texts:
I am writing a basic I2C slave as part of my code on a 20-pin 8-bit PIC16f MCU. As best as I can tell, this microcontroller has a module that watches the I2C bus and only updates my registers if there are incoming message addressed to the PIC -- I can't interact with any other messages. The master is a CPU running a linux kernel and some other software. From the CPU, I can run a I2C probe script that just tries to read from every possible device address on the I2C chain (bus).

I'm having trouble getting the PIC to respond to any probing. I've written the simplest I2C code I can manage -- it should just blink the LEDs whenever the device gets any sort of I2C message directed at it.

I hooked the lines up to the oscilloscope and was able to confirm that traffic is coming through the clock and data lines when I probe the chain.

My code is below. My compiler is the free version (without optimizations) of Microchip's XC8. I'm using the newest version (v1.34) for Windows.

Am I missing any initialization or configuration steps necessary to get my PIC to see incoming I2C messages?

#include <xc.h>                 /* XC8 General Include File */
#include <pic16lf1709.h>        /* Definitions of I/O pins */

#pragma config WDTE = OFF       // disable watchdog timer, for simplicity

// I2C address is 7 bits: 1111110
#define I2C_ADDRESS 0x7E

typedef unsigned char byte;

void main(void) {

    /* configure MSSP module */
    TRISBbits.TRISB4    = 1;    // set SDA to input
    TRISBbits.TRISB6    = 1;    // set SCL to input
    SSPCON1bits.SSPEN   = 1;    // enable SSP module
    SSPCON1bits.SSPM    = 0x6;  // SSP is in I2C slave mode, 7-bit addressing
    SSP1ADD             = I2C_ADDRESS<<1;  // set the device address (left-aligned)
    SSPCON1bits.CKP     = 1;    // release clock
    TRISC               = 0x00; // set LEDs to output
    PORTC               = 0xFF; // initialize LEDs to OFF

    while(1) {

        byte ssp_buf;           // for the data we read from the bus

        if(SSPSTATbits.BF) {    // if the I2C buffer is not empty
            PORTC = 0x00;       // turn on LEDs for a moment
            for(int i=0; i<100; i++) _delay(250);
            PORTC = 0xFF;       // turn them back off
            ssp_buf = SSPBUF;   // read the buffer
                                // BF flag is cleared by hardware
        }

        SSPCON1bits.CKP = 1;    // finally, release clock

    }

}


texts: Can I power a laser directly from a computer PSU?

texts:
I have purchased this laser with a driver from Ali.
I connected the laser to the driver and the driver to a 12V DC and the TTL to 5V (which I then disconnected since the applying 5V to TTL actually turns the laser off).
When I first turned power on, the laser worked fine and I was able to burn some paper for about 60 seconds before turning it off. Then when I tried to turn it on later, it no longer worked. (I can no longer return the laser since I had it home too long before getting around to testing it)
I tried pulling down the TTL by shorting its pins first through a resistor, the directly, leave them floating, apply 5V to them... but nothing.. the laser no longer turns on, only the fan on it spins.

If the problem is in the driver board then I could just buy a new one since it costs only ten bucks. But how do I test that the laser itself is working fine?
I was thinking about taking a PSU from an old computer and connecting the laser to the 12V DC output from the PSU. Computer electronics are very sensitive, so the PSU must have a nice, clean and smooth 12V output right? Will that work?


texts: Temperature Dependent Frequency of Relaxation Oscillator

texts:
I built a relaxation oscillator to convert a capacitance into a variable frequency square wave. The passive components have a very small temperature coefficient, but when we change the temperature of the LM2903HYPT comparator the frequency shifts by around 8kHz. How do changes in the comparator cause the frequency of the circuit to change? It normally operates at around 150kHz or so. How can I remove these temperature dependent changes in future designs?

Thanks!
-Hunter


texts: Why does an antenna trace have this shape?

texts:
I'm wondering why an antenna has a board trace that follows a certain "squiggly" shape. This doesn't have to apply to only antennas; I'm sure that there are other components that have changing paths for various reasons, but the antenna usually retains this shape.

You can see it on the right in this picture. What is the significance behind a trace like this?

(source)

This question might be related to electromagnetics, but I think the answer should be simple enough.

EDIT: I should clarify that I'm looking for explanations dealing with radiation and impedance. Also, any comments on why a design like this would not be efficient for a high-frequency system would help.


texts: How can cold temperature (refrigerator, air con) fix a broken electronic device?

texts:
I had an air con remote control that wasn't working at all. But at some point I noticed that when I turn on the air con manually and the room gets cooler, the remote control works as expected. I thought it can be caused by moisture inside the device and probably something happens with it when it is cold. I tried different batteries and it didn't change anything - the remote was operational only when it was cooler than 29 C (I live in a humid tropical country).
I ended up keeping the remote in the fridge without understanding the real reason of the issue.

Now several years passed and my Xiaomi Mi Band 2 stopped working. After a lot of searching I found out that many people had the same problem and putting the device in the fridge fixes it. I tried it and amazingly, it worked!

What can be a reason of this behavior? Temperature, humidity or batteries?


texts: How to check for quick oscillations without an oscilloscope

texts: I'm working on a 555 timer oscillator circuit, and I'm trying to get an LED to blink. The LED turns on, but I'm not sure if it's blinking. I do not own an oscilloscope I've tried a few things, such as recording with a slow motion camera. Is there a good way to test it? I was thinking I might be able to hook up a transformer to it and check for a constant voltage.


texts:
EDIT - I am happy with the comments to the first question, so I will replace it with a different question that I would like answers to. The 2 scopes in question are the Tektronix TBS1072B and the Rigol DS1054Z.

The Tektronic has a CAT II 300Vrms input voltage safety rating.

The Rigol has a CAT I 300Vrms input voltage safety rating.

I need to do some 240Vrms mains measurements and would like to know the difference between the safety rating categories mentioned above.

I'm assumming the tektronic is the much safer scope to use for mains probing due to the higher CAT safety rating?

But can the Rigol still be safely used for isolated mains measurements (DUT through an isolating transformer with ratio 1:1 or 10:1)?

Or should I be considering differential probes as well?

Thanks for the replies.


texts: I can do addition, substraction and division but i cannot do multiplication

texts:
Here are my topmodule and testbench files. What is my mistake?

library IEEE;
use IEEE.NUMERIC_STD.ALL;

entity celcius_to_fah is
  Port ( c : in unsigned (6 downto 0);
         f : out unsigned (8 downto 0));
  constant coef: unsigned(7 downto 0):="00100000";
end celcius_to_fah;

architecture dataflow_model of celcius_to_fah is
begin
  f <= coef2*c;
end dataflow_model;

testbench

library IEEE;
use IEEE.NUMERIC_STD.ALL;

entity sim is
end sim;

architecture dataflow of sim is
  component celcius_to_fah
     Port ( c : in unsigned (6 downto 0);
            f : out unsigned (8 downto 0));
  end component;

  signal ct: unsigned (6 downto 0):="0000100";
  signal ft: unsigned (8 downto 0);

begin

  uut: celcius_to_fah port map(c=>ct , f=>ft);

  process
  begin
    wait for 5ns;
    ct<="0001000";
  end process;

end dataflow;


texts:
I am starting to learn about electronics and I am still confused about current flow. Initially the book would try to be clear about the distinction between conventional and actual flow but then further in the book the circuits are confusing me. Take e.g. the following DC circuit:

Actual flow is of electrons pushing the other electrons from the − terminal to the + terminal. But then why is there 0 V between the − terminal and the first lightbulb? There has not been any resistance yet, so I would expect this to be 9 V. And then I would expect 0 V being at the + terminal.

Is my confusion clear? Could anyone then attempt to explain why my expectation is wrong?


texts:
I am using this LCD:

Plus I am using an Arduino. I am trying to hook this up but without a 10K pot. How is this possible? Every tutorial I found involved the 10K potentiometer


texts: linearize single arm wheatstone bridge output

texts:
I am installing a water depth OEM sensor that is a solid state, continuous fluid level sensor.  The sensor provides a resistive output that is inversely proportional to the level of the liquid: the lower the liquid level, the higher the output resistance; the higher the liquid level, the lower the output resistance. We are trying to monitor overland water flow depth during the winter (Ontario). We loomed into using a sonic sensor that does not require to be submerged under water but it does not work because of the small pipe diameters. Pressure transducers do not work since they cannot be frozen or the sensors that can be frozen will not give us a measurement if it is frozen in a little bit of ice.  The overland water flow is being measured in-situ on a farm fields where can collect water samples when the over land flow occurs.

The sites we are installing this sensors as well as a couple of other sensors and a data logger that will all run off of a 12v deep cell battery. The data logger I am using can measure voltage + 5v.

My electronics is very rusty since I have not used it for a long time. And the times when I used it was base on a couple of courses along within self training.

Sensor information:

Solid state, continuous fluid level sensor
Variable resistance: 3000 – 300 ohms  + 10%( 3000 at water depth of 1
inch, 300 at water depth of 24 inches)
Sensor has a reference resistor 3000 + 10% for temperature
compensation
Resolution: < 0.01 inch

I have researched a number of websites and found a lot of information on wheatstone bridges that I can use to convert the resistance to voltage. But since this will be a one arm bridge the voltage output will not be linear. I also found a one arm wheatstone with an op-amp connected to linearize the output, but I do not know type of op-amp and resistances.


texts: Powering 10.8V DeWalt cordless drill from mains

texts:
There was a couple of questions on how to power a cordless drill, but they are all about power supplies.
I've got a DeWalt 10.8V cordless drill and its battery connects through 4 pins instead of 2 or 3 that I've seen while googling. One is 12V, second 8V and to others seem to be ground. I've tried connecting only 8, only 12 and both (with common ground) but non of that worked. I know the polarity is right because a little diode under the chuck flashes for a second when I try to run it.

Maybe someone dealt with this kind of battery connection or knows the right way to power a DeWalt cordless drill?


texts: Using cam350 to find errors of a PCB file

texts:
I want to find errors of a PCB file (like disconnection between tracks and pads, etc) which I have created in Altium designer software. I use Cam350 software for this purpose.
When I run Cam350 I face with some errors like that:

I don't understand the meaning of this errors. Can anyone help me?


texts: Can you approximately detect the closure of up to 100,000 switches using a resistor chain?

texts:
Consider the following outline circuit:-

It is a series of switch controllers that can short out parts of a chain of serially connected resistors. The short is accomplished with a BJT or MOSFET. A shunt resistor at the end allows the total current through the chain to be measured and thus the number of shorted resistors estimated. This is the crux; only a    coarse estimate of the number of shorted resistors is wanted.

Assumptions:-

The year is 1999.
The circuit is custom fabricated  on a single 6" wafer of Gallium Arsenide.
The resistor chain would have to span the entire area of the wafer.
There are 100,000 switch controllers.
Each switch controller operates independently but is totally synchronised with a master clock.
The circuit operates @ 10GHz.
The missing detail is unimportant.
Cost is irrelevant.

This is not an XY problem. I'm re-posting a question put to me by someone, therefore it has be to critiqued as is.  I suspect that this cannot work, but why not exactly?

For reference, this is a proposed alternative counting solution for the TWINKLE Device. It is a hypothetical machine for factoring prime numbers. Before you scoff, it's proposed by Adi Shamir, a holy cow of cryptography and co-inventor of the RSA algorithm.


texts: Why LME49710 does not perform at least as good as LM358 for audio mic op-amp?

texts:
I built a hobby mic op-amp circuit as described here:

It gave me a pretty ok result:

Now I replaced LM358 with LME49710. The circuit is the same, except from the wiring to the LME49710 pins (LM358 pin 1 is the output while it's pin 6 on LME49710, VCC also moved from pin 8 to 7, the rest are the same)

LME49710 is supposed to be a more high-end op-amp, so I expected some improvement. However...

That doesn't look right and doesn't sound right. A lot of noise is added, and the audio is less amplified and hardly heard over the noise.

What are LME49710 characteristics that makes it less suitable for this circuit?
Is there a simple way to change the circuit and make it work better with LME49710?


texts:
we know that GPS receiver can reach sensitivty of -168dBm, and also it is possible to make receivers with similar sensetitvity can operate at another bands/frequencies .

but I just want to know if possible to build amplifier with input of -168 dBm ? I want  increase signal power at some -90s dBm range to make the system able to receive high bitrate at very weak signals "-160s dBm" .

I know the noise will also amplified , but the SNR still unchanged or slightly.

thanks,


texts: Identifying and finding replacement for LCD display module

texts:
I have a Line 6 POD X3 amp modeler. It has a small LCD display module which was shattered during my last move and the device became unusable.

I have attempted to identify the model of this display to try and find a replacement. I have opened the casing, disconnected the module and found the model number on it.

Full info as appears on the display:

Sticker:
CGM12864CFAA, KS070705E002403

On plastic itself:
CGM12864 C-A, VER: 3.0

However when I search for it, I can't find this specific module. So what is the way to precisely identify this display module? Do I have enough information here?

Front:

Back (it seems that the chips are sealed). At the bottom, following text appears: MADE IN CASIL, CGM12864 C-A, VER: 3.0

These schematics were found here (Thanks to @Passerby). However I am not experienced enough to realize what replacement LCD can be used here given this information:


texts: Apparent contradiction on ideal OpAmp equations

texts:
For an ideal OpAmp the voltages at the inputs are said to be of equal value and the currents 0, however, for we also know that $$V_\text{out}=A(V_p-V_n)$$ but if the voltages are the same the output should always be 0!

I know that what I'm saying is wrong, but I don't know where the loophole is, and I can't find it anywhere.


texts:
While comparing schematics of two old analog oscilloscopes (Tektronix 475 and Goldstar 9020,) I was expecting many differences to get better frequency response since the first is a 250MHz and the second is only 20MHz.
My question here is about the way of getting the voltage offset to control the vertical position.
The following figure shows both circuits:

In the Goldstar it is quite straightforward since it creates an offset on the base of one of the emitter-follower driven push-pull.
In the Tektronix a kind of Wheatstone bridge is used to create the offset at the input of the common-base transistors.
Could you please tell the benefits of using the Tektronix solution?


texts: How to choose electric motor for a linear actuator?

texts:
First of all, I'm an undergrad student of Mechanical Engineering, and I'm working on a project where the main component is a type of linear actuator which I'm going to design. I will use a roller screw mechanism for the actuator, and it's main job will be to compress some material. One of the specifications for this project is that the electric motor needs to deliver between 2-3 horsepower, and still be precise enough to control the speed of the linear actuator (between 0.5 and 2 mm/s).
Which kind of electric motor should I use for this project? I've thought about using a commom electric motor like this one (link) with a reductor. Would that be enough? I have little background in electrical engineering, so any insights would be helpful.


texts: PIC18F microcontroller supply pins getting shorted when WiFi is running

texts:
I am working on a PCB with PIC18F26K22 which connects to a Redpine Wi-Fi module through UART.

I initially checked if PIC works with a simple LED blinking program with internal oscillator and it does. I check the same blinking with 11Mhz external oscillator + 27pf capacitor circuit and it works.   As soon as I write code into the Wi-Fi module, my supply i.e. 3.3V and ground pins are getting shorted, burning up my microcontroller. This has happened on all the PCBs with this layout.

My observations/doubts(all suggestions/criticism welcome). My biggest suspect here is the PCB layout -
1. I initially doubted the external oscillator layout and removed the grounding below the crystal. I also placed the caps after the crystal after reading some posts on this forum.
2. Since the above didn't work , I checked Wifi working with the internal oscillator only ,but the burning persists.
3. Next I cut the Rx and 3.3V supply tracks on Wifi and hardwire them but still the problem persists.

I have attached my layout here. Any suggestions would be great!

Note : I have my PIC+ WiFi module hardware combination and code working on a number of other project PCBs but not this board :(


texts:
How can I do a two-port response calibration to measure S-parameters (Reflection and Transmission) for an  HP 8752A Network Analyzer?

The DUT (two coils, one in air and one in salt-water) is connected to the analyzer with two cables (one cable is connected to Reflection port and the other one to Transmission port.)

The manual is not helpful at all, VERY confusing. When doing calibration, should I connect the two cables together, then one head to one of the ports, the other head to the calibration part?

In response to answers:

Yes, I do have a cal kit.

The problem is that I need to calculate Max Available Gain and for that I need to find the S-params.

My experiment is with two small coils, both in air, one is constant and the other with change distance. One coil (coilA) connected to Refl port of NWA (using a cable) and coilB to Transmission port (using another cable). Each time I change distance one cm, I run a Matlab simulation to get the graphs (mag and phase.) Then I have to switch coils (coilA to Trans port and coilB to Refl port.) Same dist. Run Matlab again.

Then I change the distance one cm, run matlab, switch coils, run matlab again. Of course saving the data.

So basically it is measuring reflection response and then transmission response at each port for each coil.

Now,
My question is about how to calibrate for this specific type of measurement? I heard that I should connect the two cables together, then one head to the NWA's port (say Reflection, if I'm doing Reflection response measurements.) and the other head to the calibration part (say open or short). Then, on the NWA press the Measurement button and select the type of measurement I want, say Response. Also, I should set the Number of Points, Start freq, and End freq. Then press the CAL, CAL Menu, Response, then Open (F)/Short (F)/Through, Done Response, (Re)Save to register.

I performed one calibration for Reflection response, save it in register 1, then calibrate for Transmission response and save it in register 2. This is because when I'm running the Matlab simulation and then need to switch coils, I can do that without having to calibrate again. I can just recall the calibration using Recall button.

I have to add that I have already read HP 8752A NWA manual, from beginning to end, not much helpful.

I think there were mistakes there: So I was told many times from different people that when I want to do Transmission (or Reflection) calibration, as a part of the calibration step I have to press the Measurement button(key), then select Transmission (or Reflection.) Then continue with performing the calibration. However, in the manual it is not said so which seems odd!

Anyway, I hope all these information make sense and is not overwhelming or confusing. Also, hope to hear some feedbacks and ideas. I'd greatly appreciate.


texts: Curious noise on FPGA Microcontroller connection

texts:
I have the following setup:

An FPGA eval board has a daughterboard with pin headers connected to it. From these headers I have connected 16 ~10 inch 24-gauge wires to feed a bus to a TI OMAP-138 Microcontroller eval board's built int connectors wired to its GPIO pins. I am generating audio waveforms (speech) on the FPGA and sending it across the bus at a constant 8Ksps. The FPGA's clock is 30 MHz and the Microcontroller is 300MHz. The FPGA also sends a clock signal I use to sample the data.

The problem is when I display the data from the Microcontroller I see major distortion in the read audio (I get it from a memory dump). I also read the data from the FPGA with a logic analyzer from a Mictor connector on the same daughterboard and that signal is not distorted.

Here is a picture of the two (not quite aligned but close enough to see).

http://imgur.com/lTsS1Ag

I have no experience with dealing with transients like this. At these speeds is this kind of distortion expected or is it likely a problem with how I am reading data with the Microcontroller?


texts: Using asymmetric secondaries of power transformer with bridge rectifier for bipolar supply

texts:
I have a power transformer that has one secondary rated at 15v 1A, and another 15v 500mA.  I would like to use it to create a bipolar supply.

If I use two separate rectifier bridges, one for each secondary, I will get bipolar with different current load capabilities.

What happens if I join one lead of each winding, and use it as a "center tap"?  See schematic.  I think this would be ok if the two secondaries had the same current capability.  But what if they are different?

Obviously, for this to work (vs catching fire), the correct winding leads would have to be connected, that is, the low wire of one connected to the high wire of the other.

I am thinking that this could mean that the result ia a bipolar supply capable of 750mA, with the DC voltage being 15*1.414-Vrectifierdrop for each of positive and negative terminals, with respect to COM.

Do you think that would work?


texts: Temperature compensation of LSM303DLHC accelerometer / magnetometer

texts:
ST Microelectronics makes the LSM303XXXX, a popular range of 3-axis accelerometer / magnetometer sensors that are used on Arduino breakout boards, etc.

The older LSM303DLH sensor has been replaced by the LSM303DLHC with has improvements in power and data transfer. However, the new LSM303DLHC sensor has a zero-g acceleration delta of 0.5mg/deg compared to the much tighter 0.1mg/deg for the older LSM303DLH.

Using the newer sensor, variation with temperature is noticeable in our data. Fortunately, the LSM303DHLC has a temperature sensor onboard.

What method should I use the compensate for sensor drift using the temperature readings? Just a look-up table / simple formula?
For batches of instruments (10 - 100) is there any alternative to calibrating each instrument?
Will the effect of temperature change over time? i.e. how long until another temperature calibration needs to be done?

EDIT: mg units


texts: How do I check whether my GSM Modem works in some other country?

texts:
I am a new to choosing RF modules and I am trying to choose a module that works in Qatar.

I see on FrequencyCheck, Qatar is having GSM band of 900 and 1800.

So, if I choose GSM800 C, having quad band 850/900/1800/1900MHz, will it work in Qatar? I am believing that when checking bands for say Qatar, you need to see whether 900 and 1800 are present in GSM modem?

Is there anything, I have done wrong? Please guide me.


texts: Controlling initial phase of carrier during modulation?

texts:
During the process of modulation, any of the three parameters, viz \$\ A_c\$ , \$ω_c\$ and φ, of the carrier wave can be controlled by the message signal where φ is the initial phase.

How is it possible to control initial phase of carrier wave by baseaband signal?


texts:
I read many informations from many webs,
all never give an answer with easy understand.


texts: PT4115, where should I put output capacitor?

texts:
The PT4115E datasheet states:

  Peak to peak ripple current in the
  LED(s) can be reduced below 30% of the average
  current, if required, by adding a capacitor across
  the LED(s).

Can you confirm that "across the leds" is:

from : between Rs and led
to : between led and L

?


texts: In the lesson on BJT Amplifiers, we were told the we can find the AC equivalent circuit by replacing all capacitors by short circuits, inductors (if any) by open circuits, dc voltage sources by ground connections and dc current sources by open circuits. What I don't understand is WHY should we replace dc voltage sources by ground connections and dc current sources by open circuits ?


texts: Why would an op-amp use BJTs over MOSFETs?

texts:
I've always been told that ideally, op-amps have infinite input impedance. So when I was looking at the LM741's transistor level schematic, I was confused when they used BJTs instead of MOSFETs.

Wouldn't using a BJT result in current flowing into the input pins?


texts: JTAG on a board with optional components

texts:
This feels like it ought to be a common problem with a conventional solution, but I'm struggling to find one.

I am designing a board with several JTAG-conforming components. It has a mezzanine with another.

The mezzanine may or may not be fitted.

How can I arrange that JTAG works properly both with the board present and absent?

The obvious, but clunky, solution would be to fit a TDI-TDO link when the board was absent. Perhaps a TDI-TDO tristate buffer with pull-down on nOE, driven high by a presence-sense line from the board?

Obviously, with JTAG I care a great deal about robustness. Is that robust? Are there any complications to consider?


texts: How much current does an FPGA consume, anyway?

texts:
I'm in the R&D stages of a V4 of my project, which may replace the high-speed DSP with an FPGA.

I was looking at this FPGA, because it is cheap: XC3S50A (about £6.50/each.) I think I can probably fit the project onto there, with one concern. I can't find anywhere in the datasheet about how much current it will consume. Is it a fixed amount, or does it vary, depending on how much logic I am using? Is there a quiescent current draw by it, when no logic is in use? What about the current draw by its clocks/PLLs? I've looked through the datasheet - it has many characteristics, but these ones in particular don't seem to be mentioned.


texts: Why are synchronous counters synchronous?

texts: Doesn't the input signal having to propagate through the AND gates cause a propagation delay anyway? With the asynchronous counter the delay was caused by the clock signal -  with the synchronous counter wouldn't the delay exist anyway, just with the input instead?


texts: How to calculate the current / power consumption of instrumentation amp with op amp as an impedance converter at REF input

texts:
I have a measuring bridge and want to connect it to an ADC with an AD8227 instrumentation amplifier (Datasheet). For the reference voltage, I have connected a voltage divider to an LP358 as an impedance converter (Datasheet).
How can I now calculate the current or power consumption of the op amp and instrumentation amplifier?
Below is the schematic of my circuit.

simulate this circuit – Schematic created using CircuitLab
I have found a short calculation for an op amp here, but I don't know if I have to use the output and supply current mentioned in the Datasheet or does it only show the maximum  possible current provided by the op amp? Or does it depend what is connected to the LP358 output, in my case the reference pin of the AD8227? Does the gain resistor of the AD8227 (not in the schematic) have an impact on the current consumption?


texts: Trying to understand range and frequency of an RFID reader

texts:
I am trying to understand how range of communication between RFID reader and tag is related to frequency and power.

So if I increase frequency, the range will be shorter or larger? why? (I need to understand basic mechanism)
I have an RFID reader. This one is having  a range of only 5-10 cm. I want to increase its range to say 1 meter. I understand that if I can increase output power I can transfer energy to larger distance, so I can energize the tag kept at larger distance. So can I increase the range by amplifying the signals and possibly connecting it with a different antenna which can send the signals to a larger distance? If yes how?


texts: I guess the output state of a D-flipflop is unknown upon power up. But what are the chances that it is neither 0 nor 1 but an intermediate state such as VDD/2? The D-flipflop in this question has an output driver inverter.


texts: Is capacitor voltage coefficient a function of frequency?

texts:
I have learned that the value of capacitance in a capacitor can vary slightly compared to nominal based on the voltage across it. This is called voltage coefficient of capacitance (VCC) It is actually a polynomial with first and second order terms. The sources I've found online indicate it is mostly due to the characteristic of the capacitor dielectric.
My question is this: Is VCC a function of frequency? If you have a capacitor with an AC voltage (on top of a given DC voltage) at say 100 kHz, would the measured VCC be different compared to 1 kHz, or 1 MHz?


texts:
I have a PCB mount Right-angle DC Barrel Plug with three connections and am wondering if it is a switched jack as described in the thread What to do with third contact in DC barrel plug with only two input contacts and if so how to tell (like this question How do I tell sleeve from sleeve shunt on this connector?) (apart from the inside connection) which one is the sleeve and sleeve shunt or if one is just for mechanical support.

I do not yet have the jacks I am going to order them however I am currently making the pcb and wish to send it away before they would arrive otherwise i would simply test with a multimeter.

Mechanical Drawing

Brochure


texts: Purpose of second resistor in zener-based voltage regulator with low-pass filter

texts:
Trying to understand the purpose of the lower resistor R in this example from TAoE

The upper resistor R and the capacitor form a low pass filter, but why the lower resistor R? What would change if it was omitted?

Simulating this in LTSpice with a 7V input with a 10KHz 2V peak-to-peak sinusoidal ripple with R=5K and Rc=100, Rload=1K (emitter to ground), C=1uF and a 4.7V zener doesn't show an obvious difference with the lower resistor removed.

The output ripple without the low pass filter is ~250mV
The output ripple with the 2 R resistors is ~1.25mV
The output ripple with the lower R omitted and R=10K is ~ 2.8mV


texts: Transient voltage protection on an automotive circuit

texts:
I am currently working on a DIY quickshifter. This stops the spark for a very short time when changing up gears so that gears can be changed at full throttle.

I have a working circuit, but it currently has no protection from load dumps or transient voltages.

The quickshifter will be controlled by an Arduino microcontroller. When a gear change is detected the Arduino will stop the coils from sparking for a number of milliseconds.

Here is a basic circuit of how the coils are fired.

The red wire connected to the Pri pin on the ECU supplies a constant 12V to the primary coils. Once a signal is recieved by the relevant PNP transister the 12V feed is stopped momentarily and this causes a spark to fire.

I plan to cut the wire feeding the primary circuit of the coils between A and B and then connect these wires to my Arduino circuit. This circuit will be powered by another wire, labelled C above.

Here is the circuit I want to add to the motorcycle.

I need to add some protection to this circuit to protect the MOSFET and MOSFET driver. The datasheet of the MOSFET driver advises to use a bypass capacitor but doesn't mention the size I would need to use.

Please can someone recommend some improvements to this circuit in order for it to be protected when in use on a motorcycle.

Thanks,
David


texts: Relationship between eigen values and state feedback

texts:
so lets suppose we have a state space model

x[k+1] = Ax[k] + Bu[k]
y[k] = Cx[k] + Bu[k]

and we want to design a state feedback, assuming that the system is controllable.
so now if we assume that our input

u = -kx

assuming k is the state feedback vector

Our function becomes something like

x[k+1] = (A - Bk)x[n]

Now here (A - Bk) is the new A matrix and if we want to find the eigen values of this system because we have full control over k(if we are choosing K through poleplacement) , My question is that even if we have control over eigen values of this new vector how does that help us control the system i.e. to bring our system to our desired state?


texts:
I am designing a PCB model of the ATmega32 using Altium Designer
I have found the word "TYP" in the dimensions of the ATmega32 in the datasheet.
What does this word refer to?


texts: Finding the Resonance Frequency of a Piezo

texts:
Using the circuit outlined in this white paper I have been able to find the anti-resonance of the piezo in question. I am using a Rigol DG1022 to create my signal, a sine wave at 20 V p-p, and a Yokogawa oscilloscope to look at my signal and measure the voltage over the R3 resistor.  However, what I am having difficulty with is finding the resonance frequency. I believe what I need to do is use lower value resistors for R1 and R2 as the change in voltage around the resonance is to small for me to see.

It has been a few years since I have messed with electronics at all so I have a few questions.

1) What is it about the piezo being in a low impedance state that makes it so that the oscilloscope is not measuring the changes in voltage?

2)If I in fact do need lower resistance values for R1 and R2 in order to measure a voltage change at the resonance. How would I go about calculating what those values should be?


texts: Transformer duality model with capacitor

texts: I want to know if it is possible to transfer power through the instruments using capacitors? As you know instruments such as Marx generator actually increase the power but we aim to have sth to work as transformer (equal power transmission)


texts: NPN transistor seams to be "leaking" in simulation. What is wrong with my circuit?

texts:
I am kind of new to electronics, and I am eager to learn how to work with transistors; especially in realizing logic gates with them. I tried to build a very basic circuit with a transistor as my "switch", turning an LED on and off. However, even if I have no Powersource connected to the collector, there is current indicated by the amp-meter and my LED is turned on (please see screenshots below).

My questions are:

1.) How is my circuit wrong? Why is there 1/4th of the current present even though there is no connection from the +6V to my collector?

2.) When it comes down to transistors I often run accross schematics where the NPN's collector and base are connected to individual plus-power-sources (e.g. +6V), while the emitter is connected to ground (with some load in between).
I am wondering how the +x V nodes and the ground are realized in a "real world environment"? Would you use 2 Batteries and connect both -Nodes with ground?

Circuits:

1.) NPN-Setup, no connection to the NPN's collector:

2.) NPN-Setup, NPN's collector powered:


texts: Smartphone camera wired trigger over audio

texts:
I'm trying to build for myself a smartphone camera wired trigger over audio input/output port (a.k.a. 3.5 mm jack used for heaphones/headsets). I'm completely lacking electronic engineering skills (only what learned back in school). So here it goes..

There is such 3.5 mm Headset: Accessory Specification, which I think is the go to for what I'm trying to do..

After trying the headset that I have both Volume - and Volume + perform the same task - take a photo, no matter which button you press. Thus from specification it would be either Function B or Function C - doesn't matter much which.

So the questions that I have are:

Can I safely remove buttons (and resistors associated with them) that I don't need in this case from the schematics safely (in this case Function A and Function D buttons, and optionally one of Function B or Function C), leaving with just one button - either Function B or Function C in the schematics?
Can I safely not include both speakers in the schematics?
Can I safely remove the microphone from the schematics or do I have to replace it with a resistor?


texts:
Situation

I'm looking to add Raspberry Pi 3 near my door and detect when the doorbell is pressed. But I don't want it to change the operation of the chime (if Pi is off/unplugged, the chime should still work). I don't want to put something next to the chime because all of my connections/electronics are near the doorbell button itself.

I saw this question and that diode rectifier looked interesting.

This is the circuit I'm thinking of
I read that the Opto-Isolator wears out 50% in 5 years, so in series it would only be on when pressed, as opposed to reverse logic and using the NC side of the button.

Can I put that rectifier in series with my chime?

R1,R2 are power resistors


texts: Can someone explain how to find the currents in the circuit? I am using mesh-current method but I don't know if I have to use twice \$R_2\$ and \$L_1\$ for each branch or not.


texts: How could I give pad to this antenna section?

texts:
I have a SC20 schematic diagram.
From the diagram, there is an antenna section as shown.
How can I give a pad to this antenna for drawing PCB in EasyEDA?
The schematic provided some information like 1.55MM, but I could not understand.


texts:
I read it somewhere that it should be a current source as grid is low impedance voltage source. ( whatever that means. ) I get the part where voltage is converted from DC to AC via Inverter. But what happen then ?

How grid and inverter phase matches ?
How Power moves from inverter to grid most efficiently ?

Any explanation on how it works or point to a right document helps.

Thanks.


texts: Generate and flash a binary file for STM32

texts:
I created a bootloader image for my STM32 and I stored it in a specific area of the memory. I have a new Keil project which represents the application layer. By default, Keil generates a HEX file. What I want to do is to keep the bootloader image and flash the application layer in another area in the memory. The final FW will verify a GPIO input. If it is in a high level, the bootloader image will be launched and it will upgrade the application layer with a new image, otherwise (The GPIO input is in a low level), The normal mode is activated and the application will run. My question is:

Should I convert the generated Hex file of the application layer to a BIN file in order to flash it to a specific area of the memory?
How Can I specify the start address the application layer and its length ?.
If I use a tool to convert a HEX file to binary, what should I do with the empty address reserved for the bootloader image ?


texts: How to perform transient analysis LC series in Multisim

texts:
I,m trying to perform transient analysis of next circuit:

In t=0 switch is opened. Initial condition Vc=0, IL=4A.

But that doesn't work properly in Multisim (fig. above)

Voltage across Inductor does not match estimated value. Multisim show 120V in t=0, rather than 0V. How to fix it?

Link for Multisim Design (OneDrive): https://1drv.ms/u/s!ArJljGNjPhExtDGjTEqIZTgr4fCf


texts:
I was adding some small components to a Digikey order, just because I couldn't stand to pay the shipping costs for the single item I really needed.  I just received my order to find that the SMD LEDs are moisture sensitive.

I hadn't bothered to think about this issue, mainly because I really wanted SMD LEDs on my board because they look cool.  :)  After googling, I've read that either "most" SMD LEDs are moisture-sensitive, or that all are.  I haven't found any that specifically state that they aren't, and Digikey's search tool doesn't have this as a selectable parameter.

So my questions are:

does any manufacturer make a SMD LED that isn't moisture-sensitive, i.e. does not need to be sealed and / or mounted soon after opening the package, and
are there any other cool looking LED options, besides a T1 through-hole package?  :)


texts: Inductive "kick" and possible dangerous experiment

texts:
So I have this unmarked, unknown transformer (probably from a microwave oven so it is pretty beefy) and I thought that a safe way to determine the primary from the secondary windings would be to put 1 volt of dc connected to one of the windings and interrupt it with a  switch. Then I put my multimeter across the other windings and tapped the switch pretty quickly (say 5 times a second). My thinking was that I would either see an increase or decrease from 1 volt at the meter and know the ratio of turns in the two coils.

Two things seem to be wrong with this idea:

Firstly, the experiment seemed to step-down the voltage regardless of which side of the transformer I connected it to.

Secondly, at the time I didn't know about "snubber networks" so I did not include one. I've just now come to understand a little about "inductive kick" and realize that though it was probably too transient for my meter to register, it is possible I was generating voltages on the secondary upwards to the kilo-volt range and reverse voltages on the primary in the mega-volt range. I say this because I simulated this with Lt-spice and though I know I didn't account for capacitive coupling between windings, core losses, wire resistance, etc. the simulation shows some pretty nasty voltages. I'm sure there must have been some bad arcing going on in the switch which dissipated the bulk of the energy; however, could it have damaged the multimeter, and if I had hooked it to an oscilloscope capable of detecting such a signal, would that have damaged it?

Here is the Spice schematic:

And the output:


texts: Why am I receiving "error 'Serial' was not declared in this scope" when building my Arduino sketch?

texts:
FOllowing on from this question, I'm following the tutorial for programming an ATtiny45 using an arduino.

Using v0021 of the Arduino IDE, with a Duemilanove which i've replaced the 168 chip with a 328, I'm able to upload the ArduinoISP sketch correctly. However, trying to upload the blink sketch to the Attiny results in the following error:

ArduinoISP.cpp: In function 'void setup()':
ArduinoISP.cpp:79: error: 'Serial' was not declared in this scope
ArduinoISP.cpp: In function 'void loop()':
ArduinoISP.cpp:136: error: 'Serial' was not declared in this scope
ArduinoISP.cpp: In function 'uint8_t getch()':
ArduinoISP.cpp:142: error: 'Serial' was not declared in this scope
ArduinoISP.cpp:143: error: 'Serial' was not declared in this scope
ArduinoISP.cpp: In function 'void readbytes(int)':
ArduinoISP.cpp:147: error: 'Serial' was not declared in this scope
ArduinoISP.cpp: In function 'void spi_init()':
ArduinoISP.cpp:164: error: 'SPCR' was not declared in this scope
ArduinoISP.cpp:165: error: 'SPSR' was not declared in this scope
ArduinoISP.cpp:166: error: 'SPDR' was not declared in this scope
ArduinoISP.cpp: In function 'void spi_wait()':
ArduinoISP.cpp:172: error: 'SPSR' was not declared in this scope
ArduinoISP.cpp:172: error: 'SPIF' was not declared in this scope
ArduinoISP.cpp: In function 'uint8_t spi_send(uint8_t)':
ArduinoISP.cpp:177: error: 'SPDR' was not declared in this scope
ArduinoISP.cpp: In function 'void empty_reply()':
ArduinoISP.cpp:194: error: 'Serial' was not declared in this scope
ArduinoISP.cpp:198: error: 'Serial' was not declared in this scope
ArduinoISP.cpp: In function 'void breply(uint8_t)':
ArduinoISP.cpp:204: error: 'Serial' was not declared in this scope
ArduinoISP.cpp:209: error: 'Serial' was not declared in this scope
ArduinoISP.cpp: In function 'void start_pmode()':
ArduinoISP.cpp:263: error: 'SS' was not declared in this scope
ArduinoISP.cpp:265: error: 'SCK' was not declared in this scope
ArduinoISP.cpp:270: error: 'MISO' was not declared in this scope
ArduinoISP.cpp:271: error: 'MOSI' was not declared in this scope
ArduinoISP.cpp: In function 'void end_pmode()':
ArduinoISP.cpp:277: error: 'MISO' was not declared in this scope
ArduinoISP.cpp:278: error: 'MOSI' was not declared in this scope
ArduinoISP.cpp:279: error: 'SCK' was not declared in this scope
ArduinoISP.cpp:280: error: 'SS' was not declared in this scope
ArduinoISP.cpp: In function 'void program_page()':
ArduinoISP.cpp:348: error: 'Serial' was not declared in this scope
ArduinoISP.cpp:356: error: 'Serial' was not declared in this scope
ArduinoISP.cpp:362: error: 'Serial' was not declared in this scope
ArduinoISP.cpp: In function 'char flash_read_page(int)':
ArduinoISP.cpp:375: error: 'Serial' was not declared in this scope
ArduinoISP.cpp: In function 'char eeprom_read_page(int)':
ArduinoISP.cpp:387: error: 'Serial' was not declared in this scope
ArduinoISP.cpp: In function 'void read_page()':
ArduinoISP.cpp:397: error: 'Serial' was not declared in this scope
ArduinoISP.cpp:400: error: 'Serial' was not declared in this scope
ArduinoISP.cpp: In function 'void read_signature()':
ArduinoISP.cpp:409: error: 'Serial' was not declared in this scope
ArduinoISP.cpp:412: error: 'Serial' was not declared in this scope
ArduinoISP.cpp: In function 'int avrisp()':
ArduinoISP.cpp:436: error: 'Serial' was not declared in this scope
ArduinoISP.cpp:497: error: 'Serial' was not declared in this scope

How can I fix this please? Or does anyone know if it works with a previous version of the IDE?


texts: Why does my counter count strange values?

texts:
I was designing a people counter that uses two infrared leds and two phototransistors. The logic was derived using a finite state machine where by I derived a circuit that detects an entrance sequence, then sends a pulse, and one that detects the exit sequence. Both the outputs of these sequence detectors are combined together using an OR gate. the output of the OR gate is connected to the clk pin of the 4510 counter. Meanwhile the output of the entrance sequence detector circuit is connected to the up/pin. I connected LEDs at the output of the counters to display the values in binary. The problem I'm having is that the counting is strange, for instance it will start from zero to 66 to 120... it will continue showing random numbers. When I replace the sensors with toggle switches it works perfectly but when using sensor it counts erroneously. Why is this happening and how can I fix it?

I used j-k flip flops for the sequence detector.
I'm clocking my flipflops with a 555 timer in astable mode having a frequency of 65 kHz.


texts: Selecting a switching transistor for a 5V relay

texts:
I would like to use a STM32F microcontroller with 3.3V digital io pins which can deliver a max of 22mA to switch a transistor to then power a 5V relay which pulls 28mA. I'm not entirely sure what aspects I need to consider when selecting a transistor.

I've actually got 8 relays I wanted to power so I've found an a couple of quad npn transistor ICs which I think should do the job and I'm going to use 2 of them. FFB2222A and MMPQ3904

The collector currents are 500mA and 200mA respectively which should be ample (pun not intended). (These are ratings per transistor in the IC if I'm not mistaken).

What are the other things which need to be taken into account when selecting a transistor? Again if I'm not mistaken the transistor will be in the active region rather than saturated so we need to take in to account hfe, which should be sufficiently high for both. Is there anything else that needs considering?

Two other shorter questions with regard to the design.

1) When choosing a current limited resistor at the base does one assume the drop betweeen the emitter and the base is approximately 0.7? So 3.3-0.7=2.6V so assuming we want roughly 15mA going into the base 2.6V/15mA=173ohms (ish).

2) Also what things do you need to consider when choosing a flyback diode?

simulate this circuit – Schematic created using CircuitLab


texts:
I was looking for a dimmer to control an LED strip with following characteristics:

5 meters long
14,4W (max) per meter, so 72W in total
24V

I found a dimmer on ebay that says it can handle 144W, which looks like this:

I'm having a hard time believing something so small can handle that much power.
My question is: can it?
Follow-up: if so, how? Is this a custom chip? I've also read something about those things using Silicon-Controlled-Switches or Silicon-Controller-Rectifiers, something I know very little about, obviously.


texts:
Find v and i in the circuit of Fig.3.11

I modified the circuit like:

and renamed the nodal voltages:

Now applying KCL at the supernode,
$$i_1+i_2=3.5....(i)$$
We know, $$i_1=\frac{v_1}{\frac{12}{7}}, i_2=\frac{v_2}{\frac32} (\text{Note that }\frac{12}{7}=1.714)$$
From equation(i) we get
$$\begin{align}\\
\frac{7v_1}{12}+\frac{2v_2}{3} &=3.5\\
\implies 7v_1+8v_2 &=42.......(ii)\\
\end{align}\\
$$
To get the relationship between \$v_1\$ and \$v_2\$ we apply KVL to the following circuit

$$-v_2+v_1+6=0\\
\implies v_2=v_1+6.....(iii)$$
Now, from equation (ii),
$$7v_1+8(v_1+6)=42\\
\implies 15v_1=-6\\
\implies v_1=-0.4V$$
From equation (iii),
$$v_2= -0.4+6=5.6V$$
So, \$i_1=-\frac{7*0.4}{12}=-0.233A\$.
Hence, from the main figure \$v=-0.233*3=-0.699V\$.
But, in my book the answer is \$v=-400mV\$. Please tell where is my mistake.


texts: Switching power supply 12V/3.3V for battery powered application with SLEEP mode

texts:
I'm designing a 3V3 PSU for 12/6V (lead) battery powered (outdoor) application. Supposed load is 70mA but I plan sleep mode (50uA) with periodic wake-up (ATMega1284P with 32kHz (RTC) crystal). It means I need high efficiency under very light load. Hence I believe I need switching PSU IC designed for such scenario (TI calls it light-load support), mainly very low quiescent current (<30uA or so).

As Xbee module is to be powered from PSU there is Digi recommendation "*If you are using a switching regulator for your power supply, switching frequencies above 500 kHz are preferred. Power supply ripple should be limited to a maximum 250 mV peak to peak.*".

I found Texas Instruments TPS62120 and TPS62125 ICs. The former supports only max.75mA , the latter supports 300mA which seems perfect. Both chips offer efficiency 80-90% @ 70mA, 44% @ 50uA. But the TPS62125 is available on miniature WSON socket which not too nice for hand hot air soldering. Even TPS62120 is only 75mA it has more user friendly SOT package but output current is too near to required current. There are other TPS62xxx ICs (160, 177, ...) but they are not so good at light loads.

Can anybody confirm the idea is correct or is another recommended way how to achieve good result (e.g. using big/supercapacitor and forcing PSU power down when MCU is sleeping, low/high temperature issue?, maybe less efficient because of cap self discharging?).

Optionally if somebody has another suitable chip please provide reference.


texts: Realizing 2 Resistors are in series in an RC circuit

texts:
I understand that when the switch is open, the capacitor acts like an open circuit & therefore the current in the capacitor branch would be equal to 0. When I solved the circuit using nodal analysis, I realized that the 2k ohm and the 4k ohm are in series.

How would I look at the circuit and automatically realize they're in series?
Because realizing they're in series would result in a much easier answer using KVL.
5(-10) + Vc - 4(6/6) = 0


texts: I am wiring an "on-off-on" style toggle switch from the AC mains to turn a power supply on and off. I don't need the second "accessory" line from the switch, should I just leave the third pole floating or tie it to the "off" pole? Thanks for any help


texts: How does a common emitter amplifier work (intuitively)

texts:
I know there are lots of videos, documents on the internet and I can say that I've already looked most of them. However, I cannot get the insight of the working principle, amplification operation of these amplifiers. I know basics of transistors and their characteristics. However I am stuck with amplifying action.

I guess someone may come up with a nice and neat explatory answer.

Thanks in advance.


texts: Proteus - measure current through power rail

texts:
I am trying to measure the current drawn by my entire circuit (which contains a few ICs and a microcontroller). Some of these components such as the microcontroller are connected using 'Hidden Pins' to power rails VCC and GND. How do i connect an ammeter in series with this to measure the current drawn by the MCU ? or is there a way i can measure the total current drawn by my circuit ?

Edit:

The solution provided in Connecting Switches to Hidden Supply Pins in Proteus ISIS does not solve the user's problem due to the following reason.
This is how we want the circuit to be.

Creating a schematic like this in Proteus will throw an error saying No power supply specified for net SRC1 in Power Rail Configuration

If you try to fix this by following the answer in the link above and goto Design->Configure Power Rails and add netlist SRC1 (our custom netlist) to VCC power rail, then we are essentially just creating a link from SRC1 to VCC. This essentially bypasses the switch and just connects the hidden pin VDD directly to VCC hence doesn't provide the intended result.


texts: How exactly does AM/FM carry both pitch and loudness of voice?

texts:
Almost every tutorial on AM/FM modulation shows the modulating signal as something like a simple tone or continuous sine wave. Now that's easy, and for AM you just superimpose the modulating signal over the carrier wave as an envelope, and voila, and for FM you continuously and consistently vary the frequency.  but no one seems to point out the obvious problem... Voice has both pitch, i.e. frequency, and loudness, which are two separate analog data streams.  No tutorial nor explanation I have seen then takes the next, glaringly necessary step, to explain how both aspects are transmitted over radio schemes that apparently can only take one degree of variation, i.e.
 amplitude for AM or frequency for FM.

TL;DR:

How does AM or FM modulation, each of which only have one modulatable variable, carry both the pitch and loudness of voice, which are at least two distinct analog streams of data?
Why does absolutely nobody seems to address this glaring question in any tutorials/video/write-up on radio modulation?


texts:
In an ideal world, if the transmitter is outputting 30dBm to an antenna with 100% efficiency with 10dBi of gain.  The receiver has an antenna with 0dBi of gain (100% efficiency as well) and is sitting right next to the transmitting antenna.  Based upon the link budget analysis, the receiver is getting 40dBm of power.
Since the antenna is a passive device, how can this be true?


texts: Unique IDs for physical modules added to a circuit

texts:
We have different battery packs that can plugged into our circuit, we're wanting to identify exactly which battery pack has been plugged in, but, as ever, in a very low-cost way.

I'm thinking RFID tags, but using a wired connection instead of RF... I've found unique id chips from Maxim (http://www.digikey.com.au/product-detail/en/maxim-integrated/DS2411R-T-R/DS2411R-CT-ND/2045729) but the cost is 10's of cent, and I'm looking for a solution for that's <10cents. (I'm guessing this price difference between RFID and unique ID chips is partly to do with die size)

There's a micro that's monitoring the cell, which would be doing the comms with whatever is on the battery. We're looking for a solution that effectively (24bit+ 1,000,000+unique ids)

Ideas: Passives? Crystal? Read RFID tag directly without RF? Lower cost unique ID chip?

Has anyone looked at this before?

Many thanks!


texts: How to Generate a square, sine, and triangle wave with DC input

texts:
I want to make a simple synthesizer as a start to audio electronics. I want to start with a simple square, triangle, and sine, which the user can vary the pitch.

Is there a simple circuit to do these? I know a square can be achieved with a 555 timer, but I don't know where to start on sine and triangle.


texts: How does stretch processing work for SFCW?

texts:
I've been reading about FMCW radar, and I understand that a chirped signal can be de-chirped by mixing it with a copy of itself, which yields a beat frequency which is much easier to process and is proportional to the time delay between the transmitted and received signals. However, a lot of the implementations that I've seen have used a frequency ramp with discrete frequency steps, presumably because it is much easier to implement.
Initially I assumed that stretch processing would not work with a SFCW radar, since the discrete frequency steps would create two beat frequencies instead of one when the frequency steps didn't line up (I made this model for myself). But after doing more research on how one would actually create a continuous, wideband chirp, I could only find the VCO based solution in the MIT coffee can radar (which is only as linear as the VCO) and this implementation, which uses a DDS IC with discrete frequency steps as a reference. I'm certain that I must be missing something.
Is stretch processing possible with SFCW chirps? If so, does it come at a cost of decreased range resolution? Why or why not? If it isn't possible, how are wideband continuous chirps actually generated?


texts:
I am building a new controller for an existing robot.  I need to know the voltage to send the motors.  I don't want to remove the motors from the robot, but am able to take measurements while it operates using the old controller.

The power supply feeding the robot is 24 volts, so I assumed that I should send the robot 24 volts.  I measured the current consumed by the motors at various speeds, and then used my controller to send PWM frequencies until the current consumed matched that of the original controller.  What I saw was that the motors seemed to spin faster.

Does this make sense?  Would the same current cause the motors to spin at different speeds, if the voltage was different?  If so, how do I figure out what voltage to use?

Or could it be that I'm sending the same voltage, but the difference in PWM frequency from my controller and the existing controller is the problem?

Thanks!


texts: Controlled Impedance Microstrip Frequency

texts:
Are you supposed to calculate the characteristic impedance for the frequency you are using or at 1GHz? I see pretty much everything calculated at 1GHz in all examples and papers.

For example - for GPS - you're supposed to have a 50 ohm characteristic impedance... is that 50 ohms at 1575 MHz (GPS freq) or at 1 GHz? The same goes for GSM - which can be at either 850, 900, 1800, or 1900 MHz - it always requires a 50 ohm characteristic impedance for the microstrip trace from the transceiver pad to the antenna connector.

Thoughts?


texts: Is there any junction, or branch element for jumper cables?

texts:
I would like to create circuits using jumper cables. I have male-female, male-male, and female-female jumper cables too. But I cant find any branching cable on ebay.

What should I use, to create branches without breadboard?


texts: A circuit that can clip a high voltage/ low current signal input to an Esp32?

texts:
I have a program for an Esp32 development board which detects the ignition spark from an engine and converts the frequency of the ignition to an engine RPM reading. The high voltage input peaks at about 75V but is less than about 20mA. It is an inducted current pulse from a coil of insulated wire wrapped 3 times around the spark plug lead (non-insulated) and connected to the following circuit (ignore the Arduino, its an Esp32 which accepts a signal with a maximum of 3.3V as an input):

It is a 1N4728 (3.3V) zener diode. This circuit reduces the voltage to the correct level, except for negative voltage spikes from the input signal, which shut down the Esp32 board until it is reset (see second photo). How can I improve this circuit to remove all the negative voltage spikes and keep the input in the safe 0-3.3V range?


texts: How to read datasheets effectively to connect components safely?

texts:
I understand that many questions have been posted regarding datasheets, but I hope that you can help me with my question as well. If I want to know how many infrared LEDs (SFH 4780S) can be driven at the same time by a single AFE4403 (analog front-end), then how will I go about answering this question systematically? Also, what would be the best configuration at which these LEDs can be connected to the AFE4403 (in parallel?)?
Thank you in advance


texts: Questions about stability circle and impedance matching

texts:
I'm a RF circuit beginner and got stuck in stability related issues.

According to Pozar's textbook, output stability circle is a contour in the "gamma_L" plane and its arc represents the "gamma_L" point that makes |gamma_IN|=1

so, from the above statement, amplifier is stable when "gamma_L" is sitting outside of the output stability circle while the output stability circle DOES NOT encircle the origin of the Smith chart.

But, one of my friends (who is currently studying towards phd in RF circuit area) told me that I need to ensure that S11 is sitting outside of load stability circle for output stability.

I raised following questions but I couldn't really understand his logic when he answered my question. so I was wondering if anyone in this forum can help me to understand this topic better.

Questions were:

1) Is "load stability circle" equivalent to "output stability circle"? According to Keysight manual, it is equivalent but some papers
https://www.mwrf.com/components/ensure-stability-amplifier-designs
is saying completely opposite. this part is very confusing to me.

2) Why do we need to look at S11 instead of Gamma_L?
technically output stability circle is drawn on "Gamma_L" plane (Pozar Textbook). Looking at S11 for output stability circle does not make any sense to me since S11 is sitting its own plane and not related to Gamma_L. Even if they are related, its very hard to visualize on Smith chart how they are interacting when it comes to stability issue. Plus, output stability circle is already representing the gamma_L point corresponding to "|Gamma_IN|=1". What does S11 do with this?

please correct me if I am understanding something wrong.


texts:
I'm working on a SIM Card Emulator. For this purpose I use GSM Module Huawei EM770W that is connected to USB adapter. I soldered wires from SIM card holder to MCU (TM4C123XL) and from MCU to SIM Card appropriately (MCU acts like a buffer between modem and SIM Card) and am quite sure that hardware probably is okay. I succesfully get Answer To Reset from SIM Card, GSM module sends back PPS bytes, I even get several instructions, however, after getting response to GET RESPONSE instruction (00 C0 00 00 26), SIM Card is reset by modem.

I've already tried listening to successful transmission when card is inserted straight into USB adapter, compared with bytes in my case and they are the same but modem resets SIM in my case while communication without using MCU as a buffer is succesful and I can interface it with AT commands.

What might be my mistake made?

To give more information, I'm adding chars after ATR:

GSM module sends FF 10 96 79
Card send back FF 10 11 FE (meaning 9600 Baud rate)
GSM module sends 00 A4 00 04 02 (selecting file)
Card send back A4 (ACK byte)
GSM module: 3F 00 (data from Select File command)
CARD: 61 26 (number of bytes still available)
GSM MODULE: 00 C0 00 00 26 (GET RESPONSE command)
Card: C0 62 24 82 02 78 21 83 02 3F 00 A5 07 80 01 79 (ACK and 14 data bytes)

After last instruction GSM resets card.


texts: How is fully charging a Li-Ion battery in 35 minutes possible?

texts:
I happen to own a power drill/driver that runs on a Li-Ion battery and ships with a charger that charges it fully in 35 minutes and claims to charge it to 70% in 15 minutes.

According to answers to this question the highest charging current for Li-Ion batteries is about 1C which with losses taken into account means that charging time should be at least more that one hour. This is consistent with my experience of using other devices like cell phones - they take about 1.5 hour to fully charge.

How is charging a Li-Ion battery in about 35 minutes possible then?


texts:
Well, you can say that the title is a little bit misunderstanding. I do not want to compare these architectures, it's worthless.

I am trying to understand why an engineer could ever pick for his LoRaWAN node an ARM MCU. In my opinion, if someone trying to design a LoRaWAN gateway then an ARM MCU is a good/safe option. But if you want to design an ultrasonic sensor, an air quality sensor or a magnetic sensor, i can not find any benefits on using ARM MCU.

In my designs, i have done tests using 8-bit PIC (pic18lf46k22) and AVR (atmega328p) and i can say that on the above applications these MCUs are overspec!

So, the only thing left was the cost of the MCUs for making the "right" choice.
Let's say at 100 pieces you can get an atmega328p at $0.98 per piece and for STM32F411RCT6 you need about $3.98.

My company is buying competitors products so we can check what they are using etc.

I have NEVER seen any other MCU architecture than ARM.

So this is really bad for me because i am thinking that i am missing something.

I really need advices/opinions from more experienced engineers than me.

*Reminder: * I consider as simple applications for me is to get data for one or two sensors and send them to the gateway.

P.S. We have a waste management project (40 sensors) running for 7 months and nothing "weird" happened. We are using atmega328p.


texts: High voltage power supply polarity for X-ray tube application

texts: High voltage power supplies (HVPS) in the range 100 to 200 kV are used for working with X-ray tube. Some HVPS produce negative output voltage or even bipolar output including negative and positive voltage. I want to know which type of HVPS is proper for X-ray tube; negative voltage, positive voltage or the bipolar one?


texts: Confusion with output impedance using h parameters

texts:
Regarding the below liner circuit model, as far as I understand to find the output impedance the input current Ib is set to zero and the output resistance is calculated as  Vc/Ic. I think this way of modeling and calculating the output resistance comes from the Thevenin model. So the definition output impedance will be Vc/Ic when input port is open circuit (?).

So if I set Ib to zero, hfr * Ib becomes zero and the only thing left is hoe where Ic = Vc * hoe so can we say that the output impedance is 1/hoe ?

I'm not sure above is correct but in some texts they say the output impedance is infinity theoretically? How can that be estimated? If wrong how is the output impedance is derived following the circuit above?

What is meant by the following? I had to take photo to add the original text:


texts:
Originally I wanted to drive 4 micro stepper motors (2 in series) from two ATtiny84 chips directly. I have learned that this is not a viable option and now I have a revised plan.

I have some A4988 drivers. I'm pressed for space and would like to only use one driver if possible.

The originally plan was to run the steppers on 5 volts. Now I'd like to run all 4 steppers in series to be driven by one Pololu A4988 from 9 V.

Can someone please help check my math? I don't thing I have strong grasp on it.

The NMB steppers have no data sheet. But do have a resistance of 10 Ohm across the coil.

The original math at 5 volts suggested that each motor would require 500 mA to run. That totals 2 A for 4 of them. The A4988 is rated for 2 A max.

Since the A4988 would require more voltage I decided to use 9 V. At 9 volts am I correct in calculating that this increases the amperage required thus overloading the A4988? My math comes out to 3.6 A in that scenario.

Would I then need to run two A4988 drives to divide the work instead?

The plan now is to use a 9 V source and use a voltage divider with to power the ATtiny to provide the instruction to the A4988.


texts: Altium Multi Channel Design with Bus / nested bus

texts:
Background

I am currently working on a design that is able to hold multiple compute modules of the same type. These modules shall then be tested automatically with help of some FPGAs.

To only create one schematic and only route the whole thing once I have created a multichannel design for the module connector and the surrounding circuitry. This works pretty well.

Problem

The modules have 33 GPIOs that need to be tested.
I could, in theory, create 33 IO Ports on the module schematic and then use the repeat statement on the top sheet on all 33 of those. Afterwards, i could split them into the signals for each module (33x4 = many) and connect all signals of module 1 to FPGA 1 ... module n to FPGA n. But that means id have to place around 33x4x2 net labels and no one will ever be able to look at the schamtic and sleep peacefully later that night.

Solution - possible?

It would be nice to put the 33 IO signals into a bus. Then use the repeat statement on the bus. This way, I could have 4 buses on my topsheet that i connect to the different FPGAs. Very clean and readable. But I dont think it is possible to nest busses.


texts:
So I am using an Arduino Uno in my project to communicate (SPI slave) with a very tiny pedometer chip. The chip pins want max 20mA at 1.8V however Arduino outputs 5V (or some pins 3.3V) at max 50mA. So I was thinking of using a buffer amp followed by a voltage regulator (or maybe just a Zener diode) however I find it hard to pick an exact component. I would also like to power the rails for the Opamp from Arduino 5V and I could not figure what exactly to use. Preferably I would like the chips with multiple opamps inside as I will need to talk to a lot of data pins.

Excuse my lack of knowledge, I am a mechanical engineer and I am too embarrassed to keep asking my supervisor about these things!


texts: Setting up pre-made MPLAB project with include errors

texts:
I am attempting to get an open-source potentiostat board up and running but an having issues when it comes to compiling the project. The firmware MPLAB project was provided, but it is not recognized by the program when you go to open it. The paper itself provides little in terms of setting up the code, and mostly just says the "makefile allows easy compliation because it automatically provides the compiler with the necessary flags and include paths." I am not sure how to get the files set up though and there are lot of issues with the includes and such. A hex file is provided but I would like to set up the project with the source code.
Making a new project for the PIC16F1459 device and then replacing the Makefile and copying the file structure and files from the firmware.X does not work. My closest success seems to be adding all the files to a clean project built into the root of the Project.X directory (without the provided Makefile) and then making sure the include statements in all the files are using quotes and not <>. However, now there are a lot of errors in the files regarding #error, asm, and similar statements. Can anybody comment on how the makefile is used, how to maybe even make this project build correctly, anything regarding this topic? I've been scratching my head for a couple days now trying to get this together. Thanks.
Website Link
Project file archive


texts: DAC settling time and output signal bandwidth

texts: Voltage output DACs are usually specified by a settling time. If a DAC converter has a settling time of T, can it be used to faithfully reproduce a signal which has been sampled at a frequency of 1/T? Or does this frequency has to be lower since there may be substantial ringing in the output signal if one changes the signal before the output has fully settled?


texts: Headphone jack connection: is this setup safe?

texts: Is this setup safe for the equipment? And am I going to be able to hear both of the sources?


texts:
I have been studying transistors and decided to try my knowledge in my lab to find out that nothing works as I thought it would..

I had a small lamp 12V and a handful of 2N3904 transistors, along with a 12V DC power supply.

Attached to the base of the transistor was a pin from my Raspberry Pi, along with a 150 ohm resistor to provide ~20 mA of current. The rest of the transistor was wired as the picture.

However, as soon as I plugged in the power supply, the lamp lit! Even though no current was passing through the base. I tried flipping the transistor around, to see what would happen, as as expected the lamp wouldn't light.

I switched out the lamp with a small solenoid (SparkFun ROB-11015), but now nothing happened while toggling the GPIO pin. I switched out the transistor thinking I fried it, but still nothing... am I missing something?

From what I understand, as long as there is enough current running through the base to saturate the transistor, it should allow current to pass from the power supply to the load. When the transistor is not saturated, the circuit is open.

As an aside, from multimeter readings the GPIO pin is a steady 3.3V and the solenoid draws ~500 mA initially and stabilizes at ~140 mA when wired directly to the power supply.


texts: PID controller for a very wide temperature range (∆T=190°C)

texts:
I'm designing temperature control system based on Peltier elements. And it's needed to work on a very wide temperature range - from below zero to more than 100°C. So there is two work modes - cooling and heating. I've implemented a PID controller, made different gains for two modes. And I can adjust them to go to a specific temperature (e.g. 100° or -5°) from room temperature (25°). But when I want to go e.g. from -5° to 60° it may go into oscillations or conversely grow very slowly. Should I break my large range in smaller subranges? Or maybe different gains depending on difference between current and target temperature (∆T)?
Also, I thought to implement auto tune algorithm, but I didn't found anything for the Arduino?


texts: How can I measure moisture on a conductive flat surface as an analog/digital value?

texts:
So as the title states, the question is:

Is there a way to measure moisture on a electrically conductive flat surface?

Optionally, it would be great if I could have an indication of the amount of moisture on the surface, preferably as an analog value, so I can read it via an Arduino (when I say how much, I do not need it in like mililiters, just a higher or lower value representing moisture).

Just to give some context:
I am working on a project to cool down a laser module using Peltier elements (TEC), and I want to know when moisture starts to form around the laser diode as a preventive safety feature, because water is not good for lasers diodes :) I am aware that I could just monitor the dew point, still, I am interested if this is even possible or not.

Thank you.


texts:
I'm trying to build a 5V 8A buck converter and I chose the XL4016E1 IC for this operation (datasheet). There it says I need a 47uH 12A coil. Unfortunately i couldn't find a coild with such a high current rating.

So my question is, is it possible to for example place 3 4A coils in series/ parallel, without losing the 47uH inductance.

Second, what does the 105 value near the C2 and C1 mean?


texts: How to adapt a 100 mA DC ammeter to measure up to 5A?

texts:
I have a DAS(Data acquisition system) that can measure DC (up to 30V) and I want to know what is the power a device is consuming, the current measurement available for that DAS is in the range (1-100mA).

What can I do to adapt the meter so that I can measure bigger currents (up to 5A) but that has a fair amount of precision and can be calculated linearly?


texts:
I want to control the following laser module from an arduino digital output:

Specification V2 – Aug 2010
Wavelength : 650nm +/-5nm
Output Power : 4-5mW
Operating Voltage: V2 = 3.0-4.0V
Operating Current:    15-20mA
Operating Temperature: 10 – 40°C

What's the best approach - I've looked at diodes for voltage drops, resistors and regulators but I really don't know which to use.  The variability of the voltage and current in the specs is rather confusing.

TIA


texts: Connectors and receptacles for easily plugging and unplugging cables

texts:
What are good solutions for pluggable, "free-hanging" cable connections?

As simple as this question might sound, I am currently struggling in finding components that allow me to easily connect and disconnect a set of cables. This is my scenario:

I have three devices using the Modbus/RTU protocol over RS-485 three-wire cables.
I have to connect and disconnect these cables from time to time: For instance:

I have devices A, B, and C.
A and B can be connected together, and A and C can be connected together.
From time to time, I have to unplug A and B and connect together A and C.

Therefore I am looking for a cable connection that allows for the following:

Initial assembly of the cable's connector/receptacle should be easy and reversible: No fancy crimping tools, no soldering. Just screwing the cable to the plug. Or a spring-cage connection.
Connector and receptacle shall protect against polarity mismatches (i.e., there is only one way of plugging connector and receptacle together).
Plugging and unplugging the cables shall be easy.

By now, I have spent half a day of finding viable solutions. The only solution I have found so far is a combination of MSTB 2,5/ 4-ST-5,08 and IC 2,5/ 4-ST-5,08.

How do you connect cables together?


texts: Why a lower voltage is better for modern fast CPU and other similar chips?

texts: I started to use computers in the 1980's. As far as I remember 8bit CPUs of those times like Z80 were often powered by 5 V and used the same voltage for I/O signals. Later CPUs run at higher speeds and started to consume more power. I would expect that to deliver more power to a chip we must use either higher voltage or higher current. And since high currents normally need thick cables I would expect that CPUs would go for higher voltages to keep currents low. But the opposite is true. For example a standard Intel Pentium 4 or Core 2 Quad CPUs I use at home have 95 W TDP which means that they consume more than 100 W at power spikes. Since they run on a very low voltage around 1 V, they actually need to deliver the power using approximately 100 A. So here comes my question: Why is this preffered, why is it efficient?


texts:
I am routing a PCB with an Ethernet connection and I am having a bit of trouble deciding on how best to route the TX and RX differential pairs. I have done the impedance calculations to figure out the track geometry needed for 100 ohm differential impedance and confirmed it with the board house. However, I have a bit of a length mismatch between the TX+/TX- and RX+/RX- pairs (about 5mm). Hence, I am employing the "squiggly line technique" to minimize the length mismatch of the traces in a pair.

My question is whether there is a rule of thumb or a precise calculation to figure out the squiggly line geometry? To illustrate what I mean, have a look at the attachment - I have routed one pair with "loose" squiggles (labelled 1. in the image) and another pair with "tight" squiggles (labelled 2, in the image). Which one is better and does it matter at all? My concern with the "tight squiggles" is degrading signal quality due to reflections as the squiggles are close to 90 degree angles which most app notes strongly advise against. The "loose squiggles" on the other hand take up more space and hence am I degrading my differential impedance?

Thanks and happy holidays!
-Igor


texts:
I need a transformer to get 18VAC ~ 30-40W for a power supply. Living in Europe, I am looking around for a 220V - 18V transformer. As far as I understand transformers, I should also be able to use tranformer specified for 110V - 9V. Are there any technical reasons that should not work or I should not do that?

(I know varranties will be voided, but I do not care about that) (And yes, I have been building a few mains powered things before, so I know how to handle that safely)


texts: Sinking charge from LED before taking measurement

texts:
I'm currently using an STM32 for anode sensing of a LED as shown in the following schematic:

simulate this circuit – Schematic created using CircuitLab
The LED is both used for emitting and for measuring light. When emitting light both MOSFETs are switched on and when sensing light they are switched off and the voltage at the LED's gate is measured using an analog input. In anode sensing this voltage is proportional to the received light. The emit-sense-cycle should be performed several hundred times per second.
The issue that I'm facing is the capacitance of the LED. As soon as both MOSFETs are turned off the anode is floating free. As such the voltage at the anode drops immediately to the diode's forward voltage, but then the LED's internal capacitance discharges slowly over several milliseconds, severely hampering my ADC measurements and preventing any faster cycles.
The issue could be solved by sinking the charge at the anode to ground before taking the measurement, though. The question is what's the best way to achieve this ? I could reconfigure the GPIO pin from analog in to digital and sink the charge using a LOW signal, but is there a more elegant way to do this, i.e. by activating some pull-down resistor at the analog in on-the-fly ?


texts:
Hi I am trying to relate Vx to Vf and Vf to Vin. However, R3 does not take any place in the equations. This question is so simple, yet I am very confused with it and stuck and spending last 2 hours getting through this. Can you help me what is going on? I am trying to forget everything I have ever learned. Center tapped resistors got me confused a lot.
Voltage divider equation at Vx and node equation at Vin.


texts:
The Nike+iPod Sports Kit is a device which measures and records the distance and pace of a walk or run. The Nike+iPod consists of a small accelerometer1 attached to or embedded in a shoe, which communicates with either the Nike+ Sportband, a receiver plugged into an iPod Nano, or directly with a 2nd, 3rd, or 4th Generation iPod Touch, iPhone 3GS or iPhone 4. If using the iPod or the iPhone 3GS, iTunes software can be used to view the walk or run history. Source

What type of RF communication is used between the device embedded in the shoe and the iPod? Could I create my own receiver and log data without an iPod?


texts: I would like to display the big and little dippers on the outside back wall of my house using mini light bulbs of appropriate  intensities.  I converted  those 14 star magnitudes to lumins.  Unitizing there luminosity gives a range of 1 for the dimmest star to 32 for the brightest.  Finding 120v bulbs in the 14 different wattages needed is not possible.  Is it possible to use individual resisters on each bulb to get the effect desired?  I also am considering using fiber optics with a single light source to provide the desired effect.


texts: Multiply clock frequency by three or more times?

texts:
Frequency of a digital clock signal can be doubled by using an EXOR gate (clock at one input pin and delayed clock at another).

Can we use any similar circuit which can multiply frequency by three times ?


texts:
I have an STM32F4discovery and using a pin as SPI CLK. But I also want to be able to control the pin as GPIO to generate ANY frequency I want (STM32 only lets you prescale APB clock).

How can I simply use GPIO_Toggle() on that alternate pin?


texts: Why do all transistor latch circuits (that ive seen) use two transistors?

texts:
I am looking at building a transistor latch to control a relay. I don't like soldering, so a few components as possible, especially those pesky transistors.

I am looking around at various transistor latches online, and seeing things very similar to this:

http://homemadecircuitsandschematics.blogspot.com.au/2011/12/simple-and-useful-transistor-latch.html

I am having difficulty understanding the design.

Why not just just have a single transistor, and feedback part of the output of the transistor back into it's base?

EG:
Please ignore the values, they are defaults.

To be specific, I would like to use a BC547/8, and I am ommiting a lot of the components of this diagram.

Why wont this work? Is there an elegant solution that only uses one transistor and passives?

Thanks,
Tom


texts:
I wonder if someone could help me with some general suggestions on a frequency counter project.

I'm trying to modify a 6 digit LED frequency counter that uses an integral PIC16F648A, a 13 Mhz oscillator and an I2C coupled digital display.  This hardwired design uses TMR0.  I've been able to get it reprogrammed by using modified software that was written for 6 discrete LED's running at either 4 or 20 Mhz.  I've tweaked the code here and there but I can't get the kind of consistency I need - 100 hz, or less.  The apparent problem is the 13 MHz oscillator.

I've googled the web and found that 13 Mhz is a very odd crystal frequency for a counter.  Any thoughts as to how it may have been used in this design??

I'd like it to work up to 60 Mhz as this is the upper limit of the unit when it was equipped with its original code (don't have a copy).  Auto ranging is not required.

Any and all suggestions would be most appreciated.


texts: Can I use multiple 18650 batteries in parallel with a standard MicroUSB 3.7V charger board?

texts:
There is this Bluetooth Audio Reciever/Amplifier board that I'm looking to get from ebay, and according to the diagram, there's a MicroUSB 3.7V lithium battery charger component in it.

With my understanding that wiring multiple batteries don't increase voltge but rather current/capacity, will I be able to wire in multiple 3.7V 18650 batteries in parallel (maybe 4) in order to increase my runtime, at the cost of having longer charging times?

Is this a universal case or a chip specific situation?  I've asked all of the sellers who sell that product, and none of them knows the answer.

Link to eBay item: http://www.ebay.ca/itm/181744265268


texts:
Here is the schematic:

I know that this circuit's purpose is to add distortion to a an electric guitar signal.The main components that add distortion(as far as a I believe) are the transistor(a lot,because of the 470K resistor)an the diodes.They must be clipping the top positive end of the sine wave of the signal.However,I would like to know in detail how the entire setup works,why use those resitors in those places,the role of the capacitors,etc. and if what I said is correct.
How does this circuit work?


texts: I have read this before asking this question. I understand somewhat, but I couldn't get clarity. Can someone help me understand the difference between common mode noise and differential mode noise with some pictures and circuits, please.


texts: How can I make a 4x4 switch out of 2x2 switches?

texts:
I want to design a 4x4 switch with 2x2 switches.

The 2x2 Switch

The 2x2 switches have a one-to-one relationship between inputs and outputs. As such, the select signal for the 2x2 switch is only a single bit because there are only two options: (1) The 2x2 switch is in "bar" broadcast. The inputs go horizontally to the outputs (In0 -> Out0 and In1-> Out1). (2) The 2x2 switch is in "cross" broadcast mode. The inputs cross each other as they go to the outputs (In0 -> Out1 and In1 -> Out0).

The switch is unicast. No input can drive more than one output. Also, no output can be driven by more than one input.

The 4x4 Switch

I hope my reasoning is right. I think the 4x4 switch would have 4!=24 combinations given the unicast limitations. That is, if In0 can go to any 4 outputs, then In1 has three choices left. In1 can go to any 3 leaving 2 choices for In2 and then leaving 1 choice for In3.
So: 4*3*2*1 = 24 combinations.

Since my select signals are bits I would need 5 of them to cover all the combinations. 2^5 is 32 which is enough to cover 24 combinations.

This leads me to believe that there should be 5 2x2 switches inside the 4x4 switch, but I can't see a way to design it without running into a conflict between inputs going to outputs. Any help please?

Here is the VHDL for the 2x2 switch if it helps:

library IEEE;
use IEEE.STD_LOGIC_1164.ALL;

entity SW2x2 is
port (
    In0: in std_logic_vector(3 downto 0);
    In1: in std_logic_vector(3 downto 0);
    Out0: out std_logic_vector(3 downto 0);
    Out1: out std_logic_vector(3 downto 0);
    Sel: in std_logic);
end SW2x2;

architecture Behavioral of SW2x2 is

begin
    Out0 <= In0 when Sel='0' else
            In1 when Sel='1' else
            "0000";
    Out1 <= In1 when Sel='0' else
            In0 when Sel='1' else
            "0000";

end Behavioral;

FYI: The question is related to the design, not the VHDL code. VHDL is just given as reference.


texts: Circuit to control a impulse solenoid valve from a movement detector

texts:
I have a movement detector sensor that generate a pulse (3.3V TTL) for 60 seconds when something moves in front of it. On the other hand, I have a impulse solenoid valve that close on a negative voltage (-3.6V) and open on a positive voltage (+3.6V).

What would be the simplest and cheapest way to drive the solenoid from the movement detector?

The circuit or chip should produce +3.6V output for at least 30ms when the input signal goes to 3.3V and then produce -3.6V for at least 30ms when the input signal goes low (0V).

(I also have available a solenoid that work on 4.5V rather than 3.6V if this can help)

Links:

Valve

Movement detector

24/08/2013 Update

Inspired by the answer of Jim, will a circuit like this one work?


texts: Systems Engineering Solar Energy Diagrams

texts:
I'm currently taking a grad course in Systems Engineering. I'm dreading it a bit as I've taken grad math for the past 3 years and this is my first writing course in a while. We're covering context diagrams (black box view) and functional block diagrams (white box view). Examples for the two are given below:

For an ongoing project, we're tasked to create these diagrams for a system we've conceived. In my case, I'm studying how solar energy can be more economical. However, I'm struggling to adapt this system to the diagrams. My system is not a traditional, physical product that has a beginning an end point, but rather is based on how stakeholders, including customers, utilities, and government, interact (I'm not including scientists as I'm not concerned with the production of the panels in this case). The most realizable end goal would be "have more utilities implement rooftop solar and/or solar farms". Any suggestions for how to shape this into linearized charts would be appreciated.

Edit: I'm more so looking for advice on what the system functions (blue boxes in 2nd diagram) would be. In that diagram, it's depicted as putting ingredients into a coffee maker, turning it on, and making coffee. Straightforward and simple. What would that analogy be for implementing more solar?


texts: Which assumption to consider first when there is more than one diode

texts:
In this question we can easily find the solution,but
here(in this particular question) we can make out the most forward bias voltage and solve it, but in some circuits where  we cannot identify which diode is connected to most forward bias voltage,that time which conditions to assume first when there is more than 1 diode.

I believe one assumption is more than enough to conclude about the diodes,isn't it??

For example in the above case,i assume first case as both diode on but at the same time two different voltages in parallel  are not possible which is nonsense,so i took the condition as both diode off,dere it make a conclusion that both diode should be on,but we should be capable of proving that one diode is on and one diode is off,which am unable to do??

So how to go for assumption when we have no idea which diode is more forward bias??


texts: How will I determine fundamental loop equations from a graph which contains 3 and 2 terminal circuit elements?

texts:
This is the question and details. I believe I could manage to get the graph from the given circuit. (part a)

This is the graph I drew. But I could not find part b and c, since they require fundamental loop equations and fundamental cut set equations. I can easily find them if 3 terminal element (the transistor here) does not exist.

I spent hours but could neither find any information on web nor figure it out myself.


texts: How to measure the capabilities of a wall adapter?

texts:
I purchased this from dx.com. The specs on the device claim 1A@24V.

The device exhibits 24V at no load on pins +4,5 and -7,8. According to Wikipedia, this is called a passive power injector. I tried drawing 1A from the device and failed (some protection drops the voltage to 0V).

How do I determine how much current can I draw from it? Are there some cheap variable resistor blocks or some other tricks?


texts: I have this switch it goes 3 ways, I am a noob and just started learning about electronics. I have a small oled Display connected to my nodemcu which is displaying information. The middle switch is off right? So I want the middle switch to turn the display off, the left switch to show specific information and the right switch to make the display show other information. How exactly do I wire it?


texts:
I want to receive and send packets via UART. The problem is that I don't want to immediately react on a received byte but on a certain sequence. That sequence consists of 4 UART bytes and shall only be evaluated when its completely received.

What's the best way to do that? Creating just an array that fits the 4 bytes and once I received 4 bytes just check if its correct  or would  a larger ring buffer be better, where all receiving bytes are stored sequentially?   (not sure how to implement that)

Example of a transmission:

-PC sends out zeros as long as it doesn't get any response

-a little microcontroller board is connected and receives the bytes

-if 4 bytes of zero are received by the micro, it shall transmit its 4 bytes to the PC

-the PC sees the data on its TXD and stops sending the zeros and does what was requested by the micro. When it's done the PC sends 4 bytes back to the micro to acknowledge its request and tell it that everything is ready.

What's the best way to implement something like this?


texts: How can I combine 10 amp current from solar panel with power from the national grid?

texts:
I want 10 amp current into my load.

I want my solar panel to provide as much as it can, but the remaining should come from national grid. How can I combine these two currents into one unified 10 amp current?


texts: Execute two chunks of code in sequence but the code itself in parallel

texts:
I have a piece of code that needs to be executed after another. For example, I have an addition slv_reg2 <= slv_reg0 + slv_reg1; and then I need the result subtracted from a number.

architecture IMP of user_logic is

signal slv_reg0                       : std_logic_vector(0 to C_SLV_DWIDTH-1); --32 bits wide
signal slv_reg1                       : std_logic_vector(0 to C_SLV_DWIDTH-1);
signal slv_reg2                       : std_logic_vector(0 to C_SLV_DWIDTH-1);
signal slv_reg3                       : std_logic_vector(0 to C_SLV_DWIDTH-1);
signal flag                           : bit := '0';

begin

  slv_reg2 <= slv_reg0 + slv_reg1;
  flag <= '1';

process (flag)
begin
  IF (flag = '1') THEN
    slv_reg3 <= slv_reg0 - slv_reg2;
  END IF;
end process;

end IMP;

I haven't tested the code above but I would like some feedback if my thought is correct. What is contained in the process doens't need to run in sequence, how can I make this part also run in parallel?

In summary, I have two chunks of code that need to be executed in sequence but the code itselft should run in parallel.

--UPDATE--

begin

process (flag, clk)
begin
IF (flag = '1' AND rising_edge(clk)) THEN
  slv_regX <= (slv_reg0 - slv_reg1) + (slv_reg2 - slv_reg3) +(slv_reg4 - slv_reg5); --...etc
  flag = '0';
END IF;
end process;

end IMP;


texts: How to use 2 power supplies in transistor key?

texts:
I have 2 power supplies in my scheme, one is from Raspberry Pi GPIO and one is 9v battery. I need GPIO output to work like a button, e.g. when output from GPIO is 1, battery should power the scheme and when output 0, the scheme should not work. I've read that the transistor key is what I need in this situation, but I can't figure out how to connect all of it. There is 2 grounds, 1 from RPi and 1 from battery, and 2 +'s one from GPIO output and one from battery.

Can you show me the right way to do it? Or what should I use in this case?


texts:
Are there any standards when choosing resister values for voltage divider? So far I found that we can set 10 100 1000 10000 even higher range resisters to get desired ratio. how to choose best resistance range? I am not asking the tolerance consideration when doing the calculations. I need to know which range is the best for example 0-12 to 0-3.3 I may use

E24     5% tolerance,
24k and 9.1k in 1000 scale,
240000 and 91000  in 10000 scale,
how choose best one?


texts:
I want to simulate 8-bits input for demultiplexer on Proteus. Anyone can suggest me the way to do that ??
Thanks