texts: Need help adding gain overdrive/control to my tube guitar amp design

texts:
I'm new to analog electronics, so bear with me. Consider my guitar amp design:

What we have is a 12AX7 feeding into a cathode follower, going into a James tonestack, through another 12AX7 gain phase, then through another cathode follower.

So I'm kinda doing something cool here... I'm splitting the plate load resistors and adding the feedback in between the split resistors. According to Designing Tube Preamps for Guitar, this makes the net A/C across R5 and R13 near 0, making the gain of the stage very very high.

So problem #1: I'm unsure how to actually calculate the gain of those stages, and what my output Vac will be. My limited understanding calculations say 1Vrms coming in will be about 20Vac going out for the first stage... I think.

Problem #2: I want to be able to switch the amplifier from Carlos Santana mode to Hank Marvin mode. So if there is excess gain leftover from after the tone stack, I want to shunt it to clean up the amp. Normally a voltage divider pot does this between stages... but I'm trying to figure out how do that in this case. My thought is to put the voltage divider after C2, but I'm not sure how that'll affect the tonality of the stack.

Finally, bonus round... I want to use a dual gang pot between wherever I put the gain control and have RV3 be the inverse of the gain control. Any thoughts on that? So as I turn my gain control up, RV3 shunts more to ground, reducing the output signal. I couldn't find and designs using this type of idea, but I'm wondering if it's been done before.

Many thanks!


texts: How can I switch a high current with a low-rated switch?

texts:
I'm designing and building a breadboard power supply for myself, which draws power from an ATX-like SMPS (Mains in, single Molex plug out) via a 4-pin Molex connector. The design includes a switch to select either 12V or 5V output, but the only appropriate switch I can source is rated for a paltry 30mA!

Obviously I can't switch up to 2A with a 30mA-rated switch, but what can I do (that's cheaper than the ~$5-10 local vendors want for 2A-rated switches)? I thought of using an NPN transistor (see diagram, below), but in simulations that resulted in an unwanted voltage drop, and having the load connected to both emitters seemed to do weird things to the voltage.

simulate this circuit – Schematic created using CircuitLab

(Note: Q1 & Q2 are generic NPN transistors, I've not considered part specifics yet.)

I thought of perhaps using a MOSFET, but decided that since I really don't know what I'm doing, asking for help was perhaps an even better idea.


texts: Do we need a resistor to discharge capacitor of MOSFETs while connected to MCU?

texts:
I have an STM32 MCU at home. I was thinking of controlling a load with this MCU and a MOSFET. Let's assume this is my circuit:

In this circuit, we use a resistor (R2) to discharge the gate of the MOSFET. Now let's look at the structure of the GPIO inside the STM32. Here is an image:

As you can see, there is an NMOS that when we change the output control to 0, the MCU will turn it on to connect the line to the ground. Now the question is: why should I use a resistor to discharge the capacitor of the MOSFET when there is an NMOS that can do it? Do I always need to put this resistor in?


texts: DC Motors Voltage Equation versus Power Equation

texts:
I understand the voltage equation and the power equation for DC motors. But somehow I have a problem understanding moving from one to the other. I am not interested in the IR or IdL/Dt so I will ignore those for the moment even though I realize they are important. V_emf is the back emf produced by a given w (angular velocity) times a constant k.

Voltage:     V_in        =      w * k   (i.e. assuming no losses a motor runs at w)

Power:       V_in * I    =      w * torque (assuming no other losses)

If the second equation is divided by I, you get the first; k=torque/I.

Case 1: w=0.

Voltage:   V_in     = 0 * k  (plus the losses which in this case are huge but V_emf = 0. Check)

Power:     V_in * I = 0 * torque = 0 (no motion, no power produced. Check)

Case 2: w= max, torque = 0

Voltage:  V_in      = Vemf  (The motor accelerates until V_emf = Vin. Check)

Power:    V_in * I  = w * 0 = 0 ( There is no load so no power is used. Check)

Case 3:  w and torque are somewhere in the middle

Voltage:  V_in      = V_emf   (Obviously first conceptual problem: V_in is constant, V_emf varies with torque.)

Power:    V_in * I  =  w  * torque  ( but actually there is also V_emf also so not check)

I can fix the power equation by saying:

Power:  Vnet = (V_in - V_emf) * I = w * torque

This seems more natural anyway. The first two cases still make sense. But the problem I have now is that the voltage equation now has a component (w * torque / I) that is not derived from Kircoff's laws and doesn't make sense to me.

I believe the final power equation is correct. I also believe the original voltage equation is correct. How can I reconcile the two?


texts: Does Ni-CD battery chemistry lose its discharge amperage over time?

texts: I know with Li-Ion the amperage stays the same, right up until the end of its life, then the Amp Discharge rapidly goes down, But Does a Ni-Cd Battery Chemistry lose its discharge amperage over time? I know that it loses its charge sitting on the shelf, and requires maintenance, but does the Discharge Amps go down as the battery ages?


texts: 2.4A micro USB adapter/cable with a 1.8A Micro USB connector

texts: You can find many many USB charger/cables specified a 2.4A current capacity. But I can't find the micro USB connectors rated 2.4A on the market, the maximum is only 1.8A. So, it's safe to use a fast charging adapter labeled 2.4A with a connector labored 1.8A? Or there exist 2.4A connector indeed?


texts:
Backstory
I've got these old Technics RP-F600 headphones in my closet that I wanted to use. I bought them ages ago (don't remember, probably over 10 years ago), and for the past year or so they've sat on a shelf unused. Before that my wife used them at work and she says that they worked there fine.
The problem & what I tried
As I tried them today, the right speaker didn't work. I thought that it would be a simple issue of a faulty wire which I have fixed myself many times before. So I opened them up and got to work with my cheap multi-meter, only to find that all the wires are fine. Even weirder, the right speaker started to produce sound again even though I did nothing. However it is now slightly quieter than the left one. Measuring resistance also confirms this. The left one is a little below 60Ω while the right one is around 80-90Ω and weirdly keeps fluctuating way more than the left one (although I don't know how much of that is simply bad contact or the cheapness of the multi-meter). For reference - the Internet says that the rated impedance of these headphones is 56Ω and the resistance of the wires was around 1.8Ω and didn't fluctuate that much. And anyway I measured both at the plug and at the speaker itself and got the same results in either case.
The question
What is going on here? Is the speaker itself dying or is this normal? Can the impedance/resistance of the speaker change as it ages? Is there some known phenomenon that would explain this?


texts: what is the formula for charging a capacitor with constant current?

texts:
I read that the formula for calculating the time for a capacitor to charge with constant voltage is 5*tau=5*(R*C) which is derived from the natural logarithm.

in another book i read that if you charged a capacitor with constant current, the voltage would increase linear with time. Is this true and if it is, what is the formula used for calculating this? would a complete voltage charge be possible in constant current?


texts:
On a wire designated as '3x14AWG' what does the '3x' part mean?

It is on a wire that is part of a surge protector power strip.


texts: Voltage divider Vout not powering ESP8266

texts:
I have an input voltage of 12V from my power supply and i need 6V to feed into the ESP8622. I was giving it all the 12V but the wifi module becomes increasingly hot with time and so i decided to have a limited voltage feed into it.

Am not getting it to fire up however. It still stays blank.

I tested providing the 6V from the power supply and got positive results.

My resistors are both 100 ohms and when i probe the interconnection rail of the resistors on the breadboard, i can see that 6V is there. But when i feed the link into the ESP8266, it doesn't light up. It only does when the 6V are coming from the power supply.

Here is a pic of my circuit


texts: A confusion with power ratio jargon used in antenna directivity (dBi/dBd)

texts:
Below is an excerpt from a book:

Two common terms you'll hear in specifying the gain of an antenna are dBi and dBd. These terms are defined as dB of gain referenced to an Isotrope (dBi) and dB of gain referenced to a dipole (dBd). A dipole has 2.1 dBi of gain, but 0 dBd of gain. It is critical to know which reference the antenna manufacturer uses, because it will have an effect on the path loss and power calculations we will discuss later.

I don't get how dBd and dBi is related with the ratio of 2.1.
Can these units and 2.1 ratio be explained in an easier or pictorial manner?


texts: What type of potentiometer to use for 240v AC power application?

texts:
I'm working on my first Raspberry Pi project which is to change the brightness of standard household light bulbs.

I have my Raspberry Pi and relay switches which together let me control when the power will come on. Now I want to use Raspberry Pi to control the brightness of the light.

What component do I need to use for that? also any pointer to tutorials are appreciated.


texts:
I am looking to create a high q passive notch filter using a crystal.
I am not very familiar with crystals, hoping that someone who's had a similar experience can enlighten. I know crystals are mostly used for generating signals, but I mainly need to filter.
My working frequency is 40KHz

I know there are such parameters as series resonance and parallel resonance.

How do I pick the right crystal for the job? The datasheets don't always state whether the crystal is designed for series or for parallel operation.
What is the actual typical difference in frequency between the two?
Is it possible to use the same crystal both to generate my signal and also to notch filter it? I read something about "pulling" the resonant frequency.
How would you build a notch filter with a crystal?

Thank you so much.


texts: Simple and Cheap method to detect object proximity in the dark

texts:
I am interested in detecting if an object (e.g. small box made of non-conductive material like plastic/acrylic/wood) is placed on top of a surface (e.g., a table), I don't need to identify the object, I just want to know if it is there.

There are various methods to doing this, but I wanted the easiest/cheapest way. I first thought of using a Mini Photocell ($1.50), which is a simple light sensor, however, this will not work if the room is initially dark.

Then I found the Optical Detector / Phototransistor - QRD1114 ($0.95).

I believe QRD1114 should work regardless of lighting conditions,
since this uses IR?
I need to consider the approaching object (e.g., small box) should be able to reflect IR?
Any ideas on the IR beam?

The detecting sensor must be very small and cheap.


texts: What would happen if the output leads of a multi-phase transformer were shorted together?

texts:
Just what the question states, and there isn't any design rationale behind the question.

I just opened up a dead CFL (6 tubes; 3-pairs), and it looks to have an itsy little transformer within. This transformer has super-fine wires in the winding with, what looks like, a large number of coils. The output appears to come in 3-pairs of wires - probably 3-phase HV - one for each pair of tubes.

Anyway, I'm curious what would happen if the hot-lead of each phase were shorted together; the same with the cold-leads.

Thus I would be binding the output wires as ABC, and A'B'C' to form a common output.

My guess is the transformer (if that's what it is) would heat up, and have a reduced life-span.


texts: Why cascode is not used often as a power switch

texts:
Say, we are building a synchronous buck and we have some beefy 600V 10A MOSFET, but it is not really suited for high frequency application - we need to be aware of dv/dt limits and it is hard to achieve fast switching with FET  huge capacitance. Also it may have up to 20V at gate.

What if we add a dirt cheap 20V 20A logic level MOSFET at source of our HV MOSFET.

simulate this circuit – Schematic created using CircuitLab

It sound like this way we will be able to achieve insane switching speeds even with a bad driver in cost of small switching loss of bottom FET. In case of ZVS topology, our switching loss will even decrease because of smaller gate voltage.

I've never seen anything like this in practice however (except GaN and some other scientific stuff). I suppose there is a good reason for it (layout? diode recovery/freewheeling? some other severe problems?)? Why not use two different cascoded FETs as a power switch?


texts: Question regarding a charger modification for a Dell 3100 docking station

texts:
I'm quite new and inexperienced to this so I would appreciate any guidance I can get.

Given the quarantine situation I need to work from home more so I purchased a used D3100 docking station but with no charger. I have an adjustable charger that I cut and modified with a pin that would fit the charging port (it was quite challenging to find for this model)

This was the modification I made: https://i.imgur.com/0lfKsDe.jpg

These are the charger specs: https://i.imgur.com/qnubw1O.jpg

These are the D3100 specs: https://i.imgur.com/WkTunlm.jpg

I will use isolation tape later, I know it looks pretty ghetto right now.

My problem: I can get 19V across the wire (by measurement with a voltmeter) but only 1 amps.

The voltmeter I used and settings for measuring amperage: https://i.imgur.com/lX8v6QC.jpg

The charger shows it can deliver up to 4A when at 20V which should be plenty given the specs of this docking station however I keep getting 1A. Why is that? Am I getting something wrong or is the charger busted.

The docking station does not power up at all right now. I tried it with an original charger from work and it worked just fine there.

Thank you.


texts:
I was trying to design a current mode boost converter in CCM using a MCP1630 and the specifications of the design are as follow:

Vinmin=2.7V (minimum input voltage).
Vinmax=4.2V (maximum input voltage).
Vout=5V     (Output voltage).
Iout=5A     (Maximum output current).
RL=5 Ohm    (load resistor Vout/Iout).

I have calculated the components and they are as follow:

Dmin=0.16   (Minimum duty cycle)
Dmax=0.46   (Maximum duty cycle)
L=5uH       (Inductor value)
Ipeak=2.2A  (Peak current)
C=200uF     (Output capacitor)
Fc=8kH      (Crossover frequency)

The sense resistor is selected to be Rs=0.36 ohm, because the maximum current sense signal for MCP1630 is 0.9V (for Ipeak=2.2A Vsense=Ipeak*Rs=0.36*2.2=0.8v, we let 0.1V as a margin).

For the feedback control I have sellected a type 2 amplifier with the following components:

    *Divider network: Rup=Rlow=10k
    *Refrence voltage Vref=2.5V
    *C1=2.5nF
    *C2=15.6pF
    *R2=100k

I provide the circuit bellow:

Unfortunatly, when I simulated my circuit, I never get 5V at the output, instead I get 3.94 and the duty cycle approaches 90% and I don't know what is the reason for that failure.
Please try to figure out where I have mistaken!!

Bellow I provide you with the signals:


texts: How to know the latency of an oscilloscope?

texts:
How can I know the latency of a digital oscilloscope in roll mode? By this I mean the time it takes from the signal reaching a certain value to the moment this value is shown on the screen, i.e. the time it takes for the scope to sample the signal, process the samples and draw on the screen.

What's the name of this parameter? Is it usually in the datasheet? What is a reasonable value for this?


texts: How to calculate the gain of the OP-AMP in this configuration

texts:
Sorry for my ignorance in this field but I have failed miserably trying to figure the gain of this circuit:

simulate this circuit – Schematic created using CircuitLab

Simulation shows that the input impedance of the first stage is 509.4k I do not understand why not 504.7. Where this second 4k7 comes from?


texts: Improving a simple bipolar current limiter

texts:
Is there a way to remove the Vbe dependence on bipolar current limiters, or at least, lessen the effects of process variation & mismatch in the topology below?

Vin is nominal 22V, but could have transient spikes of 50V for < 100us.    The circuit below limits current through Rload to ~4mA, but that is dependent on the Vbe(ON) of the darlington pair.  A small change in Vbe will affect the limiting threshold for a set Rsense.

Is there a method to improve this current limiting circuit so that current through Rload is more closely matched to Rsense rather than both Rsense & Vbe(ON) ?


texts: Can Op-Amp (LM358) works as an integrator without dual mode power supply?

texts:
I am a noob with analog electronics, so pardon me for any mistakes.
I recently started with Op-Amp and currently working on a project whereI am using Op-Amp in integrator mode to convert square wave to triangle wave and then fro there again an integrator to convert that triangle wave to sine wave.

I tried the circuit with single power supply that is +5V and ground, but was not able to make to work. So is it mandatory to use a dual power supply like +5V and -5V for an Op-amp to work as integrator? Because all the circuits I referred to were using a dual mode power supply.

Additional details:  The Op-Amp is LM358 and the square wave is from an arduino board +5V and 0V obviously. The duty cycle of the wave is fixed at 50% and the freq. is controllable from 100Hz to 100KHz. I tested the whole set-up with 1KHz freq using my DSO.


texts: Simplifying a microprocessor controlled MOSFET switch

texts:
I need to switch a load, controlled by a microcontroller. (Actually, bypassing a load with a short-circuit.) My question is how to implement the switch.

The circuit will have available to it the following rails, in addition to the 2 V-50 V supply: +5 V, +12 V, -12 V.

simulate this circuit – Schematic created using CircuitLab

I am struggling to simplify my design of the switch. The problem is interfacing the controller with the "switch".

The following is one idea I've had:

simulate this circuit

However it strikes me that three transistors for this one "switch" could be simplified.

I'm using a MOSFET so the on-resistance would be low, but a BJT would be OK. But either way, I can't see a simpler circuit that would allow the switch to be controlled by a microprocessor.

For example, to turn the P-channel MOSFET on, when the 2 V-50 V rail is at 2 V, the gate would have to be pulled down to around -2 V or lower. And the simplest way of interfacing that with a microprocessor would be to have one BJT pulling Vgate to -12, and another BJT sourcing current into the last one's base from +5 V, which could then be controlled by the microprocessor.

Of course, if the constant current sink is programmed to sink a small current, and the 25-50 V rail is at 50 V, the MOSFET's Vgate would have to be taken to about +50 V to turn it off. My circuit would do that by turning off the BJTs.

Is there a simpler way that I've missed?


texts: I’m experimenting when some OLED displays similar to this and here’s the data sheet. My question is how do I connect the display to the PCB? I’m unfamiliar with the flat ribbon type cable and how to connect it to a PCB. Thanks in advance.


texts: Eagle - Create THT package with copper only on bottom

texts:
In Eagle 8.2.1 I want to create a package for a THT part. I only want to have copper on the bottom layer around the hole. I don't want copper on the top layer and I don't want the inside of the hole to be plated.
How can I accomplish this?


texts: Connecting Protective Earth (PE) to DC ground

texts:
This question has a bit of application background so please bear with me:

I'm working on a LED lighting system. The controller (MCU, led drivers and led supply) will be powered by a single DC switching power supply. The luminaries are the typical aluminum with leds in series PCB attached to a large heatsink and optics. The luminaries will be mounted on cable trays.

The problem is that the DC ground of the led PCBs is intentionally connected to the heatsinks by mounting screws (not my decision not anything I can do about it). In turn, the heatsink is part of the luminary chassis itself and will be in touch with any other metal supporting it, in this case the cable tray. For security reasons, the tray is connected to Protective Earth (as the luminary chassis should be..)

This, once mounted, will make an unintended connection of DC Ground to PE.

So, I'd need any advice in the following:

1) Is this installation viable? I mean, suppose a leak that goes to PE, that could affect DC grounding or even destroy the electronics, am I right?

2) Will this connection create AC noise on the DC Ground?

3) Since this connection will be made unintentionally at the "chassis" of the appliances (heatsinks, trays), should I intentionally make a lowest impedance possible connection of PE to DC Ground at the controller PCB?

This all sounds like a very bad idea, but I'm not 100% sure nor have strong arguments to argue with my boss about this, so any expert advice will be highly appreciated.


texts:
What exactly is initialization of code memory IN 8051?  Does the db directive command DB "SAM'' burn data into ROM location?

WHAT DOES INITIALIZING WITH A BYTE VALUE MEAN ?

I am all confused?

I am programming assembly in 8051!


texts:
While researching MOSFET gate drivers I came across Microchip's MIC4605-2 and it's evaluation board:

MIC4605 Evaluation Board: 85V Half-Bridge MOSFET Drivers with Adaptive Dead Time and Shoot-Through Protection

The evaluation board does not have any gate resistors for the MOSFETS:

In fact, the datasheet for the MIC4605-2 states:

  "An   external   resistor between  the  LO  output  and  the  MOSFET  may  affect  the performance  of  the  LO  pin monitoring  circuit  and  is  not recommended."

Owing to the fact that this gate driver features adaptive dead-time and thus monitors the gate of the MOSFET to determine when it has fully turned off, a gate resistor prevents proper sensing of the actual gate.

As I understand it, the gate of a MOSFET acts like a capacitor. At t(0) any capacitor will act like a short circuit. Without a gate resistor the only thing limiting the current is the gate driver's output resistance, which is supposedly low, it would not be a good driver otherwise. My thinking is this should lead to current peaks that easily exceed the driver's 1A maximum peak current and damage the chip, but the evaluation board demonstrates that this is not the case, what am I missing?


texts: 5V PWM 0-100% duty cycle output should generate 0-100mV

texts:
The project I am attempting is:

Arduino UNO receiving a data record from a battery data logger
one particular value (State of Charge) is extracted
and sent to a PWM output
going through a low pass RC filter
into an OpAmp (LM324) to provide a clean DC output
the output voltage should range from 0-100mV

The PVM frequency is ~480Hz (Arduino Uno); the 2 RC filter are 330R/10uF
I need help with the circuit design past the second RC filter.
This is what I started out with:

(source: grenkowitz.net)
Which morphed into this (and seems flawed/suspicious to me):

(source: grenkowitz.net)
But, I do not reach the 100mV at 100%, and the output is a bit spiky; assuming there needs to be another RC filter of sort.

(source: grenkowitz.net)
The circuit does not need to be responsive, because the duty cycle, thus the mV out increments slowly in 0.5mV steps over hours, and decrements over hours.
[Addition 2016-07-10 0905Z]
Thank you for your responses.
It looks like I am a bit in over my head... not really understanding OpAmps...
I have now taken a slightly different approach, and added a voltage divider on the input signal of %v to drop to .1V and since reaction time does not matter, put a 100uF cap in... then the 2 RC filters into the OpAmp; sorry for the for the Vcc for the OpAmp; now corrected to 5V.
The simulated output is 33-98mV. But I am not sure, how to configure the OpAmp to get a Voltage (as precise as possible) mathing the 0-256 step, 8bit, 0-100% duty cycle of the input.
Here the latest design:

(source: grenkowitz.net)


texts:
I have to implement a LC filter for a FT232H and its datas sheet (here) gives an example circuit (Fig. 6.1 VPLL- & VPHY-circuit). Strangely though a core-inductor is stated to be a 600R/0.5A.!

I have never come across such a way of writing inductance, or is that inductance at all? When I searched for the values, I found a ferrite-bead (here), but is that what I'm supposed to use as an inductor? It's just some ferrite... I'm confused...


texts: LM338T voltage regulator output unstable and fluctuates

texts:
Hello guys sorry for my noob question, I have LM388T voltage regulator and i created a module that can supply multiple voltage for 5 components that needed to supplied, i replace potentiometer and use a resistor instead to have a constant output voltage, but there is a problem, 12v is okay and stable,  but 7.2v is unstable and it fluctuates.

Arduino Mega = 12v
Solenoid Valve = 12v
RDS3115 Servo = 7.2v
MG995 Servo = 7.2v
GSM Sim900A = 12v


texts: Can an electrified wire ever be safe against bare skin?

texts:
This could sound ridiculous to someone with an ounce of experience, but I'm just getting started, so here we go ;) Full question is 3 parts...

First, what is the lowest amperage needed to light an LED? I think there are blue LEDs that can light up at 5 mA. 10 mA is where shocks begin to get painful.

Second, in a circuit with a battery, is there any scenario where that low voltage of a battery could deliver a painful or harmful shock if something went wrong?

Third, could you power that LED with a bare copper wire touching your skin, such as wire jewelry, or would that circuit short on your skin or provide an electric shock?

Simply, I'm trying to figure out if it's possible to wear a bare copper wire around your neck or wrist that powers an LED, or does that wire need to be insulated?

My instinct is to say no, but I'm also thinking maybe your skin would provide enough resistance to both prevent shock and force the current to continue down the wire.


texts: Is 2's complement the only way that singed binary numbers are represented?

texts:
I have only seen mention 2's complement practically everytime signed number representation is mentioned. However, I have found that there are other ways to represent signed numbers also, these are 1's complement, excess-k and base -2.

Except 1's complement I do not really understand how the other two work. However, what I want to know is, are these other representations ever used at all? If so, where and why? I know that the strength of 2's complement is that addition and subtraction become the same. However, I am not sure about the strengths of the other mentioned methods.


texts:
Is there are special circuit that says to USB socket how much current the device needs?

Our device needs at up to 200mA or little bit more.

I have been searching but I do not find a clear answer anywhere. Should there be resistors on data lines or something else?
Unit load for USB 2.0 is 100mA and for USB 3.0 it's 150mA according to Wikipedia.
How does a the host know how much current to supply?
How does the slave ask for load units?


texts:
Tasked with improving on an existing design, I need to read pulses using a reed sensor excited with a magnet, placed on the front wheels of motorbikes.
The system's core has changed, moving from a PIC microcontroller to a NXP i.MX6 microprocessor.
Based on my predecessor's design, I came up with solution A, filtering; in a brief talk, it came out how it took several attempts to design the correct filter, as older bikes bear different type of noise, due to different ignitions, alternators, rectifiers and whatnot; in extreme cases, accelerating while the bike was standing would result in the uC picking up some noise interpreted as a change in logic level, and counted accordingly as one revolution of the wheel.
In other projects I have successfully used opto isolators, and while reviewing the final design, I came up with solution B, that would cost me one extra component type in the BOM.

My reasoning:
A) 2nd order low pass filter is ok as long as I keep cutoff frequency as low as possible, to keep the most possible noise out; should I decide to reuse the same board for a different project, I'd need to change L9 and C48 according to the new frequency.
B) maximum input frequency is dictated by the chosen opto, to change the maximum frequency I'd need to find one with the same footprint, but I think this would result in overall better signal quality to the microprocessor, while also protecting the GPIOs from harm. Is this assumption correct?


texts: How do I write the equations for three inductors connected together in state space form?

texts:
The system is basically three inductors connected to each other in one end and the other end connected to three independent voltage sources.

I want to get the equations in state space form. For this I need to eliminate the intermediary variable VT.

I cant figure out how to proceed from here.


texts: Is there a depletion mode MOSFET library for LTspice?

texts: I haven't found any depletion mode MOSFET model library for LTspice. Does one exist?


texts: Cancellation of sound coming out from speaker while recording?

texts:
I am designing an embedded device for my personal project. It has a speaker which plays voice received from remote location and also records voice using a microphone while playing back the sound. The recorded voice is send back to remote location where it is delivered to the user sitting over remote location. It is similar to talking to someone over a phone call on speaker mode.

I am designed an amplifier using LM386 for speaker and it works perfectly. But i am confused over whether microphone will also record the sound coming out from the speaker and user over remote location will hear echo of his/her own voice.

My question is how to cancel the sound from speaker while recording using a microphone? Should i cancel them in hardware or in software?
How it can be done in hardware?


texts:
What does the Select and Load inputs of a RAM do (in Logisim)? Any difference? It says:

Chip select 0: disable component
Load: if 1 load memory to output

I am thinking, if I don't connect them, whichever address I specify, it will output the data in that address, if I connect them, when Select is 0, it disables output (all X) if Load is 0, outputs all X. So whats the difference?


texts: Measuring the rise time of remote device

texts:
Given a radio transmitter (like a cell-phone or wireless computer), how can you measure the rise time remotely?

I understand that you can use an oscilloscopes to measure it on components at hand, but apparently, telcoms analyze the cell-phones' rise time to obtain a radio fingerprint of each device (and being able to tell if a device is a clone of another).


texts: How to test if it is a non-multiplexed (static) LCD?

texts:
I got some static LCD's from an old cheap clock, calculator and the like and now I would like to use them for displaying simple things like temperature. They are connected with those pink with grey connector bars, if you know what I mean.

I found this article: http://www.ubasics.com/driving_static_lcds but he talks about non-multiplexed LCD's. How can I see/test/check what for static LCD I have?

It would be great if I could use these static LCD's, do you guys got more info on how to use these things (multiplexed or not)? Can I use it with an ATtiny2313?

Thanks.


texts: How to Turn the 555 Timer Output (Astable Mode) into a Decaying Square Wave?

texts:
I am currently working on a 555 timer in astable mode whose output will be fed into a 0.5W, 8Ohm speaker. I want a fading effect for the sound that will be produced by the speaker. I already acquired an envelope circuit which basically produces a voltage signal decaying exponentially for about 3-5 s. How can I turn the output of the 555 timer into a square wave that is also decaying exponentially within 3-5 s? AND can we also do that by only varying the voltage supplied to the 555 timer (i.e., the voltage connected to pin 8)? Here is the envelope circuit I already acquired:

Thanks in advance!


texts: Why would you need a floating signal on a board?

texts:
I read the following from a book titled "An Embedded Software Primer" by David E. Simon. (23rd print Nov/2014 - Page 16)

  If no part on the circuit is driving a signal, then that signal is
  said to be floating. Its voltage will be indeterminate and may change
  as time passes. The results of a floating signal vary between harmless
  and disastrous, depending upon how the parts with inputs connected to
  the floating signal cope with the problem.

Based on this, it looks like there is no good reason why would a circuit have a floating signal. If this is right, then why would such signal be allowed?

Is this done due to a mistake in the board design?

Are there scenarios where such a signal is needed?


texts: I got this LED strip that I'm trying to control with my arduino. I searched for similar strips online but couldn't find any. I only has leads for DIN (blue), GND (black, splits in 2), and +5V (red). I couldn't find the data sheet and the part number didn't generate any results when I Google searched it. All i really need to know is the name of this type of LED strip so I can continue to research how to control it, but if there are any tutorials out there that use this type of strip, a link would be much appreciated.


texts: Feasibility of a basic physical-layer wireless communications system

texts:
We would like to make simple, cheap comms chips that provide a pool of users one real or complex sample per user per communication time slot. Its footprint needs to be similar to a BLE chip (~1"x1", <15g able to be powered for a long time by a 3.7V 200mAh battery).

The most we hope for is for the system to be capable of send/receive on the order of tens of bits per second.

Here is a rough idea (I have no hardware knowledge so this might be bogus)

  \$N\approx 3\$ devices are equipped with IR beamers/receivers, and each is designated an offset \$f_n\$ from the carrier frequency \$f\$.

  Per communication frame:

  For device \$n\$ to transmit, a microcontroller's PWM with \$P_n\%\$ uptime is turned on and off with (local) frequency \$f+f_n\$ to power an IR light.
  For device \$n\$ to receive, it cross-correlates the IR receiver's signal with a bank of frequency windows centered at \$\{f+f_k:k\neq n\}\$. The cross-correlation magnitudes are averaged over a short duration and read by an ADC for processing.

All the higher-level stuff would be handled by the users, which each have a microcontroller with specs on the order of a fast Arduino.

As far as I know, here are the miracles that have to happen for this to be feasible:

The components to amplify and filter the receive signal must exist and be tiny, cheap and low-power.
The oscillators on the PWMs have to be consistent enough with each other that correlation with window functions is enough to isolate each user's signal (so we avoid heavier, more complicated things like DSPs or PLLs)
The PWMs need to have well-separated frequency response.
(would be nice) The IR blasters are powerful enough that the channel statistics are approximately Gaussian (when really they are Rayleigh)

Are any of these showstoppers, or is there a reasonable chance of success? Are there cheap off-the-shelf chips that do this?

In particular, is there a cheap, small (comparable to a to220) IC that will do the filtering/correlation? What is it called?


texts:
I said voltage divider on the title, but could be anything.

I have a DC source of 19.7V.

I need an output that varies from 0V to 18V.

I have:

Resistors (1/8W);
1k potentiometer;
5k trimpot;
2N3904;
LM358;
Capacitors.

My only requirement, besides part count, is that both potentiometers be used: the 1k being the main, and the 5k acting for fine tuning.

And the adjust... not too sensitive. The more linear, the merrier, and taking advantage of the whole excursion of the potentiometer.

In the example below I could not obey the requirement of sensitivity and excursion.

The transistor I'm trying to use has a cutoff around 680mV and saturation around 820mV.
Very small window. Hence, my trouble.

More:

The output current can be small. 5mA will work;
This whole system will control the GND pin of a LM7805, and later on, of a 7905;
LM317 unavailable;
The 1k potentiometer can be turned by hand and is what I have available. The 5k trimpot needs a screwdriver.

History:

At first I thought a voltage divider could do it, but in my attempts, the voltage hardly approaches 15V.

Still open for this type of design, though (just bear the requirements if you'd like to help me this way)

After giving up, I tried using OpAmp. It worked. But later I will need a negative version of this structure I'm trying to build, but 19.7V-(-19.7V) my opamps won't support.

Maybe I could reduce the supply voltage of this OpAmp, but then... part count.

Third attempt, more promising but difficult, was with a transistor.


texts: How do I overlap wires in OrCAD capture without having the two wires have a node?

texts: I'm doing a schematic for this in OrCAD capture CIS. In laying out my schematic I need to draw one wire going through another wire, but not necessarily intersecting with it via a node. When I drag a wire through it it automatically creates a node there at the intersection. Is there a way to draw these two wires overlapping but without a node?


texts:
I am looking for an explanation for the fact that over excited synchronous motor has leading power factor. If induced voltage due to the rotor is greater that the supply voltage, wouldn't that being a generator?

How is a motor with windings and magnetic fields act as a capacitor?


texts: What are the optimal methods for controlling specific header pins via Micro-USB?

texts:
Besides buying a Raspberry Pi with GPIO, what is involved in creating a circuit board that can send data to specific pins through a micro-USB cable, as well as read from data from sensors? I am open to designing my own PCB or using low-cost I/O controllers, but my knowledge is limited in what is actually required to design these interfaces.

For example, one usage would be:

1) Read temperature from an external sensor

2) send data to Android application through micro-USB

3) if temp > 80, turn on LED on the PCB

If I want to create many of these circuit boards without spending a solid amount of money, what would be the best method?


texts:
I'm looking for the best way to detect a weak bluish light (440nm) in a dark environment - with "best" I mean with highest sensitivity possible. I've noticed that most LDRs and photodiodes have their peak wavelength around 550~600 nm, and phototransistors at that range also include UV, driving up their prices.

So what would be the most efficient way? Using a LED to filter to the blue bandwidth, buy a more expensive UV+Blue phototransistor, rely on a IC like a light-to-frequency converter, or does it all depend on the measuring circuit?


texts: Input impedance of a GenRad 2512 Spectrum Analyzer

texts: Does anyone know the input impedance on the General Radio Model 2512 Spectrum Analyzer?


texts: What is the name of this AC plug, and do they still exist?

texts:
Many years ago, I came across a Type I AC power plug, which was effectively a standard plug and double adapter combined. The cable would run to the plug perpendicular to create a lower profile from the wall, and the flat top of the plug would allow you to insert another plug.

I have not seen one of this since, and I'm not sure if that's due to lack of popularity, practicality, safety, or price. However, I'd be very interested to know what its name would be.


texts: Driving WS2812b with STM32 and PWM strange behavior

texts:
First of all I want to say that I'm a complete beginner in circuit design but I really want to do one thing. I'b trying to drive WS2812b LED strip using STM32F103 chip. Since WS2812b use 5V and MCU works on 3.3V I use logic level shifter. Here is a scheme:

Here is my LED strip connection sketch diagram:

Here is WS2812b scheme:

MCU generates data stream using PWM. The strip is only 5 LEDs but I use only one for test.
I've connected Logic Analyzer (saleae16) to the data line(2) and I see that data is Ok, i.e. I see 24 waves, each one with period=1,25 us, as required in the datasheet. I have reset time=50us before and after the data sequence.

But the LED doesn't work. I've tried everything. And I was really racking my brain when suddenly found that if I shortly connect additional power wires 1 and 3 (you see them on the scheme) the LED suddenly begins to glow. I can't really explain it. Sometimes, maybe once in 10 the circuit works without this trick. I just switch the power off and then on and it works.

How do I fix this issue? I really hope that someone will help me.

Here is a project schematics.


texts:
Reason/Background
I have a raspberry pi (garage) that's doing some security-related monitoring, and generates a "keep-alive" signal. I would like to have an alarm go off in a separate place (attic) when either the signal stops, or someone tampers with it (cutting the wire or just applying 5v or Gnd to it). This signal consists of a pulse of 5v/150ms each second.

Question
Now I was wondering about how to create a circuit that could detect a change in voltage/frequency/duty-cycle. I think what I made below does the trick, in theory.
I do have several concerns about this:

does this do what I assume it does?
is R1 well-chosen?
is R2 even necessary?
are R11 and R23 the right values? (I don't mean the setting, but their value of 5kOhm)
is LM741 the right choice?
is 50uF for the capacitor a realistic value? Is the RC circuit and its charge resistor well-chosen for that matter?
is it reliable:

interference, should I even worry about it?
can it handle temperatures between -30°C and +50°C?
age, will this run for 10 years?
tolerances in values, what should I pay attention to?

simulate this circuit – Schematic created using CircuitLab
There are three time-triggered switches on the left, to test each condition. They're programmed to do the following:

do nothing for 7 seconds
switch to 5v for 3 seconds
switch to the keep-alive signal again for 4 seconds
switch to Gnd

This is what the time-domain plot (don't know if this is the correct term) looks like:

Purpose
The purpose of this is two-fold: I really want to make this and use it, and I want to learn from any mistakes I have made. So if you would be kind enough to explain to me why something I did was wrong, or give me resources to learn the answer myself, that would be very much appreciated!


texts: Opamp input offset voltage when saturation

texts:
I wonder, how to affect the input offset voltage of inverting amplifier when it's output in saturation?

I'm changing gain with decreasing the value of R2. When the gain is greater than 5, output in saturation. But after that point the negative input voltage of opamp also increase with gain increasing.

I cannot limit the value of R2, in this case, how to avoid increasing this offset voltage?

Beacuse I am using virtual ground property of OPAMPs. This offset undesirable for me.


texts: Cons or pros related to connecting analogue and digital grounds together using a ferrite or inductor

texts:
I'm designing a signal acquisition system with an ADC. I have these questions:

1- Any cons or pros related to connecting the analogue and digital planes using ferrites or inductors. Or should I just connect them directly with a trace/wire at one point near the main supply ground?

2- There is a document on Analog website that states:

  "Be sure to properly decouple each supply pin at the device with a
  0.1-µF ceramic capacitor. Remember to decouple to the analog ground plane, not the digital ground plane"

I find it odd that the digital supply decoupling cap is connected to analogue ground? Wouldn't digital ground be a better choice?

3- What ground do I connect the sensor shield wire to? I'm guessing digital because I wouldn't want the noise it brings in on my analogue signal. Is this correct? Edit: Or a third option, chassis ground?

Thanks


texts: What is the USB like connector on this PCB?

texts: I am just jumping into the world of electrical engineering (coming from software development) and I am examining some PCB’s trying to find UART, JTAG connections, etc. I’ve come across a board with a connection that looks like a very small USB connector. I am curious, what does this connector do? Can it be used for debugging and establishing a UART or JTAG connection? Thanks!


texts: Octal buffer/line driver need current limiters?

texts:
I have a couple of these http://www.toshiba.com/taec/components2/Datasheet_Sync//149/215.pdf I am using for level shifting 3.3 volts to 5v from a beaglebone to a stepper motor driver. The frequencies will range between 2.5kHz - 800 hZ. My questions are:

1) Do I need capacitors, and what would be good values?

2) The datasheet lists DC Vcc/GND current MAX as += 200mA, does this mean I need a current limiting resistor in series with my 5v line (Vcc) and Vcc pin? My TA says I don't, but I would like to double check.

3) For one of the IC's I want to tie the inputs to Vcc and use a Oen (G1/G2) to toggle them all at once. Do I need current limiters between Vcc and the input pins? Again my TA says I don't, but it would be nice to have a good explanation and another opinion.

The stepper driver draws between 8mA-16mA and has a 240 ohm resistor in series with it's inputs.


texts:
I am making the following solar charge controller circuit based off of the NE555:

This is the webpage I got the schematic from:

http://mdpub.com/555Controller/

The potentiometers at the trigger and threshold are set so that the output is high when the battery is at 11.9 V and it is low when the input is 14.9 V. This is done by attaching a variable power supply where the battery should be, setting it to 11.9 V and then adjusting the potentiometer so that the voltage at TP1 is at 1/3*5V=1.667 V which is about a third of the 5 V supplying the 555. For the upper set point, the power supply is set to 14.9 V and the the voltage at TP2 is made so that it is 2/3*5 V=2.333 V, about 2/3 of the supply voltage. This means that if the battery voltage is greater than 14.9, the threshold voltage will be even greater than 2.33 and so the discharge pin is on and output is low, whereas if the battery voltage is less than 11.9, the voltage at trigger will be less than 1.667 V and the output will be high and discharge pin off, in which case LED 2 will light up, indicating charging and LED 1 is off.

I am wondering exactly what Q1 and Q2 are doing. This is because I only have a normally open SPST switch, whereas the one used here is an SPDT. My situation with the relay not powered will be that the battery and solar panel terminals will not be connected.
In this case, they are connected by default, so that must mean the relay isn't powered when the output is high. I speculate that Q1 is an inverter. When output is high, the voltage at R7 will be low and so Q2 won't be on. Therefore the relay is off and the battery and panel remain connected. If the output is low, then the output of Q1 is high, which is amplified by Q2 and the relay is powered so it should switch to dummy load. Is this correct?
If it is then should I be able to remove R6, R5 and Q1 so that I can use my NO relay?
Then a high output will directly affect Q2 and power up the relay so that the battery and panel positives are connected, and a low output will have no effect.

Is this reasoning correct? And what value relay should I use.

Thank you for reading through!


texts:
I want to make a electronic chessboard that detects the position of every piece on the chessboard.

Every chess piece will have RFID tag.

My idea will be to have 2 multiplexers(1*8) one for the rows and another one for the columns. When I want to read the position of a piece I just activate the corresponding row and column of this piece.

I don't know how to user 125kHz RFID reader with traditional analog multiplexer and to sent the signal from antennas to multiplexer and then use the multiplexer to read the tags.

I tried to use the multiplexer for only one antenna, I connected the antenna to multiplexer and then I read the signal from multiplexer, but here I am stuck, I don't know how to take the signal from multiplexer and send it to RFID reader for being read.

I tried in next example to copy the signal from multiplexer in to another analog pin(A1) and to connect this pin to RFID instead of antenna but it didn't work.

This is how is looking the electronic scheme for what I did:

Here is the fritzing version of previous electronic scheme: https://github.com/neac-andrew/MUX-RFID-Reader/blob/master/MUX-RFID-Reader.fzz

And here is a corresponding Arduino code:

#include "RFIDRdm630.h"
#include "MUX74HC4067.h"

MUX74HC4067 mux(7, 8, 9, 10, 11);

#define RX_PIN                          12
#define TX_PIN                          13
#define TAG_ID_BUFFER_SIZE              14

RFIDRdm630 RFID(RX_PIN, TX_PIN);
RFIDtag rfidTag;

char rxData[TAG_ID_BUFFER_SIZE]; // buffer array for data receive over serial port

// the setup function runs once when you press reset or power the board
void setup() {
    pinMode(A1, OUTPUT);

    Serial.begin(9600);

    // Configures how the SIG pin will be interfaced
    // e.g. The SIG pin connects to PIN 3 on the Arduino,
    //      and PIN 3 is a digital input
    mux.signalPin(A0, INPUT, ANALOG);
}

// the loop function runs over and over again until power down or reset
void loop() {
    analogWrite(A1, mux.read(0));//Here I tried to copy the signal from multiplexer in to another analog pin
    readRFIDTag();
    delay(500);
}

void readRFIDTag() {
    if (RFID.isAvailable()) {  // tests if a card was read by the module

        rfidTag = RFID.getTag();  // if true, then receives a tag object

        Serial.print("TAG: ");
        Serial.print(rfidTag.getTag());   // get TAG in ascii format
        Serial.print(" Card Number: ");
        Serial.println(rfidTag.getCardNumber());  // get cardNumber in long format
        Serial.println();

    }
}

This is the library for RFID reader: https://github.com/electronicdrops/RFIDRdm630

This is the library for interfacing the 74HC4067 multiplexers:
https://github.com/nlamprian/MUX74HC4067

Here is the datasheet for RFID reader
http://www.mouser.com/catalog/specsheets/Seeed_113020002.pdf

This is the model of multiplexer
http://www.logicware.com.au/CD74HC4067-16-Channel-Analog-Digital-MUX-Breakout-Board-Multiplexer

I did some research and I found her some related questions but the answers couldn't help me to much:

RFID chessboard

https://forum.arduino.cc/index.php?topic=472479.0

Multiplex 125kHz RFID antenna

https://www.eevblog.com/forum/projects/rfid-chessboard-switchboard-similar-to-relay-multiplexer-and-other-questions/

Thank you in advance and I will appreciate any help.


texts: Transformer Leakage Inductance and power factor

texts: How does transformer         leakage impedance affect          power factor? Or how does the           X/R ratio of the     transformer change        the power factor ?


texts:
Bundled with "Standard peripheral library" for my STM32F2 chip, are "startup" files startup_stm32f2xx.s. There is actually 5 different startup files, in five different folders:

MDK-ARM, TrueSTUDIO, iar, gcc_ride7, arm

I am assuming that each startup file is specific to the IDE used. I am not using an IDE. I simply use OpenOCD and GDB. Which of the 5 startup files should I use? What is the difference between the files?


texts:
The goal is to have a button which wakes up the esp8266 from deep sleep, but can be used as common button while the code is running. This is a follow up of an unsolved Arduino SE question.

esp8266 can be wake up from deep sleep by connecting reset pin to ground. For timed deep sleep esp8266 uses io 16 to put reset LOW for wake up, so io 16 must be connected to reset pin for the timed deep sleep to work.

io 16 is a logical choice for our button. In this setup the button is connected to io 16 and reset wakes a sleeping esp8266, but resets a runnig esp8266. so we need to disconnect reset pin from io 16 (and button) while the code is running or ensure that reset pin is hold HIGH even if button connects pin 16 to ground.

simulate this circuit – Schematic created using CircuitLab

(io 16 has no internal pullup, so externall pullup is needed)

What circuit is suitable for this?


texts:
I have an application for a supercap in a 1 amp sinewave generator. It would be a  10F, 5V supercap. I can not find power ratings for the supercaps of this size available via Digikey or Mouser.

If I subject my supercap to 1 amp sinusoid for an hour, will it be damaged? If the supercap internal resistance is, say, 50mOhm, that is only 50mW. That is not enough to heat a thing the size of that component above its rated temperature (it is certainly larger than a 1/4 watt resistor), so I am below that limit. Are there other limits to the current rating for supercaps?

The frequency of the current runs from Khz to a few cycles per second. The capacitance is high enough that the voltage limits of the capacitor are not exceeded.


texts:
I volunteer with a charity making aids for people with a disability.  My current project is a key-fob gate latch for a client who can't reach a latch from the wheelchair. I have only a bit of hobby experience with electronics, so searching the web I came up with this attached design.
I have selected the Fairchild MOSFET becuase it seems to be in the appropriate voltage range and is easily available in small quantities.  I have not been able to work out how to size the resistors that will drop the gate voltage from the signal 12V, so I guessed.
Can anyone advise me whether the MOSFET component is appropriate and tell me how to calculate the size of the resistor please?


texts: How to filter out ringing current in a local battery telephone system?

texts:
We have a network of manually-switched local-battery telephones. Here is depiction of the circuit in one telephone:

Ü    transformer
OB   local battery (1.5 V)
GU   hook switch
F    speaker
M    microphone
Ind  magneto (30–100 V, 15–30 Hz)
W    ringer

We have a switchboard where we can manually connect subscribers with one-another. Since this can take a while, we would like to play hold-music while we establish a connection. Hold music is being played back by connecting the output of a sound card to the A and B leads of the telephone we'd like to play music to.

This works great unless the subscriber starts to crank the magneto. This fries the sound card. How can we construct a simple filter that protects the sound card from the ringing voltage, while letting the music through?

I thought about a simple high-pass filter, but I have no clue about how to construct one and I prefer to use a design someone more competent than me designed because frying sound cards is an expensive way of testing things.

I would prefer a solution that does not require any additional power source.


texts: When is it necessary to connect all scope probes to GND (instead of just one)?

texts:
Oscilloscopes typically have multiple input channels which have a common ground (which also happens to be earth referenced). The problem is that the probes can be connected to ground through a huge alligator clip, which is very impractical and likely to cause short-circuits with other signals. For this reason, connecting each probe to ground, which is arguably the best solution, is often undesirable.

However, I find that in many cases, connecting just a single probe to GND and let the others connect to the signal only works just as well. In some cases, not connecting any probe to GND and just letting the earth reference do its job works well enough.

In which cases is it fine to leave the probes unconnected to GND ?

In the scope of this question I assume only a single device is measured (or multiple devices which already have their grounds connected)


texts:
I'm using xilinx FPGA(xcku025-ffva-1156) . I want to use the xapp1315  in my design for 1:7 deserialization.

In Xapp1315 design file, an external clock is used to enter the fpga through IBUFGDS.

[

But in my design, there are many other logics, so xapp1315 design can not be top file.

The main problem is that I have only 50MHz external input clock port, but this xapp 1315 design doesn't support this frequency.

The solution I thought was as follows.

Since the input of IDELAYE3 was no longer coming from the IO buffer, I used a DATAIN port instead of the IDATAIN port.

(I also changed the delay_src from IDATAIN to DATAIN).

However , the simulation results are different from the original xapp1315 design.

The rx_ready signal is not asserted. The output seems as if it continues to bitslip.

Is the way I thought it was wrong?

Is it a problem to create a differential clock in mmcm or is it a problem or is IDELAYE3 misused?

Or
Is there any good method to make 100Mhz external input clk port by using 50Mhz external input clk?

Thank you for reading me the long question.


texts:
I want to know how to calculate the channel capacity without using the mathematical formula.
By definition it is the maximum number of bits per second that you can send over the channel with a very low probability of error.
So I was wondering if I make a very large number of Matlab simulations of transmitting symbols (BPSK modulated for example) from a transmitter to a receiver using a fixed Band width and a certain Signal to Interference Rate (SIR witch represents the power of the signal over the power of the noise), How can I measure the capacity of my channel ?
My idea is that I can calculate the Bit Error Rate (the number of error bits over the total number of bits). I will fix a minimum acceptable probability of error (say BER=10^-6).
Then I will calculate the number of correct received bits below my acceptable probability of error to find my channel capacity of that simulation.
After many simulations I will take the mean of all my calculated capacity witch will represent my channel capacity for a certain modulation, band width and SIR.


texts: Can you program an attiny 85 after is soldered to a board?

texts:
I'm developing a project that involves an attiny85 that is already soldered and with several components and sensors connected to it (on the PCB)
Can I program the attiny85, with the other components connected to it? Or should I preprogram it before soldering to the PCB?


texts: I am solving some problems from my text book, and in this question (image below) I don't understand why Va is 13V and not 27V. It makes sense to me if Va were 27V so that Vab would be 21V. But this is wrong, why? This question is from the textbook 'Introductory Circuit Analysis'.


texts: Translate from AVR pgm_read_byte to normal C array manipulation in STM8

texts:
I am trying to translate a couple of lines of code from AVR space data to STM8 normal C data manipulation.

As you should know, AVR has a program space which can storage data for read only operation, hence a special function should be used to read the data (pgm_read_byte()). In the case of STM8, it has a unique flash for program space and ram space, and storage data in program space is simple as using static constant keyword before the variable definition. The main problem for me is translate the AVR code to normal c code in STM8.

This is the line that I want to translate:

AMP[divider] = pgm_read_byte(envs[divider] + (((unsigned char*)&(EPCW[divider]+=EFTW[divider]))[1]))

And this is my translation:

EPCW[divider] += EFTW[divider];
AMP[divider] = EPCW[1+envs[divider]];

I am not sure if "EPCW[divider] += EFTW[divider];" is executed after or before of data reading in "pgm_read_byte()" function. And also I am not sure if the translated index are correct.

Thanks in advances.


texts: Recommendations for essential measurement/bench tools for HV experimentation

texts:
I'm making plasma sculptures, and am also really interested in making big arcs and tesla coils.  I started with some newer TV flybacks and the 2N3055 single-transistor flyback driver, and am moving on to ZFS and/or 555 drivers.  My transistors run hot (and burn up) so I need to do better measurement of what is happening (and tuning of the flybacks).

I think there is a set of measurement tools that will make my life easier, and I am hoping you can add to the list and also tell me what brands are the most cost-effective - remember, this is just a hobby (in a down economy):

Good multimeter

resistance
continuity
volts and current, DC & AC

nice to have:

capacitance
inductance
transistor testing

HV probe for said multimeter

measures up to 40kV

A frequency counter (?) up to 1MHz (?)
An oscilloscope (or digital acquisition device to show waveforms on a computer), the more inputs the better, up to 1Mhz(?)
5 (not a measurement tool) A good power supply to generate up to 16V and 50V at the same time or two power supplies

What else would be nice to have, and would speed up development? And reduce the number of transistors and MOSFETs I burn up?


texts:
I'm creating a cheap room escape in a box. The housing box has hidden doors and the Raspberry Pi inside should be able to open them at will.

I've seen people using servos to open the thing, electromagnets to release the piece of wood, solenoids to push it out of place. But I don't have any practical experience to know which will be simplest and cheapest for me to implement. Anything that can open the door/drawer/piece of wood is good for me.

Question is: which technology should I investigate further for this function?
Thanks


texts: temperature stability in current mirrors

texts: I have read here that temperature stability is one of the performance issues in current mirrors. Can anyone what does temperature stability mean in current mirrors? Thanks.


texts: Moving beyond high end microcontrollers to high performance computation embedded systems

texts:
I have been working a with relatively fast and high end microcontrollers now, and I want to move beyond them. For example, I've been using the STM32F4 chip, which has something of a 180MHz and a decent amount of memory. Now I want to move beyond these "high end" microcontrollers. I want to develop platforms which are in the GHz-range, which can manage a lot of calculations, and also work together with an embedded GPU. The application I want to use it for is in the automotive industry, where there's a lot of data processing and algorithm calculations.

As I understand it, the next step is somewhat more complicated. You need a separate memory, RAM, storage, and a lot of other peripheral components to support the chip. I'm not looking for an embedded computer platform like the beagleboard or RBP, where you run an OS. I would like to run an RTOS where you can crunch decent amount of numbers (lidar data, image processing), and manage real-time requirements.

For example, if some tech company which develops autonomous vehicles wanted a prototyping platform (and I say prototyping cause it would probably be an ASIC in production) where they can do a lot of dataprocessing and algorithms, what type of embedded system would they use?

So my questions is: What lies beyond the high en microcontrollers? Could someone give me an overview of how embedded systems are built up in this domain?


texts: How am I supposed to connect two logic circuits which are not of the same family

texts:
Say I have to couple a NOR \$I^2L\$  and an ECL logic circuit, in such a way that the output voltages of the \$I^2L\$ are suitable for ECL use. Let me show you what I mean:

I thought adding a voltage divider might do the trick. When we have either A or B high the output of the \$I^2L\$ is 0.2V, the collector-emitter saturation voltage. Using a voltage divider as shown in the image, I can convert this logic zero of 0,2 V to a logic zero of let's say -1,7V( less than Vref) which is the input for the ecl circuit, and will be a logic 0 in terms of the voltages present in the ecl. However, I am not sure how to make a logic 1 using this divider. The first cicruit gives us a logic 1 if both A and B are zero, and in that case the input for the second circuit is just -Vee, a logic zero, not a logic 1. Note that this is just for academical purposes, so I guess there are solutions which are easily grasped.


texts: How can I determine whether this is a "rail to rail" opamp from its datasheet?

texts:
I know that rail to rail means that the opamp output can have a swing upto its power rail voltages.

So for a rail to rail opamp lets say if the supply test condition is +-12V, I would assume that the output swing can reach upto +12V or down to -12V.
Similarly with a +-15V supply the swing would reach upto +15V or down to -15V.

But nowhere in this datasheet "rail to rail" phrase is indicated.

In electrical characteristics I can only see some section called "Maximum peak output voltage swing" without any given supply voltage condition.

So briefly, I'm not able to verify whether this opamp is rail to rail and I guess don't know to focus on the right parameters.

How can it be inferred from this datasheet whether this opamp is rail to rail?


texts:
I am trying to read a current waveform from a shunt resistor series with the power line.

Using a full bridge rectifier, I got the following waveform:

The waveform was sampled every 2 millisecond using an Arduino. Upon fourier analysis, I found that it contained a 100 Hz signal.

Since the supply frequency is 50hz in my region and being rectified the waveform is 100 Hz.

But I want to use opamps as a precision rectifier to get smaller voltages than the diode drop. I am using the below configuration. I tested the configuration by setting the input as positive and negative DV voltage from a battery and the negative DC was given as positive DC by the opamp.

simulate this circuit – Schematic created using CircuitLab

This is the current waveform obtained I got from the opamp:

The zero point of the waveform keeps changing periodically.

Is this a problem with the opamp configuration, or is there a better way to do full wave rectification using a single supply opamp?

EDIT:
I meant to use 10 kiloohm resistors, not 10 ohm.
240-24 volt step down transformer signal divided between 10kiloohms and 1 ohms resistor
UPDATE:
The opamp configuration was working perfectly fine. The original signal contained the zero point oscillation.The full bridge rectifier's output was not showing this output because it was not strong enough to overcome the diode voltage drop. After increasing the voltage i was able to see the same signal from the full bridge rectifier as well. Phew!!!! Finding out ground truth is very important.


texts:
Which package is better for hand soldering with solder paste and hot air:

SOD-323
SOD-323F;
SOD-323FL;

Also what is the difference between SOD-323F and SOD-323FL.


texts: Current sense amplifier working principle

texts:
i am running a bldc motor Infineon TLE9879 chip. Now i want to measure the current flowing through the motor. so i use the current sense amplifier where the motor current is converted to a voltage by means of a shunt resistor RSH(0.005 ohm).

I want to measure current from 0.1amp to 3Amps which gives the voltage drop at RSH (0.1*0.005=0.0005volts to 3*0.005=0.015volts).
Considering 5V reference voltage of ADC I will not be able to get a good number for the above voltage drop. Also with the maximum gain of CSA the output is still negligible. The data sheet says you need to do linear calibration but how to do it for the entire current range?
If anyone has experience with CSA please share how to do it?
Attachment CSAdatasheet

I am adding some new information here.
Actually, when I checked the current in one of the phases of the bldc motor it appears like the following

Its amplitude increases as the load on the motor increases.

I was doing a mistake of reading the ADC value in every 100ms without any synchronisation with the actual current waveform. That's why the ADC value always shows the offset value of the opamp.
I think I need to measure the RMS value of the voltage developed at the shunt.
Please let me know if I am correct!!!


texts:
I'm trying to communicate with a NRF24L01 transceiver module with a PIC24HJ128GP202. Besides all the code, here is the important part:

void NRF_Config()
{
  NRF_WriteRegister(0x02, 0x01); //PIPE 0 ENABLE
  NRF_ActivateSR();
  NRF_WriteRegister(0x1D, 0x06); //FEATURE REG - Enable Dynamic Payload && Enable ACK Payload
  NRF_WriteRegister(0x1C, 0x01); //ENABLE DYNAMIC PAYLOAD PIPE0
  NRF_WriteRegister(0x00, 0x5A); //CONFIG REG
  Delay(Delay_2ms);
  NRF_EN(); //CHIP ENABLED PIN = TRUE
}

with the WriteRegister function being:

unsigned char NRF_WriteRegister(unsigned char reg, unsigned char data)
{
   SPI1_BEGIN(); //CHIP SELECT = LOW  (START COMMUNICATION)

   IFS0bits.SPI1IF = 0;
   while (SPI1STATbits.SPITBF);
   WriteSPI1(0x20 | reg);
   while (!IFS0bits.SPI1IF);

   IFS0bits.SPI1IF = 0;
   while (SPI1STATbits.SPITBF);
   WriteSPI1(data);
   while (!IFS0bits.SPI1IF);

   SPI1_END(); //CHIP SELECT = HIGH (END COMMUNICATION)
   return ReadSPI1();
}

This works fine (at least it seems to work). Code runs ok and O'scope shows CS pin going low, then 2 groups of 8 pulses in the SCK pin followed by CS going high.

Then I have this:

unsigned char NRF_PutTXPayload(unsigned char *data, char len)
{

   if (len > TX_DATA_SIZE)
       return 0;
   SPI1_BEGIN();

   //SEND BYTE 1
   IFS0bits.SPI1IF = 0;
   while (SPI1STATbits.SPITBF);
   WriteSPI1(0xA0);
   while (!IFS0bits.SPI1IF);

   //SEND BYTE 2
   IFS0bits.SPI1IF = 0;
   while (SPI1STATbits.SPITBF);
   WriteSPI1(0xEF);
   while (!IFS0bits.SPI1IF);

   //SEND BYTE 3
   IFS0bits.SPI1IF = 0;
   while (SPI1STATbits.SPITBF);
   WriteSPI1(0xEF);
   while (!IFS0bits.SPI1IF);

  SPI1_END();
  return ReadSPI1();

}

As you can see this function above is a modified version of the original one I wanted to use. I'm currently not using those arguments and I used to have a For loop to send variable length group of bytes. Then I came into to this version above because it was freezing my PIC somewhere inside the For loop. Then I realize that if I keep only the first two blocks (SEND BYTE 1 and SEND BYTE 2) it's ok. When I add the third one, it freezes the PIC.

I know that I could reduce my code when taking care of flag bits but I copied exaclty the same lines from the WriteRegister function on purpose to make sure it should work.
Also, it should work because first I reset interrupt flag; then I wait for TX empty buffer to start copying; then I simply write to TX buf; and then I wait to interrupt flag which means transmission has finished. Altough not being the best/fastest way to do that, I think it should work well, but it does not.

It's strange because it works with 2 bytes but not with three. The O'scope shows CS pin going Low, then it shows the three groups of 8 clocks in SCK pin but the CS pin never goes back high (and the PIC is freezed).

Any idea what might be happening?


texts: It seems common that PBX and other telephone hardware use a positive-ground power supply, where the "hot" line is at -48v.  What's the reason for that?


texts: What approach to take in modifying a 8051 based board?

texts:
I'm hacking a massage chair board based around a 8051 microcontroler (a QFP44 SinoWealth SH88F516). Images of the board here. I am not familiar with this IC so I come to you in hope of advice for a best approach.

Is there a way to get a dump of the current hex code that is on the chip? After messing with my own code, it would be a good fail safe to have so I could always revert to the original code.
Can I use any 8051 toolchain to work with this specific IC, or do I need to use whatever SinoWealth is offering?
Someone suggested certain Atmega's are pin compatible with the 8051 but I cannot find much info on that. Is it true?
As an alternative to reprogramming the 8051, I thought to pull down the RST pin and use another IC instead. However the 8051 doesn't reset when the RST pin is pulled down, however it does crash until I cycle the power when pulled high.

Why doesn't it stop functioning when pulled low and would it be safe to keep it high?


texts: Wiring a capacitive touch sensor to the Arduino?

texts: I have just recently bought a few different ic's from Mouser.com, not thinking i never even looked to see if i could use them. I Wound up getting a few Azoteq IQS128 capacitive touch sensors, but I have absolutely no clue which pins are which and how to wire them to an arduino. Any help would be appreciated.


texts: What is the difference between 3 axis and 6 axis gyros?

texts: Is there any real difference between those two modules? If so what is that?


texts: Impedance calculators differ pretty much?

texts:
As you can see here to calculators I found show huge difference or didn't I set it up correctly? I didn't found hints on possible validity limits. Can someone say if one of those given out results is correct? I mean a mismatch of 18 ohm is a no go... Both freeware, is there a commercial software with higher quality?

Edit: Added image with changed material, no significant change, as to my knowledge only the dielectric constant is important, which was set to same value in first 2 pictures. Am I missing something?


texts: Wired GFCI vs. 40v 5a battery use near spa

texts:
My wife has recently taken to running a cord out near our pool to watch TV.  She's very careful, but I was thinking of doing what I can to make it safer, since the outlet in question is NOT a GFCI outlet (It's a standard US 110v outlet).

One obvious solution is an inline GFCI.

The other more expensive idea that occurred to me is using a 5ah 40v lithium battery that I can purchase a 300w inverter for.

My guess here is that if the wired TV were to go into the water, a GFCI would be better than nothing, but unsafe...whereas the battery would be practically speaking likely to be completely safe.  Can anyone enlighten me as to which approach would be the safest, and if either or both is actually "safe"?


texts:
I have a problem when trying to test send and receive lines on RS485 communication, anyone know what may cause a problem here? It works without interrupt but with interrupt won't work. I am working on NXP LPC1788, and trying to make an interrupt echo program for RS485 (what I send, it sends me back to terminal). Thanks in advance.

int main(void) {

    uart2()

    NVIC_EnableIRQ(UART2_IRQn);

    while(1) {

    } //while

} //main

void receive(void) {

    SMR_485RECEIVE; //Receive data flow
    delay_1_ms();
    delay_1_ms();
    receive_byte = LPC_UART2->RBR;
    }

void send(void) {

    SMR_485TRANSMIT; //Transmit data flow
    delay_1_ms();
    delay_1_ms();
    LPC_UART2->THR = receive_byte;
    }

void UART2_IRQHandler(void) __irq {

    BYTE tip = LPC_UART2->IIR & 0x06;
    if((tip == 0x04) && !(LPC_UART2->RBR == '\0')){
        receive();
        delay_1_ms();
        send();
        }

    }

If I'm right before sending I need to call SMR_485TRANSMIT and then store BYTE to output data register THR, when I want to receive byte I call SMR_485RECEIVE and then store data from input data register RBR to variable receive_byte. I deleted delays of 1ms and my code looks like this right now:

void receive(void) {

    SMR_485RECEIVE;
    delay_1_micro();
    receive_byte = LPC_UART2->RBR;
    }

void send(void) {

    SMR_485TRANSMIT;//Transmit data flow
    delay_1_micro();
    LPC_UART2->THR = receive_byte;
    }

void UART2_IRQHandler(void) __irq {

    BYTE tip = LPC_UART2->IIR & 0x06;
    if(tip == 0x04){
        receive();
        delay_1_micro();
        send();
        }
    }

But it won't work, I dont understand whats the problem in my code when switching direction of data flow?


texts: How do I find the resistance between three terminals?

texts:
I'm trying to self-study this problem and I found a bizarre problem with an unusual circuit.

I have never faced this in all the problems that I have solved. What do they mean by finding the equivalent resistance between b and e. I don't even know if this is possible. If you look carefully, you'll see that there is a terminal c between terminal b and e. I have no idea how this could be solved.


texts: Finding the Average Power Loss in a Series RL Circuit

texts:
Question :

  A current \$I=3\sin(400t)\$ amperes in a series RL circuit in which
  \$L=1mH\$ and \$R=100Ω\$. What is the average power loss?

Answer :

$$ APL = 450 \space W $$

My Steps :
\begin{align}
P&=IV\\
 &=I(IZ)\\
 &=I^2Z\\
 &=I^2(jwL+R)\\
 &=I^2[j(400)(0.001)+100]\\
 &=(3\angle0)^2[j(400)(0.001)+100]\\
 &=[9\angle(0+0)][100+j0.4]\\
 &=[9\angle0](100\angle0.229)\\
 &=(9\times100)\angle(0+0.229)\\
 &=900\angle0.229\space W\\
\end{align}

So the APL should be 900W. What is wrong with my idea?

Thank you for your help.


texts: Lead Acid Battery Charger with Load in Parallel

texts:
I have a circuit with a sealed lead acid backup battery, which it charges automatically with a constant current of 350mA at ~15V.

I wish to connect an additional module to the circuit (gsm gateway) which draws between 50mA and 150mA, with peaks of 2A when sending an SMS or communicating through Wifi (periods of seconds), at 5v. DC-DC step down will be used.

That is: the charger would be providing 350mA (~5W) to the battery, and some of this current (~1W) would be diverted to the gateway. I assume the battery would automagically be providing energy for the short peaks (~10-12W). DC-DC step down efficiency will be higher than 75%.

1) Considering that most of the time the gateway will be resting in low power mode, what is the short and long term effect of connecting the gateway in parallel with the battery?

2) Is this potentially safe for the battery and charger?

3) Without power failures, would the battery still be mostly at 100% charge? I assume the duty cycle must be analysed.

4) From a system engineering point of view, would it be substantially better to have a >16v (higher than charger) power supply in parallel with the battery, protected by schottky diodes, or a power multiplexer? Battery recovery time would be better, but the number of components, power dissipation and space required would also be higher.


texts: Switching from full to half wave rectification

texts:
The Context:
Multiple manufacturers of electro-magnetic brakes offer rectifier modules to switch their DC brakes with an AC feed. This can often be tied to the same phases turning the motor, so that the brake lifts when the motor is powered:

(Image from Mayer document linked below)
They often also offer these modules with an "over-excitation" option. The idea being that half wave rectification provides enough power to lift the brake, but by briefly using full wave rectification, the RMS voltage is higher and the brakes lift more quickly.
Both Mayr and Precima offer the same sort of module:
Precima (p.g. 5 of the pdf)
Mayr (p.g. 4 of the pdf)
The Question:
Using only a 2 phase supply, how do you switch from full wave rectification to half wave after a specified time period?
So far, a thyristor seems like a fairly good choice for switching 'off' the full wave rectifier. In the example below, if the switch is closed, the thyristor conducts as a diode, when open, it blocks current both ways.

simulate this circuit – Schematic created using CircuitLab
Tested here (as Circuit Lab cannot simulate thyristors): Falstad Circuit
How can I add some sort of RC network/similar to the thyristor's control pin that would allow operation similar to the devices talked about above, with a resistor value setting a time for the full wave rectification to be active before the 'switch' opens and the thyristor turns off?


texts: How to design aluminum alloy melting furnace with nichrome coil heater of 800 watt 26 swg coil?

texts:
I have 800 watt 26 SWG of length 9 meter nichrome wire and 220 volt AC supply.  I want to heat nichrome coil up to 850C degree for aluminum alloy melting funace.

How much current will I need?

Will this work?


texts: Microprocessor 8085 regains control of the bus

texts:
a) immediately after HOLD goes Low
b) immediately after HOLD goes high
c) after half clock cycle has passed once HLDS goes low
d) after half clock cycle after HLDA goes high

This question was asked in GATE IN paper 2001. As per the answer key, the answer is B.

I think the answer is (a). The way I understand it, since HOLD pin in a 8085 is active high, once a peripheral device sends a high to the hold pin, 8085 relinquishes control over both the address and data buses in the next machine cycle. So not immediately. The 8085 uses the HLDA pin (active high) to indicate it's ready to relinquish control.

Now once the peripheral is done with it's work. It sends a LOW signal to the HOLD pin and the microprocessor IMMEDIATELY regains control of the buses. Anything wrong here?


texts: Mixed (Analog and Digital) signal USB interface

texts:
I am working on the problem of having a USB interface be used for dual purpose: a normal digital session and an off-specification USB plug signaling.

To obtain a normal USB session no changes need to be made to the cable.

The off-specification signaling needs modification of the cable and is common among shutters of digital cameras. Example Samsung NX1000 picture trigger.

What I would like to know is if I can safely trigger the circuit like in the image and on-demand change turn on the USB functionality with some form of GPIO.

The application I have in mind does not need both modes active at the same time, as I believe that would crash the USB session.


texts: How can one mount PCB-mounted TO-247 devices to a large plate heatsink?

texts:
I want to mount multiple PCB-mounted TO-247 devices to a single large heatsink, something comparable to this:

My devices may or may not have mounting holes through them, and their tabs may or may not be isolated. Any approach will have to support the use of mounting clamps and isolation pads. I'm using TO-247 devices for cost reasons; the smallest chassis-mount devices I'm aware of are SOT-227, which cost much more than similar parts in TO-247 packages.

What approaches to this problem are used? What difficulties are presented by those approaches?


texts:
I'm a software development student, who want to improve its hardware knowledge.

I'm reading Structured Computer Organization by Tanenbaum. In the chapter 2, the author says the following:

  "[...] In recent years, nearly all computer manufacturers have standardized on an 8-bit cell [...]".

I thought this was correct, but searching over internet, I found there is no memories with 8-bit per cell!

So, my question is: Is it an error of the author or I misunderstood what he tried to explain? If so, what is, "usually", the number of bits per cell and how could I see the bits per cell of my memory?


texts: MOSFET: What is considered "large voltage" when finding early voltage via experimental method?

texts:
I have found that to get early voltage you can take the tangent a I vs V MOSFET characteristic graph at "large voltages" and wherever the lines intercept the negative x-axis is the early voltage (see wikipedia graph below)

I am trying to do this with my graph, but am having trouble determining what constitutes "large voltages". At first I just added a trendline for the entire curve and realized that did not work.
At what voltage do I need to start extrapolating my curve data to get early voltage?


texts: why plot of ''To Workspace'' of matlab does not fit the scope of simulink?

texts:
I am simulating a complete system for control loop. since I need the data to be saved on matlab, I wrote a small code that saves the data in matlab and I could plot.
my system has a sample time of 156Hz, so on the scope I can see this sampling as you see on the pic

Now after writing the code in matlab to save the same plot is:

x_sim= (dummy.time);
x_sim1 = x_sim(1:end);
y_sim = (dummy.signals);
y_sim1 =y_sim.values(1:end);
plot(x_sim1,y_sim1)
xlabel('time in seconds');
ylabel('voltage');

here is the plot of the output:

I used structure with time to save the data of the signal.
here is the simulink scope and workplace


texts: Identifying manufacturer logos on components

texts:
This question is inspired by this question.

I'm interested in on-line resources which can be used to identify logos. Are there any databases of commonly and not so commonly used logos on ICs which can help there?

I know that http://www.datasheetcatalog.com/ brings up logos of manufacturers when searching for datasheet, but it happened to me few times that I was looking for a component with unknown manufacturer and none on the logos matched.


texts: Using a voltage divider so i can see voltage ripple on my cheap scope

texts: I have been trying to measure the voltage coming from my boost converter to see how clean the signal is but i only have a cheap oscilloscope so when i set the range to the millivolts the signal jumps out of shot. Is using a voltage divider to reduce it down to a level i can see going to give me an accurate visual indicator of the ripple even though its been reduced by a large amount? I will be a 5v signal i'm testing. many  thanks.


texts:
I built the following schematic and I made a mistake. I wired the 4.7M preset reversed.
This is the original schematic:

And this is the schematic that I drew in Kicad:

I already built the PCB but I am wondering what can happen if I wired the 4.7M multi turn preset reversed ? Will the soldering station work correctly ?
I know that the direction of increasing the resistance changes, but I am wondering what other things can occur ?


texts: Can I get a DC output if I connect my laptop AC adaptor to a battery?

texts: I am trying to DIY an external battery for my laptop. I know I could cut the laptop connector part off my laptop adaptor and then connect the connector to a battery however this will damage my AC adaptor, I am just wondering whether it is possibly I could connect the battery to the AC adaptor directly through the 3 prongs that connect to the wall outlet. in other word, the input that will go through my adaptor will be 12v Dc instead of 120 v AC. do I get 12v DC output through my adaptor if I do that?


texts:
I'm wondering if there is a clear and measurable difference or benefit to using a stepper motor as opposed to a standard DC motor controlled via solid state relay?

For my application, I need to move a particular distance, but am having some real difficulty getting my 12v stepper motor (not sure of brand) and Velleman Arduino shield to play nicely.

I've gotten solid-state relays to work no problem, so wondering if I just switch to using a DC motor connected to the relays will that be a similar result?


texts: MCP1700 voltage regulator instantly overheats and starts to smoke, no load

texts:
Newbie question. I have a MCP1700-3302E LDO voltage regulator to power ESP8266 using a 3.7V battery.

However, as soon as I connect the negative lead to the ground pin and the positive to Vin the voltage regulator overheats and starts to smoke.

I tried 2 different MCP1700s thinking maybe the first one was defective. Tried using a different, stable power supply at 5V, same result. Tried with 1uF input capacitor, same.

What am I doing wrong? I just wanted to test the output voltage to be 3.3V.

Thank you in advance.

EDIT 3: Burned a few more, without seemingly any consistency. Some are stable at 4.6V and live, some go up in smoke right away, some burn out slowly at 2.6-3V. One was in expected range of 3.4V but was very hot.

I added a 2K resistor before Vin and input capacitors and it doesn't heat up any more but the output voltage is 0.002V. With a 100 Ohm resistor it's 0.016V, with a 47 Ohm one it's 0.03V (and resistor got hot). So looks like amount of current affects Vout. I'm close to giving up.

EDIT 2: In the setup below, it doesn't overheat anymore. Vout is a steady 4.61V, instead of expected 3.3V

EDIT: Latest setup, fresh LDO, 0.1uF ceramic + 47uF aluminum caps on input, 1uF ceramic on output.

Vin = 5.1V
When it on, I'm measuring Vout = 4.6V until the problems start. Vout is supposed to be 3.3V.


texts: Maxim/Microchip (can't tell) IC Identification

texts:
Part No. is 024 134A. Says Japan M5 on the bottom, visible through a hole in the PCB, not pictured. It is a memory lockout chip for Gameboy, it disables the SRAM when the Gameboy is powered down. I'm looking for a pinout.
Edit: This photo is of Tetris DX. Pokemon Yellow marks the IC as 001 134A. is there a difference? Also, google turned up nothing.


texts:
I am trying to fix an old Kenwood Chef kitchen mixer that's motor is only working very intermittently. I opened up the unit and found that one of the power resistors are cracked - that is likely causing continuous conductivity issues:

A few months ago the appliance spewed a massive amount of white smoke, which I attribute to the popped paper cap on the bottom right, but it continued to function fine until recently. I am planning to replace that as well in any case.

My question is actually whether that cracked resistor is:
 - 56 Ohm (10%) resistor?
 - 90 MegaOhm (.5%) resistor?
 - Something else?

The colour codes look to be [White;Black;Blue;Green] (90 MOhm) rather than [Green;Blue;Black;Silver] (56 Ohm), but I am really struggling to find 90 MOhm 1-2W resistors on the market.


texts: Can you measure voltage along a wire a multiple points simultaneously?

texts: Basic EE question here.  Suppose I have a piece of wire a foot long.  Suppose there is some signal (for example a clock signal) going through the wire.  Is it possible to simultaneously measure the voltage on this wire at (for example) 4, 5 and 10 inches along this wire?  Is it correct to assume these readings would not all be the same?


texts: How to slow down only one edge of a pulse?

texts:
I'd like to make the rise time and fall time of a logic signal be different.   I have a microcontroller pin driving a 10pF load as push-pull.  If driven directly the rise and fall times are both around 1.5 ns

I can change the rise and fall time by putting a resistor in between, for example 3 kohm gives around 30ns for both rise and fall.  What I'd like to do though is to slow down the fall times only.  I tried putting a diode in parallel with the resistor, and somewhat to my surprise the fall time is still short.  This is with a 1N914 and a 1N5711 both of which are pretty fast as diodes go.

How can I slow down the fall times only?  Would the diode idea work for some choice of diode, and why isn't it working for the ones I tried?


texts: Does non-matching impedance of amplifier and speaker distort the sound?

texts:
I'm about to buy a pair of headphones and an audio interface with built in amplifier. The specs say that the amp's impedance is "<30 Ohms".

The headphone I'd like to buy is a Beyerdynamic DT 990, which has versions of different impedance.

I'm only qualified in electronics enough to know that the higher the headphone impedance, the more "amplification" (for a lack of a better word) required to achieve the same power.

However, I'm concerned that the impedance being significantly different introduces distortion to the sound. I'm not talking about saturation necessarily, but maybe a slight change in transfer characteristics, which is obviously not something I want to deal with.

Any insight on this topic is highly appreciated.


texts: How to calculate the SQNR of the PCM system in dB?

texts:
Assume that the input signal S(t) is sinusoidal with amplitude A and quantized to R number of binary bits, how can I calculate the SQNR of the PCM system in dB? I know that the output signal-to-quantizing-noise ratio (SQNR) in a PCM system is the same as the ratio of the average-signal power to the average-quantization-noise power.

$$SQNR_{PCM}=\frac{P_{AvgS}}{P_{AvgQN}}$$

I know that \$P_{AvgS}={σ_x}^2\$ but how about \$P_{AvgQN}\$? Average-noise power (\$\frac{Δ^2}{12}\$) seems not the same as average-quantization-noise power since the answer should not be 1.76+6.02R when using this.

Thank you for your attention.


texts: LTC3525 Shutdown feature reacts to wrong thresholds

texts:
I've be thankful if somebody can help me with my energy harvesting board problem.

I've created an energy harvesting board based on the step-ups Linear Technology LTC3105 and LTC3525-3.3.
Below please find the schematic and board design.

A small 3V solar panel charges via the LTC3105 a 2.7V 3F Supercap up to max 2.66V.
The LTC3525 steps up the voltage from the supercap to 3.3V that goes to the load.
An SPDT slide switch is between the supercap and the LTC3525, to turn off the board (no energy consumption from supercap).

I want to use the Shutdown feature of the LTC3525 and disconnect the output when the supercap voltage is less than 0.9V is and turn on again when it is 2.3V.
So I connected the SHDN pin to the supercap via a voltage divider with 100K and 75K resistors.

I've tested the board using a 100Ohm Resistor as load and also with a 3mm white LED after a 100Ohm Resistor.

I've charged the supercap to 2.6V. I've connected the load and I see 3.3V on the ouput until the supercap reaches 1.47V and the SHDN on LTC3525 is at 0.62V, then LTC3535 disconnects the output (0V).

Then I wanted to test the output reconnect. So I've discharged the supercapacitor down to 0.7V and then charged it, while monitoring its voltage and the output of the LTC3525. The LTC3525 reconnected the output at 1.47V.
This is not as it should be, because the LTC3525 should disconnect the output when V_SHDN is less then 0.4V and reconnects when more than 1V.

I have an other board but with SHDN of the LTC3525 connected to its V_IN (shutdown feature disabled) and the board can provide 3.3V on the output until the supercap reaches 0.7V (same load). This means the problems is not caused by too low voltage of V_IN of LTC3525.

This also means the Shutdown feature on the other board works, but for some reason it reacts to the wrong thresholds.

Does anybody have an idea why?

LTC3525 Datasheet LTC3525 Datasheet

Thank you very much and happy new year!

Sincerely


texts: Sending Serial Data Over FTDI causes loop

texts:
I'm trying to send and receive serial data from an atmega328 (using the arduino library) over an FTDI (FT232R) chip. I can send data to my pc and view it in a serial monitor. I can send data from my pc and flash an LED. But, if I try to send data from my pc and return a "received data x..." over serial it creates a loop of echos.

The following code is from the arduino site

String inputString = "";         // a string to hold incoming data
boolean stringComplete = false;

void serialEvent() {
    while (Serial.available()) {
        // get the new byte:
        char inChar = (char)Serial.read();
        // add it to the inputString:
        inputString += inChar;
        // if the incoming character is a newline, set a flag
        // so the main loop can do something about it:
        if (inChar == '\n') {
            stringComplete = true;
        }
    }
}

void loop() {
// print the string when a newline arrives:
   if (stringComplete) {
       Serial.println(inputString);
       // clear the string:
       inputString = "";
       stringComplete = false;
   }
}

When I send "hello" I get back:

  he

  l

  o

  he

  ll

  o

  he

  ll

  o

  he

  ll

  o

  he

  ll

  o

  he

  ll

  o

  he

  l

  o

  ...

And it goes on forever.

In case it's a hardware issue, here is my schematic.

What is causing the loop-back and how can I go about fixing it?


texts: How does the negative feedback in this oscillator work?

texts:
EDIT: I don't think I'm using the term "negative feedback" correctly. What I meant is, how does the feedback that makes the closed loop gain equal to 1 work?

I'm trying to understand the very basics of oscillators and I came across this article (if the page is down, go here (page 3)). Here is the circuit:

As I understand it, there is a positive feedback through C2 because when, for example, the voltage across L1 rises then the voltage across R3 must fall. Since that increases the base-emitter voltage then the collector current will increase accordingly (alternatively, the collector-emitter voltage drops and the voltage across the tank must increase).

Now I'm not so sure about the negative feedback, which apparently (see the link above) is because the dc build up in R3 (or C2) makes the amplifier go from operating in class A to class C.

For that purpose I ran some simulations in TINA. First I added a resistor in series with the tank capacitor so I could see the feedback response more clearly. Then I took out the resistor to confirm the circuit was working as an oscillator. The values used were taken from the page following the article linked above. Here is the circuit and the results INCLUDING the "lossy" resistor (labeled R4):

As you can see the oscillations in Re tend to build up a DC level with increasing amplitude. This seems to suggest that the transistor is operating in the cutoff region when the wave goes negative, and operating as usual (as in class A) during the positive part. Over time this will charge C2 and provide the automatic sliding towards class C described in the article (this is what I incorrectly called "negative feedback"):

I would like someone to confirm if this is what's happening or if I'm wrong.

Here is what you get when you short R4 (the added resistor):

So the circuit is indeed working as an oscillator.


texts: Using a ferroresonant regulating transformer as an isolation transformer

texts: I'm looking to use a (surplus, NOS) Sola (catalog number 22212) ferroresonant voltage regulating transformer (120V primary and secondary) as a low-power isolation transformer (4A) in case I need to float some project.  Will this work?  What safety issues would I run into vs. using a designed-for-purpose isolation transformer?