texts: Reducing noise in audio circuit (optical pickup + op amp)

texts:
I am building an optical pickup using a photodiode connected to a LM741 op-amp. My circuit is similar to this one:

Except that I've added a passive high-pass filter after the output of the op-amp, to eliminate DC (since I am using 0V and +12V as my V- and V+, respectively). I use Rf=500K Ohm (is this way too much?). In addition, I have an LED adjacent to the photodiode that serves as a light source. The LED is powered by 5V and the op-amp is powered by 12V, both from a PC power supply. The photodiode and LED are connected to the circuit using a 2m long guitar cable ("PL").

The circuit works and produces audio signal when I modulate the intensity of the light shining on the photodiode, but my problem is that the signal is very noisy. I can hear/see two types of noise:

Electrical noise similar to a noisy electric guitar pickup. I suspect that it originates in the long cable (or the tip of it, where the photodiode and the LED are conected) collecting ambient electromagnetic noise. This noise is present all the time, even when no light is shining on the photodiode.
Another noise is present only when a signal is generated, i.e only when I modulate the light intensity. I suspect it is a result of amplifying thermal noise, since my gain is very high.

I would like to know what is the best approach, or in other words where to start in my effort to eliminate the noise:

Improving the signal to noise ratio at the source, i.e by optimizing the physical conditions (ambient light, precision of the position of the photodiode, etc.).
Using a different circuit - I've seen many suggestions on the web and started with the simplest.
Using a different op-amp, one that is more suitable as an audio pre-amplifier.
Improving the shielding of the pickup itself, to eliminate electromagnetic ambient noise.
Using batteries as power source instead of the PC power supply (I am thinking maybe part of the noise is coming form the mains).
If none of the above, What would be your suggestion?


texts: What do I need to power a 20V 3A device using "D" or "AA" batteries?

texts:
I'm going to try and build my own battery pack for a portable speaker. It uses 20 volts and 3 ampere as input. I realize I will burn through quite a few batteries if trying to power it with just AA or even D type batteries. That's not a problem, the problem is that I'm a bit rusty when it comes to my electrical knowledge.

What I would like to know is if I need some kind of regulator for something like this, or if it's enough just to keep below the 20 volts and the device will automatically draw the right amount of amperes? This would mean that I could connect thirteen 1.5 volt batteries in serial to get roughly 19.5 volts out.  Or do I also need to parallel connect those 13 to get the right amperes?

So, for you TL;DR people out there:

How would I connect AA or D batteries (serial/parallel) to power my 20V/3A device? Do I need some regulator type device for it, or is it safe if kept below those values?
If I need some regulator/other for my desired setup, what can you recommend that's suitable for my situation?


texts: Is unstable system unstable for ALL inputs?

texts:
We define system to be stable if for all bounded inputs, it will give bounded output at all times.

But does unstable system means it will have unbounded output for any input?

This question is motivated from a different problem I came across which was to find dc gain of a system having closed loop poles on right - hand side of complex plane. The answer states that since poles are in RH s-plane, dc gain can't be defined. My question is it valid to deduce that unstable system would be always unstable or are there inputs to which 'unstable' system might be stable?


texts: Implementing feedback shift registers in a FPGA

texts:
I am not up on the latest FPGA capabilities.  What would be the lowest cost FPGA chip that can implement 1050 linear feedback shift registers of 71 bits each register?

The shift registers have to be independent and be configured for serial to parallel out. This does not mean I need an I/O for each tap, but the internal circuitry has to have the serial to parallel capability.


texts: What are advantages of Two's Complement?

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In some ADC/DAC devices their are options to output/input the data in 2's Complement form.

What are advantages of representing digital data in Two's Complement form When you can simply have straight binary code and save time of conversion?


texts: Half-wave coiled antenna or quarter wave straight?

texts:
The transmitters for hobby projects working on 433/868/915 MHz (RFM69) require an antenna connected to the board. The board is battery powered, without metallic chassis and overall much smaller than the wavelength (i.e. 20x20 mm board vs 700 mm or 345 mm wavelength).

I can choose between full, half- and quarter-wave. I also read I can use a straight wire or a coiled antenna.

Would a coiled half-wave perform better than a quarter-wave straight? A coiled one with large coils could also allow placement of the micro inside the coil itself, resulting in a compact device.

What are advantages and disadvantages of longer, coiled vs shorter, straight?


texts: How to go about designing an impedance matching circuit for microphones

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I have a black-box circuit attached to a condenser microphone. I would like to replace this condenser microphone with another. I have output impedance data for both microphones across frequency. The microphones do not have identical impedance profiles.

How would I go about designing an impedance matching circuit to get similar performance from the new microphone when fitted? Subtle gain differences can be corrected with post-processing of recorded material.

Could connecting a microphone with different output impedance to the original potentially cause damage to the black-box/new microphone, or is this highly unlikely?


texts: NPN BJT Transistor Circuit Analysis Problem: Is This Question Solvable?

texts:
I've been doing some circuit analysis questions as practice but came across one that seemed very odd:

As far as I can tell, this question is missing information and therefore unsolvable? I was able to find Iload since I had all the information needed there. However, I am unable to find RB simply because I'm missing V (voltage for the base). As there are two unknowns there, the problem cannot be solved. Am I correct in this judgement, or am I not seeing something?

Thanks.


texts: When is it neater to use VECTOR representations vs INTEGERs?

texts:
In the comment thread on an answer to this question: Wrong outputs in VHDL entity it was stated:

  "With integers you don't have control or access to the internal logic representation in the FPGA, while SLV lets you do tricks like utilizing the carry chain efficiently"

So, in what circumstances have you found it neater to code using a vector of bits representation than using integer s in order to access the internal representation? And what advantages did you measure (in terms of chip area, clock frequency, delay, or otherwise.)?


texts: Difference between TTL I/O type vs Schmitt trigger I/O type

texts:
While reading microcontroller data sheet i came across  i/o  types like

i) TTL

ii) schmitt trigger.

I came to know that TTL i/o logic means 0v-0.8v -logic state 0, 2-Vcc means logic state 1 (as per wiki   [1] http://en.wikipedia.org/wiki/Digital_signal#Logic_voltage_levels ).

my questions are

i) what will be the logic state when my input voltage is 1-2 in TTL in i/o type

ii) as per definition  schmitt trigger is a circuit with positive feedback, but i didnt understood how it works, advantage of using schmitt trigger type input over TTL


texts: What happens if a voltage is applied to an output MCU pin?

texts:
As in the question suppose that we have an I/O pin configured as an output.
What could happen to the pin if we apply a 5 volt to it while it is on High state and while on low state?
If you need technical specifications ,i am using an atmega 328 p.


texts: I've ordered this LCD module, and I'm trying to find a suitable connector for it. It's 26 pins with pitch of 0.8mm, but as you can see, the right hand side is "sticking out" of the connector. Is this module compatible with the standard FFC 26 pins socket?


texts: How to properly step down the voltage of a DC+AC signal that then goes inside a pin of a PIC?

texts:
The reason of the question is because i don't know if this is the correct way of regulating a signal that goes inside the pin of a PIC that accepts a signal that goes till 3V3.

In the following image it's the circuit i have, where DATA_IN is the input signal:

And then in this graph with the green light is the LOOP PROTOCOL signal

With the blue color the DATA_IN signal:

I was thinking a diode would be enough to step down the voltage, to the levels we want, which is starting from 0 to 3V3.

Opinions?


texts: Shorting issue with STM32F446; PCB or schematic design

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I'm working on designing a PCBA which uses the STM32F446 as the micro. The issue I'm dealing with is that something seems to be shorted between 3.3V and GND, likely due to some fault with my schematic.

Things I've tried:

3.3V supply is known good with micro not populated. No excess current is drawn.
Micro has been populated by board house so that is also known good. I tested a couple boards with the same result as well, so some manufacturing error can be ruled out.
The micro is oriented correctly (I've been particularly careful about this because STM has a weird marking system).
Resistance drops from ~5k to ~400 ohms when the micro is present.
I grabbed the schematic and PCB footprint from STM, so that is also known good.

At this point I've ruled it down to an error in my schematic, but after poring over the datasheet I've been unable to find where that might be. Any and all help would be greatly appreciated. Please let me know if there's any more information I can provide.


texts: What does this schematic symbol mean? Looks close to variable resistor

texts: Looking at a schematic for a power regulator I found this symbol I am unfamiliar with. It looks like a variable resistor but only two connections are used. What does it mean?


texts:
I'm new to EE so my theory isn't that strong. I want to trigger a srd-05vdc-sl-c 5v relay with my Arduino using a PN2222 transistor and a flyback diode. I plan on using the schematic below:

simulate this circuit – Schematic created using CircuitLab

Now my question is: If I'm powering the Arduino via USB, will the current draw be too much for the Arduino's Vcc pin, thus requiring external power? I believe I'm reading that the relay will draw ~90mA and the Vcc pin from the Arduino can handle up to 200mA total. However, the transistor drives how much current is actually drawn, correct? Which is a function of the digtal pin voltage, R1 and the Hfe rating of the transistor? So if you were to mess that up, the current flowing to the relay would be incorrect and would not trigger it?

Thanks!


texts:
I am building a 18W tube amplifier based on this layout. I found a schematic for a similar amp.

my problem is that there is low plate voltage on all of the tubes (by plate I mean pin 3): when I measure the pins without the tubes it's around 120V and with the tubes it drops to ~17V. there is clearly something wrong.
After rectification I can measure ~300V on the (+) of the bridge rectifier.

I am concerned about that 220K resistor, which is (in the layout) next to the rectifying diodes. would it make a difference if I remove it? because i cannot see it on the schematic.

note: I have a power transformer without center tap, which is rectified using a bridge rectifier as discussed in tube amp power transformer


texts:
I am trying to wire 7 LEDs together, and failing.
Lights: (Numbers are for image below, I have no clue what other info to put here, so I just made them links) They are 3V.
Lights 3&4
Lights 1,2,5,6,7.
Resistors:
I think this is 100M ohms (It came marked as “5.1-9Vdc use”)
Battery: 9V With battery adapter. I have tried multiple batteries, so this is not the issue.
I am trying to wire these together, and read that parallel is the best way to do this. I kind of did a series/parallel mix.
I think the best way to explain this is to show an image, and than say what's not working, hopefully you can help me out :)

Key:
Red: Positive wire/power
Yellow: Negative wire/ground
Blue: Resistor (I think it is 100M ohms.)
White: LED (3V, 3&4 are white, rest (1,2,5,6,7) are warm white)
Pink: Battery (9V) and mess-up number

Only LED #5 works here, and it's nice and bright. Others are off or super dim.

LED #5 is full strength (The only one lighting up this bright out of all the diagrams below. I wish the rest could be this bright), and LED #3&4 are on but dim. The rest are off.

Everything is on (Except for #5, but it's not plugged in), all are a little dim, but not much.

Again, any help would be appreciated, thanks to any ideas!
Also, I guess I should note that I've only been doing this for about 2 days, so sorry if the answer is obvious.


texts: Adding switch debounce to discharge circuit

texts:
We use the attached circuit for some diagnostic timing prior to doing experiments. Basically when the momentary switch is closed, from a location away from the generator box, the left side of C2 is pulled up to ground from ~-6V and C2 can discharge through the oscilloscope. The goal is to have a battery powered box driven by a switch that can close without bounce.

It seems like a p-channel mosfet could act as the switch if the gate is driven to -9V.  That solves the switching, but not the debounce issue. I need the switch to close somewhat quickly, <1us, so an RC debounce doesn't seem to make the most sense. I have used monostable multivibrators before but couldn't find much about getting them to output something like the ~-9 volts I would need to drive the p channel mosfet. Are there any simple solutions that I've overlooked or would a different type of switch make more sense?


texts: How to read a high voltage logic signal with pic microcontroller

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On my circuit I have a voltage detected (TC54) to detect when the level of the battery gets low. The output of this ic is high when there is enough battery, but it will be at battery voltage (12 or 15 volts). I am using a LM7805 to supply power for the microcontroller. Will feeding this high voltage level into the microcontroller cause damage? ( I would say yes to that). How can I read the signal out from the TC54? Would putting a large resistor in series with it solve the problem (1-5Meg)?
Here is the schematic for the design. The RB0 goes to the microcontroller. J2 is the input terminal on the board.


texts: Best connection node of sense pin for regulator?

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I'm tring to get a high as PSSR as possible from my ADP7142 LDO. Observe the following application circuit taken from page 1 of the datasheet:

The softstart (SS) pin is not available on my package and not needed in my design.
I'm wondering about the best connection for the sense pin, since I have multiple output capacitors. First a 2.2uf cap as specified by the datasheet, followed by a 100uf electrolythic:

I assume the reason for the separate connection of the sense pin is to measure the actual voltage present there instead of directly on the output of the LDO, which would probably not be equal.
Is the current connection the best, or would it be better to connect it to the pad of the 2.2uf cap?


texts: Running LEDs on low voltage for long time

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I've made a series of 4 LEDs connected in parallel. Supply voltage is 12v. Those LEDs are brighter than than I need, so I've connected an 18 ohm resistor in series of each set of 4 LEDs. After connecting the resistor, I got the brightness I wanted and the voltage was 10.8V.

So can I keep this setup for a long time, like for 5-8 hrs continuously? Will those LEDs become dim or unusable after some period of time?


texts:
According to Wikipedia's definition, a cathode is "an electrode through which electric current flows out of a polarized electrical device". However, the direction of current flow is purely an arbitrary convention, and is in fact the opposite direction to which electrons flow in a metal conductor. Hence, this definition seems to be a bit lacking.

If the definition is referring to the current carriers, then the definition might be rephrased as "cathode is an electrode through which the charged current carriers flow out" (or "in"?).

How would you define this term clearly and unambiguously? Does the common use of the term "cathode" really reverse when the current carrier is positive, as suggested in the article?

Edit: What actually confuses me is the phrase "Cathode polarity is not always negative". If electrons always flow into the cathode (by way of definition of cathode), this statement implies that the cathode can be at a positive voltage relative to the anode. Can this happen in a "simple" conductor like an electrolyte, or does this require some special circuit?


texts: What breaker should I use to protect downstream?

texts:
I have a 16A supply connected to a junction box to split into a 16A feed and a 13A double socket.
The issue is the 16A is connected to a load that will have high inrush current.
I have protection for the 16A supply upstream but will there be an issue with anything downstream of the 13A socket due to the load on the 16A side, and if so, what sort of protection can I use?


texts: Why Does Op-Amp Output Voltage Always Saturate (in a Non-Inverting Amplifier Circuit)?

texts: I am trying to amplify the voltage measured across a shunt resistor (Rs). I am using a non-inverting amplifier circuit (as shown in the figure). The expected voltage across the shunt is in the 0-50mV range, and I would like an amplification gain of around 100 (40dB), so I can measure it with an A2D channel with an input range of 0-5V. To achieve this, the resistors I am using are Rf=10,000Ohm and Rg=100Ohm, giving a closed loop gain of 101. The op-amp I am using is a NTE778A. I am powering this circuit using a 12V DC power supply. The problem I am facing is, whatever voltage there is across the shunt, the output voltage always saturated to a value that is (very) slightly lower than Vcc. I am not sure what mistake I am making, either in the construction of the circuit or in my basic understanding of this amplification concept, and any help is appreciated. If this is a common rookie mistake, please do excuse me.


texts: Conversion of 11,200 MWh to a XX MW facility

texts:
How large of a battery storage facility (in MW) would be needed to supply 11,200 MWh of electricity for 4 hours before becoming completely discharged.

The facility would be comprised of lithium ion batteries.

The text below may supply some context:
"The Applicants assume that a smaller-scale, alternative energy battery storage involves the installation of smaller-scale batteries and associated equipment to supplement the gas supply system at times when additional capacity is needed... assume that smaller-scale battery storage would supply four hours of electric supply, including approximately 11,200 MWh of energy storage capacity."

Please don't put on hold. there was some incredibly useful discussion coming from this horribly presented question.


texts: Calculating resistance for zenor diodes?

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I am an electronics student, and I was set some homework online. Am not having trouble with the question itself but the theory. It says that the current through the resistor is the same as the maximum current that the diodes can safely handle, but as you can see, there are (V-out) volts being dissipating to the right, and a minimum required current going through the diode to maintain consistent voltage.

How could the current through the resistor be the same as the current through the diode, as voltage=J/C, or, joules per coulomb, so that means there must be some energy carried by the coulombs, and ultimately, some electrons. But then this is contradictory, wouldn't the current going through the resistor be the total current, the current dissipated to the right and current through the zener? Or... Is it that there isn't, then, any current passing at V-out? and it doesn't represent voltage being dissipated?


texts: Which is the preferred approach to PCB layout for signal vs power traces in analog circuits, and things to consider?

texts:
I have had to layout 2 layer PCBs several times now for analog signals, and am just beginning to learn the process. I often face a similar question in one form or another with regard to laying out signal vs power tracks to avoid crossings, etc, and would like some advice.
I have provided the following dummy schematic to try help explain the question. There is some input analog signal, which then passes through a series of components (in this case, inverting op amps with some gain) to manipulate the signal in some way, followed by an output. There are various resistors which are required in each stage, and also the signal is broken out at various points and sent to connectors. All stages require both the V+ and V- PSU connections.

My question is really about the high level approach to the layout in general, and in particular the power traces vs signal traces. If the components are on the top layer, and the bottom layer is to be flooded with a ground plane (not drawn), there are two obvious approaches I can see: you could either have the power traces brought to the chips on the bottom layer, and then up to the chips using vias (Approach A);
or you could bring the power on the top layer and then take the signals to the bottom layer when necessary to avoid crossings (Approach B):

Approach A) : This will in general allow all the signals and components to be kept compact and tight around each of the chips, and signals can be brought to connectors without requiring vias for them. The problem is that the power delivery is more elaborate, and the ground plane on the bottom layer is significantly cut up by the power tracks.
Approach B) : The power delivery here is tighter, without vias, and doesn't break up the bottom layer ground plane so much. The issue is that the signals have to pass through vias to avoid crossing the power.
So my question is what kinds of things should I be worrying/thinking about when faced with laying out power vs signal for such an analog board? How to think about which of these might be a better way to go for future projects? Is there actually a better approach to the layout that I haven't mentioned? Are there any pros or cons that trump all in these situations?
General advice and thoughts would be very welcome.

Extra info:

Let's assume that in reality there are also sufficient bypass capacitors for each chip, but they are not drawn in the interest of clarity.
My applications are generally sensitive to noise on the analog signals, but the bandwidths required are not high (on the order of hundreds of kHz).


texts: Is the smoke of one blown capacitor toxic?

texts:
A few minutes ago I was desoldering micro controllers from an old laptop of mine. Unfortunately I didn't pay enough attention to the area that I was heating with my hot air gun and eventually managed to blow a cap. I remember seeing a rather big ring of white smoke and immediately rushed outside, coughing as much as I could.

I'd like to know if there are any health concerns I should be aware of regarding the toxic smoke that came out. Can It cause serious lung damage?

It's a surface mount capacitor:

Source: http://img.dxcdn.com/productimages/sku_156107_2.jpg


texts: LM35 gives very high values in room tempratures, and decreases when we exposed it to a heat source!

texts:
So we bought five LM35DZ, in the previous days, when we use the multimeter to measure the voltage between Vout and GND, the results were correct and logic, and when we exposed LM35 to a heat source, the voltage increased, But the problem was with Arduino, the results were unstable and illogical! We checked internet, and we found some possible reasons!

Sharing the GND was one of them, but we only use the LM35, so we don't share the GND with any other device
Another possible reason is due to the unstable source, because we're feeding the Arduino from the USB and this can lead to wrong results, because of the ADC converter, there are some ways to eliminate such problem, we chose to read the 3.3 V pin of Arduino and use it as a reference

unsigned int temp = 0;
unsigned long temptot = 0;
unsigned int REFtemp = 0;
unsigned long REFtemptot = 0;

int x;

int REFSensor=  A1,
LMSensor=A0;

void setup() {
    pinMode(REFSensor,INPUT);
    pinMode(LMSensor,INPUT);
    Serial.begin(9600);
}

void loop() {
    temptot = 0;
    REFtemptot = 0;

    for(x = 0; x < 64; x++) { analogRead(REFSensor);}

    for(x = 0; x < 64; x++) {REFtemptot += analogRead(REFSensor);}

    for(x = 0; x < 64; x++) {analogRead(LMSensor);}

    for(x = 0; x < 64; x++) {temptot += analogRead(LMSensor);}
    temp = temptot >> 6;
    REFtemp = REFtemptot >> 6;
    float y= (float(REFtemp)*3.3)/676.;
    Serial.print("Vcc: " ); Serial.print(y*1023./676.); Serial.print("v  ");
    Serial.print("REF: " ); Serial.print(y); Serial.print("v  ");
    float volt= (float(temp)*3.3)/float(REFtemp);
    // Serial.print("V.LM: " ); Serial.print(volt*1000.);  Serial.print("mv   ");
    Serial.print("T.LM: " ); Serial.print(volt*100);   Serial.println("C " );
}

Another problem is the noise and many attempts to add a 100nF capacitor between Vcc and GND, we don't have 100nF so we used 10nF
Also to smooth the results we add another capacitor (1pF to 10pF) between Vout and Arduino pin (A0 in our case)

So today and after making all these changes, what happen is that the results were stable but illogical; in room temperature we read 10C to 12C, and when we removed one or both capacitors the results go crazy (between 100C to 10C) and the most strange event is that when we expose the LM35 to heat, the temperature decreases

We checked the LM35 using the multimeter and here the surprise! The voltage between Vout and GND was between 1000 mV to 3000 mV, and when we expose the LM35 to heat it decreases to 200 mV. I'm saying it is a surprise because all the five LM35 start acting in the same way. Is it possible that we burn all of them at once? If this is the case, how and when this happened? I remember we switched between the Vcc and GND of one of the LM35 which can cause damage, but as I said just one. Not all of them.

So anyone can help? We decided to buy another LM35 and check it, who knows!

UPDATE-------------------------------------------------------------------------

The big capacitor is between GND and Vcc it is about 100pF, sometimes we don't use it, in this case the signal become very unstable, the small one is about 1pF, sometimes we put it between Vout and Gnd! I don't know why we used it, but it made the signal more stable!

this is the signal between Vout and GND, we removed all capacitors, it gave 0v, I don't know why! it gave 1v to 3 volt using multimeter

we fed the LM35 with 5 volt

The signal here was taken between Vout and Vcc(5volt), it should be 5volt, because it is 0v between Vout and GND!

I don't know why it looks like that! apparently there is no big noise!

The last picture is between Vcc and GND, it gave 5volt as expected!

Now! I'm not sure why we got such illogical results! maybe the LM35 was damaged but even with this possibility, the signal between Vout and GND shouldn't be  0!


texts: What value of inductance and type of inductor should i choose for my motor driver circuit?

texts:
I am current design a DC motor driver circuit for 24 volts and 50 amperes since the motors I am using take 25 amperes nominally. I will be using PWM signal to control the output. I was suggested to add a inductor in series with the main 24 volt because it will reduce the inrush peak current as well as any other noise.
Kindly suggest the appropriate inductor type and a way to calculate proper inductance value.
Furthermore, any guidance regarding the safety and design will be very helpful.

ps: I am using mosfets ir3205 and driver ir2103 as basic components. If there are any better and cheap components availabe, please tell.


texts:
I'm looking to use a RBO40 reverse battery & over voltage protection. I was unable to find the RBO40-40T (with 3 pins) anywhere so had to get RBO40-40G, which is slightly different, it has the middle GND pin cut and the data sheet says this goes to the TAB instead.

I'm not really up on this chip packaging, how am I meant to connect this GND when the TAB is a flat metal surface on the back of the chip?

Data sheet is here

Thanks


texts: Using NPN transistors as switches for low-current, 3VDC infrared transmitter device

texts:
I'm currently trying to hack up an IR remote for electric holiday candles so that I can use Amazon Alexa or Google Home to turn them on or off.  To do so, I need to trigger the switches on the hand-held IR remote that comes with the candles.

I attempted to do this using NPN transistors controlled by a micro-controller.

I connected the remote to the micro-controller's VCC and ground pins to provide it with power.  I then used two GPIO pins to supply voltage to a pair of NPN resistors (separately).  When I pushed either pin HIGH, it would allow current to flow across the transistor associated with that pin, acting as a closed switch (I hoped).

I then placed each transistor in the remote control's circuits in place of the mechanical switches.

The problem I have is that I can get the remote to treat whichever transistor is across the ON circuit to work, but the one for OFF fails.  It doesn't matter which transistor or which PIN is used.  ON works, OFF fails.

I have tested all both orientations of emitter versus collector in the OFF switch location, as well, in case current flow direction was an issue.  It has no impact.  ON works OFF fails still.

So why can I get the one to work and not the other?  I don't have a diagram of the actual IR remote circuit, I merely followed the traces to see how the switches are wired up.  I know I have that much right because I can use a physical switch of my own in place of them (or just a wire shunt) and they fire exactly as if the remote's own buttons had been pressed.

What's going on here?  Why can't I use NPN transistors for this job?

UPDATE: I measured the voltage across a few points for further insight.

ON PIN 1 to Ground = 3.3V
ON PIN 2 to Ground = 0V
ON PIN 2 to VCC = 3.3V
ON PIN 1 to ON PIN 2 = 3.06V

These make sense.  On pin #2 is basically ground.  The switch allows the current from pin one to make it to ground, completing some internal circuit that causes it to fire the IR.

OFF PIN 1 to Ground = 3.13V
OFF PIN 2 to Ground = 3.13V
OFF PIN 1 to OFF PIN 2 = 0.01V
OFF PIN 2 to OFF PIN 1 = -0.01V

Perhaps this will shed more light on the problem.  It seems that the voltage potential is so low between the OFF pins that it would not be usable, but I confirmed that touching pins 1 and 2 of the OFF circuit together turned off the candle and the measurement of 0.01V is consistent.


texts:
Any ideas on how to get 3.3V from 5V - 35V at a low 10mA current level? 3.3V need not be precise. It can be 3.5V or 3V, it is powering a small microcontroller.

I'm looking for a small and cost effective solution. That pretty much rules out through hole stuff.


texts: 2-bit comparator using multiplexers only

texts: I have to design comparator using multiplexers only? Here is what've done arleady.


texts: Use one power source for two atmega chips

texts:
I'm working on a big project recently that requires 2 atmega chips one to handle input midi signals and one to transmit output midi signals. Because of the complexity of the project I cannot use one chip to receive and transmit midi and simultaneously control everything fast enough. Is there a way to use a common power input for both chips? I'm thinking one Voltage Regulator sending 12V parallel to two 5V Voltage Regulators powering each atmega chip. Is this going to work or is there any other way to do it like directly connect 12V DC input from external power supply to the 2 regulators?

Thanks in advance.

P.S. I'm going to use one atmega2560 for lots of output and an atmega328 for input if this in any way helpful.


texts: Capacitive coupling Ethernet on backplane

texts:
Sorry in advance I am fairly new to the electronics world and Ethernet signaling. I am a physics postgrad student doing some hardware work rather than an electronics engineering background.
I have to connect two ethernet modules on a backplane PCB over Ethernet. The modules are pre-made and I have no choice but to use them. Since they are on the same board and in very close proximity I am trying to eliminate the magnetics modules.
One of the devices uses a KSZ9031 ethernet PHY by Microchip for which there is lots of documentation and the other uses a BCM54210 ethernet PHY by Broadcom which unfortunately there is virtually no published information.
I have been researching capacitive coupling of Ethernet and dug out this:
https://microchipsupport.force.com/s/article/Capacitive-Coupling-for-Gigabit-Ethernet
So it seems that by luck this is a good choice as it has termination and voltage mode interfaces on board. So far so good, just stick a capacitor in each line.
But this assumed that both ethernet PHYs are the same.
More generally both Microchip and Texas Instruments both publish documents like these:
http://ww1.microchip.com/downloads/jp/AppNotes/jp578072.pdf
which show me how to couple and terminate for PHYs that either have an internal DC bias or without an internal DC bias.
Since I do not know anything about the second PHY by Broadcom including termination and DC voltage bias how do I know which circuit type to pick?
Also, if anyone has any information they know about the Broadcom ethernet PHY I would love to know and if anyone has any general hints or experience with capacitively coupling ethernet that would be great too!
Thanks very much :)


texts: Reverse saturation current in a BJT: active and reverse active modes

texts:
In (Sedra; Smith. Microelectronic Circuits), as well as in several other sources, the value of the reverse saturation current (\$I_S\$) is considered the same for the active mode and for the reverse active mode of the BJT:
*all the equations are for an NPN BJT

\$ \alpha_R I_{SC}=\alpha_F I_{SE}=I_S \$
(reciprocity relation)

\$ i_C=I_Se^{v_{BE}/V_T} \$
(in active mode)

\$ i_E=I_Se^{v_{BE}/V_T} \$
(in reverse active mode)

Since it depends on the area of the junction (\$ I_S=\dfrac{AqD_nn_i^2}{N_AW}\$) and - as the primary source itself explained - the area of the BC junction (in forward bias for reverse active mode) is much greater than the area of the BE junction (in forward bias for active mode), I am having trouble understanding how \$I_S\$ does not change from one operation mode to the other, which leads to \$i_{E (reverse)}=i_{C (active)}\$.

I would think that since the only parameter that changes in the equation of \$I_S\$ is \$A\$, maybe this would make more sense to me:

\$ I_{S(active)}=\dfrac{A_EqD_nn_i^2}{N_AW}=\alpha_F I_{SE}\$

\$ I_{S(reverse)}=\dfrac{A_CqD_nn_i^2}{N_AW}=\alpha_R I_{SC}\$

\$\dfrac{\alpha_R I_{SC}}{A_C}=\dfrac{\alpha_F I_{SE}}{A_E}\$

I really appreciate any help. Thank you very much.


texts: If I have 3 batteries 100mAh 200mAh and 300mAh what the total charge in series?

texts:
I have a tiny questions about the total charge the 3 batteries (E=1,5V) in series.

I compute that way:

\$ Qtotal = C_{eq}\cdot 3E\$

\$1/C_{eq} = 1/C1 + 1/C2 + 1/C3\$

\$1/C_{eq} = \frac{(C1C2+C1C3+C2C3)}{C1C2C3}\$

\$C_{eq} = C1C2C3/(C1C2+C1C3+C2C3)\$

\$C_{eq} = Q1Q2Q3/E^3/(Q1Q2+Q1Q3+Q2Q3)/E^2\$

\$C_{eq} = Q1Q2Q3/E\cdot (Q1Q2+Q1Q3+Q2Q3)\$

\$Qtotal = 3\cdot Q1Q2Q3/(Q1Q2+Q1Q3+Q2Q3)\$

\$Qtotal = 3\cdot 100\cdot 200 \cdot 300/(100 \cdot 200+100 \cdot 300+200\cdot 300)\$

\$Qtotal = 3\cdot 100\cdot2\cdot3/11 = 1800/11 = 163.63mAh\$

But seems its not right because the weakest batterieshas the 100mAh.

What am I miss?


texts: What does the PAM4 level value represents?

texts:
I have a question regarding  PAM4 levels here in this figure.
The PAM levels  show -3 at 00, -1 at 01 and so on. Do you know what does -3 and -1 represents?


texts:
I'm currently building an in-car alert system using a Raspberry Pi. My car has an AUX port  (3.5mm jack) which I currently use with my phone - to play music.

I wish to be able to play music, and play alerts from the Raspberry Pi through the AUX channel.

As it stands, the phone is connected to the AUX jack via a 3.5mm jack cable. If I was to wire the Pi's audio output into the back of this jack would the two audio signals (phone & pi) be played together or would there be distortion or any other issues?

Appreciate any help here!


texts: Export restrictions when sourcing parts for PCB assembly in foreign country

texts:
If a company has a PCB design and wishes to assemble them economically, a natural choice is China.  Some Chinese companies are asking for the parts (or some of them) to be shipped to them.  This means buying the parts locally, shipping them (export), having them assemble the PCBs and shipping back (import).

In a specific case, the design company is in the USA, and the assembly house is in China.  The design includes a Texas Instruments RF chip (CC113L) and a MCU (MSP430).  Actual quantity is 1000.

What regulations do you need to comply with for this 'temporary export for fabrication purposes' and do you know of any special considerations to take into account?

PS. For the 'off-topic' sheriffs of the site, please allow me to reference a couple of reasonably high voted similar questions, with the hope of giving this question a little time to live.

Export restrictions on programming equipment
Export restrictions on components like FPGAs


texts:
I'm on a system with external flash, so I'm unable to program it easily. However, I can load firmware through JTAG - OpenOCD - GDB chain. I automated it as far as I'm able with bash and .gdbinit, but it's, well... shit. Doesn't work most of the time, I have to constantly fix it by hand or power cycle the board.

So I was wondering, does anyone knows a way to load a program using only OpenOCD?

In essence I'm looking to implement following GDB commands in OpenOCD script:

monitor reset halt
load
continue

EDIT:

The board is for Kendryte K210 risc-v microcontroller. The board is using an external flash and normally programmed through USB-UART converter (bootloader flag maybe?).

They've got their own fork of OpenOCD. I'm pretty sure I can't use OpenOCD's program or flash commands, it's the first thing I tried.


texts:
I have a 12V DC Series Motor - a car starting motor - for an experimental aircraft to pre-spin helecopter-type blades before takeoff. Usually, it works correctly but occasionally with power on, no rotation is developed. Turning it off and back on causes proper operation. Even more rarely, the motor develops rotation in the reverse direction. Turning it off and back on achieves normal operation. What can cause this? I'm thinking it's related to the commutator or brushes. The other possiblity being gremlins.

Second question on the same appplication. The motor develops enormous torque, spinning blades with a 25-foot diameter to 60 RPMs in three seconds. It's putting more stress on the airframe than I like. Is there a way to dial down or stage the acceleration of the motor to reduce the torque for the first few seconds?

Many thanks


texts: Reading an Analog Voltage Waveform with a Programmable Scope

texts:
I am trying to automate the use of a Tektronix TBS 1052B digital oscilloscope in order to get the waveform for an analog voltage signal. Or in other words, get a number of voltage measurement samples over time.

There seem to be at least two measurement modes for configuring the scope to perform the measurement, MEASurement and WAVFrm. This is where I am having some trouble. Based on the way that WAVFrm works, it seems like that is only used for interpreting binary data (this is where I could be wrong) so that seems like the configuration I should not be using. On the other hand, the documentation for MEASurement does not describe a way for taking a specific number of samples (which is what I need to do in order to get the analog waveform), so this also does not seem like a reasonable configuration.

It seems like no matter which configuration I pick, it will not give me the result I am looking for! I must be getting confused by their documentation [here].

Can anyone help shed light on which configuration I should be using, MEASurement or WAVFrm?


texts: How to drive paralleled mosfets with a microcontroller?

texts:
I want to make a DC switch with mosfets as follow:

Now I want to know does this circuit work with reliability?
And I want a circuit between avr microcontroller and this circuit to drive the mosfets to switch current.
Frequency of switch is very low about 10 switch in one hour.
In fact the 60 resistor is a heater that has 22uH inductance.
Thank you in advance for your helpfulness.
Best regards.


texts:
AD620 is commonly used for DIY EEG/EC/EMG projects. I've seen an instrumentation amplifier that is designed by using 3x TL081 opamp for EEG project.

For example :

I've checked that AD620's input offset voltage is in uV and TL081's in mV. As you know input signals are in the range of micro volts for EEG.

1) Do you think using the figure above as instrumentation amplifier would just work fine or would have high error level ?

2) How can I choose what resistor value is best for me ? In the figure Rg = 220 ohm, for example. What would occur if Rg was 3.3k ?

3) As known, high and low pass filters are used in EEG project and those filters have opamp inside. What should be the gain value for them ?

Thanks in advance for your help.
Have a nice day.


texts: Microcontroller GPIO ports referred to as Parallel Ports

texts: A coworker of mine, quite frequently, refers to the GPIO ports of say an 8051, AVR, or any microcontroller as "parallel ports". Is this a common nomenclature in industry? I find it kind of confusing, I always just referred to it as the GPIO port.


texts: Board to Board Connections in Potted Electronics

texts:
We are contemplating a design which will need 2 PCBAs and be potted.  One board is quite "special" so it's rather impractical to reduce the design to a single PCBA.

The conventional wisdom is that soldered wires should be used as conventional board-to-board connectors such as FFCs or pins headers will be unreliable in a potted design.

What other techniques can be used for board-to-board connections in a potted design?  In this instance, there would be 10 lines, two of which will be 12Mbps USB (no genuine high-speed signals).  Of course, soldering wires is still possible in this design, but time consuming and possibly error prone in production.


texts: What causes the uncertainty in the threshold voltage of a CMOS switch?

texts:
CMOS switches such as the DG419 have a threshold voltage - i.e. the voltage at which the output state is flipped - which is dependent upon the logic level and the positive supply rail. However, the exact threshold voltage at which the state will flip is undefined. For the DG419, the threshold occurs within a region spanning many volts, particularly for lower supply voltages:

What causes this uncertain region in switching? I guess it's not the material itself, but rather something else such as stray capacitance or source impedance.


texts: Maintaining clearances in HV MOSFET footprints

texts:
I'm thinking of making a prototype PCB which would use a bridge rectified AC, which will end up with peaks around 350V in my area (+/- some smoothing). It's a through-hole design and the circuit will use a MOSFET, e.g. IRF840 (comments welcome). I'm new to AC, and I'm educating myself.
The problem is - I'm not sure how can I maintain recommended clearances since the MOFET's footprint (TO-220) has about 0.5 mm clearance between the pins, and I will be using it to switch the low side of the rectified power line.

By most standards, there should be at least 1.5mm between exposed metal there, right? How is this done in general? Are there different, larger MOSFET footprints? If so, why are there MOSFETs like this one which are rated to 500V+?


texts: Ideal temperature and humidity for preventing problematic ESD conditions?

texts: I know manufacturers often keep components sensitive to ESD problems in climate controlled rooms and I'm just wondering what the ideal temperature and relative humidity is to prevent ESD problems?


texts: Could someone please help me to get a better understanding as to how to calculate the current flowing through the resistor and the voltage drop across the silicon diode with the assumption that the silicon diode has a forward-biased junction potential of 0.7V


texts: I am honestly confused, A transformer "Steps up the voltage and steps down the current" or vice versa. So how does it obey Ohm's law? for example, a transformer with a winding relation of 2:3, should make 4V 30mA become 6V 20mA, right? but I=V/R, so is there some internal resistance on the secondary winding? I know that impedance could be the answer, but does varying the input resistance varies the inductance of the secondary coil?


texts: Impedance of a circuit that contains a 2 port network

texts:
simulate this circuit – Schematic created using CircuitLab

So, firstly, find the y parameters of a network ( says the assignment). Which I did. Now for the impedance I get the a parameters (for the box), from those y.

I get $$ \frac{V1}{I1}=\frac{ a_{11}*V_2 -a_{12}*I_2}{a_{21}*V_2-a_{22}*I_2}$$

Can I use this expression to find impedance of a whole circuit? That is, to express I2 as I2=Ig-V2/4 and plug that into above equation. Will that give me the correct result?


texts: Do multi-layer ceramic capacitor specifications vary within a dielectric class?

texts:
According to the linked pages below:
Class 2 MLCCs are most commonly made of alkaline earth titanates, specifically barium titanate, along with suitable additives such as aluminum silicate, magnesium silicate, and aluminum oxide.

Do differences in the specific dielectric material or additive affect the specifications of a class 2 MLCC? In other words, can I expect every 0805 50V X7R to behave the same?

Comparing two 1206 X5R 10% 25V capacitors (datasheet links below), there are clear differences in the DC bias characteristics. Can parts be expected to vary more than this?

https://psearch.en.murata.com/capacitor/product/GJ831CR61E106KE83%23.pdf

http://www.samsungsem.com/kr/front/downloadcms.do?path=/kr/support/product-search/mlcc/__icsFiles/afieldfile/2016/01/21&fileName=Data%20sheet_CL31A106KAHNNNE.pdf

Thanks

https://en.wikipedia.org/wiki/Ceramic_capacitor#Class_2_ceramic_capacitors
https://passive-components.eu/class-ii-ceramic-dielectrics-types-performance-and-applications/


texts:
I have a 3-AA battery holder and I am looking to build a solar battery charging circuit.

I am planning on using 3 AA NiMh 1.2V batteries to be placed in the battery holder.

I am planning to use a 1N5817 blocking diode, so current does not get drawn back to the solar panel.

If the batteries are placed in parallel, then the total voltage for the battery pack will be 1.2V, 2300mAh * 3 = 6900 mAh. I have concerns about losses at such low voltages ?

I could also wire two of the batteries in parallel and 1 in series for 2.4V, 4600mAh.But I would have to balance the cells somehow ?

According to this page: http://www.amazon.com/Sunnytech%C2%AE-100ma-Module-System-Charger/dp/B00HQ9CUMO, it says that for a storage battery of 1.2V, you need a solar panel that outputs 2-2.5 V, and for a storage battery of 2.4V, you need a solar panel outputting 3.5-4V.

My questions are:
1) What voltage of solar panel do I need? I did some research online and I can only find 2.5V panels from China (for e.g. here: http://www.aliexpress.com/item/High-Quality-0-5W-2-5V-Solar-Panel-Solar-Cell-DIY-Toy-Panel-Polycrystalline-Solar-Cell/32435616123.html), they don't seem to be made in the US.
2) Do I need a charge controller? If so, why? According to this link: http://www.solar-electric.com/solar-charge-controller-basics.html/, if the panel outputs 2w or less, I wouldn't need a charge controller.
3) If I use a 2.5V, 200mA max panel with a 1.2V, 6900mAh battery pack, I would plan on using 3 of these panels in parallel for a max output of 600mA. Does this seem reasonable? Or should I use more panels? 600mA would be roughly 10% of the battery capacity, which I have read you shouldn't exceed.

Any information would be much appreciated. Thanks.


texts: How long will it take to kill a MOSFET with heat?

texts:
Example; http://www.aosmd.com/res/data_sheets/AOK42S60.pdf

With this; http://www.irf.com/product-info/datasheets/data/pvin.pdf

As I was taught in another question, the 40nC gate charge being hit with 10uA at 10V gives you 40/10 = 4mS of switching time.

I'm gonna be sticking 3-4A~ of 300VAC@150kHz into the drain/source.

If I turn this FET on manually, i.e. 100% duty cycle, will it just die instantly because it's in the linear region for 4uS?

Or do you need to turn the gate on and off really fast for it to kill your FETs?

According to this;

$$ P = (I^2R) $$

It should dissipate;

$$ P = (4^2*0.099) =  1.584$$

Do I get the I(ds) graph per unit of V(gs) and integrate over it, changing \$ (I)^2 \$ each time for each change in V(gs) over a period of 4uS in the graph? So like, the power dissipation at \$ 0V + ... + 10V  = total Power Dissipation \$

I'm really confused as to why this MOSFET would burn up instantly like a guy said in the  other question.


texts: How to shorten fall time on high-side BJT drive?

texts:
I have built a PCB with a set of high-side BJT drives shown in the schematic below. I'm using 8 of these to drive the columns of an 8x8 RBG LED matrix.

While debugging the board with my oscilloscope (with the load, i.e. L1 and R4, disconnected), I noticed that the circuit was showing a much longer fall time than I expected. I got 660us while I expected a fall time below 1us. Below are a series of scope shots I took.

Switching at 250Hz (T=4ms):

Switching at 1kHz (T=1ms):

Switching at 2kHz (T=500us):

I'm switching the drive using an MCU through the MCU_OUTPUT signal and the scope shots were measured at the PROBE label.

The problem is that I need to switch the drive at around 14kHz, but above 1kHz, it doesn't even get to 0V during fall anymore. So above a certain frequency, the drive doesn't turn off.

Well, I only (sort of) understand how BJTs work in simple switch and amplifier configurations, so I'm puzzled with these results. I tried googling for it, but I don't even know what search terms to use. I'm stuck.

My questions are:

Why is the fall time so much longer than the rise time on this circuit? The fall curve looks like that of a capacitor discharging, but I don't have a capacitor in the circuit. Or do I?
How can I shorten the fall time on this circuit? Can I shorten it by changing the resistor values or the transistors?

I'm hoping I can learn something new about transistors with this opportunity.

Update: Testing with the load connected

I took Michael's answer into consideration and took another set of measurements with the load now connected. The scope shots are below. The results were much lower fall times, in the order of 660ns. That's 1000x lower than the original 660us I was getting with the load disconnected.

Switching at 2kHz with load connected (T=500us):

Switching at 14kHz with load connected:

The end result is that the circuit I built is capable of switching my loads at the required frequency. It's just that I was making an incorrect measurement with the load disconnected.


texts: Increasing the opamp gain is decreasing the DAC resolution

texts:
I want to control for example LM317 ADJ pin with a 12 bit DAC to get 1mV precision, it's an 0-5V DAC. In below schematic I increased the gain of opamp to two so I can achieve a higher voltage, but now the problem is every step is doubled as well; (5 / 4096) * 2 = 0.0024.

simulate this circuit – Schematic created using CircuitLab

How can I increase the opamp gain without actually losing the DAC resolution?


texts:
If I will build this circuit in real life, I will probably see a mV noise with the scope due to high cascaded gain and probably some oscillations.

I use LPC358 which is specified to (Input-referred voltage noise) 178nV/SQRT(HZ). I am trying to figure out how small can be the input signal (now is GND at C3) to be masked by noise generated by circuit itself.

My simulation is clearly wrong, showing a clean output with some nV flicker.

How can I add some noise in LTSpice, based on the fact that any opamp has specified noise, that will emulate real worlds noisy output so I can select from several opamps, gain, etc?


texts: How to reduce an audio signal to proper input level?

texts:
I'm working with an audio ADC that supports a max audio input of 500mVRMS before it will start clipping.  This is sufficient for lots of equipment that does a 1VPP/.35mVRMS line level, but I'm finding that lots of equipment like computers, and MP3 players and things will use up to a 3.5VPP/1.25VRMS output voltage.  I need the input to work with both the high and low voltage signals. I am considering simply cutting the input signal to roughly 1/3 so that any of these signals will fall under the 500mVRMS level, but then my SNR will be worse on signals actually coming in at 1VPP/.35VRMS because I'll have to amplify it much more to get a good volume on the output.  I've tried it and it works, but it may not be ideal.

Is this my best option, or is there a more effective way of reducing the higher voltage inputs to prevent clipping before it gets to the ADC?

Note: Changing the ADC would really not be ideal, so solutions other than that would be particularly helpful.


texts: Is it possible to use the same RJ-45 connector?

texts: Given that the wires are connected to the pins and crimped with a crimp tool; is it possible to "un-crimp" the wires such that they can be unattached from the RJ-45 connector? Whereafter the connector could possibly be used for another cable e.g. CAT-5e cable?


texts: Flashing a brand-new ESP8266EX with empty W25Q32

texts:
I made my own WiFi circuit board using ESP8266EX and a W25Q32 flash (bought from Mouser). My problem is it is not flashing. I used NodeMCU flasher and ESP flashing tool. It only gives boot mode 1,7 when try to flash and boot mode 3,7 when I reset, at 74880 baud rate (which looks correct according to my knowledge).

For test my surrounding circuitry, I replaced ESP8266EX and flash with an existing ESP01's ESP chip and flash. I can flash my circuit with that chip and flash, without an error and I can run code. (Also I tried several new ESP8266EXs and W25Q32s and they didn't work.)

Are there any additional things I should do when I use a brand-new ESP8266EX and empty W25Q32 to make it flash?


texts: 3 phase AC: Can I terminate at main service junction to mitigate line loss? Harmonics?

texts:
Suppose I am running very long 3 phase wye distribution from a generator. At the end of my run I will have great line loss and low voltage so i must increase the voltage at the source.  This will then cause an over voltage condition early on in the run.  Suppose I terminate my run by splicing the end back into the initial breakout point so that I will have a loop. My initial analysis is that it would effectively double the size of the conductor, reducing line loss, but my conductors would be split between two uneven lengths (close to the source, I would have one very short leg, and one very long leg, while at the farthest point i would have an equal length split between two conductors) Assume both linear and non-linear loads.

Would the load equalize between the uneven conductors?
What kind of effects would this have on the line loss?
Would this introduce any harmonics into the system?
What other factors should i could consider.

If you understand this, would you mind giving me some insight on how to calculate and prove this myself?
Thank you.


texts: Where does the input resistance formula of a BJT amplifier come from?

texts:
I just solved the (a) question of this problem from one of my past exams. And I am a bit confused on to why the solution is as follows:

Rin = 100kΩ || Rib

Rib = (rπ + (1 + β)Re)

And the way Rib is derived is using this equation:

Vb = rπib + (ib + βib)Re

Rib = Vb / ib = [rπib + (ib + βib)Re] / ib = (rπ + (1 + β)Re)

Now, what I don't understand: Why is the input resistance Rib = Vb / ib? Where did that come from? Is that derived from the Thevenin equivalent of the BJT?


texts: How to turn on and off LED when ESP32 board reach specific internal temperature threshold?

texts:
I'm a beginner and I'm working on a project to turn on and off an LED using a phone app. I'm using DOIT ESP32 Devkit V1 which I control via Wifi using Blynk app, jumpres and LED.
at first I wrote a short code to turn on and off the LED when I press a button in the app, and it worked. After that, I added some more code to display the internal temperature of the board (I don't need it to be very accurate) and at last, I've added some more code to turn off the lamp if the temperature is between 67 - 69 deg Celsius and to display a message "OVERHEATED" and then turn it on again, and display a message "NO MESSAGES" when the temp is above 69 deg Celsius. The problem is that when the temp shows between 67 - 69 the LED is turned off and the message is displayed correctly, but when it goes above 70, the LED won't turn on although the message is showed correctly. my code:
#define BLYNK_PRINT Serial
#define RELAY_PIN 32
#define TEMP_PIN V5
#define MSG_PIN V6

#include <WiFi.h>
#include <WiFiClient.h>
#include <BlynkSimpleEsp32.h>

// You should get Auth Token in the Blynk App.
// Go to the Project Settings (nut icon).
char auth[] = "...";

// Your WiFi credentials.
// Set password to "" for open networks.
char ssid[] = "...";
char pass[] = "...";

#ifdef __cplusplus
extern "C" {
#endif
uint8_t temprature_sens_read();
#ifdef __cplusplus
}
#endif
uint8_t temprature_sens_read();

BlynkTimer timer;

void setup() {
  pinMode(RELAY_PIN, OUTPUT);
  pinMode(RELAY_PIN, HIGH);

  Serial.begin(115200);

  WiFi.begin(ssid, pass);
  int wifi_ctr = 0;
  while (WiFi.status() != WL_CONNECTED) {
    delay(500);
    Serial.print(".");
  }

  Serial.println("WiFi connected");

  Blynk.begin("...", ssid, pass);

  timer.setInterval(1000L, myTimerEvent);
}

void myTimerEvent()
{
  bool was_overheated = false;
  Blynk.virtualWrite(TEMP_PIN, (temprature_sens_read() - 32) / 1.8);
  if(((temprature_sens_read() - 32) / 1.8) > 69){
    Blynk.virtualWrite(MSG_PIN, "NO MESSAGES");
    if(was_overheated == true){
      digitalWrite(RELAY_PIN, HIGH);
      was_overheated = false;
    }
  }

  if(((temprature_sens_read() - 32) / 1.8) > 67 && ((temprature_sens_read() - 32) / 1.8 <= 69) && (was_overheated == false) ){
      was_overheated = true;
      digitalWrite(RELAY_PIN, LOW);
      Blynk.virtualWrite(MSG_PIN, "OVERHEATED!!");
    }

}

void loop(){
    Blynk.run();
    timer.run();
}

What could be the problem?
Thank you.


texts: How can I turn off a MOSFET when the temperature rises?

texts:
I am using a MOSFET as a pre-regulator.

When the voltage is too high, the temperature of the MOSFET is getting too high. (Even if I take 15 mA current.)
As a safety precaution, if the junction temperature of the MOSFET exceeds 100 degrees, I want it to enter the cut-off region. What are your suggestions?
(Note:I am using a iron cooler.But  still, there is a rise in temperature.)


texts: How to achieve digitally adjustable supply rail sover a wide range (low up to 300V)?

texts: I need to be able to vary the supply rail over a wide range (low voltage up to 300V DC). Current consumption will be from 1 mA up to 40mA. The thing will be powered by AC mains 120V. I am wondering what is the best way to achieve a DC rail that can be adjusted digitally through a microcontroller, that stays stable enough with current output 1 to 40 mA. I was thinking of using a buck and drive it with PWM but I've been told this won't be good enough if output current is not stable. Thank you.


texts:
I have been combating EMI from a motor switched by a relay but have managed to get it under control or so I think:

It started like this: 30+ voltage swing @ 5.000us+

After an AC snubber, opto-couplers, decoupling caps it's now: 2.5 volt swing @ 200ns

It's all connected to a Arduino (5V) and various other components (LCD, LEDs, shift registers, etc))

So I'm trying to figure out if I have suppressed it enough so it won't effect the other components.  I can't seem to find any best practices around, that say keep voltage spikes to X percent over X duration. Is there any guidelines like that I can follow? Is a 2-3 V spike over 200ns acceptable in this situation?

Circuit diagram for clarity:

Thanks


texts: I2C Communication between Arduino Uno and mbed

texts:
I have an Arduino Uno and mbed sharing the same USB power supply/ground.

When connecting the two to allow I2C, I would have assumed I'd need to attach the Arduino's SDA pin (PC4) to the mbeds SDA pin, and the SCL pin to the corresponding SCL pin.

However, the examples I've seen seem to only make use of the Arduino's A4 and A5 pins.

Which is the correct (if any) way of doing this?


texts:
simulate this circuit – Schematic created using CircuitLab

I'm using a precision OP AMP LMC6062AIM as a buffer (Voltage follower). The supply is +5V and GND.

The INPUT is a DC voltage (no modulation). If this voltage gets within 1V of the High Rail (so bigger than 4V or about), the output of the OP AMP goes to 5V (the rail). Also tried raising the supply to 7.5V and just like before, at 6.5V Input, the Output goes to the rail.

I've never seen this phenomenon before. I tried the same setup with a similar OP AMP (LMC6482) and this doesn't happen. It works as expected.

Anyone how any idea why this happens, or how it can be corrected?


texts:
I am building an app that is supposed to detect a bluetooth signal from a device.  I have been looking at a lot of blueotooth 4.0 boards but I am clueless as to what I need or what other components I am supposed to get with the board.

All I want is for the device to broadcast a bluetooth signal with a unique ID.  Nothing else.  This signal will then be picked up by the app on the phone.

What kind of component do I need to achieve this? What is the cheapest most dependable solution for broadcasting the signal?


texts: What stops AC from my UPS leaking into the grid?

texts:
In many parts of the world (where power cuts are relatively frequent), we use "Uninterrupted Power Supply" (or UPS), which is an inverter connected to one fraction of the household circuit (loads like lights, computer etc..) and a battery.
I wonder what stops this current from going to the rest of the household circuit (heavy loads like boiler and refridgerator) or even the wider grid (ie power supply)?


texts: Is mechanically switching SATA drive signals possible?

texts:
Since SATA has made it possible to do all data interfacing to a drive through 4 wires, what I'd like to do is physically route two SATA ports to two drives, through a switch that simply swaps them. This way (for example) the one I want to boot from becomes SATA-0 and the other becomes SATA-1.

For background, many times I've wanted to be able to boot from one of two hard drives on a desktop PC, WHILE keeping both drives accessible to whichever drive I boot from. Often the purpose is to have a choice of operating systems, and to have all the time I need to migrate from one OS to another, while always having the data on both drives available.  I'm fully aware of many dual boot schemes available in some system bios, and of course I know i can always open up my machine and manually swap SATA cables. There are all kinds of solutions other than what I'm asking about, but for now I want to explore this purely electrical/mechanical drive swapping idea.

I realize that swapping two SATA drives would take an 8PDT switch, which might be hard to come by, but I could do it with two 4PDT switches ganged together mechanically, or I could do it with several miniature signal relays, such as those made by OMRON. It certainly would be a universal solution, unbounded by bios limitations and a lot less prone to software "Murphy" problems. But my critical concern that has made me hesitate in designing such a mechanism is that the signals going over an SATA wire are pretty damn fast (I think 5-6 gigabit,a according to wikapedia.

How can I implement an electrical circuit to switch between two SATA ports?


texts:
I Have Few Doubts on AMBA Bus Architecture and its clocks

I am working on Propriety SOC with non-detailed docs , the SOC is based on ARM9 Architecture which has peripherals connected to it through AMBA2.0

Every Peripheral (lets say UART) needs a clock which is given after prescaling and postscaling through PLL and fed to the respective peripheral, so we are clear that we need a clock for a peripheral to work

As these Peripherals are connected over a APB Bus, each has a PCLK input which is connected to the core through the matrix

Now my doubt is how APB master(the arm core) is handling the PCLK while its been generated from separate block APB clock generator, is PCLK generated by slave in contrary ?? does the peripheral work with PCLK itself ???

if possible suggest me some references on AMBA in arm based SOC


texts: Using a Ryobi 36v battery to power an electric kart

texts:
I'm attempting to use a BPL3650 36v Ryobi battery as the power source for replica electric willy's jeeps I've constructed for my kids.

The batteries charge fine in the standard chargers available off the shelf
The batteries work fine in the standard Ryobi 36v tools and respond as normal to the pressing of the battery stength indicator

However, when I go to use them in a circuit not in a Ryobi tool, they only appear to show 18.6v across the positive and negative terminals.  I can exclude them from the circuit and just test the batteries with my multimeter and get 18.6v.  Bizarrely, the actual behaviour the batteries exhibit is to start off at around 39v and over a period of about 10 seconds, drop to 18.6v (or approximately half voltage) as indicated by the multimeter.  However, the batteries are actually fully charged.
There are 4 terminals on the battery, the middle 2 appear to be thermistors (designated T1 and T2)and when I opened the charger to have a look, only one of them was connected to the charging circuit board.
I'm 'assuming' that the battery must be getting some form of voltage across the second thermistor when in the actual hand tools that disables the battery protection circuits.  Apart from dismantling a Ryobi 36v tool to see what might be triggering the circuit protection in the battery, I thought I'd post here to see if anyone has any thoughts or had already achieved this process themselves.
In short, does anyone know how to get the full 36v+ from a Ryobi battery outside a Ryobi powertool?

Second Update:
Including an image of the completed Jeeps (from a while ago now).  On the 36v Ryobi batteries and a geared 500w ebike motor, they go faster than my ride-on lawnmower...

Update: Ended up dismantling a 36V strimmer to see what was going on.  In the first picture below you've see the trigger switch (Jaiben DBW-2036E).  The multimeter before the switch exhibits the same behaviour as before but after the swtich, a steady 41v.  Would someone be able to tell me what the electrical component is that's connecting the two poles after the switch?  All I can read on it is 10A so assuming amps of some form.


texts: Create MIDI instrument with 52 inputs and low delay

texts:
I'm building an electric xylophone, or at least trying to, which is velocity sensitive. I approach this by using piezo-sensors. The sampling of the notes will be done on a raspberry pi. So far, I have connected an 8-channel ADC (MCP3008) to the raspberry pi and connected multiplexers (4051) to the ADC. This would allow for up to 64 analog inputs. However, with some experimentation I found that reading all 64 inputs sequentially would take about 8ms on the raspberry pi in python.

Velocity sensitive in this context means that if I hit the bar (piece of wood with piezo underneath) harder, the sound will be louder. The midi protocol calls this velocity and determines it by a value between 0 and 127, so that is also the precision I need from the analog input (7 bits).

The goals is to have a 4 1/3 octave instrument (52 keys), read the piezo-data, find the peak when hitting the piezo and extract midi-signals from that. Some extra inputs would be used for volume control and things like that. With some research and extensive personal experience I found that an audible delay would start at around 10ms. Since there will be some delay between the sampler and my ear (due to DC) I estimate the delay for the piezo-to-midi should be around 5ms total.

I figured that using two MCP3008's would cut the time by half if I use one thread per ADC. I'm afraid that 4ms is still too much to find the peak though. The solution I'm looking for doesn't necessarily have to be extremely cheap and doesn't necessarily have to run on a raspberry pi (sending the signals from an arduino over usb to the pi for example is fine too).

Some personal background to show experience and skill I can apply to the project:
Bachelors degree in computer science, working on a masters, so programming in whatever language should not be a problem. Superficial and mostly self-taught skills in electronics, but of course willing to learn. Over 10 years of musical experience with drums and a variety of other instruments.

What are my options to build this setup with the different cost options? If any more information is wanted I will gladly provide it.

Edit: added information about sought-after delay, meaning of velocity sensitivity in this context and contextual personal background.


texts: How does the Villard circuit double voltage? I don't understand the capacitor role when the voltage sinewave goes negative.


texts: Quiescent Power Dissipation in output Transistor

texts:
I'm trying to calculate the quiescent power dissipation in output transistors, the circuit below is part of a larger AB Amplifier circuit. I can't figure how to go about calculating the power dissipation.

How can I calculate quiescent power dissipated in the transistors?

I know that power dissipated is Voltage drop across C-E junction times Collector Current, however cannot figure out how to find those values.

I'm assuming that by quiescent power dissipation it means when there is no input signal for the amplifier, correct me if I'm wrong.


texts: Problems building project with .c and .s

texts:
I'm using Atmel Studio to program my board

I have a solution open with 2 projects as ".c"  I have created the proper dependencies for the projects but one of the include files is a ".h" and uses a ".s" to define its functions... how can I make this build work?

The .S and .h files are inside the include folder.

The error I get is:

  undefined reference to "function_foo"

which is in declared in .h but the .s is defined... they aren't linked somehow.


texts: stepper motor driver constant current under load, motor driver powering off losing brake effect

texts:
I am building a CNC-like machine using a microcontroller and 'FMD2740A Microstep Driver' modules to drive the stepper motors.

My problem is the vertical axis where, despite a counterweight, there is a load to lift. I want the driver to keep current flowing even after I've stopped sending it pulses. This particular power driver module (MFD2740A) turns off the power a fraction of a second after the last pulses were given. The motor can then free-wheel from the weight of the machine.

I imagine that this is a common problem. My question is two-fold, 1-has anyone used a stepper motor driver in a way to keep the power on, and 2-is the heating issue of having current on constantly a problem?

For the controller I'm using GRBL on an Arduino, an 36V motors.

(later edit) turns out the Gecko GM215 has a dip switch which turns off this behaviour.  Looks like I need to just buy this module and not use my MFD2740A.  See my answer below.

(another edit) the GM215 does indeed fix this problem, with the DIP switch setting for the standby mode set to OFF, it keeps the current flowing.  And after keeping it on for 20 minutes I don't feel any appreciable heating, so that addresses my overheating concern.


texts: Why arbitrary dependent current source is not working at all?

texts:
I am just trying to make an AC analysis at one frecuency in a circuit. I have set an arbitrary dependent current source (bi symbol) to 3 times the current through a resistor (R1). There is current trough this resistor but the current through the arbitrary dependent current source is 0.
I also tried to do the same with the current with symbol bi2 but nothing changes.
Why does this happen?
I put a current dependent current source (symbol f) and it worked but i would still like to know why it didn't work? What did i do wrong?


texts:
Suppose I have the following circuit:

Are resistors R1 and R2 in parallel, assuming that through resistor R1 flows current because this circuit is connected as a feedback to another circuit? And if so, why?


texts: Tips to find the rated voltage of the induction motor without nameplate data

texts: I am doing a project in which I need to find the parameters without nameplate data of the induction motor. I am looking into finding a way/method to find the rated voltage of motor. Can I get any tips?


texts: Tow Thomas biquad filter output amplitude is increasing as I increase frequency

texts:
I was trying to simulate the Tow Thomas biquad filter and measure the output amplitudes of the second order low pass filter output.
The input is 100mv peak at 100Hz and I varied it gradually till 100kHz  but the amplitude of the output kept increasing.
Can anyone explain the increase of the output voltage amplitude? Shouldn't it be decreasing as I increase the input frequency?
This is a picture of the circuit I used to observe the output.


texts: How to draw logic gates in conformity with official standards?

texts:
I know there is a standard that defines how to draw logic gates very precisely, based on precise rounds, angles, proportions etc. I heard about ANSI/IEEE Std 91a-1991, but I am not sure it really defines the rules ('algorithm') to draw the gates.

However, that is not so easy to find on the web. Maybe some of you know what I mean and can point to a document explaining how to achieve these drawings ?


texts:
I had read in TCA0732 datasheet that its current supply can't be greater than some decades of mA (+14mA for +15V voltage supply) but it can provide 1A of current how can that be possible, the same thing for OP2544 max supply current is 30mA and it can provide 2A of output current these amplifiers amplify voltage and also current where the power comes from ??
Datasheets:http://www.onsemi.com/pub_link/Collateral/TCA0372-D.PDF

http://www.ti.com/lit/ds/symlink/opa2544.pdf


texts: Unnecessary (?) loading PC register with following instruction's address in ARM

texts:
I'm trying to comprehend the assembler starting code for my ARM7TDMI processor. I Got most of it, but there's one thing that bothers me. I found this line:

//------------------------------------------------------------------------------
/// Initializes the chip and branches to the main() function.
//------------------------------------------------------------------------------
            .section    .text
            .global     entry

entry:
resetHandler:

/* Dummy access to the .vectors section so it does not get optimized */
        ldr     r0, =resetVector

/* Set pc to actual code location (i.e. not in remap zone) */
       ldr     pc, =1f

/* Perform low-level initialization of the chip using LowLevelInit() */
1:
        ldr     r4, =_sstack
        (...)

The one I don't understand is ldr  pc, =1f. Is it necessary? Why would someone load the next instruction's address explicitly? Wouldn't it be read automatically if the line was omitted?

        ldr     r0, =resetVector

/* Perform low-level initialization of the chip using LowLevelInit() */
1:
        ldr     r4, =_sstack
        (...)

What's the difference? Does it have something to do with linking or memory remapping?

EDIT:

OK, thanks to the comments below I think I got it. Looking at the whole code:

125 resetHandler:
126
127 /* Dummy access to the .vectors section so it does not get optimized */
128         ldr     r0, =resetVector
129
130 /* Set pc to actual code location (i.e. not in remap zone) */
131         ldr     pc, =1f
132
133 /* Perform low-level initialization of the chip using LowLevelInit() */
134 1:
135         ldr     r4, =_sstack
136         mov     sp, r4
137         ldr     r0, =LowLevelInit
138         mov     lr, pc
139         bx      r0

The flash is first aliased to 0x0 (and accessible at any time at 0x100000). The RAM is at 0x200000, and is to be remapped to 0x0 at later time (in LowLevelInit function). So line 131 loads the pc with the address in flash so that the instruction at line 135 is executed directly from flash. If it wasn't for that, the 138 instruction would load the lr register with pc value from the aliased space (0x0 - ...). And because LowLevelInit does the remapping, without the 1: label the lr would be loaded with an improper value (pointing to RAM after remap). So when we return from LowLevelInit (bx r0) we would end up in a different place than where we wanted to start off. Is that correct?


texts: Eagle cad replace command using command line

texts:
I am using Eagle Cad and changed my libraries to another folder. I needed quicker access. Now I have to update my components in my schematic and wanted to use the replace command from the command line.

I read the manual but it lacks at providing syntax for this command. I have tried many different variations and I get many different errors. I was wondering if anyone knew the correct syntax and could post a working reference?

P.s. Also, there are spaces and quotes in some of my components. Example of failed attempts:

REPLACE C "BUTTON-CONDUCTIVESMD-0.1" (BUTTON-CONDUCTIVE)@MyLibrary" BUTTON-TRACE@000_Mylib"
Error:Invalid point:(BUTTON-CONDUCTIV...

P.p.s. Also I have looked at the set command as a possible alternative, but haven't tried it out. Is it a viable option? If yes, please provide a working reference as well!


texts: What happens when a power metal film resistor is exposed to higher power?

texts: What is the worst thing that could happen if a power metal film resistor rated for 2W is exposed to 15W due to a short in the circuit? I have seen smoke being emitted but switched off the power supply immediately. If I hadn't, what would have been the end-game? I am using this particular Vishay resistor: http://www.vishay.com/docs/28729/pr010203.pdf


texts: Cheap/old consumer devices to recover FPGA boards from

texts:
Various FPGA suppliers claim that their devices are increasingly used in mass-market consumer devices. Given the general depreciation of device prices with time, and high price for even old FPGA boards, this opens possibility to "scavenge" the boards for use as accelerators for various projects, via JTAG or other interfaces onboard.

For example, it's rumored that many 10Gbit ethernet switches and broadcast-level Video Processing appliances use FPGA's. In fact, some old extension boards from such devices can be bought from ebay for $50 a piece, which contain various FPGA devices, such as Xilinx Virtex-II, for example (make a search on ebay for "virtex", sort by lowest price).

Such techniques were used by CCC in 27C3 conference, for example, to brute-force DSA key recovery, using recovered FPGA boards from video processing equipment, bought on ebay.

A more recent example, new Apple MacBook Pro's include an FPGA (search for "Macbook FPGA"). Many Network IP Cameras contain FPGA's too (often Xilinx Spartan-3 variety). These cameras cost quite a lot new, but sold for next to nothing when replaced by new ones.

A list of devices with their FPGA variants would be a great help to both people starting to learn about FPGA's and people that want to test new ideas with larger or multiple FPGAs.

A valid answer would be a new list (preferably wiki-editable) or pointer to an existing list of devices that can be found on the market for relatively cheap and have relatively modern FPGA chips inside. Relatively modern in the meaning that the modern design tools by either the FPGA manufacturer (Xilinx/Altera/etc) or non-hardware company (Aldec, Mentor Graphics etc) support the recovered FPGA as target, either natively or using some simple workaround method.

Thank you.


texts: If there is a cable and jack standard for I2C?

texts: I want to do a connection of multiple current and voltage meters, they connect by I2C. Is for to monitor solar panels and batteries, they will be a considerable distance from the master. I thinking use a 6P6C or RJ45 connectors for this. But first I want to know if there is a standard for cable colors or another type of connector for this, just for follow the protocols in case I want to expand my system or buy a new device.


texts: How to setup the RTOS Object Viewer on Code Composer Studio?

texts:
While configuring Code Composer Studio 9.3 to use RTOS Object Viewer from Texas Instrument I encountered the following error. The computer is running windows 10.

Below is error in text format

js: "C:/ti/xdctools_3_31_00_24_core/packages/xdc/xdc.tci", line 354: xdc.services.global.XDCException: xdc.PACKAGE_NOT_FOUND: can't locate the package 'xdc.rov.monserver' along the path:

'C:/ti/tirtos_cc13xx_cc26xx_2_21_01_08/packages;C:/ti/tirtos_cc13xx_cc26xx_2_21_01_08/products/tidrivers_cc13xx_cc26xx_2_21_01_01/packages;
C:/ti/tirtos_cc13xx_cc26xx_2_21_01_08/products/bios_6_46_01_38/packages;
C:/ti/tirtos_cc13xx_cc26xx_2_21_01_08/products/uia_2_01_00_01/packages;C:\ti\xdctools_3_31_00_24_core/packages;'.

Ensure that the package path is set correctly.

Below is CCS XDCtools configuration setting

The error indicates that the package path has to be set.

Note: RTOS object viewer can be initiated from following menu option on Code Composer Studio 9.3

Question

Can anyone point to the location where the path should be set? Any insight to the content of the path.


texts: How do i read the RGB values of an image in Verilog from a hex file generated in Matlab for processing?

texts:
I have used Matlab to generate hex file for an image (1200 * 900 resolution). The hex file is like
There are such 3240000 rows. How do i read this in verilog to performing some processing (filtering out areas where R,G,B values are in some desired range) and then write it into text so that Matlab could return how the image looks like after processing.
Any lead on such image processing is much appreciated.


texts: Why do 2-1 muxes forming 4-1 mux have common selector?

texts: Why is s0 common for both 2-1 multiplexers? Shouldn't each one have it's own data selector? Doesn't such setup remove some of possible logical outputs from multiplexers, if s0 value is same for both? I'm pretty new to multiplexers and probably don't understand the logic behind it yet.


texts: Does linearity of a N-MOSFET continue for \$V_{DS}\$ below \$0V\$?

texts:
I operate a N-MOSFET (2N7000) in a simulator in the linear region very close to \$V_{DS}=0\$. In fact \$V_{DS}\$ is between \$-50nV\$ and \$+50nV\$.

In the simulator the output seems linear, but is this in reality happening? What happens if \$V_{DS}\$ goes a few tens of \$nV\$ below \$0V\$ ?

\$V_{GS}=5V\$ constant (on state)


texts: What does a circuit's frequency response in dB refer to?

texts:
This is a simulated AC analysis of a small noise generating circuit.

and comes from this circuit

I have one of those fundamental but embarrassing beginners questions.  What does the solid curve refer to?  My circuit is powered at 30V, and the LTSpice AC sweep analysis was set to an AC current amplitude of 80 nA.  One of my circuit nodes is called output, and there is an output signal there of magnitude 1 V p-p.  The curve is flat at approximately -7 dB, but that is a relative measure.  Relative to what please?


texts: Difference between RF splitter and coupler?

texts:
I am trying to connect three nodes(A,B,C) through RF cables in the following manner :
A can communicate with both B and C(and vice versa), but B and C cannot communicate directly.

Somebody suggested using a splitter for this work, but when I tested one I found that all three nodes could communicate with each other. Now, somebody is telling me to use a coupler. Can a coupler achieve what I want? What is the difference between splitter and coupler?

PS: I am working in the 2.4GHz band(wifi), if that makes a difference.


texts: I am working on a system that uses a AAA alkaline battery but I am concerned that AAA lithium batteries that run at 3.7V exist (Amazon link). Can anyone suggest simple circuits that have a low leakage current and could protect the system in case 3.7V is applied at VBAT (designed for alkaline 1.5V)?


texts: Voltage source and two resistors in series, voltage vetween Vs and R1

texts:
So, two resistors are in series. So \$ i = \frac{10V}{3k} = 3.33mA \$

So Voltage across R1 should be: \$ V = i \cdot R_1 \$

So it should be 3.33V, no?

Why is it 10V?


texts: Implementing a function with 4 inputs with 2x4 decoders

texts:
I'm a bit confused on how it is done. In the pdf we were given it only showed the solution, no explanation whatsoever.

My guess is in order to implement 4 inputs with 2 input decoders, the decoder with AB was distributed to the other gates as positive-enable input but Im a tad bit stuck there. How do you implement this step-by-step?


texts:
I want to make a simple setum, where I can measure the opacity of air. I want to use a simple laserbeam, which I shoot across the room, and on the other side I want to measure how much is blocked/travelled through.

Is it a good idea to use an LDR or should I use something else? I saw these photodiodes, but they cant determine how much it is, just if or if not.

Ideas?


texts: Headphone amplifier for guitar with stereo MP3 input - mixing

texts:
I'm building a practice amplifier for my girlfriend who is learning to play the bass guitar. I'm a reasonably experienced electronics builder so building something to plug a guitar and headphones into is very simple.

What I would also like to do is add a TRS input so she can play along to her iPod/anything with a stereo output. This signal does not need to be amplified as it will be going straight to the headphones. The amplification circuit for the guitar is based around an LM386, much like this:

But with both headphone cables connected to the 220u capacitor instead of one speaker. It works well. I also need the stereo input from the iPod to go into the headphones, but without any drop in volume for either source. What is the simplest principle to do this?


texts: why is RC= exactly 63.2% full charge, and how is 5RC considered 100%?

texts:
The voltage of a charging and discharging capacitor is given by the formulas:

$$U_C=U e^{-t/(RC)}$$

and

$$U_C=U \left(1-e^{-t/(RC)}\right)$$

respectively, but I don't understand why RC is equal to 63.2% of full charge.

I also don't understand how 5RC is found and why it is chosen to be considered a full charge.


texts:
At work I have the problem that I seem to collect a lot of static charge as soon as I leave my desk and return.
I am not quite sure why this happens. Strangely enough the effect is stronger the briefer I am away.

Since I work with electronics being charged can damage the things I am working with. So what I am doing at the moment is discharge myself anytime I return at my PC housing. This works, but it always causes flickering in my monitor and sometimes I have to replug my mouse to make it work again.

I know that most electronics have some kind of ESD protection built in, but that these get less and less effective the more they are used and will someday break.
That is why I am worried about my equipment in the long term and would like a safer way to discharge myself.

I tried using the earth contact of the mains power outlet, but it hurts a lot more and the effect on my equipment seems to be even worse. I think it has to do with the fact that the PC housing is painted and therefore has a lot higher resistence.


texts: How does this e-match igniter circuit work?

texts:
I'm working on building a circuit to ignite an e-match for parachute deployment in an amateur rocket. Unfortunately, my background is in CS, not EE, so I'm a bit lost in the hardware portion of this endeavor.

I asked a friend of a friend for some pointers and was given the schematic below. Building it isn't a problem, but what I really want is to understand how & why it works. I understand the basics like the switch is used to enable the fet which will fire the igniter and that the capacitor is used because the lipo battery isn't capable of drawing upwards of 1A instantaneously, but beyond that and my understanding gets more cloudy.

That said, my questions:

First and foremost, at a high level, is my understanding of how this circuit works correct?
How do I determine the necessary resistance and capacitance values? I understand basic Ohm's law, but I'm not sure how to take the capacitor and fet into account.
Why is there a resistor between the switch and the fet gate?
What modifications do I need to make if, instead of a switch, I want to control the fet from an output pin on a microcontroller?
Are there any considerations I need to make if I wanted to put another igniter circuit connected to the same battery?

Any insight is greatly appreciated!

simulate this circuit – Schematic created using CircuitLab


texts:
How does a transistor work in a circuit if its base has no connection to any part of the circuit?
How can I find its working state?
Thanks in advance
Edit:
Yes, this is a BJT. My assumption is that the transistor's base potential is negligable in this case.
The working mode of it is similar to a voltage-controlled switch, using only its breakdown effect(s).


texts:
This question is somehow the continuation of this question : Batteries and running time (reed the comments for more information)And my question is, can I protect my lithium battery in parallel like so ?I got this "trick" from this document : http://www.ti.com/lit/an/slva139/slva139.pdf

simulate this circuit – Schematic created using CircuitLab

The PMOS have a very low Rdson.


texts: Can we go with a square wave disturbance for power supply impedance measurement?

texts:
How does a power supply impedance measurement instrument work?

Create a sinusoidal load disturbance and measure the o/p voltage disturbance-> take the ratio-> Repeat for the entire freq range?
Instead of sinusoidal disturbance is it possible to apply a square wave disturbance (sweeping the fundamental freq throughout the range of interest)?


texts: Correcting error while reading a number in binary format

texts: Suppose I have a binary string: 1111 1001 which in decimal is -121 (sign magnitude form). But the computer read this as two number: -7 and -1. From -7 and -1, how can I recover -121.?


texts:
I am working on a communication switch that is digitally controlled and I am using four MUX506IPWR from TI to choose the output channel. The switch has on the input a DSUB9 for a CAN channel and a DSUB9 for a RS232 channel.

So I want to switch RX/TX on the RS232 and CAN_LO/CAN_HI on the CAN channel and each of these lines are connected into a MUX506(so a total of four MUX506).

On the output side I have DSUB9 connectors for the communication where the communication lines merges so that RX goes with CAN_HI and TX goes with CAN_LO.
This circuit behaves very odd when all the MUX506 are soldered to the PCB. If I choose one output by sending the right adress and enable the chip all of the outputs will show a voltage level that is about 50% av the signal voltage(I use +-12V for RS232 and 3V3 for the CAN).
I suspect that there might be something wrong whenever there is a higher voltage that wants to go from the output on the RS232 to my output connector and then back into the output on CAN chip.

The circuit seems to work fine whenever I remove the IC's for either CAN or RS232.
I have tried connecting the MUX506's VDD for the CAN channel to 12V(single ended supply is from 10V to 36V so its wrong in the schematic) but it still behaves the same way.
Can anyone point me in the right direction for solving what I have done wrong here?

Datasheet for the MUX506


texts: Why are smartphones and tablets ARM based?

texts:
Why don't these devices use Intel processors like laptops do?  Why are they restricted to ARM?

Also for Windows 8, do they want ARM just for tablets and smartphones or is it also for laptops/desktops (is that even possible)?


texts: What does the D stand for in "D Flip-Flop"?

texts:
I'm rather interested in the history of eletrical engineering, and I've seen some discussion here and there about the origin of the names of the various flip flop circuits. Some time ago I took part in one such discussion here: Understanding D flip flop function - what this thing does, and became so interested on the subject that I purchased an early textbook from 1957, which supposedly is the first university level textbook where flip-flops are discussed.

I promised to report my findings, and I'll do so below. But sadly it didn't answer all my questions. It seems that using flip flops was already an established tradition in 1957 and the book doesn't discuss any history. So please answer if you have any info on the subject.

So I am looking for references that predate 1957. I am also interested in the origin of the characters J and K in a JK flip-flop, in case someone would be able to verify or clarify the answer given in What is the meaning of JK flip flop's J and K ?.


texts: What is the name for this Encapsulated SMPS

texts:
I found this and I'm a little confused.

It appears to be a simple component in to which I can put mains voltage and out of which get 3.3V DC without needing any other components - precisely what I want. Maybe I'm missing something, but from various googling this doesn't seem to be common, or used in circuits as a component of its own.

Could I, for example, use this single component to run an Arduino from mains? (there is a 12V version here)? Or to charge a mobile phone? Or, in my specific case, to connect a mains supply to a 3V relay 24/7 using minimal standby power.

Assuming I've understood what this component does, is there a better name for it? Googling "encapsulated electronic transformer" only returns this MYRRA product, but surely this is a generic thing... or is it?


texts: On a previous question I just asked it was about storing an led's previous state with the eeprom. Without a microcontroller, it seemed not possible, so now Im asking if you can buy single floating gate transistors anywhere, because I have searched, and nothing showed up. Do they even make this?


texts: What will be the effect of changing the order of the filters on the sound coming from each speaker in my audio system?

texts: What will be the effect of changing the order of the cross over filters on the sound coming from each speaker in my audio system?


texts: Can LEDs or optocouplers be used without a resistor if PWM is used?

texts:
LEDs are often connected through a resistor and the purpose of this seems to be to lower the voltage across the LED to around 1.8V. Can PWM be used to lower the voltage instead of a resistor? If so, what is a reasonable frequency to avoid burning out the LED?

My actual application is to connect an optocoupler directly to a micro controller but I figured that most people will be more familiar with LEDs and the answer will be the same.

This "experiment" would answer my question but he never posted his results.


texts: Why is the output frequency of the zero crossing detector (square wave generator) double that of the input signal?

texts:
I have built a zero crossing detector that acts as a square wave generator according to the circuit diagram shown.

It is connected to a potential transformer.

The output from the potential transformer is measured to be 6V at 50 Hz.

However, the output from the ZCD is measured to be 100 Hz. How has this frequency doubled?

BTW, when I connect a current transformer to the same ZCD set up, the output from the current transformer is 50 Hz and the output from the ZCD is also 50 Hz.

The IC used for the Op Amp is LM358 and the diodes are 1N4148.


texts: How is a CAN Transceiver's common mode voltage range extended?

texts:
The CAN Standard states a max. common mode voltage of -2 V to +7 V. There are transceivers however, that allow for e.g. +-25 V common mode voltage range. How is that acheived? I imagine (I do not really know and that is why I am asking), internally such a transceiver will have some transistors, at the input as well as output, which need to be biased in order to switch on and off.  At the input there may be a sort of comparator to sense the differential voltage. My question is how a higher common mode voltage rating is acheived at all (by which means)?. Is there an example schematic of a CAN-Transceiver's internals which would help me understand?
edit:
I thought about little more and came to the conclusion that maybe a differential input would be appropriate to sense a differential signal. So with this in mind I came up with the following possible (?) input structure (please see the screenshot from Ltspice below). Next step would be to think about where common mode limits may arise. I have no idea yet. Who does?
Q1)"..what techniques exist to increase the common mode voltage range CAN-Transceivers" ?
Q2) What about differential input structure (see below)?
Q3) Where does the common mode range restriction arise for such a structure ?