texts: Shouldn't the output resistance of a class B amplifier include r_o?

texts:
If you apply the small signal T model to the picture above, and try to get the output resistance R_out, isn't there a r_o from each emitter to the collectors, which should be in parallel to the r_e resistances from emitter to base?

The output resistance should be (r_en // r_ep // r_on // r_op), no? I've seen in other sources that the output resistance of an AB amplifier is r_en // r_ep, for example:

This model is wrong, is it not? r_on and r_op should be from the collectors to the emitters, not from base to collector.


texts: What will happen, if we charge a battery with current, above its maximum charging current?

texts: If capacity of battery is 50mAh, and its fast charge capacity is 1C, then its maximum charge current is 50mA. If we are using 2500mA charger and charging the battery what will happen? whether we can program the charger to maintain charge current provided to battery?


texts: Instrumentation amplifier (weird layout)

texts:
I'm having a hard time figuring out how the following circuit works.

I studied the theory behind instrumentation amplifiers and from what I learned they are used to measure a difference between two voltage inputs and amplify the signal.

Now in the following configuration I don't understand the roles of the three amplifiers (for example, why is A3 buffering Vref?).

I'm not looking for a solution, but just an explanation of how it works.


texts: Can DC voltage on a DC relay switch an AC circuit?

texts:
Can I use a DC relay with 5VDC to switch a 120V highpowered circuit?

Thanks


texts: How Do I Limit My Motor Current While Maintaining Voltage Drop Across It?

texts:
I am trying to build my knowledge of working with dc motors by using an IRF510 MOSFET to switch a motor on and off. Please refer to the schematic below to see how I hooked everything up.

\$S_1\$ = jumper I used to toggle the gate voltage to \$0\$ or \$5V\$
\$R_P\$ = pulldown resistor (\$9.85k\Omega\$, measured)
\$R_M\$ = electric motor resistance (\$1\Omega\$, measured)
\$i_{DS}\$ = drain current (\$\approx750mA\$, measured)
\$R_{DS}\$ = drain-source resistance when MOSFET is on (\$0.6\Omega\$, from \$V_{DS}/i_{DS}\$)
\$V_{BATT, open}\$ = open circuit voltage of 9V battery (\$8.68V\$)

The first thing that put me in a loop was when the battery voltage dropped after closing the switch. I took some more measurements to get a grip on what was going on:

\$V_{BATT, closed}\$ = battery voltage when \$S_1\$ is closed (\$3.11V\$, measured)
\$V_{M}\$ = motor voltage (\$2.57V\$, measured)
\$V_{DS}\$ = drain-source voltage (\$0.54V\$, measured)

After some research, I determined that the voltage drop was due to the internal resistance of the battery. This is what I was able to figure out after some more calculations:

\$V_{R_i}\$ = voltage across \$R_i\$ (\$5.11V\$, from \$V_{BATT, open}-V_{BATT, closed}\$)
\$R_i\$ = internal resistance of the battery (\$2.87\Omega\$, from voltage divider)

My gut reaction tells me to use a voltage divider to maintain the voltage across the motor. I want to do this because my motor is rated to operate between 5V and 9V. I also want to add a current-limiting resistor in series to prevent the current from getting so high that it burns out my circuit and drains my battery. Ideally, I can achieve the desired \$V_M\$ if I add a resistor in parallel to the motor (\$R_P\$) such that the equivalent resistance of the motor and its \$R_P\$ (\$R_{EQ}\$) is much larger than \$R_i + R_{DS}\$. However, since \$R_M=1\Omega\$, the best equivalent resistance I can achieve is \$approx1\Omega\$, which puts be back squarely where I started. Furthermore, the series current-limiting resistor will take the lion's share of the voltage drop, thus robbing the motor of the voltage it needs.

How may I achieve the voltage drop I want and limit the current? Any help would be greatly appreciated. This is the first time I posted to StackExchange so I apologize if I broke any protocol.


texts: Questions Regarding Ground, Single Power Supply, & Dual Power Supply

texts:
I need some help wrapping my brain around what ground, single supply, and dual power supplies physically look like in a circuit.

I have an AC to DC wall adapter with a positive lead and a negative lead. I can consider this a dual power supply correct? If so, what would a single supply look like? A battery? How would I create a single supply from a dual supply?

Lastly, to generate ground, would I be correct to use a voltage divider as shown below in the schematic? R1 must = R2, but what value should I choose for R?

Thanks for your help.

simulate this circuit – Schematic created using CircuitLab


texts:
I am having trouble understanding the definitions for the transistor.
I am checking many different transistors and unfortunately every company has different words/symbols.
For example, in one company's transistor datasheet Io was the max output current, very easy to understand and Von was the voltage required to turn on/off the transistor.
Checking different transistors and datasheets I came through different terms.
On this datasheet  I understand that I can have up to 10A current flow through the transistor (the load which the transistor drive to be up to 10A), up to 60V but max 20W(V*I).

Where is it written though how much voltage/current needs to be applied to base to turn on/off the transistor?
Why every company is using different terms?
EDITED:
The other transistor I was referring to, wasn't mosfet but NPN transistor. Datasheet can be found here
I am applying 3.3V from a microcontroller and transistor seems to work.. however from what I read here from you I understand that its not the voltage that enables this transistor but the current.. Is that correct?


texts:
Possible Duplicate:
  Learning about electronics

I am 40. I am an architect by profession. I am very interested in learning electronics.

I don't have time to go to college for an electronics degree.

What should I do to learn electronics at home?

Or is it possible at all?

What minimum instruments do I need to buy?

EDIT:

This question helped me a lot.


texts:
I'm trying to understand how CI HT7A6322 starts up.

Relevant part of the datasheet says:

  Control circuit power supply. Also provides a charging current during start
  up due to a high voltage current source connected to SW. For this purpose,
  a hysteresis comparator monitors the VCC voltage and provides two
  thresholds:

  VCCON: Voltage value (typically 14.5V) at which the device starts switching
  and turns off the start up current source.

  VCCOFF: Voltage value (typically 8V) at which the device stops switching and
  turns on the start up current source

When the circuit is connected to mains the internal current source is ON state which is connected together with SW pin.

This current source in winding A induces a voltage in winding B powering the VCC pin. Is my explanation correct?


texts: Do IC step-down/buck converters generally boost voltage when the input falls below the desired output?

texts:
I’m trying to select a buck convertor to regulate the output of a LiPo battery so I can use it to replace two AA batteries. Ideally I want the regulation to happen only when the battery is above 3 V. When it drops below that I want the voltage to flow as normal and not be boosted up to 3 V. (My aim is to reduce the voltage of the LiPo battery before the buck convertor so that as the battery discharges it is able to trigger a low battery warning that kicks in at 2.4V).

I’ve found an TI IC that seems to fit the bill, the TPS62698: http://www.ti.com/product/TPS62698 . The max input and output voltages are perfect (4.8 V and 3 V), but I’m a bit confused by the minimum voltages. The minimum input specified is 2.3V, and the minimum output is 3 V. Does this mean that this is actually a buck-boost? Or is this just some sort of technicality and there is no regulation below 3 V? All of the TI step-down ICs seem to be like this from what I can see...


texts: What's the circuit diagram symbol for a variable reluctance sensor transducer?

texts: I know I've seen the symbol before, it's something like a circle with an open triangle facing in the direction of current flow with a line through the middle. I'm specifically thinking of the transducers in electric guitar pickups. I've seen the symbol before but now I can't find it.


texts:
I have been trying to calculate the core loss of my inductor E70 core but I was not able to calculate it. I calculated the operating flux density of my inductor which is 104mT and compared with the grapgh of the ferrite material (N87) Ploss vs B. I am getting around 80kW/m3. I do not know how to proceed from this also not sure how to convert it to Watt. I tried doing that but I was getting some unreal value so I thought it was wrong. Please let me know how can i do it. I attach the datasheet of the core. Please let me know if any data is necessary. Also I have a airgap of 4mm on each legs.
https://www.tdk-electronics.tdk.com/inf/80/db/fer/e_70_33_32.pdf


texts: For example if you wanted to created a datasheet with an item specifying that the device requires AC power, what would that item be called. My first thought is current type but that does not seem right.


texts:
I'm attempting to fix an SMPS for a sewing machine that is having all of its outputs voltages a third from what's expected.
I've replaced all electrolytic capacitors and nothing seems to be producing heat that would indicate a short circuit, so I'm thinking it might its feedback loop. This board utilizes the module MR4030 to control the Energy transferred from primary to the secondary but I didn't see any TL431 and I suspect it's the 4A 0F3 that I don't know about but I couldn't find what it is to consider to replace it.

There's another component as well that I don't recognize shown below. Do you recognize it?

Full board (the model of this board is HSV-MC122072):

Down below the two blue capacitors on the "small" heat sink, there's the bridge diode and down under the circuit that controls the motor of the sewing machine through a relay and other stuff. On the left of the two blue capacitors with the bigger heat sink the MR4030 which has the mosfet that does the switching, then more on the left the transformer then the secondary part. I believe the feedback loop with his optocoupler voltage divider and what I thought it would be the Zener diode for voltage reference from the secondary is below the big heat sink.
And here a look underneath.

Picture comparison of the unknown component with a SOT-223 package.


texts: Pull down resistor value in debouncer circuit

texts: I am from computer background and have made debouncer circuit (SR) using NOR gate IC HD74LS02P as a part of digital electronics project. I have used pull down resistor at all inputs of the gates used. But when R (Reset) pin is provided input high, the output Q becomes low, and now when as soon as R pin is provided input low the output Q becomes low. But after 15 minutes the output Q becomes active even if R and S are both low and previous output Q was also low. Is there a problem with pull-up resistor value ? I have used 100 ohm resistors. I have used old mobile phone charger which gives 5.13 V and 0.48A current. I have attached my readings as well as electrical characteristics of IC


texts: Differential amplifier common mode and differential mode gain

texts:
I need some assistance on the derivation of the formula for AV(cm) depicted in the figure below. the +/-2 delta_R/R and +/-4 delta_R/R are giving me hard time deriving.

The book probably provided enough information to the reader for them to derive it but I'll be honest I still cannot proceed on going about it.


texts: PLC (Power Line Communication) data line coupling to speakers

texts:
I have a PLC (Power Line Communication) to provide internet thorugh cable to all rooms.
The problem I have is that this internet data is coupled to the speakers. I can hear like a "noise" (not white noise) and when I disconnect the PLC this "noise" dissapears.
The speakers are powered via USB cable. I have tried to power on the speakers by connecting the USB to the PC and also using a power adapator (like the phone charger adaptors) but in both cases the noise continues.
From what I have read, this data is sent via the house power line modulated in a carrier wave in the range of 1-100 MHz. So, in my power plug I will have 220V at 50HZ (Europe) and then coupled to this the 1-100 MHz carrier wave.
How could I filter this 1-100 MHz wave in order to get rid of this noise in the speakers?


texts: Voltage detected in off position of SPDT Switch

texts:
I have an ALPS Electric SSSS810701 SPDT switch which I am using to control power to my PCB.
In the "switch on" position, I get 5 V as expected. But in the "switch off" position, I get 1.7 V instead of a value closer to zero

Output to PCB
Connected to 5 V
Floating

How do I fix this issue, please? Do I need to make a connection to ground across a resistor at position 1?


texts:
I'm trying to power over 100 LED matrices laid out in a long, single chain similar to a stock ticker on news buildings. I do have the control part figured out but bringing power to the matrices is beyond my understanding.

It appears the matrices consume 5v with less than 4A at full brightness (seller did not provide a lot of info). The control unit consumes less than 0.5A, and can control 12 LED matrices so maybe the system should only be designed for 12 at once then replicated if that's easier.

My questions are:

What kind of power supply should I get? I was looking at 5v 60A power supplies which if I am not mistaken should be able to power roughly 15 matrices at once. (see picture)

If using said power supplies (and sticking to groups of 12), should I use the three 5v outputs to each power 4 matrices?

The matrices each come with power cables capable of plugging into two matrices, but they are not long enough (since I need a single, long chain). Can I extend those cables or should I just replace them entirely?

If extending or replacing, what kind of wire will I need to support the loads I expect? Would voltage drop be an issue?

This might be a stupid question, but do I need to set it all up in parallel? It seems that is what the provided cables are doing, but I would rather make sure.

As a bonus question, would I have issues with the HUB75 8 pins data cable over longer distances as well?

The matrices themselves are 25cm wide, so in the worst configuration power/data would have to travel up to 3m (10ft).
Thanks for all the help, this is really outside of my element and I don't want to fry it all up!


texts: Why does this regenerative receiver not just turn into an oscillator?

texts:
I'm trying my hand at making a radio transmitter and receiver and I'm not sure exactly how this receiver works. I understand its a continuous wave receiver which is good for on/off transmission. I'm not exactly sure how the circuit doesn't have any continuous oscillations.

Taken from: Simple Pyro RF Receiver (27 MHz).

From what I understand it is a regenerative receiver which means the signal is amplified by passing the amplified signal back into the amplifier. I found a similar question asked here: Can someone break down how this receiver works? From what I understand in that question, L2, C2 and C1 act to filter a specific filter which gets amplified again.

My confusion comes when I was looking at an FM transmitter schematic.

Taken from: How to make FM transmitter.

From what I understand about FM transmitters they are voltage controlled oscillators and essentially the mic in the circuit affects the voltage which then modulates the frequency. The circuit however is still continuously oscillating.

The only real difference I see between the regenerative receiver and the transmitter circuit is that R1 is introduced in the receiver circuit (the other question doesn't talk about it either). How does this cause the circuit to not oscillate on its own and only when a radio signal is picked up?


texts: Differential Amplifier to Scale Down DC Voltage

texts:
I'm using a 3.7V LiPo to power a device that normally runs on 3V (and draws about 100-200mA). I've determined that my device can run properly if I can achieve an output voltage that scales the input by a constant factor of about 0.7 (I could also use a diode to simply drop the voltage rather than scale, but I'd like something less affected by current and temperature). Please note that I do not want a constant output voltage, or I’d just use a regulator. I need to track the voltage curve of the LiPo somewhat.

So the desired transfer function is:

Vout = 0.7 * Vin

I think a differential amplifier circuit of the following configuration should work (see schematic), since it gives:

Vout = Vin * (R2/R1)

(according to this article)

simulate this circuit – Schematic created using CircuitLab

To achieve a scale close to 0.7 and have a low parasitic current (since the battery will always be connected), I'd like to use R1 = 1M and R2 = 680k. You can see a simulation here.

I don't know a whole lot about op-amps in practice, so I have a few questions:

When applying a load, does that inadvertently affect the output voltage, due to current draw from the output of the op-amp? In simulating, it didn't seem to have an effect, which is nice. I'm avoiding a simple voltage divider for the very reason that the load ends up affecting the desired scaling.
Is it practical to use that high of resistances? I typically see ohms in the hundreds, or maybe 10k, but I don't often see circuits using 680k or 1M. Just want to know if that's a smell of some sort. Side note: for a 1000mAh battery, it would take about 30yrs to drain, according to a quick calculation with these resistances.
Is it unwise to use an op-amp in a DC application? I typically see examples with AC circuits.
Are there any blatant bugs in my circuit design that I might be missing?
While I'm not asking for part recommendations, I am considering an LM158 or similar. If there is a good reason to avoid this for my application, letting me know would be much appreciated.

Thanks so much for your help and advice!

EDIT

I'm using Rload to represent the device being powered. I don't know its exact resistance, but I estimate it to be about 20ohms on average.


texts:
I'm facing with a problem regarding debug session.

When I start debug session, after the configuration of USART2 the debug session is closed.

Keil message:

  Cannot access target. Shutting down debug session

The shutdown occur with this instruction:

__HAL_AFIO_REMAP_USART2_ENABLE();

This is my configuration:

STM32F103
IDE Keil
Keil project created with STM32Cube MX
Debug Serial Wire with SWCLK, SWDIO, NRST.

Without debug the board works well, but I need the debug to solve some bug.

Thanks!


texts: High voltage battery charging with low voltage charger?

texts: I have two 3.7V batteries to be used serially for my device. Is there any way to charge these batteries with 3.7V charger? Or do someone show me a circuit having a button which when pressed connects the two batteries serially which then can be used by the device. And when the switch is not pressed connects the two batteries in parallel which then can be charged with 3.7V charger connected in parallel to the two batteries.


texts:
I am required to generate and measure squared signal (PWM like). I should cover a 0-30VDC amplitude. High level of the signal is 30 VDC, low level is 0VDC. The bandwith to be covered is 0-20kHz. I should use Arduino to generate and measure these signals.

I thought that the more convenient way to achieve these operations would be a kind of "logic level shifter", but I cannot find a suitable component for my application. I would like to bring the 30V back to 3.3V and vice-versa so that the Arduino can both generate and measure the signals.

To circumvent the issue, I thought about transistors, comparators, voltage divider, amplificators,... but I am unsure about what to choose (COTS if possible) and think a bidirectionnal voltage level shifter would be the best solution since it would cover both the need to generate and the need to measure.

Any idea to address this issue ? It would be better if the component would be on the shell, but if a design from scratch should be done, it may be OK too.


texts: Op-amps, why do they have such low output currents

texts:
An introduction to my question is that ultimately op-amps drive something with their output stage (i.e., they source or sink current). I am looking specifically at the current sourcing scenario for the remainder of this question.

The current that an op-amp can provide is sometimes shown on the datasheet as its Output Current and even more rarely a Short-Circuit to Ground Current is also provided. Quite often these values are very low, perhaps single digit mA or maybe 10-20 mA, maximum. Manufacturers are quick to point out how little current their op-amp uses, but it's the driving ability of the op-amps that is paramount for many circuits. Without drive ability, one has to add additional gain stages that reduce the wonderful characteristics of the op-amp (e.g., noise, offset, etc...).

This current drive ability seems very small and I am wondering why the op-amps are designed to source so little current, forcing one to add another active stage after the op-amp for current amplification in order to drive larger loads.

To get higher currents, one has to venture into the world of so called power amplifiers, but often these have much worse characteristics on their datasheet than good op-amps. Also, they are much more expensive for decent ones (e.g., 10x as expensive).

Is the low drive ability of op-amps a side effect of trying to give them their good characteristics? Do these characteristics get worse if an op-amp is designed to source more than say 20 mA or so of current, that being the reason why they are so limited in their drive ability?

Update
Perhaps an aspect of my question is why there is such a large gap between op-amps and power-amps (i.e., the jump from 10-20 mA to 2 A).


texts: Computation of the Scattering Matrix of a Transmission Line

texts:
let's consider this transmission line (with losses) in which a and b denote respectively the reflected and the incident waves at each port:

This exercise asks to find its scattering parameters normalized with respect to an arbitrary impedance Zc1, which is different from Zc.

It starts with the computation of S12 and S22: in this case, according to the Scattering Parameters' definitions, we have to analyze the network in case a1 = 0 (i.e. port 1 adapted) and with a source applied to port 2. The exercise so analyzes this situation:

What I do not understand is this: why is port 1 closed on Zc1 and not to Zc? The exercise asks to find S-matrix normalized with respect to Zc1, but if we close port 1 on Zc1, it will be non true that a1 = 0, from my point of view. In fact, there will be physically reflection, since there is an impedance mismatch between the load Zc1 and the transmission line which has characteristic impedance Zc. How can this procedure be correct?


texts: ESP32 : Latching power switch circuit fails to boot

texts:
I tried to reproduce a little circuit I found on the web :

source : https://randomnerdtutorials.com/latching-power-switch-circuit-auto-power-off-circuit-esp32-esp8266-arduino/

When I push the switch, the ESP32 starts and I have to remove the cable from GPIO to stop it. But the ESP32 fails to boot and does nothing but to reboot. I tried multiple power source with 3.3v and 5v but nothing changes. I have exactly the same components as in the image so I don't understand what is wrong.

Can anybody help ?

Thanks


texts:
Okay, I know this might sound really offtopic. I made a PCB a while ago and got some ferric chloride stains in my clothes. I've been trying literally everything, from lemon juice, salt, vinegar, coke, bleach, sodium bicarbonate...
I think it's really difficult to remove, but not impossible.
Any advice I can get to save the clothes?
Thanks!


texts: will the difference between a .001 cap and a .0015 cap matter?

texts: I am doing a build for a guitar stomp box from this website and was wondering if a .0015 capacitor could be used instead of a .001 capacitor. The build i got from https://www.tonefiend.com//wp-content/uploads/DIY-Club-Project-2-v02.pdf and im using version 3 for the build


texts: Forking a 3 phase 380V line into three 220V single phase?

texts:
I need to feed several loads with single phase 220V AC, namely:

Four 60V DC transformers rated 350W 5.9 amps.
One VFD transformer connected to a 8 amps motor.

Could I connect everything over a 3 phase 380V line (5 wires 2.5mm each, 3x16amps fused)? I was thinking about forking two phase to the four 350W transformers (2x2) and use the third for the VFD, each branch closed through the neutral. But I am not sure if the single neutral can hold everything.


texts:
I need help analysing this BJT circuit. What I need to find is the equation for IB, IC, and VCE for this circuit. So far what I've got is from KCL :
a: I1=Ib+Ic
b: Ie=Ib+Ic
So I find that I1=Ie, and since Ic=hFE.Ib, I1=Ie=Ib(1+hFE).
Now, what I'm confused with is the KVL. Do I need to make 2 loops or is it possible to make R1 and R2 into a Thevenin Circuit? How do I find the Ib equation?

Thanks in advance


texts: What is this component: 48-27SD50020222?

texts:
I was digging through my things and found this component (48-27SD50020222) but am not sure what it is.
I've tried searching for variations of the number 48-27SD, 48-27SD500, 27SD500, etc. but no luck.
Would any of you know?


texts: Input capacitance of a differential amplifier

texts:
This lecture (page 11) shows how to calculate input impedance of a differential amplifier.

As you can see from the image below the input capacitance is calculated through the steps shown at the right.

Could anyone explain the principle or how the method shown at the right works?


texts: Explain the use of NPN and pMOSFET in this 8x8x8 LED cube

texts:
I've got part of a circuit diagram for an 8x8x8 RGB LED cube from http://www.kevindarrah.com. See the entire schematic. I'm having trouble working out how it does what it does.

I know that a high voltage coming to CNTRL_L0 will illuminate the LED attached to ANODE_LEVEL_0 but I'm not sure why all of this is necessary?

The 2N3904 is an NPN transistor, so when the CNTRL_0 is high the transistor is active and allows current through so that would mean the circuit connects from the first (on the left) +5V to the first GND and you effectively get a low going into the IRF9Z34N (the pMOSFET). That means the pMOSFET does not conduct, but so what? No matter what happens the ANODE_LEVEL_0 is connected to GND, wouldn't it always be illuminated? And if all that is needed to get this to work is that the 2nd +5V is cut off from the ANODE_LEVEL_0 then wouldn't a single PNP transistor joining CNTRL_L0, 5V and ANODE/GND do the same thing?


texts:
RFID 125kHz card readers are very cheap (< 5$) and very simple (USB Plug & Play).

Is it possible to chain / multiplex 20 readers to create a very accurate plug-and-play smart shelf?

What are the limitations?

Tags must be 3cm wide
Tags must be set at the bottom of item (not on the side of a book)
Items can't be stacked
How to multiplex reader to have "reader Id" + "tag Id"?

Is there a simple, plug-and-play, low cost smart shelf alternative? Everything I found (UHF reader + antenna + multiplexer) is for > 5000$


texts: Using capacitors to make LED lighted dice

texts:
I've had this idea for quite a while, as I got the idea from The Stormlight Archive book series, in which they have marbles that glow. I have a limited understanding of electronics due to some intro to physics classes in college.
Does this sound like something that would work?
If you connect a capacitor to a resistor such as a small LED, and then in case it in epoxy, but then place it on a inductive charger such as a wireless phone charger, will the capacitor charge and then release light?


texts: Why does line current become half when load becomes half of full load in a dc shunt motor?

texts: So, suppose a dc shunt motor is running at full load. I wanted to know what happens to the torque, speed, armature current and line current when the load changes? How are these related mathematically. In my book it is given that " when load becomes half of the full load, line current also becomes half ", but why? What I think is that when we increase the load from no load to full load, torque increases and since torque is proportional to armature current for a dc shunt motor, armature current should also increase. But when we already are working at full load, maximum armature current would be flowing. So when load becomes half, shouldn't the armature current also become half?


texts: My laptop USB port is outputting 5.8 V. Is this in tolerance?

texts:
The USB standard is for the host to provide 5 V to peripherals. When I measure the voltage on an attached Arduino, I have 5.78 V. Is this much too high or within specification?
Update:
The measurement that gave rise to the confusion is in measuring the 5V line on the Arduino, which I understood was directly passed through from the USB port if that was the power source.
Final Update:
To end confusion, the issue was caused by a multimeter whose own battery was critically low, making the device unable to function accurately. Answers and discussion below add detail.


texts:
I hope that this community is the most suitable for this kind of question.

So I have to make a graph representing dependence of BER as a function of antenna's diameter (BER(D)) I know that antenna's gain is defined as a G = 10*log((pi^2*D^2*eta)/lambda^2). Is there any way to see how does bit error rate depend on diameter using this forumla?


texts:
I've been designing microwave power amplifiers and LNAs for school, I design in microstrip and my matching networks usually consist of stub/line sections or similar arrangements, I have also designed more sophisticated networks for wider bandwidths, however I usually achieve maximum bandwidths of say 200-300 MHz.

My main problem is that I have seen many commercial amplifiers which achieve bandwidths of 2 GHz or more and they dont seem to use any stubs at all or any kind of matching networks for that matter, in fact they dont seem to use anything aside from a single transmission line. A quick search for cheap commercial wideband amplifiers will reveal something like the following 0.1Hz to 2GHZ amplifier:

It looks so simple, a couple of dc blocks, some PSU decoupling, and thats it! so how do they achieve such wide bandwidths using just a regular transmission line at the input and at the output?, how do they match the impedances? is it Coplanar Wave Guide instead of MicroStrip? what is the secret?

I have read books on wideband amplifier design and it usually involves much more complicated networks, complicated algorithms such as the Real Frequency Technique, or something like distributed amplifiers.


texts: Replacing broken capacitors with ones that have bigger capacitance

texts:
I have a Samsung 205BW screen, and over the time, the capacitors on the power board broke down. I have to wait up to 30 mins for them to warm up so I can use the screen. I bought replacement capacitors according to the youtube video how to replace samsung 205bw capacitors:

4 x 1000uf 35v
1 x 470uf 63v

But after I opened up the board, the capacitors I had installed were:

5 x 820uf 25v
1 x 330uf 25v

I also took pictures.

Is there a way to replace the broken capacitors with whatever I have?


texts: Can TI CC2540 chip process simple logic by its own?

texts:
In my project, I need bluetooth 4.0 TI CC2540 module works like a beacon to broadcast an ID to space. And it needs to sniff other beacon's signal. In some condition, it needs to trigger an event. Is that possible?

Is there any other processor required in this kind system?

I found modules on ebay like this: BLE module with TI CC2540, Bluetooth 4.0

I am new be, what I should to do to program this kind module. Does those modules must connect to a system (like Arduino or Raspberry Pi) via UART to work?


texts:
I am trying to write a VHDL code that displays an image on a monitor. The purpose is to do some image processing with VHDL. However, I am getting trouble with this segment of code. The image that I am using is small one in terms of resolution. Using a java code that I wrote I took every single pixel's RGB values and pixel locations then RGB values are converted them into binary. That binary data is used to draw image. The problem must be with "when" statements. It says that "this construct is only supported in VHDL 1076-2008". How can I overcome this problem?
I am out of ideas.

 IMAGE: process(clk) is
 begin
 if clk'event and clk = '1' then
 vgaData <=  "111111111111" when pos_x = 0 and pos_y = 0 else
 "111111111111" when pos_x = 1 and pos_y = 0 else
 "111111111111" when pos_x = 2 and pos_y = 0 else
 "111111111111" when pos_x = 3 and pos_y = 0 else
 "111111111111" when pos_x = 4 and pos_y = 0 else
 .......
 ....... (goes down and down)
 .......
 "111111111111" when pos_x = 76 and pos_y = 86 else
 "111111111111" when pos_x = 77 and pos_y = 86 else
 "111111111111" when pos_x = 78 and pos_y = 86 else
 "111111111111" when pos_x = 79 and pos_y = 86 ;
 end if;
 end process;


texts:
I was wondering if there anybody out there that might be able to help me. I am trying to control an electronic car aerial with an Arduino using Mosfet switches however the circuit I have built doesn't seem to work.

Has anyone tried something like this before or know of a good walkthrough to accomplish this?

The help is greatly appreciated.


texts: building a variable bench supply using microAtx 24pin atx  then using attiny44 as voltmeter

texts: Ideally I should have a bench supply so I don't have to keep buying 9v batteries. I've taken a micro atx psu out of a pc I have. It has a 24 pin ATX connector. I'm not going to take apart the psu itself. I'm going to cut off one of the molex connectors then wire them to binding post. I was wondering would it be possible to use an ATiny44 (10bit ADC) to measure voltages up to 30volts with reasonable accuracy. I'm also going to use an LCD display to show the voltage of the variable supply.


texts:
For a project, I like to use 3.5mm type USB connector. This is for a closed system therefore I am not worried about USB approval but I am worried for signal integrity and insertion/removal problems.

Are there any common 3.5mm 4 contact point USB connectors that I can safely use? What is the usual practice for these connectors?


texts:
i am trying to create a simple 3x3 MIDI controller with an arduino nano, but i have ran into a problem.
I want to have 3x3 grid of buttons with backlight, but nano has only 13 digital pins, so using one pin per button and one pin per LED doesn't quite work. I've heard about using analog pins for buttons, but doesn't that limit me to pressing only one button at a time?
Or are there any other solutions to drive 9 buttons and 9 LED's at the same time?


texts: Precision Full-Wave Peak Detector component values

texts:
so, I am a beginner in electronics...hoping to find some help... here I've found a circuit that I want to use from LM 3915 datasheet..... but the problem is I don't have 0.2 and 0.47 Capacitors... capacitors that I have are 1UF 2.2UF 3.3UF
4.7UF 10UF 22UF
33UF 47UF 100UF
220U... if I want to change c1 and c2 with capacitors that I have, which resistors should I change the value so it would reach max capability of this circuit? and I was hoping You guys can recommend best value of c1 and c2 for me based on capacitors on my possession... Thank You for helping me... I want to make 4 channel vu meter...


texts:
Before you tell me that the question has already been asked, only similar things have been asked.

I need to power a Raspberry Pi with some electrical equipment attached to it. The Pi needs to run for at least 48 hours and I need at least 2V and 900mAh to be used for the other equipment. The device must be portable, so it doesn't have to weigh too much. I thought about using more than one power source and somehow merge them together (for example using rechargeable Li-on batteries and a solar panel).

What would be the best way to accomplish it?

EDIT: I should be able to see how much power is left.


texts: Can I use an Apple charge Cube (5W power) through a Ripcord 9V to USB to feed a Roland SP 404 (2.7 W draw) Safely?

texts:
I am asking this as I want to be extra sure this setup does not damage my 404 Sampler as its an expensive item of mine and it's very dear to me so I want to be careful. Here is the scenario:
I have this device: https://www.roland.com/us/products/sp-404/ that normally runs off a 9V 300mA power supply connected to the wall or a surge protector. I am planning on making it portable through using these items:
https://www.apple.com/shop/product/MD810LL/A/apple-5w-usb-power-adapter
https://www.amazon.com/gp/product/B00GC0UZZM/ref=ppx_yo_dt_b_asin_title_o00_s00?ie=UTF8&psc=1
This setup is to run the device through the wall or any outlet on the go, as the original power supply is fairly bulky. Additionally, I'd like to connect it to a fairly large power bank, specifically this one..
https://www.amazon.com/EC-Technology-Portable-22400mAh-Capacity/dp/B00FDK2G2C
Is there any safety things I should worry about in regards to the electronics? Too much draw or output? I just don't want to fry my unit.


texts: How much current can a proto board handle?

texts: I am building a circuit on a protoboard (the type with only copper circles). How much current (DC) can that protoboard handle?


texts: eagle library--updated footprint wont show in board

texts:
I initially created a part in an eagle library, but now I need to change the package layout. I have already put the initial part in an eagle schematic, so removing/re-inserting it is not an option. So anyway, I opened the library editor up and edited the part's package layout, and saved the library. I then went back to my schematic, went to the library dropdown ----->Update library, and selected the library that I edited. I then created a board from the schematic(I didn't already have a board--I am not even done with the schematic. I just created the board to test if the library update worked.) Unfortunately, the package on the board remained the old one, not the edited version of the package layout. I then tried doing the same library dropdown ----->Update library while inside the board editor, but still no luck.

How do I update the part so that the board uses the new package library? Thanks.


texts: Producing the Sum and Difference of two signals with two Op-Amps

texts:
I have two signals, one is a baseline voltage (V1) and the other is a 'difference' voltage (V2). From these I want to produce two signals, V1 + V2 and V1 - V2. The circuit I currently have is:

simulate this circuit – Schematic created using CircuitLab
Where R is the same everywhere.

Based on the diagrams found here:
http://www.electronics-tutorials.ws/category/opamp

Using This Op-Amp

I have a feeling something about this is wrong, and I can't just drive both a summing and differential amplifier in parallel. If so, can someone give me advice on how to get both of these voltage values with just the two inputs?


texts: How can I mitigate SNR or THD for audio codecs?

texts:
During my studies at university, we didn't go too in depth about Signal to Noise ratios (SNR) and Total Harmonic Distortions (THD).  I've been trying to work with audio codecs for some time and I only now just wondered if there was anything I could do to improve the signal quality external to the audio codec.

Specifically I'm working with the SSM2604 from Analog Devices which states it has:

So I'm curious, is there anything I can do, apart from high pass and low pass filters, to the incoming signal that may improve these values?

Also how would these values change if I am using the codec at a higher sampling frequency?  I expect that the sound quality would degrade somewhat but I'm quite ignorant in this area of EE.


texts:
I am still studing OP-AMPS and I was playing around with voltage follower/buffer configuration, the very basic diagram connecting the inverting input to the output directly and put some voltage on the non-inverting input

I supplied the op-amp with 11.1 volts

what I have notice that it was working as expected with TL092 and LM741, the output voltage was following the input voltage but when I tried LM393 or LM339 it didn't work as expected actually the output voltage totally became irrelevant for example if I apply 5 volts on the input, the output measures .9 volts or something around that value

if I apply vcc on the input I get just 1.308 volts

can someone explain why is this happening?


texts: Can a PoE type Gigabit Ethernet Transformer be used in a non PoE application?

texts:
I am designing a device that will have Gigabit Ethernet ports on it.  We have a requirement that our device must be stored at -50C.  Many gigabit ethernet transformers either don't list a min storage temperature in the datasheet, or the min is -40C.
I found some non-PoE type gigabit ethernet transformers that supported storage temperatures down to -50C, but they were sort of expensive.  One example being the Pulse HX5008FNL (like $6~$7 at quantity = 100).
https://www.mouser.com/datasheet/2/336/-595196.pdf

I also found some PoE type gigabit Ethernet transformers that supported storage down to -50C, and they were much cheaper.  One example being the Bourns SM51625EL (like $1.50 at quantity = 100).
https://www.mouser.com/datasheet/2/54/sm51625el-934089.pdf

From the datasheets, both parts seem to have similar common mode rejection, insertion loss, cross talk, etc.
My device will not be implementing PoE, just regular gigabit data transfer, and I wont have the power supply controller that normally goes with a PoE transformer.  But I want to use the cheaper part...
I know you can't use a non-PoE transformer for PoE, since they are not designed to handle larger currents.  But is there any downside to using a PoE type transformer in a non-PoE application.
Also, I am using the VSC8541-2 Ethernet PHY.  Page 25 of the datasheet shows that (if I wanted to) the chip can be used in PoE applications (with a separate PoE power supply).
https://ww1.microchip.com/downloads/en/DeviceDoc/VMDS-10513_VSC8541-02_VSC8541-05_Datasheet.pdf


texts: Why additional input series damping for AD797

texts:
In AD797's datasheet, section "THE NONINVERTING CONFIGURATION", it states that because of the low \$ r_{BB} \$, that the AD797 needs additional input series damping. Shown as below:

Without the two resistors in the circuit above, it can also used as a voltage follower.
But the document recommends R1 because "very little damping of input and output reactive interactions" if we connect the output directly to the inverting input. I can't understand this well. How does the lack of damping of input and output reactive interactions degrade the stability?


texts: Calculating Total Harmonic Distortion using only the first harmonic

texts:
I have an assignment for a class where I have to calculate the thd of a signal using MATLAB.

I think I have a pretty good understanding of how this should be done, however, my professor instructed that we use only the first harmonic to calculate the thd.

Maybe my understanding is bad, but I thought the thd was calculated using the first harmonic (fundamental frequency) in relation to the magnitudes of the (other) harmonics. I have looked everywhere online and have not found anyways to calculate thd using only the first harmonic.

I have added the specific assignment phrasing below.

  A  .mat  file  is  given  with  this  project  that  contains  one  period  of  a  periodic  signal. Use  the formulas of the exponential Fourier series and the definition of the total harmonic distortion (Audio engineer’s formula) to calculate the total harmonic distortion of the given signal.In your calculations, you have to just find thefirst harmonic. You need to manipulate the THD formula and represent it as a function of only the first harmonic.

Upon emailing my teacher to clarify if he wanted the thd with respect to the first "additional" harmonic he said he meant fundamental frequency when he said first harmonic.


texts: I have a 16 ohm 1.25 ampere 25 watt rheostat that has gone bad. Is it okay to replace it with a 16 ohm 1.7 ampere 50 watt rheostat?


texts:
I'm reading the Xilinx Spartan 6 user guides. They seem to make the distinction between a Spartan 6 FPGA device and a Spartan 6 FPGA package.

I'm assuming that an FPGA package contains an FPGA device. What exactly is are FPGA packages, and what is the need for the package/device distinction?


texts:
I'm looking to power a circuit with USB-c with a trigger board negotiating 20Vin up to 2A.
The circuit would consists of a high power LED strip that runs 21.5V @1A and a DC motor water pump rated for 12V 300mA.
My thoughts are to have them connect in parallel.
I would use a step-up converter with constant current to regulate current through the LED
I would use a step-down converter with constant current to regulate current to the DC motor.
Is this a good approach or is that completely wrong?


texts: What do we mean by "ground" in an electrical circuit?

texts: What do we mean by ground in an electrical circuit? When we want to solve electrical circuits problems, we set a "ground" level which is mean that the potential on it equal to $0$. I wonder how the current will flow if the potential at a point equal to zero.


texts:
Consider the common emitter amplifier in the schematic:

simulate this circuit – Schematic created using CircuitLab

The input impedance is \$Z_{in}=[(R3\left |  \right |R4)\left |  \right |\beta(r_e + R2)]\$

Now can I just go on increasing the input impedance by just increasing the values of the resistors or is there some limit to this?


texts: Are phase angles in filter transfer functions primarily for stability?

texts:
I see transfer functions and bode plots (magnitude and phase) and it occurred to me, that I don't really use the phase plots at all. My career experience seems to have gotten away without having to use or calculate them except once where I had a stability issue with an opamp. But this just shows a gap in my experience / knowledge that I would like to resolve before I genuinely need it.

When we look at general filter topologies that show phase plots, why is that relevent to show. For instance, a single order LPF will have a phase shift of -45 deg @ fc - so what ? Why do we care about these numbers in filters ? Is it that when we cascade them, it becomes relevant when looking at phase margin ?


texts: Unwrapping measurements from Adxl345 accelerometer

texts:
I am trying to read acceleration values from a ADXL345 via I2C. I've successfully configured the accelerometer with a resolution of 16G.

Test 1: 180° rotation along the y axis in 16G resolution. The acceleration along the Z axis is shown below:

Using a 16g configuration, the resolution is too low. I changed it to 2g in order to get a more accurate value of gravity and performed the same test.

Test 2: 180° rotation along the y axis in 2G resolution. The acceleration along the Z axis is shown below:

As you can see, the is a roll over effect probably caused by the number of bits used in the register to save the value. With 16g mode the module uses a 13 bit register, with 2/4/8g mode it uses a 10bit register.

Which approach do you suggest to reconstruct the acceleration value?

In this question @davidcary mentioned the roll over effect.

EDIT

I am reading two bytes, it is the same code I used for the 16g mode

def read_word(self,adr):
     high = self.bus.read_byte_data(self.address, adr)
     low = self.bus.read_byte_data(self.address, adr+1)
     val = (high << 8) + low
     return val

def read_word_2c(self,adr):
     val = self.read_word(adr)
    if (val >= 0x8000):
       return -((65535 - val) + 1)
    else:
       return val
[...]

accel_zout = adx.read_word_2c(0x36)

Here is a screenshot of the registers containing the Zaxis values

Note

Here is another problem, I will open another question for this but it is worth pointing out the following problem. Please focus on the Z axis only

Test: tilt from 0° to 180° and back to 0° twice, then from 0° to -180° and back to 0° twice.

Figure 1: Raw data

As you can see, the shift is not costant. The average shift is around 58.000 but sometimes it is smaller than this. If we apply the same correction to all shify occurence we will end up with this:

Figure 2: Unwrapped data

If the threshold after which the correction should be applied is not correctly defined, the resulting data won't be accurate. In Figure 2 the acceleration along the Z axis after the test is different from the initial zero value which means disaster...


texts: I have to determine if the system is linear, time-invariant, and/or causal

texts:
Here is my problem:

$$\frac{d^2y}{dt^2} + 5\frac{dy}{dt} + 8y(t) = \frac{dx}{dt} + 3x(t)$$

I have to prove if this system is homogeneous and additive in order for the function to be linear, but can I prove that? It says the output should be as the input, and again how can I solve the above problem? For example, \$x(t)\$ must equal \$y(t)\$ how can I implement that rule into the function?


texts:
Are these resistors in parallel? A question is asked to find the equivalent resistance between X1 and X2; to my knowledge, these resistors are like parallel connections. But the choices are given as:

A. 2 Ohms
B. 4 Ohms
C. 8 Ohms
D. 12 Ohms


texts: Are germanium MOSFETS and Heterojunction Bipolar Transistors commercially available?

texts: I've read a great deal about the development of Germanium field effect transistors and HJTs but are they actually been manufactured commercially? If so where can I buy them? I already know where to get Germanium diodes but I want MOSFETs if they're available.


texts: Possible to use Segger J-Link with Intel Quartus to flash FPGA?

texts: Does anybody know if it's possible to use a Segger J-Link with Intel Quartus to flash an FPGA?


texts: Is it possible that the BJT will work in active mode even if emitter base junction is reverse baised?

texts:
I was going through voltage divider bias configuration of BJT and then i encountered two problems:-

The above two problems are nearly same except that the emitter terminal is grounded in case of (b) and baised in (a) .when i solved and found out the thevenin's voltage(between emitter and base terminals) then it was positive for (b) and negative for (a) .Negative value of the thevenin's voltage would suggest that the emitter base junction is reversed baised so The transistor must be operating in the cut-off region.

In some videos online i found that even when thevenin's voltage is negative the BJT was operating in the active region .Is this really possible ?If yes then how?

Edit:The calculation of Vth for (a) is given in this video.

Thank You for giving your time.


texts:
I have noticed small hangers under the Rosenberg HSD connector:

What is the purpose of these?
I can only guess it's solder paste storage for pin-in-paste technology but on the other hand, it's quite thin.

Can someone confirm?


texts: Controlling RGB LED (common anode) with Arduino

texts: I have an RGB LED (datasheet here) that I want to control using an Arduino R3 (datasheet here). How can I do this? The LED has a common anode, not a common cathode. However, the arduino's I/O pins can only be +5 volts. This is a problem, because I need to somehow hook up the LED's cathodes to the arduino's I/O pins.


texts: Calculate transfer function with Sine generator

texts:
Given this circuit I would like to know how can I find it's  transfer function.

A method I've considered was to use Node Equations on nodes 1 and 2 ,
and I have a few things that I don't find clear :

why do I have to introduce an additional equation with \$V2=0\$ ?
Once I find the transfer function in form of \$H(s) = {\dfrac{R1}{R2+Ls+CR1R2s+CLR2s^2}}\$
I must calculate \$Vu(t)\$ with \$V1=10+cos(t)\$ , the solution states that
\$Vu(t)= H(0)*10 + Re[H(j)*e^{(jt)}*1]=-10-{\dfrac{1}{2}}{sin(t)}\$
How does one achieve this result and first of all how does the \$Re\$ part of the transfer function is calculated ?

Thanks a lot for any insight provided.


texts:
Why do all the gameboy cartridge mods for nonvolatile save use a type of ram like fram? Why isn't a sufficiently fast eeprom or flash ic used?

EDIT: We all know this is about parallel interface ICs, right?


texts: Convert 9v of battery into 5v at 3.5watt

texts:
I want to run Raspberry Pi using a general non-rechargeable 9v battery.
Raspberry Pi needs 3.5W and 5V input.
Questions:

Which LDO should i use ?

For what amount of time general 9V battery is able to supply 3.5watt power ?
EDIT1:Battery is Duracell 9V rectangular battery.


texts:
I am creating follow focus system (motor with gears that moves camera lens ring).

Vast majority of such systems use low Kv high torque BLDC motors - similar to the ones used in gimbals. I think it is mostly because higher Kv motors require gearing to provide enough torque which introduce noise.

I bought such module from FeyiuTech to reverse engineer it. The BLDC motor is very small (28x8mm stator) but has 5ohms resistance and about 150Kv. At the same time It is impressively small. It has no symbols.

From my research the torque approximation can be calculated as follows (simplified):

T = I/Kv = (U/R)/Kv

Therefore my understanding is I need to buy motor with as small resistance and Kv as possible. The best motor I could find was emax 87Kv. It has 6.5omh resistance and 87Kv so it should have more torque at the same voltage compared to 5ohm 150Kv FeyiuTech, right? I measured it and turns out it is actually slightly lower. Dissapointing. On top of that it is twice as big as FeyiuTech.

My questions are therefore:

Why would 150Kv 5ohm motor have more torque than 87Kv 6.5ohm?
Where can I buy such motor? I could not find similar motors anywhere. They are either too big or have insufficient ratings. Where do companies get such custom motors?


texts: Writing commands to a microcontroller with a STM32f chip from python

texts:
Manual to the micro controller: https://drive.google.com/file/d/0B8PmY6nhQadKSVc5OE04c3ZJaFU/view?usp=sharing
, where page 18-19 introduces the serial communication protocol.

The micro controller on Amazon: https://www.amazon.com/Channel-Controller-Bluetooth-steering-Raspberry/dp/B018YP228A/ref=sr_1_1_sspa?keywords=usb+servo+controller&qid=1562646724&s=industrial&sr=1-1-spons&psc=1

The microcontroller is connected via USB to a Raspberry Pi 3b+.

I am on my Raspberry with Python 3.5.3 and pySerial.
In python command line I can write:

>>>import serial  # pySerial
>>>sc = serial.Serial('/dev/ttyAMA0', baudrate=9600)

(I found the port name ttyAMA0 using dmesg | grep tty)
Then

>>>sc.write(b'')  # Instantly returns 0
0
>>>recovery = [0xFF, 0x0b, 0x00, 0x00, 0x00]  # Any 5 bytes command packet.
>>>sc.write(bytes(recovery))                  # Stalls until write_timeout

I have been unsuccessful in sending any actual packet to the port, as when i write, the python command line never returns, unless I specify a write_timeout, in which case it raises the serial.serialutil.SerialTimeoutException. Does anyone have experience with controlling microcontrollers with python? Should I be using pySerial at all?

I can control it through the GUI of the Motor Control software, but I want a sort of API (Python highly preferred) to automate things.

Motor Control software with GUI:
https://drive.google.com/file/d/0B8PmY6nhQadKR013T2hDQXJxaWc/view?usp=sharing

Update: Read also stalls.

>>>sc.read()  # Stalls


texts: Need help to backup cellphone - I need output power 5V 1A from AA batteries

texts:
How do I get 5V 1A for my backup battery for my cellphone from four AA batteries? (Each battery is 1.5V 2500mAh.)

Is it better to use a 7805 to regulate from 6V to 5V 1A to power my cellphone? Here's a schematic diagram I found:

Or should I use this HT7750A from 2 AA batteries to 5V? Here's the schematic diagram:


texts: Does a 3-phase VFD work if one phase is reduced (e.g. with a dimmer)?

texts:
If you have a 3-phase VFD running a 3-phase motor, and you use a leading or trailing edge dimmer on one or two of the input phases, will the VFD continue to operate normally, pulling more current from the unaltered phase(s)?

The reason I ask is that I am planning a backyard stored-water hydroelectric system with a 3-phase turbine.  In order to keep things stable I will need to balance power draw across the three phases, so I need something that will draw power from only one or two phases to "take up the slack" if one or two phases are more heavily loaded than the others.

Some people have achieved this by using TRIACs on the under-loaded phases to send a variable amount of power into under-floor heating, however I live in a hot climate so don't have much use for heating.

I am wondering whether I could instead use a VFD to pump water uphill (for later use by the hydro system) but use the same TRIAC arrangement to limit the amount of power available on each phase, so that the VFD preferentially draws more power from the specific phases I wish.

I have done a little research into VFDs and they all seem to be large 3-phase rectifiers, producing DC which is then sent to the motor via PWM.  It would seem that chopping the input AC waveform on only one phase would merely introduce more ripple to the resulting DC, which would be filtered out by the capacitors already in the unit.

Is this assumption correct, or would other problems be introduced by altering the AC waveform on the VFD's input?


texts: Using the output of a Pi pin to toggle a higher powered circuit

texts:
simulate this circuit – Schematic created using CircuitLab

I've been wrestling with a circuit I'm trying to build for a few days now and a friend recommended I ask for advice here. I'm essentially trying to create an electronic switch controlled by a raspberry pi. The switch will open and close a circuit for a heating coil that needs about 0.25A and 5V and is running off a battery pack. The issue I'm having is coming up with a set of transistors or some other configuration that can allow the Pi to toggle power to the coil using only it's 3.3V output. I've fried several transistors already and have moved to Mosfets which are causing their own problems. If anyone has a recommendation or a simpler way of doing this I'd be very grateful. It's the final component I have to contribute to a group project I'm working on. Thanks!


texts: How to mathematically calculate of RMS of a Sine Wave filtered out PWM

texts:
I'm generating a Sine Wave without DC offset from a Square wave with 1Khz 1.5V offset by filtering it first with a High Pass firs (to remove the DC) and then with a 3rd Order Low Pass Active filter (fc=1kHz).

I simulated the circuit and the sine wave has a Vrms of 1.37V. What i would like to know is how can i calculate this value mathematically without simulating, just by knowing the Square Wave signal is filtered by a 1rd order High pass and 3rd Order Low Pass.


texts:
I have an RC Car that I tore apart and I am attempting to rig it to an arduino.

The front wheels can turn left and right based on which way the current is flowing and the rear wheels will go either forward or reverse based on the current direction.

So the question is if they only have 2 wires coming off of them how do you rig a Darlington Tip 120 to it so it can go both forward and backward?

Or more simply put how do I control a motor that goes in 2 directions when it only has a positive and negative wire coming off of it.


texts: Effect of switching frequency in boost regulator with switching load

texts:
I have an objective to make a pulser for ultrasonic 1Mhz and 120V, for step up DC i used a boost converter with switching frequency 10KHz, 0.9 Duty Cycle and 12V supply, the boost converter work perfectly for static load like 1Mohm, but when i attach the converter for supplying my switching ultrasonic, the voltage from the converter was continuously decreased. below is the simulation and the circuit

the green line is the supply from converter right before the zener diode, and the red line is voltage in R3, note that it is 1 MHz switching so it seems just like a solid shape. the green voltage dropped down when the switching circuit does the work, after a while the voltage will be below zener diode and the diode cannot maintain the output voltage. so how to maintain the voltage for supplying the switching load circuit

do i need to increase the converter frequency to 1Mhz, same as the switching load? but when i do this, the voltage is slightly less than 10KHz converter.
i have tried to increase C1 but the voltage still drop down but just with less step, so will huge C1 solve the problem?

thank you so much for the help


texts: Can't get consistent readings from Sharp IR range detector

texts:
I'm in the very early stages of trying to build a robot that wanders around and builds up a map of its environment.  I'm using an Arduino and I currently have a Sharp 2Y0A21 IR range detector sat on top of a servo so it can take a 180 degree sweep in 10 degree increments.

The trouble is that the voltage readings back from the Sharp IR sensor aren't consistent.  If I write an app that simple sends the value it reads from the sensor through the serial port and display it on my laptop, sitting the sensor pointing at an object, the values bounce around.

Watching the values, I can see that it tends to report one value more than the rest, so I wrote a SharpReader class that takes 20 samples and then returns the Mode of these values.  This now means I get more consistent values, but not as good as I would like.

I have some code that performs the 180 degree scan and sends the angle and distance down the serial.  I then have a python script that receives these values and draws what it sees on screen, ignoring any values at either end of the sensors range.  So putting it in front of a box, it should draw a straight line on screen, but it doesn't - the line is crooked and not consistently crooked, which confirms to me that it's the readings that are off, not my code.

I have read in the datasheet that it is advisable to put a capacitor (can't remember the value offhand) in between the GND and PWR lines on the Sharp IR - I tried forcing the legs of the capacitor into the JST connector of the Sharp IR, but it made no difference.  I'll try soldering it to the sensor and see if that makes any difference.

Can anyone recommend anything else to try, or am I just expecting too much from the Sharp IR?

I'm also considering buying a second servo and Sharp IR and running two at the same time like a pair of eyes, then trying to take an average of the two values to see if that increases the accuracy.

BTW, I'm a newbie to electronics, my background is in programming.


texts: Whats the minimum discharge for a 12v LiFePO4 Battery?

texts: I just purchased 2 "SOK LiFePO4 12v batteries", one of them after opening the box came with a charge of 7.9v the other came 12.9v. Haven't been used at all. What's the minimum safe discharge for this kind of battery? Should I be worried about the one that came at 7.9v? I am not very experienced with batteries, I assumed they should come new at a very close voltage to be ready to be connected in series. I am not sure if I should return it or buy a 12v charger.


texts:
I have one of those portable 16 Ah car jump starters that I want to use as a power pack for some 12v stepper motors. Rather than canabilize this plug, I am wondering if someone can tell me what it is called so I can see if I can find an unwired one on ebay or something to use. My current needs are very low at around 1 amp.

Many Thanks


texts:
This is mostly an educational endeavor. I'm looking into prototyping a NAND flash storage on an embedded platform running Linux. The ONFi standard seems convenient and promising, but I'm failing to see how this standard interfaces with a standard PC hardware bus. Ideally, I would like to interface such a storage device with the PCI bus (vs an IDE, SATA, or USB interface). Can anyone provide some clarity or a resource with some additional information?

References:

http://www.linux-mtd.infradead.org/nand-data/nanddata.html
http://www.onfi.org/


texts: Benefits of multiple op-amp gain stages in series?

texts:
I'm a bit lost in regards to how multiple op-amps in series will perform.
My use case would be the amplification of low-voltage audio signals (4-50mVRMS) to roughly 8VRMS.

I only found documentation on how gain will influence the bandwidth-product of the amp, but I'm lost when it comes to noise and distortion.
I was hoping to achieve better performance regarding amplification of the signal when using multiple gain-stages in series, but didn't find any documentation that would suggest an improvement in performance when doing so.

Is there any benefit in chaining multiple amps together in series other than improving the bandwidth-product of the circuit?


texts: Correlation between saturation of high current (power) transformer core and load

texts:
In an experiment I need high (\$>600A_{max}\$ or \$1200A_{pp}\$) AC currents in a range from 400Hz to 4kHz. The load is simply a short circuit. For this purpose i use a class D audio amplifier and a transformer with a capacitor in series, so I create a LC series resonant circuit. The frequency is set as it is needed to get resonance.

The transformer has 74 primary windings and 1 (2) secondary windings of HF flex cable. This HF flex cable has a length of ca 1.2m and is intertwined so that the inductance is rater low. The short circuit is made over a ca 5cm long copper bar, there applies the skin effect and this short pice of copper gets pretty hot.

The core of the transformer are two C shaped ferrites that are lashed together so i can't exclude a minimal air gap (but it has to be rater small). The exact data of the core is not present at the moment.

This is just a quick experiment for me and i used spare parts i found... Now i get two interesting effects and i don't understand the reason behind them:

(The same capacitor are used for (1) and (2) the frequency is set to resonance and differs for a few Hz from (1) and (2))

Note: i can't remember the exact numbers, they should only provide a reference point.

(1) On a first step I used 1 secondary winding. I get a primary current of ca \$5A_{max}\$ (\$10A_{pp}\$) and a secondary current of \$350A_{max}\$ (\$700A_{pp}\$). If i go up future with the input current the shape of the current goes from nice \$sin\$ to a triangle shape. The output current stays \$sin\$ for a bit and changes then also.

(2) On a second step I use 2 secondary windings. I get a primary current of \$14A_{max}\$ (\$28A_{pp}\$) and a secondary current of \$500A_{max}\$ (\$1000A_{pp}\$). If i go future with the input current the secondary current gets a strange shape and short after that the primary current gets peaks. The typical signs of saturation...

My question: Why does the primary current gets a triangle shape in (1). The effect from (2) is clearly saturation. If (1) is also a saturation effect, why does it rise with \$5A_{max}\$ and in (2) at \$14A_{max}\$ isn't the magnetic field only dependent from the product of \$I_{prim}\cdot N_1\$ and the saturation of the material constant for a fixed frequency? Is there a load dependency of the magnetic field in the core?

Note: the amplifier does not saturate (nor in output voltage, or current). It has plenty of power left...


texts: Choosing transformer for dual output forward switching converter

texts:
I'm pretty new to power supply design, however I need to design a switching converter with the following outputs: 12V/6A and 6V/16A. I've read some notes and decided on forward configuration with some TOPswitch-GX as main controller.
I'm currently reading the application note for designing forward converters based on these ICs: https://ac-dc.power.com/design-support/product-documents/application-notes/an-30-topswitch-gx-forward-design/

My current approach is to connect two secondary windings in stacked DC configuration mentioned in the application note. Since I need 6 and 12V, there should be the same number of turns for each one. The third secondary winding would be used as supply for the controller and feedback optocoupler.

The problem is, I don't exactly know where should I look for the transformer. I checked mouser, but I haven't seen any forward-dedicated transformers, and all the others was quite expensive.

I would like to know if my concept should be applied to that kind of converter. And if so, where can I look for standard forward trafos.

Regards,
Patryk


texts: How to calculate energy from power I receive every 5 minutes

texts:
I  have to calculate energy from power measurements, which I receive every 5 minutes. The values are summed and assigned to measurements, then monthly measurements and finally yearly measurements. Having that aggregates of power measurements, the question is if I can calculate energy in kWh unit by equation:
energy_sum = power_sum * (5/60) / 1000
as I want to convert 5 min to hours and W to kW.


texts: Effect of Drain-source voltage on NMOS operation

texts: I have been trying to understand the NMOS operation through various online tutorials but I am getting stuck in understanding the effect of increasing drain voltage on the flow of current and the channel length. I did understand that at similar drain and source potential current does not flow and only after applying positive potential to drain, current starts flowing from source to drain. Can anybody explain me the characteristics when drain source voltage is gradually increased and specially its relation with the threshold voltage?


texts: Area under curve within a particular time window

texts:
I am trying to make an analog circuit which would measure the area under the curve of a periodic signal within a certain time window (say, t2 and t3 in the image). I expect different voltages(say 50-500 mV) within that particular time (say 100 us) and want to compare the area in that interval with a threshold value later. I think an integrator should be suitable for the purpose, where after providing a cumulative value during the particular time, it will reset to zero. Is the idea correct and if yes how to design the circuit?

P.S. This is my first post. I hope the info is adequate. If not please let me know, I will add whatever is required.

Edit 1:

Just to be even more clear. These are the envelopes of the two signals I am dealing with. The intial part of the signals are the same. Then the voltage changes for a certain time and it decays to zero. I am trying to compare these two.


texts: What material and current do I need for a diy plant heater?

texts:
I want to heat my indoor plants with a DIY heater. I thought about using iron to heat up the soil, but I am not sure what material is the best for a heater. Also, what current would it need?

Thank you

EDIT: Could you at least explain why is my question bad before downvoting?


texts: How to design a 1-500MHz sine wave level detector to -90dBm?

texts:
I want to build a sine wave level detector that works for a single 1-500MHz sine wave in the range of -40dBm to -90dBm. This is a hobby project - so cost is not a big obstacle :-), but I want to stay below 2W and roughly matchbox sized.

My first attempt works well only down to -75dBm, so I need some help to design a better circuit to get to -90dBm. What is the best way to design a circuit to do this?

BACKGROUND

The first attempt at a design is here:

My signal chain is like this:

SMA > ADG918 (switch) -> MAX2611 (LNA) -> MAX2611 (LNA) -> AD8363 (level detector) -> A/D converter

The first switch can select a reference signal of a known amplitude for calibration. The two LNA’s have about 20dB gain each. Absolute accuracy is not important - it can all be calibrated away as long as the circuit is relatively stable.

Results from the first design:

I know I am fighting 1/f noise and thermal noise, but what is a good design that can achieve measurements down to -90dBm?

Update

I know now that thermal noise puts the noise floor above the target for a 500 MHz wide band, so a different circuit is required (just as Andy aka explains in his answer below).

The system "knows" the frequency to measure and there is a fairly pure tone of that exact frequency in the system at -10dBm.

A perfect answer would point out example key parts and sketch out a rough block diagram.


texts: How to increase the dimming range of mosfet controlled LED

texts:
I'm slowly getting into circuits and I've put together a PWM LED dimmer. The led is driven by this circuit:

I'm driving the PWM via a separate BLE device which maps a user input of [0, 100] to an 8 bit value for the arduinos PWM [0, 255]. Here is the code:

int led = 9;           // the PWM pin the LED is attached to
int intR;
int t;

void setup() {
  Serial.begin(9600);
  Serial.println("serial connected...");

  // declare pin 9 to be an output:
  pinMode(led, OUTPUT);

  analogWrite(led, 0);
}

void loop() {
  if (Serial.available() > 0) {
    intR = Serial.parseInt();
    t = map(intR, 0, 100, 0, 255); //remaps intR from [0, 100] -> [0, 255] to scale to PWM
    Serial.print(intR);
    Serial.print(" -> ");
    Serial.print(t);
    Serial.println("");

    analogWrite(led, t);
  }
}

Whenever I set the dim value to 100 (100% duty cycle), the led is shining quite brightly, but when I set the value to 0, the LED shines at probably 60% brightness.

What would I have to do in order to smoothly transition the LED from a fully OFF state, to a fully ON state?

EDIT:

After a discussion in the comments I've updated my code and circuit and something seems wrong. The following code and schematic pair give me the best dim range (visually maybe 10-100% total output) and works on multiple mosfets from my package.

New code & circuit schematic:

int led = 9; // the PWM pin the LED is attached to
int intR;

void setup() {
  Serial.begin(9600);
  Serial.println("serial connected...");

  // declare pin 9 to be an output:
  pinMode(led, OUTPUT);

  digitalWrite(led, LOW);
}

void loop() {
  if (Serial.available() > 0) {
    intR = Serial.parseInt(); //reads the next valid integer
    Serial.print(intR);
    Serial.println("");

    if (intR <= 255 && intR >= 0) {
      if (intR == 0) {
        digitalWrite(led, LOW);
      } else {
        analogWrite(led, intR);
      }
    }
  }
}

My MOSFETs are labeled P30N06LE which correspond to this RFP30N06LE datasheet. And unless my fets were made incorrectly, my drain really does go straight to GND, and my LED negative feeds into the source. The problem I have now is twofold: 1) understanding why my circuit works this way and 2) getting my led to fully power OFF when setting the pin to LOW.

With the above configuration, when pin 9 is set to LOW, the LED is at ~10% brightness, and when I physically remove the wire from arduino pin 9, the LED shuts off completely. If I then plug the wire into various unpowered pins, the LED shines at a low brightness, indicating enough voltage is present to power the fet. How can I get the led to turn off completely?


texts: The phase of voltage across a resistor in a RC circuit when the frequency of input tends to zero

texts:
Across the resistor we have
$$
\begin{array}{c}
V_{R}=\frac{V_{i n}}{\left(R+X_{C}\right)} \cdot R \\
V_{R}=\frac{V_{i n} \cdot R}{R+\frac{1}{j \omega C}} \\
V_{R}=\frac{V_{m} R j \omega C}{j R \omega C+1}
\end{array}
$$
Which gives
$$\mathrm{V}_{R}=\frac{\omega R C V_{i n}}{\left(1+R^{2} \omega^{2} C^{2}\right)}(\omega R C+j)
$$ Which then gives us the phase of voltage across the resistor. Similarly we can do for the capacitor and we have respectively ( assuming phase of input voltage to be zero)  :
$$
\phi_{R}=\tan \left(\frac{1}{\omega R C}\right)
$$ and
$$
\phi_{c}=\tan ^{-1}(-\omega R C)
$$
And
$$
\begin{array}{l}
\omega \rightarrow 0 \\
\phi_{c} \rightarrow 0 \\
\phi_{R} \rightarrow \pi/{2}
\end{array}
$$ so we see that the voltage across the capacitor is in phase with the input voltage. However we have
$$
v_{R}=v_{i}-v_{c}
$$ and from this equation we see that if the capacitor voltage is in phase with the input voltage, then the voltage across the resistor is in phase with the input voltage. But this contradicts the above equation which says that $$
\phi_{R} \rightarrow \frac{\pi}{2}
$$
Where am i mistaken. Please help.


texts: Design vs reality and what to do when they differ

texts:
I've been trying to focus a bit more on Analog circuits lately and found that my design and actual results often don't match up exactly. An example is a Pierce oscillator I built a while back, the circuit worked mostly as expected but the gain required was much less than I calculated for (meaning I got some distortion). Is it common practice to just change the values to what seems to work right and go on or is it better to make sure the theory matches up as well?

To clarify, I mean that after observing the difference and playing around with some values I change the design to match, the circuit then gives the desired output but my initial design was inaccurate. Should I go back and try to identify why or is it just not worth it? ie, no calibration on production units.

Thanks for all the replies, I'm going back to the drawing board because there's clearly something going on that I don't understand. Ignoring it would possibly create other problems.


texts: Feedback Resistor and Capacitor in amplifier

texts: What is a feedback resistor and capacitor?  Why are they are used in amplifier circuits?


texts:
I want to design butterworth filter in matlab only based on order of the filter and the cutoff frequency in Hz.

the syntax is for returning the ABCD matrix of statespace is

[A,B,C,D] = butter(____)

I tried doing below for 2nd order and 30Hz cut off

[A, B, C, D] = butter(2,30)

But i get an error saying :

Error using butter (line 41)
The cutoff frequencies must be within the interval of
(0,1).

Any help will be appriciated


texts:
Circuit shown is a VCO that reliably creates a 200MHz sine wave at 3V pk-pk. I would like to use this VCO to create an FSK modulated signal. My bit 1 frequency = 200Mhz and my bit 0 frequency = 205Mhz optimally.

When I try to add a varactor or a diode and capacitor in parallel to my original circuit as shown below instead of getting the two frequencies I would expect I get a very garbled fft (using LTspice) that is not at all what I want. I have tried using V1 (data stream in) as a square wave,sine wave or DC 0V for one iteration and DC 5V for another iteration. I have tried numerous ways of connecting the varactor (D1) to the original VCO with different orientations of coupling capacitors etc with no luck.

The two equations which I am using to generate the colpitts oscillator values as well as the value of the varactor/(diode capacitor pair) are shown below. C1 is actually C3 and C2 is actually C4.

Any help or ideas would be greatly appreciated as I am very confused and very frustrated. Cheers.

Matlab script to calculate L and C values. Then reruns it through to check correct frequency. I know I mentioned that I wanted 200MHz and 205MHz but I found these would good values that I hand tuned to get the desired frequencies.

Matlab script output. C3 is the varactor capacitance.


texts: What is the maximum charging current of the MAX1737?

texts:
I am currently trying to choose a charger IC for Lithium-ion cells batteries and thereby came across the datasheet for the MAX1737:

https://datasheets.maximintegrated.com/en/ds/MAX1737.pdf

The datasheet does not seem to mention the maximum charging current this IC is able to supply.

Hence my question: Did I miss something, or could it be that the most important characteristic of any charger IC indeed is not mentioned in that datasheet?

EDIT 1

I have understood that the charging current is driven by an external MOSFET. But when you go to

https://www.maximintegrated.com/en/products/power/battery-management/MAX1737.html/tb_tab1#tab1

and then switch to "key specs", you can see that the maximum charging current is 4 A.

So I am rewording my question:

Why is the charging current limited at all (given that charging is driven by an external MOSFET), and why is that limitation not mentioned in the datasheet?


texts: Beginner safety questions regarding voltage and current

texts:
I'm a complete beginner to electronics so please excuse the simplicity here :)

I have a phone charger that outputs at:

5V - 3A
or 9V - 1.6A
or 12V - 1.2A

I would like to use another charger while at work, which outputs at:

5V - 1.8A

I don't know what the input for the phone itself is.

I assume it's safe to use the second charger because the phone will only take the current that it needs?
If the second charger had a voltage higher than the phone's charger, should it be avoided?
In general, how would I determine if something is safe to use or not?
When do things get to the point of damaging the device, or even worse, starting a fire?

Thanks!


texts: I have a plant that I want to automatically water. I have a plan to buy a small fountain pump which plugs into a wall. I am also going to build a small soil moisture sensor to see if the soil is dry. I want to find a simple way to let power go through the wall outlet to the pump once the sensor circuit is broken from the soil dryness. I am only 12 years old and I don't have a soldering iron so please help me find a way to make a circuit to water my plant. Thanks!


texts: Switching depending on resistance from fuel gauge sender unit

texts:
I hope someone can offer a solution to the following situation:

We currently have a fuel gauge operating at between 12,6 and 14,6 VDC. The sender unit ranges from 10 ohms (empty) to 300 ohms (full).

My question is whether it is possible to use the resistance values mentioned to control a fuel transfer pump relay, preferably to switch on at 100 ohms and switch off at 250 ohms?

Your advice will be greatly appreciated.


texts: I’m bad at electronics/new, If my battery is 19V going to a 12V motor how do I lower the voltage from the battery to the motor? Would a resistor do the trick? Thanks for any responses in advance.


texts: Need help explaining behaviour of a circuit

texts:
just can't wrap my head around this one for some reason. I am sorry if it's easy for you to see. Just confused on the duality of things in circuits, Is it a filter? Or is it a peak detector? How do you know which topology to apply?

I am only talking about the positive cycle of the circuit.
Essentially the current runs from R1 -> R2 -> C1 and R3 -> GND
This cycle charges the capacitor, however we could simplify the circuit knowing which path current is taking.

As D1 is R.B And D2 is F.B and The Op-Amp isn't doing anything.

simulate this circuit – Schematic created using CircuitLab

Which becomes this. My question is, isn't this a low pass filter? If it is why is that the output signal isn't attenuated then? Why is the input voltage at the output?

simulate this circuit


texts:
Is there an IC that will enable us to have biquad filter given in this PDF?

Thanx..:)


texts: Charging Phone with a Modified Power Supply

texts:
I have converted a computer power supply into bench top power supply and I am now ready to add some USB ports to charge various devices. On the power supply label it shows the 5v rail is capable of delivering 14 amps. If I connect a USB port to the 5v rail, will it fry my phone? (I'm assuming 14 amps will most definitely destroy my phone).

I know generally devices will only draw what current they need, but I ask because my phone obviously charges faster with a 2amp charging block vs a 1amp charging block. So therefore, if the power supply can produce 14 amps, wouldn't my phone attempt to charge at 14 amps?

Sorry in advance if this is a noob question, I have only recently started messing with electronics, or anything with electricity for that matter.


texts:
This may be a silly question, but I was wondering about the resistor involvement of a DC blocking network employed at frequencies 5MHz to 2400MHz.

Most of the designs I have seen are an RC arrangement:

----||-----
       |
       R
      ///

Now the RC combination I know develops the a time constant on charge and discharge.

However, if you are just wanting to block the DC part, why put a R in at all?

From I remember the statement was always (when regarding AC and caps), what happens on one side happens on the other.


texts:
I have been working on a system which allows to turn on a PC without physical presence. I'm using an Orange Pi platform with a board designed for testing the embedded systems.

My assumption:

green cable from the ATX power supply is connected through the relay to the mo-bo
power-on button cables are connected to the circuit which acts like an open-collector.

How do I want this circuit to work:

I turn on a relay (green cable is shorted directly to the mother-board)
After 1 second I enable for a moment an open-collector circuit.
If it comes to shutdown, I turn off the relay

Is it gonna work? Remote working is what I want to gain. Orange Pi is connected to the network and I operate it using SSH.


texts:
I realize this is nearly a dupe of SBC Recommendations , but I have slightly different specs in mind.

Does anyone know of a single-quantity SBC with the following features?

32 bit CPU, something common e.g., x86, ppc, arm, atom
capable of running some fairly modern variant of Linux
built-in 100Mbit/s ethernet interface (preferably with RJ-45 jack)
built-in RS-232 or RS-232C serial port (DB-9 connector desirable but not critical)
capable of booting an arbitrary OS/application from FLASH
capable of booting an arbitrary OS/application from ethernet
capable of booting over serial port desirable, not critical
must have at least one USB 2.0 port. more::=better
must operate from a single-voltage DC supply (not more than 28V, not more than 25W)
prefer Not to have PS/2 keyboard & mouse interfaces
prefer Not to have any graphics capability
built-in SPI, I2C, or general-purpose discrete I/O bonus
price point under $250

The mission for this SBC is to sit on my network and operate custom I/O hardware. Heaviest possible use case required would be to support a USB web-cam and serve low-bandwidth (CIF) video through a custom server app. Definitely not required to run databases, web servers, web browsers, middle-ware, ESB, or anything like that. Intended s/w platform C/C++, and maybe, just maybe, J2ME or J2SE.

The best match I've found so far is the BeagleBoard ,  but this falls short by having graphics capability (not needed) in place of ethernet capability (mandatory). I know you can add a USB based ethernet adapter, but ideally there would be a better match that would render this not necessary. There are also some atom-based 'car PCs' that are near misses, mainly for power supply reasons.


texts: Line or Low or High Voltage Twisted Cable?

texts:
I understand that telecommunication cables are often twisted to cancel out electromagnetic interference (EMI) from external sources, e.g., crosstalk.

Are power cables ever twisted and if so, why?


texts: Multpile sets of rules in altium (Rules by selected area)

texts:
I'm new with altium and i'm trying to make a 12V power supply.
I don't want it to overheat more than 20 degrees, so I need to put a trace of at least 4,75 mm... My problem is that when I change the Rules in altium, it changes it for all the document. Is there a way to apply a rule on only a certain Area of the pcb? I tried using rooms, but it seems I cannot put a rule on it... Other ideas?


texts: negative binary representation and 4 bit BCD represenation are similar

texts: While representing negative numbers in binary we use MSB as sign indication.In BCD we use 4 bits to represent numbers 8-15. How does a device(ex:computer) decide whether its a negative number or a number in range [8,15].


texts:
This is my first question here from the community :)
So I have inherited some bad embedded code, the whole firmware is a messy spaghetti state-machine that has an infinite number of states! and it is so messy that no one dares to touch it because testing it would take months (we don't have any automated testing systems)! so practically code maintenance is almost impossible.
The devices are used in Automation, they are responsible to measure few analogue signals and do calculations to estimate some physical qualities. We have three different types of devices that they even send data to each other and a state of one may impact other devices behaviour.
The hardware is based on SiliconLabs 8051 series. The compiler is Keil uVision with the C51 compiler.
I want to change this sticky situation and organise the code by introducing hardware abstraction layers and modularising the code to smaller chunks.
In order to achieve this goal, I personally think that we need to develop a test bench for devices that I can test them after refactoring and code cleaning. So the idea is to use another microcontroller (STM32) to fake the PCB's or MCU's inputs to simulate the actual environment that the device should work in. Since the behaviour of different devices has an impact on others, I think we have to have a test bench that represents a network of devices so we can also do integration testing.
I have been looking around the web and reading about ways to help me test this messy code, but I haven't found any other way of doing so.
What do you think? is there any other approach that I can take? or do you have any suggestions? how would you handle this situation?
Thanks!
EDIT:
Thank you everyone for your comments and replies!
So The firmware is tightly coupled and there are hardware dependencies and global variables everywhere, the firmware has more than 12,000 lines of code. The main issue here is that even the regression testing involves a hideous and time-consuming 100% manual process that requires the tester to have lots of physical interactions with the device itself and may take more than a day or two!
So I'm looking for a way to test (regression testing for now) the current firmware running on the MCU without the need to refactor and/or changing the code since even a small change in the FW requires intensive manual testing. My understanding is that by having a black-box test rig, that emulates the real environment for the device we can test the FW much quicker and even automate the process. Most of our devices have very limited inputs (like 3 analogue input, and 5 digital I/Os) and the main output is CAN messages that can be processed easily.
Another reason to invest in a HIL test rig is that it will help me to simulate scenarios involving other sub-systems (Integration testing). For instance, there are some ancient bugs in the FW CAN Bus networking that are really hard to identify without monitoring every device and being able to track which one of the devices on the network and during which condition is messing with the network.
Currently, if we want to validify FW we have to install it in an actual environment, collect the data for months ( 2-6 months!!) and analyse the data to validify the device's behaviour. Then you'd find out that there is a bug somewhere (it might even be caused by another device on the network) that is impacting the data you've collected!! Next, you have to do the same process again for another few months :(. I would prefer to automate these process to some extend, so we can at least catch the bugs and issues before installing the device in the real environment.


texts:
Just for fun, I decided to build what I was hoping would be a relatively powerful electromagnet. I used this copper wire (20 AWG, entire 1 pound spool) and this soft iron core (0.5 in diameter, 6 in length). The total length of the wire is approximately 322.6 ft (98.33 m) long and based on some sloppy calculations, is coiled around the core about 2000 times. My goal was never to be super precise with this project, so please forgive the rough estimates.
Unfortunately, the magnet is extremely weak most likely because I don't have the proper power supply. I first tried using 4 9V Duracell batteries in series, then tried 3 AA Duracell batteries in series, but the magnet can just barely attract one paperclip from a few cm away with either power supply.
From what I've read/seen online, I should probably be using a 6V "lantern battery" or a 12V car battery, but I'm not sure what is appropriate for my setup. If anyone has advice, it would be greatly appreciated.
Thanks in advance!
Also the entire wire is coiled in one direction and, if it matters, the first few layers of wire were coiled very carefully, but obviously I got a little lazy toward the end.


texts:
I am currently working with a sinusoidal signal buried in noise.
I filter the signal with a low-pass filter of which I know the transfer function.
How can I calculate the SNR after the filtering process assuming white Gaussian noise?
How would I calculate the SNR assuming pink noise?


texts: Differential (Subtractor) op amp with low pass filter

texts:
is it possible to have a subtractor circuit with a low pass filter in it?
My thought is that I would have the possibility of doing that if I add a capacitor in parallel with R3. Is it actually possible? If not, whats the best way of doing it?


texts: STM32F103RB ADC (pics included) strange values for temperature sensor (LM35)

texts:
I've connected one battery/2 batteries (GND and A0) and the measuremet displayed on the com26 port is ok.
I've connected the LM35 (The LM35 has 1 celsius degree for 10mV measured value) on the VCC and GND and the output pin is connected to the A0(analog input). The value read on the com26 port at room temperature (26 celsius degrees) is 40 celsius degrees. I don't understand what is the problem. The sensor is ok because I've used a multimeter and the output value is 262mV, divided by 10 =26 celsius degrees. but the uC measures 400mV (instead of 262mV) that means 40 degrees. I've used external power source for the LM35 sensor and the same problem. I've used 3.3 and 5V for the LM35 (from the uC board) and the same problem...I'm very courios about this problem ...

I'm a beginner in STM32, so please help me.

**
Update: I've made firmware upgrades, stm32 library updates, picture 2 updates...
In picture two, first rows readings are from a 1.28V battery
the rest are from the LM35 sensor.
Battery seemns ok but for LM35 I get 367mV instead of 270mV (measured with a multimeter)
I don't know why the value from L35 is not ok from the uC's ADC**

code below:

  #include "test_env.h"
Serial pc(USBTX, USBRX);
AnalogIn analogValue(A2);
DigitalIn userButton(USER_BUTTON);
DigitalOut led(LED1);

// Calculate the corresponding acquisition measure for a given value in mV
#define MV(x) ((0xFFF*x)/3300)

void notify_completion(bool success) {
    led = 0;
    pc.baud(9600);
    int count = 0;
    bool enFlag = true;
    while (1) {

        count++;
        if (userButton == 0) {
            enFlag = (enFlag == true) ? false : true;
            //pc.close();
        }
        if (enFlag) {
            unsigned short meas = (analogValue.read_u16());
            float final = (float) 3300 / 65535 * (float) meas; // normal 0.0008  or 3.3v-3300mV  0,8058608058608059 3300/4095

            pc.printf("%d;%d val in mV: %d, tmp:%d  \n", count, meas, (int) final, int(analogValue.read() * 3300));

        }

        led = !led;

        wait(2.f);
    }

}


texts: Can I communicate with an Atmega32U4 through USB during runtime?

texts:
I'm designing a PCB circuit to do PID control using sensor data to control a robot. I'm new to using micro-controllers other than Arduino and I'm having some trouble figuring out exactly how everything fits together.
What I want to be able to do is figure out the inverse kinematics in Matlab and send the desired angles to the micro-controller from my computer.  I've started to put together a schematic for an Atmega32U4 (http://ww1.microchip.com/downloads/en/DeviceDoc/Atmel-7766-8-bit-AVR-ATmega16U4-32U4_Datasheet.pdf) based circuit because it has built in USB support and for now I am okay with powering my board through USB as well.
But I don't understand exactly what I will be able to do with a basic USB connection to the micro-controller.  Will I be able to send data while the circuit is running to command angles for the robot?  Is that just a question of the micro-controller's code?  My circuit is basically the same as this one in terms of USB connection: https://www.avrfreaks.net/forum/please-help-review-my-atmega32u4-board

I'm not particularly attached to this exact micro-controller if there is an easier option.  I just don't know what that would be.  The only real constraint on the micro-controller I use is that it has to have at least 3 ADC input pins and at least 3 PWM output pins


texts: Calculating weights in a particle filter experiment using multiple state variables

texts:
I am trying to implement a particle filter for coupling gyro and electronic compass for better measuring device orientation. [related question]

I understand my state vector would contain the absolute angle and turn-rate and my observation vector contains the readings for the same from the compass and gyro.

In my transition model, I just use the constant turn-rate assumption plus random noise to move the particles to their next states. Then, when I get a set of readings (angle and turn-rate from the sensors) in the next time instant, how do I assign weights to the particles? Is there a systematic procedure to assign the weights for a state vector containing multiple variables or should I just calculate it based on the difference between the predicted value and the observed value for both compass and gyro?

i.e.: weight(particle X) = RMS(angle(Particle X) - angle(sensor), rate(Particle X )- rate(sensor)), and then normalize all the readings?

EDIT:

Let me explain my problem a little further. I am working on the basis that the electronic compass alone is subjected to magnetic interferences in the indoor environment and hence the gyro should be used along with it to improve the accuracy of orientation.

Now, these magnetic interferences will form the external/environment noise of the process and will definitely be non-Gaussian, since they are bound to be biased towards the side of the metallic structure. That is why I chose the Particle filter over say, the Kalman filter although it is the most preferred method. So when I really don't know the pdf of the noise, then how do I estimate the likelihood that a predicted value is equal to a real value (which would be its weight, right?)

Assuming a normal distribution in this case would not work, because it would give me wrong probabilities for particles. Atleast, this is what I understand; please correct me if I'm wrong.