texts:
I'm trying to get an ESP8266 to wake up via external trigger. The trigger in this case is a PIR, which sends a 2+ second high signal when motion is detected.

I'm using an edge detector to turn that incoming long signal into a brief signal, and then inverting it via transistor as the ESP needs to have the RST pin grounded for a brief second to cause a boot.

This is the simplest form of the circuit:

The issue I'm having is the voltage drop on RST is not low enough. There used to be a pull-up resistor on RST when I played with a NodeMCU, but now with a Wemos D1 mini the voltage drop wasn't high enough to trigger a boot.

With the Wemos plugged into USB and providing power to everything, the circuit runs at 3.3v and RST drops to around 2v on trigger, which is enough to cause a boot most of the time, but ideally I want to get the drop lower still. Any ideas on that?

The real problem comes in when this setup is connected to a 3.7v battery. When the battery is full, everything gets around 4.2v and on trigger, the drop on RST is only down to 2.6v which is no where near what's needed to trigger a boot.

How can I get a trigger to cause a larger drop on RST? Not longer though - just a larger drop. Increasing C1 to 10uF does increase the drop, but the time it takes is too long.

Also, as the battery drains, the voltage will drop over time. I need a solution that works at 4.2v all the way down to 2.7v (at which time there likely won't be enough juice to start the ESP anyway).

In case it's relevant, Q2 is a 2N222.


texts: 4-bit bus address selection via analog input pin: Monte Carlo simulation shows overlapping address values

texts:
I designed a small sensor PCB for my master thesis with an ATtiny44 microcontroller. I need about 200 of these boards for my application and 16 are always locally connected to controller board. The whole network looks like this:

To communicate between the controller and the sensor boards I wrote my own 1 pin bus (timing based). The only problem is the sensor board must have an address to know its location in the network, when I send its data to the controller board.

As I only had 1 pin left on the ATtiny I came up with a jumper based DAC circuit which should generate an analog voltage based on the setting of four jumpers.
As the sensor circuitry uses the values (47, 470, 1k, 3k, 4k7, 10k, 100k, and 220k) and I wanted to optimize for production I used the below values for the DAC (basically 100k, 50k, 20k, and 10k). Which should give me a nice value between 0 V and 760 mV based on the jumper setting. Exactly what I needed to read as an analog voltage with the internal 1.1 V reference of the ATtiny.
On start-up the ATtiny reads this voltage and should know its position.

simulate this circuit – Schematic created using CircuitLab

In theory this works fine. I even did a Monte Carlo analysis in LTspice to confirm I get no overlapping areas, when considering the tolerance of the resistors (all are 1% BTW). Below you can find the pictures of this analysis.

Now I produced several (luckily not 200) of these boards and yet some failed to get correct readings on their address (specially in the higher address regions where all tolerances come to play at once). I measured all possible solutions and finally figured out my problem. My original analysis did not include the the tolerance of the 5 V supply voltage, which is locally generated from 12 V with an MC7805 on each controller board. Per datasheet, the MC7805 has an output voltage between 4.8 and 5.2 V.

After I figured this out I modified the Monte Carlo analysis. It now looks like this:

As you can see there are nice overlapping areas, where I can not definitely say this voltage can only mean this address. Basically all addresses starting with no. 8 can get a false reading (with higher possibilities for false readings for higher addresses).

I would not like to add different resistor values than the one already used on the board (as for the thesis I want to optimize for production).

I would not like to add a voltage reference (e.g, Zener diode) to feed the DAC resistor network.

I cannot modify the controller board any more (and use there a more precise voltage regulator).

I can still modify the PCB design / schematic of the sensor board!

How can I make sure to get always correct readings on the address (either by program or by changing the circuit)?


texts: My MOSFET operated solenoid circuit destroys my Arduino inputs

texts:
I made a series of PCBs to power some solenoid valves that use an external power supply. I switch them with BS170 MOSFETs using an Arduino as gate signal.
I based it a solution by Jason S.

This is an illustration of what my circuit looks like:

On testing the PCBs, I noticed that most of them work fine, but some of them don't. No problem, probably a soldering thing.

However, those faulty ones did manage to destroy two Arduino digital pins!
On one, I get a constant voltage of 5 V, and the other one outputs 0.2 V when I send a HIGH signal to it, and 0.5 V when I send a LOW signal. Strange stuff.

So I guess the faulty circuits somehow caused (some of) the 16 V to flow through the Arduino, destroying them.

How do I protect the Arduino in this scenario from too high current?

I know about zener diodes, but I have no idea how to place them to protect the inputs.

Technical information:

1/4" NPT Electric Solenoid Valve 12-Volt DC, 12VDC, N/C, RO, Air, Water BBTF
BS170 (MOSFET ) datasheet


texts: Op-amp circuit analysis with capacitors on feedback and input lines

texts:
I'm studying for my circuit analysis exam and I stumbled upon a problem I can't understand. Here it is:

The voltage source is 0V for t<0s and 10V for t>0s, and I have to find the Vout voltage formula for t>0s.

I can't understand what happens as soon as the voltage source gets turned on. I calculated the final Vout voltage using KVL (Vout = -10V, assuming that the voltage in all the capacitors is the same and no current flows through the resistor after a while), so my result would be:

$$
Vout = 10(e^{\frac{-t}{τ}}-1)  [V]
$$

I know the result is correct but can anyone explain the logic behind this circuit? Also how do I calculate the time constant τ ?

Thanks!


texts: A basic opamp configuration which resembles the non inverting one

texts:
In the following picture, the second circuit is a non inverting opamp, the gain of which is well known to be \$A_v = 1 + R_3/R_4\$ and the demonstration of this formula can be easily found on many websites.
My problem is with the first circuit in the figure which makes me a little bit confused as it looks different from the second one, furthermore the voltage gain I calculated is \$A_V = 1/(1 + R_1/R_2)\$, but I found on some web sites that still this configuration is a "non inverting opamp" with a gain \$A_V = 1 + R_1/R_2\$.
If I am right, and this is not a non inverting opamp, still I found such configuration in some other cases such as in instrumentation amplifiers. So the question is: is this another well known opamp configuration?


texts: ACS758 current sensor output voltage cannot be read by Arduino

texts:
I have two ACS758 current sensors, specifically the 050B and the 200B.  I want to monitor the current coming in to and out from my buck converter circuit. I attached the output of the ACS758 directly to the Arduino analog input, but it seems that the voltage from the sensor is too small for the Arduino to read. How do I deal with this? I have read that using op-amps might work, and I have tried using an UA741 as a non-inverting amplifier, to no avail. Any suggestions will be much appreciated. Op-amp circuit image here: http://i.stack.imgur.com/xjDXw.jpg

Edit: The buck converter is has a 10W solar panel as its supply, and the current from the solar panel is around 0.5 A. I'm also expecting the same current for the output.


texts: How can I get this 12v motor to run smoothly, and is it set up safely?

texts:
This is my first attempt at electrical engineering, so I'm sorry if this question seems basic, I couldn't seem to find answers anywhere.

I want to wire a 12v motor to an on/off switch and power with a wall plug. I intended this motor to be 18v so that is the power plug I bought, though come to find out after receiving it it is 12v, I firstly want to know if this is safe to power with the wall plug that I currently have.

Secondly, as it is currently connected (positive wire to switch and switch to motor, negative wire directly to motor) the motor runs smoothly when power is first supplied, but then goes on and off how can I prevent this so my motor runs smoothly?

Again, I am completely ignorant of this field and have tried my best to piece together my understanding of everything i'm working with, so please keep that in mind.

Thank you!


texts: From what I understand, USB has 4 lines just like an audio port. So why can't we have a USB port which is circular? I feel it can be more convenient to plug in and also would have a smaller form factor. May be, we can have the same 3.5 mm jack port switch between analog audio output and a digital USB function. What am I missing?


texts:
I am using these two ICs in my design:
EEPROM CAV24Cxx and Analog MUX 74HC4851.

What is the value of input decoupling capacitor that I must connect near the Vcc pin?

The recommended value of the input decoupling capacitor on the Vcc pin is not mentioned in the datasheet or is it mentioned by someother name which I didn't see?


texts: Measuring current - shunt resistor or current transducer or something else

texts:
I have to measure current which is sine with 37Hz frequency 1350 mA(DC) + 190 mA(AC).

The voltage in circuit is generated using PWM 27V, 600 Hz, PWM dithering adds alternating part of current. I want as small voltage drop as it is possible. There is no chance of current going negative but I would like also reverse polarity protection.
The measurement system is intended to measure many examples of circuits.

What will be the circuit for measuring current going into load (top side) and out of the load (bottom side)?

I have 0-10V input on my DAQ card.

Which solution will give more precise signal measurement: shunt resistor or some current transducer or you recommend something else?


texts: When laying out circuit board traces, what impedances do I need to consider?

texts:
I do low-speed circuit design for microcontrollers and such (usually at less than 20 MHz), and now I'm getting started on some more high-speed circuits. What I want to know is:

What considerations need to be made for traces in high-speed circuits?
Do I have to impedance-match each line between two high speed devices?
Do all the traces need to be the same length?
Is there a good reference for these rules?
Can this be done using open-source circuit design tools (gEDA and company)?


texts:
I have a situation where I'd like to delay the closing of an off the shelf relay by ~5 seconds. Assuming it is a 5V coil, and switching 12 V, I'd like the following:

t 0:00: 5v applied to input, relay switch open.
t 0:05: coil closed, relay switch closes.

I think some simple RC network may do the trick, but I'm struggling to imagine the right configuration. Any ideas?


texts:
I was looking for a quick way of attaching 10 wires to a PCB Header. This is for a production job of 50 units at a time, the header style/ design is fixed. Three components are to be attached to the header, 1 x 2 wire solenoid and 2 x 4 wire sensors.

From what I can tell the options are using barrel crimps with a connector or an  IDC Receptacle.

I would ideally like to use an IDC but have found that it is tricky to align each wire correctly, probably why they're mainly used for ribbon cables...

Crimping 10 individual wires seems time consuming but is looking like the only viable way. Would appreciate some recommendations / alternatives.


texts: AC Voltage source terminal polarity and grounding

texts:
Ill try to make it as clear as possible. This may seem like a simple question, but it is something that I havent quite figured out. It has to do with polarity on the leads of an AC source. Every book I read, pictures an AC source with two leads such as this:

Now, on the books, I see that the + symbol is used on upper lead, and the - at the bottom when they are picturing the positive half of the waveform, and they use a - symbol on the top and + on the bottom when they are picturing the negative half of the waveform. So far so good.

Here are the 3 scenarios and the thing that really confuses me:

Is only one lead changing voltage while the other stays stationary at 0V, meaning that the upper lead will go from + to - and from - to + and so on while the lower lead stays at 0v?

Or

For the positive part of the waveform the upper terminal will be + and the lower 0V, and for the negative part of the waveform the lower terminal will be - and the upper 0v?

Or

The upper terminal will have an alternating current and the lower terminal will have a mirror signal with opposite polarity? in which case, where is my 0v reference?

Comparing it to the AC wiring on any house, theres 1 cable which is "Hot" and the other which is the "neutral", I know the neutral doesnt carry any voltage and its the 0v reference, so the HOT cable is the one which changes its polarity.

Now, what exactly happens when I ground something? for example what is the difference of having that 0v floating or connected to ground, and what happens when I ground a circuit at something else rather than 0v? For instance say I have the following circuit: An ac source feeding a transformer, there are a couple of resistors across its secondaries and the mid point between the resistors is connected to ground.

So let say that the transformer has a 1:1 ratio and both resistors have the same resistance, 100ohms for this example, that means they will form a voltage divider of half the total voltage.

I know all that because thats how they thaught it to me, what I dont know is this, if ground potential is 0V, and my transformer's (bottom lead) is at 0v, why will I get a voltage at point B with respect to ground?

I get very confused between the diference of 0v and ground reference, and when I see circuits like the previous one which are grounded at some place different from 0V, specially on AC circuits. On DC it makes sense, if I ground the negative side or 0V side, I will have a positive voltage, if I ground the positive, I will get a negative voltage. But on AC it confuses me the fact that I dont know if the only alternating current is on one side of the terminals or if the 2 terminals are switching between each other.

It seems like on some cases its only one side (like in a house electrical installation) and on others like in a balanced push pull circuit its both sides.

It seems I dont have a clue of how exactly AC works.


texts: Specific differences in electronics for similar spec 12V power adapter/suppy?

texts:
I would like to understand the specific differences in power adapters that have similar input/output spec's but have different described purposes. In other words, can I use any power supply/adapter as long as the spec's are the same?

In this case, I have a hard disk system that has a supplied adapter that I suspect is bad.  I have measured the voltage and it is within spec at 12.6Vdc.  I do not know how to measure the amperage output without taking it apart, but I assume it is not outputting the needed amps because the hard disk enclosure does not start.  So I want to first replace the power supply.
Power supply is:
Input: 100-240Vac
Output: 12Vdc up to 6.67A

If I order one from the manufacturer, it is $70.  But there are many LED and general system power adapters on Amazon that have specs like:
Input: 100-240Vac
Output: 12Vdc up to 8A

for about $20.  So what am I purchasing for $70 versus $20?  I understand the mfr would be more for their own costs, but they're OEMing the product as well.

So am I safe in getting a 12Vdc 8A output power adapter, like LED purposed or other, or is there some specific reasons I cannot do this?


texts: What is the 5th wire used for in the USB optical mouse?

texts:
I know that USB cables usually have 4 wires - power, ground, data+ and data-.
In this optical mouse cable I have there is a 5th. It is black, but also thicker than the others, almost suggesting that there is more than one wire in it.
What is it? My best guess is that it is another kind of ground wire.


texts: How to find out what radio frequency is being emitted?

texts:
Let's say I have something akin to a garage door clicker.  How can I discover the frequency and message it sends with no other information on the device?  I want to decode this to the electrical signal and build my own device to retransmit it.

Is something like this good?


texts: What type of capacitor is most stable for use in 555 timer circuit?

texts:
I am building a 555 timer circuit with a frequency of 15, 30 and 60 Hertz. I will most likely use a 1µF capacitor but I was wondering what kind of capacitor would be best for keeping a stable value even when the temperature changes (goes down most likely)?

I will be putting potentiometers so that if the values do change they can be calibrated again, but that will only be done before we deploy the systems. Once deployed, we cannot calibrate again until retrieved days later).

Basically, I am asking what kind (ceramic, electrolytic, etc.) of capacitor will keep its capacitance constant at a value of 1µF and with varying temperatures.


texts: Can this example prove that bode plot is not correct?

texts:
Bode plot implies that for a linear system, if the input is a sinusoidal signal, output of the system will also be a sinusoidal signal with same frequency but different amplitude and phase. Knowing input, we can estimated steady state output based on bode plot. Note that it states input and output have same frequency. But I found an example which seems doesn't match this rule.
The system is a simple mass-spring system,

For simplicity, set m=1kg, k=1N/m, then equation of motion is

If system input is F=sin(2t),
the output is x=(2/3)*sin(t)-(1/3)*sin(2t) by solving differential equation.
As can be seen, input has only one frequency component, but output has two frequency components, one is the natural frequency of the system, the other is the same as input frequency, and the two components are steady state rather transient. Obviously, in this case, the output can't be estimated using bode plot of the system.
I am not sure if people have realized this phenomenon, I was always sure about that input and steady-state output should have same frequency before I found this. Can this example prove that bode plot is not valid in some situations?


texts:
I want to interface a pH probe. The Op-Amp I would like to use is INA128.

My ADC's range is 0 to 5 volts. pH sensor gives a voltage output that is ranged from -0.5 to 0.5 volts, for 0 pH to 14 pH respectively.

Perhaps, I need to give an offset of about 2 volts to Op-Amp and set its gain  to 2. If I do that, will negative voltages be substracted from 2 volts?


texts: How to align components for front panels

texts:
I am struggling with the front panel setup. I need to align 3 types of components: push-buttons, potentimeters and 5mm leds.

The potentiometers have a nut to fasten it to the front-panel, for the leds I have small plastic mounting rings. The push buttons would need to go onto a pcb, that I could mount under the front-panel with stand-offs - the height looks good to me:

With this approach getting the leds mounted is complicated - not a lot of space and I would push the pins in millimeter perfect so that the led body would click into the panel mount rings.

I could also just mount potentiometers and leds into the front-panel and wire things freely, but then I have no idea how to handle the push buttons.


texts: Bus voltage measurement in a compact way

texts:
I need to measure bus voltage and guarantee my ADC is protected in a compact way. I came up with the following measurement circuit a long time ago in another design.

simulate this circuit – Schematic created using CircuitLab

The LED characteristics: starts conducting at 2.7V with 30mA at 3.3V.

The bus being measured has motors on it and may rise above 40V if/when they are generating. The goal is to prevent ADC damage from unforeseen overvoltage. Typically the bus will be at 24V or 36V nominal. The system would take action to prevent excessive overvoltage over 40V.

I had tried a zener in place of the LED and it did not work. I don't remember why and I would not be surprised if, at the time, I either did not drop the divider resistance down enough to supply enough breakdown current, or even stuffed the part in backwards. I'm using 0402 1/10W resistors. Probably I was concerned with them dissipating the 5mA needed for zener breakdown. The 3mA for the LED circuit was a bit closer to what they are rated for.

I have severe space constraints. Is there a better way to do this?


texts: ESP32: 0.1uF Cap Between SENSOR_VP and SENSOR_VN

texts:
According to the ESP32 Hardware Design Guidelines, a 0.1uF cap should be added to the SENSOR_VP and SENSOR_VN pads when using them as an ADC. Why is it then that the subcircuit schematics shown in the document don't include it? The Sparkfun ESP32 Thing schematic also doesn't include the 0.1uF cap in their design.

Another curiosity, why does it show these pins as part of the RF matching circuit? Can we not use the SENSOR_VP and SENSOR_VN pins for ADC if they're part of the RF matching? And in what way do they contribute to the RF functionality?


texts:
Sorry (as in the previous post I said it would be the last component question).

However, this one I also cannot find:

They both look very similar:

I had to put them on some other components to fix them into place for making a better picture.

The left one shows: 806, SVP, 180 16
The right one: (onknown symbol) A 85K, 1500 2.5V

Initially I thought these are transistors (since they have 2 legs and look like them), but they are not (I think).

I'm almost sure these come from a computer VGA card (old one).


texts: Why did they design new connectors for USB?

texts:
At the time when the USB standard was being developed, there were a number of widely-available connectors that they could have used instead of making a new custom connector. Why did they not use mini-DIN or DE-9 or some other common connector of the time, instead of inventing entirely new physical connectors, which would then need to be manufactured with entirely new (expensive) machinery?

I can think of a few possible partial causes (e.g. something new would be less confusing to consumers, or maybe the new connectors are more mechanically sound than anything else available at the time) but I'd like to see a more developed analysis of what was available at the time and why it wasn't suitable--and hey, maybe someone who actually worked on the spec can give the actual definitive reasons, if we're lucky.


texts: Challenges to design high-density power inverter

texts:
Google has announced a contest to design a kW-scale (>2 kVA loads) power inverter with 90% size reduction compared to present designs.  The goal is running household appliances from a small inverter, which somehow encourages more usage of solar power. (It would also be useful in their data centers.)

What are some challenges in such a design?  In laptop wall adapters, the power density has been dramatically increased over time by moving towards higher-frequency switching regulators, which permit use of smaller components.  Also better 3D modeling to permit packing components more tightly into the space.

Are such techniques likely to improve inverters as well, or would they present different issues to overcome?  What approaches are likely to be taken?  They are directly encouraging use of gallium nitride (GaN) and silicon carbide (SiC) components.  Is it likely that custom silicon or other components would be necessary, or is it plausible such a design could be built largely with off-the-shelf components?

http://www.littleboxchallenge.com/


texts:
i'm new here and not English native. i'll be very appreciative of pointing out my grammar errors.
i designed a new topology with four MOSFETs which low two operate as switches in 100kHz and high two are constant on.

however, the high side output is always low while the bootstrap capacitor is 15 volt. when i exchange the PWM signal, low side is constant on and high side is 100kHz switching signal, both low side and high side works.

here are the layout and waveform. the dark blue is low side output and the light one is high side output. the MOSFETs are C3M0065090


texts:
I saw a guy making Qi receiver module with ATTiny13A: Qi wireless power receiver from scratch.

In his circuit, secondary shorted through capacitors to ground to send data.

My question is how transmitter side (base) reads this data?


texts:
I need to design a input overvoltage protection for a 45W DC-DC converter rated for a 9-24V wall wart input (so, 45W / 9V = 5A input current at max). So far I've seen two approaches (schematics below):

Crowbar circuit. The idea is that the TRIAC (or SCR) in case of an over-voltage will close and therefore short the input power terminals, therefore blowing the fuse and disconnecting the device.
MOSFET switch. In case of an overvoltage the MOSFET simply opens and the high voltage simply doesn't reach the device.

I am not sure which one should I use and I haven't found anything comparing these approaches to design the overvoltage protection. So, my questions are:

What are the general pros and cons of each of these circuits?
What are the guidelines to which circuit one should use in a particular application?
Which one of these should I use in my case?
Are there any other overvoltage protection circuits I am missing?

UPDATE:

In my particular situation, I am mostly trying to protect the circuitry that the DC-DC converter is powering, since it can be pretty expensive and the DC-DC converter itself. I have no idea about the typical transient voltages when the power is plugged in; mostly I am trying to protect the circuitry from an "idiot user" who might plug something over 24V in the power inlet (I've seen up to 36V common wall warts and I am sure there are ones with even higher voltage), since the DC-DC converter is not designed for it and might output anything it wants at this point.

This is not a medical device, nobody will die if the device fails and (AFAIK) nothing could cause a fire in case of input or output overvoltage except for, maybe, potential tantalum capacitors filtering the power in the downstream circuitry which I do not control; the end user does (the DC-DC converter is for a modular synth system).

I am interested both in an answer for my particular case and in a more broad/common one showing the guidelines for selecting the method of overvoltage protection in any case.


texts: oil exponent in transformers (oil-filled transformers)

texts:
The oil exponent n is said to depend upon the cooling state. In other words, it is an empirically desired coefficient selected for cooling mode to approximately account for a change in the resistance with load.

My doubt here is that suppose I have an oil natural air natural type of transformer. Then n will be around 0.8.

But if the weather where the transformer is becomes extremely windy, then in that case, am I supposed to take the n value corresponding to oil natural forced air type of transformer (i.e. n = 0.9-1) since the wind kind of acts as forced air on the transformer ?

Does this n value ever change for a particular transformer ?

I am talking about this n (encircled in blue and the definition of which is highlighted in yellow) :

The paper "Modelling of Oil-filled Transformer" by Marius-Constantin O.S. Popescu, Nikos E. Mastorakis, Liliana N. Popescu-Perescu had this table explaining the value of n in different cases :

I just wish to understand this oil exponent parameter and will it ever change based on conditions that the transformer is subjected to.

I wish to understand the factors on which this parameter depends. When I am calculating the top-rise oil temperature (as in the above equation), I believe , that n is subject to change depending upon the environment the transformer is in. If the transformer is indoors, then the ONAN transformer will function normally and the n value can be safely assumed to be constant. However, if its an outdoor transformer , then the weather conditions change. For instance, we can have a very windy type of weather which can act as the fan used for cooling in case of Oil Natural Air Forced (ONAF) transformers. So, while doing the computations, will the n value still remain same or will it change ?


texts: Suppose you have a resistor that leads to a parallel connection of a capacitor and an output wire. I am having tremendous difficulty understanding how the capacitor steals all the current that would not otherwise leak into the output wire, reproducing the frequency that entered in, only with a different amplitude from the resistor. Does the capacitor simply build up to its maximum capacitance and then release all at once when the buildup leads to the repelling of electrons? It's a parallel circuit. The voltage is running through to both the output and the capacitor, so wouldn't the capacitor actually increase the frequency of the input from those releases?


texts:
I have multiple PCBs which are communicating via CAN and are supplied by two power sources (5V and 24V). After the first field test we noticed a considerable voltage drop at the power supply between the slaves (0.4V for ~30m). Of course this is a common effect.

What is the best way to 'counter' this behavior when some parts of the PCB need an accurate 5/24V.

My thought: Increase the supply to 5.5-6V (max distance ~50m) and create the reference voltage on each PCB individual using a 'linear voltage regulator'. Since the delta between the 'supply' and the 'reference' is relatively short I would also not burn too much power while regulating.

Is there a better way too accomplish a stable 5V (\$\pm 1\%\$) supply for my PCBs?


texts: Can this optimized barrel shifter be made arithmetic?

texts:
Every schematic I've seen for a barrel shifter looks as such:

bit  3   2   1   0
     |  -|  -|  -| 0
     | | | | | | | |
     MUX MUX MUX MUX--Select bit 0 (To all stage-1 MUX)
     |  -|---+   |
     | | |  -|---+
     | | | | |  -|-+---0
     | | | | | | | |
     MUX MUX MUX MUX--Select bit 1 (To all stage-2 MUX)
     |   |   |   |
     |  -|-+-|-+-|-+---0
     | | | | | | | |
     MUX MUX MUX MUX--Select bit 2 (To all stage-3 MUX)
      |   |   |   |

Instead, I came up with this:

bit  4   3   2   1
     |  -|  -|  -|
     | | | | | | |
     MUX MUX MUX AND--NOT-- Select bit 0
     |  -|---|   |        |
     | | |  -|---+         - To all MUX on first stage
     | | | | |   |
     | | | | |   |
     MUX MUX AND AND--NOT-- Select bit 1
     |   |   |   |        |
     |   |   |   |         - to all MUX on this stage
     |   |   |   |
     AND AND AND AND--NOT-- Select bit 2 (to all AND on this stage)
      |   |   |   |

When made bidirectional (not shown:  n-bit has n muxers on the front and back, reverses the input, then reverses the output), a 32-bit shifter has 16% as many gates, a 64-bit shifter uses 15% as many gates, and a 128-bit shifter uses 13% as many gates (not counting inverters. of which the circuit has log(n)).

This can implement SLLI, SRLI, SLL, SRL, SLLIW, SRLIW, SLLW, and SRLW from the RISC-V RV32I and RV64I specifications, as well as the 128-bit versions when released.

It can't implement SRAI, SRA, SRAIW, or SRAW.

The arithmetic shift right works like any other barrel shifter, but extends the sign bit:

 bit  4   3   2   1
      |  -|  -|  -|-   --Arithmetic Shift
      | | | | | | | | |
      | | | | | | | AND
      | | | | | | |  |
      | | | | | | |  Sx   Sign-extend bit
      | | | | | | |
      | | | | | | | Sx
      | | | | | | | |
      MUX MUX MUX MUX--Select bit 0 (To all stage-1 MUX)
      |  -|---+   |
      | | |  -|---+
      | | | | |  -|-+---Sx
      | | | | | | | |
      MUX MUX MUX MUX--Select bit 1 (To all stage-2 MUX)
      |   |   |   |
      |  -|-+-|-+-|-+---Sx
      | | | | | | | |
      MUX MUX MUX MUX--Select bit 2 (To all stage-3 MUX)
       |   |   |   |

Above, when shifting right (input goes through 4 more MUXes, output goes through 4 more muxes, not shown), the shifted-in MSBs become 0 if not arithmetic or if the MSB is 0, and 1 if arithmetic and the MSB is 1.  I have found no method for improving on this.

I suppose this is why I couldn't find a barrel shifter schematic that wasn't just all MUXes:  it's just not useful if you need an arithmetic shift.  At 128-bit you add 254 gates; at 64-bit you add 126 gates; at 32-bit you add 62 gates; all to support sign-extension.


texts: Find the frequency of the sawtooth (voltage accross the capacitor)

texts:
Q:Is my work right, finding the frequency of the sawtooth (voltage accross the capacitor)?:

My work:

Vdd(t) and Vss(t) are DC voltages and:
$$\text{V}_{\text{ss}}(t)=-\text{V}_{\text{dd}}(t)$$
Assume at t=0, Vc(0)=0V and Vout(0)=Vdd(t)
Charging the capacitor:
$$\text{V}_\text{C}(t)=\text{V}_{\text{dd}}(t)\left(1-\exp\left[-\frac{t}{\text{C}\text{R}_1}\right]\right)$$
When:
$$\text{V}_\text{C}(t)>\frac{\text{R}_3}{\text{R}_3+\text{R}_2}\cdot\text{V}_{\text{out}}(t)=\text{V}_-(t)$$
then Vout(t)=-Vdd(t)=Vss(t)
Discharging the capacitor:
$$\text{V}_\text{C}(t)=\text{V}_{\text{C}}(0)+\left(\text{V}_{\text{dd}}(t)-\text{V}_{\text{C}}(0)\right)\left(1-\exp\left[-\frac{t}{\text{C}\text{R}_1}\right]\right)$$
When:
$$\text{V}_\text{C}(t)<-\frac{\text{R}_3}{\text{R}_3+\text{R}_2}\cdot\text{V}_{\text{out}}(t)=-\text{V}_+(t)$$
then Vout(t)=Vdd(t)

So, when we want to find the frequency we can say that, solving for 't':

$$\text{V}_-(t)=\text{V}_{\text{C}}(0)+\left(\text{V}_{\text{dd}}(t)-\text{V}_{\text{C}}(0)\right)\left(1-\exp\left[-\frac{t_1}{\text{C}\text{R}_1}\right]\right)\Longleftrightarrow$$
$$t_1=\text{C}\text{R}_1\ln\left(\frac{\text{V}_{\text{C}}(0)-\text{V}_{\text{dd}}(t)}{\text{V}_-(t)-\text{V}_{\text{dd}}(t)}\right)$$
$$-\text{V}_+(t)=-\left(\text{V}_{\text{C}}(0)+\left(\text{V}_{\text{dd}}(t)-\text{V}_{\text{C}}(0)\right)\left(1-\exp\left[-\frac{t_2}{\text{C}\text{R}_1}\right]\right)\right)\Longleftrightarrow$$
$$t_2=\text{C}\text{R}_1\ln\left(\frac{\text{V}_{\text{C}}(0)-\text{V}_{\text{dd}}(t)}{\text{V}_-(t)-\text{V}_{\text{dd}}(t)}\right)$$

Then, the time of one period is given by:

$$\text{T}_{\left[\text{s}\right]}=t_1+t_2=2\text{C}\text{R}_1\ln\left(\frac{\text{V}_{\text{C}}(0)-\text{V}_{\text{dd}}(t)}{\text{V}_-(t)-\text{V}_{\text{dd}}(t)}\right)$$

So, the frequency is given by:

$$\text{f}_{\left[\text{H}z\right]}=\frac{1}{\text{T}_{\left[\text{s}\right]}}=\frac{1}{2\text{C}\text{R}_1\ln\left(\frac{\text{V}_{\text{C}}(0)-\text{V}_{\text{dd}}(t)}{\text{V}_-(t)-\text{V}_{\text{dd}}(t)}\right)}$$


texts: Found an old LCD in an old radio, how to test it?

texts:
I found this here LCD in an old radio, it has no number or anything on it, so I have no idea where to find a specsheet.

Is there any safe way to see how this baby works?


texts: Why is my simulation results are not matching to the theoretical data?

texts:
I have a circuit You can down here

I am trying to find out the transfer function of Voltage across L3/Input Voltage.

When you probe at L3, you can see the voltage generated. This is what I am trying to replicate in my transfer function output.

I am using lsim to calculate the system output.

lsim(test,input,time)
here input = modulator output at Q.

time = 1:1:length of input;

I am getting strange result incase of transfer function output.

I have verified the transfer function multiple times and it seems to me that the derivation of transfer function is proper.

What is wrong here ? can someone help me to verify this.

Thanks.


texts:
I have a large power supply with multiple DC output modules. 2 of the modules are connected, positive to positive, through a 1.1 ohm resistor (really, 2 2.2 ohm resistors in parallel). When I measure the voltages without the resistor, I have the correct voltages (3.65V and 5.35V) but with the resistor I measure 5.9V on the 5.35V module, and 2.8V on the 3.65V module. I am probing across the + and common terminals of each module. I was also curious as to see if the commons were corrected, and when measured, it reads 67.5 ohms (However, inside the machine when all hooked uo, the commons become connected.) So I suppose my circuit would look a little something like this (outside of the machine)...

simulate this circuit – Schematic created using CircuitLab

My question is, what is the exact purpose of this circuit (My guess is to share the current for the loads) Also note, the resistors are only connected to the 2 positive output terminals. And how should I properly measure the voltages? (This goes to an Ultrasound Medical Device, the computer reads the voltages correctly, but am I probing wrong? Red probe is indicating the 5.35V module and black is 3.65V. The blue line coming off the terminals is the power resistors located somewhere else.)


texts: arduino burning bootloader. avrdude issues

texts:
When I try to burn a bootloader to my atmega328 the arduino IDE gives me an error:

avrdude: usbdev_open(): did not find any USB device "usb"

When I burn a program to my avr chip i change the port to com3 and it works just fine, but I only know how to burn the bootloader via the arduino IDE and do not know how to change the avrdude preferences to use com3 instead of "usb". Any help on how to do that?


texts: Trouble chaining multiple low noise op amps

texts:
I want to experiment with receiving ELF signals.  In particular 76Hz.  The goal is to attach a coil of a few thousand turns of magnet wire, place it on the ground, and read the signal level.  My thought is to chain a couple of low noise op amps (OPA211) to take what I would expect is a few microvolts and amplify it and then run it through a switched capacitor filter configured as a very narrow bandpass filter.  I would expect another stage or 2 of amplification and then a peak detector to measure the amplitude of the positive going sine wave.

To start this I wired up 2 OPA211 op amps as inverting amps.  100ohm resistors into the inverting input and 3K resistors for feedback.  100 ohm resistors from the non-inverting input to ground.  For initial tests, I am using a signal generator to feed a sinewave of 76Hz at 4mV (minimum for my sig gen) into the 100 ohm input resistor and looking at the output of each amp, I get the expected gain of 30 with only a positive peak and clipping of the negative peak of the signal.  When I connect the output of the first stage to the input of the second stage, I get no output from the second op amp.  I tried to capacitive couple the 2 stages as well but no change in behavior.  I'm sure I'm missing something but after much reading and searching for an answer as well as experimenting, I'm getting nowhere.  I would appreciate some help at this point.

I have a PDF of my circuit but as this is my first post I didn't see a way to attach it.


texts:
After turning on the machine at our facility or our workshop the RCBO doesn't trip at different facilities the RCBO trips but when you arm it again the machine turns on no problem
Main culprit is the contact ringing of the mains switch which can be measured by a osciloscope and comes to around 4A with no load attached
Only phase and neutral is interrupted by the switch grund is continuous
Any advice or test procedures are welcone


texts: How does skewed conductor on the rotor of squirrel cage decreases crawling affect?

texts:
My questions, as stated in the title, is how does skewed conductor on the rotor of squirrel cage decreases crawling affect?

I've gone through articles in about cogging and crawling affect on induction motor, but I still don't fully understand how skewed conductor help decreases the affect of the low torque created by the 7th harmonic. The only explanation that I've found is...

"Skewing primarily helps in removing crawling phenomenon by reducing slot harmonics, as if rotor bars are skewed by such an angle where the rotor bar terminations fall under two same poles (order of harmonic X no. of poles) created by harmonic fluxes in stator and as a result production of same polarity emf takes place in the termination and they effectively gets cancelled.."

So my understanding is since slot harmonics depends on the number of rotor bars, by skewing them there is now less of the rotor bars and henced improve performance. So by doing this mechanical design, electrically we see an improvement in motor efficiency..am I on the right track?


texts: High Voltage input and output microcontroller

texts: I am new to this, but I am looking to regulate a few ballast controlled fluorescent lamps with a micro-controller.  Everything I look at has a low operating voltage and below 10 volt input/output voltage.  I want to have a/c hookup to the microcontroller with full power output to the ballast (when told to do so by the program on the chip).  Am I misinterpreting what the input/output and operating voltages mean, or are high voltage applications of microcontrollers not too common? I was looking at some arduino products or something similar.  Any direction or clarification is much appreciated.


texts: If the voltage at ground is 0, why is there current flow?

texts:
From what I understand, voltage is required to motivate electrons to flow through a circuit. With KVL we have that the voltage will essentially be depleted at the return point (ground). So, if this is the case then why can we have current flow (at the return point)?

simulate this circuit – Schematic created using CircuitLab


texts: Variable Current Amplifier for Fan Control

texts:
I'm working on a project where I need to vary the current supplied to a DC fan. I am currently trying to use a BJT as a current amplifier to amplify a low current analog output (0 to 100 mA to vary the current received by the fan unit at 12V.

Schematic below.

In short, the circuit below I can get working for a low current fan (nominal 12V at ~80 mA) but not for the high current equivalent. My BJT is overheating to the "too hot to touch level". If I wait for the BJT to cool, I can sometimes get this circuit working, but only if I spike the analog voltage up rapidly to the max output. If I slowly ramp it up I'll get a low current draw on the fan (~70 mA) and then nothing.

I have measured a voltage drop of 11.6V across the BJT consistently.

Fan specifications:

12 V, 640 mA nominal operating current
Max of a 900 mA startup current draw before settling to ~600 mA
Varying current between 200 and 640 mA

BJT: Is the 2N2222A NPN transistor. https://www.digikey.com/products/en?keywords=%E2%80%8E2N2222ACS-ND%E2%80%8E

My current schematic:

simulate this circuit – Schematic created using CircuitLab

Any thoughts on a better way to design this circuit or what is causing the problems I'm seeing? Thanks! This is for a personal project and I'm clearly a newbie to using electrons.


texts: How do I set a new reference point within Eagle CAD?

texts: How do I change the reference point in Eagle CAD for placing parts correctly? I'm using MARK  but it did not set the new mark point as a reference. Is there a way to do this?


texts: Can I switch between two analog references to read signals with different ranges with the ATmega328P?

texts:
I want to read two voltages of different ranges with an ATmega328P ADC with the highest resolution possible:

The 1st signal varies from 0 to 1V. It's the output of an LM35DZ Temperature Sensor. I wanted to use the internal 1V analog reference to get the highest ADC resolution possible.
The 2nd signal is the battery voltage, that varies from 0 to 5V. I feed it to this Over-Discharge Protection circuit that Russell McMahon proposed and based on that reading, it will turn off the circuit if battery levels are too low. To read this signal, I have to use the ADC 5V voltage reference.

My questions are:

Is it ok if I keep changing the ADC voltage reference from the internal 1V to the 5V reference to make one read then the other?
When I switch to 1V internal reference, will the other 5V signal damage the other analog input? I got the impression that the 1V reference would be a limit for the ADC and the 5V on the other input would somehow violate this.
I actually tried to switch between 1V and 5V reference, but when I do it, the reading of the 1st signal (with 0 to 1V range) starts fluctuating. Why is that? I tried giving the ADC time to settle (10 to 50 ms), but that didn't work. How do I get a stable reading after switching the analog reference?


texts:
As I checked some documents about library ieee.std_logic_arith it seems resulting length of A+B will be 64-bit when both A and B are 64-bits.

I want to know if ieee.std_logic_arith have an add operator which generates carry (so that operator generate 65-bit output for adding two 64-bit operands)?


texts: LM317 thermal cutoff for voltages more than 37V above ground

texts:
I'm using the LM317 and LM337 for regulation of positive and negative high voltage rails. I noticed in the datasheets (LM317, LM337) that they have a thermal cutoff, but I wonder if this could actually lead to device failure.

I use the regulators floating, so they regulate 220V down to 200V using a voltage divider on the output. The output is therefore 200V with respect to ground, and the input is 220V with respect to ground. Let's also say that I connect the output to an op-amp's power rails. If the thermal cutoff operated, would it not lead to the situation where the input was 220V, and the output 0V? The op-amp could in theory drag the power rail to 0V if one of its signal inputs were grounded, leading to 220V potential across the LM317, which far exceeds its 37V rating.

Would this still be ok for the regulator, or lead to some smoke?


texts: What is the purpose of the ferrite bead on DC Adaptors?

texts:
According to WikiPedia: Ferrite bead suppress high frequency noise.

In the case of wall power adaptors, are they trying to protect the device being powered or are they protecting the PSU from high frequency noise?

Why is it placed on the plug end rather than on the adaptor end?

What would be the consequence were the ferrite bead not installed?

Thank you!


texts:
How will the carrier concentration and the band diagram in a n+ p junction will look like when the p region is cut short before the actual barrier width? (or) In other words how does the n+ p junction look like when the width of p layer is so small?
i understand that the pn junction depletion layer expands until it reaches equilibrium but what happens when it is not allowed to expand further than a given width?


texts: Difference between 5G vs 4G in terms of energy consumption

texts:
I want to build a device that is expected to consume very little energy.

I don't know if it will be better to have it compatible with 5G or just leave to be compatible with 4G.

So, do the 5G consume less power than the 4G for very low transfer rates? my device will send a at most 5MB per minute.

I have heard also somewhere that with 5G the devices will be able to choose what is best connection, that is, will be able to automatically switch to 4G, 3G or even 2G if the requirements won't be too demanding.

My project is to make smartwatch like the thor-5, which has localization technology and 3G capability.

But with my smartwatch, I will just track the location and be connected to the internet to send its coordinates to the server and better determine its position.

I have to decide if I will implement it with 5G or other technologies to better optimize its energy consumption.

I think that for all my needs GPRS (2G) will be enogh, but anyway, maybe 5G will be better.

My smartwatch will have also WiFi 6 and bluetooth 5.1.

Btw, will it worth putting a more modern SoC/SiP ?

I plan my smartwatch to have google wear OS or android go.


texts:
Hi i need help in understanding the binary division restoring method
From -2, we stored the value to 5 by adding the divisor which is 7
After adding 7 to get 5, why does it automatically jump to 10?
So from 5-7 = -2, restore -2+7=5 => 10-7=3
Where does this 10 from, and can anyone explain why this form of divison works?
Source:
https://userpages.umbc.edu/~squire/cs411_l10.html


texts: Lots of noise in the microphone amplifier circuit when idle

texts:
I come again to get help from the experts.

I am using this BJT transistor in the circuit.

http://www.fairchildsemi.com/ds/2N/2N3904.pdf

Here is the microphone that I am hooking up in the circuit.

It's an electret condenser microphone from digikey.

http://www.cui.com/product/resource/cma-4544pf-w.pdf

Here is my design

I am following the tutorial from this link to build the amplifier. It's exactly the same circuit but with different values to make it work with microcontroller. For that, I have used the supply voltage of 5V instead of 9V as in the tutorial. I have also tweaked the values of resistors to make the correct biased voltage.

http://www.youtube.com/watch?v=Br3uOM0IVjc

The problem is that I get a lot of noise. I checked with oscillosope and it is biased correctly, i.e., midway between the 5V. But you can see a very noisy signal. I hooked the circuit to a computer speaker and you can hear the noise after you hook up the circuit. The output works correctly though, i.e, when you play a sound in the microphone you can hear clearly in the speaker but during idle there is a noise that is audible.

What is the reason of this noise and how to minimize it while the microphone is sitting idle? Thank you for the help.


texts: Can somebody explain me about the working and waveforms of Buck converter with LC input filter? I can't figure out the output voltage expression using Vg, R and D(duty cycle) and the dc voltage and current of inductor L2 ,L1,C1 and C2. Please explain in details.


texts: Using Thevenin's theorem, how do you find the Thevenin voltage?

texts:
The above image shows a circuit.  It is required that we simplify the circuit using Thevenin's theorem to find the Thevenin voltage, current and resistance.

I've done a countless number of problems but only succeed in finding the Thevenin resistance. Having difficulties with finding voltage, in turn, unable to find the Thevenin current.


texts:
I am looking into a implementing a low-cost RS-232/422 opto-coupled receive circuit. The aim is surge protection and tolerance to DC offsets.

The challenge is that the inputs should be completely floating and work over a wide temperature range, say -40°C to 85°C. Speed up to 4800 baud. Logic null input 1.6V - 25V.

I considered simply chaining a 5kOhm with the diode input but the resulting forward current is too small to produce a useful current transfer ration with inexpensive opto-couplers. (Especially at high temperatures.)

How does this solution look to everybody? Am I overlooking something?

simulate this circuit – Schematic created using CircuitLab

My understanding is that this should cut in abruptly at (Vin1-Vin2)=Vf of the optocoupler with a rise and fall time of about 10µs and be fairly tolerant to CTS degradation and voltage surges on the Vin side. - Is this right?

Is it likely to be a problem, that the input impedance is 10kOhm at high input voltages rather than the standard 5kOhm?

Edit 1

simulate this circuit


texts: common mode ground and its connection to main ground

texts:
I am trying to understand concepts in common mode voltage and EMI due to it. Now, I understand that differential mode is the difference between the P and N wires/signals. The common mode is the - (P+N)/2.This is w.r.t ground. Now, the common mode currents are induced due to noise generated via long wires that are connected to PCBs(that carried signals or power).

Now, the common mode current is dumped into the ground and thus making my ground noisy. Now my doubts are the following -

Common mode noise is generated in power lines(Vcc and GND) or in differential signal lines(RS422,485) or in both ?
If common mode noise is dumped into my ground and if I have a common ground my whole ground will be corrupted,right?
How should the common mode ground be coupled to my main GND plane ?

Also, I have long wires bringingin in Vcc,GND,and RS422 signals. So, where all should I put common mode chokes to filter common mode noise ?


texts: Safety with wireless MCUs with internal ROM

texts:
I read that the ESP32, as long as other MCUs like CC3200, they have an internal ROM not user accessible and usually not open source, used to initialize the device, if I am correct. This means that mine code starts after the ROM initialized everything and give the control to the bootloader+application in flash (external or internal to the device).

Now, if one get really paranoid, is there a threat in using a communication system with some software that is not known? How can one be sure that there is no spy software or not documented backdoor, like it was to be the case in some HDD in the past, from the NSA scandal?

I also know that this apply to any non open source system, so any phone or computer could have such issue in a way greater order of magnitude.

I would like to know just out of curiosity, and I am not at all a security expert.


texts: Old 7-wire Autosyn resolver: how to use it?

texts:
I have just bought online what I thought was a synchro as described in this page, but I am trying to get my head around how to use it since it does not correspond to any of the types I currently know: it has 7 wires.

It's not a resolver transmitter, because it does not have 6 wires (or 4 if all returns are tied together), and it's not a synchro as defined above because it has more than 5 wires (4 if the wires are tied together). I thought it could be redundant as well but this doesn't check out either. I hope it's two-speeds somehow.

My objective is to do do a proof of concept of a resolver (transmitter)-to-digital chain. I have a Scott-T transformer. What do you reckon is this component exactly, and what do the wires do? I have not found any datasheet online, it's too old.

The nameplate reads "Microtecnica Autosyn resolver AY 528 A 45 A 2, manufactured under Bendix licence. rotor 2 phase 26V stator 2 phase 11.8V".
Wires on a rear view:

At 0° (vertical): black 1, yellow 1, red 1, blue
At 45° CW: red 2
At 180°: black 2
At -45° CW: yellow 2

Edit:
 - Black 2 to yellow 2: 202Ohm
 - Black 2 to red 2: 200Ohm
 - Yellow 2 to red 2: 400Ohm
 - Yellow 1 to blue 1: 40 Ohm (not 400)
 - Black 1 to red 1: 40Ohm
 - Everything else > 1Mohm

It looks like one side has two phases back-to-back (centerpoint), and another has two isolated phases.
Nonetheless this does not correspond to anything I know. Perhaps the primary (rotor, then) is compatible with 2 different excitation voltages (and the higher resistance would mean less current draw + lower output impedance)? I'll test this theory this week-end if no one answers.


texts: Is it wrong to charge a laptop/cellphone battery when the device is on?

texts:
I always try to charge my laptop or my smartphone after turning them off. I feel that leaving these devices charging when they are on could be detrimental to them.

But... is it? And whether the question is "yes" or "no", what would be the electrical reasoning behind that answer?

I believe that (almost) every battery in these devices are lithuim-ion ones nowadays, so the question would be oriented to this kind specifically.


texts: Powering inverter gate needed for enabling a DC-DC converter

texts:
I'm designing a plugin card that's powered at 12V from the main board. Now, I need a 3V3 and a 2V5 voltages on the card, so I'm using two buck converters MUN12AD03-SH (I'm supposed to use this specific converter, so I can't change that).

The signal for enabling the converters comes from the main board and is active-low  (I can't change that as well), while this the converter's enable is active-high, therefore I'll have to use an inverter gate.

So the question is what's the wisest way to power this inverter gate if the DC-DC converters aren't enabled yet (only have 12V)? I wasn't able to find a 12V tolerant inverter gate. Can I use a voltage divider as the inverter gate won't draw big currents? Or should I use another buck or LDO or something else?


texts:
I am trying to replicate the circuit I found here:

(source: cogeco.ca)
This is a photograph of what I have built:

In my photo I have labeled one diode in the bridge rectifier which has burn out twice now. Unfortunately my supply of diodes is running low and I can not see what the error is in my circuit when I compare it to the schematic.
Can some one please try to spot what I have done wrong?
Edited: Updated Picture with new Layout that the Poster has made. Still burns out the same bottom diode.
Original: http://imgur.com/SL5ycic.jpg


texts:
I have a small circuit with a µC in it. Sometimes it can happen that the circuit looses the power connection, resulting in instantanious shutdown. I am looking now for a capacitor which provides me powe for a short time so that my µC can shut down correctly (the µC gets noticed when the main power is lost, so it can start its shutdown routines.
The capacitor has to provide power for maximum half a second only for the µC for writing the current data into its memory and afterwards shut down. The µC is an ATtiny, therefore it does not need so much power while kept alive.
Is using a 100 µF-cap enough for this task?
Additional Informations:
Voltage level: 3.3V
Supply current: max. 300 µA

Regarding the questions, how to detect the power loss: The circuit is connected to two different power sources, one of them running at 32 V, and the other at 3.3 V (µC circuit). If there is a power loss, both circuits loose power at once, so I can test the 32 V circuit for power loss.


texts: What type of LED/lighting mechanism is this?

texts:
I am trying to identify the "name" of these LED components embedded in the monitor, so that I can purchase some for a medical device project.

What are those illuminated lights on top and the side of the monitors composed of?
Thanks!


texts: Measurement of s11 with reduced power on NanoVNA

texts:
I am developing a 10.7 MHz IF amplifier for a radio receiver. In order to match the input to the output of the driving mixer stage (330 ohm) I need to measure the input impedance.

I did the measurement with a NanoVNA (I don't have access to a professional VNA), that I bought via the well known Chinese website. Though I have reasons to believe the Nano is reasonably accurate, the problem that I encounter is that the output level of the VNA drives the amplifier way past it's 1 dB compression point, so it is unsure if the measurement is correct. The capabilities of the NanoVNA are very limited, and it may not be possible to reduce the power level internally.

I read a suggestion to pad the S11 output with a T or PI pad attenuator, and use the output of the pad as reference plane, so in effect do the OSL calibration behind the pad:

simulate this circuit – Schematic created using CircuitLab

Is padding the output like this a common approach, and will the measurements be sufficiently accurate? I estimate the required attenuation to be 10 up to 20 dB.


texts:
Recently, I read Tektronix's Probe Bandwidth Calculations. It point out that Tektronix and Agilent have different probing philosophy:

  There are two schools of thought on what an oscilloscope probe should
  actually display on an oscilloscope. Tektronix subscribes to the
  philosophy that a probe should measure the unloaded, or original,
  signal. Agilent subscribes to a different philosophy that says a probe
  should measure the loaded signal.

Because I've never used Agilent's scope, I want to know if you've noticed this. And what about other scope vendors such as LeCroy, RIGOL, etc, which philosophy they subscribe to.


texts: How do I calculate the DC blocking capacitor at the output of a transistor amplifier?

texts:
Suppose this circuit of an audio amplifier:

How is C calculated?

I suppose C is there to block DC, so it is a high pass filter.

If this is the case the formula for C would be something like

C = 1/2ΠRf

I can choose for example, f = 20Hz but what about R
?

How do I know the output impedance of that circuit?


texts: LTSpice transient analysis and current amplification problem

texts:
Im simulating LC circuit in LTSpice:

It's tuned at resonance at 1 MHz in the transient response simulation plotting the source and R1 current. Both of which are equal in amplitude 600mA but with a 180° phase difference.
In this picture we see the ac transient response for curent in R1 with a value of -20dB at 1 MHz which is considerable:

So the question is if the attenuation is -20 dB, besides the phase difference, why is the R1 and source current amplitude the same and/or what am I missing?


texts: Insertion Resistance of Current Transformers

texts:
Given a current transformer like this:

there is an insertion resistance that appears as a very small equivalent series resistance on the measured circuit.  Since it is usually small (say, 0.0001 \$\Omega\$), it can be neglected.

If you were to feed the current-carrying wire you are trying to monitor through the transformer multiple times to amplify your signal, does this also multiply the insertion resistance by the same amount?  If I loop the wire through 10 times, does this multiply the insertion resistance by a factor of 10?

To clarify what I am asking, here is a link describing what insertion resistance means in the context of the type of transformer shown above.


texts: Calculating the Output Resistance of a Widlar Current Source

texts:
I'm currently struggling to understand the small signal equivalent used in the following calculation:

http://en.wikipedia.org/wiki/Widlar_current_source#Output_impedance

My problem is: How come they neglected the transimpedance current source of the LHS BJT (connected to R1)? When doing the calculation myself (using a slightly different way) I ended up needing it.

Regarding this question: Is there maybe a "rule of thumb" to decide when to leave out current sources in the small signal model?


texts: How could I power an IC over the Ethernet?

texts:
I was looking foward to powering a small Integrated Circuit using only the power provided by the ethernet outlet of my room. Is that even possible?

I've googled and I've found that the voltage that it provides is something in between 2v and 3v. Since it is not a DC voltage, but a random AC one, I believe that it would be not possible to power an IC without having to use some sort of AD conversor or a simple peak detector circuit in order to maintain the voltage.

Am I wrong? Would you have any advises for that case?


texts:
I'm a computer programmer by trade who has taken an interest in Arduino with the hopes of eventually producing a particular hardware project that has captured my hobby/side-business interest.

I understand only a very little bit of electronics and am trying to fix that. Please be gentle if my questions are very basic or silly. I'm really trying to understand some new concepts.

I'm reading "Introduction to Electronics" 5th Edition by Earl D. Gates. I'm really enjoying it and finding that it lays out material in a structured and helpful way. It was well worth the $1.00 I paid on Amazon! ;-)

I'm reading through a section that deals with Ohm's Law and Kirchhoff's Current Law, and I'm struggling to understand some concepts.

I can understand (or at least do the calculations for) the I = E / R equation. It's basic math, so that's not hard. The explanation of what figures in a circuit go where is also fairly easy to understand.

The book has drawn circuits with ? values for various parts of the circuit (voltage, current or resistance), and I am able to successfully solve for the missing values. Not too hard, actually.

What is currently confusing me is "voltage drop". I have a question that gives the following circuit:

simulate this circuit – Schematic created using CircuitLab

The question asks, "How much voltage is dropped across resistor R2 in this circuit?"

So, first, we solve for current, which calculates to I = 4.5mA. (Actually, 4.485981308mA.)

Then, knowing that current is the same for the entire circuit, we can set up the following equation:

I2 = ER2 / R2 (which, why is it suddenly ER2, not just E?)

0.0045 = E / 3900

Therefore, voltage drop is 17.55V.

But what does this mean?

Using the same calculations, voltage drop for the different pieces of the circuit are:

Resistor 1: 0.0045 * 5600 = 25.20V
Resistor 2: 0.0045 * 3900 = 17.55V
Resistor 3: 0.0045 * 1200 =  5.40V

And those total to 48.15V, so our math is close but has minor rounding issues.

But, again, what does this mean?

Does it mean that tapping into the circuit between resistors 1 and 2 would give me 22.8V (48V - 25.2V)?

If I have a sensitive electronic component that accepts 3V-6V, would it be safe to draw this power from the circuit after resistor 3?

Am I even close to a proper understanding?

What I'm interested in is working with some 3.3V components, starting with with an input voltage that's maybe 3.7V (LiPo), maybe 5V (USB), maybe 9V, etc. I understand that my Arduino Uno already has power regulators that output 3.3V @ up to 50mA, but HOW does it do that?

It says it can accept 6-20V (but USB is 5V!), and somehow it deals with all of that excess voltage to provide a steady, regulated 3.3V. What dark magic is taking place here? ;-)

I realize that there are many, many components out there that will "just work" to give me the electrical output I desire (I've been playing with a few, like the LM317), but I'd like to really understand what's going on, not just know which component works. Thus far, all attempts to actually get the LM317 to work have failed, because I apparently have a serious lack of understanding on this issue.

Anyway, I really appreciate if you've read this far. Thanks for any help!


texts: Fridge/cooler circuit unnecessary diodes

texts:
I am modifying a mini cooler/heater to turn it into an incubator in which I can program the temperature sequence in time. I have reconstructed the electric diagram of the cooler/heater and I don't understand why the maker chose to include the circled diodes. Here is the diagram:

There is a switch which controls whether the heater works as a cooler or as a heater, resulting in the two different wirings shown in the figure.

I don't understand why the maker used the circles diodes, being that the following diagram should do the same job, without needing the diodes:

The wiring would be as in the figure above, depending on whether it's a cooler or a heater.

My question is: is there a reason to prefer the maker's design to the one I propose?


texts: How to calculate total amperes in two component circuit?

texts: I have two components, a fan and LED strip, that I want to drive with the same power source.  Both the fan and the strip are labeled 12 Volts, So I'm pretty sure I need exactly a 12V DC power source to drive them both.  However, the fan says it requires 0.10 amp and the light strip says it needs 5 amps.  How do I determine what the power source should provide in terms of amperes?  Does that mean I need 5.10 amperes total?  Also there's no Wattage mentioned on the fan but the lights say 5W. Again, how do I choose a single power source for these two components running at the same time?


texts: Need help design active crossover circuit

texts:
I need to build an active crossover circuit for my 2-way speaker design. I decided to use TDA2009 as my audio amplifier. TDA2009 is shown connected below in the picture. My question is: how can I modify the TDA2009 circuit to implement the circuit in the gray box?

I know that C10 and C11 are need for the DC battery to minimize noise as well as C1 and C2 (2.2uF). So these 4 capacitors need to stay in the circuit. What about C4 and C5 do I need them? or I just connect the high pass filter of the gray box directly to pin 8 and 4 of TDA2009 and the low pass filter directly to pin 10 and 2 of TDA2009? What do you think?

Finally I need it to be active filter that is my TDA2009 need to be placed after the filtering circuit (gray box).

Please I need your help concerning this. I came to this forum after weeks of research because I am really stuck.

Thank you for your help in advance :)


texts:
for a couple of years I have been trying to make this one oscillator circuit. 10/10 times it does not work. The best result I can get is the led being constantly on and dimmable with the pot resistor. amplification with out oscillation???

I know I could make the circuit in eagle cad, put together on a pcb and make it work. what am I missing????? I have tried trouble shooting the circuit and the best conclusion I can come up with is something is not working right or being bypassed around the two transistor ans capacitor.


texts: 555 fading in&out if possible with pwm & led array

texts:
i'm new here and also in the electronics world so pls be patient with my ignorance.

I's now months that i'm  fascinated by the 555 timer. The stuff you can do with such a tiny thing is impressing.

As you can immagine i already tested most of the http://www.555-timer-circuits.com/ circuits, and also from other sites. And again ... wow!

Anyway, you know, reality is cruel.You never find what you really need.

This maybe simple for you, but for me it's a nightmare.

What i'm trying to do:

A Monostable 555 timer circuit

What should it do:

Triggered by a switch, sensor (PIR) fade in 2-3s
stay high for 1-3min *
fade out for 2-3sec

A simple light timer for the stairs, right??? NO

What it does:

Triggered by a switch, delay for 1-2sec
It fades in for 2-3 sec
It stays high

This is where i'm stuck atm.

But thats not all, i would like to attach mosfets or npn transistors delayed by another 100-300ms
those driving a led strip of 3 leds and triggering the next one. Each strip is a stair (or step???).

I made this circuit knowing nothing and don't looking to much about if its correct because of the fact that i could use maybe npn transistors,pnp, or mosfets for this setup. using npn transistors would be cheaper but i would need to take the current from somewhere else to trigger the next one as i lose 0.7v at every gate.

simulate this circuit – Schematic created using CircuitLab

A. So is there something that would delay each step at about 200-300ms or less?

from what i read about electronics i could use capacitors. but the capacitor needs to be small as it has to fit in a tiny place over the stair so 1cm * 2cm * 5cm max
I guess it needs to be a big capacitor to delay 200ms or even 100ms??
are there other components that i'm not aware of that could create a delay?

each step could have his own 555? but thats $$ and probably the worst approach?

B. naturally i also need to solve the main problem, fading out the output of the 555 after 1min or so.(monostable)
it's useless if i post my circuit for the fading led as there are hundreds with a simple google search and i really don't understand them all.I use a 220uf,20k and 100k i think,  a npn 2N3904 to create the fading effect. but its not working correctly.

  Everything could be done easely with microcontrollers, but i really
  like to understand more about ic's and electronic in general.

Notes: The whole question is based on the naive idea of a fade in effect. i didn't event thinked about the fade out effect result in the array. It probably would disastrous. So my first guess is to put one 555 at the base of the stair and one on top. Both ends have triggers, and both circuits flow in a different direction once activated. But that is another sotry.


texts: How can i create a dead time between two signals in Matlab/Simulink?

texts:
I have a curcuit which outputs two different  pulse signals from  two different "PWM generator(DC-DC)" block. I will apply these signals to two different mosfets. Thus I need to create a dead time to prevent short circuit.

To achive this, i tried to use "transport delay" and "on/off delay" blocks. The shifting part worked but after applying them to the mosfets the current become weird.

I thought to transfer the signal to the workspace and try shifting there or using "Matlab Function" block but i don't  have an idea how to.

I would appreciate any idea and help.


texts:
I'd like to use I2C signals on the FPGA from cypress 2.0 module with i2c pins as below.
but It does not work well.
enter image description here

Xilinx FPGA  <--------------------> MCU module (I2c)

.UCF
NET in_scl LOC = "A1";
NET in_sda LOC = "A2";

NET out_scl LOC = "C1";
NET out_sda LOC = "C2";

and in verilog as below, I'm implemented.

module top();

inout wire in_sda;
inout wire in_scl;

inout wire out_sda;
inout wire out_scl;

assign out_sda = in_sda;
assign out_scl = in_scl;

endmodule

Can you help me what am I missing?


texts: Karplus Strong - getting a pluck of particular frequency

texts:
So I have been lately looking at a python implementation of Karplus Strong algorithm, or more particularly of the system:

\$ y[n] = \alpha y[n-M] + x[n] \$

From what I understand, \$ x[n] \$ is supposed to be a signal defined from 0..M-1 and 0 everywhere else.
Also \$ y[n] = 0  \forall n < 0 \$

Now if we start \$ x\$ with a random input noise of M samples, then we'll get back a signal of fundamental frequency M from the above system.

To simulate a guitar chord of say following notes: D4,A4,D4,E4...
One calculates the required frequencies as: \$ 440 \times 2^\frac{n}{12} \$ where n would be number of half tones between A4 and the required harmonic.

Now the sources I have referred to,
(for instance, http://www.cs.princeton.edu/courses/archive/spr08/cos126/assignments/guitar.html)
Calculate the M (the buffer/delay of system) as:

\$ M = \frac{F_s}{F_o} \$
where \$ F_s \$ is the sampling frequency, while \$ F_o \$ is the frequency of the signal I am interested in (say D4)

So for \$ F_s = 44100 Hz \$ and \$ F_o = 441 Hz \$ then \$ M = 100 \$

This calculation confused me. It seems like now I'll get a signal whose fundamental frequency is 100 Hz, when I needed a signal whose fundamental frequency was 441 Hz. So according to my understanding, shouldn't M be simply,
\$  M = F_o\$ which will then give my requried signal.

Thanks :D


texts: How can I connect multiple 24LC04B's on the same I2C

texts:
I'm trying to store some data on a EEPROM, but unfortunately I cannot fit it into a single 24LC04B, therefor I want to connect another 24LC04B to the I2C line to compensate for the lack of memory.

The 24LC04B has only two actual addresses/pages (0x50, 0x51), but the problem is that it's also using another 6 addresses/pages as a mirror of the first two for some reason..:

i2cdetect -y 1

      0  1  2  3  4  5  6  7  8  9  a  b  c  d  e  f
 00:          -- -- -- -- -- -- -- -- -- -- -- -- --
 10: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- --
 20: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- --
 30: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- --
 40: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- --
 50: 50 51 52 53 54 55 56 57 -- -- -- -- -- -- -- --
 60: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- --
 70: -- -- -- -- -- -- -- --

For 24LC128, I can change the I2C address of the EEPROM by connecting A0, A1 and A2 pins to the VCC pin, which gives me an address selection in a range of 0x50 to 0x57.

For the 24LC04B this seems to have no effect and I cannot find any information on how to disable the address mirroring ether. Even if the 24LC128 was big enough, I still can't add it to the I2C line, because 24LC04B is using up all the address space with the mirrored addresses..

Is there a way to connect two 24LC04B's on the same I2C line? Thanks!


texts: Problem driving IPB065N15N3G MOSFET with HCPL-316J driver

texts:
I want to drive an IPB065N15N3G MOSFET. I am making a boost converter. The driver I am using is the HCPL-316J (a combined optocoupler and driver). Below is a picture of my schematic.

Please tell me what is the problem in this schematic and why can I not get the desired output? Since I am providing a triangular wave, why is the gate of the MOSFET not driven?

Since the HCPL-316J is not available in CircuitLab, I am providing a link to a Google drive with the Spice model. It is a .asc file. Please use LTspice XVII to open the file.

          -----------X-----------X--------------X------------

I redesigned the circuit using nodes. Also added and replaced some components in the circuit.
The voltage at drain is like this:
The voltage at gate is like this:
As we can see there is no pulse at the gate, so the mosfet can not switch on and off.

       ------------X-----------------X------------------X-------------

After simulating the above circuit, I am trying to simulate the same circuit with different mosfet.Datasheet of mosfet is here. Please suggest what should be the necessary modifications to be made in order for the circuit to work.


texts: How to draw a bode plot for this function?

texts:
How do we draw the phase and amplitude diagram for the function below?

$$T(s)=\frac{100(s+10)}{s(4s+1)\cdot(s+25)}$$

I cant seem to figure this one. I found the zeros and the poles like I usually do in bode plots but I dont know how to build the diagrams.


texts:
While i was looking for STPM32 Energy meter chip, i saw a ratio named Rb[V/A]. I really searched at Google for it but really can't be sure what is exatcly is.
And my X5 currunt transformer's datasheet really doesn't help me. The ratio Rb is at page 48 above and middle of page. And datasheet right below.
Thanks
STPM32DATASHEET


texts: A source generator connected to a receiver with a lossy transmission line

texts:
Consider that we have a 50-ohm source generator that is connected to a 300 ohm transmission line. This line has a loss of 10 dB for every 100 ft and is connected to a 50 ohm receiver.

The source indicates an output of -30 dBm and we need to find the input voltage to the receiver in dB(uV).

My steps are as follows :

First I have converted the source output power (-30 dBm) to the corresponding voltage in absolute value to be equal to 7.07 mV.
Then I have converted this value to dB (uv) to be equal to 77 dB(uV).
Finally I have calculated the input voltage to the receiver as V = V
source (dB (uv))  - loss (dB) = 77 -10 =67 dB (uV) .

However, the answer is 71.7 dB(uV). So what is wrong with my steps?

Edit : This problem is taken from Introduction to electromagnetic compatibility by C.paul.


texts: Better to regulate voltage by supplying or subtracting base current to BJT pass transistor?

texts:
As a learning exercise, I'm designing new guts for one of my venerable HP 721A (circa 1959) DC bench power supplies.

With help from members of this site I was able to vastly improve the reference voltage:
How improve temperature sensitivity of HP 721A DC Power Supply voltage reference?

Now I'm on to the error amp and driver amp.

On the matter of controlling the pass transistor, a power BJT, the original circuit provides enough current for the pass transistor to turn on hard, then regulates the pass transistor by diverting a portion of that base current through a current sink to ground. It does this via a separate transistor that could be called the "drive" amplifier. Call this drive current subtraction for the sake of a working term.

simulate this circuit – Schematic created using CircuitLab

Please take this schematic for its general topology, I haven't tried to get all the component values exactly correct.

Simple DC power supply circuits I've found online generally take the straightforward approach of having the driver supplying all the base current, call this the direct drive approach.

simulate this circuit

However, circuit designs that seem more sophisticated always seem to use the subtraction method.

My question is: "Are there inherent reasons why the subtraction method is preferable to the direct drive method for controlling the pass transistor in a linear regulator?"

I'm not able to see any so far, but have a few hypotheses:

Control voltages for the subtraction method can be lower than the output voltage, although possibly inviting instability when an op-amp is used.
The subtraction method keeps the drive transistor in its active region, improving the regulation speed
Once one gets the voltage regulated, applying current control in next in line and combining the two is easier when using subtraction, i.e. whoever subtracts the most wins.

Can you help me understand the design considerations on this aspect?


texts: Does Surge Spike Protector box can protect my PC even from Thunderbolts?

texts:
My house isn't wired for an Earth ground. I am using a Surge/Spike Suppressor box to protect my computer.

Will this box protect the computer during lightning strikes? Is the design of the suppressor such that it requires the presence an Earth ground?


texts: Power and Ground planes The Henry Ott way or split ground planes

texts: Seeing a lot of mixed infomation around involving ground planes on multilayer boards. For a mixed signal mulitlayer PCB which is the preferred method? I know every board is different and it depends what your board is doing but I see alot of people with isolated ground planes yet Henry Otts advice is to do the exact opposite and partition the board in segments. Any advice or comments on this would be great!


texts: Switching polarised capacitors in a guitar effects pedal

texts:
I'm building a basic guitar distortion pedal, the Two-Transistor Fuzztone from the book Snip, Burn, Solder, Shred. I want to add a multi-throw rotary switch to select between input capacitors, and so change the tone (I'm guessing the cap actually works as a filter.)

However I'm concerned that if I connect them as in my diagram, the caps might be damaged by reversal of polarity, as charge comes from the selected cap? Or are they safe so long as only the negative side is connected and the positive is floating? Sorry I'm a bit new to all this!
If I had to I could use diodes on each cap I suppose, but might that add extra clipping? I'm hoping I don't need to anyway.
Also I have had a look at a similar question, but they don't appear to be using polarised capacitors.
Anyway, thanks in advance.


texts: How to make two isolated power sources from one source?

texts:
I need to have two electrically isolated power sources.

Here are the details of the application: http://revolectrix.fmadirect.com/support_docs/item_1377.pdf page 26:

I need to make this work with a car 12V DC installation as the only power source. This should work with a current up to 70 A (max of my car alternator).

Is there something I can attach to the car's 12V installation to make two isolated power sources out of it, to power these two FMA Cellpro Powerlab 8 units?

Clarification: the isolation of the power supplies is required because the two battery-charging devices connected to them are connected to each other in series, so the (+) terminal of the first one is connected to the (-) terminal of the second one. If the power supplies would not be isolated, then they would have common (-) and effectively the (+) and (-) terminals of the first device would be shorted.


texts: Is silver-bearing solder appropriate for general hobbyist use?

texts:
I've been soldering on and off for quite some time, and I've always used whatever Radio Shack had available. Now, I'm about to attempt a bit of SMT soldering (by hand), and I'm having some difficulty sourcing appropriate combinations of diameter and composition.

The general consensus seems to be that Sn63/Pb37 solder is easier to work with than 60/40 solder, and it seems to be widely available. One wonders, in fact, why 60/40 solder continues to be as common as it is today.

When it comes to SMT, the general consensus seems to be "smaller is better", and I'm probably looking for 0.015" diameter solder, if I can get it.

If I wanted to buy in quantities of one pound, I could locate appropriate solder, but it is quite expensive in quantities that high, and I am fairly unlikely to use that much solder in less than a decade or two. I tried Allied, Grainger, Mouser, and even Amazon.com without success.

The closest thing I could find, in fact, ends up being available from Radio Shack: 0.015" diameter 62/36/2 silver-bearing solder.

What I don't know, however, is how this compares to "normal" 63/37 solder. Is this just as good, almost as good, or better? Is it the "right stuff" to use for everyday PTH and SMT soldering (other than it being too small for PTH)?


texts:
Why is it generally a bad idea to formulate node voltage equations for an op amp circuit at the op amps output? Does this idea only apply in the ideal op amp model?

I recall it has to do with the idealized zero output impedance of an op amp, and maybe I'm just not understanding the consequences of this, but why does this mess up the analysis? I would really like to get a better understanding of what I can and can't do when playing with different network layouts that utilize op amps. As of now when I write out a possible op amp configuration I am wary of my design because of this ambiguity in where the analysis starts to become wrong. A cascaded op amp design is even worse because I do not know where to even start.

I guess the greater question is:

What is unique about the op amps network topology and/or variable relations that may lead to inconsistent equations? That is, what do i need to look out for while forming equations pertaining to a given (ideal) op amp model?

EDIT: I realize this is a rather broad question, so I added an pic/example of a situation where the analysis leads to a contradiction.this is just the simplest case of what im talking about. In general I find eqns formed at an op amps output tend to lead me to wrong answers.
 I have an introductory textbook for circuit analysis that specifically tells me not to formulate node equations at OP AMP output nodes but does not expand on why. I find it hard to gain confidence in working with op amp equations when a underlying contradiction might pop out of nowhere.

EDIT2: Basically, I have a voltage source in series with \$R_{in}\$ (a resistor immediately prior to the op amp) into an ideal op amps non-inverting input and the op amp forms a unity gain follower (output is connected to the inverting input of the op amp). Following this, there is a load resistor which is then in series with the negative terminal of the original voltage source.  Here's the schematic:

The contraction comes from the fact that the input current to the non inverting input to the op amp is the same current that runs through the load resistor that follows the op amp. The ideal op amp input current is zero and yet the current through the load resistor is non-zero (this is a contradiction).


texts: NVIC Pending register vs EXTI Pending register (STM32F4)

texts:
Why there are two pending registers for interrupt? One of them is EXTI_PR and other one is Interrupt Set-pending Registers(ISPR) which is in NVIC controller registers.

EXTI unit pending register:

NVIC unit Pending Register:

Are these two having the same purpose? If not, what is the difference?

Also I am confused about Interrupt Set-enable Registers (ISER) in NVIC unit and Interrupt mask register in EXTI unit. What's the difference between them?


texts: Can power specs be used without extending the margin to account for losses?

texts:
Looking generally at the 74FCT family, I saw that it's power pin should be held at \$5V \pm 5 \%\$ to be in specs. From my understanding, \$\pm5\%\$ power supplies are widely available, but are the top  of the cheaply available ones.

Considering a reasonable (devoted layer) ground and power plane on a PCB, would it be reasonable to power a PCB from a 5% precise supply (at 5V) ? Or would the losses and parasitics be too much of a problem ?

If I needed a more precise voltage, how should I tackle that ?


texts: STM32L1 GPIO pin configuration - Power supply current increase due to pin with open-drain setup

texts:
Setup
I have an STM32L151 mcu(application processor) and on its PB5 pin I have a peripheral (SARA-N3) connected. The requirements for the peripheral are that the pin is configured as an open drain output and is only used to pull it down for 1 second. The peripheral has an internal pull up to 1.1V and a max allowed voltage at 1.3V, however the mcu pin levels are at 3.6V. The mcu side is configured with no pull-up/pull-down resistor.

Problem
The problem I am having is that when the mcu goes in stop mode (low power), there is a power supply increase due to that connection pin, i.e. PB5.

1st attempt was to set that pin to output 1 and open drain. In theory, this should mean the pin should no be driven and keep the voltage of the peripheral(as observed), but observed the additional current.
2nd attempt was to enable the pull up on the mcu side ( pin is still output). This had the effect to drive the pin to 2.7V which is not allowed by the peripheral pin and still there additional current was observed.
3rd attempt was to set the pin to analogic or input mode but the effect was the same as attempt 1
4th attempt was to disable the Schmidt trigger of the mcu pin (pin is was output). This improved a little bit but still not what I expect
5th attempt tried a different pin, i.e. PA11. The pin is configured as open drain output with no pull. The power supply current is still there. It only stops when I disconnect the pin and connect it to the Vdd of the MCU

Guess
My guess is that the voltage level of the pin compared to the voltage levels of the mcu pins is probable considered digital low and hence causing some FET to let current through
Question
Is there any suggestion on how to configure the STM32L1 GPIO pin operating at 3.6V so that it does not leak current when the pin connected to has a voltage value of 1.1V?


texts: Do digital multimeters require calibration?

texts:
This article Understanding Digital Multimeter DMM Specifications / Specs mention

A digital multimeter will only be able to meet its specifications when it is within a certain environment. Conditions such as temperature, humidity and the like will have impact on the performance. Also conditions such as line voltage can affect the performance. In order to ensure that the digital multimeter is able to operate within its uncertainty specification, it is necessary to ensure that the external conditions are met. Outside this range the errors will increase and the readings can no longer be guaranteed.
A further element to be considered is the calibration period of the digital multimeter. As all circuits will drift with time, the DMM will need to be periodically re-calibrated to ensure that it is operating within its specification. The calibration period will form part of the specification for the DMM. The most usual calibration period is a year, but some digital multimeter specifications may state a 90 day calibration period. The 90 day period will enable a tighter specification to be applied to the digital multimeter, allowing it to be used in more demanding applications.
When looking at the calibration period of the digital multimeter, it should be remembered that calibration will form a significant element of the cost of ownership and after some years will be significantly above that of any depreciation. A long calibration period for the digital multimeter is normally to be advised, except when particularly demanding testing is required.

Is it necessary to calibrate a digital multimeter every year? (From my understanding, only analog multimeters require calibration)


texts: Need advice what method or algorithm to use for calculating topology matrix for node voltage method in matrix form

texts:
I want to make a program that will calculate everything in a scheme with the node voltage method in matrix form.
The problem is I don't know really how to do this.
I want to translate this scheme with this edges to the matrix A0.
edges=[(1,2),(1,3),(2,3),(2,4),(3,4),(4,1)]
A0=[
[1,0,0,-1,1,0],
[-1,1,1,0,0,0],
[0,0,-1,1,0,-1],
[0,-1,0,0,-1,1],
]
Could someone tell me what algorithm or law to use in this situation?
Thanks in advance.


texts:
Many of us have lots of devices that uses AC mains (110V/220V) to DC (typically 12VDC) adapters. There's my LED table lamp, my Wi-Fi router, my Gigabit switch, my powered USB hub,.....

Such AC/DC adapters are dirt cheap from China, so I highly doubt efficiency is built into them.

So here's my idea. Can I somehow combine all these into a single device; do the AC/DC conversion once and have everyone tap the DC line, instead of each doing the conversion themselves?


texts: Find linear relation between stacked iron blocks

texts:
I want to find a linear relationship between stacked iron blocks, one by one on top of each other, and some electrical property. Then create a arduino circuit that could precisely determine the number of blocks stacked on top based on the relation. What electrical property should I be measuring? I was thinking creating a EC probe but the sensitivity may not be very precise.

Any ideas on how to get a linear relationship between the number of iron blocks stacked on top of each other and some electrical property?

I have one base iron block which will have the circuit internally built in, and then 5 iron blocks, each should have some identifiable electrical variable as they are stacked.

Load cells would not be possible for this project since the circuit is internally positioned within one of the iron blocks (the base block).

The dimensions are around 15cm (lenght) x 20cm (width) x 5cm (height). The surface black oxide, there is no way to have a transducer over the stack

I think the best way to do it would be to use a coil to find magnetic field pulses, but the coil diameter might be quite small and not sure if there would be sensitivity with more blocks added, unless there are some other design idea with the coil, possible short circular but long vs large circular diameter?

The objective is to count the number of iron blocks up to a total of 5.


texts: Closed Loop Transfer Function - PD Control

texts:
For the following control system, I am trying to find the characteristics of the system.

I have firstly found the closed loop transfer functions \$T(s) =\frac{C(s)}{R(s)}\$ , to be:

\$G(s) =K_p(s+9)*\frac{10}{s+12}*\frac{1}{s^2+6s+15}\$

\$G(s) =\frac{10K_ps+90K_p}{s^3+18s^2+87s+180}\$

Now as feedback is Uniity Feedback, therefore H = 1, I get;

\$T(s) = \frac{G(s)}{1+G(s)H(s)}\$

Which means \$T(s) = \frac{10K_ps+90K_p}{s^3+18s^2+87s+180+10K_ps+90K_p}\$

My first question for this problem is, is this Transfer Function correct, or have I miscalculated during a particular step up to this point.

Continuing on, I am now trying to find the \$K_p\$ value that leads to less than a 15% Overshoot for the system.

Unfortunately, I am unsure what to do next to find the \$K_p\$ value for this problem.

Any working or help as to how I go about this would be greatly appreciated.


texts: CC2530: adapting AVR/pgmspace.h for Zigbee

texts:
Goal: Adapt ENC28J60 codes written for ATMega328p (http://tuxgraphics.org/electronics/201204/embedded-ethernet-client.shtml) for CC2530.

Problem: No equivalent library for AVR/pgmspace.h available for easy transition.

Need to make equivalents for:

prog_char
uint8_t
*progmem_s
pgm_read_byte()
PROGMEM

Any help regarding this issue will be highly appreciated.


texts: How to implement this scenario for a stable opamp integrator?

texts:
I want to make a circuit using opamps and passive components where the input is a pulse train and can be with a frequency between 100kHz upto 3MHz and the duty cycle can be 100% or down to 1ns ON time. I want to average such an input and set a threshold like 0.5V. And if the average is less than 0.5V the final output will be logic zero otherwise logic 5V.
I tried the following approach myself using an RC integrator and a buffer:

How can this circuit be improved regarding the definite input? Response time I need is less anything than 10ms.


texts: On a 800 AMP heating unit that is fed from 480VAC, 3 phase power. Will each conductor pull 800A or 266A ?


texts: Choosing a Shunt Resistor for Low Current Applications

texts:
Is it possible to use a shunt monitor to measure current for low values(10 mA-100mA) and if is it possible, should I use low resistive values like in most of the power circuit applications? I know that I need low resistance because it shouldn't effect my load(I don't know the value of it but probably in the order of magnitude of M(\$ 10^6 \$)Ω) but from this pdf I learned that for my application I need a resistive value of 2kΩ(200V/100mA[estimated]). I am starting to getting confused because there are also other parameters like tolerance, temperature coefficient and type(wirewound, metal, smd etc.) and I do not know which one should I take into account.

I am sorry if I can not point the question clearly, but I am a bit lost!

Edit: I just noticed that I didn't tell about the application itself. It will be an I-V tracer for  samples of SiO2 wafers etc. that can log current data(using the above configuration with an instrumentation amplifier) and voltage data with a daq.

Edit2: Also as Neutronned suggest I also add the pieces of information that can be needed:
Voltage range is 0-200V and the input impadance of the sourcemeter is bigger than 10GΩ as datasheet suggests.


texts: Some USB hubs have status LED that shows activity. Let's say, I want to make a USB3 cable with status LED that would indicate any activity on the bus (changes of differential voltage). Is there a way to achieve this without disturbing communication?


texts: Missing data in truth table and commenting on missing value

texts:
I was trying to solve the attached question from the book Digital Design: With an Introduction to Verilog HDL, 5e however the values of f1 and f2 for the entry (1,1,0) are missing.

If we use sum of product or product of sum form the function we get would be valid for all the values however it would also give a result for (1,1,0).
Will that value be the missing value from the table?
I tried both POS and SOP and the result for 1,1,0 is 0 in both the cases so is it correct to say the original truth table must have had 0 for the following entry or do we not talk about it since it was not one of the readings which we had.
(Note: I have no idea about K Maps just yet so please refrain from using those to explain unless that's the only way.)


texts: How does snubber circuit work in phase control circuit of Single Phase AC Motor? I have tried to know the causes but I was confused with RC circuit function with this phase control circuit.


texts:
I ordered a kit that is missing its 78L05.  Can I substitute a 7805, or would I need to also adjust the cap values?  Here is the entire schematic.

Here is the voltage regulation portion of the schematic:

I have emailed Bleep Labs, but I thought this forum might be faster.


texts:
Is there a viable way to detect urine using some gas sensor?
If there is such way, what would be the maximum distance between such sensor and the "sample"?