read incoming charge current from the charger as well as discharge current. I have lots of ideas - but all of it hinges on being able to read current from the 24V system into the RasPi as numeric values.)


texts: Calculating for Load Resistance given a T network in between the source and the load

texts:
Problem: Calculate the value of load resistance (Rl) for which maximum transfer occurs.

Attempt: What I know is that for the maximum transfer to occur, the load resistance must be equal to the source resistance, in our case, the equivalent resistance of the resistors in T network.

Maximum transfer results to 50% efficiency, \$n = 0.5 = \frac{Rl}{Rl + Req.} \$. So If I could get the equivalent resistance of the T network, I can plug it in on the formula and get the load resistance. Problem is I don't know what to do next.

Any tip or help will be appreciated or a thorough / step by step explanation would be great for a newbie like me. Thank you.


texts:
I've made a single transistor preamp for an electret mic. The curcuit is like this:

simulate this circuit – Schematic created using CircuitLab
I want to use this on a computer. The mic input of the pc has a GND an a mic wire. Should I just connect the GND to GND and OUT to mic or sth else is needed?
Newbie here. Thank you


texts: Designing an optimal BPSK and/or QPSK transciever in SDR

texts:
I'm currently working on writing firmware for the modem on a cube satellite for my university's satellite team. My primary goal is to implement the data uplink & downlink.

The RF system, completed before I arrived, receives on the 2m band and transmits on the 70cm band. The RF system takes the signals (IF of 10.7 MHz) and converts them using an I-Q transceiver to a 48 kHz wide zero-IF complex baseband, which are passed to and from the digital realm through an audio stereo codec.

The DSP itself is to be performed on a PIC32 microcontroller using fixed point arithmetic, and my task is to write the firmware for it.

For the data channel, I was just planning do something "simple" like BPSK or QPSK as they have good performance under high noise conditions.

My question then is this: what is the ideal structure of an optimal BPSK transceiver, and what would be the most efficient way to do it in SDR?

I know that I'll need to include some sort of pulse shaping, such as a root-raised cosine filter. As far as I know, the ideal BPSK transmitter should look something like this:

Input bitstream at 2 kB/sec
Differentially encode bits
Upsample differential bitstream to 48 kS/s and pass through Root Raised Cosine filter for pulse shaping.
Take output of RRC filter to be I(t), and take Q(t) to be zero
Multiply by complex sinusoid to shift up by a few kHz (there will also be an FM voice channel and I would like to keep them well separated)
Pass complex samples to codec output where they will be mixed to RF by the upconversion chain.

Does this seem correct?

I'm a bit lost for the receiver though. As far as I know, this is what I need to do:

Recover and track the carrier, use it to train the local oscillator.
Downconversion using synchronized oscillator, giving I(t) and Q(t)
Assuming perfect synchronization, I(t) is the message signal and Q(t) is zero, so pass I(t) through a RRC filter to eliminate noise and ISI.
Perform clock synchronization, differential decoding, and and data recovery on I(t)

I'm a bit confused on how to best perform carrier recovery. I know about Multiply-Filter-Divide, but that would mean I may need to upsample the signal depending on its frequency offset (as aliasing may occur if the outside edge of the band is less than half my upper bandwidth, or less than a quarter in the case of QPSK).

I know that Costas Loops exist, but not much beyond that (my university has never been very big on practical stuff and my comms textbook essentially mentions "these are a thing") - would this be a reasonable way to do carrier recovery in SDR?

Clock synchronization is another iffy point - what's the best way to do this? Barker code preamble? 8b/10b?


texts: Can I replace a 101 ceramic capacitor with a close value one?

texts:
I'm kind of new to electronics and sorry if this is a bad question.
I am trying to repair my father's old radio transmitter and I noticed that the PTT won't pick up your voice. I opened it up and found that in the microphone there is a ceramic capacitor that is burned. It is a 101 but I only have a 56, a 104 and a 220 at hand.
Can I replace the burned one with one of those mentioned without breaking the PTT?


texts: Current through a Push-Pull Output connected to a Microcontroller

texts:
I am using S32K142 64-pin Microcontroller.  3V3 Supply.
I am interfacing this Stepper Motor Driver to the Microcontroller using SPI lines.
I have already asked a similar question over here
The SDO pin from the Driver IC is the output and Microcontroller takes this signal as the input.
The SDO pin is a push-pull output. And this is connected to the GPIO pin of the Microcontroller.
I am trying to understand on how much current would flow (source or sink) from the push-pull output to the Microcontroller input pin (sourcing current or sinking current).
Like, on what parameter is the current dependent upon?
Like, does it depend on the internal pull-up or pull-down resistor of the microcontroller? Should I enable the internal pull-up or pull-down resistor?
I am doing this because, I am trying to make a logic IO compatibility between the Driver IC and the Microcontroller.
Since the Microcontroller takes input from the SDO pin, I have not mentioned Voh and Vol levels under the Microcontroller column. And similarly, since the SDO pin is output from the Driver IC, I have not mentioned the values for its Vih and Vil.

So, can someone tell me how to find the Voh and Vol voltage of the SDO pin on the Driver IC?


texts: Testing the condition of an old sealed-lead-acid (SLA) battery

texts:
I have a small 3 year-old 6V 1.2Ah SLA battery that is used in a solar powered burglar alarm sounder box. The sounder recently stopped operating and the battery shows a voltage of about 4V so I am recharging it (using a charger designed for this purpose). I will clean the solar cell and replace the unit's 9V PP3 battery which is really only for initial start-up.

However I know that SLAs have a finite lifetime and are typically replaced every five years.

I also have a spare 6V 1.3Ah battery that is probably of similar age but which has not been used for 3 years (1V shown).

After charging them back to 6V, is there some way I can test these batteries using a multimeter, a load such as a light bulb of known wattage (and possibly other components) to see which battery is in best condition or whether I really should buy a new one?


texts:
I would like to build a passive band-stop filter for my earphones. I recently had some help from the user "Andy aka" with designing that type of filter and he also pointed me to the LTSpice application for running simulations.

After playing with some values, I think I have what I want, but i have a few questions before I go and purchase the necessary components.

Here is the circuit:

And here is the list of components from mouser:

I would just like to know if I'm missing anything or if these components and graph look correct?

I want to cut the 5800-6000hz region by roughly 7.8-8db with a Q between say 14 and 17. The resistor R2 in the schematic is there in place of an adapter I will connect at the earphone jack (R3). This is because my audio interface is 32 ohms. If I use the filter on that interface I remove R2 and the values of the graph remain the same. When using a 1ohm device like my portable amp, the adapter brings the graph values back in place.

I just want to verify that this should work and I have all the components I need. I added an extra components as a fail safe. :-P

Also, are any of the other values critical with the components? I tried to get the best tolerances I could for each and the highest reasonable power handling...


texts: When do truth tables use the "Don't-care" term?

texts:
In which situation can be used the Don't-care term?
Suppose that I want to use 6 symbols: I need 3 bits, which in turn can generate 8 combinations. Since the last two combinations aren't useful in my case, should I put them to 0or Don't care?

This is the truth table of the useful symbols

0 0 0 | 1
0 0 1 | 0
0 1 0 | 0
0 1 1 | 1
1 0 0 | 0
1 0 1 | 1
------

The output of the combinations below doesn't exist, or it's irrelevant

1 1 0
1 1 1


texts: Operating principles of a sawtooth wave generator bootstrap circuit

texts:
In one of my assignments, I was asked to explain the working principles of the sawtooth wave generator shown below. The input voltage is a spiked waveform obtained from a differentiator circuit.

I realise that the transistor is supposed to act as a switch and C1 is getting discharged by it, but what I don't understand is the role of Vcc, capacitor C2 and the op-amp.


texts: What is the source of this shape on my USB eye diagram?

texts:
I have designed a USB device around an STM32F105.  It is USB 2.0 Full Speed CDC device configured as a Virtual COM Port using ST's USB Library.  It uses the STM32's built-in PHY, and runs at 12 Mbps.

I'm sending data in 254-byte packets.  Occasionally (averaging 1 in 17000 packets) the host computer receives bad data.  It is generally constrained to a single byte in the packet.

So I'm looking at the signals using a Tektronix TDS2025 O-scope (200 Mhz).

Most of the transitions look great:

But my low-tech eye diagram shows something unexpected:

I managed to trap one of the bad waveforms, which looks like this:

What might be causing this?  I'm not sure where to start looking.

When I first plug in the device, the enumeration takes place successfully, and the eye diagram looks clean.  But once I open the COM Port (using PuTTY, Hercules, or my custom java software), the glitches show up.  I'm using a Lenovo Thinkpad with Windows 7.

Here is a picture of the layout:

The TVS IC is an NXP PRTR5V0U2F, and the Charger Detector is a TI BQ24392.

The USB traces travel about an inch on the back side of the board, then they come back up and connect directly to the microcontroller's USB pins. They are impedance controlled and appropriately length-matched to each other.

I'm probing from the USB connector's solder pads to the ground point which I've labeled on the picture.  The probe had a short ground spring, not a long alligator clip.

If more data would help, please let me know.  Also, this is my first USB device, and my first eye diagram test.  If you see something wrong with my setup or assumptions, please let me know.


texts:
I have a power supply that can output 3V, 4.5V, 6V, 7.5V, 9V or 12V and 24 white LEDs 3,2V - 3,5V (I think I'll need resistors as well, right?).
I need a circuit that lights all LEDs and uses as less power as needed.

If you can help me that would be great.

Thank you


texts:
Is this ok? Or should we avoid using a loop like this

3 phase cables connecting from an isolater to terminals.
 The cables have a coil like loop in them.. a single loop to make it less stressed because the distance between the two is very limited.

http://imgur.com/gallery/hlQ3XaC


texts: how can I "ruggedize" a 3.5mm jack on consumer electronics?

texts:
I'm not sure if this is the best place to ask this.

I've had repeated issues with stress on 3.5mm jacks causing breaks to the solder which means either rewiring or throwing the headphones out. Usually it's more sensible to throw them out and buy a new one considering the time commitment (I'm terrible at rewiring small devices like this, it's a minimum of an hour of work to get it right if it's a TRRS).

Here's a typical connector:

My first thought is to wrap it in several layers of heat shrink tubing at the connection between the TRRS and the cable. That area seems to see the most stress.

Skill level: basic soldering and that's about it. I have soldering iron, wick, solder etc. Perhaps the answer is to buy better equipment, but I've spent much more on IEMs and still had the solder point at the jack fail.


texts: How can I model/understand this isolation module's CMR rejection ability?

texts:
Before asking the question here I have to show how I was demonstrating the CMR simply:

The first circuit above represents a 100dB CMRR and the second circuit shows how the 1k Ohm source impedance degrades the CMRR at DC. 10uV becomes 19.5mV and the CMRR degrades to 35dB !!!

Now regarding my question:
I'm planning to use these isolated signal conditioning modules in my case will be 8041-03 which has also built-in 1kHz filter. I have been in contact with manufacturer several times but I couldn't get some information settled.

The thing is I want to use these modules for single ended very low frequency transducers(always lower than 150Hz) such as temperature humidity or load cell transducers which are powered by SMPS power supplies and currently they are transmitted by coaxial cables around 15 meters length.

In the module's datasheet the CMRR @50 Hz is given as 100dB. According to them these modules are single ended but because the they are isolated, the input stage behaves just as well as or better than a differential input.

So since I don't know the transducer output impedance I asked them about how much would the CMRR degrade with different output impedance. And the answer I got was they specify CMR at 50/60 Hz, but the CMR results are valid for DC common mode voltage as well. They performed CMR test setup and they used discrete wires, 2-3 feet long. The frequency was 30Hz.

Their basic setup was as follows:

So they shorted the two inputs of the and applied a common mode voltage along the inputs. The values of R they used were 0 ohm, 100 ohm, 1 kOhm, and 10 kOhm. In each situation they measured the output voltage and determined the CMR in dB. The results obtained are as follows:

0 ohm: 100.5 dB

100 ohm: 100.3 dB

1 kOhm: 100.1 dB

10 kOhm: 99.9 dB

Their conclusion was even with a source impedance imbalance, the isolation in these modules will still provide a high level of CMR. Very little degradation of CMR takes place even as the source output impedance increases.

I have two questions I couldnt figure out:

1-) They say these modules are single ended with a 100kOhm resistor on the positive input. However, the 1500Vrms isolation barrier in the module will reject any common mode voltages or noise as a result of an impedance imbalance.

I really dont understand how can that be achieved. This doesnt fit the model I presented before the question. How come the CMR does not change with output impedance? Is there a way to model this module roughly maybe by using transformer? I need to demonstrate it.

2-) They also mention coaxial would be alright for my purpose. How can I model the BNC would not have much effect on overall CMR for under 1kHz? I though 50Hz can magnetically couple to BNC inner and outer lines and would create common mode noise. Would I really need STP in this case?

Edit:

Can I use the following model for such an isolated high CMR module?:

For a very high CMR I made the input resistors infinity.

But because of coaxial cable is not symmetrical the total parasitic impedance to ground will be for inner wire Rs+j/ωCp1 and for outer(shield) wire will be j/ωCp2.

So it seems the differential noise due to common mode interference seems independent of high CMR. I really don’t understand why they claim I wont have an issue upto 1kHz common mode interference with coaxial(not STP) and source impedance Rs.

Can this be a model for coax and Rs effect to the degradation of CMR?:


texts: Can anyone explain the term Rd/ro in the gain of this amplifier?

texts: Actually the half circuit is a simple source degenerated CS amplifier so i am not getting how the term \$R_D/r_o\$ came into the gain equation.


texts: Two-Terminal Passive Analog Component Tester Using the DE1-SoC Development Board

texts:
I am having hard time understanding this problem. I have to draw a Level 1 block diagram for this system. I really appreciated it if somebody can help me. I am new to DE1-Soc.

use the Intel  DE1-SoC development board, additional custom circuitry (Bread board) and possibly an external source for input waveforms to implement a system that will allow any of four possible types of two-terminal passive analog components to be connected to it, and identify the connected two-terminal as being one of the four types. The four types of components are as follows:

Resistors
Capacitors (non-electrolytic only)
Inductors
Diodes

test results for a particular connected component should be displayed on the seven segment LED.

Thank you for your time.


texts: Stepper Driver pulses control (with Arduino)

texts:
I intend to control the speed of a stepper motor thanks to a driver connected to Arduino (Mega).
Basically the driver has, among others, 2 pins, PUL+ (Vcc) and PUL- (GND, common cathode), and each time a cycle LOW / HIGH is executed on these pins, the motor does one (micro)step (in "single pulse mode", there is another pin for the direction, but that doesn't matter in the context of this question).
The driver manual says

Question: I'm wondering about "dutycycle of pulse is recommended 50%": since the level reference seems to be HIGH, according to the graph below, does it mean that the HIGH level following a LOW, when doing a pulse, has to be at least the same duration as the LOW, or do they both simply need to obey by the \$\ge 2.5\text{μs}\$ rule? (and in this case why does the manual mention the recommended 50% duty cycle?)

Added details: the Arduino loop will be quite complex, and based (empirically) on the speed of the Mega, I initially thought about doing a LOW for \$50\text{μs}\$ followed by a HIGH of at least \$50\text{μs}\$ for a max speed of \$\dfrac{1}{1600\cdot 10^{-4}} = 6.25\$ RPS (1600 microsteps setting). And when reaching the max speed the LOW might last more than \$50\text{μs}\$ (due to Arduino doing other things in the meantime), while the following HIGH might last less, thus we could have something like
$$\text{LOW}_{80\text{μs}} \to \text{HIGH}_{50\text{μs}} \to \text{LOW}_{70\text{μs}} \to \text{HIGH}_{50\text{μs}} \to ...$$


texts:
When I design something or going to add a fuse to place where fuse isn't used now, should I prefer slow or fast fuse? I understand that this depends on situation, but I'd like to hear what do you prefer if there are no special circumstances.

To be more specific, I am going to use a 20x5mm 250 Volt glass fuse. I know how much current the circuit takes, so it is not problem to choose a fuse with the right current I need. But should I take slow, or fast?

If I understand it correctly, the slow fuse is more tolerant to shocks during power-on of the device. For example today I think of a fluorescent lamp ballast in my kitchen which is a weird chinese unfused circuit and fuse addition seems to a be good idea. Since there can be a higher current moment during start of fluorescent lamps, a slow fuse possibly allows me to use a lower Amp one.

On the other hand, if I use a fast fuse, I can safely use a higher Amp one and still it will react sooner in the case of short circuit. A higher Amp fuse also has much smaller resistance. So for example I personally would prefer 1 or 2 Amp fast fuse instead of .150 Amp slow fuse for that kitchen lamp. Is this a good idea, do you agree with me?

(The kitchen lamp is a real example, but it's just an example. I'd prefer to know if you prefer slow or fast fuses. I mean classic replaceable 20x5mm glass fuses / 250 Volt.)


texts:
I've just been learning about the monostable circuit in electronics and have a question about its function. So, we have this circuit:

simulate this circuit – Schematic created using CircuitLab

Now, the capacitor charges to 5V almost instantly when !A is 0. This causes an output of 0 at !Q, which causes the NAND gate to continue outputting a 1. My question is: Why isn't this a stable state? Why doesn't the circuit continue outputting 0 at !Q?


texts:
I understand that thee voltage level for LVDS standard has a typical offset voltage of 1.25V and voltage swing of 350mV. However, when I am doing some pin mapping on Xilinx FPGA, I encountered some different LVDS standard: LVDS_25, LVDS_18 etc...

May I know what is the voltage range for LVDS_25? Does that mean offset of 2.5V and voltage swing of 350mV?where for positive output of (2.5+0.35)V is a logic '1' and (2.5-0.35)V is a logic '0' and vice versa for complementary output port?

Thank you


texts: Custom Bluetooth 5.0 audio transmitter analog LINE IN input attenuator from a 3W speaker amplifier

texts:
I'm not a professional electronics engineer so I'm looking for some help in solving this problem:
I'm developing my own custom Bluetooth 5.0 audio transmitter module using a FSC-BT802 module from Feasycom, and I have a toy sound board with a 3W 5V mono speaker audio amplifier differential output.
This board also has an I2S or SPDIF audio output, but I would prefer to use it's speaker analog output instead (just for easier setup, I want to be able to swap a 3W 8 Ohm or 4 Ohm speaker with this Bluetooth transmitter module having a single 2-pin audio connector for both).
My BT802 module also has a differential analog LINE IN audio input (instead of the microphone) and I2S or SPDIF, but again, I prefer to use analog LINE IN. So I followed a recommended schematic by Feasycom in BT802 datasheet, made the PCB with audio level attenuator from 5V to 1V level using 10k resistors for Audio Negative and Audio Positive with a 5k resistor across them.
Sound gets lower volume but I always get a "white noise" on background in the remote speaker that receives this audio signal from my custom BT802 transmitter.
I also tried a recommended "single-ended" LINE IN input setup and it worked much better without a "white noise" on background, but I can't use it because I also need to connect a common GND wire between the toy sound board and the BT802 transmitter module in order to use RX/TX UART remote control interface (yes, I also need to use it in this setup). And since toy sound board has a differential speaker amplifier output, once I short the negative speaker audio output to GND, it loses audio, so I can't do that.
So the issue I'm struggling with is the "white noise" in the audio receiving remote speaker, which I think can be caused because of a too high LINE IN gain settings in the BT802 module itself.
So if lower the gain, noise may go away and will need to adjust audio input attenuator resistors for a good output volume. But why there is a noise only with "differential" input but no noise if I use "single-ended" LINE IN input schematic? End can you recommend a better audio LINE IN level attenuator schematic for my setup?
Thanks in advance!
Toy sound board speaker amplifier:
PDF Datasheet
Single-ended input diagram:

Differential input diagram:


texts: Need help with setting up Li-ion battery parameters in a Solar Charge Controller?

texts:
I am trying to set up the parameters for a LiFePO4 battery bank for a solar charge controller. I have tried to search the internet for understanding the parameters listed in the charge controller, but couldn't find any direct specification from where I would be able to calculate the parameters. So please pardon my ignorance regarding the basics.

The charge controller I am using is: Wanderer by RENOGY.
The battery bank is consisted of 7 individual Li-ion battery cells (2500 mAh, 3.7 V) in parallel and three such paralleled cells in series.

The aim is to disconnect the load from the battery when the battery voltage would become <10 V. Also, the voltage level of individual cells shouldn't be more than 4.15 V and less than 3 V. Depending on these conditions, how should I set up the below parameters in the charge controller?

High Volt Disconnect(V)
Charge Limit Voltage(V)
Equalize Charge Volt(V)
Boost Charge Volt(V)
Float Charge Volt(V)
Boost Charge Return Volt(V)
Over Disc Return Volt(V)
Low Voltage Alarm(V)
Over Discharge Volt(V)
Over Disc Relay Time(S)
Equalize Charge Time(Min)
Boost Charge Time(Min)
Equalize Charge Interval
Temperature Compensation(mv/C/2V)

Thanks


texts: Is it okay to use wider trace than actually required while designing a PCB?

texts: I used eagle to recently, design a board with all trace widths 30 mills except a few as 20 mills. I actually didn't require traces this wide and 15 mills would probably have been enough. Does this cause any sort of issues in the functioning of the board?


texts: How to export and print the PCB in Altium

texts:
Hi I have done a very basic PCB (only one layer) with Altium, but when I'm trying to export the pdf, the obtained file has different sizes: in particular my 15x15cm circuit is expanded to the whole A4 page.
How can I export the PCB in a manner such that the defined sizes are respected?
I don't need the gerber file, since I'm going to use press n'peel to print it, I need only a proportionel and well sized pdf or image.
Thanks


texts:
I have the following LCD: http://www.xmocular.com/Upload/CMpdf/GDM1601C-01010742776.pdf

I am trying to hook this up to my Teensy. I assume that because it has 16 pins that it's a HD44780 display. Am I correct?

I'm following this guide to hook up the LCD to the Teensy: https://wiki.natenom.com/w/Connecting_a_Teensy_3.0_to_a_LCD_(HD44780_display)

The problem I'm having is I'm getting nothing on the screen. I have a pic of my breadboard but it's probably mostly useless: http://imgur.com/cepm6p6

I don't quite understand where the pins from the LCD should be going into the Teensy - I followed the guide. I noticed that pin3 is the contrast, but on the guide pin3 is going to a digital pin on the teensy. I'm not sure if that's correct.

What could I be doing wrong?


texts: Wiring an on-off switch to the inputs of a daq

texts:
I have the following reed switch sensor:

I need to connect this switch to counter input of this daq hardware.

The only info is the following:

How should I connect this to the counter-input? Any diagram would help.
And do I need a debouncing filter?


texts: What is the ratio of antenna length to power?

texts: A question that came up in class; what is the relationship between length of a solid cylindrical antenna (wire) and transmission power? I would imagine it's frequency dependent


texts: Making use of bike battery to charge mobiles without any other power resource?

texts:
I need to make my mobile charging in bike, while I go long tours. Actually the bike battery has DC 12-9 volts power and I saw on the phone charger that there is DC 5 volts (or) can I connect the mobile charger directly to the bike battery (12 volts dc to give 5 volts dc)?
By implementing this we can charge the mobiles whenever we need or when our our phone battery drains.


texts: How does interdependent state logic work?

texts:
I'm deriving the logic for an up-down counter and have equations which connect bit states \$Q_{n+1}\$ to previous states \$Q_n\$.
On each rising clock edge, the data bits of the counter change depending on the state of some UP/NOT_DOWN line and, as with all counters, the states of other bits of the counter.

I'm a little confused on how to express this logically though (for programming a CPLD), because surely, unless every bit changes instantaneously (not possible), the logic will fall apart (as the logic for one new bit would suggest "reading" the logic of an already changed bit).

Is this all part of the "timing optimization" procedure you see implementation and synthesis tools do, or is this something which needs to be considered at the design level?

EDIT: I suppose another way of asking the question would be to address whether each bit needs to be stored in some temporary storage between states, in which case, why don't we see such architectures discussed often?


texts: Fix the Problem for Shunt Resistor due to Temperature & Current Sensor

texts:
I am trying to build a current sensor here. My original thoughts starts from this paper [real-time current-waveform sensor with plugless energy harvesting from AC power lines for home/building Energy-management systems][enter link description here]
Anyway, if you do not scan that paper is OK.  [link]: http://ieeexplore.ieee.org/stamp/stamp.jsp?tp=&arnumber=5746292

Now just take the DC battery into consideration. I wanna detect the current as accurate as I could be when it charges. The charging current could be very small or very big(the up limit is several or decades amps, and the down limit is smaller, and better I hope)

I have two main thoughts how to realize it. One way is use the Hall effect current sensor, but I know it is costly, and I am still trying to find more things about it. (I am not sure if it is the best way, what is the state-of-art hall effect current sensor now? )

The other way is use the shunt resistor way. Depicts like this:

WRT the current detecting device, I can use a Differential Amplifier or more complex device to get the voltage, but here is the Question, the resistor is changing when it charges, the resistor's value is a function of the temperature parameter T. So as I wanna have a very accurate current sensing, how can I deal with the resistor's change by temperature?

BTW, the resistor with low coefficient, such as the open air sense resistor, their temperature resistance range is like 0.005 ohm~0.03 ohm @70°, which is big to me. So is there any possible, I dont even need to know the exact resistor value(just know the vague value, 'cause it is changing due to temperature.), and I can also detect the current flowing the resistor? Or is there any temperature compensation way to make the change smaller than the open sense resistor?


texts:
Can't find a Datasheet for this charging ic from an iPhone 6. Hopefully someone can explain its function to me.

Things I'm confused about; Does it take USB power and convert it to both vcc_main and vbatt? Or does it output vcc_main and vbatt is also an input to the chip?

What's q1403's role?


texts:
I have an idea for wiring the lights in a room, which I have run past a few electrician friends, and have received contradictory and unsure answers.

There is a large room with two sets of lights - one on each side of the room. Each circuit consists of two 50W 12V halogens. There are currently two switches and two dimmers controlling the circuit.

I like being able to switch on each half of the room individually, but I have realised the dimming levels I want from each side are always the same.

My idea, when I get some other work done, is to put one dimmer upstream of the two switches, so one dimmer controls both circuits.

(i.e. active -> dimmer -> two switches in parallel -> each set of lights -> neutral.)

The sensible advice I have received:

Check the lights are of a type that can be dimmed. (Yep, they already are being dimmed.)
Check the rating of the dimmer can handle the extra load. (Yes, with a good safety margin, because they get hot in a wall cavity.)

The conflicting advice I have received:

If one set of lights is on, and you turn on the second set, (a) yes, the original lights will remain the same brightness, and (b) no, the variable resistor will heat up a little, affecting resistance and the brightness will change slightly.
More importantly: leaving a dimmer upstream of the switches, permanently connected to active will (a) be perfectly fine, (b) will be more susceptible to damage due to spikes (e.g. lightning strike) or (c) will make the dimmer burn out more quickly and should be discouraged.

Would have a dimmer attached to active but disconnected from a load cause it to fail more quickly than having it wired normally (i.e. downstream of the light switch.)?


texts: Emulating a switch with open drain outputs

texts:
I need to replace mechanical switches with some kind of digital switch. Specifically I want to sent control inputs to various arcade games that use standard JAMMA inputs, which are basically switches to ground for each button/joystick. The inputs will come from a 3.3V microcontroller, but most games use pull-ups 5V so a buffer is required.

The obvious solution is to use open drain outputs. I'm trying to decide what type is best. The two candidates I have are the SN74LVC07 hex buffer and a ULN2003 or similar Darlington array. The SN74LVC07 is MOSFET based with open drain outputs and rated up to 5.5V, where as the ULN2003 will accept higher voltages (arcade systems do use 12V, although I doubt any use it for control inputs) and is probably a bit more robust.

Any comments on which of these would be best, or would some other option entirely be better? What about unused buttons? I can't see any issue with leaving those outputs disconnected and the datasheets don't say anything.

Thanks.


texts:
I know that the electrical generators have mechanical and electrical power losses.
But does electrical or magnetic phenomena in a generator produce a counter torque?
Or all the electrical power losses are related to current losses?


texts: What is the plastic barrier surrounding this choke for?

texts:
I disassembled the mains power supply from an audio mixing desk. Immediately after the switch and inrush protection NTC is an Epcos B82722 10mH / 1A choke (the blue component in the photo below).
The choke is surrounded by something wrapped in white plastic, which is held to the board with a cable tie.

I assume this is some form of shielding, designed to minimise any effects from the magnetic field on the adjacent switching circuit.
Is this assumption correct? What are these shields typically made of? I am trying to repair the power supply so would rather not remove it from the board to find out.


texts: How to use ATMega USART in synchronous mode using XCK pin

texts:
I'm working on a project with ATMega64 and I have a problem with one of the USART interfaces which is going to work in synchronous mode.

when trying to send a test data like:

char data[10] = {'1', '2', '3', '4', '5', '6', '7', '8', '9'};

everything goes fine, but trying with:

char data[10] = {'1', '2', '3', 'A', 'B', '6', 'C', '8', '9'};

causes a problem with non-number characters. it looks like my problem is in MSB bits that they can't be  transmitted properly.

As this error occurs on every letter character that seems to be something that I've forgotten to set / check. since I haven't worked with this type of micro-controller for a while, maybe I've missed some configurations.

every sending and receiving data works fine in asynchronous mode but setting UMSEL to enable synchronous mode and using XCK pin effects the transaction.

here is my synchronous configurations:

Master micro (XCK output):

PORTD = 0b00000100;
DDRD  = 0b00101000;

// USART1 initialization
// Communication Parameters: 8 Data, 1 Stop, No Parity
// USART1 Receiver: On
// USART1 Transmitter: On
// USART1 Mode: Sync. Master UCPOL=1
// USART1 Baud Rate: 2400
UCSR1A=(0<<RXC1) | (0<<TXC1) | (0<<UDRE1) | (0<<FE1) | (0<<DOR1) | (0<<UPE1) | (0<<U2X1) | (0<<MPCM1);
UCSR1B=(1<<RXCIE1) | (0<<TXCIE1) | (0<<UDRIE1) | (1<<RXEN1) | (1<<TXEN1) | (0<<UCSZ12) | (0<<RXB81) | (0<<TXB81);
UCSR1C=(1<<UMSEL1) | (0<<UPM11) | (0<<UPM10) | (0<<USBS1) | (1<<UCSZ11) | (1<<UCSZ10) | (1<<UCPOL1);
UBRR1H=0x08;
UBRR1L=0xFF;

Slave micro (XCK input):

PORTD = 0b00100100;
DDRD  = 0b00001000;

// USART1 initialization
// Communication Parameters: 8 Data, 1 Stop, No Parity
// USART1 Receiver: On
// USART1 Transmitter: On
// USART1 Mode: Sync. Slave UCPOL=1
UCSR1A=(0<<RXC1) | (0<<TXC1) | (0<<UDRE1) | (0<<FE1) | (0<<DOR1) | (0<<UPE1) | (0<<U2X1) | (0<<MPCM1);
UCSR1B=(1<<RXCIE1) | (0<<TXCIE1) | (0<<UDRIE1) | (1<<RXEN1) | (1<<TXEN1) | (0<<UCSZ12) | (0<<RXB81) | (0<<TXB81);
UCSR1C=(1<<UMSEL1) | (0<<UPM11) | (0<<UPM10) | (0<<USBS1) | (1<<UCSZ11) | (1<<UCSZ10) | (1<<UCPOL1);

the problem comes again exactly on every iteration so I don't think this data loss would comes from a connection problem.

or maybe in synchronous mode I should always send a spare bit and using 9 bits for a 8 bits data. does this have a meaning?

I'm using CodeVisionAVR as the compiler but also every other code in C language would be helpful.


texts: I've been reading about resistors vs. voltage regulators, but can't settle on which would be better in my case. I have a power supply for a mic preamp that has 15V and 48V. I want to add an LED to the power switch. Would it be best/most efficient to use an appropriate 1/2 Watt resistor, or a voltage regulator? I have both so I'm not worried about cost, but which is the "right" way to do something simple like this? The regulator I have on hand is the LM317T. I also have a 7805CV, and I think any of the 3 options will work fine with the 15V, but if someone could briefly explain which works best here or point me to some literature on the topic, I would appreciate it!


texts:
I want to use an Analog Devices LDO regulator (ADP7104ARDZ-5v.)

When I checked the datasheet, I found out that it requires just a 1uF capacitor on the output pin.  Then I searched more and I found an evaluation board (EV-ADF4159EB1Z) that this regulator had been used on. On the evaluation board, there is a 4.7uH inductor,  a 0.33 ohm resistor, and a 100 uF capacitor rather than just the 1uF recommended in the datasheet.

I want to know why they used a very low value resistor together with a high value capacitor.

Here is the circuit from the evaluation board:


texts: How to check receiving 16-bit data using a serial terminal?

texts:
I am using an FPGA vhdl UART code to send 16bits of data with a 1 start bit, 1 stop bits and even parity bit. I need to check whether the sent 16bit packets are correctly receiving using a terminal software on windows pc. I did a research on google and found many terminals that only allow for 8 bits of data with parity check + start + stop bits, in my case its 16 bits. so how can I monitor this 16 bits of data using a terminal?

Updated,

I have performed something like this (pseudo-code) and did not work

X_16_bit --> 16 bit data
X_16_bit --> AB

A ---> upper 8 bits

B ---> lower 8 bits

this 16-bit X_16_bit updates at every 0.5 seconds. in a 50MHz clocked process, in the same process, I do below operation. (did not work)

x <= 0; and y <= 0; are initialized as varibles inside below process

process(clk_50)
variable x  : STD_LOGIC:= '0';
variable y  : STD_LOGIC;
variable A  : std_logic_vector(7 downto 0)              := x"00";
variable B  : std_logic_vector(7 downto 0)              := x"00";
variable X_16_bit   : std_logic_vector(15 downto 0)             := x"0000";

begin

                  ------------------------
***THE CODE THAT calculates X_16_bit at every 0.5 seconds***
                   -----------------------

//SPLITTING code runs in 50MhZ clocked process

if (x ='0'){ // stop A and B is being mixing with a new value
 A :=  X_16_bit(15 downto 8);
 B :=  X_16_bit(7 downto 0);
}

if (x='0'){ // 1stly send upper 8 bits
  tx_data <= A;
  y:=1;
  x:=1;
}
if (y='0'){ // 2ndly send lower 8 bits
  tx_data <= B;
  x:=0;
}
y:='0';
end process;

the below error was solved,
tx_data is a signal that used to transmit data in tx transmitter process
i got error

 Error (10028): Can't resolve multiple constant drivers for tx_data

UART transmitter is another process I use baud rate 19200 even parity
the VHDL I have used is in this link

UPDATED

process(clk_50)
variable x  : STD_LOGIC:= '0';
variable y  : STD_LOGIC;
variable A  : std_logic_vector(7 downto 0)              := x"00";
variable B  : std_logic_vector(7 downto 0)              := x"00";
variable X_16_bit   : std_logic_vector(15 downto 0)             := x"0000";

begin

                  ------------------------
***THE CODE THAT calculates X_16_bit at every 0.5 seconds***
                   -----------------------

//SPLITTING code runs in 50MhZ clocked process

UPDATED

        X_16_bit := x"4563";
        IF(x = '0') THEN
            A := X_16_bit (15 downto 8);
            B := X_16_bit (7 downto 0);
            tx_data <= A;
            x := '1';

        ELSIF(x = '1') THEN
            tx_data <= B;
            x := '0';
        END IF;
end process;

UPDATED
with this code i get only 63 on tx output. i dont get 45 at all.


texts: Can anyone tell me how to find permittivity of a dielectric sample using a rectangular waveguide

texts: Im trying to find the material paramters of a dielectric sample using a waveguide(X band) employing the Transmission/Reflection technique. While performing simulation in CST, how to properly orient the sample inside? Is it necessary that the waveguide is flared?


texts:
In the picture below, I am connecting a constant power resource and a battery to each other by a lipo charger.

The circuit should consume power from the adapter (NOT battery) while it is available. When the electricity goes off it should consume power from the battery.

Is this coupling correct?


texts: ESP8266 (Wemos D1 mini) analog thermistor

texts:
I'm trying to connect my floor heating thermistor (NTC) to ESP8266 (at Wemos D1 mini board). But I'm unable to get good results.

I get an approximation formula from this table (after I input my values in). calculation table

But I get 41°C (should be around 24) what is really not even close. So what could be bad?

My candidates for bug are:

I use 230k Ohm at 25°C in the table to calculate formula (10k
thermistor+220k voltage divider)
I use 3.3V as the supply for NTC but wemos D1 A0 is maxed 3.2V (but how to fix it?)


texts:
I have this simple LED configuration:

Voltage source is 24VDC so with the 1k resistor and three 2V LED, current is around 20mA.
I want to put a PLED device across each LED. how do I select correct part number?
PLED link is here:
https://www.littelfuse.com/~/media/electronics/datasheets/led_protectors/littelfuse_led_protector_automotive_pled_unidirectional_pledxux_a_datasheet.pdf.pdf


texts: I have this problem where I was able to solve for both a and b but I am stuck on c and d. For part a I came up with 0 Hz, 4.77 Hz, and 14.33 Hz using fn = w/2π.  For part b I came up with 29 Samples/sec using fx > 2 fm where fm was my largest frequency of 14.33Hz.  Please let me know if I am doing this correct and how to do and understand part c and d.


texts: Can i change 5 pins tact switch to 4 pins tact switch?

texts:
I have AOC brand monitor with a manuall buttons which operate the menu OSD.
I would like to change the original tact switches(there are 5 tact switches) buttons in the circuit board.The problem is that the tact switches have 5 pins while i have only the 4 pins ones(6X6X5mm).
If i will solder the 4 pin switches instead of the original 5 pins tact switches ,will it affect the operation of the button?will it works?Does the fifth pin has important function that without it,it will not function properly,if at all?

Thanks in advance.


texts: Why does ceramic capacitor ESR change with frequency?

texts: In most datasheets, I see a typical table which shows that ESR of ceramic capacitor changes with frequency. I understand that impedance of every kind of capacitor must have a minimum due to its inevitable serial inductance. But I don't understand why its ohmic resistance changes as well. Can you please explain this?


texts: Low RPM, Low Power, Low Torque Motor (to be solar powered)

texts:
I am trying to build a small contraption/artwork to be mounted on a wall indoors. Ideally it will solely solar powered from a small solar panel (10cmx10cm). It needs to spin slowly anywhere between ~5rpm-~30rpm (this can fluctuate). The load that will be spinning is relatively light (~100grams) so high torque isn't essential.

Most DC motors tend to be high speed and then geared down to low speed, which also comes with the bonus side effect of higher torque. But this high starting speed requires a relatively high starting current (?). Could someone please advise of a suitable type of motor with minimal power consumption for this application?

Perhaps a pulse motor, or solar engine would be the better way to go...


texts: How to choose the correct ARM chip and understanding the pins at a more intuitive level?

texts:
I'm just starting out my journey developing my own board and need some advice how to get started and understand a few things in better context.

I will ask my first question first and provide the preconditions- I need to create a board that supports: bluetooth, audio out, LCD  screen, camera, various LEDs. Those are the preconditions; from what I understand ARM Cortex M7 would work quite well for this but do not want to over-do it and need some professional opinions on what you recommend? etc. I would like to stick to ARM here as I have invested some time into understanding it etc. and all the boards I currently have are utilising ARM so it's nice to stick to this.

For my second question here; As a newbie to Electrical Engineering the part that really stalls me is the pins and their functions- I am aware of the different communication protocols and what they do, but there are many other pins on perhaps the ARM board that are not immediately intuitive and connecting the components I mentioned seems like a real challenge and i'm sure it is, so really my question is- are there any great resources to learn these pin functions or does someone have a pin cheat sheet they can point me to so I can advance my understanding on how these components connect with one another and work in an expected fashion. I do understand with every chip there comes a datasheet which one needs to look at but my misunderstanding seems to be coming before this step - probably because I do not have formal education in this domain. Thanks in advance.

ADDED INFO-
Operation or expected scenario of the board goes like this. User takes photo of them self using their phone as a controller connected via. bluetooth. Photo is taken and sent to the phone where X handles the rest of the process. So really this board has a job of (1) being connected via. bluetooth in bidirectional communication (2) displaying various lights such as red light on green light on etc. (3) playing a voice file that was sent from the users phone which will be played through an audio out speaker.


texts:
Before I begin, I understand this is a very broad and open ended question, please be patient with me. I am a complete newbie to this.  After looking around I found various ways of interacting withe the Kinect sensor.
ROS, OpenCV, Processing,Matlab....

But they all seem to need a PC in between. Is there a way to transfer data to a microcontroller like Arduino directly and processing the data ( say depth image like a matrix) without a PC?

I would assume there are some C frameworks that would be available for this.


texts: Cable identification: Euro plug to triangular shape

texts:
I recently found a cable near to a TV that didn't fit anywhere and didn't look familiar in any way. It's a Euro plug on the one end, and on the other end it's three contacts in a triangular shape, with an indicator(?) light on the back.

picture of the cable

What might this cable be used for?

Potentially useful: country where I found this cable is South Africa

Dimensions: the unknown plug part is 32x20mm for the casing, the connector is 13x13mm, with the centers of the holes being 8mm apart from each other. Each hole is about 3mm in diameter


texts: Making dc barrel usb cable and can't find the positive polarity

texts:
I have found out that my dc barrel is tip positive. after cutting the the barrel I realized that there is on insulation inside the black insulation itself to identify which one is positive and which one is negative.

the only thing I can find out it, one wire has - - - - - on it, and the other has 300v 80C 14guage F11 A, and so on. Could the - - - - mean its positive 12v DC?


texts: How current leads by 90° in capacitor while charge on other plate is always opposite, should we not say it lead by 180°

texts: When we start charging the capacitors the charge on the other plate is always opposite & equal then how come we say current lead voltage by 90°, should not we say that it lag/lead by 180°.


texts: Switch symbol: Which line is normally-closed?

texts:
The symbol below is for the component TL32P0 (TINY SWITCH ON - MON), included in EAGLE 6.5.

In this symbol, which pin is normally-closed (NC)? 1 or 3?

Or is the symbol not a typical one, i.e. not somehow standardized?


texts: In the basic electronics lecture today not only I but whole class  became confused by an explanation of our teacher that in high impedance value electrons movement become easier while in low impedance value electrons movement is congested. How could be that? I have always read the opposite in many texts.


texts: Setting I/O voltage on an embedded linux board

texts:
I'm using a LPC313x based linux board (Embedded Artists). I see in the LPC3141 DS that the I/O can be either 1.8 or 3.3V.
How/where can I set the voltage level in Linux?
Is the input somehow automatic? and the output?

I assume the procedure is similar to other boards..


texts: Replacing AGC 1.0 Amp High Breaking Capacity fuse (rated 1500A)

texts:
What other alternatives do I have in order to replace the fuse (above subject line)?
Will a Slow blow or fast blow fuse will perform the same goal?
What type of fuse do you recommend for a perfect match?
Fuse is part of the wiring harness, installed on a 2006 HD motorcycle
While dismounting harness black wire touched red wire; fuse went and I am not sure of the integrity of the fuse holder as I speak.
Would like to know if there is a fuse that can be use to replace the original *AGC/3AG 1.0 Amp High Breaking Capacity fuse (rated 1500A).
A google search does not bring any results using the * string


texts:
The problem is quite articulated so I will start from a more generic description and get more specific as I go on.

I need help to design a braking resistor system for a fairly uncommon application. The whole traction system looks something like this:

Power line are rectified with a 3 phase passive bridge. The DC Bus voltage (540V) is then divided by a capacitive voltage divider giving
2 virtual DC busses of 270V each. Each motor inverter is supplied by these artificial 270 V. The motors itself are fairly small and
have approximately 40 W nominal power. There are approximately 300 of these motors and motor inverters supplied by the same DC bus. Half of
them on fed by the "upper" side and the other half by the "lower" side.

Now the problem I am trying to solve is the shifting of the "virtual" DC middle point (I call it virtual because it's only given by the
capacitive voltage divider).
In a normal operation all the motors are equally loaded and turn with the same RPM, but it can happen that some motor have to stop. If many motors fed by the same DC "side" need to be stopped, then the dc middle point shifts and the voltage on the dc bus is no longer equally divided. This can lead to get, for example 350V on the high side and 190V on the lower side.

To solve the issue and keep the middle point in the middle I have come up with a braking resistor system that helps dumping the excessive
power of one or the other DC side. The circuit looks like this:

The idea is pretty clear: if, for example the upper voltage gets dangerously high, turn the high side on and dump the energy with the
braking resistor. In the same way if the lower voltage gets too high the low side MOSFET is turned on to burn the excess energy.

In the schematic there is 1 switch but in reality I am paralleling 4 MOSFETs to distribute the current. an important point is also that
I am not driving the MOSFETs with a PWM. Either on or off. It might happen that the unbalance persists for minutes and maybe even hours
so the gate needs to be kept continuously on. This is my question:

Is this the right circuit for such application?

I tried answering the question by building the circuit and testing it. I added a couple of fuses in series with the MOSFETs to prevent
blowing up 8 MOSFETs in case a shoot-through happens. I than turned the low side MOSFET on and the fuses turned into nice lamps
for a brief moment. I assume the high side also turned on but I can't figure out why and how I can prevent that from happening.
is there an alternative/safer method to drive the MOSFETs "always on"?


texts: Failed attempt to make LM3404 drive a 10W white led

texts:
I'm attempting to drive a 10W white led (ebay type, 8-11V, 1A) with a LM3404. I've approximated their reference circuit:

I've used a 33uH (1.6A) inductor as L1 and a schottky diode (SS24, 2A 40V) as D1. For the boostrapping capacitor Cb, a 10nf ceramic did the trick. I didn't used any Rsns for the reason explained below. Vin was set to 12V. The decoupling capacitor Cin was the typical electrolytic 100uF.

My problem is that the IF measured through the LED is a mere 20mA, and I'm baffled to why that is so. Varying the Rsns only makes the current go lower. Doubling the inductor from 33uH to 66uH makes absolutely no difference. I attempted Vin from 8v to 25v. Going from 12v to 25v did absolutely nothing. But going down to around 8.8v did made the led get a little brighter.

What am I missing?

Addenda:

I replicated the circuit as follows; with these settings, the voltage across the led is 5.2V and (obviously) it doesn't lit. The PWM is being controlled by an ESP8266 (I confirmed it is working with a regular led).

simulate this circuit – Schematic created using CircuitLab


texts: Problem with chaining many small DMX cables

texts:
In DMX cables (used for lights), all cables are daisy-chained.

In my band we are normally on small stages, but occasionaly on bigger.

To prevent buying very long cables, I wonder if it is a good idea to buy quite some 5 m (or yard) cables and just connect them together (without a DMX device in between) in case we need longer length.

I assume it is not a problem, but just wondering.

There is some 'common' used maximum of like 10-15 fixtures, but does this count the number of DMX devices or the number of 'cable connections' ?


texts:
I've got a few HTC Desire A8183's in which I would like to power directly off the wall socket.

I've got a 12volt 1amp transformer which I've put through a voltage regulator to bring that down to the required 3.7volts as stated on the back of the phone. WHen I connect the +3.7 to pin 4 of the phone and ground to pin 1 it doesn't boot.

I know there must be something I need to do with the other two pins. Some people say one is for the temperature of the battery and the other is a batter status indicator or something like that which needs a resistor.

I've tried a few different approaches so far. I've linked 1,2,3 to ground and supplied positive 3.7volts to pin4. This resulted in a orange & green flashing light which means it has detected the battery is over heating. I then tried putting a resistor on pin3 to ground of 82KOhms but that didn't help.

Here is some advice which I've already tried;
http://www.instructables.com/id/How-to-use-phone-without-battery/?ALLSTEPS

How can I run this phone directly off power?
I still have a working battery which I can use for testing the voltage supplied.

Update

Here are the read outs;

Phone
3&4 = 1M1
2&4 = 1M3

Battery
1&2 = 4K7
1&3 = 690K
2&3 = 20.3 @200M
3&2 = 1.1 @200M

Battery
Pin 1 & 2 = 0V
Pin 1 & 3 = 0V
Pin 1 & 4 = 3.5V
Pin 2 & 3 = 0V
Pin 3 & 2 = 0V


texts: Why is a Buffer+RC-combination recommended for driving a SAR ADC analog input?

texts:
In various places, e.g. this tutorial video by ti, a circuit like the following is being recommended to drive the analog input of a SAR A/D converter:

simulate this circuit – Schematic created using CircuitLab

The general intention is to ensure that the sampling capacitor of the ADC will be charged with sufficient accuracy by the end of the sampling period. If the source has a sufficiently low impedance, it can be connected directly to the analog input, but otherwise this circuit should be used.

I understand the use of the buffer amplifier, and that it has to be fast enough to settle to the required accuracy within the sampling period. I also understand how to choose the values for the extra RC filter, but I'm not entirely sure about its purpose. So why is it there? And as part of that, why is the recommended value for C1 10x to 20x the value of the sampling capacitor?


texts: Cannot upload sketech to uno by upload using programer in one usb port

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When i connected usbasp to uno spi. Its mcu got detected by avrdude but i cannot upload sketch to it using arduino ide. I tried by upload using programer but i got an error "could not find usb device with vid=
But the problem solved when changed the usb port but mcu not detecting by avrdude.
In summary if avrdude detects mcu ardunio ide canot upload sketch
Each oprations i have to switch the usb ports.


texts: What are these boxes mounted inline on each of the 3 phase wires of a high voltage power line in Miami?

texts: They were only on this run and not any of the lines in the area. And what is the function of the flat u-shaped guards in front of each?


texts: I was reading about Audiotechnica's new "Pure Digital Drive" headphone drivers here, and I can't understand how their drive scheme would be better than having a regular DAC feeding into the voice coil. It seems like the first curve they show, 'Analog Input to Driver' provides a smooth interpolation between the signal that would be more desirable than a choppy digital transition like they show in their 'Digital Output' waveform. I know the specifics of their technology is proprietary, but I was wondering if anyone here could better explain why this scheme is a good idea.


texts:
I recently got an electronic engineer to make a design of a circuit for me. He completed everything except for the fact that he never included in the design a way to detect when the battery was running low. I asked him to include this but he just claimed he couldn't do it for whatever reason. So now I'm trying to figure out myself how to add this to the existing design.

By browsing answers to similar questions I came across this question: Low battery detection the first answer mentions voltage supervisors and from what I've read it sounds like the ideal solution to my problem, the thing is that I'm not sure which one would be the correct voltage supervisor to detect when a 3.7 volts battery is low.

I've been looking around and from what I've found I think the NCP301LSN20T1G Voltage Supervisor would be the appropriate one to use, but I'd like to make sure I'm not making a mistake here. My background is in programming not in electronics so I apologize if this is somewhat of a innappropriate question for this site.

Thanks for any help!


texts: Charging time of capacitor when used with this transistor configuration?

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I´m trying to calculate the charging time of the capacitor in this circuit.

I know the PUT is on when the voltage in the anode is higher than the Vp
 Va > Vp
 Va > Vg + 0.7

For this circuit Vcc = 15v
Having the voltage in the gate and Vp:

 Vg = 10v
 Vp = 10.7v

With that the capacitor is going to charge to 10.7v, and then is going to discharge through the Rk resistor.
How to find the charging time of the capacitor?


texts: What is the minimum temperature for FR-4 PCBs?

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My company is working on developing a product that will go into commercial freezers, so my boss asked me to provide operating temperature specifications for the product.  I can find "operating range" temperatures listed for everything but the PCB itself, which is just plain old FR-4.

Wikipedia helpfully lists "Temperature Index" (whatever that means) as 140 C, but there are no indications of a minimum temperature.

I'm not really worried, as I'm sure that the other components on the board will be the limiting factors, but for the sake of completeness, I would like to have it listed.

Does anyone known the minimum operating temperature of FR-4?  (And what would the failure mode be?)


texts: How to design a 2 way switch using Triac and SPST standard switch?

texts:
I have a triac which I turn ON and OFF by giving a gate pulse through microcontroller. With the help of triac I turn ON/OFF a light in my bedroom. The bedroom light is connected to a standard SPST switch. I want to control the light (ON/OFF) using both microcontroller and SPST switch. I want to have exactly a 2 way switch action. But how could I achieve this 2 way action using SPST switch and a Triac acting like a NO switch ?

Please any feedback would be appreciated. Please find below the arrangement.

Also suggest any design or other arrangement for a 2 way action using SPST and Triac (as NO switch)

Thanks in advance,
Gaurav


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Mains SMPS converter chips (e.g. L6565) usually have pre-charge function to prevent the inrush current into a completely discharged capacitor. In high-power PSUs, a precharge resistor is often used, which is shunted by a relay once the SMPS starts providing output voltage.
What precharge circuit could be used for small low-power USB devices? For instance, I have this DC-DC converter I power from USB, which has an input capacitance of 2x220uF (44 times the allowed limit of 10uF). Not surprisingly, when I connect it to a USB port, it produces overcurrent. With most USB hubs, this results in all the devices connected to the same hub to be re-connected.
Are there better options for a DIY-rework than a pre-charge resistor plus a small relay? How is this problem solved in properly designed USB devices?