texts: Troubleshooting butterworth bandpass gain stage issues

texts:
I am having issues solving the gain stage section of my bandpass filter design. I used a multiple feedback 6th order lowpass and a 6th order sallen-key high pass to get a bandpass filter with cutoff frequencies 700,4200 Hz respectively. I built and tested it using the Analog Discovery 2 (AD2) device since school labs are closed right now due to the quarantine. My filter works great before I implemented any gain stage. Almost perfect cutoff frequencies at the measured decibel range. For the record, I am using TL084 quad op-amps Now, when I tried to make a non-inverting op-amp for the gain, I came across odd and frustrating behavior. When I try increasing the gain, the inband gain will stop at ~10.9dB (~3.5 Volts). Now only this, but this will also stretch the bandwidth so I no longer have my desired cutoff frequencies. It is weird because the AD2 can supply 5 volts (V+ and V-) and when I tested with an external 9 volts it still will peak at the same in-band gain.

I am seeking guidance on why this is happening and what I can do to rectify it and have proper gain behavior that matches my LTSpice simulations. I greatly appreciate any help with my issues. Thank you all and please feel free to ask me any clarifying questions.

Below is my AD2 network analyzer (or Bode Plot) screen capture before and after the gain stage.

]3

UPDATE: I have added my LTSpice simulations to clarify my circuit for those who said I should which I should have done. There are many helpful suggestions, but it would be best to show you my schematic and maybe that will clarify any confusion. Also to clarify, my "gain stage" is referring to the non-inverting configuration that will increase the output signal. Right now my AD2 is putting a 1V test though the circuit. Maybe the AD2 cannot actually give complete 5V to the rails, but I do not understand why the cutoff frequencies are stretched when the rails are hit.


texts: How to assert multiple properties in System Verilog

texts:
What is the most efficient way to assert multiple properties in SV ?

Example:

property x;
   if(expr1)
       a===b;
endproperty

property y;
   if(expr2)
       c===d;
endproperty

Is something like this is needed: assert (x && y)?


texts:
I have a fuel level sensor that varies its resistance from 9.5 ohm(empty) to 155ohm(full). The sensor is powered using 12V battery connected to a 30kVA Generator.

The problem is that the level that I get fluctuates,i.e, 47.57% for 30s and then 48.4 for 30s or so. The level is calculated using the equation level(%)=187.41 * V(adc port) - 7.38. The fuel level sensor forms a voltage divider with a 1.2k resistance. The voltage at the ADC pin does change but very little about +-1mV.

I have two more analog signals connected to ADC of 16f877a. The other two signals namely battery voltage and temperature are fairly stable.

I using 7805 to power up the controller circuit and a separate 7805 to power up the SIM900 module


texts: How to filter RF signals to get the average value?

texts:
I am designing a system that will use a phase frequency detector with 400-450 MHz signals. There is a filter required on the output of the phase frequency detector in order to obtain an average value (ie: Low Pass Filter).

I first was planning on using an active low pass filter with just a basic op-amp, but I can see the bandwidth of the op-amp being an issue.

In the answer to one of my questions, Mark recommended I use an LC filter but said:

  One issue you do need to consider is the input impedance of the LC
  filter. You'll need to take it into account when deciding how to treat
  the transmission line between the filter(s) and the IC.

Also, the phase frequency detector has 4 outputs (D, !D, U, and !U). Initially I was just planning on using D and U and referencing to ground, but I think it might be best to use the differential pair.

The IC specifies that 50 ohm impedance is desired. The filter will ideally provide me an average over about 1 second, so whatever is required to get rid of all switching noise and provide the average.

I plan on feeding the averaged signal to a differential ADC (but can go with single ended).

Size and Cost are not huge constraints in the project but high quality is a must.

What needs to be done to make sure that this is done properly?


texts: Understanding metal oxide semiconductor gas sensors' datasheet.

texts:
I just need some help understanding how a circuit that I already built works.

I am using the the Figaro TGS 2201 air quality sensor. The datasheet for it can be found here:
tgs 2201 datasheet from manufacturer

Currently, my sensor setup is as follows:

I am not using R2 but only using R1, which makes the air sensor targeted at gasoline exhaust rather than diesel. My R1 is equal to 10k ohms, as specified as the minimum value in the datasheet.

From my understanding, as the concentration of the gas that the sensor is targeted for increases, the conductivity across pin 3 on the sensor increases proportionally (logarithmically) to the concentration of the gas in the air.

I have a micro-controller read the DC voltage from pin 3, and i measure between 420 and 410 milivolts.

In order to translate this value into parts per million (concentration of the gas),
the data sheet provides the following equation for calculating Rs:

Rs = (Vc - VRL)/VRL *RL

How do i measure RL and VRL? I assume that Vc is 5 volts because that is what my voltage regulator outputs.

Furthermore, in order to obtain Ro, do i need to run a control, and record RL in clean air and assign Ro to that value?


texts: What is the meaning of zero voltage switching (ZVS) and zero current switching (ZCS)?

texts: I was reading about induction heating circuits in a electronics textbook and saw the terms ZVS and ZCS which are abbreviation for Zero Voltage Switching and Zero Current Switching respectively. There are many academic articles about these topics, but for a novice like me these articles are very theoretical and i can't get a grasp of topic. I would be happy if someone could help me and explain the idea behind ZVS and ZCS.


texts:
I have an Arduino based circuit that performs a mechanical job and I'd like the circuit to turn on when it detects a magnetic field. I want to use a magnet as a trigger for the circuit. When a magnet is attached to something like say a stick and put near the circuit board I'd like it to detect the magnetic field and turn on.

I have learnt that an operational amplifier can be used for this purpose but need guidance on how to do it as I am a novice in embedded systems & electronics.


texts: Why is collector current independent on collector base voltage in active region

texts:
I read many books but none of them explains why the collector current is independent on collector base voltage in common base transistor in its active region.

Please explain it with clear mechanism.


texts: I am trying to make a time delay circuit (see the image) in which when press a momentary button the relay will stay open for a specific time. I tried my circuit but I cannot calculate the time (I tried the T=RC formula and it did not work). Does anyone knows how I can achive something like that to stay open for a specific time?


texts:
My work:

I am shorting terminal a to c then finding the equivalent resitance between terminal b to d so now a=c
so 9 will parallel to 5 from b to a so equivalent 3.21
similarly from a to d it its 3.21 and both will be in series so total  I got \$\boxed{6.43\Omega}\$

But answer given Opion (A).Is there any mistake?


texts: What is the relationship between electrical resistance and heat generation?

texts:
An incandescent light bulb has some amount of resistance (let's say 30 ohms) and generates a large amount of heat. It's my understanding that a resistor with the same amount of resistance (30 ohms) generates considerably less heat. If you short out a battery with a piece of copper wire, there is very little resistance, but a large amount of heat is generated.
What causes these differences?
Is the physical process that resists current flow different than the physical process that generates heat?
It seems like it must be. It's my understanding that the more resistance there is in an electrical circuit, the slower a battery will drain, suggesting that the resistance is somehow decreasing the speed that energy exits the battery, not just expending all the energy as heat.
I was once told that resistors work by creating friction for the electrons passing through them and expelling the lost energy as heat, but it seems like that can't be the whole story.


texts:
I'm using a full bridge motor driver to control a brushed DC motor.
The motor driver can provide up to 20A at 24VDC and I'm using 24VDC, 200Ah AGM batteries.

The driver offers the possibility to monitor the current output and this is very interesting for me because I can limit the maximum current by software.

I tried to search for current limiter circuits and some of them are based on the use of a transistor that is able to reduce the current when it turns ON.

Since the maximum current is very high for my application and so its power (20A*24VDC=480W), would it be better to use a current limiter IC? I wasn't able to find any commercial IC able to handle high currents.
Or should I use the transistor to limit the current?

My need is to be able to set a maximum current value for different working conditions.


texts: On load tap changer controller switching

texts:
A 20/25 MVA transformer has an On load tap changer (oltc). Here a HMK7 Controller is used to control the motor drive of oltc. Which seems like

There are two buttons 1-N & N-1. Red seven segments show the tap position. To increase voltage we press N-1 button which reduces tap position by 1. There are 25 tap position. For details see this

May be the tap changer connection diagram will be helpful to understand the question.

So my question is instead of being two buttons named raise and lower why there are 1-N & N-1 buttons? What's the meaning of these two notations?


texts: How to estimate the overall CTR of this optocoupler from its test conditions

texts:
As a part of a system I need to replace a proper opto-coupler with an old one which had insufficient CTR for the given circuit section without changing any other component:

The pulse input is 0..5V pulse train with 50% duty cycle and the frequency of the pulse train is between 10Hz upto 550Hz.

So the forward current If roughly becomes (5V-1.5V)/470 = 7.5mA. And the opto's output current(collector current of the opto) is 12V/2.2k = 5.5mA.

Previously the old opto had min 20% CTR. So If  should have been 5 x 7.5mA= 37.5mA but it was only 5.5mA.

So down to overall CTR of 80% is enough for a guarantee operation since If is 5.5mA and output current is 7.5mA.

But for a reason instead of changing R1, R2 or R3; I need to replace the opto-coupler with a proper CTR. I want to use a CNY17F-4XG where its data sheet is given here.

The current transfer ratio versus If  is given in the following plot:

What I understand from above, at 25°C where Vce = 5V and in my case where the If  is 7.5mA the plot shows a CTR of 190%.

But in my case the ambient temperature can be between -30°C upto +30°C.

I'm stuck at couple of points to estimate the worst case CTR.

How can the temperature effect on CTR be interpreted in this case? Like how can I estimate the variation CTR at different temperatures relative to their 25°C.
The test results in the datasheet are for where Vce = 5V. Does "Vce = 5V" here mean when the LED of the opto-coupler is off? In my case is Vce = 12V? Again how could we estimate the variation of CTR at 12V relative to their 5V Vce test?


texts:
Please see the image below for the circuit. I am trying to find the currents through each branch in the circuit. However one part, which is essential in finding currents through all the branches, confuses me: when current flows from the source (I1), it will divide into the three branches containing R2, R3 and R5. But how can I calculate the currents through these branches?
I know the current division formula when it divides into two branches, but this one is a different case with three branches. Any guidance would be appreciated.


texts: Confusion with voltage rating when sizing wire gauges

texts:
This is a conceptual question. I mean I have a confusion about voltage rating of a wire. So I want to ask with an example:

Above 80V DC power supply will power the load which needs around 80V voltage and sinks 1A current.
The one-way length of the wire L is 20m.
I want/tolerate 1% voltage drop between the power supply and the load.
So to size a suitable wire I do the following:

One way voltage drop ΔV tolerated is:

ΔV = 0.5×80×0.01

This ΔV is for L one-way distance, so to calculate Ω/m:

ΔV = R_wire(Ω/m)×L×I

R_wire(Ω/m) = ΔV/(L×I)

R_wire(Ω/m) = 0.4/(20*1)

R_wire(Ω/m) = 0.02 Ω/m

So I go to this table and find out the corresponding AWG for a 0.02 Ω/m wire.

In this case the table shows it as 24.

Imagine I use the following AWG 24 cable:
https://www.velleman.eu/products/view/?id=18950

In the specs, max current 4.3A which is great for my purpose.

But how about "max. voltage: 60 V" in the specs?

Does that mean I cannot use this wire for this application?

I thought what matters for heat was current. Is my sizing method correct?

Is that 60V max voltage applied across the wire without a load?


texts: What are the meanings of the fields of this cache memory?

texts:
I have a cache memory simulator with this cache memory shown.

The cache size is 64 bytes and the block size is 8 bytes. What is the decomposition into fields? If block size is 8 bytes, then log(2^3)=3 bits are for block offset to point out a byte within a block. For 64 bytes with 8 bytes per row, it will have 8 rows and hence 3 bits for index bits, one bit is the dirty bit that should flag for dirty data and the rest = 25 bits are for the tag. Is this interpretation correct? Then what is meant by the 31..6..3..2..0 and the white and grey color of the incoming address?


texts: I am designing a board with mixed signals. There is an SPI bus and also an ADC chip. Now, during layout phase is it recommended to to have a specific impedance for these traces ? The length is not much for both SPI and analogue signals. Have seen some engineers do layout of SPI with 50Ohms characteristic impedance and analogue of 75Ohms. Is this so critical ? My SPI is a max of 2MHz and analogue of 100KHz max. So, is impedance considerations coming in for such a design ?


texts: auto shift on keypad press in lcd using fujitsu F2MC-16LX MB90385 Series

texts:
We are using LCD and Keypad in our MCU and I was wondering how do i initialize my LCD so that every time there is a key press the display will automatically shift right and fill up the LCD as more characters are inputted, at first i though of doing this by assigning the individual address for each input i.e on first input it will be placed on 0x80 as it is the address for the first character in the LCD and so on.

but then i was informed that i can do this by simply changing the initialization of the LCD.

but i am not sure as to what part of the initialization do i need to change. i do realize this is basic but im still new to this.

here is my initialization code in C:

instCtrl(0x28); //function set: 4bit; dual-line
    instCtrl(0x08); //display off
    instCtrl(0x01); //display clear
    instCtrl(0x06); //entry mode: increment; shift off
    instCtrl(0x0F); //display on; cursor on; blink off

void instCtrl(unsigned char inst)
{
    int x;

    IO_PDR2.byte = inst>>4; //shift right
    IO_PDR2.bit.P24 = 0;    //set RS to 0 (instruction register)
    IO_PDR5.bit.P53 = 0;    //set RW to 0 (write mode)
    IO_PDR5.bit.P52 = 1;    //set E to 1 (initial state)
    delay(8000);            //delay
    IO_PDR5.bit.P52 = 0;    //set E to 0 (H-L: final state)
    IO_PDR2.byte = inst;    //transfer lower 4bit
    IO_PDR2.bit.P24 = 0;    //set RS to 0 (instruction register)
    IO_PDR5.bit.P52 = 1;    //set E to 1 (initial state)
    delay(8000);            //delay
    IO_PDR5.bit.P52 = 0;    //set E to 0 (H-L: final state)

}


texts: How should I make a constant AC current source to drive an electromagnet?

texts:
The inductance of the electromagnet is about 0.05H and the resistance is under 50 Ohm and I need about 2 to 5 Amperes to drive it.

I need to be able to change the amplitude and also the frequency at least up to 1kHz.

I have a function generator (SM5075) and a couple of power amplifiers ( https://www.bksv.com/-/media/literature/Product-Data/bp1928.ashx &  https://www.bksv.com/-/media/literature/Product-Data/bp1948.ashx)

I need to control the current as the force is proportional to the current in the electromagnet. The impedance will be proportional to the frequency of the current source.


texts: Limit the amount of current passing through a circuit to a set threshold?

texts:
Here's the situation: I've added an aux input to an old hifi system by tapping into the circuit previously used by the magnetic read head of the hifi's built-in 8-track player. That part works pretty well, as both a 3.5mm headphone jack and the read head have 3 wires: left, right, and ground. I just switched them out and it worked as expected

The problem (I think) is that a modern cellphone pushes more power to the headphone port than the 8-track read head ever intended. Unless I turn my phone's volume way, way down, the sound is horribly distorted. I'm worried its probably not good for the circuit either.

I've thought about putting some resistors inline, but I have no idea what they should be. I'm not an electrical engineer - just took a handful of electrical course while getting a comp sci degree.

Is there some kind of simple device i can put inline to limit the power coming from the aux input? Ideally it would be something that blocks all voltage above a certain threshold.


texts: Saving a resistor on an NPN transistor current source (sink) when driving LEDs

texts:
The typical circuit to drive an LED from a low-power microcontroller digital output pin, using a transistor, might look something like this (assume a 20mA/2V LED):

simulate this circuit – Schematic created using CircuitLab

Now, of course individual transistors have current gain values that vary widely from one to the next. However, when building a circuit myself, I know the exact individual transistor I'm going to use. Therefore, I could measure the current gain of that transistor when it's not in saturation, with a circuit like this, for various values of R1:

simulate this circuit

And then (in my example), I could keep trying different values of R1 from my stock of resistors until the output current is exactly 20 mA:

simulate this circuit

And then use that in the LED circuit, now omitting the current-limiting resistor and letting the transistor do that instead:

simulate this circuit

Of course if the transistor were swapped for a different one, the process needs to be repeated.

This saves one (potentially high-power) resistor per LED, by simply choosing an appropriately-measured resistor in series with the transistor base.

Is there any particular problem with this method?


texts: What is the recommended trace width for this TI ZHH 144 BGA package?

texts:
I wanted to become more familiar with BGA package PCB design and have selected a chip to learn with. This is a Texas Instruments DSP here. I've studied several 'BGA at home' guides and believe to have an understanding of what is required for design and assembly.

However, it seems like this chip requires very small traces compared to chips used in several guides I've read. This BGA package has a pitch 0.8mm and 0.55mm ball diamater. The resulting width between balls is ~10 mils. This seems like a pretty unfortunate pitch to ball diameter ratio.

I haven't even gotten to the assembly portion yet and this seems like it will be difficult to get a PCB printed that satisfies this spec.

My question: What is the recommended PCB trace width for navigating this 10mil gap?

How would a manufacturer do this? It seems like anything smaller than the typically 5 mil trace width would add further costs.

BGA footprint provided below:


texts:
Details:
I am trying to build a circuit using a photocell resistor, a thermistor resistor, an LM324 op-amp, and of course regular resistors and wires. I am also using Analog Discovery 2 to provide power for my circuit.
Goals:
My goal is to build a circuit (using the above compenents) where one LED lights when the shadow passes the photocell and turns off when some heat is introduced in the thermistor.
Attempt:
I have tried many designs and nothing works. I tried putting the sensors in parallel and series with the LED. This didn't work. I tried using two op-amps, but I was unsuccessful again. I am new to electric engineering so maybe this is why I am struggling so much.
Any advice/suggestions with circuit design or even a systematic diagram would be really helpful. If you know of any similar project like this on the internet that I could study and learn from, that would be appreciated as well.


texts: Voltage sense multi range - how to switch with no voltage drop

texts:
I have an application where I need to measure precisely (<0.05%) a voltage level which can be from 1V up to 500V.

To do so, I use several voltage divider that are then multiplexed to a

ADC.

However, in order to keep the current through the voltage dividers as small as possible, I need to have some sort of switch mechanism, on the high side, that is able to withstand 500V and has minimum voltage drop.

The current through the channels are in the order of 10mA.

I checked if that could be done with P-Channel MOSFET, but the Rds on is in the 30ohm range which would introduce an error of about 0.06%.

Another option would be to use small relays, but I would prefer to avoid mechanical devices.

Is there any other options possible ?

simulate this circuit – Schematic created using CircuitLab


texts: Why does this BGA component have a keep-out layer?

texts:
I've pulled the Telit GE864-GPS (datasheet) from the Altium vault. The footprint has a keep-out layer, which prevents me from placing tracks to any pad without using vias. As the pitch is 2.5mm the component could be fanned-out on one layer, and I don't want to have antenna connections going through vias anyway.

Why would this (or any other BGA) component have this keep-out layer? Can I remove/disable it?


texts:
I can see: Ic2A Pin1 is V1=Vref-Id*R25
where Vref = Vcc*R24/(R24+R23)
Id is the current flow through the D6 which is a photodiode.
Question is: How to calculate the final output of Ic2B Pin7


texts: Delta total line current - Basic electricity problem

texts:
I'm reading the book Basic Electricity from Milton Gussow and there's a problem that is driving me crazy, I'm not able to get the result.
Can anyone provide me with a guideline to resolve it?

This is the problem:

Thanks.


texts: Can someone help me understanding the working of 3-stage comparator/ discriminator, shown in attachment?

texts:
I am working on a project and I need a high DC gain comparator for it.
M1,M2 are tge main differential amplifier and M1a, M2a are used for hysteresis.
As per my understanding its a 3 stage comparator: differential amplifier, common source amplifier and inverter.
But I can't understand the connection of main differential PMOD pair, encircled in red circle as current loads.
Can somebody kindly explain it?


texts:
I am trying to use an array of sensors to trigger a series of stepper motors based on peoples' presence within different areas of a hallway. It is for an interactive kinetic art piece at an elementary school.

I've tested with ultrasonic sensors, but because they will be overhead, facing down (ie, into people's soft, ultrasonic wave dampening hair) they are unreliable.

I have tested with PIRs, and they seem to be much closer to the behaviour I want. The only problem is the large time between readings. This is a problem because it allows people to pass parts of their body under the sensing area without being detected. I think kids will want to play with the sensors in this way, rather than just walking underneath, and the lack of responsiveness will become apparent quickly.

I've tested with both Parallax and ITEAD brand PIR sensors, and spec'd out a number of others. The shortest time between readings I could find was with the ITEAD, at around 2 seconds.

The ITEAD sensor uses the BISS0001 IC, and after looking at the IC's datasheet and the ITEAD's Schematic, I managed to shorten the time between readings to closer to a half a second by shorting across R13 and R33.

That said, I don't know if this will affect the performance or lifespan of the sensor, and I'm wondering why I can't find a PIR sensor with shorter read times. Do they exist and I just don't know what to look for? Or is there a practical limit to their read times?


texts:
I have a HT subwoofer that the volume is stuck on high. No matter what I do
with the knob, the sound is at full. I have redone some solder on the volume side and got some cleaner in but it had no effect; it's still on full. How can I troubleshoot this problem? I don't have the schematic for this but any information on how to check it would be nice. The sub I have is a Sound Dynamics THS1000.


texts:
I have noticed that AA (or AAA in that case) rechargeable batteries are always of nominal 1.2V while non-rechargeable have nominal voltage of 1.5V.
This works just fine in some cases, e.g. when the voltage requirement refers to just one battery and to a not really demanding load such as a tungsten lamp. In the latter case only the lumens would be affected and since this amount of voltage would normally be used as an indication lamp no harm is made.

However, in the case where more demanding loads exist, e.g. when added 3 or more batteries for an electronic device then this might just lead to stop functioning. 3*1.5 gives nominal 4.5V while 3*1.2V gives 3.6V so if the threshold is at 4V then even really fully charged batteries are inadequate to use.

I know that the nominal voltage is just an indication and a typical battery has a declining voltage, e.g. for 1.5V this means 1.6 or 1.65V fully charged, but the question is still valid.


texts:
I'm developing an application with my software defined radio (SDR) Board and it is very critical that I have some control over the actual power I am transmitting at every time.

In order to do this, I have first measured the impedance of the TX antenna port and unfortunately it is not a purely 50ohm impedance. In fact we can treat it as a complex Z = R + jX impedance, with the values of R and X known.

Knowing this, and assuming that I'm transmitting pulses with voltage U(t) well known, my question is the following:

I believe that if Z = 50 ohm, the total power P(t) of the signal would simply be (right?):

$$P = \frac{1}{t_1-t_0}\int_{t0}^{t1} \frac{U^2(t)}{50} \, dt $$

In general, since U(t) is known, I don't believe that I have to pursue any approximations in computing that pulse power.

However, if the impedance is complex, as it is the case, what is the relation between transmitted power and transmitted voltage? I mean, am I simply interested in the absolute of Z, i.e:

$$P = \frac{1}{t_1-t_0}\int_{t0}^{t1} \frac{U^2(t)}{|Z|} \, dt $$

or am I interested in the Real part of P only?


texts:
Suppose I am using a 8051. I compiled a code which has a static variable.
Where that Static Variable will be stored? In RAM? In Stack? On Heap?? In flash? Where?

Also, Correct me if I am wrong:
CONST are stored in ROM. And global variables are stored in Flash.(What if I don't have Flash?)

I am expecting answers with respect to Embedded Programming. It's not like in Code Segment or in .bss, but exact where on my board?


texts: What is the red-outlined white square that contains a red dot in this diagram?

texts: I'm new to circuit design and reading schematics but have a little familiarity there. On this diagram which shows a circuit built on a strip board, I don't quite understand the meaning of the red-outlined white square that contains a red dot.


texts: Audio: what do I need to do to get SPDIF data to a speaker?

texts:
I'm working on a speaker project where I'd like to use a microcontroller's SPDIF output (aka IEC 60958) to drive audio data to a speaker.
I've' been doing research on the topic, and I'm having trouble grasping exactly what steps are required to convert the SPDIF data into an analog input signal for an audio amplifier.
I believe the SPDIF is a compressed data format, so some type of converter is required to decompress the SPDIF data into a standard I2S data stream. From there, I'd need to convert digital to analog, then amplify the analog for the speaker:
Microcontroller --SPDIF--> I2S Converter --I2S--> DAC --analog--> amplifier --audio--> speaker
Is there any way that this approach can be simplified? I'd like to minimize complexity/part count where possible.
Is this the standard approach for handling a SPDIF interface? Or are there simpler approaches for driving a speaker with SPDIF data?


texts: Why does the capacitor exist on this breakout board but not others that have same function?

texts:
I am looking at using either of these parts to connect to a server power supply. I realize a capacitor helps to regulate voltage. Why would each of these parts that have similar function not both have a capacitor. That makes me think that a capacitor is not needed.Could it possibly be due to inductance. But it still does not answer why one has and one does not.

Any input is appreciated:

With capacitor:
http://www.ebay.com/itm/DPS1200FB-A-Power-Supply-Breakout-Adapter-Board-10-PCIE-Cable-fr-Ethereum-Mining-/322705408187?hash=item4b22bdc0bb:g:sS4AAOSwcQlZqoHk

Without Capacitor:

http://www.ebay.com/itm/DPS-1200FB-QB-A-12-ports-Power-Supply-Breakout-Board-Adapter-For-Ethereum-Mining-/253139686137?hash=item3af04d12f9:g:hlAAAOSw23lZsQsL


texts: Micro-controller failure problem as the temperature raises

texts:
I'm using at91sam3s8b(cortex-M3) for my project.The hardware board connects to PC using USB port. The firmware contains some cryptographic algorithms (it includes shifts, Xors, memory substitution operations). The algorithm output is correct when the board is powered on but it starts to fail as time passes.

The master clock is configured at maximum (64 MHz).

my observations are:

if I lower the MCK frequency the failure rate decreases. (it's not related to the frequency decrease rate. The failure completely fades if I use a frequency of 55 MHz)
If I raise the board temperature the failure happens sooner and if I lower the temperature enough the failure fades again!
Some micro-controllers fail (the most of them). but some others do not. (even at an artificial temperature of 85 degrees of centigrade)

The malfunctioning boards and hardware are sent to Atmel for test. they conducted a few electrical tests and answered there is no problem relating to our board or their micro-controllers.

Any idea how or where I can track this Issue? Any technical suggestion?

Edit:

More information:

The project is being built using keil 4.7
The cryptographic routines are implemented in assembly and c and are linked to the main project as static libraries (there is 2 separate libraries. assembly is built using code sourcery).
changing the order of libraries in the project displaces the fault to another algorithm. changing the name, place or declarations of some functions removes or displaces the fault.
The hardware board is simple. a microcontroller, a USB port and a SPI flash memory(winbond serial nand flash) + that little LED. The USB port and  SPI flash are not used in the simplified test code which is still faulty.


texts: As of now most of the negative feedback systems I have encountered have a feedback factor that is less than 1 but positive. However in some situations it seems the system can behave as positive feedback if the feedback factor is not negative.. I just don't seem to comprehend how this negative attenuation is accomplished just using resistive networks.. Ones I have used till now in my studies.


texts: Split-Core Current Transformer - Disconnecting secondary load questions

texts:
I have heard that disconnecting the secondary load from a current transformer while the primary line is passing current causes a huge voltage spike (from a question about CTs that I can't find again). I am planning to build a similar power monitoring system as one shown on openenergymonitor.org, but I don't have a dedicated Arduino, and I would like to disconnect it at times to work on other projects.

1) What causes the voltage spike/Is this info correct?

1) Is there any way to disconnect the secondary load without any issues?

2) Is the voltage spike in the primary or secondary lines?

3) Will any harm come to the CT without a secondary load?

4) Is the burden resistor (the resistor used for voltage measurement) enough of a load?

5) If not 4, what is considered to be the load? The thing measuring the resultant voltage
or the 5V I must supply to the circuit?


texts: Does an LED’s free electrons ever run out?

texts:
I’m aware that LEDs are doped with impurities on each p-type and n-type material to increase the charge carriers of each semiconductor.

My curiosity now is, how does each side continue to have extra charge carriers after a certain amount of time?

In other words, I imagine each side wants to be balanced and neutral and when power is applied they recombine at the depletion zone where photons are released. So, why does it keep happening and not ever stop? Is it the power source that keeps it going or am I missing something?

My confusion could be stemming from how a battery works and once depleted that’s it.


texts: How to determine which rail is under load

texts:
This might be a dumb question, but suppose I want to determine the total load on individual supply rails and I come across a circuit like this:

simulate this circuit – Schematic created using CircuitLab

Is the load shared equally between the supply rails?

EDIT: Rephrasing the question: Assume you have a resistor in between a connecting a -15V rail and a +15V rail like I (attempted) to draw here. These rails are separately generated via 2 different power supplies. They both have a finite amount of current they can push (+15V) and pull (-15V), which supply is doing the work?


texts: Getting square impulses from square wave input

texts:
I can't get this problem right... This problem was given by my professor as a possible exam question. I took a considerable amount of time thinking in it, but I'm yet unable to solve it.
The problem is the following:
Build a circuit that accepts a square wave as input and outputs a square impulse when the  input reaches a rising edge(or at the falling edge, or in the middle of the square).

Since English is not my native language it may be better explained by this image:

So far the most complex circuit components we have learned are opamps and diodes(normal and zener).

I've tried everything I remembered but the closer I got was a simple impulse...


texts: Flip-flop vs latch: Do flip-flops have an edge detector integrated?

texts:
As far as I know, a latch and a flip-flop are the same excepting that flip-flop only "works" with an edge of the clock (let's supose rising edge for the question.)
To make the flip-flop "work" only with a rising edge, we need a rising-edge detector:

So, as far as I know, a flip-flop is equal to a rising edge detector + a latch.
But my question is: Imagine a CPU with lots of flip-flops. Do all those flip-flops have an own rising edge detector inside of them, or there is only one rising-edge detector shared by all the flip-flops?
I mean, this is the typical "external" image of a D flip-flop:

Where you can see that the signal that is arriving is the clock (CLK), and this makes me think that ALL the flip flops in a CPU have their "rising edge detector" inside of them. But on the other hand I think that this cannot be possible! Because, why would they replicate a rising edge detector for each of the flip-flops they have, when they can save money and space by creating a single edge detector shared by all flip-flops?


texts: Hi I am in an introductory circuit analysis course and we just got to the portion over time varying voltages and currents through inductors and capacitors. We aren’t on the alternating current section yet but I don’t understand how these time varying voltages can be considered DC seeing as how the voltages and currents aren’t constant. Can anyone explain this to me?


texts: Thevenin Equivalent With Two Voltage Sources

texts:
I've been working through a few examples of Thevenin Equivalent circuits, and came across this one.

Find the Thevenin Equivalent circuit as seen by a load resistance between points A and B.

Finding the equiv. resistance wasn't too hard (75ohms), but I'm having trouble calculating the equiv. voltage.

I've attempted the questions, but am not sure I got the correct answer. Here's my working.

The total voltage of the circuit is 12V because of two aiding voltage sources being in series. From this, you can use a voltage divider between the two 150ohm resistors, getting a value of 6V. Another voltage divider can be used to find the voltage at node B, that being 2.4V.

Not sure I've done the next thing correctly -

I've assumed that Node A is 3V, and since the Thevenin voltage is the difference between Node A and B, Thevenin Voltage = 3-2.4 = 0.6V. Have I done this question correctly?

Anywho, any help is greatly appreciated.


texts: How can I safely prototype a mains power circuit?

texts:
I'm building a device that has a mains power component, which I need to prototype before building to make sure everything works. I know I need to make sure wiring—and insulation!—is thick enough to cope with the higher current, and that I need to make sure there's enough space between exposed components so there's no arcing. I'll also be stashing whatever I prototype in a nice, insulated box before applying power, and I'll be include a small-value (250mA) fuse just in case. I'll be considering everything double-insulated rather than earthed (plastic enclosure, and there's nothing I'll need to touch while it's operating).

My plan is to solder (through-hole) components directly to each other, then insulate everything (with heatshrink tubing or electrical tape) as much as possible, then use screw-type cable joiners to connect the power cable.

I know I can't use traditional prototyping tools such as breadboards and stripboard for mains voltages, but what can I use to make prototyping at mains voltages easier?

(To be clear, 'mains voltage' in my area means 230V AC +10/-6% at 50Hz; GPOs are generally rated at 10A.)


texts: How efficient is a capacitive power supply?

texts:
Something like this

Falstad sim version of it

(I'm tired, I keep making mistakes, so please excuse me for the second time.)

Now these are not very safe PSU's, due to the lack of isolation. But in sealed units, they can be a cheap way of getting the supply voltage for a microcontroller without an SMPS or transformer.

They are not 100% efficient due to the zener and resistors. But, I have several questions.

How does the capacitor step down the voltage, anyway? Does it waste power as heat?
If the zener were gone and the output was let to float around 50V, would it approach 100% efficiency?


texts: Deriving resonance frequency of RLCC circuit

texts:
I am trying to determine the resonance frequency of an RLC resonator with added capacitor, as shown below:

simulate this circuit – Schematic created using CircuitLab

Two cases are easy to determine:

$$Rp=0 \rightarrow \frac{1}{\sqrt{LsCs}}$$
$$Rp=\infty \rightarrow \frac{1}{\sqrt{Ls\left(\frac{1}{1/Cs+1/Cp}\right)}}$$

Now I'd like to derive a formula that includes Rp. How should I approach this?


texts: Generating the hardware delays using timers in STM32F2

texts:
I am new to this controller STM32F2xx.

Here is my code, this code was given by my senior. It is working, but I don't understand how to calculate the prescaler and ARR value for 1ms delay.

Can anyone help me learn how to configure the timers so they can generate the hardware delays? Please explain in detail.

#include "stm32f2xx.h"
#include "stm32f2xx_gpio.h"
#include "stm32f2xx_rcc.h"
#include "stm32f2xx_conf.h"
#include "stm32f2xx_tim.h"
#include "timer.h"

GPIO_InitTypeDef GPIO_InitStructure;

/* timer3 globalIntrupt  request */
void TIM3_IRQHandler(void)
{

  if(TIM3->SR & TIM_IT_Update)
  {
    /*clear interrupt flag */
        TIM3->SR = (uint16_t)~TIM_IT_Update;
        GPIO_ToggleBits(GPIOC,GPIO_Pin_5);
    }

}

int main()
{

    timer3_Init();

    RCC_AHB1PeriphClockCmd(RCC_AHB1Periph_GPIOC,ENABLE);

    /* filling the members of the GPIO_InitStructure */
    GPIO_InitStructure.GPIO_Pin = GPIO_Pin_5;
    GPIO_InitStructure.GPIO_Mode = GPIO_Mode_OUT;
    GPIO_InitStructure.GPIO_Speed = GPIO_Speed_100MHz;
    GPIO_InitStructure.GPIO_PuPd = GPIO_PuPd_NOPULL;
    GPIO_InitStructure.GPIO_OType = GPIO_OType_PP;

    /*configure the GPIOC */
    GPIO_Init(GPIOC,&GPIO_InitStructure);

    while(1)
    {
    }

}

void timer3_Init(void)
{

  RCC->APB1ENR  |= RCC_APB1ENR_TIM3EN;                              /* Enable timer3 clock                */

  TIM3->PSC   = 30000-1;
  TIM3->ARR   = 2-1;
  TIM3->EGR   = 0x0001;
  TIM3->CR1   = 0x0001;

  NVIC->ISER[TIM3_IRQn >> 0x05] =
                        (uint32_t)0x01 << (TIM3_IRQn & (uint8_t)0x1F);        // enable interrupt
  TIM3->DIER  = 0x0001;                                               // enable intrerrupt

}


texts:
I have connected circles, but I dont know what is this exactly and do I need them on a PCB?

thanks for feedback.


texts: RF Isolator or Circulator for Commercial Product

texts:
Circulator and specifically isolator are used in microwave system to prevent unmatch load damage the transmitter.

As circulator that I seen are very bulky I'm started to think how commercial product like WiFi Access point or LTE modem prevent damage from disconnecting antenna from SMA connector? what small footprint SMD part can do this?

I'm suspecting that as the transmitted power is < 30dBm the transceiver IC can bear with the reflection.


texts: High Voltage ADC Measurements using a PIC and OpAmp

texts:
I need to make a device to measure voltage of a series stack of capacitors which will reach a maximum of 100V (DC only).  On the schematic I have omitted several from the stack, balancing circuitry and the PIC support devices (xtal, decoupling), for simplicity of getting my point across.  Each cap will have 5V max across it (in house made supercapacitors if you are interested!).

As the dynamics are quite fast, my usual Arduino solution just isn't quick enough so I am back to the old days of PICs, which I haven't touched for many years!  1-10ms for all 20 channels in total, ideally.

In order to measure the high voltages I assume a simple resistive divider would suffice, however this would need to be as high an impedance as possible so as to not skew the readings and require high power resistors.  This puts the impedance well over the max 10k for the PIC I am using (PIC18F25K83).  The PIC is running at 5V.

Current thinking, using this as inspiration, is to use an opamp to buffer the output.  Not used opamps before.

Is there anything glaringly obvious that would make the magic smoke appear, or is there a better solution?

EDIT: Image cropped as requested.  Quantified how fast.


texts:
I have a sheet of annodized metal that I need to connect a wire to. In the past I have tried wire glue and soldering but each are really ineffective in their own ways. Soldering is slow and best for one-off projects while wire glue becomes less effective or breaks over time.

What I would really like to try next is some kind of alligator clamp or paper clip or screwhole attached to a clamping mechanism. A wire would go in, I would screw it down, and at the other end there would be a clamp against the piece of annodized metal. Annodized metal is annoying to solder to but still conductive, so this should work ?

The annodized metal is only about ~4mm wide and 1mm thick. So I would really like to find a product category on Digikey or Mouser that is able to fulfill this need.


texts:
I was curious, what is viewed as the practical upper frequency limit of circuits using discrete components?

It's well known a 20Ghz oscillator is hard to design using discrete components due to the parasitics but very easy to design in an IC because such parasitics are dramatically smaller in magnitude.

So what is viewed as the practical upper frequency limit for discrete circuit design?


texts: What can shock you in an unplugged electronic device?

texts: I'm trying to do maintenance on my stereo system and I know that capacitors will hold an electrical charge, but is there anything else that could shock me? I'm not sure this is the right place to ask this, sorry if its wrong.


texts:
I want to create a circuit that has an input of the form v(t) = A + Bsin(wt) where f is between 20Hz and 20kHz and B is between 1 and 6 V. How would I create a circuit that outputs the same amplitude regardless of the input amplitude using only op amps, diodes, capacitors, inductors and resistors?

Thanks.


texts: Power Amplifier Bypass Switch Convention?

texts:
I have an RF power amplifier (PA) for a transceiver module I'm designing. My transceiver is capable of outputting +14 dBm at the 915 MHz ISM band and the RF PA will be used to further amplify the output to +30 dBm. When not requiring the 1W output power, I would like to use the shutdown mode of the PA.

Would it be possible to have a SPST RF switch with one end connected on the RF input to the PA and the other to its output to bypass the PA when shutdown? Will this affect the RF too much (if so, how)?

The other option would be to have two SPDT RF switches to create separate RF paths - except this adds an extra 0.5 dB insertion loss.


texts: How to decrease 83v 17ah DC battery to 72v?

texts:
I purchased a 72v 20ah battery pack for my electric bike. When the battery came, I tested the voltage and amperage and found that the battery came to be ~83v and ~18AH. My bike's controller can't function properly with this overvoltage, so I need a way to decrease the voltage to the intended 72v, while trying to keep the AH as high as possible. Is there any way to achieve this? Maybe by the use of resistors? I really don't know where to start.

Thanks!
Dave


texts: Why NAND FLASH is slower than flip-flops?

texts:
I find that both NAND FLASH and flip-flops are made up of NAND gates. The only difference between them is NAND FLASH uses floating gate transistors to store charge.

Your Flash drive is actually made up of NAND FLASH and cache memory which has speed equivalent to CPU is made up of flip-flops.

My question is if both operates at 5V and both are made up of basic cell unit NAND gates then what makes flip-flops so faster than Nand-flash? Or What makes Nand-flash slower than flip-flops (probably due to floating gate transistors?) ?

In other words what makes cache memory so faster than a flash drive? The drift velocity of charge in both the architecture must be same as 5V is used for them.


texts: Repurposing or obtaining a cheap audio signal amplifier for school physics lab

texts:
I teach highschool physics, and want to connect my smartphone (LG V20) to a Chladni plate (vibrating plate for studying interference patterns in sound in solids).

I have successfully done this by connecting a standard 3.5mm male-to-male lead to the phone, and crocodile clips on the other end, connected by 4mm leads to a vibration generator with the Chladni plate attached.  This works, and I can play tones and even music through the Chladni plate, and see interference patterns start to form.

However the amplitude is far below what I need.  I have a signal generator with amplifier which works well, and provides a peak output of around 6V; the speaker cable sending the same signal provides around 0.4V.

I therefore need a signal amplifier, ideally that inputs and outputs on 3.5mm or 4mm, and outputs with a variable setting up to around 20x.  I know almost nothing about electronics, and the school doesn't have a tech lab, but I do have an old Marshall G10 Mk2 (10W guitar amplifier) .  I would like some advice on how to cannibalize this speaker/amp to achieve my aims.

I did already connect these, attaining an appropriate voltage, but the quality was very poor - a lot of hissing and apparently poor connections.  I'm unsure if this is to be expected, or a sign of a problem with the amplifier.  The speaker in the Marshall is broken, but may be fixable.


texts: In Altium Designer, how can you set the autotracer to route all traces with as equal lengths as possible?

texts: Note that this board does not require a power or ground plane, since it's just used to bridge two boards. I want the traces to be as equal in length as possible in order to minimize any difference in voltage propagation speed between any two traces. Thanks.


texts: Is it better to use discrete components or voltage regulators for a variable power supply?

texts:
I'm a recent graduate EE student and this is my attempt to gain experience and strengthen my resume so I'm eager to figure this out. I'm designing a dual channel floating output bench power supply that will supply 0-32V @ 5A with CC and CV operation modes. I intend on this being a long-term solution so I'm aiming for good power efficiency with a clean output signal. The safety and protection features I plan on including are a microcontroller based emergency thermal shutdown, reverse current protection, overvoltage protection, and of course a fuse.
At first I intended on creating it using IC voltage regulators: switching pre-regulation + second stage linear regulation. My plan was that the switching output would match the linear output to minimize power loss in the linear regulator. The problems with this are wildly varying CC under load and difficulty finding regulators with the desired specifications.
Having decided to check out the few schematics for commercial bench power supplies that I could find, I noticed that they don't seem to use IC voltage regulators at all! This leads me to wonder if it would be easier to create the linear regulator portion with discrete components instead of ICs. I've been having trouble finding resources which discuss the best methods of PSU design so I wanted to come here for a second opinion.
Which method do you think is the best for me to create my desired product? Switching + linear, switching + discrete or something else?

The post here Integrated voltage regulator chip versus discrete circuit utilizing op-amps and power BJTs for DIY bench power supply poses the same question but it doesn't look like there was an answer to the actual question. I looked at it and it seems like they just discussed the safety of using a negative reference voltage.


texts: Driving 34 White LEDs in Series with Linear CC Source with 110V Mains

texts:
I have 102 White LEDs in total and I want to drive them from the 110V  rectified Mains in 34S 3P configuration.
  Here's the graph about the LEDs (Red Line).

I want to pass only about 50mA through them so that they remain cool because they would be mounted on a flexible material with minimal heat-sinking.
  They would require output power from IC -- One Led = 3V x 0.05A = 0.15W
  102 Leds 0.15W x 102 = 15.3W
Now I have chosen an appropriate mains rated LED driver for these LEDs (Transformer Less non isolated type, low flicker, high PF, Low EMI etc). And while I was designing the circuit and reading the power dissipation of the IC
it showed power dissipation from 2W to 3.5W from best to worst case scenario.

That's when I thought why not design a linear constant current source for mains voltage to drive the LEDs because when I thought about it it did made sense.
Best case scenario: Led driven at 3V @ 50mA each, 34 Leds in series = 102V
3 parallel strings total current = 200mA
Power Dissipation = 110V - 102V = 8V and 8V x 0.2A = 1.6 Watts.
Worst Case: Mains Voltage reaches 130V and thus
Power Dissipation = 130V - 102V = 28V and 28V x 0.2 = 5.6 Watts.

So I personally think that in this case the Linear Approach offers a lot of advantages like very low EMI, low flicker and can be made compact as well because space is limited.
Something like this:

Thus I have two questions:
1. I know the advantages of this approach but I do not know the cons when you compare it to any transformer-less switching IC like the ONSemi FL77944 so any help would be appreciated.

2. I search for this kind of implimantation on the internet but was not able to find anything like this, and it is a fairly simple approach but why are manufacturers avoiding this kind of approach for high count LEDs in Series. Is there something I am missing?

Edit:
1. There is very limited volume to place the PCB like 12 cm3.
2. As @Transistor pointed out I forgot to considered the variation in the AC how that would affect the efficiency.
3. The PCB would be encapsulated and sealed in something like a potting compound.
4. The Driver I am considering to use is Seoul Semiconductors Nano driver SMJR-N-1-24 so any info on how to connect those string to this driver would be helpful and as this driver also does not require an isolation transformer then would that meet the commercial requirement?
5. I am now abandoning that idea and would like that off the shelf solution like the Nanodriver because there are a lot of factors involved that I had not considered and would likely mess something up.
6. Also what are those different currents in mA in the graph below.


texts: Detecting an open circuit by sensing current flow using a shunt and comparator

texts:
I need to detect if a load resistor is taken out of circuit. The load resistor is a photoresistor and can vary from 50k\$\Omega\$ up to 2M\$\Omega\$ and is driven by +5V to ground.

The approach I thought of was to put a small sense resistor between +5V and the load, and use a comparator to detect the voltage drop across the sense resistor. When current is flowing, there will be a drop across the sense resistor, one comparator input will be higher than the other and so the comparator output will go to (say) +5V.

When the load is disconnected, there is no drop across the resistor, and so the comparator inputs are (very close to) equal. However, I can't be sure if the output will switch to ground, since the output state of the comparator is undefined when the inputs are equal.

Is there a simple way to add a tiny offset so that the comparator switches at (say) \$ V_+ > V_- + offset \$? That would allow me to guarantee the comparator output when the inputs are equal. I don't want hysteresis here but just an offset to the point where the transition happens.

Alternatively, is there some other way to solve this problem? Basically, I want to detect the difference between even a small current flowing and no current flowing.

Edit: Especially to those who suggested the wheatstone bridge, what if the photoresistor varies from 50k\$\Omega\$ to 50M\$\Omega\$? At the higher end of that range, the two inputs to the comparator become very close to being equal again... If I use a gigantic (i.e ~50M) resistor (R3 in @markt's diagram) in the static arm of the bridge to compensate for the larger load range, then V- is going to be very, very close to rail; when the load is disconnected, the two comparator inputs are again very close to being equal to each other.


texts:
I am looking for the formula to convert the power level of an OFDM RF signal to an absolute power level.
For example if I have my typical rectangular RF spectrum and the bandwidth of the signal is 10MHz, if my signal power needs to be 23dBm, what power do I need to measure on the plateau of the rectangular OFDM signal?

For example I saw a measurement function in a spectrum analyser where you could bring up markers and it would give an RF power level measured across that bandwidth, I remember seeing the waveform peak at about -20dBm but integrated across the bandwidth the power level came out to be around 1dBm.

I would like to know the formula. if I know the bandwidth of my OFDM signal and know what power level i need to reach, what level should I measure at the peak of my RF signal?


texts: Practical consequence of the noise spectral density

texts:
For a particular current transducer,
http://www.digikey.com/catalog/en/partgroup/ho-p-sp33-series/49533,
it states an "Output rms voltage noise (spectral density)" of 6.13 uV / sqrt{Hz}.

If the frequency of interest is from 1 Hz to 100 Hz,
what would be the resulting peak-to-peak voltage variation of the output?

Would it be:

,

meaning the resulting output voltage of the transducer is likely gonna vary by ~403uV peak-to-peak from noise within the transducer?

(NOTE: The 6.6 presumably is some number related to statistical probably of the resulting peak to peak voltage)


texts:
I'm a photographer. A friend of mine gave me two big flashes, which I can use without grit. There is a generator, which generates 300-320V DC from 12V DC. This voltage loads the capacitors directory inside the flashes.

The big problem is, because of this he donated the flashes to me, the generator is oscillating in a very annoying audible whistle.

Now I'm searching for a circuit, to transform 12V DC or the better 24V DC (2 lead accumulators) into that 300-320V DC. The flashes are 300 Ws each. I hope it's possible to load them together in less than 4.5 seconds.


texts: I have an RF repeater (for an alarm system) that requires a 12VDC 100 ma power source. If I use a transformer/power supply that rated at  12VDC 500 ma, will I do any harm to the RF repeater or the power supply?  From high school electronics class, I think I remember that this should be OK -- but I just wanted to check.


texts: LC Filter / Matching - Why does this cap help?

texts:
this is my first question on the site, so please let me know if there's something I can do to write it more helpfully.

The Problem: I'm building a small radio. At the output of my mixer, I need to build a narrowband filter at 455 kHz, and also convert the signal from double-ended to single-ended.

My Solution: Build a resonant LC filter that feeds a balun transformer. I first tried a shunt LC tank, which worked okay. But I realized that the filter was heavily dependent on exact L and C values, so I decided to try tuning it with a varactor (which would allow me to use L's and C's with looser tolerances).  Unfortunately, varactors are very small, and the parallel inductance of my transformer placed a limit on how small I could make my capacitors.

So I decided to try out a series LC. Unfortunately, this put the mixer's \$R_{out}\$ in series with my inductor, which destroyed my Q. I was about to give up when I read this SE answer, which seemed to suggest that I could match a high impedance by adding a shunt capacitor.

On a whim, I threw in a 100nF cap... and it worked perfectly! My Q and insertion loss are both much better. But... why?

Here's my (simplified) circuit:

V3+R3 is my source, C5+L3 is my filter (L3 has \$R_{series}\$ = 250 mOhms), and L4 is my transformer ( \$R_{series}\$ = 75 mOhms).

Voltage across L4 without C6:

And with C6:

Learning is the goal of this project, so any advice / additional resources would be welcome. Thanks!


texts: Charging 3.7V battery from 300W+ generator

texts:
I am doing a project involving a bike generator of 500W. All of my previous projects were small LiPo battery powered devices so I want to double check certain aspects of this relatively high power project with people who might know more.

All the basics are in place, the generators output is rectified and so on. The main issue I'm having is the dc/dc buck converter LMR16020 which is connected to a battery charger MCP73812 to charge 3.7V LiPo. The dc/dc out is at 5V and according to the datasheet of LMR16020 the max current output is 2A. So the max output power in this case is 10W.

Now assuming there is a constant 5W load connected to the output of the buck converter, to prevent issues when no battery is charged, and the MCP73812 battery charger is charging with a total of 400mA (battery charging current and the required supply current for the unit, the value is hypothetical). This should get us to a total load of 5W+2W=7W on the buck converter's output. For the sake of simplicity let's assume that there are no losses in rectifier and a dc/dc buck converter.

If this is all that is connected to the generator is it safe to assume that the output that generator sees is 7W and the buck converter is safe from high current damage? Since it's a bike generator the 7W load should only affect the difficulty to turn the rotor. And since it's a small load it should just be easy to rotate. The current of the generator should be determined by the load of the generator if I'm not mistaken.
If the output voltage of dc/dc is increased via FB resistor adjustment the max power that can be connected to the buck's output would increase because P=I*V? This is assuming the input power and voltage are high enough. In this exact scenario a different charger might be needed but that's besides the point.

I'm aware that some components and the generator are not ideal for the application, but they are the things that were "laying around" and they seem to meet minimum requirements for the project. There will be additional loads on the generator so this isn't a case where a 500W generator is used to charge a LiPo battery, it's just the aspect of the project I'm least certain about. I'm also aware that this isn't some unique or difficult concept, but I could't find the exact answer to this and as mentioned before I haven't done anything with this kind of high power so I would prefer to be called bad at searching or stupid than ruining components or generator in any way.

My main worry with the high power is that for whatever reason the dc/dc circuit will take the some of the extra power and fry itself and it's load. In previous projects LDO converters were enough so the dc/dc converter experience is lacking.

Edit1: Don't have the model or datasheet of the generator, but its fairly similar to
this


texts:
I am working on a breaboard prototype involving an Arduino; it used to work fine (connection point (a)) until last day when SCK went missing. Or not missing but distorted; sometimes the logic analyzer would not catch it at all. As a result I always read back zero via SPI (probably written garbage as well).

The setup:

ADC part soldered to an adapter PCB (the green one)
which further connects to a copper breadboard through some thick pins (sacrificed paperclips)
which connects to a strip of standard 100 mil female connectors through some soldered wires on the breadboard
which further connects to Arduino pins through some wires

The problematic thick pin is pictured as a red wire running from it to its 100 mil standard female connector.

Problem

The only way I can get my SPI communication up again is by firmly pressing a female wire against the thick pin in spot (b). Doing the same but in spot (c) does not work. The fix is temporary; as soon as I move the contraption around SCK connectivity goes flaky again.

Tried

changing SCK wire between the black connector and the Arduino
continuity test with my DMM on all the SCK track

Why am I seeing this behaviour ?


texts: Bitwise operators: Whats the difference ^= vs &= ~(smthg)?

texts:
I'm coding for microcontrollers and I've come across two styles of bitwise operations that quite confuse me a lot because they are used interchangeably.
First let's assume our REGISTER has 4 bits; bit 0,1,2,3. The default value of REGISTER on reset is 1100.

1.what the difference between:

REGESTER ^= (1<<3) | (1<<2);

&

REGESTER &= ~( (1<<3) | (1<<2) );

2.Is the first one correct? ( I'm not certain that it's correct )

3.If the first one's correct, then why use the second statement as the resulting value is same as the second one?

Final Result: 0000


texts: I have a portable clock radio that uses two 1.5v batteries, [3v total, obviously], & has an optional 3v, 300ma, [center pin -], DC adapter input on the side.  I found a 3.7v, 340ma DC adapter at a thrift store, & would like to know if that difference would harm the unit.  I think the 340ma part is ok, as that's just the maximum output rating for the current load on the adapter, but the 3.7v part is what concerns me.  Any input would appreciated.


texts: Why should any unit be used instead of the watt (W) as a power unit?

texts:
I am taking a course on AC circuits and so far I have seen that for the different types of power (read real, reactive and complex) different units are used.

For the real power, which is power in fact dissipated by the system, the SI compliant watt is used. I am very much in agreement with this.

However, for reactive and complex power the equivalent SI derived unit volt-ampere is used. In the special case of reactive power, a lowercase "r" is appended.

Now, I wonder: why should any other unit be used instead of watt, if the purpose of the unit is to specify the type of magnitude of a value? Moreover, why should a symbol be appended to the unit when its use is simply that of a reminder?

Also, is there a reason why using watts for reactive power would be considered wrong?


texts: How do I get ngspice to output the values of the variables in batch mode?

texts:
I have a relatively  simply netlist and I want to know the node voltages/currents through all components.  The netlist is:

circuit2
V1 0 4 dc 10
R1 0 1 2k
R2 1 4 4k
R3 1 4 2k
R4 1 2 6k
R5 2 3 10k
V2 3 4 dc 20
.dc v1 10 10 1
.end

I try running this in batch mode with the commmand

`ngspice -b -r circuit2.raw -o circuit2.log ../../circuit2.cir'

and my .raw file just has the variable names, but not their values:

Title: circuit2
Date: Thu Aug 03 10:16:31  2017
Plotname: DC transfer characteristic
Flags: real
No. Variables: 7
No. Points: 1
Variables:
    0   v(v-sweep)  voltage
    1   v(4)    voltage
    2   v(1)    voltage
    3   v(2)    voltage
    4   v(3)    voltage
    5   i(v2)   current
    6   i(v1)   current

How do I get it to say "i(v2) = whatever" instead of just naming my variables?   Is it also possible to get the currents/powers through all of my components in a similar way?


texts: Impact of the channel length on the threshold voltage in CMOS transistor?

texts: Is there a monotonic relation between the channel length and threshold Voltage and is it proportional or inverse?


texts: Easiest way to add Bluetooth communications to a Microchip PIC project

texts:
We are at the tail end of a development project that is currently based on the PIC12F683 microcontroller.  Fairly simple project: a couple of A/D channels, a bit-banged DC-DC converter, an output firing stage that uses IGBTs.  The prototypes are working well.
Now that we are about to deliver the final design, the client has made two requests.

Add another A/D channel.

Allow field programming of the A/D threshold values using Bluetooth connectivity.

The first request is easy - simply migrate the current code to the PIC16F688.
The second request is also fairly easy - we can get serial comms using the EUSART module in the '688.  That would be fine if we wanted to use wired comms (either Serial or USB).
But the client has specifically requested Bluetooth.  Moreover, I am certain the customer is also going to ask us to develop apps that run on Android and iOS.  They haven't asked yet but I'm certain it will come.
I've been looking at the plethora of ready-made Bluetooth modules that are currently available as well as looking at migrating the entire project over to something like the ESP32.
I'm asking for advice and the easiest and most cost-effective way to proceed.
Something I should mention is that most of our products have extremely-long lifetimes.  I need to be able to source the parts our products use for 20 or 30 years from now.
Microchip makes that easy - to my knowledge, they have not deprecated any of their mainstream microcontrollers.  But I can't be certain that will be the case for 3rd-party Bluetooth modules.
Advice greatly appreciated


texts: MOSFET not keeping charge - Help understanding

texts:
My question is simple: Shouldn't a MOSFET keep the gate charged as long as a negative or at least zero voltage isn't applied to discharge, i.e. turn the MOSFET off?

I am trying some experiments with power MOSFETs like IRF540 and IRFP450 applying 12V between gate and source for a moment, disconnect the voltage source (the transistor is disconnected from everything) and measure the voltage between gate and source. I expected 12V in the reading but my multimeter reads 0V. Did I understand something wrong? Is this normal or are my MOSFET broken?


texts: Issues with parasitic voltage at VIN of MCP73871 Li-Po charger

texts:
I'm currently using a MCP73871 (datasheet) to charge a LiPo battery and power my core circuit. However, I'm noticing parasitic power on my VIN pin even when no input is connected. This is affecting the circuitry before the battery charger.

I'm looking at ways to resolve this. One idea is putting a diode before the VIN pin on the MCP73871. My concern is that according to the datasheet, they recommend a value of Vreg + 0.3 for VIN. I'm not exactly sure what Vreg is - I'm assuming that is the regulated voltage my battery is being charged at. If so, knowing that I need to charge my battery at 4.2V, that would mean I require a minimum VIN of 4.5V. If I put a diode before VIN, the forward voltage drop means the voltage at VIN when connected would be 4.3V (which is less than 4.5).

Does anybody know if this is a legitimate concern / issue, or would the MCP73871 work properly? Am I reading this datasheet wrong?

Also - if anybody has any alternative suggestions to combating the parasitic power at the VIN, I'm all ears


texts: Peak detection comparator simulation problem.(Process and no VSS version)

texts:
Here is a peak detection comparator schematic and simulation,i have three question about them.

1.Why is there a high signal in C point,but not in A and B point?

2.There is VSS in this peak detection comparator schematic,is there a peak detection comparator schematic without VSS in it? I connect it with gnd,but the wave is wrong.

(1) peak detection comparator schematic

(2) peak detection comparator simulation

The purple line is the \$V_{PZT}\$,and the blue line is the \$V_D\$,the red one is the output of comparator,that is ,\$V_{CP_PK}\$


texts: Can no-connect pins on EEPROM ever be connected to VCC or GND?

texts:
I created a circuit in which all the address inputs of an AT28C256 are connected to outputs of shift registers (74HC164).

In the future I will do many of these circuits, however I haven't yet decided if I need the full 32KB of memory.

Let's just assume that I later decide I need only 8K of memory for my application (for example, AT28C64).

After looking at the datasheets, I notice the difference in pin-out between the two chips is that on the AT28C64, A13 and A14 are replaced with NC (no connects).

Is it OK anyway to connect such pins to outputs of shift registers (and be able to make a AT28C64 like a drop-in replacement for AT28C256) or are the NC pins internally connected to something?

All chips in my question are DIP ICs.


texts: How does the current flow in purely inductive circuit?

texts:
Consider the equation

$$
 E = -L\,\dfrac{di}{dt}
$$

The negative sign in the above equation indicates that the induced emf opposes the battery's emf.

If we're talking about a purely inductive circuit, the induced emf is equal and opposite to applied emf. Isn't it just like two identical  batteries in opposition?

If that's the case, how does the current flow?

The expression for inductive reactance and the relationship between current and voltage in an inductive circuit are derived from this equation which assumes that the circuit under consideration is purely inductive.

I always think that the current in an inductive circuit is only because of the resistance associated with the coil. If the value of resistance tends to zero,  the induced emf becomes equal and opposite to applied emf resulting in no net current.

Am I right? Is there anything I'm missing here? Please explain me in detail. :)


texts: Rotary switch to turn LEDs on cumulatively

texts:
Problem:
I have a 12 position rotary switch and 11 LEDs that I want to switch on one after the other until they are all on (on pos 12).

Limitations:
It would be easy to use a μC, but I wanted to keep this simple and the part count as low as possible

Things I tried:
In my head I planned on using a diode for each pin of the switch to connect it to the previous (works for about 2 leds) but forgot about the diode voltage drop that adds up.
And using a diode for every connection (about 66) is just to much of a mess…
@jonk explains this approach perfectly in his answer below.

Question:
Any elegant ideas what I could do to archive that?
I'm a beginner and probably miss something :)

Other ideas

I found cumulative rotary switches but they seem to be quite rare and I did not find one with 12 positions
Using an incremental rotary encoder to feed a two shift registers instead (would this work? / might be easier to cave and use a μC)


texts:
A polymer lithium ion battery is rated at 3.7v, 6600mAh and a maximum discharge current is specified at 3.3A. I take it this means the battery can be discharged at 3.3A and last for two hours since 6.6Ah/3.3A = 2 hours.

However, in addition to the above specifications, the battery has a nominal capacity of 6600mAh at 0.2C discharge. How does this extra bit of information affect my above calculation? I.e. How will it affect the battery life for a given current draw?


texts: Where exactly does the ground line go in an AC-DC power supply?

texts:
I'm working in the United States. I'm looking into working with mains power, and I cannot for the life of me figure out where the ground line connects. For example, a simple power regulator from mains power:

Assuming that I'm using the standard mains, there are three pins. Two are "hot", and one is "ground". I understand that the two "hot" pins carry the AC and the ground pin is used to divert current in the case of a short circuit (I think?).

I've heard people say that "ground" should be attached to the case.

Where do I solder the ground line, with a metal and a non-metal case?


texts: how do I implement a start timer in a digital circuit

texts:
In vhdl, I know how to code a start timer behavorially. However, if I have to implement such a counter to start based on a trigger, how could I implement such a counter?

My trigger is another signal that will be active for only one clock cycle.
I'm breaking my head trying to think of how this is done. I could add logic to check if my trigger is active high (1 and-ed to my signal) but then it will go inactive after 1 clock cycle.

I've seen counters with enable but I want to count and stay counting no matter what.


texts: How to sell excess electronic components for highest price with least effort

texts:
This question relates to Electrical Engineering with respect to the management of spare electronics parts after a production build of circuit boards.  This question is specifically not being asked on economics.stackexchange because I believe the best answer would be created by people in the electronics industry with direct experience in dealing with excess parts (rather than an answer based on general economics/business principles).

I have a reel containing 487 opto-isolators of part number G3VM-61ER that never got used.  I was hoping to sell them rather than throw them away.  I am not trying to sell them here, I just want to ask what the best way in general will be to sell them somewhere.

My objective criteria for "best" is that I get the maximum amount of money for the parts without spending a lot of time managing a lot of small transactions.  For the purposes of this question "small transactions" would be defined as under $100 each.  "Lots of transactions" would be defined as more than 20 separate sales.  Ideally I should not spend more than 20 hours total related to the sale.  All transactions should be completed within one year.

The parts were purchased from an authorized distributor and I have the original paperwork that shipped with the parts.  The parts are stored in their original packaging and were purchased less than one year ago.

Given the above, I was wondering what the best way to sell these spare electronic parts?

I see the following options so far.

1)  My research shows that these parts sell for about $20 each on e-bay or amazon.  It would be great if I could make that work because my total sale would be around $10,000.  The problem is that buyers on those sites would probably be people who just need one part to repair something (rather than a product manufacturer who wants to buy the whole reel).  My time is valuable and I could easily see myself wasting $10,000 worth of my time selling the parts a handful at a time.

2)  I have found several chip brokers online that would probably buy the parts.  Some examples include Online Components, Jameco, Quest Components, 4-Star Electronics, Chip 1 Exchange.  I could probably get one of them to buy the whole reel.  The only downside is that they will probably only pay 5 to 10% their actual value.  The price from the authorized distributors (Digi-key, Mouser, Avnet, etc.) is around $10 each for one and $6.00 each for 500.  That puts the resale value of my reel at about $2900.  Which means the chip brokers probably won't give me more than $150 to $300 for it.

3)  I could Design the opto-isolators into a new product.  Rather than getting money for the parts I could use them and avoid having to buy parts for another build.  The only downside is that I only have a limited amount of parts and these are fairly expensive opto-isolators.  If I need more than the 487 I have on-hand I would find myself forced locked into using this expensive part.


texts: AP4306 has paralleled two op amps in it's block diagram, is that possible?

texts:
Thank you for taking some time to read this.  I've recently come across a nice constant voltage/current source (http://www.mouser.com/ds/2/115/AP4306A_B_C-271586.pdf) called an AP4306.  Upon reading its datasheet, I was interested in the fact that it could potentially (I think) be used as a voltage comparator with a built in voltage reference.  I'm putting together a over-discharge circuit for a lithium polymer battery which will be done with a voltage reference, voltage divider, MOSFET, and an op amp.

My major hangup is this block diagram:

I'm not interested in actually using this device as much as I'm interested on why it can work when it's tying the outputs of those two op amps together, wouldn't that just make this device a magic smoke generator?  (Obviously not, but right now I don't know why)

Let me know what your thoughts are if you'd like, thank you for your time!


texts: Solving for RC circuit transfer function

texts:
How do I calculate the transfer function of this circuit? \$H(s) = \dfrac{V_o}{V_i}\$

I apply the Kirchhoff's law at the node \$V_x\$ but I still have \$V_x\$ as unknown :
\$\dfrac{V_x - V_i}{R1}+\dfrac{V_x - V_o}{R2}+(V_x - 0)sC = 0\$

simulate this circuit – Schematic created using CircuitLab


texts: Transfer Program to TI MSP430 (MSPF5308IRGCR)

texts:
I have a free sample of the TI MSPF5308IRGCR MCU and I want to program it.

Is there some simple way to transfer a program without having to invest in the relatively expensive JTAG? The JTAG is in the vicinity of $100 and looking at the tutorial for other microcontrollers such as Atmel, the program transfer modules available there are rather cheap, in the vicinity of $10.

Is it an inescapable cost to buy a ~$100 to start with a TI MSP530 for a newbie hobbyist? Or is there something rather simple that I am missing.


texts: Why use both high side and low Side diode-ORs for redundant power?

texts:
This question is in regards to an example application circuit that appears in the Linear Technology / Analog datasheet for the LTC4355, and is discussed in this article. The circuit uses ideal diode controllers to provide redundant power from dual power supplies in an AdvancedTCA application. While I'm familiar with diode-or'ing redundant power supplies (either with real diodes or ideal diodes), I'm used to seeing this on the high side only with low sides just tied together. I understand that AdvancedTCA uses negative supplies, and would therefore  understand low-side-only diodes... but why both?

The AdvancedTCA specification does not seem to address this. It mentions that fuses are needed both high side and low side, but does not seem to require both high and low side diodes.


texts: Is Phase shift limited between -90 to + 90?

texts:
In electrical engineering power systems I see several times a voltage or current in instantaneous form, as follows for example:
For the current"
i(t) = I cos(ωt + 3π/4)
And the voltage as follows:
v(t) = V cos(ωt)
However, it's known that the maximum phase shift is:
+90 degrees for a pure capacitor circuit where the current leads the voltage by 90 degrees phase shift.
-90 degrees for a pure inductor circuit where the current lags the voltage by 90 degrees phase shift.
So, how would the phase shift be more, since 3π/4 = 135 degrees?


texts:
The tracks used as an edge connector are gold coated to improve contact with the female connector: bare Cu oxidizes, and also wears out if they are inserted and removed repeatedly. Au cannot be applied directly to Cu, so electroless Ni + immersion Au (ENIG) is used.

Well, the question is: since Ni has good resistance to abrasion and oxidation, why are never edge tracks plated with Ni only? I don't think it's because of the lower resistivity of Au: with or without Au there are always the microns of Ni in the middle, practically no resistance. And female connector contacts are also Au coated.

Anybody knows? Thank you!

I am NOT answering my question. I am writing here just because I needed a place that is common to all contributions.

My real need was not exactly about edge connectors, but making printed contacts for a sliding switch, this will be to choose tuned circuits for a 'ham' receiver. I aim to make the construction easier for the DIY builder, that's why I looked forward to avoid the gold process, not because of cost but added complexity.

I am delighted to have been quickly and correctly informed in my very first tour into StackExchange. Thanks to everyone!


texts: How can I add additional components and connections to make this USB hub functional?

texts:
I started designing a simple 4 port USB hub based around the FE1.1S IC. Using the datasheet, I managed to connect connections to almost all the pins... but there are some that confuse me. Schematic included at the end.

Is the EEprom necessary, and if so, what IC should I use?
What voltage do the status LEDs receive?
Do I use a voltage divider or a linear regulator for the three voltage levels required on pins VDD5, VD33, VD18? (I have put in two voltage dividers for the time being)
What do I need to do for pins VD18_O and VD33_O?
Why does the datasheet say for pin REXT (14) that I need to "A 2.7KΩ (± 1%) resister should be connected to VSS to
provide internal bias reference.", Do I have to connect a resistor between REXT and VSS?
What other connections and components do I need on the other pins to get the hub functional?

Schematic:

Also, Here is the PCB design that I have in mind:


texts: USART2 Rx not working, Bluepill / STM32F103C8T6

texts:
I'm using Libopencm3, USART1 and USART3 are working fine, but the USART2 makes problems.
I can send bytes, when i get one, the IRQ handler function is called, but using usart_recv() i get nothing, do i need to do more configuration for using USART2?
TX = PA2
RX = PA3
Here my code:
void usart2_isr (void)  {
    static char data = 1;

    /* Check if we were called because of RXNE. */
    if (((USART_CR1(USART2) & USART_CR1_RXNEIE) != 0) &&
        ((USART_SR(USART2) & USART_SR_RXNE) != 0)) {

        /* Retrieve the data from the peripheral. */
        data = usart_recv(USART2);
        // ECHO
        usart_send(USART2, data);
    }
}

void UART2::setup() {
    rcc_periph_clock_enable(RCC_AFIO);
    rcc_periph_clock_enable(RCC_GPIOA);
    rcc_periph_clock_enable(RCC_USART2);

    /* Enable the USART2 interrupt. */
    nvic_enable_irq(NVIC_USART2_IRQ);

    gpio_primary_remap(
        AFIO_MAPR_SWJ_CFG_JTAG_OFF_SW_ON,
        0);

    gpio_set_mode(GPIOA,
    GPIO_MODE_OUTPUT_50_MHZ,
    GPIO_CNF_OUTPUT_ALTFN_PUSHPULL,
    GPIO_USART2_TX);

    gpio_set_mode(GPIOA, GPIO_MODE_INPUT, GPIO_CNF_INPUT_FLOAT, GPIO_USART2_RX);

    usart_set_baudrate(USART2,9600);
    usart_set_databits(USART2,8);
    usart_set_stopbits(USART2,USART_STOPBITS_1);
    usart_set_mode(USART2,USART_MODE_TX_RX);
    usart_set_parity(USART2, USART_PARITY_NONE);
    usart_set_flow_control(USART2, USART_FLOWCONTROL_NONE);
    usart_enable(USART2);

    USART_CR1(USART2) |= USART_CR1_RXNEIE;
    usart_enable_rx_interrupt(USART2);
}
```


texts: Translate logic gates into logical expressions

texts:
I’m trying to understand the conversion of this particular logic gate to prove satisfiability.

I know the basics—AND, OR & NOT and also how the truth table works. I have this solution but I don’t understand this particular one is derived. Any explanation would help...

I want the logical expression not the evaluation of the logic table , for eample ((x1 OR x2)) AND (~(~x3)....


texts: How does the \$Q\$-factor of a parallel RCL circuit scale with the inductance?

texts:
I want to be able to show in an expression that the $Q$-factor of a parallel RCL circuit scales with the inductance. If we remind ourselves of a RCL circuit:

simulate this circuit – Schematic created using CircuitLab

The \$Q\$-factor is defined as
$$Q = \frac{\omega_{0}}{\Delta\omega} = 2 \pi \frac{E}{\Delta E}$$
and is a statement about the amount of energy lost from the system in one cycle of oscillation. With $$\Delta\omega = 1/ C R$$

The resistance \$R\$ can be shown to be
$$ R = \omega_0 Q L$$

The resonance frequency, \$\omega_0\$, scales as
$$\omega_0 = \frac{1}{\sqrt{C L}}$$

If I think about what happens physically, it makes sense that the energy stored in the system is defined by the inductor -- this is also what my experiments have shown. If I increase the inductance then I increase the \$Q\$-factor.

I'd like to be able to show the a function that describes the \$Q\$-factor as a function of \$L\$: \$Q(L)\$. This seems easy enough but I encounter circular problems because the \$Q\$-factor is embedded into many of the definitions I have listed, the resistance \$R\$ is especially problematic.


texts:
There is no problem with uploading program on the first chip by using Arduino IDE.

However, the following chips doesn’t work. Status is shown as uploading and it hangs there. I think it could be because datasheet says 20Mhz for these. if so, how can I use them? Why doesn't it work?
Thank you for help.

I have posted my question here and also on the arduino forum.


texts: Using Arduino-UNO to control LED pins Greater than the Number of I/O Pins

texts:
Our class have been given a project to create a miniature of our department building. It will have 11 laboratory rooms, 1 server room, 1 faculty room. Each laboratory room will contain 18 pc's, each one represented by an LED. Server and faculty room will each have 3 LED.

Now each group of 3 LED's must be controlled individually using a computer program. So that's 68 groups of LED that needs individual control.

We are planning to use an Arduino UNO which have only 13 I/O pins. Is there any way to use those 13 I/O pins for 68 separate controls?

The deadline is near and we're in quite a pinch. Any answer will be tremendously appreciated, thank you in advance.


texts: Is there a paradox in the superposition principle?

texts:
I came across this problem for the first time when I started thinking about the clever circuit of Howland current source (see What is the brilliant idea behind the Howland current source?). Let me explain what this is all about with a simple example.

Imagine a simple current source assembled by a voltage source V1 and resistor R. At best, it would be short connected, and the current would be simply I = V1/R.

Unfortunately, it is loaded by another voltage source V2 with lower voltage... and the current decreases. We can explain why in two ways - in terms of voltages and in terms of currents.

First we can say that, according to KVL, the effective “current-creating” voltage VR = V1 - V2 across the resistor R decreases… аnd this decreases the current I = (V1 - V2)/R. That is, the current decreases since another opposing voltage is subtracted from the initial voltage.

But with the same success we can say that, according to the superposition principle, the current decreases since another opposing current I2 = V2/R is subtracted from the initial current I1 = V1/R.

If we replace the voltage source V2 with a resistor R2, we can continue to think the same way… but in the second case we will not be able to make physical sense of what is happening.

That is right, because the superposition principle assumes at least two sources… and here there is only one. The load voltage V2 cannot create current I2 = V2/R1 since it is zero when V1 is zero. That is, this statement makes no physical sense.

At the same time, the principle of superposition is formally valid… and this is the paradox…

I still have an idea of how to see physical meaning. If we measure V2 and replace the resistor R2 with a voltage source with the same voltage, nothing will change… but it will make some physical sense.


texts:
I use an LED installation for night lighting that uses 2 R6, 1.5V batteries.
I want to give up buying batteries and for that, I bought a DC power supply that gives an output voltage between 3 and 12V. I set it to 3V.
I connected the power supply to the installation and after a few hours a light bulb burned out.
What I noticed is that the light is stronger if I use the power supply compared to the batteries (so I can deduce either that the batteries are older or that the power supply does not output 3V a little more).
What can I do so that I can use the installation connected to the power supply? Does the power supply amperage have any influence?
Should I buy a better quality power supply?
Batteries are in series, not in parallel.
This is the power supply https://www.bueromarkt-ag.de/netzteil_goobay_eco-friendly_1000_ma,p-542901.html


texts:
I have an issue with an NXP SE95 temperature probe that has been working just fine up until now on other systems. At some point, either on boot or soon after, the probe will have some sort of meltdown and hold SDA low until power is cycled. I have a PIC microcontroller on the same bus and it is ok. I'm running at 3.3V (probe's voltage range is 2.8 - 5.5V)

I have two of them and both behave in the same way. They are connected to an OMAP4430 (Gumstix Duovero) through an isolating level shifter of this design:

Edit: This turned out to be a red herring and the lockup was unrelated to the level shifter.

I believe the 4.7k pull up is adequate here - it gives a rise time in the 700ns region. Not particularly fast but within spec. The Gumstix has pullups on about 1k0 so the 10ks are superfluous really.

I've used the same probe on a different ARM (at 3.3V, no level shifter) and from a PIC without issue. Is there something wrong with using a level shifter like this? I cannot see any reason why the probe should lock up. It does this without its own address ever being transmitted.


texts: Could this resistor be intended to do anything other than inrush limit?

texts:
Repaired a little board today that had a simple half wave rectifier on it. The capacitor had a resistor (R1) in series, that was obviously getting hot and wasting a lot of power. I assume the resistor is just to limit inrush, but it seems really inefficient. The board generates a DCish voltage from stepped down AC (12V) for driving a magnetic lock coil.

Schematic:

A quick analysis shows that if the load is reasonably constant current, and the capacitor voltage is fairly constant, then the average ripple current through the capacitor branch is the same as the load current. That means unless your load is equivalent to significantly higher than a 100 Ohm resistance, you're wasting half your power or more in that extra resistor.

Am I missing another purpose for that resistor? I've simulated the circuit waveforms, and can't see any desirable difference when the resistor is added.


texts: Connecting Atmel AVRISP to JTAGICE header

texts: I have an AVR board with 10-pin JTAGICE header and a 6-pin ISP. Can I somehow connect the ISP to program this board without having JTAG functionality?


texts: What functions do EMC filters in variable frequency drives serve?

texts: Most VFDs I've seen have EMC filters in them, though in many cases they're optional or can be disabled by the user. Exactly what function do these filters perform? What problem are they intended to solve or prevent? And under what circumstances would one enable or disable such a filter?


texts:
I can't find any definitive description of how oil-filled switchgear uses the oil and manages to keep it from ignition and boiling. For example, the Wikipedia article says

  Oil circuit breakers rely upon vaporization of some of the oil to blast a jet of oil through the arc.

which sounds rather strange. The arc will be very hot, so oil moving anywhere near the arc would likely be ignited or start boiling and neither is good for any equipment.

How is oil used in oil-filled switchgear without igniting and boiling?


texts: I used the "c2d" to discretize a transfer function initially but MATLAB automatically took it as zero order hold because I didn't specify any kind of hold. The result for the zero order hold is different from the expected result. I’m not trying to use any hold in my discretization. Is there a way I can do this?


texts: Using change in magnitude of accelerometer to calculate speed?

texts:
I have a wheel (say 60cm in diameter). And I am planning to attach a small board with an AVR and an accelerometer about 10-20cm from the centre.

As the wheel spins, I will get acceleration outwards. When the accelerometer is going up the wheel, it is going against gravity, while going down will be going with gravity.

In theory if I took the magnitude of the acceleration over time and I plotted it, it would look like a sine wave. Which I could then use to determine RPM and hence the speed.

My concern is that at 100 km/h (60 mp/h) that the change in acceleration would become too insignificant and I couldn't determine speed.

Any advice?

EDIT: The accelerometer isn't a necessity, the main objective is measuring the velocity.

EDIT2: I am after the velocity of the wheel. In either RPM or m/s (as i the speed as the wheel moves along the earth)


texts: Put outputs of 2 computer power supplies in series?

texts:
I've been working to figure out an LED lighting project for my classroom for a while now, readings on this site has helped. One part of the solution is to combine in series computer power supplies (which we can get free) to get specific voltages. This will help us use the ideal voltage for the different needs of the different LED strips. For example, By adjusting resistance to the correct lower value and also set the power supply to 8V, Red LED strips can go from around 50% efficient to better than 80%.

It's well explained on this site that you can not connect say the 3.3V and the 5V rails from a single computer power supply to get 8.3V since they share the same negative terminal. I remember some page here (can't re-find it) that talked about combining separate computer power supplies to get combination voltage. BUT, I wonder, wouldn't the separate power supplies actually have a common ground (the grounded wire on the plug?) If this is problem, any easy work around? Any better way to get about 8 volts using computer power supplies?

UPDATE: PICTURE SHOWS CURRENT SETUP:
Note that black wires (ground) are divided into 2 bunches and the yellow (12V) gathered into 1 bunch. Green and Black wire are connected (so that power is on) as per this instructable: I tested with an ohm meter and the mains earth ground IS electrically connected to the output DC power ground. Can I fix this problem?


texts: Understanding ECU Lowside Output Circuit

texts:
Hello StackExchange,
I'm trying to understand this low side output circuit so that I can interface it with a load.

I will have to add another MOSFET/Relay/Driver of some description on the lowside output given that the ECU this is from runs on 12V and the lowside outputs are only rated to 24V.
However the load is an 60V 1A Fan.
What is stopping the lowside load just grounding via the 110nF Capacitor when the IRLR3636 MOSFET is off?
Below is another schematic of a lowside driver from the same ECU Series, different model and they still have the Capacitor to Ground (albeit 10nF)


texts:
I have used the ICL7660 successfully to generate a -9V negative rail from a +9V battery.
I wonder how this works.
Between -9V output and +9V input there is suddenly an 18V difference.
Is the chip stepping up the voltage to do that? Is this effective at all, compared to, say, a dual full bridge rectifier generating a positive and a negative supply from AC?