texts: How to create a switch that when pressed opens, but after a time delay returns to the original state?

texts:
I am creating a buzzer driver that turns on when the output of an AND gate goes HIGH. What I would like to create is some way to shut off the signal to the buzzer by opening an SPST switch, but the switch must be able to return to the original closed state after a time delay so the AND gate can drive the buzzer again in the future.

I thought about creating an RC network to create the delay but I don't know how to implement a switch that after it is opened, closes again on its own after a certain amount of time. Ideas?


texts: Rc car, power supply instead of alkaline battery?

texts:
I have an RC car which works with 8 AA alkaline batteries, which make a total of 12 volts.

I want to replace the battery with a 12v 2A power supply (batteries cost away too much...)

Do you think the 2 A of my power supply are enough ?


texts: How does modules in an asynchronous circuit know when to signal that their output is ready?

texts:
I have recently become fascinated by asynchronous CPUs, which have no central clock and each module instead sends a signal, when their data has been processed. However, I have been wondering how such modules actually know when their output is ready and stable?

In the following example of an asynchronous sequential circuit, some modules communicate using a simple handshake protocol as follows:

A module is triggered by a READY signal from a previous module.
The module then starts manipulating the input data.
The RECEIVED signal is sent to the previous module, when the input has been read and can be modified by the prevous module.
When the output is updated and stable, a READY signal is sent to the next module.
When the RECEIVED signal is sent as a reply, the process starts over.

simulate this circuit – Schematic created using CircuitLab

Is it possible to send a READY signal when the output of a module is stable, without specifically timing the propagation delay of the module circuit?

If not, what would be the simplest way of delaying a READY signal based on a circuit's worst case propagation delay?


texts: How many pairs of wire to use for Power over Ethernet?

texts: I have a custom setup to supply power over Ethernet cables. I used a pair to connect to a telephone and another pair for power. The device needs 12 Volts at 0.5Amps to run. In normal setups, which usually have devices that need 24 Volts to run I see 2 pairs (4 wires) being used to supply the power. Is it ok to have just 1 pair running to my device to supply the power with a DC terminator that  I am using?


texts: How is a power cord connector polarized?

texts:
For example, the common PC power cord cable (IEC 60320 C13).

How is it polarized if you can just switch the power plug upside down (EU)?
Does it have any internal circuitry?


texts:
My requirement is to keep running supply of low power devices like DSL modems, etc.
Most of these devices input 12V/9V DC so i don't see the value in using ordinary UPS which converts DC to AC then back to DC, lots of conversion lots of power loss lots of money involved.
I want a DC UPS output which can be directly input into these devices.

I am not pro, so I need a circuit diagram for a DC UPS, that:

Takes 12V input.
Gives 12V output to devices.
If input current is available it will also charge the battery.
If input current is not available, will provide current from battery to attached devices.


texts: Can I use the power from a computer to run my board?

texts:
I have an industrial PC which has some usb ports, and I want to use that port to get 5V and convert it to the 3.3V (with decoupling caps). But now I need to use that 5V to drive 12 relays on my board.

My question is that, Can I directly use that 5V, or should I add some filters or sth? I worry about the computer, when I connect them, can any current flow back and destroy the computer? Here is the schematic of my power port and 3.3V output.


texts: Pull-up resistor in parallel with Schottky barrier diode

texts:
I was looking at the Zynq-7000 SOC startup sequence designed in the Zynq Evaluation and Development board (ZedBoard), which requires specific voltage level regulation sequence (1.0V, 1.8V, 3.3V and 1.5V precisely). To achieve such sequence, the designers used a quad comparator LM339 to ensure the previous voltage level is properly regulated and settled before start regulating the next voltage level.

The LM339 output is a transistor which goes HIGH impedance when Vin+>Vin- and ties to REF when Vin+

Since the output is already pulled-up to 5.0V, what is the purpose of the Schottky barrier diode? (Precisely D23 and D24)

And, since the LM339 inputs are transistor, don't they require input resistors?

Datasheets of components here:

LM339 quad comparator

RB751S40 Schottky barrier diode for D23 and D24

Xilinx Zynq7000 DC&AC switching characteristics (sequencing info on page 8)

ZedBoard schematics, from where I grabbed the circuit of the attached screenshot

EDIT:
Added datasheet for the Zynq-7000 and link to the Zedboard schematics for more info


texts:
I have this power bank and connected it using the white (not super charged) USB port to a Arduino Nano, to power it up. I have also used the Arduino's 5V and gnd to power up a HC-06 bluetooth module.
Now I have a L9110S motor driver and since I didn't want it to draw power from my Arduino I have powered it directly from the battery before the board supplied with my power bank and I also connected the grounds of two circuits to have the same logic level. There is also many data connections that seem fine to me and I have omitted them. You can see my very poorly drawn image here. (Sorry)
Everything powers up fine and works as planned except that after a few seconds suddenly USB power cuts out and small lights on the battery board go dark as well. It never starts until I move the board (as in, shake it. There is no loose connections but I need to move the board to turn it on)
If I connect Arduino to pc usb port it runs indefinitely but on battery stops after 3 or 4 seconds of running. I have searched all over the internet and found nothing. Thanks for your time


texts:
I want to make hardware ID of a board without using microcontroller or any kind of pre programmed eeprom. All boards of same type will have the same ID. One ID per board type.

I was thinking of using i2c I/O expander and connect different combination of input pins to vcc via resistors to define ID of a board.

Is that good way of doing it? Will that be robust enough?


texts: Digital Multimeter to RS232 Serial Port or USB - DT830D

texts:
I am new to Electronics and doing a hobby project. I want to take some readings and get them on the computer/laptop. I am ok with both RS232 (Serial) or USB (preferred). I have a DT830D Multimeter.

I tried to follow the hack mentioned on Instructables.com but this appears to be a DT830B and not DT830D. The IC shown in this post has 44 pins (11x4), whereas, the instrument that I have (DT830D), has 48 pins (12x4).

Assuming that the same instructions would work for DT830D too, could someone suggest me:

How to go ahead with this conversion?
Which IC is used by DT830D Multimeter? DT830B is using ICL7106 IC.

  Note: I am planning to go for an optically isolated conversion and for that I have a pair of IR receiver and transmitter LEDs and an LM358 IC.


texts: What is this cartridge fuse style component?

texts:
This is a Sony EVO-9500A (old 8mm tape player/recorder).

What is the cartridge fuse style component? It is 1/4" by 1 1/8" about the same size as a 3AG fuse. It has a scale on the front going from 0 to 10 and looks like a thermometer. The only markings on it are on the back "FC". The PCB has its slot labeled "FC901" (as can be seen in the last picture).

This thing reads about 3.2k ohms resistance (readings fluctuate quite a bit 10k on the high end down to 2k ohms).

I'm not sure if those reading can even help because I don't know if this component even works. (The tape player is not sending video or audio out, which is what started all this.)

So what is that thing and what does it do?


texts: How does only transistor and inductior without a capacitor oscillator work

texts: It has been more than 10 years, I left electronics. I saw this circuit of wireless power transfer, it has to do with induction, but the oscillator circuit shown doesn't contain a capacitor. can anyone explain to me how this will work?


texts:
I built this small circuit to test if the op amp is working; or if I understand how they should work.

I don't have a bench power supply so I take the 7 voltage that I have, I used a resistor divider to create 1 volt max; around 900mV and send that into the op amp's inverting input. I ground the non-inverting input.

I also run the +7 volt to the v+ of the op amp chip and v- is set to ground.

I tried switching the inverting and non inverting wires as well while using a multimeter to measure the output pin and ground.

I am getting 32mV from the output.

The op amp is OPA2604; dual op amps in one package.

Do I need resistors or something on this op amp? How come I am getting a max of 32mV at the output and zero if I switch the inverting/ non-inverting inputs?

simulate this circuit – Schematic created using CircuitLab


texts:
Ripple counters have output bits not change states in synchronism. On the other hand, synchronous counters have their bits connected to the same CLK pulse.

However, I ran into circuits, which I thought it was a synchronous counter, noted as ripple counters in "Digital Systems" of Ronald Tocci.

I just wonder if they are some other types of ripple counters?


texts: Checking whether two voltages are similar

texts:
I am pretty new to electronics so this may seem like a basic question, but how could I check whether two voltages are similar? For example, say I want to check whether | V1 - V2 | < 1.5V and output either Vcc ( true ) or Gnd ( false ) accordingly.

1.5V is just a figure. It doesn't need to be a very specific value. Instead, I should be able to tune it with a potentiometer or by choosing different resistors.

Low power is definitely a bonus.

I already have a few LM324's ( op amp ) which I think could be helpful.


texts: Creating a two input two way digital switch

texts:
I'm very much a beginner here, so bear with me.

I'm looking to create a digitally controlled switch that has two inputs and two outputs. (Update: The signals are 0V-1V analog.) Here are the two states (excuse the crappy ASCII):

     _____
A----|---|---X
     |   |
B----|---|---Y
     -----

     _____
A----|\ /|---X
     | x |
B----|/ \|---Y
     -----

So, basically in one state, A is connected to X and B is connected to Y, but in the other state, A is connected to Y and B is connected to X.

I spent some time googling around and reading answers seem to be pointing me towards using a mux, but that would only switch one of the outputs. What would I use to get the other output to be routed to the opposite of what the mux selects?

Or...I'm sure there's another way to do what I'm trying to get at? (The beginner terms for googling this kind of thing (switch, cross, flip), aren't the best, as you can imagine.)


texts:
I'm thinking about signal to noise ratio of CCDs and I hope this is the right location to post my question. The Hamamatsu Learning Center seems to be a good starting point to learn about CCDs. I learned the SNR is proportional to the square root of the integration time. With signal averaging it's similar, the SNR is proportional to the square root of the number of measurements.
Now if I have 5s time to expose the CCD to a light source, should I integrate for 5s and then read the CCD for a better SNR or should I read the CCD after let's say 0.1s of accumulation and therefore increase the number of repetitions to 50? Is there a difference? (Assuming reading is instantaneous)


texts: Have a transformer welder with ocv of 45 volts. Wanting to Increase voltage from 45 volts to 75 volts. Is there a way to increase the voltage by adding another transformer with diodes and varistors for both transformer to keep the voltage from entering each other.


texts:
I was looking around the internet the other day and I saw this PCB picture.

And since then I am trying to replicate this HIGH VOLTAGE warning using altium

But I cant get the polygon to be cut around the letters as in the picture, insted Altium keeps cutting a rectangle around the whole sentence. Here is a screen shot.

I know it is a weird thing to ask, but if anyone has an idea on how to replicate this HIGH VOLTAGE warning it will be great.


texts: Why has the auto-router put my PCB traces on two different layers?

texts:
This is my first PCB design.
I want to design the PCB layout of the following switched mode regulator:

This is the resulting PCB layout in which I've placed my components and the auto-router function of EasyEDA has created the traces:

Can you tell me the reason why the auto-router has put the traces to J5 and J2 on a different layer (bottom layer)?
Do you have any particular advice for components placement or routing? I'm quite hesitant since it's my first project.


texts:
simulate this circuit – Schematic created using CircuitLab

At a coffee house recently, I saw a napkin drawn schematic at the table before the waitress cleaned up after the previous patron. I do not remember the part number for the P ch JFET, but the N CH was MPF102.
I cannot figure out what the point of such a circuit would be.
It looks to me like the JFETs are going to be biased off unless the voltage rises past the source drain breakdown voltage. Anything that high would damage the microcontroller input pin.
What am I missing here?


texts:
i am making a arduino project using 5v ws2812b 300leds/meter. Its going to be a motion activated led strip that runs along the side of the stairs. I will be using 3.5m of the led strip so 210leds at 60mA so if all white on full power they will consume 12.6 amps.

I have a 5v 40a meanwell power supply so plenty of overhead. I will put a 1000uf capacitor on the positive and ground leads of the wires just before they reach the leds and 480 ohm resistor on the data line.

I am concerned with voltage drop over 3.5 meters so i will run the wire along the led strip and inject power every meter. My question is what gauge wire should i be using?

The psu will be under the stairs so wire will be 5m long. I am worried about heat and would like some advice about any safety or fire concerns i should be thinking about.

Should there be a fuse in the circuit?

This is the best schematic i can find to show how its wired, where would the fuse go? Power is coming in from both ends of the led strip, would this suffice for a 3.5m strip


texts: Solder a push button directly to Raspberry Pi Zero GPIO

texts:
I would like to solder a push button directly to the Raspberry Pi Zero's 40 GPIO row (without the header). I am looking for instructions on how to do it and also possibly for a suitable button type/part that will nicely fit to Pi's GPIO hole dimensions. The button has to betall enough so that it could be enclosed in a 3D printed case and still be accessible with a finger from outside the case.

This 10 mm tall Omron type B3F is nice but I think the dimensions of its "legs" are not very compatible with the GPIO row.

Alternatively, I could use Zero WH with header, and solder the button directly to the header. But still a suitable button part is needed.


texts: Will standing on a non-conductive surface with wet feet prevent grounding and therefore electrocution?

texts:
It is a well known fact that one should not handle electrical equipment in general and electrical home appliances in particular when barefoot, or when one's feet are wet (even when wearing flip-flops/crocs).

I was wondering, could one stand on a non-conductive surface to avoid the grounding / electrocution even when on'e feet are a little wet (say after the shower)? Perhaps a couple of newspapers? A rug?


texts: How can I use modport of an interface for a DUT without parameters

texts:
I have a testbench in SystemVerilog (mostly verilog, but trying to use more SV) and a DUT in just VHDL.
My DUT uses one generic for device selection, but not important to testbench sim purposes.
I do not want to modify the DUT. But I want to same some lines of space in my tb.
Current Code:
interface clk_if
    wire clk;
    modport dut_mp (input clk);
endinterface

module tb;
    clk_if clk_if();
    ....
    dut(
        i_clk_h (clk_if.clk),
        ....
    );
endmodule

How can I use the modport instead if I do not want to create an extra parameter? Also, can I use different signal names? (clk in interface, i_clk_h in dut)
EDIT: to add what I'm thinking I would like done:
interface clk_if
wire clk;
modport dut_mp (input .i_clk_h(clk)); // I am assuming I could tell interface that the dut has a different signal name but it will be mapped to clk
endinterface
module tb;
    clk_if clk_if();
    ....
    dut(
        clk_if.dut_mp, // clk doesn't have multiple signals but
        rst_if.dut_mp,
        cde_if.dut_mp  // this interface would have three signals and I'd like to only call the modport where I assume I could map it in the interface and not here
        ....
    );
endmodule


texts:
Newbie question :
I have an external power supply which gives me 10volts reference.
The machine I need to command is reading an analog order from 0V (minimum speed) to 10V (maximum speed) and I use a STM32WB55.

My solution is to add a DAC and then an op-amp.

Do you see another solution?

Thank you


texts: How to make my Deo-nano work on 100Hz with internal clock?

texts:
I searched lots of websites to decrease the frequency of the FPGA, but all the coding I found left me with "no clock defined in design verilog" and one of the coding is like this:

// generate 100 Hz from 50 MHz
reg [17:0] count_reg = 0;
reg out_100hz = 0;

always @(posedge clk_50mhz or posedge rst_50mhz) begin
if (rst_50mhz) begin
    count_reg <= 0;
    out_100hz <= 0;
end else begin
    if (count_reg < 249999) begin
        count_reg <= count_reg + 1;
    end else begin
        count_reg <= 0;
        out_100hz <= ~out_100hz;
    end
  end
end

but I could not simulate the result and get the waveform, does anyone have a solution to this? Do I have to setup the clock in the Quartus II ver 13.0?
Sorry, but I am new to this verilog programming.


texts: FPGA board for implementing wireless video

texts:
I want to  build a FPGA based prototype for uncompressed video over wireless connection with  one box being transmitter and other a receiver (to display). The transceiver speed for HD video (1080) is 3-4Gbps. But it would need an expensive FPGA board. I am thinking of VGA and I guess it needs around 1 Gbps (correct me if I'm wrong).

What type of FPGA board should I use (preferably cheaper)?

Also, I would need to interface the FPGA with an RF module. Are there any RF module available for that could be interfaced with FPGA and support 1Gbps speed?


texts: Control 5V supplied seven segment led group with 3.3V PIC microcontroller

texts:
Although the microcontroller voltage required to control the LEDs is 3.3V, the LEDs were connected to 5V for more brightness. The Q9 transistor stays always ON, even if HIGH or LOW is coming from PIC. In this state, i can't control the LED. I have no chance to supply the PIC on the PCB with 5V right now. How can I control the transistor by adding the least components or changing the component values only?

EDIT
I'm redesigning the board while trying the suggested methods. The starting point of this problem was to connect the LEDs to 5V to increase the brightness of the LEDs.

If I connected to 3.3V and changed the value of the R2 resistor, wouldn't I still get the brightness?
Also in the current circuit, when PIC pin1 is LOW, 87mA current flows through the LED. Isn't there a problem here too?

Note: Please warn me if it is wrong to write here instead of a second question.


texts: kicad: LM1117 can't choose Power output line

texts:
I have an LM1117 regulator and I have this problem:

When I "Perform electrical rules check" I have this error:

ErrType(5): Conflict problem between pins. Severity error.
- @ (224,79 mm,92.71 mm): Pin 4 (Power output) of component U1 is connected to
- @ (224,79 mm,92.71 mm): Pin 4 (Power output) of component U1 (net 1)

Well I can see an 2 and 4 numbers in the VO, I click here and I have a list to choose values:

- Clarify selection
- Component LM1117-3.3, U1
- Pin 2, Power output, Line
- Pin 4, Power output, Line

Whatever I choose it doesn't work.


texts:
The old fashioned way to configure a lot of boards is to use pin headers with their jumper cap, i.e.:
https://www.tme.eu/en/details/jumper-kpl/pin-headers/connfly/ds1027-01-2ab801/

On my board I need something similar to configure a high-power power source.
Basically I have three screw connectors, and the user needs to select which one to use to power the driver.
To be clear:

simulate this circuit – Schematic created using CircuitLab
The three power sources are rated:

24V 4A
48V 6A
60V 8A

Obviously I cannot use the tiny headers like above. Well, I can put several of them in parallel but it's an ugly solution and error prone. And the customer doesn't want a solder jumper.
I searched with keywords like "high power jumpers" but I found nothing - at least nothing useful to use on a PCB.
Does this kind of high current jumpers exist? How are they called?


texts: what is output voltage Vo in steady state?

texts: **If looking to symmetry in the circuit, the both terminal of resistor would be at same voltage? I am confused to deal with this circuit and how to start the procedure? Please help me **


texts: Why do Ion Thrusters require such high voltages but have relatively low currents?

texts: I have done a lot of research about these kinds of thrusters, and they all seem to require a relatively large amount of voltage but low currents. I see that they produce a low thrust per watt of power, but in general it seems that there are usually kilovolts and microamps, or something along those lines. I know that because of this, the resistance is high, but a part of my question is why must the resistance be high in the first place?


texts: reactive power for power meter test (load bank)

texts:
I want to test a power meter and I need to test both active and reactive power. I use a resistive load bank to test active power. Now I want to see power meter performance in reactive loads. For achieving this goal what should I have to do?
Do I have to use a capacitor or inductor to consume reactive power?
for a 5kw load, which values of elements I have to choose and how is the calculation formulas?


texts: Sink current for TLP521 via 74HC595 or ULN2803A

texts:
I have a TLP521 driving a set of relays. The circuit is shown below.

To switch on the relay, I will need to sink the current to complete the P521 circuit, which will trigger the relay.

I am thinking to use a ULN2803A to sink the current as shown in the below diagram. This would mean that when I pull the Qa pin of shift register as HIGH, the 1C point (on ULN2803A) should be zero (grounded) and the circuit should be complete.
Is this the correct way to do it? Please note that the common and gnd of ULN2803A are grounded and there is no +Vcc on the IC. Is this OK, or should I connect the COM to +5? (I don't want to source current to 1c by mistake or during initialization)

Another question: Can I get rid of ULN2803 and directly sink the current from 595? I dont think it can sink this current.

Datasheets:

ULN2803

TLP521

TI SN74595N


texts: RLC Circuit with a resistance combined with the inductor. Is my solution correct?

texts:
I am tasked with finding the current I through the following circuit at an array of frequencies.  I have a solution however I am fairly new to AC systems and just want to make sure I am on the right track.

The values of \$ V_R, V_C, \$ and \$ V_L\$ were measured using an oscilloscope, and we can assume for the purpose of this question that they are 0.8 V, 3.8 V, and 5.6 V respectively.

Here is my solution assuming a frequency of 500 Hz and a voltage of 14.1 V peak-to-peak, also there is a correction that the capacitor is \$2.2 \ \mu F \$ not \$0.22 \ \mu F \$:

\$ I = \frac E Z \$

\$ \omega = 2\pi f \$

\$ Z = Z_R + Z_C + Z_L\$

\$ Z_R = 480 + j0 \ \Omega \$

\$ Z_C = 0 - \frac j {\omega  C}  \ \Omega = 0 - j144.7 \ \Omega \$

\$ Z_L = 88 + j {\omega  L}  \ \Omega = 88 + j314.2 \ \Omega \$

Summing the impedances we obtain an effective impedance of \$592.8 \ \angle \ 16.6^ \circ  \ \Omega\$

Now we need the phase angle which can be found with the vector sum of the measured voltages.

\$ \theta = arctan(\frac {V_L - V_C} {V_R} ) = 66.0^\circ \$

With this the final answer for the current should be

\$ I = \frac {14.1 \ \angle \ 66.0^ \circ} {592.8 \ \angle \ 16.6^ \circ} \$

Which gives a final current of \$ I = 23.8 \ \angle \ 49.4^ \circ \ mA\$

Why might my measurements be different from the calculated values?

Edit: the measured voltages are peak-to-peak not RMS.


texts:
I am learning op amps and am confused about one concept.  The output current of the op amp.  Assuming ideal op amps the input side would have infinite resistance and therefor 0 amps.  However the output side would have 0 resistance.

Using V=IR
V/R = I

if R = 0 then its undefined...

Does it have something to do with R2 in the drawing?
The resistor values are just arbitrary values.

simulate this circuit – Schematic created using CircuitLab


texts: DC-DC buck converter low input voltage behavior

texts:
I am using this DC-DC buck converter.
Schematics :

Buck Converter Specifications :

Input Voltage - 18V to 32V
Switching Frequency - 300kHz
Output Voltage 9V
Load Current - 0mA to 200mA Maximum.

I was just curious to understand what will happen to the buck converter when I provide an input voltage of less than 9V.
So, I started to increase the input voltage from 0V. I noticed that I didn't get any output voltage below 5V.
Only when the input was 5V, I started getting some output voltage.
I provided an input voltage of 5V, 9V, 10V and increased.
Below are the waveforms of the input voltage, output voltage and switching frequency of the buck converter and I provided a load of 0.1mA at the output.
Input Voltage of 5V :

Input Voltage of 9V :

Input Voltage of 10V :

Input Voltage of 14V :

My questions :

Can someone tell me why I was not getting any output voltage when I provided an input voltage less than 5V?

When I provided an input voltage less than 9V, the duty cycle of the switching frequency is 97% and the switching frequency is around 37kHz. I understand that DC-DC switching converter architecture is totally different from linear regulator, but why doesn't the input travel directly to the output when the input voltage is less than the 9V? From the datasheet, the oscillating frequency (switching frequency) is only between 270kHz to 330kHz. But how am I getting a value of 37kHz when I provide input of less than 9V? Can someone explain what is happening internally during this low input voltage state?

When I provide an input voltage of exactly 10V, we can see then the switching frequency is halved from what we desired. We get a switching frequency of around 150kHz and there is some sort of glitch or inverted triangle between the switching pulses. Can someone tell me why is that?

After I increase above 10V, the waveforms of input, output and switching frequency are as expected, except the ringing.


texts: Raspberry Pi input protection with optocoupler?

texts:
I need to isolate a noisy input to a Raspberry Pi 4. Would this be the most correct way to implement it? I feel like the protection on the input side of the Pi is overkill.

Note: Schematic uses a SSR that is overkill but I have hundreds of them left over.


texts:
I need to charge 12V e-scooter battery with DC-DC converter. Specification of the battery charging voltage is:

Standby use - 13.5V - 13.8V
Cycle use - 14.4V - 15.0V

Can I charge the battery in cycle use with 13.5V. What would happen then?

Thank you!


texts:
I'm building a Twin-T active bandpass filter as shown on this schematic:

simulate this circuit – Schematic created using CircuitLab

My aim is to build a simple drum-like synthesizer that rings at a stable frequency sinusoid, when you give it an impulse. Furthermore it should give the same length of impulse response at different frequencies. Such that, it doesn't matter what note you tune it to, the note length would always be the same.

The circuit is adapted from here:
original circuit.
I excluded the additional circuitry that adds a frequency sweep, since I need a constant frequency oscillation. (I want to add an exponential converter instead of R1 for voltage controlled frequency.)

When I run a transient analysis in LTSpice for different tuning resistor values, not touching the Q trim pot, I get a nice ringing of equal duration at different oscillation frequencies (see the picture below).

However, when I build the circuit on breadboard, the ringing dies out very quickly with increasing frequencies, as shown on the scope pictures below.

breadboard: 100K tuning resistor.

breadboard: 22K tuning resistor.

breadboard: 6.8K tuning resistor.

Why is that? Is there a way to compensate for that, to get the response like in the simulation?

My supply voltage is +-15V, with a buffered voltage divider as the ground point.
I already tried different Opamps with 3Mhz and 35Mhz gain-bandwidth product. I didn't notice a difference there.

Thanks in advance!

[EDIT:] I played around with the caps and resistor values, imitating 10% off precision components in the similation. I still get the same nice high Q response at high frequencies in the analysis results. Is LTSpice reliable in this regard? I also matched the resistors R3 and R4 to 0.1% on the breadboard. I could not measure a change in Q response.


texts: Triggering reset & wake from deep sleep from same pushbutton on ESP8266

texts:
I have drawn up a circuit of what I am doing. Board in the middle is the Firebeetle with ESP8266.

The objective is to trigger a reset of the MCU upon button press (connection via the capacitor to RST), and if the button is pressed for say 5 seconds, an internal software function is called (note the connection to GPIO13).

GPIO13 has an internal pullup enabled. RST is triggered when the signal on RST rises from GND (or so I gathered).
I am doing this because I am putting ESP8266 into deep sleep and cannot wake it via interrupt sources on GPIO pins, so I am producing a short trigger on RST to wake it.
Firebeetle is powered either via USB or an external 3.7volt battery (not via any of its header pins, separate connector).
Components have been selected purely experimentally, which capacitor triggers the reset. (1uF was not enough, the next biggest I had was 100uF).
Now this setup works and I've successfully achieved what I'm describing above (for more details see code on https://github.com/sensor-dashboard/sensor-dashboard-ESP-BME680-reader), now my question is am I doing something stupid with the circuit or does it look safe and sound? I am a complete beginner but I know these components can sometimes handle more than they are rated for and then fail after a short while.
My question is also, could have I also connected the resistor supply rail to VCC instead of 3.3V and what would be the difference?


texts: We are having a water well dug on the other side of a mostly dry creek except when we get a lot of rain and we need to run the electricity to the front of the property.  Which means we need to run the electricity thru the creek which at time is full of water, but most of the time it is empty.  The point where electricity would be run through is very shallow, maybe 2 feet at most.


texts:
I've recently bought an air compressor with a cigarette lighter socket cord. It plugs into your car.

The specs say that it takes 12V dc at 14A but I want to power it with small batteries (AA, AAA, 9V) so I can carry it on the go. I know that there are heavy car batteries that would work, but I want a light solution.

I tried using 2AA's and a 9V, only to realise that the current was too low.

Without putting 105 batteries in parallel, is there any way to amp up the current of a battery?


texts: Understanding oversampling in control system

texts:
Oversampling means to sample at significantly more than the Nyquist Rate. I can well understand it in signal re-construction: more samples can improve the ADC's resolution, signal-to-error ratio, etc.

However, when in a control system, I have some difficulities understanding it. Assume that the frequency of the process variable is \$f\$, so the Nyquist Rate is \$2f\$, and we sample at \$2f\$ (the controller will take action upon each sample). Maybe we don't get a stable process variable, so we decide to improve the sampling rate.

Next, we sample at \$20f\$, a sampling frequency 10 times higher (also the controller takes action upon each sample), and this time we obtain a stable process variable. However, because the controller action is also 10 times faster, the frequency of the process variable is no longer \$f\$, but much higher, say \$f'\$.  Now the Nyquist Rate becomes \$2f'\$.

Comparing sampling frequency \$20f\$ and new Nyquist rate \$2f'\$, they may be very close, so we cannot call it "oversampling".

Is my understanding towards oversampling and Nyquist rate correct?


texts:
Thanks to the help from this community I am much closer to finishing my new design. Right now I am most worried about my USB 2.0 traces, and I want to make sure that I am doing everything right with spacing and what not. I'm using the USB0 port on the NXP LPC4337.

Before I had the USB traces:
 - grouped together with 6mil spacing except 10mil spacing for D- and D+ like this
   { USB ID Trace >>
   6 mil gap>>
   USB D+>>
   10 mil gap>>
   USB D->>
   6 mil gap>>
   USB VBUS }

I consulted some colleagues at my school and found that if things were traced this way I could get a lot of noise from VBUS and quite possibly the same with USB ID. I learned that I should isolate D+/D- as much as possible. So I moved the VBUS line onto the bottom layer and far from the D+ D- lines. I'm not sure what I should do with the USB ID line, I've been digging through my data sheet and I can't seem to find anything about running the trace, most of the stuff in it is in regards to control registers and driver development. Any ideas on what I should do for the ID trace?


texts: bitbanging i2c problem with ACK from slave

texts:
I am trying to implement bit-banging i2c to communicate between an atmega128A's GPIO and an SHT21 (I2C bus was used for some other devices). The first task is to send a write sequence to the SHT21. Using an oscilloscope, I can see that the sequence sending out from the atmega has the correct start signal, correct order of bits, correct stop signal, signal levels looks correct. The serial analyzer from the scope reads out correct I2C message: S80W~A (SHT21 address is 0x80, writing so last bit is 0). Yet there is not any ACK response from the SHT21. The SDA and SCL are both pulled up to 3.3V via 6.7K resistors.

I really need help finding out what is wrong.

code sending the first byte repeatly if no ACK receive:

 i2c_start();
  while(!i2c_send(0x80)){
    i2c_stop();
    i2c_start();
  }

code of i2c protocol:

void i2c_start ()
{
    // Pull data high and sck low to ensure transition of start sequence
    DATA_HIGH ();

    SCK_HIGH ();
    DATA_LOW ();
    SCK_LOW ();
}
void i2c_stop ()
{
    DATA_LOW ();
    SetBit (DDRD, 7);
    //pull data high while clck is high to end transmission.
    SCK_HIGH ();
    DATA_HIGH ();
}

uchar i2c_send (uchar command)
{
    uchar i;

    for (i = 0; i < 8; i++)     // Send command
    {

        if ((command & 0x80) == 0x80)
            DATA_HIGH ();
        else
            DATA_LOW ();
        SCK_LOW ();
        SCK_HIGH ();
        SCK_LOW ();

        command = command << 1;
    }

    Delay(5);
    ClrBit (DDRD, 7);       // Change Data Direction
    //SetBit (PORTD, 7);      // Turn on internal pull-up

    //SCK_LOW ();
    SCK_HIGH ();

    if (!CheckBit (PIND, 7))     // Read ACK
    {
        SCK_LOW ();
        SetBit (DDRD, 7);
        return 1;
    }
    else
    {
        SCK_LOW ();
        SetBit (DDRD, 7);
        return 0;               // NO ACK
    }

}


texts: What's the difference between these varieties of octocoupler?

texts: It looks like ON Semi makes a bunch of different kinds of optocouplers for various applications. The array of choices is kind of bewildering. What, exactly, is the difference between an optocoupler made specifically to drive triacs (e.g. the MOC3023M) and a standard logic gate optocoupler (e.g. the H11L1M)? What about AC line monitor optos (e.g. the MID400 - which, strangely, is much more expensive than the others despite a lower isolation rating and lower tolerance for high frequencies)?


texts: I need a VERY simple latching circuit using comparator that will simply be off until a signal hits it (can be either + or -, I have no preference) and the circuit will remain on until I reset it.


texts: Detecting a 15KHz burst with logic output

texts:
I want to build a simple and ultra low cost circuit that can detect a timed (let's say 200ms) burst of a single sine frequency - say,15KHz. Amplitude will be around AC ~1Vp-p. Detection will give a logic '1' on simple 3.3V TTL output while the single frequency is detected, and '0' when not.

what would be the simplest circuit?
(My guess is a narrow bandpass filter and a logic level comparator/converter, but I'm looking for a simple implementation)

btw, I am running from a single 3.3V supply


texts: Safe to tie erase pin on MCU to a GPIO pin?

texts:
I'm making a device based on the Atmel ATSAM4S2B mcu, and I want the user to be able to update firmware if they want. For this they need to be able to erase the flash to enter the SAM-BA bootloader that can flash the chip over USB.

At first I was going to add a pin header on the board that can be used to short the erase pin to 3.3V by moving a jumper. But this requires them to open up the case to expose the PCB, risking ESD damage and increasing cost and so on.

So I thought of coding a software erase by tying a GPIO pin to the erase pin and setting it high when a certain command is written over USB. But it just gave me pause.. Is this a good idea? Can it lead to the MCU erasing itself accidentally? I checked with an oscilloscope and GPIO pins seems to output some voltage for around 25ms when powering up and also a small spike when shutting off. However the datasheet of the MCU says that the erase pin is debounced to the system clock and also needs to stay high for at least 200+ ms to activate. So in theory it should be fine, but I can't help thinking I might be missing something. Can someone offer any insight?


texts: Working voltage vs dielectric withstanding voltage

texts: What is the difference between working voltage and dielectric withstanding voltage in resistor components? Or both the working voltage and dielectric withstanding voltage is same? Can I apply the working voltage value to the dielectric withstanding voltage?


texts: Amplifying DAC output with common-emitter configuration

texts:
In my current project setup I generate audio signals from my MCU's internal DAC. These audio signals are transferred to a speaker box with an internal amplifier via phone jack. To make the whole project more portable, I thought about giving my \$8\Omega/0.25W\$ speaker a try. Since the DAC should not output too much current I decided to add a class A audio amplifier with voltage divider biasing to the DAC's output.

The result would look something like this:

simulate this circuit – Schematic created using CircuitLab

Now my problem is that the DAC's output is always positive (between \$0.2V\$ and \$3.1V\$). Because C3 is an AC coupling capacitor, it will feed current back into the DAC when the audio signal becomes negative. Will this damage the MCU?
And at which voltage level should I bias Q1?

By the way, the MCU I'm using is the STM32H743ZI.


texts:
I have a master microcontroller that can control 4 slave microcontrollers. Each slave microcontroller is connected to 3 sensors.

The master microcontroller asks to retrieve the value of a specific sensor on a specific slave, and the slave sends the value to the master. And so on...

Can I use the full duplex protocol ? Like this (where RO = RX and DI = TX) :

Is it better to use half-duplex ? When is it necessary to use half-duplex ? It implies enabling receive and driver at a specific timing which can be annoying compared to the full duplex method.

I have never used an RS-485 before so I am a beginner :)


texts: What is the common application of a Power Resistor Decade Box?

texts:
I recently found a Power Resistor Decade box at a thrift store.  It looked cool and was only 10$ so I figured what's to lose.

I understand what it does (allows you to specify any resistance in it's range), but I don't understand what it's commonly used for.

As a hobbyist who sometimes tinkers in electronics (I'm a software guy, so mainly microcontrollers), do I have any need for this?

(clarostat 240-c)

Also, I tested each of the individual setting (using this multimeter) and these are the results.

(google sheet link)

Are these variances standard or is this one broken? (I realise I shouldn't have converted but instead left it at actual measured precision)


texts: How do I know if a current source supplies or receive energy?

texts:
In example, I have this circuit:

I know that in a current source if the polarty is \$-\rightarrow +\$ it supplies energy to the circuit, but how I can determinate the polarity in this case (of
\$I_{f}\$)?


texts: How to calculate an op-amp's current usage based on datasheet's supply current and its Vout terminal?

texts:
This might be a dumb question so if yes, I apologize. I would like to power an op-amp off of a boost converter and I need to know how much current an op-amp would use.  I'm using TI's web bench and there's a lot of cost / space differences depending on the max output current. So I have to pose this as a question even if it sounds dumb because it has a lot of space / cost ramifications.

On a datasheet, it says that the "supply current" for an op-amp like the MCP6002 (https://www.digikey.com/product-detail/en/microchip-technology/MCP6002T-I-MS/MCP6002T-I-MSCT-ND/669500) is 100 uA. The MCP6002 is actually two op-amps in one integrated component.

I will be outputting roughly ~1 mA from one of the op-amp's Vout  terminal. For now just assume the other Vout terminal isn't used.

When I design my boost converter, I'm assuming the booster should only require a max output of 1.1 mA. This is for the 1mA coming from Vout and the 0.1 mA going to the "supply current".  I can round up to 3 mA to be safe. Is this a correct assumption, however?

Another question: If I do wind up using the other output's Vout, do I need to also 2x the supply current (e.g. 200 uA).


texts: Understanding Schematic utilizing step-up transformer

texts:
I have the following schematic. It's designed to step-up voltage and frequency, in range of ~10kV and 20KHz, from 230Vac-50Hz, but I have problems in understanding it. In schematic the box for transformer with 8 pins is shown in the other attached image . Transformer is having a feedback winding on top of primary winding, and two secondary windings.
I tried to simulate it in Proteus and NI Multisim, but both of them crashed. I know that the schematic is correct and working, but I cannot understand it. For instance, I don't know what is the usage of C1, C6, C7 & C8. Also, R2, R3, R4, R5, X1 and DZ1. After D1, voltage is half-rectified, but I don't know when C1 charges and discharges, or when X1 (Thyristor) is conducting and when Q1 (IGBT) is turned on and off and when the signal is taking the path through R4 or R5. what is the use of transformer feedback pins (pins 3 and 4)? Is there anyone who could help me? Can you simulate this schematic in any software?
Thanks in advance

simulate this circuit – Schematic created using CircuitLab


texts: Opamp Compensation For Input Capacitance

texts:
I am going through the datasheet of LM7171 for one of my applications. Please see the below circuit.

May I know how they arrived at the equation for CF?
Is this equation is valid for non-inverting configuration also?
How the input parasitic capacitance causes instability.If the pole created by the gain setting resistors and parasitic capacitance falling inside the closed-loop bandwidth will create instability?
Please reply


texts: Estimating battery capacity remaining from SLA connected to motors

texts:
I have an SLA battery, at say 10 Amp-Hours, connected to 3 high power motors. Each motor can draw up to 10 Amps each (worst case / max power). Using Q = It as an approximation, I see that I get 1200 seconds of usage. (Q = 3600*10, I = 30, t in seconds)

For my application, what circuit can I built/add on to measure (estimate) the charge remaining? Right now it's literally just SLA battery --> motor controllers --> motors, with an Arduino connecting to the motor controllers.

I was wondering if something like this: https://www.sparkfun.com/products/11005 could connect to the battery leads, the other end to Arduino, and then I sample the current every few milliseconds and "subtract" the charges from my total of 10 Ah. E.g. charge_used = sample_period * current_measured; followed by charge_remaining -= charge_used;.

Are there better ways of measuring the remaining battery capacity? Is my approach even feasible?

Cheers


texts: Bode plot gives negative stability margins for a stable plant

texts:
I have a plant whose transfer function has all the poles in the left half of the s-plane (obtained the poles using Wolfram Alpha). However, its bode plot gives negative phase and gain margins; I obtained the bode plot from both MATLAB and Wolfram Alpha and they agree with each other. I am not able to get around this fact. How is this possible?
My characteristic polynomial is


texts:
For my project, I'm trying to work with the principle of electrovibration. This principle is about simulating textures using low current electricity on an insulated conductive surface (see Wikipedia).

In order to do this, I will be experimenting with generated AC signals of 80 to 160 Vpp at 60Hz to 400Hz. I will do this by using an DC - AC converter, usually used for EL lamp applications.

My only concern is how to limit the current coming from the converter. Are the techniques for limiting AC current the same as DC, by using a simple resistor? Or is it, as I expect, more complex?

I need to limit the current to 0.5mA, for safety reasons.


texts:
I'm curious if anyone has experience with getting a simple board like the Adafruit Trinket or DigiSpark or any of the other ATTiny based clone boards running on solar power. E.g. with a solar panel and a lipoly or other rechargeable battery.

There are a combination of things that must be accomplished for that to work "well" (e.g. with the smallest possible battery and panel) which are not trivial.

The Trinket has to sleep in low power as much as possible. That probably requires cutting off the power indicator LED, and then using some tricky code to actually put the chip into low power modes.
The Solar Panel has to be controlled so it doesn't discharge the batteries at night, and doesn't over charge the batteries during the day time.
The battery needs minding as well, depending on the type.

When you add all that up... well... I'm hoping someone else has done it? Or part of it?


texts: How do I wire a trs jack to a dual channel amplifier?

texts:
So I have a bluetooth audio amp circuit board. I believe it is dual channel it has two chips (one for left, one for right)
The outputs are R+ R- L+ L-, but I want to wire them to a trs jack, which has a common ground.
However it stutters horrible if I simply combine L- and R-.
I have tried using diodes and this works but it squeals and sounds terrible.
If I use one diode and connect it between L- and common ground with R- connected straight to ground it sounds better but still squeals on Left Side audio.
How do I do this properly?


texts: Low-side current sensing, raising the ground?

texts:
One of the main reasons why we don't use low-side current sensing for PSUs is that we want the ground to be, 'ground'. adding a shunt resistor will rise the ground slightly higher.

In real world wires and even traces of PCB have resistance, I saw it in several designs and datasheets that it's suggested to use a short trace of PCB as a shunt resistor.

Does it mean in real world there's no ideal ground reference? so we can safely use a 10m ohm resistor at the low side of the circuit without being worried about rising the ground reference?


texts: Eagle CAD custom SMD pad for bushing contact

texts:
I want to attach a panel mount potentiometer to a PCB. But I need the bushing to be grounded. Ideally I would just make the hole for the pot thru plated but the fab does not permit really large thru plated holes. So my first attempt is two SMD pads with a thru plated hole in the middle like this:

This obviously has issues. Can anyone recommend an alternative solution?

If not, do you think this would work if I accept all of the overlap and clearance issues with these pads? Will the hole actually be through plated so that the top and bottom pads are in fact connected?

UPDATE 1:

As suggested by Peter Bennett, a possible solution is to make a circle using the bStop layer to expose the ground plane:

So there would be no contact on top but I think because the tin is slightly raised and soft it should make good contact with the bushing. We'll see ...


texts: 14 x 14 LED Matrix - How can I control it?

texts:
I intend to build a 14 x 14 standard 3mm blue LED matrix, for a WordClock-like project, but I have no idea how to control it.
I've heard of multiplexing with NPN transistors, but I'm concerned about the resistors values. And still, 28 ports it's still too much for my Arduino Nano.

What can I do to control the LEDs? Is the multiplexing idea right, or am I completely on the wrong path?


texts: Quartus II hangs when trying to create new project

texts:
I have Quartus II installed under Ubuntu 13.10. It starts up fine, but when I click "finish" on the "Create New Project" wizard, it loads infinitely, stuck at 0%, then stops responding.

I have tried this in both the 32-bit and 64-bit versions, with the same results from both. Anyone know what might be causing the issue, or how to figure out what is causing the program to freeze?


texts:
I need to run a big circuit for thousands of times. Therefore, I am looking for a fast way.

I was wondering if MATLAB has any toolbox that can be used instead of HSPICE.
When I searched online, I saw people mentioning "SimPowerSystems", but I did not use it yet.

For huge number of circuit simulations, is it better to use MATLAB or HSPICE? (in terms of timing and functionalities)

What are the differences?
Which one is faster?
Can I measure voltages, currents, power, ... as I can do in HSPICE?
Will I have the same output files?


texts: MEGA2560 only starts program after pressing RESET button multiple times

texts:
I am working on a program where I am controlling an MP3 player by using UART between my MEGA2560 and the MP3 player. The MEGA2560 sends serial commands to the MP3 player when external interrupts are generated on INT4 and INT5 and it all seems to work fine.

When I want to test my program I press the RESET button on the Arduino in order to start the program. However, sometimes the program only starts after pressing the RESET button multiple times. This happens often but not all the time, which is weird.

What do you think could be the reason for this?


texts: Nonlinearities in Fully Differential Op Amp

texts:
I am trying to construct an amplifier circuit using a fully differential op amp (THS4503) to interface with an ADC (ADS5232). I will be reading a 0-5V sensor, which needs to be converted to a 1Vpp differential signal. I have the circuit constructed according to the datasheets of the respective components along with the help of a TI app note (sloa054e.pdf) (p.17-19), since my sensor requires a 50 ohm termination. I'm simulating the circuit in LTSpice using models created by TI for the amplifiers. When I sweep the input voltage, I am getting some weird nonlinearities at the end of the range, and I'm not sure how to resolve it. I checked the datasheets and I am within the voltage swing of the amp, and I checked current flowing through the components and I am within the current rating of the amp. Plus, it doesn't quite make sense, since the amp is able to provide the same voltages at the beginning of the input range, just not at the end.
Here is the circuit (V1 is the sensor, the regular op-amp is just used as a voltage buffer to bias the sensor):

And when sweeping the voltage input from 0-5V linearly, this is the output:

Thank you for your help!


texts: nucleo-f401re button interrupt keep getting into the irq handler

texts:
the nucleo board button is pulled up to high to gpioc13 so i made the interrupt on a falling edge , the code keeps getting into the irq handler without me pushing the button
my main.c

#include "Board_LED.h"
#include "stm32f401xe.h"

void PIN_CONFG();
void PIN_EN();
void clear();

int main(void) {
  LED_Initialize();
  PIN_CONFG(13);
  PIN_EN(13);

  LED_On(0);
  while(1){
  }

  return 0;
}

void delay(void) {
  int i;
  for(i = 0; i < 5000000; i++) {
  }
}

void EXTI15_10_IRQHandler(void) {
  clear(13);
  LED_On(0);
  delay();
  LED_Off(0);
  delay();
}

my interrupt functions.c

#include "stm32f401xe.h"

void PIN_CONFG(uint16_t pin) {
  EXTI->FTSR |= (1 << pin);
}

void PIN_EN(uint16_t pin) {
  EXTI->IMR |= (1<<pin);
  NVIC_EnableIRQ(40);
}

void clear(uint16_t pin) {
  if(EXTI->PR & (1<<pin)) {
    EXTI->PR |= (1<<pin);
  }
}


texts: Is a 2N3906 an appropriate replacement for a BC158(B) in audio amp circuit?

texts:
On a long but educational process repairing a vintage German stereo. I have identified a failed (shorted) PNP transistor in the power amp section. (Schematic with highlight is below.) The part on the actual board is a BC158B; the schematic specifies only "BC158". The only difference between the BC158 and the B variant is the hFE gain value (higher value in the B). Here's a datasheet showing the BC158 series.

I have asked before here and gotten good advice on how to think about transistor equivalence in audio when going from vintage euro parts to current US replacements.

It appears to me that a standard general purpose 2N3906 would seem appropriate relative to the base BC158 (has same or higher max voltage, higher max current, and similar hFE.

I'm not knowledgeable enough to look at the circuit and see why the schematic shows the BC158 and the actual part used was a BC158B-- they appear to be likely different in amplification function, but maybe (presumably?) it doesn't matter here.

Can anyone offer a theory for why the original part used could be a higher-gain model without messing anything up?
Do I need to seek out a higher-gain replacement part? I'll use a 2N3906 if it would seem to work. If not, there are some random parts I groused up on Mouser based on the filters that seem like they might be appropriate, but I'm for those I'm casting around in the dark a bit.

Thanks!

Schematic-- T601 is the one that needs replacing:


texts: Connecting arduino to existing pcb power grid

texts:
I have an idea about a project to control a device with the help of Arduino+wifi shield and an android app.

The device that is to be controlled, already has its own power supply. Internally it provides* a regular 5 v dc to the PCB grid (*well, that's my guess, since most electronic components run at 5v dc. I haven't actually measured it with multimeter). What I want to know is if I can integrate my Arduino(with wifi shield) with the device "drawing power from the same" 5 v PCB grid?


texts: Need help to vibrate a motor for an original musical instrument

texts:
everyone. I am asking you to help me out for making original musical instrument.
The goal is to vibrate a small motor by square wave signal witch is generated in a synthesizers in my Mac.

Here is what I tried;

Square wave sound (in my laptop)
-> stereo output
-> stereo cable
-> headphone amplifier
-> stereo cable
-> motor

I cut the end of the stereo cable to connect the left(or right) wire and the ground wire.
(please check the photo below)

However, it doesn't work. I could hear the sound from the amplifier by headphone, so there might be problems between the amp and the motor.

Let me tell you the specs of the amplifier;
make/model: Pyle Audio, PHA40
input impedance: 100K-ohm, Unbalanced
Max Input Level: +15dBu
output impedance: 80-Ohm, Unbalanced
Max output Level: 40mW in 100ohm
Max Gain: 20dB
S/N Ratio: More than 90dB
THD: Less than 0.03%

And the motor is DC 1.5-6V 1750-7000(<- I have no idea what does this, mA?)

Hope I can get any ideas/answers from you guys.

Thanks,


texts: What is the "function reserve" of a photoelectric retroreflective sensor?

texts: When looking at data sheets for optical sensors, I'm seeing a graph relating "function reserve" with distance (e.g., as shown here and here).  "Distance" is presumably the distance between the active end of the sensor and the target; what is the "function reserve"?


texts:
I would like to implement a home-automation system on my arduino.
For this project I would like to communicate with the different devices by radio frequency.
So that would be different 433 mhz receivers and one 433 mhz transmitters.

Now my questions:

How can the transmitter differentiate the signals of the indiviual devices. Do they each have an unique id or such? Or do i need some other part or controller to identify them?
What is the purpose of a transmitter encoder?

I'm rather new with electronics and arduino so any comment or suggestion is appreciated.


texts: How does linear phase shift of bessel filter avoid distortion of nonsinusoidal inputs?

texts:
I thought \$0\$ or a constant phase shift was necessary to avoid distortion of a square input.
How does linear phase shift help here? I'm familiar with some fourier series but I don't get my textbook explanation. Any help?

EDIT(My attempt):
Say the input signal is \$f(t) = \sin(t) + \sin(2t)\$.
Then the output will be \$g(t)=\sin(t+\phi) + \sin(2t + 2\phi)=f(t+\phi)\$
That's it?Wow! But this means a constant phase shift actually distorts a nonsinusoidal input?  Doesn't this seem counterintuitive?


texts: Does current source affect flow of current in circuit with a variable resistor?

texts:
Suppose you have a current source in series with a resistor R the current through the R resistor would be the current generated by the current source. How would the current through the circuit change if you replaced resistor R with resistor Y, where the value of resistor Y>R?
Original circuit


texts:
So this seems to be a generic issue. "libc.a" is associate with some sort of incompatibility with floating point math and/or the correct library used.

I've added the "-lm" as suggested on the forums, but still unable to link/compile correctly?

Any other suggestions?

/opt/local/lib/gcc/avr/4.0.2/../../../../avr/lib/avr5/libc.a(cmpsf2.o):../../../libm/fplib/cmpsf2.S:58: multiple definition of __ltsf2'
/opt/local/lib/gcc/avr/4.0.2/avr5/libgcc.a(_lt_sf.o):/opt/local/var/macports/build/_opt_local_var_macports_sources_rsync.macports.org_release_ports_cross_avr-gcc/work/build/gcc/fp-bit.c:1272: first defined here
/opt/local/lib/gcc/avr/4.0.2/../../../../avr/lib/avr5/libc.a(floatsisf.o):../../../libm/fplib/floatsisf.S:44: multiple definition of__floatsisf'
/opt/local/lib/gcc/avr/4.0.2/avr5/libgcc.a(_si_to_sf.o):/opt/local/var/macports/build/_opt_local_var_macports_sources_rsync.macports.org_release_ports_cross_avr-gcc/work/build/gcc/fp-bit.c:1334: first defined here
/opt/local/lib/gcc/avr/4.0.2/../../../../avr/lib/avr5/libc.a(modf.o):../../../libm/fplib/modf.S:88: relocation truncated to fit: R_AVR_13_PCREL against symbol `__subsf3' defined in .text section in /opt/local/lib/gcc/avr/4.0.2/avr5/libgcc.a(_addsub_sf.o)


texts: LSM6DSM unreliable MISO unless disconnected

texts:
I'm having an issue with bringing up an ST IMU (LSM6DSM on an MKI189V1 eval board). I am using SPI to connect my host micro to the IMU and trying to read back the device ID.

The issue I'm facing is that the response from the IMU is sometimes correct and sometimes incorrect. I'm speaking to ST directly and exploring the firmware side of things, but I am seeing very similar behaviour on two separate micro controllers from two different vendors, so I'm trying to see if anyone has some suggestion as to a potential hardware issue. Here are some more detailed symptoms:

Microcontroller, IMU, Logic Analyzer, Oscilloscope are all on the bus.
IMU is powered from host micro VDD
Removing scope or logic analyzer from the bus does not fix issue
However if I am consistently reading the incorrect value, and remove the logic analyzer then while removing it the correct value will be read fairly consistently
If I disconnect the MISO from the host micro (logic analyzer, oscilloscope still connected) the output is consistent and correct
When the incorrect value is read it often looks close to the correct value in that I see pulses where the MISO should be toggling, but they are very short
I've tried both supported SPI modes (and both unsupported), and tried clocking as low as 10kHz to no avail
If I use I2C everything works fine.

All this is leading me to believe there is some sort of hardware drive strength or contention issue.

Item 4 seems to indicate the micro is holding the line somehow, however I'd be surprised if the same issue existed on two entirely different platforms.

Item 3 is very consistently able to get the correct value, however it does not stay consistent once the analyzer is removed.

Any suggestions would be appreciated.


texts: Calculate Base Resistor in a NPN transistor switch

texts:
I am building a switch for a buzzer that will charge up a capacitor and sound the buzzer as they hold the button down. When they release the button the buzzer will fade away as the capacitor discharges. The Charging and discharging will only happen on the initial switch down (charge) and the switch up (discharge)

Everything works as expected and works well. But the question is why. I have used transistors to make switches and h-bridges before and understand the function and how to calculate the variety of currents and resistances, but the addition of the active buzzer has thrown me.

Part of the issue is that I know nothing about the active buzzer. It came in another kit with no information or part number. So basically I started with a high resistance for R1 and worked my way down until it worked (even a 470 Ohm resistor was to much). This is not a great way to do it, but I figured if I had a working model, I could reverse engineer why R1 had to be that resistance.

What I know from using my multimeter:

The buzzer is a 5v buzzer
The current on the Load when R1=220 is 13mA

So if I wanted to calculate R1 (or the current going into the base) without just using trial and error, how would I go about it? It just seems that a current of ~7mA is a lot to control a small load.

UPDATE

Sometimes you have to learn the hard way. Indeed the transistor was backwards. I was looking at the wrong spec sheet. credit to @JIm Dearden for first suggesting that and to @Olin Lathrop for crunching the numbers and reconfirming the backwards transistor debacle.


texts: inconsistent inrushmeasurment depending on "power plug"

texts:
I'm measuring inrush current with a current probe ( tektronix P6303) that is connected with an amplifier between, which is powered by an AC line before it's connected to an oscilloscope.

I got some struggle with my measurement so I changed oscilloscope to another oscilloscope of the same model, suddenly I realized that despite the setup is the same it gives totally different result in amplitude and shape.

So I changed the power cord between the oscilloscopes with the result that they displayed the same result as the other part did before the change.

After this I rotated the contacts in the AC line with the result that it for one oscilloscope resulted in half the amplitude still same shape and for the other one another totally new shape.

There is only one possible earth loop and it's between the current amplifier and the oscilloscope not against the DUT. I can't really see why it in this case should matter that much.

Have anyone else experienced this before and how did you proceed to get a "true" measurement?

::Extra

I inserted a isolation transformer to the osilloscope, in this config it seem to give a consistent result, even if I change the power cords rotation and oscilloscope. Maybe I've found a solution.

Current inrush Measurement with isolation transformer

White = with min voltage

Yellow = with max voltage


texts: Debugging the physical components in a circuit

texts:
What is the best approach to debug the physical components of a circuit that does not work?
I set up a circuit for a simple audio player following this tutorial.
However it simply does not work. The code portion of it seems to be functioning fine, but I'm unclear as to where to start debugging the physical components of the circuit. What would be the best approach to debug what is wrong in the circuit itself?


texts: Issue on Serial Port Communication (in JAVA)

texts:
I've written a Java program to read my Arduino's outputs through Serial port (using RXTX Library). There's a small issue I'm facing.

Arduino continuously writes to serial. But every time, after running the Java program I have to reset the Arduino to make the program see the serial port values. Otherwise it won't read any value.

Hope it's clear. I need to know whether there's a way to fix this. How can I make my program to read serial port values when it is started without doing anything to external devices.

Thanks!

EDIT
This is the method which'll initialize the serial port.

SerialPort serialPort;
private static final String PORT = "COM32";
private InputStream input;
private static final int TIME_OUT = 2000;
private static final int DATA_RATE = 9600;

public void initialize() {
        CommPortIdentifier portId = null;
        Enumeration portEnum = CommPortIdentifier.getPortIdentifiers();
        while (portEnum.hasMoreElements()) {
            CommPortIdentifier currPortId = (CommPortIdentifier) portEnum.nextElement();
            if (currPortId.getName().equals(PORT)) {
                portId = currPortId;
                break;
            }
        }
        if (portId == null) {
            System.out.println("Could not find COM port.");
            return;
        }
        try {
            serialPort = (SerialPort) portId.open(this.getClass().getName(),
                    TIME_OUT);

            serialPort.setSerialPortParams(DATA_RATE,
                    SerialPort.DATABITS_8,
                    SerialPort.STOPBITS_1,
                    SerialPort.PARITY_NONE);
            input = serialPort.getInputStream();
            serialPort.addEventListener(this);
            serialPort.notifyOnDataAvailable(true);
        } catch (Exception e) {
            System.err.println(e.toString());
        }
    }


texts: What is the output type of the 74AHC594?

texts:
What is the output type of the 74AHC594 IC?
I didn't find the answer in this datasheet. There is stated in some datasheets for the 74594 IC from other manufacturers that the output type is buffered. What does that mean?


texts: The secondary of a transformer with a cap connected across it  - should it be considered as a parallel tank circuit or a series one? It looks like parallel, but in reality the voltage rises on it when you drive it at resonance using the primary coil, which is somewhat counter intuitive


texts:
I am trying to figure out the significance of the two capacitors recommended for use in an LM317 DC-DC converter circuit.

Recommended circuit diagrams show that I should be using a 0.1uf Ceramic Capacitor and a 1uf Electrolytic capacitor.

Why the difference in capacitors (size and makeup)? Can I use two capacitors that are the same type and composition, assuming they are of the larger size? For example, can I use two 1uf electrolytic capacitors instead?  Will this just make the circuit slower to level out?

I understand how capacitors work (roughly) but I don't understand their purpose in this circuit.

The reason I ask is because I took a look at Other Voltage Regulators and they seem to have the exact same capacitors.


texts: Op Amp: signal measurement that is below its common mode input range

texts:
I was wondering, how is possible to use an op amp, which its common mode input voltage is (V-) + 0.2V to (V+) - 0.2V  to measure signals as low as 10mV for example?

I'm looking for an instrumentation amplifier and most of them I see have very narrow Vcm range with respect to their supply.


texts: Resulting current waveform of square wave voltage applied to capacitor/inductor

texts: If a square wave voltage waveform is applied across a pure capacitor or inductor of a given capacitance/inductance, how will the resulting current waveform look? How should I calculate this using the theoretical formulas of Ic and IL?


texts:
I wanted to build a circuit where i would be able to control 90 LED's using one WS2811 and have a total of 60 WS2811.

In this circuit I hope to connect 30 LED's per channel, there is no need for me to control the individual LEDs thus there is no point in me going for the WS2812s which is commonly used.

I tried a few circuits that i saw online (sorry! dont have the links) and not of them worked, all i ended up was buring two of the IC's, and the circuit which did work I was unable to turn off the LED there was always a small amount of brightness.

Working voltage: 12V
No. of LED's per channel: 30

This is how the LEDs are wired

I believe this is the circuit that i used

EDIT 1:
I tried this circuit as well but the output is very low (brightness)

EDIT 2:

I modified the above circuit to 100ohm at R1 and 10k ohm at R2, the transistor T1 is BC547 and T2 is BC817. After modifying the resistors and transistors, I am able to get a much higher brightness however, if I am to connect the negative directly to ground the Strip (the one i am testing with) consumes 1A current but via this circuit it is consuming only 600mA. Do i need to change T1 for better results?

Datasheet:

LED: https://www.dropbox.com/s/wz7xp7ghupoif5z/SMD5050-warm%20white%20specification.doc?dl=0


texts: Hamlin Reed Relays for Audio: Sink or Source?

texts:
I'm building a small stripboard audio switchbox using some hamlin 5v reed relays (HE3621A0550, mouser link here).

A small SPST momentary switch activates the relay. Wondering if the best practice is to ground the relay from the switch (sink) or send current to the relay (source) from the switch. Since the switch is SPST, the other end (ground or current) would be permanently wired to the relay from the switchboard.

I am leaning towards sinking but I wanted to make sure this was a safe practice.

Any other general tips to ensure a long lifespan and good, safe operation for these relays?

edit: I am aware that the Hamlin relay I selected is not latching. The momentary switching is intentional.


texts: DC-DC Buck Regulator: Embedded or External MOSFET

texts:
What are benefits and drawbacks of using Buck Regulator with external MOSFET compared to Buck with embedded MOSFET? Is there some general rule?

In my case I need 5V 3A from 9V-30V supply.


texts: How can this inductor I built (picture in post) have such a low inductance?

texts:
I needed to study the rate of change of current (dI/dt) in a DC circuit, so I built an inductor using a laminated soft iron core from a small electronics transformer. I chose soft iron for I could make a reasonable inductor with a few turns and avoid saturating the core with the DC current (which can go up to 10 A).
I needed a thick conductor, so I twisted an AWG 19 wire 2 times over itself in opposing directions (once cw and then ccw) and wound that in the core.

The problem came when I measured the inductance. First I used a configuration with a 25W audio amplifier + smartphone (as a sine wave generator), a bench multimeter to measure the RMS current and an oscilloscope to measure the voltage drop on the inductor. I measured its impedance at 15 frequencies from 100 to 10000 Hz, subtracted the DC resistance and made a linear fit.
The fit was excellent, with R² > 0.99, but the problem was the value I found. From the slope (and its standard deviation) it was 24.5 +-0.5 uH. This is nonsense, if it had air as a core it would be no much lower.
But everything has been double-checked. I checked the multimeter against the oscilloscope, both agreed perfectly in both DC and AC voltages, and the AC ammeter of the multimeter also agreed with the voltage drop on a resistance, as measured on the oscilloscope.
Today I thought the noise from my audio amplifier (which use a SMPS) could be messing with the measure, once the multimeter was measuring the RMS current with all of its harmonics, while in the oscilloscope I was only looking for the peak amplitude of the frequency I selected on the smartphone.
So I decided to make everything with the oscilloscope and filter the noise by eye. In this configuration I used a resistance in series with the inductor and measured the voltage drop on the resistance and on the whole series with the oscilloscope.
I made measurements when the series impedance was 2,3,4 and 6 times that of the resistance alone (which is a 0.5 ohm resistance) and made a linear fit again.
Now I found 22.0 +- 0.8 uH. Basically the same, meaning nothing was wrong before.
So, I beg the question: What the hell could happening here?
I know the laminated soft iron isn't good for high frequencies, but form what I measured its inductance only dropped perceptibly after 10 kHz.
I also know that all the 4 stands of wire are properly soldered in each end and have no shorts in the middle, because the resistance at ambient temperature matches perfectly my annealed copper estimate (6.38e-3 ohm  vs 6.8e-3 ohm), if anything happened it would have to be off.
By last I even made a replica of the setup in MultiSIM to check if a 20-something uH inductance show produce that result, and I found that yes, none of my calculations were wrong.
So what's left to consider here? I know that once that I had to disassemble and glue the core back together it surely became worse than it was originally, as now the laminations are slightly more distant, but it can't be so bad. I don't think they're shorted either, which could reduce the overall inductance, but they seem well insulated still, I didn't damage the original insulation and the glue I used is also insulating.


texts: I am currently using the Dragon AVR to program ATMEGA88 chips on board using ISP I/F. My problem is that it seems somewhat flakey. Is there a reasonably cheap non-Atmel alternative? Ideally a more universal machine.


texts: How do microsequencers in CPUs parse data from RAM in the control unit/control store before determining what to do with the bits/voltages?

texts:
I have been reading up on machine code, and in many architectures (x86 IA-32, IA-64, AMD K6, ARM v7, ARM v9) and microarchitectures (Intel Core, P6, P5, etc.) machine code is additionally translated from the source of the RAM itself in to smaller microprograms that do the actual circuit work. However, the microsequencer is what apparently does this. My concern is what is the purpose, why do some microarchitectures not use this, and why do some additionally implement it as well?

Oh, and the main question, most importantly, of course ... how does the microsequencer actually turn electrical signals from RAM in to circuit-level operations correctly?


texts: Optical switch for visible light from multiple endoscopes

texts:
This may not be a total fit for the electrical engineering exchange, but its a pretty specific hardware related technical question.

I am interested in multiplexing visible light optical fiber signals. It would actually be endoscopes (not for medical use) that are multiplexed back to a single camera. Each endoscope would get a chance to relay an analog image back to the camera before the next one.

Are there such switches in existence? When I search for optical switches, the results are not surprisingly all about digital optical switches.

A method that would work would be a mirror that is driven by a stepper motor to align the path of a single endoscope


texts: Parallel resonant circuit depending on voltage

texts:
In a parallel LC circuit, does an applied amplitude of voltage change anything when it comes to choosing the capacitor and inductor (except the voltage rating of course)?

I know that bigger L causes bigger Q, but besides from that, will the same current flow if I use a really small capacitor (speaking about ideal elements now) and a really big inductor at resonant frequency, or are we searching for specific capacitors when it comes to reaching the highest current at given supply voltage (and frequency ofcourse, but we choose L and C appropriately to achieve resonance every time)?

What are the differences when we change the values of capacitance and inductance while still maintaining the same resonant frequency (besides Q factor)?


texts: Is it OK to have flying leads on a differential pair?

texts:
I'm designing a small daughterboard that contains a microcontroller and a USB port. This board also has a connector to allow it to connect to a motherboard.

What I'd like to be able to do is to have a USB port on the daughterboard so that I can power it up and program it without it connected to the motherboard.

The daughterboard may also contain a USB port so the D+/D- pins are also routed out through the connector.

Is this going to be a problem, having open-ended differential "leads"?

Assume that:

The board size total is 50mm x 50mm, the USB data traces will be no more than 5mm to the board-to-board connector or the USB connector.
The USB connector on the daughterboard may be a more significant distance away, 100mm or more.
The USB connector on the daugherboard has TVS diodes, I don't know if the motherboard has this or not.
The USB on the daughterboard will not be in use at the same time as the one in the motherboard, but the connector and circuit will be there.
Both USB ports will be full speed, USB 2.0
The board is 4 layer with a standard stack up, signal, ground, power, signal. The daughter board USB is on the top.

So basically what I'm asking, is it OK to have this:

simulate this circuit – Schematic created using CircuitLab

Where X1 may not be connected on the "motherboard" side? Or if it is connected, that only J2 is used (but J1 is still present)?

I'd like to avoid, if possible, using a "USB-hub" type chip, only one USB port will ever be used at once, and there is very limited board space for what needs to go on there.


texts: Stability and loop gain of negative feedback systems

texts:
When we look for stability of a feedback system, why do we only concentrate where loop gain is unity and check the phase margin there. The phase of the closed loop system might be passing through 180 but it would still be stable if the phase near the unity loop gain frequency is less than 180. Like in the figure shown below (for negative feedback system), the phase reaches -180 at frequency A but since it is less than 180 at B (unity loop gain) system is stable.

Why doesn't the system gets unstable for frequency A?

Shouldn't the signal Vi  (in the figure) add constructively to signal Vf (inverted twice once due to phase shift of 180 and then due to negative feedback) and grows with time giving unstable system, if operated at frequency A?
I know the negative feedback equations (in figure) and the transfer function getting infinite only for |GH| = -1? But still why doesn't the above reasoning holds valid for frequency A?


texts:
I'm trying to make this circuit (components in question are R10 and R11).  I have two really nice sliders I bought from Science + Surplus.  Problem is, I'm a teensy bit confused on how to wire even regular pots - and these ones have eight (8!) pins each.  I think they're dual-gang sliders for stereo systems, but I can't for the life of me pick out the three connections I should be making.  Which are my left/right/wiper pins (or how can I find out)?

The sliders in question:


texts: Lead acid battery and lead acid battery charger -- specs don't match, but can I use them anyway?

texts:
I have the following:

Lead acid battery

Specs: 12V, 7.2 Ah

Model: Portalac PXL12072

Description: Kind of old, so maybe sulfated, but I won't know until I try to charge it.

Lead acid battery charger

Output specs: 10 Amps max., 14.4 VDC, 144 W max.

Model: Denryo BP-1210A

Description: New. "3-stage high tech battery charger"

The charger manual also contains a table that lists other chargers Denryo makes and their recommended batteries. My charger seems to be for batteries between 12V/30Ah (minimum capacity) ~ 12V/100Ah (maximum capacity). However, at 7.2 Ah, its capacity is below the recommended minimum capacity.

My question

Is there a safety risk to use a 7.2 Ah battery with a charger of minimum recommended capacity 30 Ah?

Similar questions

Charging lead-acid batteries?

This question states,

  The charge current for small lead-acid batteries should be set between 10% and 30% of the rated capacity (30% of a 2Ah battery would be 600mA).

In my case, 30% of 7.2 Ah is 2.16 A. My charger outputs 10 A max., i.e. 0~10 A. But I don't know how smart the charger is to adjust its output.

What can happen if I try to charge lead acid battery outside charger's capacity range?

This is like my question, but it is unanswered.


texts:
I have question about specifically FM radio receiver that use the heterodyne principle:

How Intermediate Frequency, that's fixed in one frequency (10.7 Mhz), works in FM receivers if FM radios need frequency modulation to pass a useful signal?

Does the mixer with local oscillator in a FM receiver pass a bandwidth or just one frequency?


texts: AD9850 comparator problem. How to calculate is frequency?

texts:
I want to convert a sine wave produced from AD9850 (opens *.pdf) into square wave with its inbuilt comparator. AD9850 has a fast comparator with 3ns rise/fall time and propagation delay= 5.5ns.

without accounting the propagation delay , it should work up to 1/(2x3ns)= 83MHz. If I add propagation delay, it will be 1/(2x3ns + 5.5ns)= 43.48 MHz. if I account the same time for settling and flat part of the square wave and some error tolerance, it should at least tolerate around 20MHz.

But it is not what really happens. the output wave is not a square wave higher than 5MHz ( it is more like a noise). The input signal of the comparator is well low pass filtered and is a clean sine wave with around 2v pk-pk.

Is there anything wrong in my calculations?

EDITION: I am using this module with a reliable ground plane:


texts: How to add Lptmr ISR to Interrupt Vector Table for Freescale K60DN board, ARM Cortex M4 Processor

texts:
I am attempting to use the low power timer of the Freescale K60 board. I have an interrupt handler written, and now do not know how to add the address of the handler to the interrupt vector table defined in startup_MK60DN.s.

Forgive me, I am struggling to fully understand interrupts


texts: Determining JFET substitution parameters

texts:
I have a design (see page 3) that uses a JFET to linearize the charge current for a capacitor used as an integrator. I've been using the BSR56, but that's been discontinued.

I am used to looking at MOSFET datasheets to determine substitution parameters, but I am unfamiliar with JFETs. What parts of the datasheet can I compare to obtain the best match?


texts: What happens when you rectify phase cut current?

texts:
Forgive the simplicity of the question, since I'm not a professional, just a tinker with a soldering iron.

Just dancing with the idea in my head, I believe that if I rectify a current that's been phase cut (ie through a dimmer), it will just produce added noise in the output. Is my analysis correct? How would adding a capacitor to filter the output of the rectifier be affected by the modulated current?

For anyone curious, I bought several 50 watt LEDs on ebay along with a rectifier for an LED light rope. The plan is to link the LEDs in series on 120v instead of spending $50 on a 32v power supply. This is totally just for the fun of playing with it. Adding a dimmer was a thought experiment because I like thinking about things. I understand that hooking this fire hazard up to a dimmer probably won't work, but I'm interested in why it won't work. I suspect it's because the capacitor in the rectifier will fail to filter the modulated output once the current being drawn drops below a particular threshold. I'm unclear on exactly why that is or how it would affect the output from the filter.

:Edit:
A circuit diagram drawn by someone who doesn't know how to draw circuit diagrams, by request. See comments.

simulate this circuit – Schematic created using CircuitLab


texts:
I´m running out of ideas here.

I have a device that should always output a 5v signal, with a maximum tolerance of 100 mV (4.95 to 5.05 V).

I´m building a "tester" device. My tester will compare the received 5v signal with a minimum and maximum reference voltage (Uref Min=4.95 V Uref Max=5.05 V )

If my device is faulty I want my tester to emit a signal, this signal will be connected to a binary counter that will be telling me if my device failed and how often it failed.

On the plan below, if I understood it right, the LM139 should be closed (0 V) when my device is =>4.95 V or =<5.05 and open (~6 V) if <4.94 V or >5.05 V. Given that I want a single signal from my LM139, I built an OR-Flip Flop with two transistors (2N2222). Joining the two outputs together was impossible to make it work.

The last picture are the connections I soldered on my LM139, I tried grounding the others inputs but it didn´t change anything, I tried many things but nothing worked I can´t get this guy to work properly...

Observations:

MinV: Below DeviceU (5 V) the output2 will be almost 0 V. From deviceU (4.96 V) the voltage will slowly rise till it reaches DeviceU (5 V) and the output2 will emit a solid 6 V.

MaxV: The voltage stays stable at the output1 (6 V) when I drop the deviceU bellow 4.95 V. Everything above, the input1 will throw almost random values...


texts: Why does the high reverse bias voltage in a PIN diode circuit not damage the op-amp?

texts:
In this circuit designed to measure high frequency light pulses, the 30V high voltage bias input has a direct connection to the inverting input of the op-amp, despite also being connected to the reverse bias PIN diode.
Why (or how) does the 30V bias voltage pass only to the diode and not damage the op-amp input?


texts:
What do you think of this schematic for my Arduino keypad? Are the diodes pointing the right way?
I will make col1 "high" and then check pins row1, row2, row3 and row4 and see if current is flowing through. Then make col2 and col3 "high" and again check if current is flowing through the row pins.

Update:
Ok so I´ll change the direction of the diodes. In my code I will declare my rows as inputs and my columns as outputs. Then I will set all columns to "HIGH". To check which keys are pressed I will set col1 to low. There should be current flowing if any key in that column is pressed. I will then check my rows if their state has changed to "LOW". I will repeat the process for col2 and col3. The anti-ghosting diodes should still work. This way it could work right?


texts: Charging 3.7 V Li Ion battery with 5 V DC

texts:
I am trying to create a charge circuit to charge nominal 3.7 V (range of 3.5 V to 4.2 V depending on state of health) li-ion battery from 5 VDC. I don't want to use specialized charging ICs if possible.

I have tried using discrete BJT to do it. But the overhead from the 5V VDC is not enough.

I figure there must be a way to do it since most portable charger are 5V output into the phone's 3.7 V.

Do I need a boost converter in between so I can create enough overhead to charge a nominal 3.7 V battery (since the max is 4.2 and if I use BJT, there is some voltage losses and I only have 5 V). I am trying to get at least 100 mA of constant current into the li-ion battery during charging stage.

Thanks!


texts: How to bypass S-type connector for connecting a servo to an MCU/SoC

texts:
I have a TowerPro SG920 servo that I'd like to connect to an MCU/SoC (Pi or Arduino).

However, the servo has an "S-type" connector (see pic above) and its 3 wires (red, black and orange) are bound/glued/stuck together. In reality I need the three wires to go to 3 different locations, so can I just cut off the connector and pull the wires apart? Or does some kind of special care need to be taken?


texts: Is the Wien Bridge oscillator essentially a resonant filter?

texts: According to chapter 21 of Electronic Principles(8th edition), the Wien bridge oscillator uses the Johnson-Nyquist noise from one of the resistors as the startup voltage. It selects for a desired harmonic and amplifies it. Some schematics show a Wien bridge oscillator using a tungsten lamp as a source of resistor noise. Now is this also true for the phase shift oscillator? This seems quite different from other oscillators which use the rising voltage on a capacitor connected to the DC power supply to build up oscillations. Part of this question is based on the fact that neither the Wien bridge oscillator nor the phase shift oscillator have inductors.


texts: How to handle multiple GND, and +5v vs VCC

texts:
I'm starting my hobby electronics journey.  I know how to read all the symbols and know how to solder.  But I'm a bit confused with reading schematics that have multiple GND and the difference between VCC vs +5v.

Please take a look at this schematic.

Where do the ground points physical connect to?
Do they symbolize the negative terminal on power source and therefore all GND points should connect to each other some how?
There are VCC points and +5v points. Are they the same? If not, where do the wires connect to?
Which power adapter can I use to power this station? THe schematics have +5v.  If I got a laptop charger that was 19v 60watts 4amps, how would I use it to power the +5volts which is less than 19v of the charger?
Also from one power adapter how would it get 15v ac and 9v ac power from?

I'm trying to replicate this soldering station. here.


texts:
I have a U shaped magnet (like the one we used to see in school, half red half blue) that I want to make out of it an electromagnet by winding around it a 0.5mm diameter insulated copper wire, covering it from end to end, with n layers ( n still being undetermined).

The goal is to rise some metal off the ground, the magnet being suspended over it in the air; once the circuit is running, the electromagnet’s field will get intense and be able to lift the weight, and once turned off again, the metal will fall back to its place due to its weight.

How would I get the best magnetic attraction out of that system? I’m working on it for a university project, so I want something to attract the judges with.

Any advice would be extremely welcomed.


texts:
I've just bought an illuminated sign that contains 25 orange LEDs and runs off two AA batteries. I've opened it up and the LEDs appear to be wired in parallel, but I can't see a resistor. (I assume a resistor is unnecessary here due to the number of LEDs running off just 3v?)

I'm going to replace the batteries with a mains adapter, but I would also like to increase the LED brightness if possible, as they are quite dim at the moment. How could I accomplish this?


texts: Tape recorder head has only 2 pins, which one is for grounding?

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I am trying to make my own cassette adapter that will help me play my music on my iPod through my car stereo system that supports only cassettes. For that I've bought a 3.5mm earphone jack and a cassette player head unit. Here's the layout:

As you see, the head unit has only 2 pins. But the jack has 3 - one for left and right each and one for grounding. Now what do I do in this case? How do I connect three wires into to pins on the head unit? Thanks in advance.

ADDED

Here's the head from the other side


texts: Dual pump system with a counter that changes between duty pump and standby every few times it runs

texts: I have a dual pump setup controlled by 3 floats. The lowest float stops the pump/s then the next one starts the pump selected for duty. The third float starts the other pump. The pumps can be changed manually to select which pump is on duty but I'd like to have it change every 4 times it runs. I'm just at a bit of a loss at trying to find the right style of relay/counter to make this possible. I have thought about using a timer to change them but can't see how it would ensure even running of both pumps as the duty pump.


texts: Emitter-follower as regulator with low voltage difference

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I'm trying to figure out emitter-follower voltage regulator for my solar panel. Panel outputs almost 7V on open circuit and 1.2A at short circuit. I want to use it as phone/powerbank charger -> 5V output.

I would like setup like this (but with floating input voltage):

Since input voltage will vary anywhere up to 6V (under load) I think standard regulators won'tdo it for me  (high voltage drop, doesn't work near 5V input).

I have some question I couldn't find answers to though.

In emitter-follower setup is it possible to have input voltage lower than zener diode voltage and still get some output (even if the output would be lower than 5V)? Or is the transistor closed once input reaches zener diode voltage?
Is there some other thing I need to consider besides zener diode voltage (which should be 5.6V for my setup) and bipolar transistor Ice (which should be at least 1.5A for my setup)?
Is it even feasible? If "yes", what transistor would you recommend me? What should the resistance of R1 be? Does it even matter (100 ohm, 1k or 100k)?

I think I'm a little experienced in electronics but it's still a hobby for me and I learn something new almost everyday.

Thank you for your time and possible answers.


texts: Understanding Schmitt Trigger from datasheet

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I've asked this question before, but I don't think I worded it correctly, as I got answers to a question I didn't intend to ask... So I'm giving it another shot:

I am having some difficultly understanding the values described in this product sheet for the SN74AHCT14 Schmitt Trigger Inverter:

http://www.ti.com/lit/ds/symlink/sn74ahct14.pdf

Vcc will be 4.5V.

If I understand correctly, this trigger is an inverter, so a high input results in a low output.

If the input is at 0V, I expect to get a high output. As my input slowly increases from 0V up to 4.5V, what is the lowest voltage that may cause the trigger to begin outputting a low output? And what is this value denoted as in the product spec?

I am not interested in what will guarantee a low output, but instead, what is the earliest value that may cause the trigger to switch to low output.

Thanks for your help!


texts: Lithium-ion battery charger circuit design

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For my project I need to charge a 2s, 7.4V LiPo battery pack from an 18V 10W solar panel. This would not be an issue if I was able to use ICs such as the BQ2057WTS, but I am required to do design a circuit in place of the IC using parts lying around lab (Transistors, voltage regulators, op-amps etc.).

LiPo batteries require careful charging using a method called CC/CV (Constant current/ Constant voltage) where the battery first charges with a constant current and rising voltage to a specific point and then undergoes constant voltage charging where the voltage is kept constant and the current is changing until the battery is fully charged.

I am currently struggling with the design of this specific circuit in place of the IC to ensure the battery is not damaged, any advice would be greatly appreciated.

Update: My supervisor finally agreed to let me use the arduino ATMEGA328P microcontroller to aid with the design. Therefore, am I correct in saying that I can make use of the ADC channels to measure the voltage of the battery and control the separate CC/CV accordingly?

____________________________________

Battery - Ansmann 7.4V, 2600 mAh.    Datasheet here
Nominal charge 0.5C, max charge 1C, endpoint charge 0.01C.
Vmax 8.4V +/- 1%
Temperature: Charge 0 - +45C, Discharge -20 - +60C, Storage -20 - +40C


texts: What's the name of this component (Mechanical Switch?)

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I am searching for the name of this electronic component (and a place to buy it):

It is some kind of mechanical switch.
When nothing pushes against the platic triangle, the switch is closed.

I have a couple of toy guns with this component, and this component always breaks.
(The part with the plastic triangle breaks off).
I want to replace it and fix the gun.


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Right now I am using Vivado design edition which I got for free with my diligent basys 3 FPGA.  I am currently looking to upgrade my card to Nexys Video which has a lot more features.  http://store.digilentinc.com/nexys-video-artix-7-fpga-trainer-board-for-multimedia-applications/

It says on their site "Design Edition licenses for Vivado are not yet available to purchase with the Nexys Video. We are working to get them in stock and hope to have them for sale soon.".  It also says "The Nexys Video is compatible with both ISE® and Vivado® toolchains. It is supported in the free WebPACK™ versions of these two tools so designs can be implemented at no additional cost." Which is good since I am not going to pay for a full vivado license since this is just a hobby.

I then looked at this comparison table between vivado design edition and webpack.  http://www.xilinx.com/products/design-tools/vivado/vivado-webpack.html

The webpack edition seems to do everything design edition does except that it only works with certain cards which is not a problem for me.  So why then would digilent need to offer design edition with the cards if webpack does everything for that particular card anyway.  What are the differences?


texts: Rigging an MRI machine with club speakers and lights

texts: I'm using a magnetic resonance imaging (MRI) machine to fMRI trial subjects while they experience club-like conditions. This means I need loud, high-fidelity speakers, flashing multicolored lights from multiple directions, etc. Big speakers usually means big magnets, obviously a problem in an MRI machine. Any ideas?