texts: Designing Switching Circuit for Raspberry Pi 3 Project

texts:
I'm working on a simple RPi project wherein I can control my garage door with my phone via Tasker. I am using an RPi to connect to my wifi network and power on a remote garage door opener. My current setup is to short out the button on the remote and use the RPi's GPIO pins to supply power to the remote (wired up to the battery terminals) when I want to activate the remote signal. This generally works, but after not being used for a short while (overnight or less) it takes two activations to operate properly, making me suspect that the capacitors are losing charge when the device is unpowered. So I need to make it more complex and traditional, continuously powering the remote via a 3.3 VDC pin from the RPi, and using a switching circuit to make the button connection.

I can easily purchase purpose-built switches for the RPi, but I would like for this to be a fun learning experience, not just a functional final product. Also, I would like to purchase my parts locally from a specific store (in links below).

The remote switch has ~2.85 VDC around it when active. I would have needed to desolder it to see what the current through it would be when active, so I don't know exactly how to spec out a relay. For what it's worth, the current through the battery is 3.2 mA when active.

I does not seem that I can operate a relay directly from the RPi's 3.3 V GPIO pins, since I cannot find any relays with 3.3 V (or lower) coil voltages, so I need to use a 5 V relay. I found a cheap relay that seems appropriate, but I cannot find a datasheet for it, so I'm thinking about this relay instead, even though it is probably overkill. The datasheet I found isn't for the exact model number, but I think it's basically the same. It seems to have a ~140 Ohm coil resistance, so at 5 V it would require 36 mA of current.

Of course, I will now need a transistor, so I think an NPN would be best to make sure my system is not "active" during boot. But I'm not sure what specs to look for. This transistor [(PREVIOUSDOMAIN)/commerce/catalog/product.jsp?product_id=13754&czuid=1481073107852] has the lowest rated current, so I'm guessing that's the current needed at the base? Not sure about the gain or if the voltages matter, or if I need a resistor in line with it. The relay will push 36 mA of current between the collector and emitter, and the RPi will push 5 mA (assuming I'm looking at it right), so does that make it ok? V_CE will be less than V_BE, so I don't know if that's an issue...

And I know I should include a flyback diode, so I'll try to figure out that part once I know the rest makes sense.

Thank you to anyone who can help me evaluate my project!


texts: Charge 12 V, 1.3 Ah lead acid battery via 12 V, 5 watt solar panel

texts:
Can someone explain me the below circuit which is used to charge 12 V 1.3 Ah lead acid battery via 12 V, 5 watt solar panel?

The circuit is shown below I need to know what is happening in this specific circuit.


texts: Am I thinking about this correctly regarding 12V, 24V and 120V LED lighting?

texts:
Most of the LED light strips I see are either 12V or 24V, which require a driver to step down the power from 120v at the wall (thus the little black transformers that come with them).
However... I only recently discovered they come in 120V with a small in-line rectifier, AND they can be run over 150ft without a voltage drop in a single strip.

Aside from cost, why bother with the 12V and 24V route with the wiring when you can simply hook up the 120V directly to a dimmer switch in the wall (with a built in rectifier of course)?

I'm new to the LED light strip world, but am I missing something when it comes to why most people go with the 12V and 24V version?

Minor clarification edit for my application: I'm looking to use a long run LED lighting setup in crown molding around a living room, and it greatly simplifies things with a single run as opposed to several power supplies to driving about 100 feet of lighting. But I'm new to this kind of lighting, so willing to learn something new)


texts: I'd like to learn how to make my own USB gadgets

texts:
I've been writing Linux character device drivers for other people's stuff for some time. I'd like to find a new hobby and the thought of making my own USB gizmos seems really neat.

I would be thrilled to be able to control some LEDs, servos, and step motors. I really enjoy learning new things on my own and the excitement when something finally works. I've not done any serious MC programming, but do know my way around.

Can anyone recommend some kits that would be helpful to a complete noob? Ideally, they are:

Linux Friendly
Able to ship internationally (I'm currently living in Asia)
Offer breadboard kits

If you have the time and inclination, links to projects on other people's sites that include schematics and parts lists would be greatly appreciated. I want to study from examples, but good examples, which is why I'm asking here.

My eventual goal is to make my own data collectors - everything from rainfall to average decibels to light levels. Sorry if this has been asked before, I did search (and searched tags).


texts:
We have the circuit in the figure.I have to find the currents in the diodes and in the resistances R1 and R2.
The diodes are real and Vd=0.7 V

Awesome.

Here is the original figure

I have drawn the circuit and I have replaced the diodes with the voltages

I apply the KVL in the first loop and I have -20+ 0.7+0.7 - I2R2=0  so I2 here is negative...what am I doing wrong?


texts: Reason for an RC motor to spin very slowly

texts:
I have the following motor:
GP307 Ultra Dash Motor by Tamiya.

I've read online that you can give this motor up to 16 volts. I have been putting in 11 volts and it spins very slowly, maybe about 200-300 rpm.

I don't know much about how motors work, so I ask you, what would make one of these little motors spin very slowly?


texts: Is there any bidirectional IC with on/off state?

texts:
I need a bidirectional IC with on/off state.

In on state, IC should have very small impedance on the line.

In off state, IC should provide very high impedance to isolate the bus.

It's for an 3-channel line isolation. To be more specific, it's for SPI bus isolation.

No need for level shifting. Just need to be able to isolate the bus with a logic high or low.

I am looking for a IC because I want to make my board more compact, not because it cannot be done use discrete components. I have been searching all this afternoon. Most of the ICs are for I2C level shifting from high to low or low to high.

Thanks

Updates:
1. Thanks for suggesting the analog IC switch. I am deciding in between analog IC switch and digital IC switch. It looks like the only difference is one is made of CMOS and one is only made of NMOS.

I also found this  Digital Bus Switch ICs Single FET. Is it bi-directional?
I found 74HC243 does exactly what I want. The trick is the to search the right name. Now that I know what name to search, I found tons of chips from different companies that does the same. thing.


texts: Voltage Dividers in a pull-up resistor circuit (why does the pin go to low)

texts: I understand that when the button is in its open state the voltage on the input pin should be fairly close to \$ V_{cc} \$ provided \$ R_1 << R_2 \$ as \$ V_{in} = V_{cc} \frac{R_2}{R_1 + R_2}\$. But, I do not understand why the voltage on the input pin changes to low (close to 0) when the button is closed.


texts: J1939 ,9pin Deutsch diagnostic connector

texts:
I am a novice,in this area Sorry!I have no communication/ connection to a excavator as in the above title
My later model machine I can connect no problems.
Between the pins for Can High and Can low I have 16.92 ohms,
I believe it should be about 50-60 ohms?
I have good earth and I have ignition voltage .
Would this resistance be enough  to cancel out diagnostic communication through can bus?
It has no effect on machine ,but in reading of faults ,no can do!
Any thoughts and solutions very welcome.
Thanks ever so much
Regards Mo


texts: How do I link two components from different files in VHDL?

texts:
Sorry for the amount of code in advance (I added the code since I was unsure whether it is needed here to resolve my issue).

My main goal is to link two components which are in two separate .vhd files together in a block in a third file.

Lets say that I have got the following code in my file chooser.vhd:

library ieee;
use ieee.std_logic_1164.all;
use ieee.numeric_std.all;

library work;
use work.all;

entity chooser is
    port(
        clk, rst : in std_logic;
        DATA : in std_logic_vector(4 downto 0);
        A : out std_logic_vector(4 downto 0);
        Src : in std_logic_vector(1 downto 0);
        SOp : in std_logic_vector(1 downto 0);
        debug : out std_logic_vector(4 downto 0)
    );
end entity;

architecture structural of chooser is
-- here
begin

end architecture;

And that I have two components in another two files called registry.vhd and MUX3x5.vhd

MUX3x5.vhd

library ieee;
use ieee.std_logic_1164.all;
use ieee.numeric_std.all;

entity MUX3x5 is
    port(
        IN0 : in std_logic_vector(4 downto 0);
        IN1 : in std_logic_vector(4 downto 0);
        IN2 : in std_logic_vector(4 downto 0);
        SEL : in std_logic_vector(1 downto 0);
        O : out std_logic_vector(4 downto 0)
    );
end entity;

architecture behaviour of MUX3x5 is

...

end architecture;

registry.vhd has an output of 5 bits

I want to connect them like follows inside chooser.vhd  registry --> MUX3x5  (on the second input). How do I do that in my chooser architecture above?

Should I declare them as components with their ports as seen in the entity declaration in the original files for the components in the architecture and then route them in the port map? Like so:

Attempt

architecture structural of chooser is

signal -- signals here

-- copy of the inputs/outputs in the entity declaration in the file above
component MUX3x5 is
    port(
        IN0 : in std_logic_vector(4 downto 0);
        IN1 : in std_logic_vector(4 downto 0);
        IN2 : in std_logic_vector(4 downto 0);
        SEL : in std_logic_vector(1 downto 0);
        O   : out std_logic_vector(4 downto 0)
    );
end component;

component registry is
    port(
         -- some signals here
         TS : out std_logic_vector(4 downto 0)
    );

begin

-- port map here
    port map(
            TS => IN1;
            -- other maps
);

end architecture;


texts: Can I use the center tapped transformer as a non-center tapped transformer?

texts:
I am building a single DC power supply from scratch. I use the transformer to step down the 120 volts wall line. I want to use a non center tapped transformer. I found a center tapped transformer (one that has 3 connectors on the secondary side).

I just want to ignore the middle one and treat it as a non center tapped transformer.

Is this possible to do? just simply ignore the middle connector? What are the "product-wise" consequences of being me ignoring this middle connector? I mean, in my schematic, it will appear as a non tapped transformer, but in reality, the product may behave in an unexpectable and unacceptable way? I am worried about this.


texts:
I've recently been working on a breadboard compatible compact debouncing PCB. I found the MAX6816, a debouncing IC - check the spreadsheet here.

I made the below simple circuit as per the "Typical Operating Circuit" on the data sheet.

The datasheet does not show a resistor between ground and the button here:

Should I add one to my circuit or would the IC include one?

Thanks for your help in advance.


texts: Is it possible to connect USB printer to Atmega8

texts: I have a usb thermal printer, that I want to control using Hex commands in its datasheet from cheap micro-controllers. But to do that I need to create USB host in my board and it requires more than just Atmega8. Instead If I just throw usb packet, which has my command, from controller to printer, would it work?


texts:
There are various RFID tags that are designed to work in close proximity to metal but generally they hope for free space or at least limited loading in close proximity.

As a work around for RFID tag sniffing various metallised wallets and card sleeves are available.

I am curious if anyone has insight into the best metal to select for making such a case?

Copper, aluminium, maybe gold and untarnished silver are good conductors.  Mu-metal is a good magnetic field absorber.  The MetGlas type materials have some funny characteristics and are used in fluxgate magnetometers and as far as I know the strange shop anti-theft tags with the two bits of foil inside.

Would the low frequency tags prefer a magnetic shield and the VHF and UHF tags prefer a conductive shield?  Could or should one use both types to cover all of one's bases?

EDIT:
Personal privacy and bank card and passport sniffing are going to become more relevant in future. If I want to market protective wallets one day I would like to make them from the right stuff.  Persons movements can be tracked, funds withdrawn and some of their identifying details may be visible to determined parties who are up to no good.  Having a flexible shield is preferable but even a trustworthy hard case would be of use in many cases.

The Wallets would be like your everyday bill fold, bank card holder, purse or wallet.  Basically any place that you might store your banking cards or card style biometric identity cards.  A larger version that can hold passports and airline tickets would also be an option for travelers.


texts:
I have a quick question about three phase transformer windings.

if I have a transformer that is Yd11 but I connect the generator to the d-side instead(primary side). Does it become Dy11 connected or what is the new connection??

Would also appreciate any hints on how to draw the phasor diagram for the new connection.

Thanks!


texts:
I am new(ish) to hardware and I have a two-part question. I'm working with the Analog Devices LTC4124 chip for wireless Li-Ion charging. I'm using the dev kit (2773A-B) for charging the receiver. The datasheet states that there are 4 LED charging states, one high impedance to denote "no charge" (which from my understanding should just pull the LED down), one pulled down for "end of charge", and then two blinky states. However, I recently got a fifth state, where the LED was pulled high and (Q1) I was wondering if anyone could help me figure out what that means since I don't see it in the datasheet.
To give context, I have the wireless charging output a fixed 3.3V / 1.6A with a buck/boost converter. This then powers an ESP32 plus a couple of peripheral sensor components. I was testing it recently to determine the runtime before battery depletion. However, once the battery is depleted such that it wont charge the ESP32(+peripherals), placing the receiver on the wireless transmitter wont immediately initiate charge. I don't plan on letting the boards cut off like this normally, but the chip has a low battery disconnect to protect the charging and it should allow for charging once placed on the charger. (Q2) Am I missing something?
The two questions are related because the LED being pulled high only happens once the battery is depleted and the board is put back on the charger to charge.


texts: Modeling the discharge efficency of grid connected energy storage systems

texts:
Short form
A battery has a charge and discharge efficiency of \$95\$%. The initial SoC is \$3 \text{ MWh}\$. It charges for an hour with \$1 \text{ MW}\$, then discharges for an hour with \$1 \text{ MW}\$. What is the final SoC?
Long form
Suppose we have a battery storage system connected to the grid, e.g. the Tesla Powerwall.
The battery is rated at \$1 \text{ MW}\$ power output (charge and discharge) and has a capacity of \$5 \text{ MWh}\$. The charge and discharge efficiency is \$95\$%, so it has a round-trip efficiency of approx. \$90\$%.
The initial state of charge is \$3 \text{ MWh}\$. Then, the battery charges from the grid with the maximum rate for an hour. The SoC increases to \$3.95 \text{ MWh}\$. In the next hour, the battery discharges with the maximum rate to the grid for an hour.
Now, what is the SoC after that?

Is it \$3 \text{ MWh}\$? The battery charges with \$1 \text{ MW}\$ for an hour, so \$1 \text{ MWh}\$ is discharged from the battery, but only \$0.95 \text{ MW}\$ arrive at the grid due to efficiency losses. The calculation is
$$ 3 \text{ MWh} = 3.95 \text{ MWh} - 1.0 \text{ MW} \cdot 0.95 \cdot 1 \text{h}$$
Is it \$2.90 \text{ MWh}\$? The battery discharges with \$1.05 \text{ MW} = \frac{1.0 \text{ MW}}{0.95}\$ for an hour, so \$1.05 \text{ MWh}\$ is discharged, but only \$1 \text{ MW}\$ arrive at the grid.
$$ 2.90 \text{ MWh} = 3.95 \text{ MWh} - \frac{1.0 \text{ MW}}{0.95} \cdot 1 \text{h}$$

The question boils down to when is the discharge efficiency "applied"?
The second option seems inconsistent, as the "real" discharge rate of \$1.05 \text{ MW}\$ would exceed the maximum rated discharge rate of \$1.0 \text{ MW}\$. But, the second option is used in the majority of distributed energy resource scheduling models in the academic literature. I'm confused.


texts: Altium trace width rule applied to blanket only

texts:
In Altium, I set a rule for PCB trace width and clearances for a high current net but I only want it applied to that blanket that I have created in the schematic.

I have monitoring lines that wont be high current but they are huge traces too can I apply the rule just to the net lines in that class/room?

e.g. apply rule to all classes in blanket excluding GND


texts: Maximizing power from batteries to a DC Motor?

texts:
I have this DC motor (the 38.2V version). I want to maximize the power put into it for 10-20 seconds, but I can only use 4 lithium 9V batteries. I know that as the batteries discharge, the voltage decreases.

From my research, I found some possibilities:

Charge capacitors, which discharge into the motor.
Use a Buck Converter, which would give me more current, but less voltage.
Use a Boost Converter, which would give me the inverse of #2.
Something else?

How would I do this?


texts: High side N-Channel IGBT/Mosfet drive methods

texts:
According to this paper http://www.fairchildsemi.com/an/AN/AN-9742.pdf

  "However, a transformer may cause half bridge crossconduction due to the offset voltage of
  gatepulse deadtime stage."

Page 9 section "Gate driver design".
looking at waveforms on page 10 figure 33 that shows the waveforms
with a pulse-transformer, I think we can assume that the windings are from the same transformer, as is in some designs.

But if use only one transformer per IGBT, or just for the top side, I think the problem is solved, as the transformer will just reverse the current without the near "0V" space on dead-time, I'm right?


texts: Possible to output sinusoidal signal with an Arduino?

texts: Is there a way to output a sinusoidal wave with an arduino? Perhaps using PWM? It would be nice to be able to simulate something around 10kHz. Is this even possible with the hardware on the Uno?


texts: Placement of passive RC filter components on PCB

texts: On a 15 cm PCB, where the MCU is on the one end and the current sensor on another, where should R and C components of a passive low pass filter between them be placed? Will the placement affect anything?


texts: Maximum safe gate current for IRFZ44N MOSFET

texts:
I'm designing a spot welder using a high-current car starter battery, and a handful of N-channel mosfets of the given type (IRFZ44N, datasheet1, datasheet2). A microcontroller (through some drive logic, probably another mosfets) sends a short pulse to open and close the gates of the power mosfets in parallel (I mean all the gates, sources and drains are connected, making one cheap "supermosfet" from 10 mosfets), sending a high-current pulse to the spot welder's pins.

Since the fets dissipate most of the power in transition (either its resistance or the current is negligible otherwise), I want to open and close them very fast. For that I need to charge and discharge the gates, and for that I need to know what is a reasonable current to do that. Fast transition also helps with balancing out small differences among the mosfets. (10 pcs in parallel, with 160 or 200A pulse current depending on the datasheet per piece, and the battery supposedly can provide around 3-400A)

The datasheets (linked above) didn't help me. Any idea how much current can I use?


texts: Frequency divider circuit of a factor of arbitrary number

texts:
We know that using T-Flip Flops in a cascaded manner(something like ripple counter) allows us to divide the clock frequency by a factor of \$2^{n}\$ where \$n\$ stands for the number of flip-flops. Now, Suppose I want to divide my original clock frequency by a factor of 3 or by 9? What can I do to achieve this?
My progress: Suppose we want to divide the given frequency by a factor of 6. Then, I thought that we can achieve our task by connecting the counter circuit and then adding some combinatorial circuit to change the clock only when 3 counts are done. This way whenever 6 counts are completed, one output cycle will complete.(Look at the circuit below):

But how do we do when we want to divide the clock frequency by a factor of 3 or 5 or 9?


texts: Controlling a DC motor speed with Arduino

texts:
I'm trying to follow this tutorial

But instead of the components specified in the tutorial, I'm using the following:
- RS-360SH DC Motor
- BD139 Transistor
- 1N4007 Diode
- 220 Ohm Resistor

I understand that the components are different than specified in the tutorial, but these components are specified in another (less clear tutorial with the same schematics.

And I have the following arduino code:

int MotorPin =  9;
void setup()
{
  pinMode(MotorPin, OUTPUT);
}

void loop()
{
  analogWrite(MotorPin, 200);
  delay(1000);
}

All I can get is a buzz in the motor. There doesn't seem to be enough current to power it on. Can anyone explain what I'm doing wrong?

Edit
This is my schematic (I put the 2N2222 transistor, because I tested with that one as well):

simulate this circuit – Schematic created using CircuitLab

And this is how I plugged everything onto the breadboard.


texts: I am designing a prototype for a unit that may go into production (not for profit organization). For some of the parts, geometry will be important. I need a power jack, a two wire fan connector, a switch, and a 10K potentiometer. Obviously, I want to design the unit with the particular part geometries in mind and I want to ensure that any parts I use will remain available, or that equivalent parts from a different manufacturer will. There are standards on transistor packages, etc. Is there any standard for, say, potentiometers? Where can I browse these standards and pick a geometry that suits my application?


texts: Cheapest way to measure .1uL volume of liquid being dispensed from pipette tip

texts:
So I think this is going to be some kind of sensor... :P

I'm looking for ideas on the best way to measure a dispensed volume of .1uL from the tip of a pipette

This is for a open source medical liquid handler =] ...
- Fluid will be mostly transparent
- Pipette tips can be clear or black
- Will be measuring the displaced volume of 8 lines exiting a peristaltic pump

thoughts?


texts:
There are instructions out there on the web on how to import a Bitmap file into Eagle CAD and it's an option in the "File" menu so it should not be a problem. I'm going through the process and finding that at no point does Eagle prompt me for the actual bitmap file that I want to import. It goes through the steps of selecting colours and gives me the Eagle CAD Logo. It's a great Logo but not the one I want to use on my boards.

I'm still on eagle 6.5.0 so maybe there's a problem on that version?


texts: Voltage divider bias (Role of Coupling Capacitor)

texts:
simulate this circuit – Schematic created using CircuitLab

Why does the voltage divider in second circuit (middle) has no impact? Vo is always equal to V4(correct me if am wrong).

And once a capacitor is introduced before the voltage divider, the voltage divider comes back into picture.
I do see, that everywhere they say that capacitor does not allow DC to pass through.But how can we correlate with this circuit?

During the absence of the capacitor, does the 6V from voltage divider flow through the Signal generator? But the Signal generator itself generates voltage, then how can this oppose the flow of a Signal generator?
I need a clear and elaborate explanation of this weird role played by this coupling capacitor.


texts: How can I modify the frequency of a simple 433MHz transmitter module?

texts:
How can I change the frequency of a simple RF transmitter?
These are the transmitters in question:

Background Research
On this question s3c says:

To change the transmit frequency you'll have to change the SAW resonator as well as some component values

I have a SAW oscillator for 304.25MHz, the frequency I'd like to broadcast at.
I noticed in the photo above that the inductor coil has a different number of turns for the 315MHz and 433MHz transmitters.
A page describing a similar FM transmitter says:

The transmitter can be modified to any frequency between 50 and 400 MHz by replacing ... the inductor which is an oscillator coil and a capacitor

Additionally there is a schematic for the circuit on electroschematics.com:

That schematic is for the 433MHz circuit and it uses two 47k resistors, and this blog shows a closeup of a the back of a 433MHz module using two 27k resistors instead:

It also offers a hand drawn schematic:

I believe this is a photo of the back of a 315MHz transmitter and it appears to use resistor values of 20k and 27k:

How can I modify the frequency of one of these transmitter modules?

I believe I need to switch out the SAW oscillator
I think I need to change the number of turns in one of the inductor coils
I may need to change the values of the resistors
Wavelength can be calculated using the formula at the bottom of the hand-drawn schematic - so a quarter length antennae for would be 17.3cm for 433MHz, 23.8cm for 31Hz, and 24.6cm for 304.25MHz
Not sure how I might calculate the values for these components.
Not sure how to test - maybe using a USB RTL-SDR tuner?


texts: Wrong Sign in the Output of 80MHz Transimpedance Amplifier

texts:
I have recently built the following circuit for (homodyne) differential detection of optical laser pulses. In fact, I rebuilt the circuit from this paper with small deviations:

simulate this circuit – Schematic created using CircuitLab

You can find pictures of the circuit board at the end of this post. The two diodes are Hamamatsu S5972 Silicon PIN photodiodes with a terminal capacitance of 3pF (10V bias). The op-amp is a Texas Instruments OPA847. The laser system works at 800nm with a repetition rate of 75.4 MHz. Each pulse is just 1-2 ps long. However, the response of the photodiodes is far longer because their bandwidth is only 500 MHz, which is ok because I can still distinguish between consecutive pulses.

In the final application, the pulses will reach the two photodiodes at the same time with slightly different photon numbers. Therefore, the photodiodes will produce two photocurrents with opposite signs which cancel each other out at the sumpoint except for a small residual current. This remaining current will be converted to a voltage signal at the output by the OPA847 in a transimpedance configuration.

Due to the bias current of the OPA847 and the dark currents of the photodiodes, there exists an offset voltage at the output. The resistor R1, which will be a potentiometer in a later revision, is used to minimize this offset. However, there is a remaining offset voltage of approximately -100mV left in the current revision.

Now to my question:
Why do I see positive voltages when I'm only illuminating one photodiode, as in the following measurement? Is there a way to suppress this behavior?

Because the current output of one photodiode can only have one sign, I would expect the voltage output of the amplifier to have only one sign. I would also expect the shape of each pulse to be less symmetric, as in the following measurement I did with just one photodiode and a Femto DHPCA-100 transimpedance amplifier behind it.

Resources

Pictures of the circuit board: TOP (empty), TOP (assembled), BOTTOM (empty), BOTTOM (assembled)
Feedback Capacitor: The original design includes a capacitor parallel to the feedback resistor (R2 in the above schematic). It's not included in the circuit board layouts, because it's constructed by soldering two copper wires on the pads of R2. In this way, it's capacitance can be changed by twisting the wires. It's normally used to suppress the circuit's noise and improve it's stability. I already performed a short series of measurements with different numbers of twists: 0 twists, 1 twist, 2 twists
Direct Current Measurement: On the basis of PlasmaHH's suggestion, I performed a measurement without the opamp with a 5.1k shunt resistor. There is no change of sign, because there is a large dc offset building up. I think the larger of two consecutive pulses is the laser pulse and the smaller one a reflection of the first.


texts: How to control four 10-pin 7 segment display

texts: I'm a student trying to make a device for our research project so I'm quite (if not entirely) new to electronics.  I'm planning to make a 4 digit display using four 7seg display using arduino and each one of these 7 seg display has 10 pins, 8 of which i have to connect to the digital row of arduino and I cannot fit all 32 pins to the 13-pinned digital row of the arduino. I'm sure there is a way including using ICs or something, I just don't know what to do it. Sorry if I seem too knowledgeable. Thanks :)


texts: Best microcontroller electrical bus for high speed synchronized sampling from slaves

texts:
I have an application which requires that I sample a dozen of sensors for each node and transmit the data to a master microcontroller in regular four second intervals. The surface area of the sensors for each node is one square metre with six adjacent nodes. What is the best electrical bus to use in such a case?

I have no experience with CAN. I have only used RS-485 in the past, so I am currently on a fence between these two. What are the advantages of CAN in such a  setup over RS-485 and how involved is the hardware part?

Also, is there any other bus which is superior to both RS-485 and CAN for such a purpose?

I need to use fairly unobtrusive wiring in my application.


texts:
For my A2 final project, I am making a buggy that can be programmed using an onboard control panel.
I have a GENIE E18 PIC Microcontroller to control the ins and outs, with an L293D Motor Driver to power the motors. The only problem I have is with the motors, they are unable to move the buggy.

I have connected up the L293D in the following way so that 5v is used to power the L293D and a 9v battery to power the motors:

Do I need more voltage for the motors, or do I need motors with more torque?

The Buggy:

If I need new motors, what should I be looking for?

Thanks in advance.


texts:
I would like to use Nordic's nRF8001 modules in Master and Slave modes and also would like to connect it with Spartan-3E FPGAs using SPI. I am considering buying the nRF8001 DevKit.

I believe it is required by BLE standards that a device can be programmed as a Master or a Slave but in Nordic website it is stated that the nRF8001 module is "Cost-optimized solution for Peripheral (Slave) role operation". Also in the nRF8001 DevKit contents section (the first link) it specifically says the kit contains "1x Bluetooth low energy master emulator". These expressions have confused me and also I couldn't see any expression similar to "can be used both as a master or as a slave".

I would like to develop my application using the boards found in the DevKit but in the end I would like to connect bare nRF8001 samples through SPI to FPGAs and use one as a Master and one as a Slave. My budget is fairly limited so it would be very convenient for me to finish this project using only one DevKit.

Is it possible to do so with the nRF8001 DevKit and nRF8001 SDK or do I need to use different products and/or different programming environments?


texts:
I'm using a PWM shield (http://www.practicalmaker.com/products/arduino-shields/pwm-shield-assembled) which allows to extend the number of PWM pins for an Arduino.

In my project I'm using NPN TIP120 transistors to control more than 5 motors.

So when I try my circuit without the shield, everything works fine, I connect the Arduino pwm pins to control de transistor (external power source with 20 A)

Then If I try the PWM shield directly powering a simple led it works fine as well, the problem is the PWM as I understand is very led-oriented and has a negative and positive pin for each PWM terminal which Arduino doesn't have. And my problem is where I connect the negative pin of the PWM shield? I tried just connecting it to the ground pin in Arduino but the motors just run, not responding to the different speeds I'm trying to achieve.

Also, I'm using a midi library, which I hope doesn't interfere on this since as I said, the PWM shield works fine when using a led directly on negative-positive pins on the shield.


texts: IRFZ44N getting very hot in Peltier driving circuit

texts:
I have got a question about my Peltier driving circuit. First of all this is a drawing of my circuit:

simulate this circuit – Schematic created using CircuitLab
I am confused because only 1 of my IRFZ44N gets very hot, even though I ran the same gate signal to both of them. The Peltier that I have uses have maximum current of 10A (TEC1-12710) so I thought that IRFZ44N should be able to handle it (the datasheet says 49A continuous drain current.)
Any idea why only 1 of my IRFZ44N gets very hot?


texts: How to derive voltage output formula for a strain gauge?

texts: Here is the strain gauge and its voltage output depending on its parameters such as R and excitation voltage. I couldnt derive how this is obtained analytically.


texts:
Let us say that there are some signals, and all of them are Fourier-transformable and are a unique, single-frequency sine wave.

Now, we combine (add) these signals into one signal. Then, we do Fourier transform into frequency contents.

Will Fourier transform show the frequency of each added signals?

Or will the transform show the different values as frequency contents?

What is the math/engineering behind these?


texts: Driving 120 V socket from two different switches/circuits

texts:
I have a garage 120 V overhead light connected to a light switch at the entrance.  When the garage door opener engages, another 120 V light on the opener lights up but that light with one bulb is quite dim for the large garage.  I would like to take the wires from the garage door opener light and connect them in parallel to the overhead light in the garage.
In that way, the overhead light would turn on either via the switch at the entrance or when the garage door engages.  Will that work, and what happens if the light switch is on AND the garage door engages at the same time?


texts: I'm looking for a simple, cheap device to detect low ac current. It will be used to detect irrigation valves. These valves operate @ 24 vac (60 hz) typically 100 - 200ma. I just need a go-no go signal, I'm not interested in the actual value. The device needs to be a "clamp on" type with no physical connections. I'm open to rolling my own, this is a one-off project.  Perhaps something with a hall sensor, clothes pin type of thing. Any ideas out there?


texts: Help understanding amperage of DC motor and heat generation

texts: I am diagnosing an issue in an automotive HVAC system and have been testing the blower motor. I would expect somewhere approximately 8A to 15A of current draw. I have test wired the motor with 14AWG wire, a switch that is supposed to be rated to 30A, and a 20A fuse. It seems to blow the expected amount of air and not blowing the fuse, but the spade connectors at the switch and at the motor are getting uncomfortably warm to the touch. I measured resistance across the motor's terminals and I am seeing 5.1ohms. Wouldn't this imply that the motor should only draw 2.4A at 12v? Note, I do not currently have access to tools to directly measure the draw when running.


texts:
What are the advantages of 6 wires LVDT over 5 wires LVDT?

Both are the same in that they could be measured using ratiometric calculation.
In case of 5 wires LVDT, it is superior in number of wires to 6 wires LVDT.
On the other hand, is there any advantage of 6 wires over 5 wires?

Thanks.


texts:
The NXP LPC1342 microcontrollers have a built-in bootloader which allows programming the device via usb: The bootloader is triggered by pulling one pin to GND on bootup. The microcontroller then enumerates as a USB mass storage device onto which the firmware file can be copied without any additional hardware or drivers with most operating systems.

Apparently there are other devices which have unusual methods of in system programming (i.e. not via a classic serial interfaces SPI, JTAG, SWD, etc).

Does anybody know other examples of devices programmable from factory in system by USB, ethernet or similar?


texts: I am designing a board using Altium Design 18.1 and I have just poured this GND polygon and it looks so roughly is there any way to make it smoother?


texts: How to connect a 4x4 keypad without a microcontroller

texts: I have the RS 331-304 4x4 keypad, and I need to connect it so that I can determine which key has been pressed without using a microcontroller. Is there a way I can connect it using logic gates? The final aim of connecting it is to determine which number has been pressed, decoding this value into BCD and storing it in an array of D Flip Flops. I can't see how to go about connecting it, and would greatly appreciate your help.


texts:
Sorry for the noob question, but I really can't figure this out. I am playing with an oscilloscope, and starting at the very basics.

I have a resistor connected to the 5V positive power rail. This, in turn, is connected to a red LED. The ground is not connected. When I measure the voltage between the resister and the LED, it is 5V, as expected. When I measure the voltage on the other side of the LED, it is 3.6V. The LED is not lit, as expected, because the ground is not connected to it.

My question is, why is that value 3.6V, and not 5V?

When I connect the ground to the LED, The voltage between the resistor and the LED is 2.6V.

Again sorry for the silly question, but I really don't understand why this is occurring.


texts: What's the real inrush current in my AC/DC rectifier?

texts:
I'm working with rectifiers and power supplies at the moment and I'm trying to reconcile simulations with real world observations about my circuit.

It's a full-bridge diode rectifier (4x 1N5821's) with 4 parallel aluminium 470uF, 63V capacitors. Input AC peaks at 33.9v and the circuit is loaded with a 330R 5W resistor.

The input AC comes from a 240v-24v transformer and has a fast-acting 1A fuse on the 24V side.

In LTSpice modelling the diodes with the built in 1N5819's and capacitors with an ESR of 0.1, there is a large current drawn from the source when first started, peaking at 18.6A.

So why doesn't the fuse blow every time I turn the thing on?

Edit: Update - I measured the slope of output voltage when I first turn on the rectifier, from which I calculate the current by i = 1/c * dv/dt. I found that I is approximately 4A during that first charge cycle.

The answer about fuses is on the right track I feel but I'm going to leave this open for a bit.


texts: It has been said that a K type thermocouple is just 2 wires of different types twisted together (basically). If this is so then can such a thermocouple be made with a copper and steel wire twisted together? What about copper and nichrome?


texts: Detect if connected battery is rechargeable

texts:
The device I am building can be powered by USB or 3xAAA batteries. While connected to the USB, the device will charge the batteries. But before charging the batteries, the device needs to make sure the batteries are rechargeable.

I've made a circuit using BQ2002 to charge the batteries. If the batteries are not rechargeable, this circuit should not attempt to charge the battery (set charge control on BQ2002 to low).

How can I make sure my circuit doesn't try to charge every connected battery?
Is there a IC that has this functionality?


texts: Controlling XL6009 / XL6019 DC-DC buck/booster Enable pin via Arduino

texts:
I'm trying to use a XL6009 module with an arduino to control whether the input voltage, or the boosted voltage is sent on output.
As per the XL6009 Datasheet or XL6019 Datasheet, the ENable pin 2 is tied/floating high with VIN. For the chip to be disabled, it needs to be 0.8v or below, or 1.4v or higher to be enabled (default).
Currently I have one of these DC-DC modules, and have disconnected the second pin from the board.
Here's my question - With a 12v input on VIN, what exactly do I need to do so I can control the output by the enable pin by setting an arduino pin high or low? Obviously I can't connect Enable pin 2 directly to a GPIO since it's outputting 12v, and will fry something on the arduino. But where I'm quite confused is what exactly I can use, and secondly how I'd connect it up.
Even if I didn't have the Arduino, how exactly would I pull this pin "low"? I thought perhaps connecting directly to GND but I feel like I'm confusing something else here. I imagine using a pull down resistor, but how exactly would this be connected?
Appreciate any help. Asking questions has come after a lot of googling and trying to figure out things myself.
Thanks!


texts: My (single ended, class A) tube amp sounds great while it's shutting off. What's happening?

texts:
So, I have guitar direct in to a single-ended class A (12AX7 and 6V6) Champ-style amp. The amp is from the 60s and unbranded, it's likely a Pepco (Pine Electronics) Silvertone style circuit. It's been re-capped and upgraded with a safety ground.

When I shut it off while playing and keep strumming, I get a really nice compressed distortion that slowly fades off as the unit powers down. It also removes the hum (which makes sense, since AC power is disconnected).

I've tried using a VARIAC with the amp to recreate this effect but it actually cleans up the tone (and lowers volume).

My non-EE's guess at what's happening-- A voltage spike from AC shut down is causing a higher-than-normal B+ (DC) voltage (causing distortion) which is stored in the power tube (?) at a lower-than-normal amperage (causing compression and a lower output volume) which then rapidly depletes (using up stored B+ from power tube) as it shuts down.

If I wanted to replicate this tone, should I use a multimeter to find the B+ line and what DC voltage/amperage it's at, then supply the same voltage/amps myself to that line (with the AC power switched off)? That is, if there isn't some kind of inductance happening or stored AC/DC somewhere besides the B+ causing my "sound".

Of course, my own guess could be totally off. I realize you all might be limited without posting the schematic (which I don't have). Any ideas?


texts: A question on voltage divider resistances used in BJT biasing

texts:
I'm reading a text on BJT common collector amplifier biasing.

Text says:

The voltage divider (R1 and R2) is used to give the input signal (after passing through the capacitor) a positive dc level or operating point (known as the
quiescent point).

The actual sizes of R2 and R1 should be such that their parallel resistance is less than or equal to one-tenth the dc (quiescent) input resistance at the base (this prevents the voltage divider’s output voltage from lowering under loading conditions):

What does that mean? I don't understand why R2 and R1 parallel resistance should be less than or equal to one-tenth the dc? What does loading mean here?


texts: Multiplexing a big 7-seg display with MAX7219

texts:
I've a problem with this circuit, it should drive 2 (or more) big 7-segment display using a MAX7219 and the relative Arduino's library. It uses ULN2003 and UDN2981 to use +12V and a series of 5 led per segment (in the image I simplify with only one led for segment).

The CD40106 is used as logic NOT adapting the inpupts for the ULN2003.

The problem is during the MAX7219 test example code, loaded into the arduino uno. The leds slightly turn on when they should stay off. A video will show better the problem.

The video about the problem

More info about MAX7219 library and test code here

I tried to change the CD40106 with a 74HC04 -> SAME PROBLEM !!!


texts: Voltage conversion +1V to -3V inside a new IC design

texts:
I am looking for a good integrated CMOS solution for creating -3V out of a 1V supply. The -3V are just used for biasing and hence do not load the supply.

This means that the solution should be switch capacitor based (only NMOS switches and caps involved). No VDS/VGS must exceed 1V.

I tried using a Dickson multiplier with NMOS diode connected devices to create 3V from 1V and afterwards use the charge pump shown in [1] to invert it. And I tried the reverse order.

While both work isolated, they fail in either order, due to the nonideal NMOS switches.

I tried the cross coupled charge pump from [2] Fig 1 which works nicely but the VGS of the devices well exceeds 1V.

Both options do not seem to be the way to do it properly. What is the simplest working option for the given scenario?

[1] https://www.digikey.tw/en/articles/techzone/2012/apr/charge-pumps-cut-switched-converter-costs

[2] http://www.sbmicro.org.br/jics/html/artigos/vol10no3/3.pdf


texts: Help with building a row of vintage lights

texts:
I want to build something like this:

I plan on connecting each bulb in a parallel connection as per below diagram.

Any reason why you would make a serial connection?
I'm not planning on using adaptors / transformers. There are standard 220 volts (Australia) bulbs going directing into a wall socket.

I'll simply gather all the connections using a terminal block and run a single wire to the wall socket.

Am I doing this right?


texts: Reading empty (new) AT24C16 I2C EEPROM - 0xFF or 0x00?

texts: What byte vaule should I see when reading empty EEPROM chip via I2C?


texts: Measuring current on 25W incandescent lamp - loud bang/spark from DMM probes?

texts:
I was trying to do a power calibration on a Tasmota smart switch, using this procedure:
https://tasmota.github.io/docs/Power-Monitoring-Calibration/
I had an 25W incandescent globe (resistive load), wired up in a bayonet holder:

I have a digital multimeter (Fluke 287), set to A (current), with the probes plugged into COM and A:

I turned on the smart switch, and then tried to measure the current by touching the two terminals on the bottom. (The smart switch was showing roughly 0.1 A flowing through)
There was a flash, and a bang from the probes. I also noticed part of the red probe tip appears to have melted.
It's been a while since my elec education, so I'm assuming I did something silly her. Can somebody explained what happened here?
Is it likely there was damage to the DMM?
What is the correct way of measuring the current here?


texts: Can I solder a capacitor on a lifted trace

texts:
I lifted and tore away a pad when soldering a capacitor on a PCB. The pad on the negative side is fine. Can I solder the capacitor lead onto the negative pad, and the other lead on the exposed trace for the positive pad?

Here is a picture so you can have a better idea:

I’m talking about the C7 capacitor pads.


texts: What is a good beginner's antenna I can design in HFSS and create?

texts:
I'm trying to get advice from people who have used HFSS and actually designed antennas. I am starting out with HFSS, and want to create my own antenna from design to creation. I have taken an Antenna theory class, so am decently understanding of how to design different types. The hardest thing for me is thinking about what can actually be created easily, but isn't so simple as two wires separated from each other. I don't have a CNC machine, only a 3d printer. Are there any cheap antenna manufacturers for small antennas, similar to how pcb's are manufactured cheaply?
Thanks for suggestions,


texts:
I tried putting two extremities of a 6 volts battery into water.
With salty water, bubbles appear close to the positive end.

With unsalted water, what looks like a thin white foam starts to squirt from the positive and and moves through the bottom of the glass.

What am I seeing there?


texts:
Currently I'm working on a project that will be implemented in a 12V automotive electrical system. To protect the onboard DC/DC, I decided to add reverse polarity protection as well as load dump protection to the 12V+ input. After some research (and referencing this application note), I designed the following circuit (note: some component values were changed for BOM optimization):

Which produces the following simulation result (reverse polarity and over voltage (>30V) cutoff), as intended:

My main question is that in the TI AN they include an additional resistor from the drain of the n channel mosfet to the source of the p channel overvoltage mosfet (R4 in the below schematic).

What is the function of this resistor? The AN mentions its to bias Q2 and satisfy its drain leakage in the off state. Wouldn't R5 + R6 complete this function anyway?


texts: I2C actually sends inverted data over the line?

texts:
It seems to me that I2C is actually transfering inverted bits which sounds a bit odd so I am seeking for a clarification.

I2C diagram from here.

Let's say we are writing to slave. A zero (0) comes to SDA out, which means nMOS is in HiZ and the receiver gets a 1 due to Pull-up. And if a 1 comes to SDA out then nMOS will connect with ground meaning receiver gets a 0.

So it seems to me as if I2C is actually sending inverted data across the SDL. This does not really make any sense to me so.. is there an inverter on the receiver's end not shown in the diagram that makes the data correct? Or did I misunderstood how it works in the first place?


texts:
First time poster:

I want to learn about opamps. I am just a college graduate with no practical experience.

What I know:

A few basic high level applications such as

Hysteresis,
Voltage follower,
Inverting and non inverting configuration,
Various Filters, and
Oscialltors

All these we studied (and some lab experiments) and passed but I want to learn deeper.

I want to use the worst(where I can feel the effects such as offset voltage, offset current, leakage current, etc) opamp available (I couldn't find the question here but I remember, it is useful)
And do practical measurements with oscilloscope and understand and see it practically.

I will put all the efforts needed. I want a direction to start with.

How can I start?

Please suggest if i have to share any other details.


texts: While replacing a 5v regulator on a Cricut machine, I clearly should not have attempted this because it appears to me that I burned away the copper around the 5 holes the wires inserts into and now there is nothing for the solder to attached to. I tried scraping and just made it worse. Is there a fix?


texts: How can a shield winding in the transformer be helpful without fully covering the core?

texts:
This article describes the Apple iPhone charger circuitry in great details. It mentions the shield winding in the flyback transformer. The shield winding is simply an extra most outer winding and the article claims that it filters out EMI.

However the transformer clearly has a core and it has so-called EQ design in which the core has huge parts not covered by the windings. Since the core contains the magnetic field I'd expect the core to "leak" it and since the shield winding doesn't fully cover the core I'd expect the shield winding to not be very efficient.

How does the shield winding help against EMI if it doesn't fully cover the transformer core?


texts:
I can't believe I'm having trouble finding chassis punches for the IEC C13 socket.  This has to be the most common way of getting 120VAC into a box, yet I can't find any chassis punches.

How do most people make a nice, clean hole for the C13?


texts: How to choose an antenna for an FM transmitter?

texts:
Ok guys I can't understand something.

Say that I have this circuit:

Assuming that I apply at the antenna 5V, how can I calculate how much power I will trasmit?

I found on internet that the current that will flow on the antenna radiation resistance, but if for example I go on ebay for try to find antenna no one quote the antenna radiation resistance, so how can I choose my antenna?

Moreover I want to know what  capacitor C1 and C2 do in this circuit.


texts: Can I use a similar AC adapter with different input but the same output?

texts:
I have a landline telephone from Japan. The owners manual says only use OUR AC adapter, {Input 100v 50/60Hz 8VA - Output DC 11V 430mA}

I want to use this in North America - can I use a AC adapter rated for Input 120 V/Output DC 11V ~430mA without damaging the telephone?

Thanks.


texts:
If we have a DC sine signal. Can we say that capacitors and inductors have impedance despite not being AC?
If yes then what will the formula look like?
And the opposite if we have an AC square signal do capacitors and inductors have impedance?


texts:
Why is it that op-amps used as ICs, such as LM741 require a +Vcc and -Vcc for biasing whereas there is no -Vcc for a 555 timer?

What determines the biasing for any IC?


texts:
I am developing a home automation project in which I'm using relays to control appliances.
I need to control devices with 220V and 6A rating.

Should I use relays to control these appliances as a long term solution?

Relay I'm using is mechanical and is rated 220V 7A. If I keep it ON to control e.g. a fan, for more than a few hours on a daily basis, will the relay cause any problems? If yes then, what are other possible solutions?


texts:
I need to sense the current of a target MCU through various periods of its on/sleep/off state and then need to send this data back to another interface MCU to read out the value. They will be both on the same board, powered by 5 V USB.

However these are the requirements I have:

5 V USB PSU
Must be able to sense currents in the range of nA to mA with high    accuracy/precision. (I figure 1 nA to 500 mA)
Only measure the current of the target MCU and not the interface.
Must output maximum 3.3 V interface MCU

I have looked at available options and current sense amplifiers by Texas Instruments can't sense nA due to higher bias currents. So therefore I feel I would need a precision amplifier.

However I am stuck on how to proceed with this because, I need to somehow have a automatic dynamic current range and I am fairly new to current sensing and am not really sure on all the specifics.


texts: Converting current signal to voltage signal with a resistor

texts:
sorry if this is dumb but I can't seem to wrap my head around something.

I am reading a book and in the book this exercise was :

Given a controller with analog output (control signal) in the range 0 — 20
mA. Suppose the controller is to be used to control a device (e.g. a pump)
that only takes voltage in the range 0 — 10 V. How can you (easily) convert
the current control signal to a corresponding voltage control signal. Draw
your solution.

and I figured:

but the solution was:

Why is my "guess" wrong?


texts: RS422/RS485 termination and noise immunity

texts:
Consider a RS422/RS485 receiver like the AM26LV32 or the DS26LV32. It is used to receive the signal of incremental encoders with differential outputs. Assume that those are using drivers such as the AM26LV31. There is only receiver on the bus, i.e., driver and receiver are at opposite ends of the cable.
Seemingly to facilitate the use of encoders without differential outputs, the schematic omits the termination typical for RS422/RS485. On the receiver side, there is no resistors between the positive and negative line of the differential pairs. Instead, the schematic has a 1kOhm pulldown and a 2kOhm pullup (to 5V) on both the positive and the negative line of each differential pair.
Datasheets typically recommend a termination resistor (200 Ohms or so) between the positive and the negative line of each differential pair. As far as I understand, that helps with reflections. Now this schematic omits it.
What will be the consequences of omitting the termination? What issues are likely to occur when attaching encoders which may reach switching rates as high as 30 MHz? You may assume that these encoders have differential outputs.


texts: Simple variable current source for approx. 2A, constant load

texts:
I need a variable current source as part of a power supply for an experiment I'm building. This part should heat up a filament, so the load is pretty constant. Timing is not a factor either.
So what I'm looking for is a pretty simple solution, much simpler than a lot of circuits I find online. But all the simple circuits, like the ones attached are often calculated for small currents.
I need a regulation between 1.5A and 2.5A and my question is if someone has experience with such simple circuits and higher currents. Of course I would use other parts like power transistor and other resistors but heat and efficiency could be problems, but I don't know to which degree. I study physics, so I'm no expert in electrical engineering.

I hope someone could give some intuitive answer. Thanks


texts: Forming mux demux trees by cascading using strobe

texts:
Some definitions

When implementing a M:1 multiplexer using N:1 multiplexers, where M>N, we cascade N:1 multiplexers, which forms tree of multiplexers.

Similarly, when implementing 1:M de-multiplexer using 1:N de-multiplexer, where M>N, we cascade 1:N de-multiplexers, which forms tree of de-multiplexers.

Strobe input is an enable input which is used to enable multiplexer, de multiplexer (or any components in the given context) etc.

Cascading using strobing refers to forming MUX and deMUX tree using most significant bit / Mth bit of target MUX or deMUX as a strobe input for two MUX/deMUX:

For example, a 32:1 multiplexer can be implemented using 16:1 multiplexers by cascading using strobe input as follows:

Note that A is MSB of target 32:1 MUX and is used to drive strobe/enable input of two 16:1 MUXes. For M1, A is a strobe, for M2, A' is the strobe.
Doubts
I have following questions about cascading using strobing:

Is cascading MUXes with strobing only possible when we have M=N+1?

Can strobe cascaded MUX trees have only two MUXes and a single level of MUXes?

Do strobe cascaded MUX trees always require two input OR gate?

Is cascading deMUXes with strobing only possible when we have M=N+1, similar to strobe cascaded MUX trees?

Can strobe cascaded deMUX trees have only two deMUXes and single level of deMUXes similar to strobe cascaded MUX trees?

I feel "yes" is the answer for first four questions and "no" is the answer to fifth question. But I need confirmation.
I believe "no" is the answer to fifth question because in below 1:32 deMUX using 1:4 deMUXes, I can replace deMUX on left most level/level 1 with Din acting as a strobe for deMUXes at level 2 and still form 1:32 deMUX. The tree ends up having 10 (>2) deMUXes and two levels, level 1 with two deMUXes and level 2 with 8 deMUXes.

Please add following tags: de-multiplexer, combinational-circuits


texts:
Is there a standard arrangement for the pairs inside a Cat7|6|5 Ethernet Cable?

As shown in the picture, they are in the sequence Orange-Green-Brown-Blue, or the Orange Brown always as opposite pairs, but I have not reach any solid confirmation for this; even, I have found contradictory sketchs, some with Orange-Brown as opposite pairs as here, others as close pairs.

If positive, the cross bone structure in Cat6 should kept that arrangement in a Cat7|6, but should one expect that arrangement to be kept in a Cat5, where no structure is between the pairs?

Thanks in advance.


texts:
For some reason, I need a Time-Variable DC power source that changes it's value according to time. I need this changing of value to be controllable.
I'll put it this way :
Say I have a 12 volt DC power source like a car battery.
In some point of time I need this value to be changed to 11 volts, then to 9 volts...etc to zero volts.
Then start the cycle backwards from zero to 1 volt, then it increases to reach 12 volts and this process is time-controlled and time-based.
I am somehow familiar with buck converters, and I know they step down the supplied voltage, but I want this step down and then backward cycle of reaching up the supplied voltage to be time-controlled. I need to be able to control the whole cycle of this time-variable DC source.

The question is:
Does such a circuit exist?
And if yes what are those circuits called?

Notice that I didn't specify any info about wattage or ampere for the circuit, but if this was a problem then I guess the example I presented gives some hints: 12 volts source power varying to zero then cycles backwards from zero to 12 volts.
Efficiency is needed as high as possible.

Thanks for contributing in any ideas that helps design or clarify the nature of the required circuit.


texts: Xilinx ISE, expression not globally static inside generic map

texts:
Is this expression allowed inside Xilinx ISE:
generic map (record1.field1'length) ??

Previously I have defined record:

type test_record is record
  field1 : std_logic_vector(31 downto 0);
  field2 : std_logic_vector(31 downto 0);
end record;

constant record1 : test_record := ((others => '0'),(others => '0'));

I get this error message:

  The actual value (Attribute name) associated with a generic must be a globally static expression


texts: Improving reception of 318MHZ remote control

texts:
We have a gate opener with keyfob-type RF remote transmitters that operate at 318MHZ.   The range from inside the car is about 75 feet -- less than we'd like due to the time taken by the gate operators to function.

The antenna is approximately 9" long, and mounted vertically on top of a metal fence post; the fence is about 1" metal mesh (similar to poultry netting) with a vinyl coating; I don't believe the fence is electrically connected to the post (at this time) due to the vinyl coating and paint on the post.

The antenna is connected via coax to the receiver; I believe the coax is grounded to the fence post via its mounting bracket.

From an online antenna length calculator, a quarter wave antenna for this frequency should be 8.83", so I believe the antenna itself is OK; my question is whether there is anything that can be improved about the way the antenna is mounted that would improve the range?   The gate is at the mid-point of the driveway, so a unidirectional solution doesn't seem appropriate.

Edit: here's an rough diagram of the area; it's about 120' line of sight to the house and maybe 100' to the turn in the driveway toward the street.   The area is wooded, and there are some low-hanging branches, but generally a clear line of sight from the house to the antenna.


texts: 9V from two AAA batteries plus charge pump: batteries in series or parallel?

texts: I am driving an OLED display via two AAA batteries plus a charge pump to step up the voltage to 9V. I was wondering if there is likely to be any significant difference in efficiency between (a) using the two batteries in parallel and using a charge pump to step up from 1.5V to 9V, or (b) connecting the batteries in series and stepping up from 3V to 9V.


texts: LED lamp with more watts than LED driver

texts:
I bought a 40W LED lamp and a 40W LED driver to power the LED lamp however, the salesman delivered me a 36W LED driver. I called him to return the item and he said that this was the right way to power the lamp. He also said that if I power the 40W LED lamp with a 40W LED driver, this will shorten the lamp's life.

Honestly, I think he is trying to fool me. I´d searched the web looking for answers, but found nothing. Does anyone know how what must be observed to fit the right driver to the lamp?

Lamp's data:

Model: OR-PAN-620620-40W
Power: 40W
Voltage: DC 36-48V
Luminous Flux: 3200lm
CCT: 4000-4300 K
RA >80

Drive Data

IN: 0.37A@120Vac
Pout: 36W
Uout: 3---62V DC
Iout: 800mA (constant)


texts: Trying to source a PCB component (a slow blow fuse I believe!)

texts:
I’ve stumbled upon this forum in a search for a replacement part for a PCB that makes up a digital ballast for a HPS light used in basil clone production.

I’m handay with a soldering iron but I am no electrical engineer so I’m finding it hard finding a way to source the replacement part.

From what I’ve gathered it’s a slow blow fuse, 10a / 350v as stated in the picture below. The ‘F1’ led me to believe it’s a fuse... (I know, a true amateur) ha!

Is this a speciality piece? I’m in the UK and which is 230/240v supply. With the ballast rated to 1200w I believe the 350v is to fascilitate the inrush of current... (excuse me if terms are spaghetti).

Any ideas on how to identify this component? You can see in the pic it has burnt out / blown and there’s also evident of a bit of water damage isolated to this fuse and the incoming L and N terminals.

Can I replace the fuse?


texts:
I am new to audio processing, I have a dsPic33F and I wrote a simple audio playback (when you speak on the mic it is played immediately on the speaker). However some vowels don't produce any sound. The vowel "e" (like in engineering) is missing.

My question: Is this due to my sampling frequency, which is 8kHz?


texts: How to check SMD capacitor for being shorted, without disconnecting it from the electric board

texts:
This YouTube video shows that you can check SMD capacitors for being shorted using buzzer mode, by touching the ground of the electric board with the negative terminal while touching each side of the SMD capacitors with the positive terminal, the one that has both of its sides making a buzz is identified as shorted.

"SMD bad capacitor test / laptop - desktop computer & electronics troubleshooting"

My problem is that I couldn't identify the "ground" on my electric board.

It's a 2 circuits (AC & DC) board.

P.S: The 2 golden squares near the microprocessor don't exist on my board, the rest is identical to mine.

Also when I checked some of my SMD capacitors using resistance mode, I got the following values:

11K Ohms
12.4K Ohms
11.6M Ohms
11.3M Ohms
0.L Ohms (after moving upwards to reach 40MOhms, the maximum of my DMM)

What ohm value should be used to consider an SMD capacitor good or bad?


texts: Capacitor 1 micro farad doesn't show any resistance reading

texts:
I have a capacitor labeled 1 μF (micro Farad) and when I measure capacitance I get 1 μF but when I measure resistance the meter shows out of range on any dial setting except on 200 MΩ (mega Ohm) where it shows a constant value.

Is the capacitor good or bad?


texts:
I was going through BJT Power Amplifiers and the efficiency is given as

Efficiency = (AC power at Load)/(Input DC Power)

I have two different questions for the above expression:

Why are we not considering AC Output power/AC input power as overall efficiency?
Why are we not considering AC input power in above expression? I mean the efficiency have to be = (AC power at Load)/(Input DC Power + Input signal Power)

Can you please explain ? Thanks in advance...


texts: How does a diode clamping circuit protect against overvoltage and ESD?

texts:
I always see this circuit when talking about overvoltage or ESD protection (does this circuit accomplish both, or just one?):

However, I don't understand how it works. Say I put in 20V at Vpin.

So Vpin is at a higher potential than Vdd, so current flows through the diode. But the voltage at the node Vpin is still 20V and the IC still sees 20V - how does this protect the internal circuitry? Furthermore, if an ESD event hit 10,000V to Vpin how does it protect the internal circuitry?

Finally, is the diode D2 there to protect against a voltage below Vss, or does it have some other purpose?

I have tried simulating this circuit, but for some reason it does not work.


texts: Using 12v 50w motorcycle light with two 7.4v RC batteries

texts:
I recently purchased two motorcycle lights (12v DC 50w) and only needed one. Now I have some 7.4v 4500mah 45c batteries leftover from my RC hobby a while back. I would like to create a 3d printed enclosure for these items, making a torch (with an old laptop heatsink).

I have read lots of google posts, however I still do not understand whether or not my LED will draw too much current if I purchase a step down transformer like this: https://www.banggood.com/DC-9-35V-to-DC-1V-35V-80W-Automatic-Step-Down-Module-Boost-Buck-CC-CV-Power-Converter-Module-Adjustable-Voltage-Regulator-p-1510115.html

I would like to know if the above mentioned method (using two batteries and stepping down the voltage) would work or if using a single battery and stepping up the voltage would also be possible (and what driver would be suitable for this).

Please note that these batteries are identical.


texts: How do we get from the exponential iv curve of a BJT to the tanh iv curve of a long tailed pair?

texts:
I have read that a long tailed pair of transistors has a tanh characteristic I,V curve.

How do we get from the exponential function of a single transistor Ie = Ies(e^(Vbe/Vt)-1) to a tanh function of a LTP?

It would be nice to have method of deriving this equation that shows intuitively what is happening in the circuit.

Here are some relationships that should be relevant here.
sinh(x) = 1/2 e^x - e^-x
cosh(x) = 1/2 e^x + e^-x
e^x = sinh(x) + cosh(x)
tanh = sinh(x)/cosh(x)

I was reading this page about OTAs from which the images below are taken, it has a description of how to get a function for a LTP, but no mention of the tanh function.


texts:
I have a DRV8840 that I am trying to use.  I have burned up about 10 of them trying to get it working.

For this application, I need the H-Bridge to Current Limit and Brake the motor.  Max current draw can be no more than 2A and it needs to stop very quickly

I have gone through a couple revisions, but always the H-Bridge blows up.

Here are the motor details:

24V
2A drawn
Brake enabled (called slow decay in the datasheet)

The voltage applied to this motor flips polarity, so I have a diode bridge in between imcoming power and the H-Bridge

Here is my schematic

Brown and white is incoming power to feed the H-Bridge.  Brown and white switch polarity and the diodes prevent the H-Bridge itself from having a reverse polarity applied

Red and Yellow are the motor outputs

Some notes on the diodes:

(I'm new to eagle and didn't really know how to create new components)

D5 = Bi-directional TVS Diode

D1-D4 = Schottky Diodes (I used these for less forward voltage drop)

I don't use the built in 3.3V voltage regulator but instead use a voltage divider and use the reference implentation on page 8 of the DRV8840 datasheet

Again, the only reason I need the H-Bridge is to brake the motor and to limit the current.  Maybe I am going about this the wrong way, but I still do not understand why the H-Bridge dies so fast.
  Thanks for your help!


texts:
The inverting circuit with the T network in the feedback
is redrawn in Fig. P2.30 in a way that emphasizes the
observation that R2 and R3 in effect are in parallel (because
the ideal op amp forces a virtual ground at the inverting
input terminal). Use this observation to derive an expression
for the gain by first finding and
For the latter use the voltage-divider rule applied to R4 and
(R2 || R3)

Above is the question
I cant understand why i cant an Req=R2||R3+R4 in feedback circuit.
But using a volatge divider considering R2||R3 and R4 to calculate Vx is valid.


texts:
Good day all.
     I am trying to process two signals to produce an output signal. I will be posting a picture for clarity (sorry if I used pencil, I am stucked at home).
My two input signals are sig, a 20 Hz and 50% duty cycle signal and EN, a signal that is manually controlled by user via switch. The time duration Thigh of EN (active-high) is expected  to be much larger than the period of sig (50ms).
What I want to do is make a digital circuit to create an output signal, EN'. EN' is created by delaying all edges of EN (+ and - edges) until the next rising edge of sig. I have read a little about flip flops, which appears to be an answer for circuits which require time delay.
Can anyone point me or suggest me some starting point for type of IC/flip flop that I might use?

I am currently considering T flip flop. When I look at what I want to happen (see picture), I see that I need delaying and toggling. I want to somewhat modify T flip flop such that instead of toggling Q when T = 1, the circuit would instead toggle Q only one time during every Thigh of sig OR toggle Q only during rising edges.


texts: How does single coax wire transmit a lot of information?

texts:
I have a coax cable entering my house.  The cable (from the Cable company), splits into a Cable modem (for computer network) and into a DVR (a.k.a. cable box).

How can a single coax wire contain digital programming information for over 100 channels and transmit data to the internet at fast speeds?

For example, my DVR box can record multiple channels while my PC is transmitting to and from the internet (via the cable).

I'm familiar with interfaces that use one bit per wire (such as Centronics Parallel) or send bit pulses using more than one wire (I2C, RS232C, USB, Ethernet).  These transmission forms are not as fast as the coax.


texts: Can I use a Step-up Power Converter with Arduino instead of a Relay?

texts: I want to make two projects that use a 12v input, a solenoid valve and a electrical lock. Both need a 12v current to work. I've seen some exemples for both projects that use a relay and an Arduino to activate mechanisms that need more than the 5v Arduino´s output. I was wondering, however, if I could use a Step-up Power Converter connected directly to Arduino´s Digital Pin. Is it possible? And is it safe?


texts: Reading recommendations to better understand how to understand the intended function of a circuit

texts:
This is a general question. Suppose I have a circuit like below from CircuitDigest:

￼

My supervisor said that about the circuit that..

  [The] circuit does actually involve an amplifier, even though it’s not super obvious: the noisy current in the Zener diode is amplified by the transistor, and R1 effectively converts current fluctuations into voltage fluctuations.

I had no idea it involves an amplifier - I don’t see one here. I see a transistor only. He also says the resistors effectively converts current fluctuations and voltage fluctuations.

What can I read to be able to make deductions such as this? Any recommendations (textbooks and the like) would be appreciated, as well as any useful links.


texts: SPI communication with MLX75306 optical sensor array

texts:
I am having some trouble talking to an optical sensor array with SPI (MLX75306, data sheet). I am using an Arduino Nano Every. I am not familiar with SPI communication and I have the feeling I am missing something essential in the communication protocol. I attached an interrupt to the Frameready pin of the optical array, but this interrupt never gets triggered. Why not?
From what I understand from the datasheet, sending the “Start Integration” command should result in Frameready going high after a set time. I have got my Arduino connected to the MLX75306 as follows:
Arduino —> MLX75306:

D12/MISO → MISO
D11/MOSI → MOSI
D13 → SCLK
D6 → Frameready
D5 → CS
+3V3 → pin 5 & 6 (3v3)
GND → pin 4 (GND)

with a 1 μF and 0.1 μF in parallel between pin 4 and pin 5 on the MLX75306.
This is the Arduino code (I am not doing a detailed read out of the sensor yet, this code is mainly to get the interrupt to trigger):
#include <SPI.h>

const int dataReadyPin = 6;
const int chipSelectPin = 5;
const byte MLX75306_CR = 0b11110000;   // chip reset
const byte MLX75306_SI = 0b10111000;   // start integration
const byte MLX75306_RO8 = 0b10011001; //Read 8bit
const byte MLX75306_SM = 0b11000110; // Sleep Mode
const byte MLX75306_WU = 0b11000011; // Wake UP
const byte TIME_INT_MSB = 0b01001110; // MSB+LSB is one 16 bit byte
const byte TIME_INT_LSB = 0b00100100; //current value 20000, for 10 ms integration time
int i = 0;

void setup() {

  SPI.begin();
  Serial.begin(115200);
  pinMode(dataReadyPin, INPUT);
  pinMode(chipSelectPin, OUTPUT);

  initiate();
  start();
  sleep();
  attachInterrupt(digitalPinToInterrupt(dataReadyPin), ReadData, RISING);
}

void loop() {
  byte inByte = 0;
  initiate();
  start();
  acquire_8b();
  Serial.println("Sent");
  delay(2000);

}
void initiate()
{
  SPI.beginTransaction(SPISettings(2000000, MSBFIRST, SPI_MODE3));
  digitalWrite (chipSelectPin, LOW);
  SPI.transfer(MLX75306_CR);
  SPI.transfer(0x00);
  SPI.transfer(0x00);
  digitalWrite (chipSelectPin, HIGH);
  SPI.endTransaction();
}

void start()
{
  SPI.beginTransaction(SPISettings(2000000, MSBFIRST, SPI_MODE3));
  digitalWrite (chipSelectPin, LOW);
  SPI.transfer(MLX75306_WU);
  SPI.transfer(0x00);
  SPI.transfer(0x00);
  digitalWrite (chipSelectPin, HIGH);
  SPI.endTransaction();
}
void sleep()
{
  SPI.beginTransaction(SPISettings(2000000, MSBFIRST, SPI_MODE3));
  digitalWrite (chipSelectPin, LOW);
  SPI.transfer(MLX75306_SM);
  SPI.transfer(0x00);
  SPI.transfer(0x00);
  digitalWrite (chipSelectPin, HIGH);
  SPI.endTransaction();
}

void acquire_8b()
{
  SPI.beginTransaction(SPISettings(2000000, MSBFIRST, SPI_MODE3));
  digitalWrite (chipSelectPin, LOW);
  SPI.transfer(MLX75306_SI);
  SPI.transfer(TIME_INT_MSB);
  SPI.transfer(TIME_INT_LSB);
  digitalWrite (chipSelectPin, HIGH);
  SPI.endTransaction();
}

void ReadData()
{
  byte inByte;
  SPI.beginTransaction(SPISettings(2000000, MSBFIRST, SPI_MODE3));
  digitalWrite (chipSelectPin, LOW);
  SPI.transfer(MLX75306_RO8);
  SPI.transfer(0x02);
  SPI.transfer(0x8F);
  inByte = SPI.transfer(0x00);
  digitalWrite (chipSelectPin, HIGH);
  SPI.endTransaction();
  Serial.println(inByte, BIN);
}


texts: logic gate's open drain output pulled to voltage higher than supply voltage

texts:
I am using 74AHC1G09, it has an open drain output. It says the maximum Vo is 7V, but also says "The input and output voltage ratings may be exceeded if the input and output current ratings are observed." My question is, what's the output current ratings means? Is it refer to "output current" or "output clamping current"? I think it is the output clamping current, because if Vo is pulled to a voltage higher than the IC's supply voltage, the output clamp diode will conduct, the datasheet want the user to protect this diode from overcurrent.

However, I see similar post "link", NXP's employee says it is the "output current" which should be observed. That doesn't make sense, because if that is true, the datasheet can only list the maximum ratings of Io, but it listed both the Io and Vo.

So can I pulled up to for example 12V through 10k resistor on the output of the gate, while only powers it from 3.3V? When doing this, will the 1mA current sourcing from 12V to 3.3V cause problem for the 3.3V supply, a linear regulator?

Thank you


texts:
I am working on a digital voltmeter circuit using ICL7107 IC. Having trouble powering it up. There is a -5 V supply to pin 26. I used a 7805 regulator for +5V supply but wondering how to supply the -5V. a) Can I use the output of 7805 to somehow convert to negative? b) is there an IC for this?( my max current rating is 3.34Amps).
Note: I tried using 7905 with 7805 but no use the 7805IC goes burning hot. As soon as I removed the connections between two it behaved properly(only7805). Please suggest some idea to achieve this.


texts:
I've seen the circuit below on YouTube.
But it has low efficiency and the p-chnnel MOSFET gets hotter as the output & input voltage difference increases (it goes above 100c with heatsink).
I don't have a true-rms current meter, but my meter shows a constant input current even if I double or triple the input voltage (without changing the output voltage & cuttent).
Can anybody help me increase the efficiency please? (Unfortunately I don't have an osiloskop, but what causes this switching loss?)
Or if you think this circuit is not practical suggest me another one. (I couldn't find by googling)


texts: Why does my transistor circuit produce a wave?

texts: Could some one explain to me how my circuit works? I accidentally hooked this up while trying to work out an amplifier. I'm thinking there's something like RC resonance going on, but I'm not sure. Please help? Thanks.


texts:
I'm working on designing a half H-bridge circuit around an IR2184 Mosfet driver chip. I've had limited success with it. Ideally it will allow me to drive a 12V/4A bilge fan when I get it working.

One iteration had the fan wanting to kick over but never full starting. Something I've attributed to bootstrapping on my HS driver. The larger issue as I've iterated over it is that I keep killing the driver chip completely with only an oscilloscope on the output.

To drive it, I am using an Arduino Micro 5V, configured to output a PWM signal on pin 10 running at 32kHz. For bootstrapping I am using a US1M Diode (Basically a SMD version of the UF4007). I have 10Ω gate resistors with US1M bypass diodes in parallel. I also have 15V Zenners with 10kΩ Gate-Source resistors on both MOSFETS.

I'm using PCB's instead of breadboards as the currents I am using are more than a breadboard can handle. Plus they are cheap(ish) enough to waste several. Either way I have destroyed enough of these chips to seek some professional advice. Without any significant load, what can be causing my driver to fail?

Schematic:

PCB:


texts: I'm trying to solve this problem where I find Vout/Vin if rπ if infinite. I also have to conside early effect.  When I try to solve it, I get Vπ = 0 and that makes gm zero, a bit confused on that.


texts: I just bought 5 boards from Allelectronics.com like this. I decided to make a circuit that involved ICs. When I attempted to solder the circuit onto the board I realized that once you solder the IC on, as far a I can see, you can't wire components to the pins because the solder sticks to the separate holes. So my question is how do you solder components to ICs?  This should be easy I just don't get it because I am a newbie to prototyping.


texts: Why can I put a resistor at either lead of this LED and still see its effects?

texts:
Just to add a little bit of context to the question, I am using an Arduino Uno and a breadboard.

I have a 5V power source running to the positive (longer) lead of an LED (rated at about 2v and 20mA). I then have a 150 Ohm resistor connecting to the negative (shorter) lead of the LED. The resistor is then connected to ground.

I am using a breadboard, so whenever I remove the resistor and connect it from the power source to the positive (longer) lead of the LED, I still see the same amount of resistance.

In other words, with no resistor, the LED is at X brightness. However, with a resistor attached to either lead of the LED, there is the same amount of resistance (thus, the LED is dimmer, at X÷resistance brightness.)

Based on my very limited knowledge of electronics, I would've assumed that you would have to connect the resistor to the power source, and then to the positive lead of the LED, so that the voltage and current would drop before they got to the LED. This seems to be false, based on my little "experiment" here.

Why is this the case?


texts: Why does the Earth's electric field affect things so little?

texts:
Starting here:

http://hypertextbook.com/facts/1998/TreshaEdwards.shtml

"Over land the average electric field is about 120 V/m …. Assuming an exponential increase of the conductivity with altitude, it can be shown that the electric field decreases exponentially with altitude. At the 30-km level, the electric field is as low as 300 MV/m [sic]. Integrating the electric field from the earth's surface to the ionosphere gives as a result an electric potential difference of about 200 kV." Standardized result: 0.300–120 V/m

Since this is the case, how come a conductor placed in this field doesn't immediately have a powerful current running through it?

This is my primitive understanding of the situation:

simulate this circuit – Schematic created using CircuitLab

But clearly this must be wrong, because you don't get 120 Amps through any random string of wire that happens to hang vertically so what am I missing?

EDIT

Is this a more reasonable approximation?

simulate this circuit


texts: Is there something to see outside the normal analog TV video frame?

texts:
I've heard from TV repairmen and read in various sources through the years  that the TV radio signal isn't shown on radio TVs in its entirety. I've noticed that on different radio TVs the same channel looks cropped differently. Some show more, some less. The displayed picture is apparently cropped to avoid showing the outside regions which carry no useful to the viewer graphics (possibly noise or just black border). I've also learned that it might contain something else which could be interesting to an enthusiast. I couldn't find much by googling different variations of my question, but it seems like there may be some lines and shapes which help with auto-tuning the frequency to make the picture straight and crisp. But I could be wrong.

Is there something outside the image frame that we normally see on TVs? If so, what does the full image look like? Does it vary between countries or radio broadcasting standards? I'd like to see a collection of different screencaps with annotations for what's what.

The format here seems to be SECAM D/K.


texts: Do polygon pours have to be either ground or supply voltage?

texts:
I was wondering if it is possible to have polygon pours but not connected to anything. Will that affect the circuit in some manner ?
Because for the pcb I'm designing, if I use polygon pours as ground planes it results in a large number of isolated islands.

So is it better to send the pcb design off without any polygons or is it ok to send it with non-connected polygon pours?
Many Thanks


texts: Why do we have a limited bandwidth in electronics?

texts: I've been looking around a bit on optical communications and it is said that the main advantage in using optical communications, namely optical fibers, lies in the gigantic bandwidth available, when compared to the few GHz that electronics can manage. My question is: what is the physical phenomena that is limiting the electronics bandwidth? In light I can see it to be the optical properties of the waveguides such as absortion, and dispersive mediums, but what about in electronics? Specially in current nanoscale electronics like transistors.


texts:
I need to design a circuit that reads the status of 6 switches and makes the status available over LAN for a professional project.
The design should be implemented in hardware (no microprocessor.)
My initial idea was:

Read the discrete status of the 6 switches (0V or 24V)
Levelshift from 24V to 3.3V or 5.0V for serial conveter
Convert to serial (RS232 or RS485)
Convert to LAN using Lantronix XPORT

This approach is inspired by the example circuits from datasheet for the KBDGRAY IC from AB Circuits. Replace the keypad by the switches.

I don't feel comfortable using an IC from this manufacturer, but I haven't been able to find anything similar from TI, Analog Devices etc.

I think that I also need a shift register or some other IC between the discrete section and the serial converter before this can have a change of working.

Under all circumstances, this doesn't seem to be an elegant solution.
Can you please point me in the direction of a solution to my problem?


texts: Capacitor question - energy from pushing a baby stroller

texts:
I’m making a circuit that will be added to a stroller.  With a 24 volt DC motor, I’m trying to power the capacitor by walking around & simulating a baby/mother experience and if I run into a hill or steep slope, I should be able to turn on the switch and with all the energy that I have stored throughout the day, it should able to power the second motor, which will assist with the work necessary to climb the hill with the stroller.

This is the diagram for that, so the two volt LED was just a test to simulate since I was only obtaining low voltages since the voltage was in a parallel configuration, just wondering if there could be a way to avoid that configuration so that the capacitor can collectively power the motor instead of providing the same voltage.

As for the diagram:

I have a switch on the far right closed & a switch in the middle open so that the capacitors will have a connection straight to the motor and charge when the other switch is open, then I’ll reverse the set up when I need to turn on the light, be turning off the switch on the far right and turning on the switch in the middle.

My issue is that the capacitors still don’t combine voltages, I have 0.7 volts for all three capacitors, so the 2 volt LED should be turning on in this configuration, but the voltage on the LED is the exact same as the capacitors, 0.7 volts,.

Any ideas?


texts: How can I switch power between two hard drives using transistors?

texts:
Application

I have two hard drives that draw approximately 1.1A / 1.5A on their 12V and 5V power pins. I  have several 2SA1020 PNP transistors which are rated 50V 2A and was hoping to use them to switch power between the two drives - the idea is that when the computer is off, opening or closing a switch would allow the 12V and 5V power sources to flow to just one drive. I considered using a MOSFET but the drives draw only a little power so it seems like these transistors would be ok, right? If not then please let me know what the main pitfalls are.

In my previous days of analog electronics tinkering this would have been a much simpler concept  - the first thing that came to my mind was an automotive relay switch because it has a N.O. and N.C. leg and can direct power between the two of them. But I didn't find anything when I was searching for a '2-way mosfet' with NO and NC pins. I'd also just like to see if I can build this using the transistors I already have.

The idea I came up with for this was to have a switch which can ground the bases of the first two transistors used for drive 1 (D1), normally a pullup to 5V circuit, and use an NPN transistor as a NOT logic gate to invert the instruction to the second set of PNP transistors for the second drive (D2).

Here's what I've come up with:

Questions

Basically, what would be the best / easiest way to accomplish this?
The circuit I drew is the best that I can come up with. Will it work OK?
If not, what are the caveats I'm missing?
And, is there some other way that is much easier / simpler to achieve this?

ps: I'm mostly curious about the 'switching' part so I intentionally omitted additional components that I believe would be good to add in, such as those which would prevent switching if the computer was powered on, etc.


texts: VHDL Loop Statement error: loop must terminate within 10,000 iterations

texts:
architecture Behavioral of INST_CACHE is

begin

    init_cache : process (INIT)
        subtype word is std_logic_vector(0 to 31);
        type storage_array is array (natural range 0 to 2**32 - 1) of word;
        --type storage_array is array (0 to 2**32 - 1) of STD_LOGIC_VECTOR (DATA_WIDTH - 1 downto 0);
        variable storage : storage_array;
        variable index : natural;

        type load_file_type is file of word;
        file load_file : load_file_type
            open read_mode is "C:\cachecontent.bin";

    begin

        -- load ROM contents from load_file
        index := 0;
        while not endfile(load_file) loop
            read(load_file, storage(index));
            index := index + 1;
        end loop;

        if rising_edge(CLK) then
            InstCacheOut1 <= storage(to_integer(unsigned(InstCacheIn1)))&InstCacheIn1&'1'; -- instrukcija & PC te instrukcije & valid bit
            InstCacheOut2 <= storage(to_integer(unsigned(InstCacheIn2)))&InstCacheIn2&'1'; -- instrukcija & PC te instrukcije & valid bit
        end if;

    end process;

end Behavioral;

I want to simulate a simple cache.
I will load instructions from a file into a structure.
However I get the error

  Error (10536): VHDL Loop Statement error at InstCache.vhd(49): loop
  must terminate within 10,000 iterations

The line the error is reported at is:

    while not endfile(load_file) loop

I'm guessing the file isn't opened correctly or maybe it doesn't have the EOF character.
First, am I opening files in the right manner?
Second, what extensions are supported?
Third, do I have to manually add EOF character.
Fourth: can something else be a problem?


texts: How much power do I need to transmit a radio signal through a solid ice crust 100 km thick?

texts: Imagine I put a floating probe inside the subglacial ocean of Encelado or Europa: how much power should my radio have to be able to communicate from external surface with the probe? Or, in different words, how much attenuation do 100 km of solid ice cause to a radio signal at, say, UHF frequency?


texts: I am going to buy a beagleboard xm. The emulator what I got is XDS100v2. Can I able to debug with this in eclipse environment? What everyone suggests in forums is we can use it with Code Composer Studio. But I dont have license for the same,and also the free license provided with XDS100v2 is time limited I guess or atleast it is node locked for the worst case. So has anyone found a way for using XDS100v2 with beagleboard xm?


texts: Dmultiplexer truth table and boolean expression

texts:
As the title says I have problem with understanding how to make the truth table for demultiplexer and how to make a Boolean expression from it. The thing that bothers me is how to make a truth table with more than one outputs. I search through google and I've found this answer

However I can't understand it, and I have no idea what to do. Any help is appreciated.

I got it, in case anybody came here with search engine, read the comments, and don't Or(+) the outputs.


texts: How to efficiently step up high amperage source by just a few volts

texts:
My car has an alternator that supplies 90A at 28V (it's a 24V vehicle). However, I have now fitted two AGM batteries in series, which like a higher (14.8V each) charging voltage. Therefore I would like to boost the voltage to the batteries to 29.6V (= 1.6V extra).

I know about step up converters and LDO's but these seem to generally work for relative low amperages, certainly not 90A.

Any idea how I can efficiently boost it by a few volts extra?

Thanks,
Sjoerd


texts: differential pair impedance and length matching

texts:
I'm designing a high speed circuit (MIPI-DSI) so I have to carefully layout the tracks. Correct track impedance is the first point usually made in various online sources I've found on the subject, so I tried to get the microstrip impedance calculator to get as close the desired 100 Ohm. For budgetting reasons I'm tied to a stock pooling layer stackup, so I went for OSHpark's 4-layer stackup (35um copper - 0.17mm FR408 - 17um copper ...). With a track width of 12mil and a 6mil track spacing, I get 101 Ohm, so far so good.

Next step is routing the tracks. Most guides mention that any length differences can be negated by adding serpentine patterns in the shorter track like this:

(grid is 6mil)

It is mentioned in many guides that the maximum trace distance when doing serpentine tracks is twice the normal track distance, so 2 x 6mil = 12mil, so I kept to this recommendation.

So far so good, but looking at the picture, isn't it more likely for the signal in the serpentined track to cut corners and just go straight through, basically following the grid lines?

I'm now considering increasing the track spacing to 12, so I get a differential impedance of 110 Ohm (just within the 10% margin), but I get to make my serpentines larger, so A) I force the signal to take the corner and B) I need less bends to make up for the length differences.

Alternatively I could break the distance rule of the serpentine with the same 12/6 width/spacing to a max. distance of 24 mil. Which is better?


texts: What is the precise use of a memory controller and RAM latency?

texts:
I'm learning about synchronous DRAM and it often mentioned a memory controller. What exactly is the point of this? Couldn't the cpu just take the job of requesting and receiving data with its own clock?
 And something else that has confused me is RAM latency. How exactly does a computer wait a certain number of clock cycles to receive information? What does the computer do during these in between clock cycles?


texts:
I have seen some amplifier designs that bias the gate by using a voltage divider and small size FETs with drain connects to gate as the picture shows. I am wondering what is the advantage of these FETs in the bias circuit. They should be always in saturation region if applied voltage is bigger then threshold voltage. These fets do not affect Vgate at all(?)
Does anyone know how this bias circuit works and what are the advantages of using this fets?


texts:
In making a breakout board for an SMD Bluetooth module, I realized that simply wiring LEDs to your signal lines is insufficient for a decent visual indication, as signal duration is too short to be visible to the eye unaided by electronics. So what is needed then is a simple circuit to extend the time the indicator LED stays on. Here's what I cam up with, with the upper circuit being for normally low situation and the lower circuit for the normally high:

Figuring about 200ms as the minimum time the LED needs to be on, a 5V circuit, 0.6V for the diode drop, 1.6 for the LED V forward, and 330 Ohms for the current-limiting resistor, I came up with around 1uF for the cap value. The Schmitt trigger/buffer is there in order not to load the signal line.  I'd like to keep this as simple as possible (just a diagnostic tool to embed in the circuit), but I probably made it too simple and missed something obvious?