texts: Determine resistor values when designing astable multivibrator with BJT

texts:
I want to design an astable multivibrator with a frequency of 1kHz and duty cycle of 40%.
My circuit is like this:

Now,all the references I have tell me how to chose the values of R3,R4,C1 and C2 according to the formula of duty cycle and frequency. But how do I chose R1,R2,R5,R6?
I have a variable power supply of 0V-25V.I have two models of BJT available, 2N3904 and BC108.


texts:
Based on the VSK-S25 datasheet which states the holes to have a diameter of 1.5 mm,

I used the following values in EAGLE

When the PCB is made, it turns out that the pins of VSK-S25 are too large for the pads. Should we have used 0.059 inches for Drill rather than Diameter?


texts: Using an AVR timer to generate a 38 kHz signal

texts:
I need a 13 microseconds delay for transmitting IR at a 38 kHz carrier wave. My chip (ATtiny84) is running at 8 MHz. I cannot figure out what's the problem is in my code:

void send(long microsecs)
{
    TCCR0B |= (1 << CS00); // Enable Timer 0 - No prescale

    while (microsecs > 0)
    {
        // 38 kHz is about 13 microseconds high and 13 microseconds low
        PORTB |= (1 << PB2); // 3 µs
        TCNT0 = 0;
        while (TCNT0 < 104);

        PORTB &= ~(1 << PB2);   // 3 µs
        TCNT0 = 0;
        while (TCNT0 < 104);

        // So 26 microseconds altogether
        microsecs -= 26;
    }
}

The delay (104 clock cycles) sums up to 13 microseconds @8 MHz and the while loop should hang up the code for the required time period, but it's not working.

But

When I replace this:

   TCNT0 = 0;
   while (TCNT0 < 104);

by this:

_delay_us(13);

everything works fine.

If I'm doing something wrong, please point out.


texts: heat sink solution for light source around 1000°C

texts: I'm going to use a infrared light source IR12k which can reach 975°C for my design. However, I'm not sure whether I can solder this light source with cable whose other end is soldered with power board. This is because the temperature of the light source is obviously above the melting point of the solder tin. My concern is that the solder joint may get loose or melted when the source light is working. If so, is there any safe heat sinking solution that can avoid the melt of solder tin in this situation?


texts:
How does the compile know that the VHDL for component ND2 is a NAND gate?
Its just a name ND2....


texts: LM386L does not amplify the microphone signal

texts:
I've encountered a problem. I recently bought a condenser microphone and I wanted to have some fun, so that if I said something into the microphone, I'd hear myself in the small 8 Ohm 0.5W speaker.

I have used an LM386L amplifier and there seems to be no sound at the output. It seems like it's not amplifying anything at all. Here's the circuit on the breadboard:

What I have basically done is:

I took an output from the microphone and put it on pin 3 of LM386L.
Pins 2 & 4 are all connected to ground.
I used 10 uF between pin 1 and 8 to obtain a proper gain.
On pin 7 I used another 10 uF capacitor.
Pin 5 represents the output of the amplifier, where I put 100pF ceramic capacitor in parallel to the 600uF electrolytic capacitor and 8 Ohm speaker to get rid of all unwanted frequencies. 600uF capacitor should get rid of any DC voltage.

When I talk into the microphone, nothing happens although when I connect it to oscilloscope, I see a voltage, so the microphone works. I'm powering it with 5V.

If anyone knows the solution, please help me. And do not mind the soldered pins on the female jack.


texts: Does somebody have a schematic for a stereo electret condenser microphone?

texts:
I’m trying to use a Cmoy headphone amp (built around an OPA2227P chip) as a hard-wired in-ear-monitor.

I bought a stereo electret condenser microphone from Jaycar this afternoon, but I can’t get any response from it when plugged into the amp.

The headphone amp works if I plug my iPad into it.

I’m assuming the microphone needs it’s own power source or a preamp. I need advice on my next step in making this work?


texts: Microchip device support - MPLAB Snap supported or unsupported devices list

texts:
Need to program and debug PIC and AVR MCU's so MPLAB Snap looks to be a very attractive option however:

"it supports many of Microchip’s newer MCU offerings but not some legacy products" - Microchip

Maintaining a list of all supported products is too hard maybe, at least devices are not supported is known, I guess?
How can I determine if a device is not supported?
Is there like a list?


texts: sync signal on parallel DC/DC-Converters

texts: I am currently designing a circuit to drive a high power laser-module at 12V/40A. I found the idea from Marco Reps https://github.com/marcoreps/laser_driver very inspiring for my design. Since the power to drive the laser is so high I decided to utilize 2 Converters instead of 1 module to save costs because DC/DC - Converters at 500W are kind of expensive. I found the I6A4W02033V from TDK which can supply 20A at 3,3V to 15V. These converters already have a sync option so I think it should be possible to parallel them. The Datasheet states https://product.tdk.com/info/en/documents/spec/dc-dc-converter/i6a4w_spec.pdf that one converter can be configured as master by connecting its MS pin to VIN and connecting SYNC from the master to the SYNC from the slave device. It also says that the SYNC signal from the master can be inverted by connecting it to GND instead of VIN. I had the idea to invert the signal to reduce noise on the combined outputs since in my theory the ripple voltages of the converters should theoretically cancel each other out as they are phase-shifted by 180°. Is this approach possible to reduce noise or do I miss something there?


texts:
I wonder if the CR2 gives much more usable energy than 2x LIR2450. If my numbers are right, the CR2, typical capacity is 800mA (to 2V), so the amount of energy is around 2J (2.5 * .8). On the other hand, the LIR2450, has a capacity of 100mAh (to 3V), so the amount of energy is around 0.37J (3.7 * .1) each - or 0.74J for two.

However, the volumes of the two are roughly the same: 2x LIR2450 is 4524mm^2 whilst CR2 is 4595mm^2.

Is my analysis correct?


texts: Inject 5V bias power ("fake" phantom power) for microphone (ModMic)

texts:
I've recently bought a ModMic4 for my PC, but the signal level is very low and have to amplify it quiet a lot digitally, which introduces ton of white noise and I have to use noise supression which degrades the overall quality. I would like to get this microphone to it's full potential.

I've read that the ModMic requires a 5V bias power to have correct output levels. It seems very few PC sound cards can supply this on the mic input. I have an ASUS Xonar U7 MKII and also tried the Creative BlasterX G5 and my onboard Realtek audio. Neither of them worked well. I could purchase the official ModMic card, but I would like to keep the Xonar which has a better headphone amp for my DT 770 and use it's input.

Is there any way to add a power injector to the system? This should be something like a middle man on the Mic wire, and could be powered from USB if I'm not mistaken.

Mod: I've found the following electret microphone powering circuits: Powering microphones Which one of these would probably work?

Mod2: also found this thread here on StackExchange for battery powering  microphones: How to provide power to a lavalier microphone? Would these work with my setup as well?


texts: This is going to sound like a childish question as it is not a very long one, but is there anything like a apa106 led or at least follows the same protocol coding wise that is more smd style and smaller, not like the ws2812 (i cant think of the full name) led. Smaller.


texts: This is from an assignment. I don't understand how they came to the answer shown, can you please explain?


texts: Depassing 15V on Operational Amplificator?

texts:
So in the book it says we can obtain the following relation using negative feedback

(Out Voltage)=1+ R2/R1  (In Voltage)

The out voltage can depass +15 V , How can this be possible?


texts:
I'm trying to create a charger that knows how to switch between OTG and charging mode. The OTG side is working, and my Samsung S4 goes into charging mode. However, charging is really slow. It even loses charge, even with the charging indicator on.

There are two things that do concern me about the schematic I came up with:

A diode is used on the Vbus line, causing my 5V supply to become a 4.3V supply. However, current is coming back as it should, at 760mA
I did not follow the S4 charging specification, shorting the data lines, adding a 10k resistor, and grounding the connection

I placed my order of 15 PCBs, and cannot exactly place a new order with new fixes. What's a good workaround for my current situation?

Some things I looked up due to the current situation:

Samsung S4 charging schematic: http://www.obddiag.net/usb-power.html
Maxim's "Charging Batteries Using USB Power": http://www.maximintegrated.com/en/app-notes/index.mvp/id/3241

Edit 2/5/15:

I modified my circuit a little bit, so that my attachment does not need to worry with the charging specifications of different devices.

Would it work if I:

Used a switching regulator to raise the voltage up from 4.3v to 5.0v rated for 1.5mA, and
Used a USB multiplexer so that my circuit can support different charging specifications, while still fully functional for USB-OTG devices?
I have attached a schematic for reference:

The chips I used were:

USB Multiplexer: http://www.ti.com/lit/ds/symlink/ts3usb221e.pdf
Switching Regulator 5V1.5A: http://www.ti.com/lit/ds/symlink/tps61020.pdf
Solid State Relay: http://www.ixysic.com/home/pdfs.nsf/www/CPC1017N.pdf/$file/CPC1017N.pdf


texts: Gain deficit and phase margin at crossover

texts:
I went through an exercise of the following specifications:

A voltage mode buck converter working in CCM mode works with:

\$V_{in}\$ min = 10V,
 \$V_{in}\$ max = 20V
\$R_{load}\$ min = 2.5 ohm
\$R_{load}\$ max = 50 ohm
L=75uH,
\$r_l\$ = 100 mohm (series resistance of the inductor)
C=220uF
ESR=70m ohm.

The PWM block using 2V peak to peak

The frequency of switching Fs= 100kHz

The question is, what is the phase shift and gain deficit at crossover frequency \$F_c = 5kHz\$?

I have simulated the model, and I have found the following approximative values, G=-8.75dB PS=-158°

In the other side, the other found G=-9.2dB and PS=-146°


texts: Placement of MOSFETs in switchable voltage divider for voltage measurements

texts:
In my battery powered application I am using a switchable voltage divider to not drain the battery. I have seen switchable voltage deviders in two versions:

MOSFET at the bottom
MOSFET in the middle

The left version seems to be better from my perspective because one does not need to take the voltage drop across R3 into account for the level of the enable signal.
What can be the reason to put the MOSFET in the middle and are there situations when one version has to be prefered to the other?

simulate this circuit – Schematic created using CircuitLab


texts: I am getting 90 volts in one line, 140 in the other and 20 in my common line. Why does this happen?

texts:
I am getting 90 volts in one line, 140 in the other and 20 in my common line. These overhead lines run to my farm yard cattle water trough.

Why does this happen? They say it is because I have a loose connection somewhere in my common line. Why does this cause the volt fluctuation in all of the lines?


texts: Positive and Negative Voltage Regualtors

texts:
I was wondering whether I could use a negative voltage regulator, specifically a 7905, as a drop-in replacement for a positive one, 7805.

On closer inspection of the datasheet, I realized that pin 1 is the most positive, pin 2 is the most negative, and pin 3 is somewhere in between.

P.S. Worst-case scenario I can simply do a quick and dirty DIY regulator with a zener, op-amp, and a transistor.


texts: 3-phase power calculation when phase to phase voltages are different

texts:
I have a 3-phase power supply rated at 230VAC per phase. However, the phase to phase voltages are not equal. Suppose \$V_{RY}\$, \$V_{YB}\$ and \$V_{BR}\$ be the three phase-to-phase voltages between the R-Y, Y-B and B-R phases respectively. I also have the measurements of the currents for each phase: \$I_R\$, \$I_Y\$ and \$I_B\$. These are all RMS values. I am applying resistive load on each phase, so the power factor can be considered to be 1.

How do I calculate the total power consumption of this setup? I do not know the load resistance values (and they may be variable). The three voltages can be considered to be phase separated by 120 degrees from each other. However, the three phase to phase voltages are not the same between each pair of phases.

simulate this circuit – Schematic created using CircuitLab

The typical formula that I see either assumes that the load is balanced, or that the phase to phase voltages is the same. For me, neither is true. If an exact formula for this is difficult, I can manage with a good guideline/rule-of-thumb formula for calculating the power.

PS: The power supply is the mains power supply, but due to poor distribution/load-balancing etc. the voltages vary substantially between each phase.


texts: How to find the voltage of a capacitor in a Op-amp + RC network?

texts:
I found this practice problem online which asked to find the voltage across the capacitor as a function of time. The circuit is:

My intended approach is to first find the initial condition when the switch has been grounded for a very long time. Then find the final condition when the capacitor is at equilibrium when the switch has been connected.

To find the initial condition, I'm trying to do nodal analysis at the top right corner (right after the 4 kilo-ohm resistor.

I know that the voltages from the two terminals of the op-amp are going to be the same(assuming ideal op-amp as given in the problem). Since the wire connecting the positive terminal of the op-amp is grounded, the node potential at the negative terminal is also zero volts. As a result, the current through the bottom 10 kilo-ohm resistor is zero amps. By KCL, we know that no current can be flowing into point between the 10 kilo-ohm resistors which means that there is no current flowing to the top right node? So is initial condition of \$ v_o = 0 \$?

I would check but the website didn't provide an answer key

Edit: After doing some work to find out the voltage across the capacitor as a function of time.

We have \$ V_c(t=0) = 0 \$. Now looking for the equilibrium voltage when the switch is closed, we know that after a long time the capacitor will look like short circuit. Therefore, the voltage across the capacitor is the same as the voltage from right before the 4 kilo-ohm resistor to ground.

Let's find the voltage by doing nodal analysis at the node right before the 4 kilo-ohm resistor.

We know that the voltage at the two terminals of the op-amp are now 6 volts (since the switch is closed).

KCL at the node right before the 4 kilo-ohm resistor(let's call that node e):

$$ \frac {0 - 6}{10} - \frac {6 - e}{10} = 0 $$
Solving for e, we get that e = -12 volts.
So, using our voltage formula for capacitors:
$$V_c(t) = V_c(0) + (V(\inf) - V_c(0))*(1-e^{\frac {-t}{RC}})$$
Substituting in our conditions that we found:
$$V_c(t) = -12 + 12e^{\frac {-t}{RC}}$$

Now it's only a matter of find the resistance seen by the capacitor. To me it seems that all the resistors are going to be in series with one another so the R should be 24 kilo-ohms. However, isn't current also capable of moving into the op-amp from the "out" terminal? How should I go about finding the resistance as seen by the capacitor?


texts: Is it safe to use a bridge rectifier at (up to) its rated current, at DC?

texts:
I'm looking through my local components distributor's online catalogue, and bridge rectifiers are significantly cheaper for a given current rating than individual diodes. I'm likely to need two or more diodes anyway, and it's okay for them to be connected at one side or the other, so I'd only be "wasting" half the bridge and not three quarters of it.

But: is it safe to "rectify" a DC input? My intent is to protect string(s) of solar panels from reverse power, so the individual diodes in the bridge would be forward-biased for hours at a time. Do hot-spots form in the junctions if the input frequency is too low? Presumably a 35A bridge has big junctions; if it's safe to pass those 35A through that big junction for 10ms at a time, every 20ms (50Hz AC input), to me it doesn't necessarily follow that the junction can safely handle 17.5A (or anything roughly half of 35A) continuously, for similar sorts of reasons that you can't just parallel BJTs without adding emitter resistors. I've just had a look at two random datasheets and there's no hint of any time dependence in the maximum average forward current. One example: the KBPC35xx series

Actually this question applies equally well to individual rectifier diodes, it's just that bridges have so much higher current ratings relative to the package size that I'm more suspicious in that context.


texts: I am searching for the IV curve of a backward diode but couldn't find anything, any help?


texts: Individually modulate two lasers diodes using sound - while using the same power suppy and preventing signal "bleed over"

texts:
I'm trying to individually modulate two lasers diodes using the same power supply.  The modulation for each laser module is created by the left and right audio channels.  Is there a way to do this using one power supply? Here's a little circuit idea I came up with but I notice that the left and right channels (signals) may "bleed over" into each other is there a way to prevent this "bleed over" so each laser is modulated by just one of the audio channels but still have the ability to use the same power supply?

See circuit idea along with website I got it from

Website I got the idea from http://scitoys.com/laser_communicator.html


texts:
The standard way to calculate the speed of information (current/voltage, EM wave) through a dielectric medium (like PTFE or fiber) is to determine the relative dielectric constant, and compute the velocity factor.
You could use this information, theoretically, to calculate the delay between a signal sent over CAT-7 from New York to London.
However, these properties are microwave/high-frequency properties. How is the propagation speed of information calculated for low-frequency EM waves? How long does it take my DC source to send information around my circuit? How long does it take a battery to turn on my device?
OP Edit
When I asked this question, I wasn't careful to put my question into words. The real question is about what the frequency component at 0 Hertz even means. How long do I have to wait to measure it? What does it mean to use a DC meter to measure voltage and current? Why is DC special relative to all other components of a waveform. I ended up providing my own answer because I realize that the answers to my question (rightly) understood me to be asking a different question.


texts: Ni-Cd battery voltage indication of 100% charge

texts:
I have a Ni-Cd battery of 1.2 V.

What is the voltage when it is 100% charged and for 0%?

What does that 1.2 V indicate?


texts: Simple power on delay for 3.4v-5v serial device being powered by 5volt VCC

texts:
What I am trying to do
I am trying to build the most simple as possible circuit to give a 3.4v-5v serial device a 1-2 second power on delay from the embedded Linux device running at 5v that it is connected to directly to an onboard serial bus.
I have found lots of examples of power-on delay circuits, some with transistors, some with MOSFETs, some with just a capacitor and resistor. I'm not sure what I need to use.
WHY?
The serial device sends out a message as soon as it has power, the embedded Linux device aborts its boot sequence if it gets a serial message within the first second of power.
What I think would work, but I am not sure, so I would like help
From what I have read, I should be able to create the power on delay with a 100mf capacitor and a 33K 1% resistor. The capacitor will take about 2000ms to reach the power on voltage (3.4v) with the 33K resistor.
I have a basic understanding of how capacitors work. But, the part I lack the proper knowledge of is, once the capacitor hits 3.4volts, does it stay there? Or does each discharge cycle from the capacitor take 2000ms? If the latter, could someone point me in the right director for a circuit design that would provide steady power at 3.4-5v with a 2 second power on delay from a 5volt power source?
Thank You!


texts: WS2812b interference and bootup behavior

texts:
TL;DR: how can a slowly rising power supply voltage on an arduino crash the WS2812bs connected to it? How can I protect a signal wire even better from electrical interference?

This my question in a nutshell. For those interested, I provide some context below:

Summary of my setup:

On my Tomos moped I use a 12V lead acid battery to power two arduino pro micros and some WS2812b leds. The battery is not yet connected to the dynamo but its negative pole is connected to the frame which is also the ground of the ignition coils. I glued a 5V buck converter to the frame to power the leds. This 5V travels to head- and taillight arduinos alongside the 12V line from the battery. In the head and taillight I use a separate circuit involving an AMS1117-5.0 regulator with some filtering caps to provide a clean voltage to the Pro Micro mcu. I connected the WS2812bs with a 390 ohm resistor as close as possible to the arduino. The two arduinos have their Serial1 hardware pins connected with a shielded wire with the shield connected to ground. In my previous setup I used I2C for communication between the two MCUs but this was too sensitive to interference as this would crash the arduinos unrecoverably without toggling power. With serial connections there is still interference (wrong messages arrive at the arduino because of voltage spikes coming from interference from the ignition). However, it doesn't crash the arduino, so I can kind of live with this as I can resend messages.

This is the PSU circuit feeding the arduino:

Bootup problem:

The voltage coming from the AMS1117 seems to rise very slowly and the WS2812bs show very weird behavior (turning random colors at bootup and failing to pass the signal after the some led in the array). Also the led on the pro micro turns on slowly. After bootup I delay the arduino some seconds so it doesn't communicate with the WS2812bs yet. But it still happens. After I turn the 12V power on and off 20 times it suddenly works perfectly and remains to do so. When I connect the arduino to a powerbank before I turn on the main power from the battery everything runs smoothly all the time. This is all without the engine even running. Tips on how to make the setup more resillient to this problem are very welcome. I was thinking of removing the TVS diode, 20 ohm resistor and 1mH inductor. Also, maybe I should connect the power to the WS2812bs through a transistor controlled by the arduino or even a simple manual switch I turn on a few seconds after I turn on main power, but the latter would just be manually handling the problem all the time instead of actually solving it.

Interference problem

This is when the engine is running and especially when it's revving up. Even though the signal wires are protected by shields connected to ground and ferrite beads, they pickup interference which distorts the messages. When I was using I2C for communication I also tried using a low pass filter consisting of a resistor and capacitor, to no avail in that specific situation. As a next level step, I was considering switching to RS232 drivers since the signal is protected better because the pumped voltages are more immune to interference. The other end would be to just handle the interference in the firmware by using some handshake protocol or sending hash codes. But the latter seems to me as a cumbersome workaround just to not handle the actual problem. Ideas?


texts: Switching current source ~1 μA — how to switch off quickly?

texts:
I would like to have a precision current source ~1 μA loaded by a resistor ~100k and a voltage source. Also I would like to switch on and off the current. The problem is that when the transistor switch turns off, since the current is very small, it has a trouble dissipating the charge collected in the channel in the case of a MOSFET or in the base in the case of a BJT. As the result switching off time is very slow. Is there a quick solution?

Upd. I need to switch off the current, not just shunt it to the ground.


texts: can't remove a pad outside the board in ALtium designer 2016

texts:
i accidently placed a pad in my pcb layout outside the pcb box. but now i cant remove it.

could you suggest a method to remove it?
i use altium designer 2016.


texts: What are non-reciprocal bandpass filters?

texts:
I am not an electrical engineer. I have come to know about a term called as "Non-reciprocal Bandpass filters" which seems to be useful to me.
Here are some links to the papers (unfortunately there is no proper citation to find definition of the term)
link1
link2
link3
I would like to know if they are nothing but a type of isolator. Are these devices discussed in any book?


texts: How are numbers with decimal point handled in an MCU?

texts: Please tell me how do MCUs handle decimal numbers like '23.3', '3.24' etc? How is it stored in a memory register? I know that I have to use float data type when handling these numbers while programming. But actually what is happening inside an MCU while handling these types. Also tell me how do MCUs without FPU unit handle Float datatype.


texts: I have read about fading of signals , and I have notice that the major cause of fading is multipath , but I have ask myself , what about attenuation , noise and free space loss , all of these make the power of signal be smaller , so my question is , why we emphasize on multipath when we discuss about the causes of signal fading ?


texts: Do the photocouplers on this module have any possible purpose?

texts:
I purchased a number of these relay module boards off AliExpress. They consist of the following

16x relays, 12 volt coils
A LM2596 setup as a buck converter
2x ULN2803A darlington arrays
16x 817C photocouplers
Header for inputs (current sinks)
Terminal for DC voltage input

There are some LEDs on the board as well but they don't really have any function other than convenience of display.

When I purchased these, I had some ideas about how they work. However, what I discovered is there is a terminal (blue) labeled "VCC" and "GND". If you feed this with 12 volts, the 12 volts is used by the LM2596 to make 5 volts. The 5 volts is actually measured at 4.83 VDC, but that doesn't matter here. It drives the
 the "isolated" side of each 817C via some resistor. The 12 volt input is also carried to relay coil. So when one of the transistors in a ULN2803A pull a relay coil to ground, it closes the relay. Each 817C is normally high and if you sink current from the output pins it closes a relay.

The nominal "+5VDC" rail that is created by the buck converter is obviously not isolated. Measuring with a continuity tester confirms the ground of the entire board is common.

Do the photocouplers on this board actually accomplish anything when wired in this manner? I know they function as a logic inverter, allowing any current sink to actuate a relay. But that isn't really significant, for example a 2N3904 could do that.


texts:
I build a quite lot of projects to learn electrical engineering, and since I was first introduced to what's called a fuse around 2 years ago and I always put one in my high voltage 220V mains for protection, but when I worked with precious LiPo batteries, I wanted to add a fuse for protection.

The problem is that what's written in my pack of fuses is "220V 250mA" here comes the question, what make a the fuse fuse or pop-open circuit? Is it the current rating or the voltage rating?

As I am a student who loves experiments, I went and did an experiment, where I used a 7.4V 1AH LiPo battery which was rated at 20C and hooked a 1 ohm load, theoriticaly I should be able to draw 7.4 A but due to resistance of wiring I was able to  draw around 4 A (used high watt resistor). When I hooked up the fuse (220V 250mA) in series with the load, I was expecting it to pop open, but it took around 1~2 seconds till it popped up, although the rating was at 250mA 0.25A which is way less than the 4 A drawn by my dummy load.

I wanted to know if is this normal for an electric fuse, or my fuse is very bad manufactured? As a side note my fuse works perfectly fine in 220V circuits

I done a bit of research if there is anything called low voltage fuse, found some webpages,but I couldn't understand anything

One of the pages I saw is: here

My fuse type is the normal glass fuse.

this is not my image, source : here

In short what pops a fuse (sorry but is pop the right word to use in such thing?)
Is it the over specified voltage or over specified current or it's the power through it? And in the other side what kind of fuses used in low voltage application like fuses in digital multimeter? Is it the same fuse I have?

Thanks in advance.


texts: Driving LEDs with open collector outputs for Tally system

texts:
I thought it best be start with some context. We're trying to connect two "Tally" systems together - system that turns on a red or green light when a camera in a studio is live or on standby.

The main system we have has a GPIO output (a 2.5mm connector) that seems to be two open collector outputs, one for each LED colour, green and red. The manufacturer provided us with this diagram:

I can get this to work no problem - BUT the LEDs we need to switch are switched positively. All have a common ground, and need the positive supply switched to turn the green and red LEDs on and off.

I've given this a real good go by myself first and doing a lot of research, but the closest I've got is having it work the opposite way. i.e. green light on when its meant to be off, green light off when its meant to be on. I did this by wiring up a 5V source to the open collector (top pin) with a pull up resistor, then wiring that to a MOSFET, but it did the opposite as I mentioned.

This is most of the circuit that we're building, but missing the part that connects the open collector outputs to the Positive supply that drives the LEDs...bit messy, I'm only DIY apologies.

What would be the best way to drive the LEDs? I want to avoid relays and the clicking so if have to go relays, solid state, but would prefer a solution like MOSFETs or similar.

I really appreciate your help and patience.

Proposed circuit:

Supplied by manufacturer:

Products:

Main system: FlexTally - https://flextally.cerevo.com/en/other-functions/lamp-gpio-output/

LED we're trying to drive: DataVideo TD-3: https://resource.datavideo.com/Instruction_Manuals/TD-3_G082060738B1_A6.pdf


texts: What rechargeable battery is suitable for severe frost (−10 Celsius and below)?

texts:
Suppose I want a rechargeable battery for a hybrid electric vehicle like Toyota Prius - one that can power the vehicle traction motor at low speeds. The vehicle would have to operate in a region where −25 Celsius is not uncommon and −10 Celsius is typical for several months per year.

What battery chemistry is suitable for such requirements?


texts:
Suppose I have a capacitor and I want to observe its charge decay over time.  How can I do that without affecting its discharge rate through measurement?

AFAIK a typical voltmeter runs current through a known resistance to determine voltage, but in the process this would discharge the capacitor being measured.  With increasing complexity one could reduce the current required to make an accurate measurement, and then reduce the frequency of measurements, but in the limit the measurements will still drain some voltage.

In the hydraulic analogy it's possible to measure the pressure (voltage) by putting a spring gauge on a piston impinged by the two sides of the reservoir.  No water flows from one side to the other, but we get a constant reading of the pressure.

So is there a meter, mechanism, or circuit that can do that for voltage on a capacitor or other power supply?


texts: Why was a capacitor called a condensor (condenser?) in the early days of electronics?

texts:
I refurbish old tube type radios. I know when I was a child, my father referred to capacitors as condensors (condenser?). I see references to condenser in old manuals and parts lists. I know terminology does change, such as using Hertz rather than "cycles per second" (cps) as reference to frequency.

Does the word condenser have a basis in understanding capacitance?

What was condensed? There must have been reason to use the terminology.


texts: I've designed a simple circuit with three LEDs in series with a matching resistor, all powered by an IC.  I want to make my circuit less susceptible to electrostatic discharge since it will be deployed in an exposed area. I've read that I need to add a capacitor, and perhaps a resistor in parallel but I don't understand where to put these components. If anyone has any advice or resource I could look into, I would love to hear about possible solutions. What components should I add to my circuit to prevent ESD?


texts: High speed data interface for upto 5 meter

texts:
I have to interface two processor boards sitting at a distance of about 5 meters away. The data transfer rate is about 128 MBps (Mega Bytes per seconds) or 1 Gbps(giga bits per seconds).

Which interface can achieve such high data rate full duplex communication?

Thanks


texts:
I'm trying to learn more about electronics. So to do that I decided to implement boolean logic gates in a circuit simulator. So far I have made NOT, AND, NOR and a S-R latch.

I wanted to try connect them together to make a S-R latch with only one input - a momentary switch.

My idea was that if you press the switch, the output of the S-R latch just flips. To do this I figured that if I take the output of the latch and AND it with the input of the button, I could take this signal to either the S or R input of the latch. And then for the other input I would AND the NEGATION of the output of the latch with the button.

Here are the circuits I made:

NOT gate:

NOR gate:

AND gate:

S-R latch:

And finally the full circuit:

What seems to happen is when the momentary switch is pressed, both inputs of the latch are being pulsed which causes it to never flip over to the other state.

What can I modify or add to this circuit to make it work correctly?


texts: How to determine the ideality factor (N) of a diode from the datasheet?

texts:
I have to find Is an N from the datasheet of diodes 1N4004 and 1N4148. I did this by estimating both of these by accomodating a straight line in the log-linear Id vs Vd graph in the datasheet of each diode. Is there a different way of getting to know these two parameters form de datasheet?
Thanks.


texts: Checking EEPROM for corruption / methods to avoid corruption

texts:
When working with EEPROM I'm working on developing methods to expand the life of the EEPROM as long as possible but also checking it for corruption and doing everything I can to avoid corruption upon several occurrences that may happen on a daily basis such as power failure.

What are some methods I can take upon developing to protect the EEPROM on the Controller i'm using?
"Have a plan for power loss during a write cycle. Will your hold-up cap keep things afloat long enough to finish the write? Do you re-initialize the EEPROM when the CPU powers up in case the EEPROM was left half-way through a write cycle when the CPU was reset?" Found at: https://betterembsw.blogspot.com/2011/11/avoiding-eeprom-corruption-problems.html

How would this be possible to check if it was in the middle of a write cycle?

"Don't use address zero of the EEPROM. It is common for corruption problems to hit address zero, which can be the default address pointed to in the EEPROM if that chip is reset or otherwise has a problem during a write cycle."

Is this true?  Is address 0 considered a bad seed that shouldn't be used?


texts:
I have a +5V power supply and need to invert to a -5V supply sourcing about 25mA. I've got an LMC7660 running now. It's ok for the short term, it outputs -4.4V with 100mV p-p switching noise, but that's unacceptible for my long-term needs.

Anyone have any experience with LMC7660 / ICL7660 - like switched capacitor inverters? There must be some better parts on the market nowadays, we've had those LMC7660's in a drawer for at least 12 years. I can probably hunt something down, but figured I'd ask here.


texts: How can I solder this circuit board without breaking it?

texts:
I bought a current sensor (link). I would like to connect it to my project, and I was planning to do so by just soldering on copper wires.

There is a resistor on each side, with blobs of tin on each side to keep it in place. These blobs reach out to the place where cables are supposed to be soldered on.

I haven't tried yet, but I imagine, that if I try to solder on the wires this, the tin blob will melt enough that the position and connection of the resistor will change. Thus the resistance will change and the current sensor is no longer useful.

How should I go about this?

In general I wonder about the construction of this board. If the blob on one example reaches just a tenth of a milimeter further towards the other side of the "resistor bridge", then the resistance will be lower.

On the picture from the website (shown below) the blob is smaller, and it would be easier to solder witout changing the connection to the resistors. However it does not look like the resistance is the same from board to board, with this type of "human" soldering. It looks very imprecise.


texts: Why does these capacitances have no effect on the output of this amplifier?

texts:
Below shows a piezoelectric sensor connected to a charge amplifier:

The text claims that the output voltage Uout is to a good approximation only charge q which is going to be measured divided by the feedback capacitor value Cf.

The text then says the amplification is independent of the capacitance of the sensor and the cable without explaining why.

I dont understand why Cg and Cc have no effect on the output. (?)


texts: Are photoresistors reliable for light sensing applications?

texts:
I've used photoresistors for hobby projects before, such as this one:

http://www.foxytronics.com/learn/electronics/kit-guides/starter-electronics-kit-guide/making-an-led-light-sensor

However, now I'm working on a commercial product that needs to sense when it's dark and I'm unsure of whether the circuit I designed on the above page is adequate. The reason I'm concerned is that in my experience photoresistors have very low wide tolerances (i.e. high deviations in photosensitivity).

If you were designing a low cost circuit that could output a HIGH logic level when dark and LOW logic level when light (or vice-versa), would you use a circuit with a photoresistor like the one I designed, or is there something else that is more reliable?


texts: Does winding a choke inductor produce a transformer?

texts:
I obtained schematics and build instructions for a device which generates low current, high voltage (50-100V) signals. The high voltages are generated from a normal 5V USB supply.

The instructions specify to get a 390µH fixed inductor (the Bourns 5800-391-RC to be precise), and wind magwire around it 16 times. The ends of the inductor are connected to the high-voltage section, and the ends of the magwire are connected to the input signal (0-5V).

This implies that the inductor is acting as a transformer (assuming the instructions are correct). That makes sense, since in some sense there's a winding on the inside (the inductor's winding) and a winding on the outside of a magnetic core. But I've never seen a transformer constructed this way.

If this is in fact a legitimate way to construct a transformer, then (a) how can I compute the transformer's voltage ratio (given that I don't know how many turns are inside the inductor), and (b) how does this actually work electronically?

EDIT: Here's the relevant part of the schematic (from EAGLE).

The part in question looks like a transformer, and is labeled TRANSFORMER in the document. The capacitors are on the "high-voltage" side of the circuit, and the "V+" and transistor on the left are on the "low-voltage" side of the circuit.


texts: I would like to have a router speed controller that can keep constant torque at all speeds. I will be running the router at around 5000 rpm or lower. I tried a triac controlled commercial unit once but it did not have enough torque at the lower speeds. Does anyone have a circuit for a controller that really maintains constant torque or are there commercial units available that really work well? Thank you!


texts: Finding the number of poles in BLDC motors

texts:
I actually have a 3 phase BLDC motor ( The datasheet is not available) with 3 hall sensors. I would like to measure the motor speed (rpm). Therefore I need to know the mechanical revolution or number of poles and the frequency.

How can I find out the number of poles?


texts: CAN0 confustion in Datasheet for ATSAMC21G uC

texts:
I currently narrowing my search for a uC with a CAN controller and a few ADC inputs. One of them is the 'ATSAMC21G' 32bit uC from Microchip.

In the datasheet on p.31 is the table of the pin configuration.  My question: Why are there 4 entries for CAN0 (CAN0/TX->pin33, CAN0/RX->pin34 and CAN0/TX->pin37, CAN0/RX->pin38)? Can I choose between the four pins OR is one pair for receiving and the other for transmitting?


texts: How to ensure a RF module is indeed FCC compliant as advertised?

texts:
Suppose a buyer buys RF modules from China and wants to ascertain that they're indeed FCC compliant as advertised. I'm guessing that this should be a fairly common issue since Chinese manufacturers/suppliers don't have the best reputation in the world, so I wonder if there's any common practice to avoid getting cheated.

Even when the FCC ID can be verified, there are good chances that the parts have been swapped out for junk.
Even though the FCC website has the internal photos, it's difficult to eyeball the discrepancies.

How could the buyer ensure that what they get is what was tested by the FCC?


texts:
I'm trying to build uninterrupted power bank for my 9V 1A router and 12V 0.9A ONU. I have made a circuit Mindmap. But I think I have done some questionable things in it. Such as, I don't know the efficiency of the LM317 based 12V to 9V linear voltage regulator. I think I'm loosing 50% of power during the conversions. So there isn't much power to run this devices and charge the 18650 lithium battery simultaneously.
Joint box means only wire joints.
|<, >| This are diode symbols.
On 2nd mind map the relay cut's off when the battery is changing.

Which one is better than other from the above? What can I do to improve the better one even more?
Is there any good quality diagram exist for this application?
What type of diode should I use, like, zener diode?
Also I want to build this as cheaply as possible. Thanks in advance for the support.


texts: How to make clamping circuit to clamp exactly at 3.3 volts

texts:
I am building a circuit that attenuates the signal and sends it to 3.3V ADC, so I need to limit max voltage to 3.3V. After testing out some circuits for clamping the voltage(various schottky or zener diodes configurations) I found out that they are not really as precise, for example I managed to get 3.5 or 3.7 Volts when applying for example 5 V sine at the input. I suppose for short duration 3.8V is not so bad for ADC, but ultimately it still not a good thing, especially if I leave it like so for a while.

Is there a way to make it more or less precise?
I tried to find some advice on the net and textbooks, but seems like most of the time people don't really care about precise clamping voltage or if they do they promote to use some special input protection ICs (which are good thing, but I just don't have one around at the moment)

simulate this circuit – Schematic created using CircuitLab


texts: Impedance matching headphones and carbon microphone adapter

texts:
I'm trying to convert a regular pair of headphones (audio technica anc-9) with a electret microphone (headset buddy) to a converter box so I can use that setup as a aviation headset. All the information I have found isn't very straight forward and I'm hoping to get some help with a adapter box. I know the headphones have 100 ohm impedance and when I wire them together I get 50 ohms (the aircraft uses mono output). The aircraft needs a 150 ohm impedance. My question is: I figure I need a audio transformer of about 1:3 but I have no idea how to search digi key for the one I need, all I know is I want it to be small as possible.

The next part is that I'm stuck on is the microphone. I know the aircraft is expecting a carbon style microphone so the electret microphone needs to be adapted to work. From what I understand this requires around a 1volt output and I can get the power I need to amplify the voltage from the bias voltage provided from the microphone leads. I have found a diagram posted by Andy aka from this post:

Electret microphone amplifer for general aviation

Will this produce the required voltage? And do I need to match the impedance for the microphone too? Also what would I have to change be able to change the gain of the microphone?

to summarize:

how do I go about choosing a suitable transformer?
Does the microphone also require the impedance to match?
what would I do if the bias/phantom voltage is not 5-7 volts?

Thanks for any help


texts: 2.6 GHz microstrip patch antenna with 100 MHz bandwidth

texts:
I'm trying to design a microstrip patch antenna @ 2.6 GHz. The result I got is good but the antenna is very selective and I haven't been able to increase the BW.

Currently, the BW is 40 MHz and I need it to be 100 MHz (S11 = -10 dB @ 2.55 GHz //**// S11 = -10 dB @ 2.65 GHz). I've tried all the 7 optimization algorithms in CST studio but none of them was able to increase the BW. I've tried everything: modifying the dimensions of the patches, the insets, and the Tx lines, changing the polarization, adding tabs, adding slots into the patches, adding a small gap between the patch and the Tx line, placing the ground plane over the patches and modifying the air gap between them, and reducing the ground plane; but none of these methods have increased the BW in more than 5 MHz.

I can't increase the thickness of the substrate because I am already considering the thickest one I have.

This is meant to be a MIMO 2x2 photonic antenna and each patch is fed by a photodiode, the photodiodes receive their signals from an optical splitter, one patch should be able to transmit any of the 2 signals regardless of the one it gets. So there are 2 channels with central frequencies @2.575 GHz and @2.625 GHz, the BW for each channel should be 20 MHz with a guard-band of 5 MHz.

Here are the parameters of the PCB:

PCB width: 190
PCB length: 70
Distance between the antennas: 71.5
Antenna’s width: 42.5
Antenna’s length: 29.3
Insets’ width: 4
Insets’ length: 7.1
Transmission line width: 3.37
Transmission line length: 20.35
Copper’s thickness: 0.035
Substrate’s thickness: 1.524
Dielectric constant (): 3.67
Dissipation factor (tan): 0.0021

I would really appreciate it if you could tell me the adjustments I need to do in order to achieve a BW of 100 MHz.

I attached the schematic of the PCB and the S parameters I got.

Thank you very much in advance for your help!


texts:
Is it possible to generate AC power by powering an alternator using a DC motor? If you think about it is much easier and better sine wave than a circuit?

Why isn't it used then? What are the drawbacks?

Also, will the loss be greater? I am estimating a 20%-30% loss (even less with better quality equipment ) but I don't really know how to calculate it nor have the equipment need for testing


texts: Controlling a very small DC motor with PWM?

texts:
I have a very small DC motor (from a Walkman), I would like to control the speed from a micro-controller. For that I would like to connect a MOSFET in series and apply a PWM signal to its gate in order to change the speed of the motor.

I have measured the motor's L & R = 4.7mH, 11.5Ohm (Tao 0.41msec).

From running a few experiments with the motor using a bench power supply I can see that it runs well from a voltage of 0.2V up to somewhere around 0.4V - that is all the range I require.

The power supply I have for this is set to 1.8V (used for the digital part of the circuit) so this makes using standard MOSFETs a bit difficult because I can not supply the voltage required for the gate saturation. I bought a few P-channel MOSFETs like this.

So even though I would have thought this setup would work (Vcc -> motor -> FET -> GND) I can't seem to get good resolution over the control and I don't get as much torque from the motor as I used to get when ran from a DC power supply.

I am not sure what freq. I should be using and not sure what other parameters need to be checked in order to make this work as intended. Any help on this will be appreciated.

* UPDATE *
Following Olin's answer I have built the circuit he suggested. I have used a 2N3904 transistor, 180Ohm resistor paralleled with a 4.7nF cap. Attached is the collector voltage when running from PWM code 100 (out of 256). Vcc is 1.8V.


texts: Use external reference for frequency counter

texts:
I recently bought an HP 5316A frequency counter. It has the ability to use an "external reference". Does that mean it ignores its internal clock and uses the external signal in lieu of the clock?

Is it complicated to provide the external reference signal? What is involved?


texts: Modeling Capacitive Discharge Ignition (CDI) Circuit

texts:
I am trying to model a capacitive discharge circuit (see Fig. 1 below), but I'm having difficulty properly coupling the two inductors on the transformer and also estimating the energy dissipated across the air gap between the spark plug. If we apply KVL to the circuit components on the left, noting that \$L_1\$ is the inductance of the primary inductor, then we would get an equation that is completely independent of the secondary portion of the transformer:

$$V_c(t)+R_{L_1}i_1(t)+L_1\frac{di_1}{dt}=0$$
$$\rightarrow \frac{d^2V_c}{dt^2}+\frac{R_{L_1}}{L_1}\frac{dV_c}{dt}+\frac{1}{L_1C}=0$$

Unfortunately this creates an RLC circuit that will simply oscillate back and forth until the energy is fully dissipated from the resister, \$R_{L_1}\$ (this is the resistance of the primary inductor). This does not account for the energy that is being transferred to the secondary portion of the circuit and dissipated across the spark gap. My first question is:

1) Is there a way to couple the two inductors (assuming an ideal transformer) to theoretically account for the transfer and dissipation of energy in the secondary circuit? Or is this something that is only simulated via software?

My second question is:

2) I'm not quite sure how to theoretically model the spark gap. Would it be possible to approximate it as an equivalent resistor (see Fig. 2 below) that would dissipate the energy transferred to it via the capacitor and transformer? And if so, what's the best way to approximate this resistance value? I can approximate the initial breakdown voltage of the spark gap given the gap width (approx. 2.6 mm), and that would give around 8-10 kV for air at standard pressure. But how would I go about coming up with the equivalent resistor without first knowing the current that is being passed through?


texts: What's the best type of tape to cover a pin on a connector?

texts: I have a pin (the flat kind--think a PCIe card) that I need to tape over to block the signal. What type of tapes work well for this? I tried electrician's tape, but it's a bit too thick and stretchy. I thought about masking tape, but I wasn't sure if it's electrically resistive enough for the job. The pin carries 5v.


texts:
Apparently noone ever needed anything like this on the internet because I was not able to find any example, so I hope this will become the reference question.

I need to repeat a vga 800x600 signal up to 15 meters away but can't find any decent reference for this.
The signal is a CCTV dvr output signal.
Commercial VGA repeaters are quite expensive ($160 each) and I'd like to be able to make one on my own.

It seems as if it is not that easy but after all it's an analogue signal, is there not any atmegaXXX chip which can repeat an analog signal on its outer pins?

All I found was examples of very poor graphic quality like below, very far from being a 800x600 color video!


texts:
I found a link http://www.electronics-tutorials.ws/opamp/opamp_6.html that discusses about AC Op-amp Integrator with DC Gain Control

I am wondering how I derive the frequencies (1/CR2 and 1/CR1) ???


texts: main 200 amp circuit breaker, is it really open when turned to off?

texts:
My house has 2 year old service, a main 200 amp circuit breaker at the top of the main box. We had a 4 day power interruption and I wanted to hook up a generator to a 220 volt outlet located outside the house.

Before i would do this i would turn the main breaker 200a to off and trip the breakers on the water heater. I was confused to see when I turned the breaker off (lines were down outside) and checked the resistance between the incoming and outgoing connections on the main breaker, when "on" .2ohms but when "off" 3.0 ohms: it seemed like the breaker couldn't possibly isolate the incoming current from the rest of the circuit breakers.

I even took a light and battery from the input side of the breaker to the output side it lit when the circuit breaker was on, and also lit when it was off, but dimmer.  I continued to use the generator through extension cords to the appliances i needed.

The power is now back on and the main does shut everything down when tripped, but I need to know why the meter doesn't show infinite resistance when the breaker is open! I can't take the chance of having a generator working and have the main power come on at the same time...


texts: Help me decide if this opamp circuit will work as purposed

texts:
please help me decide if this will work:

Primary objective: Amplify 0~3v input signal to 0~12V output signal.

I understand that this whole setup is a bit unusual, since I can simply connect the +input of opamp to 12VDC, and with my resistors' values, 3v input could be amplified to 12V (I'm 80% sure). But nevertheless I want to know if this odd scheme will work? I think I'll have to be very careful with my OpAmp output, which dictates the 3904?

Edit: My most sincere apologies there SHOULD BE a pullup resister between the collector and the 12V, for some reason this slipped through my double check, incredible, I'm new to eagle and the copy paste in it isn't that intuitive.

The resistor has a value of 2K.

Edit #2:

Sorry for the delay but a few things to clarify, apologize again if I overlooked your question, there are too many and I'm kind of really busy:

200mA is supposed to be the current drawing in. This whole setup is kind of to sink current from lower-tier components that will be connected to this interface, so 12v/2K = 6ma isn't what I'm talking about.
The resistor should be 90k/30k, as some of yous suggested, my mistake.
Oscillation: I believe your concerns are quite legit but please be advised  that the input will be mostly "static" voltage signals, meaning it rarely changes more frequently than 5 times per second, so I'm skeptical that it will be that huge of a problem, I could very well be very, very wrong.

Matt


texts: PWM to DC converter with op amp - slowly but steadily rising output voltage

texts:
I assembled a circuit to convert a PWM signal generated by an Arduino to a DC voltage in the range 0..10 V.

I use the 10k-10u RC filter to convert the PWM signal to DC voltage in the range 0..5 V, then the single-supply op amp in non-inverting configuration to amplify it to the range 0..10 V. I adjust the virtual ground and the gain with two trimmer potentiometers.

The circuit is almost working, but it is producing a strange error: the output voltage is rising slowly but steadily (if it is not too close to 0 V). I have included the 100k resistor to provide a path for the bias current, but it had no use...

Any help on how to solve the problem would be appreciated.


texts: current limiter after a voltage divider for op amp input

texts:
I am doing a two-stages amplifier for a very small signal (-+300uV), coming from a radar sensor.

The following two images are taken from application notes.

I know R2 and R3 are voltage divider. 2.5V is required to shift the input signal.

What is the purpose of R5 in both circuits?

Why is it not used in stage 2 at the amplifier A and used in both stages at the amplifier B?

Is it a current limiter? If so, who can I design its value?

Also note that I have applied the amplifier B with LM358 instead of OPA2365 and I sensed a very weak (micro Volt) periodic (10 Hz) oscillated signal and I did not see that at amplifier A. and the difference is clearly the first stage (inverting and non-inverting).

However, the main question is: what are R5 doing?


texts:
im a beginner in coding and I was wondering if I could control an old servo using the Blynk app. I want to control the direction, so it can unroll the screen up and down. We opened the servo to look inside and there was some kind of sensor hooked up to the green and yellow wire. Red and black are power supply. Does somebody know how can I control the motor using an ESP8266 or an Arduino? It runs on 12-16V, 0.7A.

Thank you very much!


texts: TTL Long Distance Transmission Alternatives

texts:
I am working on a system that gets data from a sensor via a TTL connection.  Currently, the data that is gathered from the sensor is sent to another part of the system via a set of modems.  The distance between the modems can range anywhere from a few hundred feet to up to 4000 feet or more.  I'll try to provide a rough schematic:

 ------  TTL  -----   TTL  -------     CARRIER SIGNAL     -------  TTL  -----
|Sensor|=====|PCB A| =====|MODEM A|======================|MODEM B|=====|PCB B|
 ------       -----        -------                        -------       -----

So, my question is this: what other alternatives are there other than the use of modems to send the data from the sensor to PCB B?  To me, it seems using a modem for a single connection is overkill, especially because the modems have to connect to establish a data link (which is time consuming for this application).  I had thought of using a Digital to Analog to Digital conversion scheme, but I am not sure what repercussions (if any) there would be to this at distances up to 4000 feet.  I imagine a direct TTL connection across that distance would dissipate the signal fairly quickly.  Any insight or suggestions (or corrections) are appreciated.

EDIT:  Current data rate is 19.2 kbps. As for the modems, we have actually used two types.  One was a spread spectrum modem and the other was a standard dial-up modem.  There are only two wires (essentially a tip and ring) connecting the two modems as of now and the system is half duplex.


texts: What does the LED blinking on Arduino boot mean?

texts:
When an Arduino (Uno) starts, under some circumstances it flashes the pin 13 LED three times in quick succession, while in other circumstances it does not.

What does the LED blink indicate?

Under what conditions should it and should it not blink?

I think this is to do with the bootloader, but I'm not sure (and searching for "blink" in relation to the Arduino is not helpful). I find that if leave my bench power supply turned on and disconnect/reconnect power with a jumper, the rapid blink happens. The Arduino power LED also cuts out and comes on instantly.

If I turn off the power with the push button (soft button on digital PSU), the power LED on the arduino fades out quite slowly and back in rather faster, and the blink generally doesn't happen if the PSU is off for about 1sec, but the sketch does start afresh from setup(). If I turn off the bench supply, then remove the jumper, reconnect the jumper and turn back on, it blinks. That could be to do with disconnecting, or it could be to do with the time it takes to go through the process. If I turn the PSU off but leave connected, and turn back on after 2 seconds I get the blinks.


texts: Truth Table to check if 4-Bit binary numbers are in the set?

texts:
I know truth tables are pretty easy but I am just confused with this one. I have this question which says:
Question: indicate if a 4-bit unsigned binary number is in the set {1,2,3,5,9,11,13,14} (decimal) or not?

I know there are going to be 4 inputs A,B,C,D and then the output. My question is how am I going to check if the output is going to be true or false for the above question. What should I check in the set {1,2,3,5,9,11,13,14} before writing the output as '1' or '0'?

I hope I made the question clear, I have an exam early morning. Any help would be highly appreciated


texts: How to convert Proteus NC drill file to Altium Designer?

texts:
I've read some articles about how to transfer the Proteus project into Altium project. When I followed their instructions, most steps are fine except when I wanted to generate a netlist from the CAM file, the error pop up says "Netlist Extraction Error: No tools defined in  NC tools table." I know this is probably because Altium cannot recognize Proteus's NC drill file format, so my question is how to generate the NC file from Proteus to Altium.
This is my layer setting:


texts: Arduino uno, control two lights with microphone

texts:
I am new to arduino and other electronic things, I want to try to control two lights on my room using it, I made this a sketch oh how I think the circuit would go, can someone with more experience tell me if it's going to work? or if there is any component I need to add?

Here is the sketch:

Edit
Apologies for not posting a schematic, as I said this is my first project ever on electronics.
This was the schematic that was generated, I hope it's good.
About the microphone problem, the one I was intending on using would be one from my old headset, thought it would work, would it be hard to make an amplifier?
Also wanted to add just one more question if it's okay, if I want to add to the project a speaker and a sd card reader I would not have enough pins for it, is there a way to get more pins? maybe using and IC?

Cheers.


texts: Can I read smartphone batteries gas gauge info with a PIC?

texts:
I'm in a quest trying to find some easy way of having my batteries charge level displayed. I've found it not so trivial as I thought it would be (because any smartphone is capable of doing that). Than it hits me, it must be something to do with theirs batteries.

I've learned some models of battery have one or two terminals for communication to an gas gauge integrated inside the battery package.

So the question is, are those terminals easy to be read? If I decide to use that kind of battery in my project, can I read that gas gauge with a PIC? What kind of protocols are used normally for that communication? Do OEMs give that kind of info?

Does anyone knows where to find that? Any datasheet. I could not find anything actually on the web.


texts: Converting an analog Butterworth filter into a discrete filter

texts:
Here again to ask about another question. This time asking how to convert an analog transfer function to a discrete transfer function using standard continuous to discrete methods.

The application that I am trying to achieve is to have an audio source fed into an arduino A/D then have the output of the A/D fed into the plant then take the output from the plant into a D/A and capture that.

Recap: Audio Signal -> A/D -> Digital Filter -> D/A -> Output

The analog transfer function: a Low Pass Filter Fc = 20kHz

$$H(s) = \frac{1}{6.416\cdot10^{-11}s^2+1.133\cdot10^{-5}s+1}$$

Upon researching about this topic I learned that each continuous to discrete methods are used in different applications, for instance.

Tustin: Used to preserve the frequency response from the continuous function.
Zoh: Used to preserve the step response from continuous
Matched: Preserve the pole and zero locations of the continuous function

etc..

Where I am getting confused is that I believe you should be using the 'ZoH' transform whenever you are converting from continuous to discrete due to the fact you will be adding the dynamics of the D/A. Now, I have read/watched online that you have to be careful doing a 'ZoH' transform, as if you already have a D/A in the system you might be adding the dynamics of a D/A twice. Wouldn't you always have a D/A in the system when doing things like this though?

Guess what I am asking is when is it and is not appreciate to use ZoH, Tustin, and the other methods then and how do I appropriately transfer that continuous function to a discrete function properly.


texts:
Is it a standard in D-shaft, right-angle potentiometers for one endpoint to point the flat face of the shaft to the right of noon, sweep clockwise, and have the other endpoint to the left of noon? And for the corresponding knobs to align the flat face of the shaft with the indicator line?

I'm looking for the right combination of knob and potentiometer for my application. From the user perspective I want a front-panel knob that indicates low at 7:30, mid at noon, and high at 4:30. The board is perpendicular to the front-panel so the pot needs pins perpendicular to the shaft. Before noticing the note "shaft shown in CCW position", I bought this pot (https://www.bourns.com/data/global/pdfs/PTV09.pdf) and this knob (http://www.newark.com/pdfs/datasheets/spc/TA-790.pdf). They look and feel great except for this one problem: the angles are wrong by 180degrees.

I looked around a bit more for alternatives: Either a knob with the indicator line opposite the flatted side of the shaft, or a potentiometer with opposite endpoints (and keep in mind the knob needs to point parallel to the board, not orthogonal to it). So far this seems impossible. Everyone I've looked at seems to be in agreement that this is the standard.

Some alternatives I would like to avoid:

mounting the pot on the other side of the board (there's no space)
using a round shaft with a set-screw knob (it needs to be fairly precise and not change with time)
panel-mount pots

The best alternative I can think of is to use a knurled knob/shaft but I really like the D shaft because it's so hard to screw up alignment.


texts: Adding a +15/-15 V chip on a 0-5 V board

texts:
General Question:

I would like to integrate a specialized chip that requires symmetrical power +15, 0 and -15 V to operate on a 0 V (GND) / +5 V (VCC) board I designed. If possible, I would also like to support 3V – 5.5 V power supplies.

I am pretty sure it should be possible, but I do not know how to do that (I have very little knowledge in electronics) and searches turned up nothing.

More precise question:

The part I would like to use accepts from ±12V to ±22V power supply, so the supply does not need to be exactly 15 V. Also, the part includes an internal precision 10 V reference, thus, the power supply of the chip does not need to be outstandingly stable. The 5 V supply I have on my board is stabilized.

Below are the characteristics of the part given by the manufacturer:

  Supply: ±22V  Input Current, Continuous: 40mA  Input Current
  Momentary, 0.1s: 250mA, 1% Duty Cycle  Common-Mode Input Voltage,
  Continuous: ±40V

I am mainly interested in learning, so any explanation will be highly appreciated. Thank you very much for reading me and for your guidance.


texts: What amp rating of 24vac transformer for LM317T?

texts: I want to know what size transformer for LM317 at full 30 VDC. I know its a 24 VAC center tapped transformer but is 1 A or 5 A transformer best suited for a linear power supply of 1.5-30 VDC?  I will be using a standard LM317 variable power supply circuit with the 2200 uF 50 V smoothing and the 240 ohm drain resistor and potentiometer. I have a homemade oversized aluminum heat-sink that is quite large.


texts: Can I safely reduce a stepper motor's power consumption by applying a PWM to the driver's enable input?

texts:
I have a stepper motor driver breakout board based off the Allegro A4988 chip. I noticed that when the motor is static, it has much better holding torque than when moving. I have a battery operated configuration and a majority of the time the stepper motor is only used to hold a position. The limit setting potentiometer is already on the breakout board so I can't change it with my micro-controller.

Would I able to apply a PWM signal to the enable pin of the motor driver to change the current going into the motor so that I can drive the motor at a higher current level when actively moving and reduce the current for holding position?

I'm mostly interested on the effects a PWM signal will have on the driver circuit's life. Nowhere on the data sheet dose it say you can or can not do something like this.


texts: I have been working for a while with a HC06 bluetooth module along with an Atmega 168A microcontroller and everything was fine until a day ago when the bluetooth transmission just went off. Data is being sent along with the correct protocol and I discovered that transmission ocurred only when I place a finger between the TXD and RXD pins of the module. I have tried to vary pull up resistors, baud rate and capacitors between VCC and GND but only the finger trick seems to work. What could be the problem?


texts: I have an Android tablet and have it fixed up onto an external keyboard via a micro USB cable. But whilst using the tablet I would also like to be charging it. So would like to know if there is such a cable that splits from one male to two female micro USBs. I can't seem to find one anywhere. Thanks in advance for any help.


texts: How do I cause one switch to "lock out" other switches in parallel?

texts:
I have several momentary switches that are foot pedals (just two are shown below).

simulate this circuit – Schematic created using CircuitLab

The goal is to supply the LED (or whatever) with different levels depending on the variable resistors.

The problem is that pressing two switches simultaneously combines the resistances.

When one switch closes, it should prevent the others from affecting the LED.

I cannot use a mechanical selector switch like a rotary switch because the switches are foot pedal switches that are physically far apart.
I could use a microcontroller but if there is a simpler option I'd prefer that.
The other options I can think of are logic gates, a latch circuit or an IC.

Which of these is the easiest to implement conceptually?

Are there any other options?

EDIT: Answer

I chose the NAND gate idea as the answer because it fits my question. But the relay idea was also good if you have those switches.


texts: Do high and low side labels on bidirectional logic level converters matter?

texts:
Logic level converters like this one from Sparkfun have high side and low side labels on them. Now i have an application where I think I need to shift logic levels but the high side and the low side are likely to swap at some point due to changes in battery voltage over time.

This is intended for a battery powered project with an expected runtime of a year where an ATTiny85 that can natively work between 2.6V and 6V and is directly connected to the battery will be talking to an ESP that is behind a 3.3V regulator because it can not handle more than +-0.5V deviation from 3.3v on any of the pins. The ESP (regulator) will brownout much earlier but that is OK.

I started reading the BSS138's Datasheet and could not find any mention for or against swapping sides.

So I built a very minimalistic simulation of the circuit. According to the simulation the source-drain is passed in either direction in "normal" operation while sticking to the high and low side labels.

Further simulations swapping the high/low sides and even having them the same voltage did seem to work.

Is there any downside to swapping the high/low sides with a logic level converter based on a BSS138?

Thank you Dave for your answer.

Now I see that the sides do matter and swapping them would lead to failure.
Here is the sideswapped state with both sides pulled high which would lead to failure:

The left side is pulled down to 4.1V (should be 5V) and the right side is pulled up to 3.8V (should be 3V) potentially destroying the ESP, definitely destroying the ESP if the battery was at 6V and connected to the converter's low side!


texts:
Incremental delta-sigma are mostly used in systems like sensors arrays. However, most of the time we are examining them in transient operation. Why? Is it too difficult to account the reset operation in the z-transform? An additional question: at what extend are the z-transfer functions, e.g. STF(z) & NTF(z), applicable in incremental sigma-delta (with other words, are these a decent approximation).

Thanks!


texts: Advice making simple solar shed vent from salvaged panel

texts:
I have a 10'x10' shed that gets hot as hades inside, and want some ventilation involving pushing air through a hole I would punch in a wall near the roof peak and screen over so my friends the wasps don't move in.  With a gas-powered mower and weed whacker, gas cans, and spare propane tanks for the bbq and camping lantern, it gets thick with fumes, and I'm uncomfortable with how hot it gets in there.

I have myself a salvaged solar panel in a weather-proof frame, which in its former life charged a battery that then ran a string of little LEDs at night.  It being March, I don't know what to expect from summer sun in terms of juice production, but I did test with a single 60w incandescent bulb in a reading lamp pointed directly down at the panel.  The multimeter registers 6.5v/1.3a at a distance of about 6", and with the bulb just about directly over the panel, just barely 9v/2a.  This is direct from the panel; the battery and charging bits have been removed.  They had stopped charging and/or holding a charge, which is how I inherited this.

I have a fan in this vein that came from an old external hard drive enclosure which puts out enough air, I think, to do the job:  en.wikipedia.org/wiki/Centrifugal_fan

It's marked 12v/0.38a.  It would be inside the shed blowing through the opening I make.  Solar shed vents sold for this purpose are $40+ and reviews say they all just plain suck and are worthless.

What I'd like advice on is how to take this panel's output, which I can't imagine ever getting above the 9v/2a number, and probably hoping for the 6.5v/1.3a is optimistic, stepped up to 12v at sufficient amps to turn this fan.  I found the items below which to my novice eye seem like they might be steps in the right direction:

http://tinyurl.com/457sr8t

http://tinyurl.com/4vkqapo

Am I out of my mind?  Could a device like one of the above take the panel's output and put out enough to get me 12v/0.38a if I get enough direct light?  Is there some other, better way to go about this based on the panel I have?


texts: Plugging the same device on a jack of smaller tension will draw more or less current?

texts:
I'll put a set of ''right's''numbered based on my current assumptions, so if one of them is wrong, you can just point a couple out.

Let's say I have a device that is labeled ''660W/220V'', so It delivers 660W on a jack of 220V, right(1)? Then, let's move on: Based on Ohm's law: P = U²/R, applying the values, we get an INTERNAL RESISTANCE of the device of about 73,3 ohms, right(2)?

With U = R * i, the device draws a current of about 3A, right(3)?

So, if the internal resistance doesn't change, plugging the same device on a 110V jack now will only produce 165W and will only draw 1,5A right(4)?

Thing is, I've seen a video of a dude plugging 2x 60W lightbulbs on 2x outlets each, one in 110V and one in 220V. The one in the 110V drawed twice the amount of current compared with the one in 220V. That doesn't make sense.

Maybe the bulbs were different and designed to operate on the voltage he plugged? So in that case, a 60W/110V bulb have a smaller internal resistance, so it need to draw way more current to produce 60W, is that it?

Extreme stupid question: I don't understand the logic behind P = V * i,  The amount of voltage in an outlet should only determine the capacity of current it can provide. More voltage should equal more current. More voltage equals less current makes sense in the formula, but not in my head lol.


texts:
I'm currently designing a 555 timer to provide a 38kHz square wave to drive an IR LED as part of a beam interrupt detection system.

This beam interrupt is a part of an embedded product where we cannot easily modify the existing processor software, and do not want to add a second MCU with a separate software installation step just to spit out a 38kHz signal.

The goal is to use the VSOP38338 as the receiver, so 38kHz +/- 2kHz should be sufficient for this application.

I am having trouble getting the output frequency of the 555 to match the calculated value I expect. Here are some value combinations I've tried so far:

R48      R49      C11      Fcalc      Fobs
1k       191k     100pF    37.67kHz   31.4kHz
150ohm   1.82k    10nF     38.07kHz   31.9kHz
10k      10k      10nF     4.81kHz    4.68kHz
1.82k    1.82k    10nF     26.43kHz   23.5kHz

Regardless of the R/C combinations I've tried, the output appears to be significantly off from what I would expect. For reference, the resistors are 1% tolerance and the capacitors are 5% tolerance. The specific 555 chips I ordered are from Texas Instruments and all of these parts were ordered new within the last 3 weeks. I have verified the resistor and capacitor values with a multimeter out of circuit before installation. Also note that there is not currently an IR LED plugged in to connector J4.

Am I missing something obvious? I would expect some amount of variation due to the part tolerances, but the deviation seems unusually large.

I have tried replacing individual Rs and Cs as well as replacing the 555 chip itself. This has not led to any noticeable performance changes.

I have noticed that most examples decouple Pin 5, CONT, to GND with a 0.01uF cap. I am using an 0.1uF cap instead, because it was already on my BOM. As this is a decoupling cap, I didn't think going a bit bigger would make a difference.

Any suggestions on what might be causing the high level of frequency error?

Here is my schematic and layout for the 555 timer:

Here is an oscilloscope capture for the first arrangement, with the 100pF capacitor:

And here is an oscilloscope capture for the second arrangement, with the 10nF capacitor:


texts: Standard ways to make a variable low pass filter

texts:
I tried out a basic low pass filter on one of my analog synthesizers:

simulate this circuit – Schematic created using CircuitLab

and this seems to work. I was wondering how I can create a variable low pass filter. I first thought that I would replace the capacitor with a variable capacitor, but I have a hard time finding these at the range of about 470 nF. Then I did replace the resistor with a variable resistor and this seems to work somewhat. But I am wondering if it is just that simple. My question is therefore:

What is the/a standard way of making a variable low pass filter? (used for synthesizers.)


texts:
I have a somewhat complex circuit controlled by an Arduino, which is supplied by a self powered USB hub (earth grounded 5V supply). A part of the circuit has to be powered by 12-20V DC.

When I plug in a earth-grounded supply to provide 12+V, everything works as expected. When I provide the 12+V through a floating supply, instead, and then connect the Arduino's USB to the hub, sometimes the hub 'bricks' and I have to disconnect and reconnect it to make it work again.

Arduino's ground (hence the hub's ground) and the ground of the other supply are joined in a single ground point. I am absolutely sure I'm not exceeding any of the Arduino/power supplies/hub current ratings.

So my question is, is it possible that connecting a floating supply to an earth grounded circuit, when the former is already powered on, could cause some voltage spike/imbalance or wreak havoc in the entire circuit?

P.S. A super-simplified schematic to show the situation:

simulate this circuit – Schematic created using CircuitLab


texts: When it is written that to check if some flag bit is set, you have to look at for example 0x74[2], does that 2 means 3rd bit of register or 2nd? From which number they count in datasheet 0 or 1, how to determine that?


texts:
I am solving some question to prepare for my exam but got stuck on this one and need your help.
Giving the following circuit:

Where input x gets updated 10ns after clock goes down, I'm also given that clock cycle is 50ns such that half of it the clock is 1 and the rest the clock is 0.
Plus giving the following timing table:

I need to calculate T_cd(XOR).

The Final answer is: We can't determine how the circuit behaves those can't find the requested value.
So from this I understand that T_Hold and T_Setup requirements aren't met, So I made a quick check:
Is T_CD(FF1)+T_CD(Logic)>=T_H(FF2)? (In this case FF1 is also FF2 and Logic is XOR and OR gates) Answer: True
Is T_PD(FF1)+T_PD(Logic)+T_Setup(FF2)<=T_clk? (In this case FF1 is also FF2 and Logic is XOR and OR gates and T_clk is the time for full clock circle which is 50ns) Answer: True
Conclusion: T_Hold and T_Setup requirements aren't met thus we can calculate T_cd(XOR).
I think I am missing few things here especially since in my calculation I never used that value of 10ns...


texts: How do I make a battery voltage indicator using the battery being tested?

texts:
I am trying to make a circuit that will test if a 5V battery is under 5V, with the testing circuit running off the battery being tested.

I have seen other answers to this question, however they rely on separate power sources to power the circuit. I am looking for a system similar to those found in flashlights or smoke alarms, telling you to replace the battery.

Any help would be great :)


texts:
I want to protect my power supply ouput and I know that there are foldback solutions suggested by LM723 circuits, but I'd like to understand what is happening inside the circuits.
Consider the simple concept in the circuit below. I used a simple resistor to protect my output. The problem is shown in the image below:

As you can see in the right circuit I don't have efficient behavior, how should I replace the block on the right to make such a chart?


texts: What can cause a Drain-Source short in a FET?

texts:
Background:

I am using a Si7456CDP N-channel MOSFET in a switching power supply. The power supply and load are housed in a plastic enclosure. Yesterday, the power supply and load were working perfectly. This morning, when I came to power it on, nothing worked. No power. Eventually, I discovered that the MOSFET's source and drain had shorted together. Replacing the MOSFET fixed the problem.

Question:

What could cause an N-channel MOSFET to suddenly fail with a source-drain short?


texts:
I am working on a project with an energy friendly MCU from Silicon Labs. The EFR32BG1B132F256GM32 to be exact. My goal is to use as little power as possible to maximize the lifespan of the CR2032 battery I am using to power the application. The consumption in idle and the lowest energy mode possible for what I am doing turns out to be like 4uA which is to be expected according to the datasheet. Now the problem:

I have a reed switch, one side is hooked up to the VDD rail and the other side to a GPIO pin. The GPIO features pull up or pull down and button debouncing internally. In my case I have button debouncing and the pull down enabled. If the reed switch is open, the current draw remains at 4uA, but if it closes, the current goes up to 80uA and remains there until the switch is open again. I assume since there is a path from VDD to GND via the pull down resistor power gets dissipated according to its resistance (unknown - could not find it in the datasheet..). But the problem is, that the application I want to use the reed switch in, holds it closed like 50% of the time and I cannot afford the high current draw during this time. I also tested it with pull up and the other side of the reed connected to GND - obviously same result. What could I do to resolve this? I thought about letting the pin floating and use a very high pull down like 10M externally but I also do not want the switch to trigger if it gets touched or something. Any comments are appreciated!


texts: Arduino Mega 2560 like board but with more ram

texts:
I am making a POV RGB LED Globe that plays animations on its surface. Currently I am using a Arduino Mega 2560 with 256k of Flash Memory. My program and the boot loader take up 20k of memory leaving me with 236k.

There are 64 RGB LEDs using 8 bits of brightness that change color 64 times a revolution. $\left( 64 \cdot 64 \cdot 3 \cdot 8 \right) \div 1024 = 12\mbox{ kB}$ == 12288 BYTES

Each frame of animation takes up 12288 BYTES (12k) of memory. That only leaves me with 19 Frames of animation. Good but not great, at 10 frames a sec thats only 2 secs of animations. I was hoping for ~64 frames of animation or 768k RAM. (768+20=788k total)

I have tried a few load 'on the fly' and steaming methods (SD, Wireless) but they can't keep up with the data required while streaming the data to the LEDs. I am going to try using a simple compression method next but I don't have high hopes that the system will be able to uncompress the data while steaming the color information out to the LEDs.

I have currently tested 10 frames of animation using the Arduino Mega 2560 and it works. Kind of, there are still some bugs. But I don't really want to switch off an Arduino board if I can help it.

My questions are:

Are there pre-built Arduino boards with more ram?
Can I add RAM to an existing Arduino board?
Suggest a different Dev board thats is VERY similar to the Arduino with a c++ compiler.

Thank you for your time.

Edit:
I am using the "PROGMEM" keyword to store my animations in the Flash memory not the SRAM.
http://www.arduino.cc/playground/Learning/Memory


texts: Turn TTL output of logic IC into output capable of driving 50 ohm devices

texts:
I want to provide front-panel trigger signals with the microcontroller inside my device. The trigger signal will be fed via a 50 ohm coax cable to another device with a 50 ohm input.

A direct connection would overload the digital output pin drivers of the controller, so I'm looking for something like a buffer amplifier IC. I'd also like to make this trigger output a bit idiot-proof: shorting it shouldn't destroy anything. My idea was to put a resistor in series with the final output, with a resistance enough to limit the current in a short-circuit situation to the absolute maximum rating of the final driver. Of course, this resistor should be small, to still have as much voltage drop on correctly connected 50 Ohm devices as possible. Is the series resistor the correct approach to make the output hard short-circuit proof (PTC "fuses" are too slow for that, I assume)? Further, if someone plugs in a 1 MOhm device, I'd like the trigger pulse to still turn off in a timely manner.

So far, I have these three ideas for amplifiers/drivers:

Use a simple transistor to allow more current to flow. For example BC337 has a max rating of 500 mA and seems to have a good rise/fall time. Connect the collector to VCC, the base via resistor to the microcontroller pin, and the emitter (via idiot-proof-resistor) to the output BNC. Seems too easy, what's wrong? My guess is the problem will be with 1 MOhm devices, because there's no pull-down. Once the trigger is high, it would take some time to go low via the 1 MOhm alone, is that correct? Maybe use emitter follower configuration with 10kOhm or so, to allow quicker transitions to low?
Use the Line driver SN54ABT126 which seems almost like it's designed for what I want to do. But the maximum current output at high-level is -32 mA, which isn't quite enough for 50 Ohm + idiot-proof-resistor if I'm not mistaken. I haven't found other devices like that which can provide notably higher currents. They all seem to be optimized for sinking high currents in low-level, rather than sourcing in high...
Use a darlington array like ULN200x. This seems to be the easy way out for controlling higher currents with digital output pins, but their timing specs aren't that great (~µs). Further, they might have the same issue with lagging high-low-transitions as the BC337 suggestion above?

I'd like comments on those three ideas, as well as of course "the right way to do it".

Some info that might be interesting:
I'm aiming for switching times (and rise/fall times) below 100 ns when a 50 ohm device is connected. I have VCC +5V easily available, and with some extra effort +6 V and +12 V. I need two trigger outputs, so I'd like to avoid buffer ICs with >8 channels. I'd like to achieve a high level of >=3V at the 50 Ohm device (that should properly trigger any device, right?)


texts: Charge battery when power up, use battery when power down

texts:
I have a tiny little esp8266 that runs happily on 3.3V and draws about 250mA and I can make it sleep and use very little battery power at all.
What I want to do is use supplied power when possible but switch to battery when needed.

Are there any existing components that can do this for me or do I have to fire up the soldering iron (It needs to small as well)

I had a look at some of the answers here but didn't find anything that answered exactly what I require

Help appreciated


texts: Why would a 74HC595 return all logic highs on all its outputs at start up?

texts:
I did a little test on a 74HC595 shift register as follows:

I tied OE (pin 13) to ground to enable outputs.
I tied MR (pin 10) to VCC (+5VDC/logic high) to prevent a reset.
I connected SCK, RCK, and DS (pins 14, 11, and 12) to individual I/O lines of an uninitialized AT89C2051 microcontroller and connected 10K pull-up resistors to each line.
I connected the lowest bit output (pin 15) to a LED through a 1K resistor to see what's going on.

The AT89C2051 doesn't ground any I/O lines when it is initialized with no code, and even with an accidental reset on the AT89C2051, the I/O lines would remain unchanged.

I also used several 2.2uF decoupling capacitors.

Once I powered it up, the LED immediately turned on. I tested every output pin of the 74HC595 and they all were logic high instead of logic low.

Why does this happen?

I have verified that the 74HC595 works by replacing the AT89C2051 with an empty 20 pin socket and applying logic levels to the appropriate pins but I don't understand why it (74HC595) would start up with logic high outputs instead of logic low.


texts: Do function generators produce AC signals in the sense we know?

texts:
When I examine function generators, there are a wide range of products. I see products between 7 USD and 600 USD.

If they can do the same job, why is there so much difference in price? I can't make sense of it. I don't think these cheap products can actually produce a sine wave with a negative voltage portion. Maybe they are producing PWM like Arduino (no negative side). For example, in the video below, do it yourself function generator.

link 1 , Link 2

I take the function generator to use in diode tests. When I give an AC voltage without disconnecting the diode on the circuit, I will decide whether the diode is solid or not with the oscilloscope.

This is the function generator that I think can generate the AC signal that I intend to buy. I think there are a few good brands such as RIGOL, UNI-T


texts: Current branching in transformer circuit

texts:
I'm looking to calculate the voltage u(t) over L2 in this circuit however have run into some problem determining the current going into the transformer.

I know io and the relation N1/N2 and are using the impedance method.

My idea was to simplify the circuit by representing C1, L1 and R1 with only one impedance in parallel with io. Same thing for the right hand side. Finally I would calculate the current I1 going into the transformer using current branching.

Now to the question. Is it possible to use current branching in this case?

From what I have learnt, since the transformer is ideal, the winding inductances  of the transformer are infinite. Would not this however make the current going into the transformer 0 according to current branching?

This is schoolwork. no solutions please, just a push in the right direction :).


texts:
I'm currently trying to implement an IP-Core on a Cyclone V 5CSEBA6U23I7 FPGA-HPS System using Altera Quartus II and TimeQuest Analyzer.
The Verilog code pasted below produces a timing problem, namely the assignment fifo_wdata_289[255:0] <= {fifo_out,fifo_wdata_289[255:16]};, which writes the output of one FIFO into another FIFO register array.
The FIFOs in use are asynchronous, but the signals used are on the same clock domain.
This is being placed on the chip with a clock skew of -2.255 ns, which is a little bit less than a whole period (288 MHz clock => 3.47 ns), and makes TimeQuest complain, that the constraints are being violated.
The recommendation of TimeQuest is to Reduce the levels of combinational logic for the path (Issue Long Combinational Path) with Extra levels of combinational logic = 1.
The 288 MHz clock is generated via PLL and I'm using Timeconstraint files (sdc) with commands derive_pll_clocks and derive_clock_uncertainty.
My question now is how to solve this problem, since I only have one layer of combinational logic (Demuxer and routing, as suggested by the assignment) and thus have no idea how to reduce that. Is there any other way I can make sure the timing requirement is met, or is there a better way to program this statemachine?
Thanks for your help.

            case(stateProc)
                2'b00:
                begin
                    if(~fifo_empty&~fifo_full_289)
                    begin
                        fifo_wdata_289[255:0] <= {fifo_out,fifo_wdata_289[255:16]};
                        fifo_wdata_289[287:256] <= {2'b11,fifo_wdata_289[287:258]};
                        if(imgSize >= maxImgSize - 32'd2)//image done, transmit data and fire irq
                        begin
                            fifo_wdata_289[288] <= 1;
                            stateProc <= 2'b01;
                            imgSize <= 32'd0;
                        end
                        else if(fifo_wdata_289[258])//process transfer without irq //258 high means that 256 has been written in this cycle and 258 in the previous cycle
                        begin
                            fifo_wdata_289[288] <= 0;
                            stateProc <= 2'b01;
                            imgSize <= imgSize + 32'd2;
                        end
                        else//accumulate more data
                        begin
                            fifo_wdata_289[288] <= 0;
                            stateProc <= 2'b00;
                            imgSize <= imgSize + 32'd2;
                        end
                    end
                    else
                    begin
                        fifo_wdata_289 <= fifo_wdata_289;
                        imgSize <= imgSize;
                        stateProc <= 2'b00;
                    end
                end
                2'b01:
                begin
                    fifo_wdata_289 <= fifo_wdata_289;
                    imgSize <= imgSize;
                    stateProc <= 2'b11;
                end
                2'b11:
                begin
                    fifo_wdata_289 <= 0;
                    imgSize <= imgSize;
                    stateProc <= 2'b00;
                end
            endcase

EDIT:

The TimeQuest failing paths look mostly like this:
Slack:
-3.178

From Node:
soc_system:u0|CamConnector:camconnector_0|FIFO_289:FIFO_inst_289|dcfifo:dcfifo_component|dcfifo_6up1:auto_generated|wrptr_g[0]

To Node:
soc_system:u0|CamConnector:camconnector_0|fifo_wdata_289[267]

EDIT2:
I'm currently using MLAB cells as FIFO storage, which are rated for 290 MHz.
Both FIFOs are asynchronous and have a synchronizaton setting of 3.

Timing closure Recommandations of TimeQuest reports the following two issues:

Unbalanced Combinational Logic
Long Combinational Path


texts: Output impedance of Op Amp with Voltage Divider?

texts: I'm trying to figure out the output impedance of this op Amp circuit and I keep getting infinity. I'm not sure if the steps I'm doing are wrong. The reason I ignore everything besides the voltage divider is because those are the only currents I need to find ix. The problem is that I'm finishing ix to be zero. Any ideas of where I'm going wrong?


texts: Is there a "faster" photoelectric beam sensor?

texts:
We've been experimenting with some Velleman PEM10D sensors.  (So, something like this.)

The main reason chose, was they have a 10m length (we need a good 6m or so).

I have found that, the response is a bit slow for our needs.

So for example: if you drop a basketball through the beam from a height of two feet, it is travelling slow enough it will register.  However if you drop a basketball through from 6 feet height, it is too fast, it will not trigger the device.

I surmise, we need the device to be (let's say) a good ten times faster.

Now, the spec of the device suggests .. "Response time: 5 - 100ms"  I don't really know what that means - is that the minimum time of cutting the beam which will register? If so, what does the 10x spread mean?  Perhaps someone here will know.

Secondly, in general is this a well-known problem, are there "much faster" photoelectric beam sensors? Or no, or ...?

Thirdly, indeed could the whole thing be a fubar on our end ... say, poor programming on the Arduino, wrong ... power supply or something, or some other mess-up by us?

So, to be perfectly clear, the thing cutting the beam in our setup is a fast-moving ball-like object, which can be moving quite fast .. some 10 or even 20 m/s.

Finally I apologise if this is not in fact the optimum forum.  Thx