texts: How to safely ground a device plugged into an isolation transformer

texts:
I am working on an old turntable power supply on my workbench. I have acquired a 1:1 bench isolation transformer to increase safety while doing this. It seems to be a well known "issue" with at least the model of transformer I have that the earth ground pin on the 3-prong isolation (output) side is linked to the transformer's chassis-ground and on to the input side (neutral?) and is thus not itself isolated.

My understanding is that this adds risk where risk should be avoided, and some people proactively snip out that earth ground connection from the output pins inside the transformer (effectively disconnecting the earth-ground on the output side and fully isolating the device that's being worked on). Other, simpler isolation transformers don't include a third earth ground pin on either side.

I believe I understand the circuit-completion rationale for this. But what if the device under test has an earth ground pin? Aren't you defeating the safety ground on the device you're working directly on? Is the idea that that no longer matters since its circuit is isolated anyway? Can anyone speak to whether disconnecting the ground pin is as safe, safer, or less safe, or whether once you've done so, you're intended to use it or ground it in some different way? Thanks.


texts:
I don't quite understand this type of circuit:

When light strikes Q1 (phototransistor), if the light is intense enough, Q1 is turned on, then current flows into the base of Q2 which also turns Q2 on, then what happens? Where is the current through the relay coil coming from, and how does the 2nd circuit work? Thank you.


texts: What is the origin of multiplicative noise from a DSLR sensor?

texts:
I'm trying to understand the behavior of my DSLR camera sensor (Canon 80D). I've taken a picture of a gradient from top-right to bottom-left corners of a square. This square is positioned at the right-hand side of the picture, so that it'd be easy to just take the diagonal, starting from the top-right corner, that would be composed only of green-filtered photosites.
The shot is done with a defocused lens, so that the detail of the monitor pixels pattern couldn't cause any interference like moire. ISO sensitivity is set to the smallest value: 100, exposure is 1/10 s, and aperture is f/3.2, with f=24 mm.
What I get is that as the intensity registered by a photosite increases, the noise amplitude also increases. See this plot of the raw data of the diagonal, taken from the CR2 file:

The fact that noise amplitude is correlated with signal amplitude makes me wonder. Thermal noise should be the same on all the photosites, regardless of their illuminance. Quantization noise wouldn't even be noticeable on this scale of ~10000 counts (and it's also additive). Shot noise also shouldn't be noticeable at this illuminance.
So what is the origin of this multiplicative noise then?

I've done some more captures to find the relation between the mean and the variance of the pixel values. I've taken 15 shots of a gray gradient, used every 50th row and column of the resulting data, and computed mean and variance in the sets of 15 values for each resulting pixel.
Here are the results. Blue the variance, orange the least-squares fit:

Blue the variance/mean ratio, orange the estimate of gain from the fit above:

The plot above smoothed with moving average with 100 points in the window:

Is this consistent with the shot noise explanation given in the answers?

After some more comments I've subtracted the DC offset of about 511.9 from all the pixels, and now the smoothed ratio of variance to mean (i.e. estimated gain) as a function of mean looks like this:

So, now the answer that explains the noise as the shot noise makes sense.


texts: Using op-amp and diode switch to drain capacitors – how to limit current?

texts: I want to use a diode switch to drain a capacitor. The switch in the circuit is opened and closed regularly. The op-amp will flip between ground potential and 5V at its output. When the output is low, the capacitor gets drained through D1. Do I need R2 and if so, how do I calculate its value based on the op-amp (and diode?) characteristics? Does it simply depend on the maximum output current of the op-amp, so if e.g. the maximum is 50 mA, I'll use a 100 Ohm resistor for R2?


texts: Interfacing a FPGA to an Intel processor

texts:
So I gave my laptop a long overdue processor upgrade and it left me with a spare Intel Core Duo T2300E processor in perfectly working condition. So I am thinking maybe I can forgo the standard Intel (or nVidia) chipset and slap an FPGA to it and begin using this assembly like something on the line of a Zynq, just with a dual-core x86 instead of ARM as the processor block. This project is purely for LOLs (maybe for science) and may never leave the drawing boards though.

My questions would be:

What FPGA should I use? Preferrably beginner friendly in the sense of low price, easy to solder package, and friendly development interface. Bear in mind this chip need to be able to work with the 667MHz FSB the Core Duo chip is looking for.
What are the required functionalities I have to implement to support this dual-core processor properly? Linux-only is okay for me.
What are the good candidates of other components, besides a powerful DC-DC converter to power the processor and the FPGA and corresponding heatsinks, to put on the module? DRAM in the form of chips or slots for computer memory modules? Maybe a PCI Express connector? Some Flash storage? SATA ports for attaching hard drives? HDMI port? Or something exotic?
What is a good form factor for such a board? Is 170mm by 170mm "mini-ITX" with mounting holes allowing the resulting board being used in a PC chassis a good idea? Or an PCI Express expansion card for another computer?
What kind of experiment can I perform on such a board, with an appropriate form factor? For mini-ITX form factor is trying to create my own chipset (or in this case a single supporting chip) a good idea? For PCI Express card form factor is making this some kind of compute card or something akin to a GPU a good idea?


texts: I am measuring the voltage with the STM32L011K4 MCU. When the processor goes into low power sleep mode, I start reading the wrong values from an ADC. I think the reason is caused by the system clock settings. Because in low power mode only the LSI clock is running and the ADC is working with the MSI clock. So when the system clock changes, the ADC starts reading meaningless values. How to set the ADC before and after low power mode?


texts:
In experimenting with a follower circuit using an NE5532 opamp, I am trying to determine the maximum allowable output current for design purposes. The datasheet is lacking curves in this area, but here is an excerpt from the specs.

From another post here which I can't seem to find, it was explained that Vopp is the guaranteed voltage attainable for the given load, which comes to 20mA amplitude (12V/600Ohm). However, below, the minimum short circuit current is given as 10mA.

So should I assume that some NE5532s can only output 10mA, and design around that? Or is the Vopp calc better? And what if I'm running the opamp from a single supply 12V instead of +/-15V, can I assume that it's the same?


texts:
I have the following circuit to plot X-Y plot in an Oscilloscope to get Hysteresis curve.

R2 and C2 are kept so that the cutoff frequency of low pass filter formed is less than 2Hz.

   1
------- < 2*π*(2Hz)
(R2*C2)

The circuit is realized using a Transformer with two input and output terminal pairs. One of the input and output terminal pairs are kept open while plotting the X-Y plot.

Now, if I short the output terminal that was kept open, what will happen to my hysteresis loop in the oscilloscope? Could you please explain?

Following circuit is expected after shorting.


texts:
I just received my newest board i've designed and wanted to solder the first prototype.

One of my Chips has a QFN88 Footprint. I'm quite experienced, but i just couldn't do it. Because of the small pitch, there are always short circuits.

I tired adding tin to pads and pins, and heat everything with the "hot air rework tool". When this didn't worked i tried to add solderpaste with the stencil i ordered, and placed the Chip by hand. Also didn't work. The chip was blown away by the "hot air rework tool".

Has anyone a tip on how to solder QFN88 by hand?
I'm glad the production will be done using a P&P machine.


texts: Is there any standard for the input impedance of an audio amplifier

texts:
Ebay and other stores are full of items like this.
These are audio amplifiers for various uses and output impedance. But for almost none of them, I was able to find any specification regarding the input impedance. I suspect there is something to know about that: is there any standard input impedance for audio amplifiers? at least sufficiently probable for taking the risk to buy such an item?


texts: Sparkfun RS232 Shifter SMD TTL Waveform DC Offset

texts:
[updated with final, working waveform at end of question]

I've been trying to connect some automotive gear with a Teensy 3.2 for serial communication at 19200 baud. To interface between RS232 and TTL logic, I'm using this shifter from Sparkfun.

Teensy is configured to user Serial2 for that connection. And if I connect a CP2102 on Serial2, I do get proper serial communication at 19200 baud 8N1. This confirms the pins are correct, and the UART is functioning.

Serial from the remote device arrives over three conductors; Ground, Tx, Rx.

I connect all three to the level shifter and find this nice clean waveform across Ground and TX (RS232 Pin 2) which is labelled on the shifter schematic as RS-OUT >

When I use Vcc=3v3 from the Teensy, I see this waveform on the Rx line (JP2 Position 4)>

And while my scope can decode the serial data, my Teensy is not recognising the serial data.

The only obvious thing I can see wrong is the DC offset..

Should this kind of TTL waveform work directly into a UART?
Do I need to pull up or down for proper TTL levels??

Have I wired it incorrectly? (This RS232 cable works when I connect to a USB<>RS232 dongle and plug it into a computer.)

Followup

Yes, I had wired it incorrectly; The DB9 pinouts needed to be swapped for TX/RX.

With the correct voltage swing applied at the correct places in the shifter, logic levels are what they should be.

Note that the above screen grab is 5v/div.

This one is a closer look at 1v/div.

The teensy is now happily reading from that TTL signal.

Footnote

Scope is the Rigol DS1054Z, and it's configured for Cat5 Ethernet connected to a Mac. Screen captures are thanks to a Python project that I installed with $ pip install ds1054z[savescreen,discovery]. Then getting the screen captures is simply:

$ ds1054z save-screen 10.0.0.6
ds1054z-scope-display_2016-07-20_20-31-00.png

The RS232 decoding is accessed through the [Math] button near the channel selection buttons. You need to change the [Polarity] option of the decoder when monitoring the TTL result from the shift circuit.

Addendum

I was powering this with VCC=5V, and produced RX-I logic levels accordingly. Teensy is happy with 5V TTL, but it produces 3V3 logic levels for output.

5V VCC demands TX-O be driven with 5V TTL signal. The TX and RX lights flickered just fine, but no RS232 TX signal was generated.

Switching to VCC=3V3, the shifter detected the TX logic levels correctly, and produced the expected RS232 TX signal.


texts: Choosing resistor values to operate a Half Bridge Driver

texts:
I am designing a 10W (18-12V) synchronized buck converter with a Half Bridge Driver and 2 MOSFETs as shown below. The Driver get a PWM signal from a programmed micro-controller (a 15KHz, 3.5V pulse at HIN and LIN). The Driver IC is the IRS2003(S)PbF.

After the inductor there is a capacitor (not shown here). I feel confident about these values. However, for the MOSFET driver, I can't see from the datasheet any instructions on choosing the resistors' values. I know I must protect the IC which has a maximum Output current of 290mA for the high side driver (HO I think). The MOSFETS used are the IRL60B216. The MOSFET datasheet shows that the gate resistance is 2 ohms. How do I determine the resistors' values? where do I look at within the datasheets?

Update:I tried this out. As in the answer below: "When designing a mosfet driver the important thing is ensuring those capacitors are charged and discharged quickly while not overly stressing whatever is driving them. The IRS2003 has a minimum dead time of 400ns and so you need then to switch well within that number."
I got this waveform for the Vgs of the MOSFETs, the upper one is for the higher side.

I got this waveform for the dead time

which I'm assuming is wrong because the charging and discharging of the equivalent MOSFET's "capacitors" are taking more than 400nS. I'm staring the 18V input a 0V and increment it by .1V, which is causing a short circuit as I exceed the current rating of the power supply after 2V. What can I do to prevent this? I tried 10 ohm resistors and it improved the dead time a little. but I can't go below that I think.


texts:
For the latest iteration of my prototype, I replaced a quartz oscillator with (what I thought would be) a drop-in MEMS replacement: the DSC6013CI2A-033.0000.
It is suppling a 33 MHz clock to a TLC5955 led driver, trough a 51 ohm resistor (starting from pin 3 on the MEMS):

The previous hand-assembled iteration with the XO worked fine, but this one (assembled by a third party) doesn't seem to be running.
3v3 is present at the decoupling cap below the MEMS.
Apart from the MEMS not being soldered correctly and not making contact, could it be that somehow the trace capacitance is too much for the MEMS? And the MEMS output driver is just blown?
The datasheet states that this is the "low-drive" version, which has a 1mA drive capacity along with a 15pf load capacity (stated on the mouser product page).


texts: Can I use a resistor to slow down a DC motor?

texts:
I have a few DC motors of 1.5 V and 9 V and need them for some applications. These motors run at a certain speed (rpm).

But I need to slow them down. Will it be a good idea to connect a resistor in series with the motor and the battery in order to reduce the motor speed?

Will doing so create any bad effects to the motor? I know there are other methods I can employ to reduce the rpm of the motor such as using gears or a PWM circuit, but I'm interested in knowing whether using resistor is a good idea or not.


texts: We discussed a topic in the computer organization course. The professor told us that when the computer first turned on, all the transistors on the CPU are instantly electrified. So he said, keeping the computer on is better than constantly turning it off and on. Is this really true? Is electricity flowing through all transistors when first powering up?


texts:
Newbie and trying to understand the concept of instantaneous frequency in FM.
Basic equation is \$A\cos(2\pi f_\mathrm{c}t+ 2\pi k\int (\mathrm{message})\,\mathrm{d}t)\$. I wanted to know how the term   \$2\pi k\int (\mathrm{message})\,\mathrm{d}t\$ term creates chirpiness in the carrier frequency


texts:
Never though transformers would be so confusing to many - I found about a dozen similar questions here. Adding mine to the pile.

Here are the datasheets for 3 Transformers: 750313975, 750313445 and 750311088.

They all have 2 secondary coils, but the drawings are different. Is that supposed to reflect the physical coil arrangement on the core somehow?

The second says it "allows" to parallel two secondaries. But the pinout is exactly as the first one, so what's the difference?

More than that, the third one says "customer to tie terminals on PCB", which I understand as we must tie them together. A rather weird requirement.

Finally, the wire diameter or current rating is nowhere to be found. Should I assume that it would be at least close to saturation current?

UPDATE:

To clarify the question: Is there any specific convention for drawing coils I am not aware of?

All my life I used to draw transformers as the one on the first picture, with primary and aux coils on the left, secondaries on the right, all lined up along the core lines.


texts: Should I use constant current or constant voltage drivers for driving my PWM 24V DC Fans?

texts:
Hi everyone thanks for stopping by to lend your thoughts.

I need to run 2 circuits separately and control via Arduino uno PWM.

One circuit is 2x Noctua NF-A14 industrialPPC-24V-3000 Q100 IP67 with 4pin PWM connection. The spec sheet says:
Max. input power 7,92 W
Max. input current 0,33 A
Operating voltage 24 V
Voltage PWM Signal 5 V

The second circuit is 3x Noctua NF-F12 industrialPPC-2000 IP67 with 4pin PWM
Its spec sheet says:
Max. input power 1,2 W
Max. input current 0,1 A
Operating voltage 12 V

Do I need to use constant current or constant voltage drivers for these circuits and what kind of resistors and other things might I also need to pull this off? I am leaning towards using Meanwell LED drivers for this task as the only other electronics I'm somewhat familiar with is those.

Thanks for the help.


texts: Will cutting the data lines of USB still let the power to go through?

texts:
I am trying to Charge a USB connected device through a computer without transferring data.

An USB 2.0 cable should have 4 wires: Vcc, Data+, Data- and Ground. If I only cut the Data wires and let the Vcc and Ground wires connected, will it still be able to transfer power or will the power cables be shut off because of the disconnected Data wires?


texts: How to modify this DTMF Controlled Home Automation System?

texts:
I am planning to set up Home Automation System to my reading room using DTMF Technology. For that, I have searched different websites and found a post - DTMF Based Home Automation System Circuit.

That circuit seems to be simple and interesting. But, they mentioned few limitations.

1) It is limited to 16 tones only. Is it not possible to extend it by adding any other component?

2) It is mentioned that it has no security. Is it not possible to solve this problem by setting up a security password?

If anybody have an idea about it, let me know the solution. I would like to implement this same circuit to my room on next week.


texts:
Have you ever had any experience with an ADG3304 IC? I've prepared a circuit which allows to translate logic levels in SPI interface.

I want my circuit to be compatible with both 1.8V and 3.3V logic levels. That's why I used a relay for selecting the output voltage. My master device is attached to Y-signed pins and slave is opposite. My problem is that I can't communicate with neither 3.3V nor 1.8V-supplied slaved-devices. The circuit of the voltage selector works good.

What could be a possible issue?

I used a logic analyzer to check periods. The first screen is wrong communication

This one is correct:

I tried 3 another methods:
- I added decoupled capacitors near VCCa any VCCy (100 nF)
- CS pin has been pulled up to VCC via a 10k resistor
- Voltage divider has been created on a MISO line with 2 10k resistors

Still no results. SPI doesn't work


texts:
I got a piece of fiber optical cable that is in the form of a "ribbon cable" (see pictures). I have seen tools and procedures for making connections on a single strand of optical fiber. I would like to know how to work "ribbon" type of optical fiber cables and what tools I would need.

Thanks.


texts:
I would like to have some feedback on this circuit.

V1: 0,6A Solenoid
V1_LED: Arbitrary small LED
V1_IN: Input signal from Arduino (3.3V, 20mA)

Should I change something?

Is the IRLML2502 suitable? Is there a better choice?

Edit:

Link to MOSFET:
http://www.infineon.com/dgdl/irlml2502.pdf?fileId=5546d462533600a401535667f44d2602


texts: What exactly are size, ratio and line distance in Eagle PCB text tool?

texts:
What exatly does size quantify in the Eagle text tool?

Also, changing ratio and line distance does not seem have any affect. What exactly are they used for?

How do I know if I need to use vector, proportional or fixed Font?


texts: How can I implement this Truth Table with MUX4 only?

texts:
I have implemented twice this function with MUX4, but I always fail at some point. I need some help, please

Thank you so much

edit: This is what I've done:


texts: typical value of contact resistance: 1) banana connector, 2) solder joint

texts:
Two separate questions:

1) What is the typical value of contact resistance in electrical connectors? I am interested mostly in a banana connector for delivering power supply from the source to the PCB.

2) What is the typical value of contact resistance of a "good" handmade solder joint? This is assuming the contact was soldered properly (in particular, enough solder was used).

Appendix 1. My particular situation
My particular situation: 1.8 V, 1 A DC are delivered from the power source to the PCB and I am going to use a thicker copper wire to decrease IR drop. I calculated 1 mm diam copper wire, 50 cm length has a resistance of about 10 mOhm (so, 10 mV IR drop at 1 A). So, if I buy a thicker copper wire, solder it to banana jacks which are to be inserted into the power source and the PCB, I'll have four parasitic contact resistances: two for the banana connectors and two for the two solder joints. So, I wonder, does it make sense to fight for 10 mOhm (if thicker wires are used) if contact resistances could be greater. This is a test PCB (to test a chip), no VRM on it.

Appendix 2. Some contact resistance values for banana connector found in the Internet
URL1, page 2: 10 mOhm maximum.
URL2, page 5: 0.5 - 1 mOhm maximum.
URL3, page 4: 0.5 - 1 mOhm maximum.
URL4: 1 mOhm maximum.

Appendex 3. Questions about conact resistance found at Stack Exchange
Relay with contact resistance less than 10mohm
How the relay contact resistance is measured?
What kind of effects does a relay have on signals?
What causes contact resistance?


texts: Depletion P-channel JFET that's saturated at \$V_{GS}=0V\$

texts: Is there any depletion-mode P-channel JFET that is saturated at \$V_{GS} = 0V\$?


texts: How do you know what resolution a gerber file has?

texts: Viewing Geber files in Gc Prevue but don't know how to find out what resolution they are using


texts:
I've heard that SiGe chips can be faster than ordinary silicon chips.

What is SiGe and why is it faster than ordinary silicon?


texts: Error in this explanation of instrumentation amplifier?

texts:
On this webpage I read an explanation of an instrumentation amplifier:

  The negative feedback of the top op-amp causes the voltage at Va to be equal to the input voltage V1. Likewise, the voltage at Vb is equal to the value of V2.

And the input amplifiers are marked "Voltage follower" to illustrate this, but I wonder if this is correct. Part of Vb is added, so Va can't be equal to V1, can it?


texts: use bjt or mosfet in h-bridge with inductive load?

texts:
is it better to use 2 pnp bjt in high side and 2 npn bjt in low side of an  inductive load drive h-bridge ?

or using 2 pmos in high side and 2 nmos in low side of h-bridge?

what are the advantages and disadvantages of using each one ?

if our system is intended to drive a particular inductive load continuously for 10 years with switching frequency below 50Hz, which one seems to be more reliable and durable?


texts: Composite/RGB Video from simple hardware

texts:
I'm designing a 68000-based VGM player, and I'd like it to output some sort of 'visualization' of the currently playing song to a TV through either RGB or Composite (video encoder probably for that.) I'm thinking of using this system to display video (and running the sync and RGB through a composite encoder instead of VGA) and then just taking the RAM onto my main CPU as needed, but that just seems horrid and from my calculations won't give me much more than 15-20 FPS.

So, I guess the question is this - is there an easy way I can get my 68k to somehow output RGB/composite video to a television? My requirements are relatively low as anything with the resolution of around 240x240 will work, but it needs to get me around 30FPS with my main CPU taking a considerable share of the time writing to the VRAM.


texts: Does an electrolytic capacitor degrade each time it receives reverse voltage?

texts:
I know that I mustn't connect an electrolytic capacitor reversely. It will explode if I apply the reverse voltage long enough.

But, what happens if the reverse voltage is applied for a short time? For example, a fault occurs in the circuit and the capacitor becomes reverse biased or exposed to AC voltage for a short time, but it still looks OK from outside. Does the internal physical and chemical structure of the capacitor change permanently? Would it still have the rated capacitance, voltage and life time? Is it okay to keep it using if it doesn't explode? I feel that the answer is "no", but I'm looking for an explanation for it.


texts: Can I use a 32x6mm catridge fuse with a fuse holder specified at 38x10mm

texts:
This is my first time incorporating fuses in my project. I am trying to source for some DIN rail mount fuse holders and the accompanying cartridge fuses.

After much searching, I have found the fuse I am looking for with a current specification of 500mA. This fuse also has size 32mm x 6mm.

However I can't seem to find a fuse holder with the physical specifications. All I come across is fuse holders with size specifications of 38mm x 10mm.

Will it be possible to use a 32x6 fuse with a 38x10 holder?


texts: If I have a 120V @ 50Hz AC heater rated at 750W, and I run it using 120V DC, will the DC heat it faster, and why? (Assuming I could get a clean 120V DC power source).


texts:
I am reading a book about transformers and I am confused by the following paragraph about synchronization check:

When the transformer trips or is taken out of service, the primary and secondary voltages decay because the supply voltage has been disconnected. However, the voltage on the load side of the transformer decays more slowly because of the back EMF induced by induction motors located downstream. Thus, the two sets of windings become out of synch. This occurs at approximately 40% of rated voltage, causing the synchronization check relay to activate and the transformer breaker to trip if it is not already open. This protects the transformer from electrical system upsets or loss of supply that cause a loss of synchronization while the transformer breaker is still closed.

What is the point of the relay opening, if the transformer breaker has already tripped? Also, what do they mean by "40% of rated voltage". Primary side or secondary?


texts: Pulling RGB24 signal out directly instead of LVDS interface

texts:
I am designing a display driver board. I have used a HDMI receiver ADV7619 for the same, I am using HDMI input to my board coming from PC. This receiver has RGB and YCrCb signal out. I have already defined an LVDS interface.

My question is, can i take RGB24 signal out from this receiver directly instead of using LVDS interface which I think here is not necessary.

Is it possible to interface the LVDS pinout directly to this IC.

Below I have pasted the LVDS interface that I have defined for my project. the additional pins for e.g. backlight can be ignored. The important pins  are LVDS differential pairs.

LVDS Interface

RXO0-   -lvds chan0-odd
RXO0+   +lvds chan0-odd
RXO1-   -lvds chan 1-odd
RXO1+   +lvds chan 1-odd
RXO2-   -lvds chan 2-odd
RXO2+   +lvds chan 2-odd
vss ground
RXOC-   -lvds chan Clock input odd
RXOC+   +lvds Clock input odd
RXO3-   -lvds chan 3-odd
RXO3+   +lvds chan 3-odd
RXE0-   -lvds chan 0-odd
RXE0+   +lvds chan 0-odd
vss ground
RXE1-   -lvds chan 1-even
RXE1+   +lvds chan 1-odd
vss     ground
RXE2-   -lvds chan 2-odd
RXE2+   +lvds chan 2-odd
RXEC-   +lvds chan Clock even
RXEC+   +lvds chan Clock even
RXE3-   -lvds chan 3-odd
RXE3+   +lvds chan 3-odd
vss ground
vss ground
NC  not connected
AGMODE  aging mode selection
Vcc +5V power supply
Vcc +5V power supply
Vcc +5V power supply
Vcc +3.3V power supply
Bklt_power  backlight power
bklt_pwr    backlight_power
bklt_pwr    backlight_power
bklt_gnd    ground
bklt_gnd    ground
bklt_gnd    ground
I2c_gnd i2c_ground
i2c_sda i2c_sda
i2c_ pwr    i2c_power
i2c_scl i2c_scl
bklt_pwr    backlight power
bklt_pwr    backlight power
bklt_pwr    backlight power
bklt_gnd    ground
bklt_gnd    ground
bklt_gnd    ground
bklt_enable     Enable BLK pin
GND
GND
GND
GND
GND
GND
GND
GND
GND
GND
GND
GND

Thanks in advance.


texts: Six monthly service timer with indicator

texts:
I have been requested to look at a project. The first half of the project is complete, but I am struggling with the second half of the requested specification.

For the second half of the project, I require a six month timer. Accuracy is not an issue as long as the output action is within 4-5 days of timer reset. At the six month point, an LED is illuminated and an internal sounder activates. The sounder can be muted, via a push button, but resound after a 24 hour period and repeats until the service counter is reset, which also extinguishes the LED and the timer process re-starts.

Looking into it, I believe I require a microprocessor to handle the timer event, but not to sure how to handle the buzzer/mute function. Could this be via a secondary processor (i.e. primary processor outputs to a secondary processor input and PIC is programmed to handle the LED and buzzer functions)? If so, is there anything I should be aware of under this set-up?

Appreciate any advice and help with this.


texts: What is the advantage of a tri-state output?

texts:
I'm trying to understand what is the use of tri-state output and what is the advantage of using it.

Below depicts both two-state and tri-state output:

According to the above logic, it seems to me two-state output can only be ON or OFF.
But in tri-state case, the output can be ON, OFF or floating. So to me the only difference is the floating state.

As far as I read, floating signals are not useful. But it seems I'm ignorant at some points and want to ask what is the purpose of using tri-state output?


texts: why does the parallel resistors with voltage source can be ignored as well as resistors in series with current source in term of equivalent circuit?

texts:
I have a problem dealing with equivalent circuit. I don't know why when the resistors that is parallel with the voltage source can be ignore as well as one in series with current source. Of course the voltage in the load is no difference but what about the power. Having a resistor parallel with voltage source brings a difference in total resistance compared with having none resistor parallel with voltage source

For example. If I place a resistor \$R_1\$ to 2 terminal a-b the thing will turn out for the voltage source having no parallel resistor

$$I_1 = \frac{V_s}{R_1+R}$$

but for one having parallel resistor, it will be

$$I_1 = \frac{R_p}{R_1+R+R_p}(\frac{1}{R_1}+\frac{1}{R_p}+\frac{1}{R})V_s$$

So although the voltage between a-b terminal is the same but the current is not. So how can it be considered equivalent as well as in the current source case. Please give me some proper explaination


texts: Why DAC ic costs as much as a clone arduino

texts:
I'm using the mcp4822 DAC and i'm very satisfied for controlling voltages in my circuits. But I wonder why the chip costs from 1 to 4 euro when a clone arduino costs around 3.50e.

Because I'm interested to control a great amount of signals (from 100 to 200) the price is too expensive. Are there any cheap alternatives? (i'm looking for at least 12 bit ic)


texts: Control theory - how to represent these transfer functions?

texts:
I'm learning control theory. Block diagram for transfer function:

is:

What would be block diagram for these two transfer functions:

$$H(s)=\frac{1}{s^{2}+1}$$ and $$H(s)=s\frac{1}{s+1}$$?


texts:
I have a remote unit that runs a STM32L0 MCU. It is not connected to the internet but communicates with a remote PC over radio.

I would like to update the RTC on the remote unit with a timestamp that I am receiving from  the PC.

Is it possible to configure STM32 RTC on the fly? Or this is a one-time operation during initialization?

Any alarms (A or B) that I have set stop working as soon as I update the RTC (set date/time).


texts: What causes failure in longer USB cables?

texts:
I wired up some USB-C 2.0 to USB-A 2.0 cables, and tested the maximum length I could get out of them when connecting a PC (host, USB-A) to an external hard drive (device, USB-C). I got stable power and data connections up to about 7 feet. Longer than that, I was able to make a power connection (light on external hard drive illuminated, hard drive spinning) but the PC would not recognize the hard drive. I am guessing the failure happens with the data connection? Or maybe there just wasn't enough power, I'm not sure. The USB-C connectors I use are these: https://imgur.com/a/RSkxc

USB-C spec dictates I should be able to get about 12 feet of length from this assembly, so I am trying to figure out if there is something I can do to make a stable cable that reaches 10 or 12 feet. I am using 28AWG wire, which seems to fall within spec (though on the low end for power).

Any suggestions would be welcome! Thanks in advance.


texts: Is there a non-contact temperature sensing technology that can measure the temperature of something emersed in water/other liquids?

texts:
It's pretty much all said in the title...
I want to get the temperature of a surface that my device is moving past. The surface may be as cold as -55°C. I was thinking about non-contact thermometer solutions to save myself some mechanical work in designing something to keep a thermometer touching the surface as I pass it (not a flat surface in the slightest, and not a set distance away).
My first thought was a cheap IR thermometer. However, while it would be perfect in a lot of cases, my device will sometimes be used in an under-water environment (or another fluid) where there will be a reaonable 'thickness' of fluid (up to ~100mm say) between the surface and the sensor - so IR is a no go. The fluid is likely to be up to 30°C warmer than the surface itself.
Any suggestions of other technologies (or even specific sensors) I should be considering? I'm not looking for amazing tolerances, maybe something comparable to an IR thermometer (~±0.5°C or better). My googling is not yielding anything, and my attempts to think through the physics aren't yielding any obvious mechanism by which one could assertain the temperature of an object at distance without measuring radiation...
Thanks
Edit: Added some application details.


texts:
I would like to generate computer controlled touches on a capacitive touch screen (e.g. iphone) using the following setup: I have a conductive patch (size of finger) that I place on the touchscreen which is connected to a wire. When I touch the other end of the wire, it generates a touch at the location of the capacitive patch. However, also when I do make contact with the wire, it also generates a touch. I think this is because the wire (25cm) acts as an antenna and the capacitive signal is influenced by noise. I do not encounter this problem when the wire is shorter (e.g. 5cm).

My idea now is to place an electronic component close to the patch, which I can control digitally to connect/disconnect the wire (switch). So when the "switch" is open the wire is very short and will not generate a touch. When the "switch" is closed a touch will be generated because it is connected to the longer wire which generates a touch because of noise in the environment or/and the user is touching the end of the long wire. From my basic knowledge of electronics and transistors, I though that a transistor might be suitable as this can be as a switch that is controlled digitally. However, I did not come that far as I encountered the following problem using a PNP BC327:

I directly soldered the collector to the conductive patch that makes contact with the screen. When touching the screen with this setup (leaving the base and emitter disconnected) does not generate any touches. However, when connecting a loose wire to the base or emitter, a touch is generated without even controlling the transistor. I do not measure any conductivity between the Collector, Base, or Emitter using a multi-meter so I am very surprised that connecting these wires causes a change in capacitance on the collector.

Any help to beter understand this problem would be useful as well as input on other techniques on how to make the desired system/setup.


texts: Fire pit dancing to music -- increasing the voltage from a subwoofer out

texts:
I am creating a propane "regulator" which allows the user to connect a speaker output to control a valve (0-10V max:0.185A) which opens more with higher voltage.

Here's a video of it operating (WARNING VERY COOL).

This is the valve.

It also has a bypass past the valve to allow a steady flow when no music is on.

Prinicipally:

The valve opens the most with high bass input because the voltage is higher across the subwoofer input line and the valve is opened for longer because the signal is lower frequency giving a very nice bass effect. The valve opens on either positive or negative signal but does so quickly (but not as fast as the 20-20k hz signal it's getting so I also installed a Rectifier so that the valve doesn't have to adjust open-to-close-open it can just stay in the open state as long as the wave is still occurring).

I'd like to:

a) make it more sensitive to other frequencies (I'm getting a different valve that allows me to vary the gain of the valve). But other ideas are welcome.

b) add some way to increase the voltage to just the valve so that the music volume or bass gain doesn't have to be high in order to get a good effect of propane release. I think that ideally a user might be able to adjust a potentiometer that would control the gain or even adjust it with an app on their phone. One concern is that the voltage doesn't get over say 12V or it might damage the valve, so I assume I might need some sort of regulator in case the settings are off.

c) know which type of input I should use for controlling the valve/circuit to make it most universal for users to hook the system up to any stereo system they like. I'm currently just using the spring clips for speaker wires but I was thinking that some way to hook up to the preamp output signal would be great (but that's very low voltage and would certainly require some voltage multiplication or something)

I've filed a patent over the basic structure in case anyone's worried that this would constitute public disclosure (I love this community for being so happy to help by pointing out things like that in the past).

Thank you in advance. This has been a stumbling block for me.


texts:
I have a SiPM connected to an op amp and then ADC.  Everything works great except I am just guessing at what values to choose for R2 and C1.  What questions should I be answering in choosing the aforementioned components?

simulate this circuit – Schematic created using CircuitLab


texts: Modify DPDT push button with an NPN to control with GPIO?

texts:
I have an 2-port HDMI switch that swaps inputs using a 6-pin DPDT latching push button. I want to modify it to be controlled by a GPIO pin on my Pi rather than having to push the button.

One way that was suggested to me was desoldering the button and replacing it with two H-bridges driven by 4 GPIO pins.

Alternatively, I'm wondering if I could keep the button in place, and instead replace the button "plunger" with an NPN driven by a single GPIO. Would that be feasible?


texts: Drop the current of a couple of peristaltic pumps for a microscope use

texts:
I have a system to drive two peristaltic pumps (labelled 12V, that draw 300mA) in a microscope in the lab in order to refresh the media of my cells for long term experiments. In the current setting I'm pumping 40mL/min, which is too much. I need to be able to control the flow-rate (lets say, in a perfect world, between 0.5ml/min to 10mL/min).

I am using a 2A 12V DC power source.

Pumps are in parallel. I have two 8 ohms resistors right before each pump (in each parallel branch). (it was my first try to reduce the speed of the pumping that's why they are there)

I also, now, have 4 paralleled 4ohm resistors right after the power source (I needed to drop the current for today's experiment and it was all I had nearby and I didn't want them to fume even though they are higher than 1.2watts, 6 I believe).

So my question. I want to have a way to regulate the flow. Potentiometers usually come in high resistance forms and low wattage (I found a few 100 \$ \Omega \$, and a 10 \$ \Omega \$ - 5W online. Should I use the 10 \$ \Omega \$ potentiometer?

Can I connect a potentiometer in parallel with the pumps trying to create a resistive voltage divider? However I don't know how to calculate the value to that potentiometer. Is this the best way to do it?  I also can't to spend a lot of money on this.

I am concerned about temperature since the whole system (except the 12V power supply) is inside of a 37ºC enclosure to keep the microscope warm and the cells happy.

I saw this related post, but I have no idea on what values and pieces to use.
Slowing Down a 12 volt pump with a potentiometer?

This is the state of the thing right now:

simulate this circuit – Schematic created using CircuitLab


texts: How to eliminate Bluetooth noise in electric guitar

texts:
After learning more about this problem, I have continued this question here.

I am trying to remove noise from an electric-guitar circuit that I have created called the ArduGuitar. My circuit comprises 2 opto-isolated parts: the audio circuit between the guitar pickups and the output jack, and the control circuit consisting of an Arduino Micro and a Roving Networks RN42 bluetooth module powered by a 9V battery.

A full description is available on the ArduGuitar webpage but in brief, I wrote an Android App that sends controls over bluetooth to the Arduino via the RN42 bluetooth module. The Arduino interprets the commands and adjusts PWM signals on its output pins to control Vactrol (LED-LDR) LEDs which change the resistances attached to the pickup outputs. Thus, I simulate potentiometers and switches, just as per an "normal" electric guitar circuit, while keeping the analog audio fully opto-isolated from the digital control circuit.

Globally, this works very well and I am happy with the result which I would say scores 90% of perfect.

However, despite the use of all shielded cables and a fully shielded RN42 bluetooth module, significant noise still gets into the audio and comes out the amp. This noise is of 2 kinds:

whistling: this is present as soon as the bluetooth is switched on. I have done extensive testing of the use of capacitors across VCC/GND to try to filter this but it all fails. This noise is not very strong, but significant;
clicking: at each data transmission, a click comes out over the audio. It is not very loud, but significant nevertheless.

I use all shielded cables and wiring internally on the audio circuit.

The noise level changes depending on where I position the Bluetooth module, and strangely, the best result seems to be when the module is inside the guitar electronics bay (which is unshielded). The worst result is when the bluetooth module is close to the guitar output cable that connects to the amp.

I have been working on the problem for several months and am now at a loss as to how to proceed...

I wonder how this problem is handled in wireless guitar systems?

Would anyone have any ideas as to how to reduce or eliminate this noise?


texts:
I am designing a PCB wich I need to talk with 13 IC's on a I2C bus. I am wondering how many pull up resistors should I put on the bus? The chips are MAX9611 and here is the current layout of the I2C board area (continues to right side):

As you can see R17 and R18 are current limiting resistors and R21 and R22 are pull up resistors (1 for SCL and one for SDA). The SCL trace goes over top layer and SDA goes in bottom layer).

I just saw some examples in TI I2C bus guide, and I am wondering if what I have already designed is wrong, because it seems for each device there is a local pull up resistor on SDA and SCL lines:

I would really appreciate your suggestion, before I fail miserably with cost of a bad PCB layout!


texts: How is 1 bit transfered from RAM to a 1 bit register?

texts:
I've been reading on computer RAM and CPUs. I came to the conclusion that most RAM today use arrays of DRAM while CPU registers and caches use SRAM. 1 bit DRAM is a circuit with one capacitor and 1 transistor which controls the flow of charge in and out of the capacitor.
When the transfer from RAM occurs the CPU places the address required on the address bus and the RAM controller "opens" the transistors of the bits specified by the address.
If containing a charge, the capacitor will then discharge onto the data bus to the capacitor of the 1 bit register.
My question is about the requirements of the register state when the transfer occurs. If the bit of the register is set, then even if the RAM capacitor contains a charge, it will not discharge onto the data bus. The operation is thus not necessary.
Another situation is one where the register is set while the RAM bit is not set. If the path is open between the 2 capacitors then the charge will be transfered from the register to RAM which is not the required behavior.
I think of it as with the following circuit:

Is it the right way to think about memory transfers in computers?
Is the register grounded to 0 before the transfer occurs?


texts:
I need a linear actuator for my IOT project but how do i make one and how do i use python to control it? i saw videos of people making it with glue sticks and servos but i don't think it will be effective.

And i am making a auto feeder so any actuator that open and close is ok.


texts:
When looking for a MOSFET on digi-key, I found that the current specification is given with temperature specifications, so one FET might be rated for 20 A (Ta) while another is rated for 20 A (Tc) and yet another 20 A (Tj), and many FETs have multiple of these ratings.

What temperature are they referring to here? I'm guessing ambient, case, and junction, but that doesn't tell me what temperature the spec is rated at--is it 25°C? The rated maximum temperature? Something else entirely? How can you even specify a specific ambient temperature without knowing the heatsinking and air forcing conditions anyway?


texts: How do so many high end oscilloscopes support Gsps when most microcontrollers have ADC rates at Msps?

texts:
How do so many high end oscilloscopes support scanning rates at Gsps?
Most micro controllers have ADCs reading only at few Msps.


texts: Using voltage divider to regulate voltage to a device

texts: Lets say I want to power a laptop using an external power supply. Lets say I have a 20 volt supply and the laptop runs at 12 volts. Can i use a simple voltage divider with the appropriate resistors (resistance, wattage) to drop the voltage down to 12 volts and run the laptop ? Or is there a better way of doing this ?


texts:
I have a project which requires me to drive a 100W LED (32V, 3A, CC). The only catch being, is that dimming control is required via Arduino. I couldn't find a conclusive method of doing this via internet research, but I have hypothesis'd some methods. Please let me know which one would be best, or if there is another way.

Replace the (voltage trimmer) pot on a buck/boost board with a 10k digital potentiometer.
Using a MOSFET circuit to drive the LED, controlled by the 0-5V feed from the Arduino.
Using 3 "LDD-1000H" drivers (1A each, accepts PWM dimming) in parallel .
Something completely different!


texts: How does the current pass through FET when its gate is unbiased/grounded in AC analysis?

texts:
My first question is how does the drain voltage increase V(drain) when the source voltage V(source) is increased for the below common gate FET:

And secondly and most importantly in AC analysis they short the gate and Vdd to ground. What confuses me is that in AC small signal analysis of this circuit if we short the gate to ground(meaning that the FET is not biased), how come the FET current change? So in reality on a breadboard if I short the gate and Vdd to ground the MOSFET output will always be at ground level and the FET will be in cut off and will pass no signal at all. So I hope I could articulate my confusion here.


texts: Reference design for the latching switch with momentary pushbutton

texts:
I've noticed in a few production-grade schematics that the toggling power ON/OFF switch with a (normally open) pushbutton is frequently realized with two ICs, namely:

single Schmitt-trigger inverter
single positive-edge-triggered D-type flip-flop.

This approach is also used in TI's "Electric Toothbrush Controller Reference Design":

I wonder, is this design really preferable for consumer products or is it just a random choice by a subset of electrical engineers? If it actually is beneficial, what makes it better than other approaches (like using dual inverter, for example)?

(To give you some context, I'm not an electrical engineer myself and was just looking for a widely accepted low-power design I could quickly assemble on a breadboard, as well as put inside a consumer product eventually.)


texts: What is this symbol used in this D flip flop circuit?

texts:
I'm studying some notes on latches and flip flops. After the introduction of the D flip flop, the notes go on to explain its function - how it works. However, the first circuit diagram contains this weird circuit symbol :

Does anyone recognize it?

In case it helps, here's the full circuit diagram :

Could it be just a symbol replacing the whole D flip flop? In that case the inverters seem to be there so that we can get the 2 complementary Q outputs. I don't get the whole feedback thing though.


texts: What makes an arbitrary waveform generator arbitrary?

texts:
Why are some signal or waveform generators called "Arbitrary Waveform Generators"? Am I misunderstanding the word arbitrary? This question is not necessarily about the word arbitrary but more about arbitrary signals.

How is a arbitrary waveform generator different from a plain old waveform generator?


texts:
How can I annotate a block in Proteus 8 (automatically)? For example, let's suppose I design a multiplexer and I embed it in a block and I need to copy it several times. How can I make Proteus annotate this block sequentially, instead of me writing MUX0, MUX1, etc.?

P.S.:I know how to do this with components, such as gates, but I don't get how to proceed with blocks.


texts: Trying to communicate with an external board through Arduino

texts:
I'm trying to communicate with and send commands to an external board (page 23) from an Arduino. For some reason, which I can't figure out, the external board acknowledges my serial commands intermittently.

I noticed that the Arduino board I'm working with is 5V and the TX/RX communication on the external board is designed for 3.3V. Could this be the cause of the intermittent response from the external board?


texts: Replacing a condenser mic with a MEMS mic

texts:
I'm working on a black-box piece of electronics which has a cylindrical "condenser microphone" with a main body diameter of 4 mm and height of 1.5 mm

I want to replace the condenser mic (black box) with a MEMS mic without redesigning the board.

Does anyone have a guess for the mic impedance (capacitive for a condenser mic) and/or volume-to-voltage-curve of similarly sized components? Any way to verify this with just a multimeter?

Is there any MEMS mic of good quality that has a form factor that could be a drop-in replacement for a cylindrical mic that's 4 mm diameter x 1.5 mm height, plus pins? I imagine the MEMS mic would thus either need to be passive (unlike most MEMS mics which are powered), or would need to have a jumper wire go to it from a power rail.

Thanks! Beginner here working on a black box system so I hope I'm asking the right questions.


texts: Is it possible to set starting count on binary counters like CD4020?

texts:
Can I set starting count on binary counters like CD4020, CD4060?
Only solution I know is to use reset pin and increase the frequency till you get desired count then resume normal operation.
If there is no other solution then, is there simple circuit which can feed desired number of pulses to the binary counter?


texts:
I am setting up a home electronics lab for projects with my kids, currently ages 4 through 10. What type of flooring would work best?

We will be doing art projects in the same room, so we need something easy to clean (no carpet). I would prefer something relatively inexpensive as well. I have found lots of information about flooring for a pro setting, but I have not found recommendations for home use.


texts: How does this transmitter work/how to tune it?

texts:
I have used a few 433MHz ASK transmitters. They're cheap, readily available, and work reasonably well.
Based on this application note from Murata I tried to build my own.
I replaced the NE68030 transistor with a BFR93A, and the RO3101E SAW resonator with a generic one. The antenna I'm using is this one.

The appplication note has instructions to calibrate it. The SAW needs to be removed and have a chip capacitor soldered instead. Then measure the free run frecuency. In my case I couldn't really get a stable frequency. In the datasheet of the SAW resonator I noticed they don't use L2, so I removed it. Once I did that, the free run frequency jumped to 470MHz or so.

Why does this happen? Is it because I'm using an antenna that is already matched to the frequency and does not require L2? (I'm guessing this transmitter is designed to be used with a 30-35cm lenght of wire as an antenna).

So anyways, I tried to solder the SAW. Once I did that nothing happened. It wouldn't transmit. Until I touched the antenna, and it would be near 433.92MHz. So I soldered L2 back again, and no output. I tried with different values for L2 and finally a 56nH value seemed to work. The frequency was measured near 433.90MHz, but it seems to be very weak. The only tools I have are a frequency counter with an antenna connected to its input, and a UHF portable radio. I have no VNA or even SDR.

How can the output be improved? The datasheet says L1, C1 and C2 need to be tuned for the particular application. In my case it was actually L2 that made it work. The only difference is that I have no 6pF SMD capacitor handy so I just used a really old "lentil" type TH capacitor I found.


texts: I'm have a project which is using an ATMega 328 which is powered by 5 volts. It is connected to an accelerometer/gyro breakout board through a 3.3 voltage regulator and supplying the 3.3 volts to the ATMega's AREF pin. I want to control a Jaguar speed controller via PWM, which I believe expects a 5 volt signal. My question is, when I set the AREF pin to 3.3 volts, is that going to change the upper limit of my PWM output from 5 volts to 3.3 volts?


texts:
I was coding for Atmel ATmega 32 chips. Now I have shifted to the ARM Cortex-M family.

Is there any difference in coding between AVR and ARM, or does it depend on the compiler? How I would learn programming for ARM MCUs?


texts: Differentiator (Op amp) with a square wave

texts:
I'm working on a differentiator (op amp) with a unitary gain i calculated the value of RC and the period with a frequency of (1kHz).

Figure 1. Differentiator Schematic (OrCAD).

This is the schematic that im working and this is the graphic of that schematic.

Figure 2. Graphic of differentiator schematic.

I have the problem that the graphic is not right.

Figure 3. Differentiator circuit of Texas Instruments. Source:
Analog Engineer's Circuit: Amplifiers SBOA276–February 2018 Differentiator Circuit.

Figure 4. Simulation profile.


texts: Can I use a 12V DC 1.0A adapter in place of a 12V DC 0.5A adapter for my piano keyboard? The keyboard comes with a 12V DC 0.5A adapter but it is lost. I found a 12V 1.0A and wanted to know if it can be used. I don't want to use this adapter if it might harm the electronics.


texts: Can battery inverters output reactive power?

texts:
This inverter manufacturer's Paper Bad Power Factor? – A reason to oversize your inverter mentions that "inverters can generate reactive power without using any active power."

Can battery inverters also generate reactive power?

Can battery inverters absorb (?) reactive power when charging the battery?


texts: Photodiode + OpAmp + Arduino: Further Amplification

texts:
In order to measure the concentration of a methylene blue dye in water, I am using a 660nm high power LED and a photo diode with op amp setup as described here. (schematic below):

I have tried two different photo diodes, BPX 61 and BPW 34 and with both the measured intensity from the smartphone flashlight as well as the 660nm LED were only ~0.01 V (as read by the Serial Monitor).

I then decreased the resistor used in the op amp scheme from 10 kOhm to 330 Ohm to 75 Ohm to 10 Ohm and the measured voltage increased up to ~0.60 V when I hold the LED Right on top of the photodiode.

This is a bit too small, especially as I want to put the diode further away and an absorber in between.

How I can increase the signal?


texts: Drawin max power out of solar panel by keeping its voltage constant

texts:
I wanna build a simple MPPT that keeps voltage on output of the solar panel constant. According to documentation, maximum power is drawn, when output voltage is about 4.2V. My way of reasoning is like this:

the more current I draw, the lower voltage will be on output
the less current I draw, the higher voltage will be on output

Does it make any sense? Or MPPT that uses variable, mcu controlled buck regulator will be much more efficient?


texts: Why JTAG connectors are available in 10pins/14pins/20pins when JTAG is of 5pins

texts:
AFAIK, JTAG is requires 5 pins (Wikipedia article):

TDI (Test Data In)
TDO (Test Data Out)
TCK (Test Clock)
TMS (Test Mode Select)
TRST (Test Reset) optional.

Let's add two more Power supply Pins (Vcc and GND).

If it is of 7 pins then why most JTAGs connectors come with 10 pin or 14 pin or 20 pin variants.

Most of the pins are either NC or GND. Why so many GND pins are provided? Is there any special reason?


texts:
I have shown output image description here in my Lm 393 comparator, my output is not coming proper square wave.picture is shown below.i have described my circuit. practically
I am using voltage comparator LM393 for comparing two signals, one signal is my reference signal which is a triangle wave, with voltages 2.08 volt generated by 555 timers above 200kHZ giving to the input terminal of inverting side of LM393 and input signal or modulating signal which voltage is less than 2.08 giving from function generator as a sinusoidal signal in the range of 1 Hz to 20kHz in the noninverting side of LM393. My question is when I am providing two signals it should be compared and give a square wave, but LM393 only taking triangle wave, sin wave is not going? why I don't understand. please give suggestion to the above points. In this picture below, I am referring to this circuit, please tell me what 's wrong in this circuit, when I am taking triangle wave from 555 timer ad providing into the comparator and another signal providing from the generator.


texts: How to redesign a circuit to use a current sinking IC rather than a current sourcing IC

texts:
I'm building a serial servo controller to learn about electronics and assembly language as part of my hexapod robot project. Quite early on I decided that I needed more I/O channels than my ATTiny2313 that I was using at the time supported so I investigated some 3-8 line demultiplexer chips (CD74HCT238E's) which have allowed me to create a 64 channel PWM servo controller with just 8 I/O pins for the PWM channels and 3 address lines.

Anyway. I also bought some CD74HCT138E's which are active low rather than the active high CD74HCT238E's. I understand, in principal, the differences between the current sourcing chip that I'm using and the current sinking chips but I don't really know how to adjust my circuit to use the current sinking chips instead of the current sourcing chips.

The schematic for the active high chips is here:

What do I need to change to swap the CD74HCT238E's for CD74HCT138E's?

Note that the reason for asking this question is that I bought a tube of the active low ICs by mistake and I'm curious at how much more complex the schematic and circuit design would need to be for me to make use of them.


texts: Parallel Resonance circuit Q factor formula Clarification

texts:
I'm confused with the formula of Q factor in parallel resonance because in other books its different
is it okay to be like this ?

A. This is from the  Electronics Tutorial Website

A. This is from a book


texts: Low Voltage DC controlling 120 AC, with Arduino

texts:
I'm looking for a type of device I can hook my arduino (micro-controller) to that will control a set of lights that require 120VAC. Basically I will be making a light organ, where the arduino will be processing an mp3 file, splitting up three frequencies, then turning on the set of lights which is set for a specific frequency. Basically making the lights flash to the music.

The problem is I can't just use a relay because they have a delay time, and if the music is to fast the lights won't turn off in time. So I need another solution.

Does anyone know a device that is low dc voltage controlling 120 VAC, and has a very minimal delay time?


texts: How can a capacitive touch screen be triggered without human contact?

texts:
I want to robotically touch an iPhone screen without any human intervention.

I've done some experiments but have not found a reliable solution. It seems even styluses that work through gloves still rely on the capacitive characteristics of the human body.

Carrot held by human works
Carrot held in plastic clamp doesn't
Pogo Stylus works held by human and held by human through clothes
Stylus does not work held in plastic clamp.
Stylus works held in plastic clamp attached to human through clothes via jump lead.
Stylus held in plastic clamp with jump lead dangling off seems to work most the time.

Is it possible to mimic the human element using capacitors and other components? What signal does the capacitive screen need to be triggered?

Thanks


texts:
I am the recipient of an incomplete set of data for several 120 volt, single phase, AC drive systems driving induction motors under various loads. The measurements were taken at the AC voltage source. I do not have a way to take more or better measurements so am forced to work with data I have. The only data I have available to me is:

Watts (true power)
VA (apparent power)
Frequency (60 Hz)

From this I have calculated the following:

Power factor
Phase angle
VAR (reactive power)

My goal is to figure out AC volts or AC current. Is it possible for me to obtain this from this limited data set? One major problem is that the wire run to these drive systems was very long so I am certain that the voltage measured at the drive was sagging under load at some times.

I could provide the numbers if that helps, but I don't think it'll be necessary since I would like to know how to do the calculation.


texts:
First we set fuse bits:

avrdude -c usbasp -p atmega328p -U lfuse:w:0xFF:m -U hfuse:w:0xDF:m -U efuse:w:0x07:m # same for atmega168

In the following examples we use the following commands to compile and burn all the programs:

avr-gcc -Os -mmcu=atmega328p -c -o serial.o serial.c
avr-ld -o serial.elf serial.o
avr-objcopy -O ihex serial.elf serial.hex
avrdude -c usbasp -p atmega328p -U flash:w:serial.hex

Let us burn the following program:

#define F_CPU 16000000UL
#include <avr/io.h>
void main (void) {
  DDRB |= (1<<PB5); // enable output on pin PB5 (default led on arduino)
  PORTB |= (1<<PB5); // set the led on
  while (1);
}

It makes the led to be on constantly. And it stays so for infinite period of time.

Then we burn the following program:

#define F_CPU 16000000UL
#include <avr/io.h>
char data = 0;
void main(void) {
  // Initialize USART:
  UBRR0H = 0x00; // set the speed (Higher bit)
  UBRR0L = 0x67; // set the speed (Lower bit)
  UCSR0B = 0x10; // enable receiver
  UCSR0C = 0x06; // set mode (8N1)
  DDRB |= (1<<PB5); // enable output on pin PB5 (default led on arduino)
  while(1) {
    while(!(UCSR0A&(1<<RXC0))); // wait until a byte is received
    data = UDR0; // read it
    if (data) PORTB |= (1<<PB5); // set the led on
  }
}

Then we open a terminal (9600,8N1) and press several keys, until the led turns off.
Now we burn the first program again and the led is constantly blinking. The reason for this is that watchdog times gets started when we press the keys in terminal. But why and when WDT gets started? How to make so that it will not start?

It should be noted also that we can disable the blinking only with complete poweroff/poweron - only after that the led lights constantly without blinking, as necessary.

This happens on atmega168 and atmega328p, 100% reproducible.

avr-gcc version 4.8.1 avrdude version 6.1

NOTE: bootloader is not used at all.


texts: Random activation of transistor base by capacitive coupling (ghost voltage)

texts:
I have a smart module used for home automation.  It is equipped with two relays, a wifi mcu, and two switch input.
For the switch input it uses AC mains detection using transistor (non-isolated.)
In the following picture we can see a simplified schematic of the AC main detection part:

As we can see anytime 220V is detected on input the transistor base is activated at 50 Hz frequency, and the GPIO of the MCU is sensing alternatively ground then 3.3V.  Based on these pulses it can switch the relay.
The problem i have is that I tried to use this module with a rocker light switch (2 point.)  In most case it was good, but in some cases it didn't work well - I got some random and fast light activation.
When I inspected the problem, I found that when the two wires of the rocker light were passing by close to other energized wires (220V,) it happens that the empty wire of the rocker light carry some voltage when measured by a high impedance multimeter.
The empty wire wich normaly is a open wire.  When not energized, it acts as a capacitor with other nearby energized wires.
When using a low impedance multimeter I got 0V which shows that it's just a stray capacitance and ghost voltage.
Unfotunately this ghost voltage is activating my transistor randomly as if it's a true live wire.
In other cases, where I have 3 lives passing by near a rocker light wire, changing switch state does nothing because the ghost voltage is too strong keeping the transistor base activated (at 50Hz) exactly like a live (220V) wire.
I verified that the transistor base is not floating since the base is connected to ground via a 15Kohm resistor to pick parasitance and to pull base to ground and avoid such situation but it doesn't seems to work. I think that maybe the problem is that the input is at high impedance.
I thought to connect a resistor to ground just before the two 680k resistors but I'm not sure.
What do you think is the solution to stop the ghost voltage from activating the transistor?

To provide more information , this is the schematic of one side of the PCB:

In the picture I highlighted the AC mains detection part (picture found on internet, same module that I have, I did the highlighting to show the AC mains detection part.)
On the other hand, I have done some research and found a quite similar module, used as a dimmer, using the same AC mains detection principle , but this time they have used a capacitor rated 10 nf connected to ground after the two 680K resistors instead of a zener diode used in the module I have:

I wonder if this slight modification could resolve the stray voltage sensed at transistor base. Should I try to connect the capacitor just after the two resistors to ground to resolve this issue?


texts:
I want to try my hand at producing a POE battery power supply for use with an access point [AP] for site surveying purposes.

My solution is an 11.1v LiPo 3s pack and charger fro a remote control car rated at 5000mah and a 12V --> 48V step up converter from Ebay, connect the two together and then connect the 48V to a RJ45 Jack and hey presto portable power for the AP.

Questions -

1) Given a rated power consumption of 200mw what life would I get from the battery?
2) As the POE standard allows for some negotiation on the power supply would simply presenting 48V to the appropriate pins of the Cat5 wirk or do I need some logic in there?
3) Am I likley to hurt my AP with this solution?


texts: Possible to re-program microcontroller over Bluetooth?

texts:
I am looking at making an embedded design featuring an ARM Cortex M3 MCU and bluetooth. I would like to be able to update its firmware over Bluetooth periodically.

Is this possible with the following chip? From ST:

http://www.st.com/web/en/catalog/mmc/FM141/SC1169/SS1031

I am used to connecting the bluetooth to the MCU via UART. Does the bootloader need to be modified when I want to program "over the air"? How does one load their own bootloader on the device? What does bootloader code look like?

I'm also open to other suggestions based on my objective.


texts: Diagnosing USB Power bank shut-off on load application

texts:
I'm trying to create a small bluetooth boombox-style speaker, but am having trouble powering the device from a USB battery bank.

Fundamental Problem: The power bank "shuts off" as soon as the load is connected.

The Bluetooth Amplifier Board wants 12V input, so I'm using a ZDP12N on the USB-C output of the USB-C Power Bank. I have confirmed that I get 12V output on the terminals of the ZDP12N with no load applied.

When I connect the amplifier board to the power bank (through the ZDP12N), the battery bank immediately shuts off. Thus began the troubleshooting. Here are some things I tried and the results I got:

Power the bluetooth board off of 12V from a power supply.

Result: Board works as intended. Pulls 50 mA at 12V = 600mW, so load is definitely not too big for the power bank which can output 1.5A @ 12V

Power the board through the ZDP12N with a USB-C laptop charger instead of the battery bank

Result: Board works as intended, no problems. I don't have a way to measure current here, but it doesn't seem to be any issue

Charge phone off of power bank

Result: Phone fast charges no problem

So basically I'm not sure what the best approach is here. I'm speculating that the load is too small and the device thinks it's connected to something malfunctioning and protecting itself. Either that or there is some large inrush for a very short period that is causing the device to shut off. I don't have an oscilloscope, so I can't visualize the startup current draw.

Thanks in advance for your advice on next steps.

P.S. I've made a second post about why the speaker power draw seems too low


texts: Purpose of this Resistor in Circuit attached

texts:
What is the purpose of resistor (R2, 33ohm) in the circuit below?

Q) is it for current limiting , if So the current can go 15V/33ohm = 454mA, but opamp can not give this much current , most opamp can give only some 20-50mA only, so this resistor needed

Q) or it is used for termination , if so how they calculate its value.


texts:
After my embarrassing mistake by having the component in backwards, I'm wondering if anyone has advice for the newbie (or expert) on reading datasheets.

What conventions are there which aren't obvious.

What's the first thing you should check when something's not working.

What can I safely ignore and what should I worry about?

Anything else?


texts: Can I use 2.5kW solar panels to power 2kW rated grid tie solar inverter?

texts:
Can I use 2.5kW solar panels (10x 250 watts) to power a 2kW rated grid tie solar inverter? Will anything blow up?

Panels: 10x 250W, 36V panels

Inverter: 2kW with max input voltage: 500V

Any help is appreciated.


texts: Line-out: why is there no impendance issue when plugging an amp rather than headphones?

texts:
Given that the input of an amplifier has very high impedance, while headphones have very low one, why can I plug either one or the other on the audio-out plug of my computer?

Even with a degree on Electrical Engineering (but not analog EE), I'm still often lost when it comes to properly understanding impedance issues. Today I'm wondering how it is possible for my computer sound card to sound more or less the same when I load it with a few-ohm-impedance headphones, as when I connect it to a high-impedance amplifier that drives loudspeakers.
Is the computer detecting its load to switch between two sound circuits? Or at least to adapt its impedance?

And just for my own knowledge (and assuming my sound card adapts its impedance in some way), what would happen if I plugged my headphone on an impedance-mismatched source? Would the sound sound crappy? And how crappy would it be (hashed, awful frequency response, distorted, etc.)?

Thanks!


texts:
I'm designing a device powered from USB. The device uses FTDI FT2232 chip for USB connection. Upon a command from a computer FT2232 chip should enable power via a MOSFET switch to rest of the circuit. This additional circuit has a capacitance of 50uF (FPGA + aux stuff) and is powered from the same USB port. After the switch is turned on, this additional 50uF capacitance will sink a huge current until it's charged.

How to limit this inrush current 1) to avoid voltage drop on power rails and 2) to avoid USB PTC from disconnecting power to the device?

Is it enough to put a ferrite bead in series with MOSFET switch to limit the inrush current? Or should I use a special chips, like chips for limiting current or chips for slew rate control?

Note: all devices are powered from 3.3V. So a small drop on 5V rail should not be a problem if it does not prevent an LDO to output stable 3.3V.


texts: I am Awais and I want to design a dual-band antenna in CST studio. My requirement is to design at an operating frequency of 2.45GHz and 5.8GHz. The problem is when I simulated, it was resonating round about 5.3 but have no resonation at 2.45. How I can make it at 2.45 also?


texts: Understanding slow response of multiplexed thermocouples

texts:
I have a simple circuit swapping eight thermocouples through a MAX31855 analog-temperature-to-digital converter with two CD74HC4067 multiplexers. The MAX31855 is wired to the SPI pins on a raspberry pi.

I can poll the temperatures without issue, but I'm surprised that I need a ~125 ms delay between each poll for reliable data. If I shorten this, I end up polling the same thermocouple twice. For my own education, I'm trying to figure out why this is the case.

In my current understanding, almost everything should have a microsecond response time. The thermocouples' Seeback effect is near-instantaneous, and SPI communication is 32 bits at 500 kbps = 64 us. The system is behaving like the multiplexers are slow, but nothing in the datasheet suggests that this is the case.

What am I missing?

Edit Here's a sketch of the circuit. I'm using the Adafruit and Sparkfun breakout boards, and the red and yellow stubs are thermocouple hookups. The signal outputs are attached to the screw terminal block of the Adafruit board.


texts: 'keyboard from scratch' registering key presses

texts:
For my first hardware hack I'm taking a stab at a 'mechanical keyboard from scratch' (where scratch means individual components).
I plan to use a teensy++ board (16MHz) and was wondering about how to scan for key presses, so far I was thinking of using a grid (matrix) for the keys, every row is an out pin and every column is a in pin, the switches connect them (along with a diode for limiting the direction of current to lessen ghosting).
So there would be a scanning cycle, during which a column is set to high (or low, depending) and then every row is tested for this value. My question concerns whether or not this would be accurate enough, it means that the switch has to be closed at the exact moment that row and column are checked otherwise the key wont be registered at all. Is this how it is done or is there some much better approach?
There is also the issue of key bounce, so either a delay between checking the same key (could be a result of the scanning loop) and/or a counter where a certain key to be activated a number of times.


texts: Audio amp IC: how does this output stage work?

texts:
I'm looking at an audio amplifier integrated circuit and the output stage seems a bit unusual. Has anyone seen this style of output stage, and does it have a name? And can anyone fill in the details on how it operates?

Here's my understanding of how it works:
Transistors Q12 and Q14 form a push-pull output stage for a class AB amplifier.
Q8 takes the output from the differential input stage and amplifies it.
Q16, Q17, and Q18 are part of a current mirror (with Q13 providing 3 times the current).
Q17 (and Q16?) provide base current for Q14, turning it on and pulling the output high.
If Q8 conducts, the current from Q17 and Q16 flows through Q9 and Q8, turning off Q14.
If Q8 conducts, Q11 will mirror the current through Q10, turning on Q12 and pulling the output low. Otherwise, Q13 will "dump" the current from Q18. Thus, the input current results in an inverted, amplified output.

I understand it at a hand-waving level, but I don't get why they built it this way. The transistors are carefully sized (e.g. x3 indicates 3 transistors in parallel), so there's something clever going on with the currents that I'm missing.


texts: 10kV high voltage switch using mosfet stack

texts:
I need to make a pulse generator for a 10kV power supply, few mA.

Surprisingly, I could not find any standard design of HV switch using mosfet (Sic or not) stacks.

Could someone give me some guidelines?

Ideally I would like to reach faster than 100ns commutation and use only standard components.


texts: Help solving kirchhoff's law for two voltage sources and two resistors in series

texts:
I need to find the voltage drop between R1 (4 Ohm) and R2 (2 Ohm).
I tried applying Kirchhoff's law in this way:
\$-10+4I-8-2I=0\$ and then solving by \$I\$ I have \$I=9 A\$ but that's not correct. Can someone help me?


texts: Differential Pair with non-differential inputs

texts:
consider the following

In normal circumstances, Vin1 and Vin2 change differentially, if Vin1 goes up by 10mV, Vin2 goes down by 10mV. Makes sense.

But I'm wondering, what would happen if Vin1 went up by 10mV, but Vin2 stayed the same and didn't go down by 10mV. The Ibias current source should then have a higher load current right, if it's implemented as an NMOS device?


texts: LTC6994-2 signal inverted and time delayed

texts:
I use LTC6994-2 to delay and invert input signal. I want 2s delay between input and inverted output.

However, this is what I get on the output:

Green waveform is input waveform. Output (Blue waveform) is expected to be inverted and delayed version of input signal. However, in my circuit, output goes high at the start and stays that way no matter how input changes.

Datasheet of the component:

Figure 6 on pg14 is what I am trying to accomplish.

I followed steps on page 16 in datasheets to select values of resistors:

Ndiv selection:
tdelay/16u <= Ndiv <= tdelay/1u (equation 1) => 125K<=Ndiv<=2M
Selected lowest Ndiv to reduce power consumption => Ndiv = 262,144

I selected corresponding R11/R12 resistors as suggested in datasheet:

I selected Rset from equation given in Step 3 on pg 16 (equation 2):
tdelay = (Ndiv * Rset/50K)*1u
Taking 2s delay and 262,144 Ndiv, Rset = 381.5K

Is there anything that I am doing blatantly wrong here?


texts:
I would like to synch two small DC motors so they run at the same rpm but in opposite directions. Is there a straightforward (and light) way to do this from a single battery pack? My goal is to turn a pair of props for a model aircraft. Obviously the weight is an issue due to it being an aircraft and the reason for the same speed rotation is to maximise stability.

Edit: I dunno on the subject of brush vs. brushless because I haven't even started this. It's just that I realised the synching is important because this is a free-flight model. It's an A-frame https://amablog.modelaircraft.org/amamuseum/tag/a-frame-twin-pusher/


texts: Why isn't the opamp negative input drives to 0?

texts:
I just get started to play around designing analog circuits after I have learnt something about it in my high school 20 years back, so forgive me if this question is dumb for you.

Here is my attempt to design an integrator - this is LTSpice, the opamp is ideal.

I am expecting the output to be the integral of the input. Here is my idea:

The negative feedback of the opamp should drive the negative input of the opamp to 0. (I learnt this rule in high school, but why? I am not sure)

With that in mind, the current from power source to Vout through R1 and C1 is:

$$ \frac{V}{R_1} = I = C_1\frac{dV_{out}}{dt} $$

Rearranging, getting:

$$ V_{out} = \int\frac{V_{in}dt}{R_1 C_1} $$

But here is the simulation result, something I don't expect, the negative input of the opamp is not exactly 0, it changes:

That is a small range of error, but for the opamp, it is sufficient to drive the output crazy.

How does opamp drive the negative input to match with the positive input, and
Why doesn't the negative input got drive to zero, and
What's wrong with my design?

Feel free to fiddle with the design in LTSpice by downloading it from here


texts: What is the meaning of the singular values?

texts:
I am studying MIMO control systems, and I have seen that the Bode plot of these systems is composed by the various singular values. But I have not clear the meaning of these sigular values. What I have understood is that they are related to the various inputs, but it is not very clear to me.

Can someone help me understand this concept?

[EDIT] I have found this example of a distillation process:

where are present the maximum and minimum singular value.

[EDIT 2] Here is a paper where the distillation process is discussed and it is also present a similar frequency response : paper


texts: My DC source (chrager) is 220 VDC, when measure + terminal to Ground, value is arond +110 VDC, Isn't it suppose to be +220VDC?

texts:
as question above
when i measure + terminal to G = +110VDC
- terminal to G = -110VDC
Isn't it suppose to be
+ terminal to G = +220VDC
- terminal to G = 0VDC


texts: Integrating wireless transmitter with old door chime system

texts:
The building I live in have an old door-chime system, and I wish send a wireless signal when the door-chime is triggered.

There are multiple push-buttons at different locations connected to the same circuit. The only place I can access my part of the wiring of the old door-chime system is behind one of the push-buttons, the rest of the system is buried behind concrete and walls. There's an AC transformer hooked up to the system to drive a door bell. The bell has been removed some time in the past, and the wires are not accessible - and are probably shorted.

I've measured 8V AC over the button, the button is normally open.

I've a board with a wireless transmitter, it's triggered by pulling an interrupt pin to GND. Powered by a 3v battery.

I want to pull this pin low to trigger the transmitter whenever the doorbell circuit is closed.

My naive idea is something like the following:

simulate this circuit – Schematic created using CircuitLab

Will this work? Or will the AC source (which hits the base and emitter of the transistor) ruin this somehow?


texts: Using DAC to create reference in a wheatstone bridge for strain gauge?

texts:
I am designing a circuit where a microcontroller can measure the load forced upon a load cell with strain gauges, making a half bridge.

A traditional Wheatstone bridge looks like this:

Resistors R1 and R2 should be exactly the same value so a reference of VCC/2 is made. This reference is then compared to the voltage between the two strain gauges - which is also VCC/2 when they are resting.

But from prior experience I've seen that the to nodes rarely are exactly VCC/2, either because there are some tolerance on R1 and R2 or because the strain gauges are worn. My prior solution has been to add a variable resistor i series with R1 to be able to adjust/calibrate the reference voltage between R1 and R2.

Problem is that this solution is tedious, and pricey. So my question is if I could just use a DAC (the MCU already has one) to create the reference voltage of VCC/2 - or what ever matches the voltage between the strain gauges when they are resting:

Though I haven't been able to find this solution anywhere else (which is usually not a good sign). What pros and cons do you consider with my DAC solution?


texts:
I'm still fairly new to electronics and have been teaching myself as a hobby. Currently I'm working on a project that detects a red laser beam, and once detected will turn AC lights OFF if they're already on, or ON if they're off.

I've got everything working except 2 things:
* open relay if it is closed, close relay if it is open
* not require constant laser source

At the moment it will only turn on while the laser is pointed at the detector.

How would I go about activated or deactivation the relay once the laser is detected for say 200ms? In other words how do I set it up to not require a constant laser source.

Secondly, what would be a good way to detect if the relay is already on or not? I mean I can check and see if the light sensor is active or not, but I'm trying to do this all without an Arduino or other micro controller. So how would I detect if the relay or light sensor is active or not from inside the same circuit, and then perform the opposite action to turn the lights on or off.

Am I going about this the right way or am I missing something?

Any help on this is greatly appreciated.

Thanks


texts:
I have "inherited" a Philips 2.1 Home Sound System HTS7201/7202
The official user manual from philips can be found here:
https://www.download.p4c.philips.com/files/h/hts7202_12/hts7202_12_dfu_aen.pdf
It consists of two speakers (left/right), each 5 Ohms impedance and a subwoofer with 3 Ohms impedance and of a DVD player with integrated audio amplifiers.
The dvd player was damaged with small chance for repair, the three speakers however, are undamaged so I would like to use them in my living room.
My quesitons:
1.) Does anyone know the part numer / technical name of those connectors an their counterparts?

2.) Can anyone suggest a proper amplifier for those speakers? The best thing would be of course one "amplifier box" that I can attach to a PC (via stereo jack or HDMI, whatever..?) and that in turn can feed all three speakers (data see below).
Also, I am not sure If a 2.1 home entertainment system like this one needs 3 audio channels or if it just uses a stereo signal and feeds the subwoofer with a "mixture" of L/R channels with a LP filter applied?


texts: Insufficient current using Elegoo UNO R3 and breadboard

texts:
I'm completely brand new to electronics and just bought a breadboard kit to try and get my feet wet.  I have a 9V battery and I'm trying to fire up a green LED.

I have a 330 Ohm resistor in series with the LED and if I measure the current coming out of the resistor I'm only getting about 4.5 mA, and I think I need at least 20 mA to fire up the LED. See the attached picture.

What is not visible in the picture is that the red wire is connecting to an output that reads 5V.

If I connect the LED directly to the Elegoo board it lights up fine.  Any suggestions?]1


texts: How do the backup sensors on vehicles work?  There are 4 round sensors in the rear bumper of many vehicles to provide a backup alarm.  Are they optical or ultrasonic? And what measurement principles do they use?


texts:
Does there exist a chip that will do autocorrelation over a data sample of several thousand points? I need to find the place in the data sample which most closely matches a given waveform (that I provide) At worst it is about 10k samples to match against a sample pattern of around 1k samples. Ideally I need to do this in well under 1mS.
I seem to recall that this was once done in h/w, but cannot find the correct search terms to turn up any contemporary chips.


texts: Is this part hand-solderable, or will certainly require reflow soldering?

texts:
Here are the mech specs for the part (it is a GSM module) -

Note that all dimension are in "mm".

If hand-solderable do I need to keep some specific precautions in mind (from soldering standpoint). The data-sheet, HW design docs do not specific any specific soldering type or temperature.


texts: Estimating wattage of unknown autotransformer

texts:
Update. As a result of the answers. I was able to buy this triad 100VA autotransformer. It weights exactly 1kg. so for autotransformers, it's 100VA per kg versus 50VA per kg for regular two winding transformers. Now about estimating the wattage of that unknown autotransformer. Here's the comparison with Triad branded one.

Top picture:

This is back of the unknown autotransformer

Well. I used my multitester and able to measure conduction in all leads between primary and secondary so it's 100% an autotransformer (the leads from the terminals was gone because I cut it so short). At least you know that in asia, autotransformer have leads coming from both sides unlike the Triad brand where it only comes out at front.

The unknown autotransformer weights 1.32kg. So it may be more than 100VA? using the formula, it's 132VA?

However, the construction seems to be different. Do you think they are same construction or really different so I can more accurate estimate the wattage of the unknown autotransformer.

original:

I need to acquire this autotransformer from another circuit for use in other circuit that requires only 30 watts. But it's not written how many wattage capacity is the autotransformer. Based on your experience, what is usually the range of wattage of this size (it measures 3 inches by 1.25 inches)?

50 watts? 100 watts? What is your estimate (just rough estimate)?

Here it shows there is conduction measuring 18.7 ohms between the primary and secondary leads so it's an autotransformer design. They separate the leads so it's clear which is 220v, 120v neutral, and where are the lower voltage. In the US, they put the wires in one sides only right.

It's an autotransformer. I'm just asking what wattage do you think is the above?


texts: Method to guarantee relay minimum contact switching (wetting) current

texts:
I'm considering solutions for a particular high-current switching application. My preference is to use dual-coil latching relays. The only such relays which meet the power requirements are SPST configuration.

Among my many design constraints is a requirement that the switching cannot occur under live conditions. However, as I'm using high-current relays I must ensure a minimum contact (wetting) voltage/current (100mA @ 5V in my application).

The switched loads and supplies are both variable. The supplies can range up to 120V or 33A, although there are no guarantees except that the supplies will not be live during switching. There may or may not be a load present during switching. The coil supply is 24Vdc.

I'm curious what ideas everyone has to ensure my minimum wetting current requirements. My best idea at present is to use an ancillary non-latching relay operated by the same control pulse to switch the 24Vdc (used to drive the relays) across the power relays' contacts during switching (current limited, of course). It goes without saying that there are drawbacks to this solution.


texts: Analog Reading of YL 69 Soil Moisture Sensor

texts:
I am using an ESP8266 12 F Module with 3 x 1,2 V Batteries.
I tried to connect an infamous chinese soil moisture sensor YL 69 like this (LINK) to the anaolog pin of the ESP8266 Module. The Module works from 3,3 Volt on to 5 V and comes with an electronic board that includes a potentiometer

I figured that since I am not going to use the digital output I don't need that extra board between ESP8266 12F and the sensor. The Sensor without the extra board offers two pins.

First Try:
First Pin: A0 Pin of ESP Module and Second Pin: Ground of Batteries
This got me some readings between 0.00 and 340 but it seemed quite unreliable and reacting slowly to changes.

Second Try:
A0 Pin of the ESP module to one pin and Pin4 of the ESP8266 12 F module to the other pin (the idea was that with this method I would be able to completely turn off the sensor while it's not needed and therefore increase durability of the sensor)
This got me some readings between 0.00 and 1024.
However while using digitalWrite(PIN 4,LOW); I still got readings out of the sensor... how if theres no current flowing?

I tried the same sensor with an NodeMCU Board that contains an ESP8266 chip. I used the extra board and the analog output and got very good and reliable readings.

Questions:

What could I do to adjust the setup so that the readings with the "naked" ESP8266 module match those of the NodeMCU model.
Why was I able to get some reading at the second try setup when digital pin 4 was turned off?

Is there a way to use the First try method but to shutdown the sensor completely when not needed so that it doesn't draw any current?

UPDATE Thanks again for the help: Here's my solution:
I connected VCC to one Pin of the Sensor and Ground via a 10 K resistor to the other Pin. Than I connected the Analog Read Pin from the ESP Module to a point between the 10 K Resistor and the Ground wire and I end up with usable reading between 0 and 1024 although I noticed that the readings reach 1024 quite soon but it is good enough for my uses.


texts:
I have a board with an STM32F103VGT6 MCU. Yesterday, the MCU worked fine, I had just gotten semihosting working, LED blinking, played around getting a timer running and so on.

I then decided to try to see if I can get the DAC to output a voltage. I simply turned on the peripherals (GPIO port A and the DAC itself), enabled the DAC and wrote a half-scale value. Once I uploaded the program and attached the debugger, the program started running fine, but while I was reaching for my DMM to check the DAC output, I thought I might be smelling burning electronics, though apparently the smell wasn't too strong as I wasn't worried at the time. Then the MCU suddenly stopped working, i.e. it stopped outputting the timer values on the debug channel, LED stopped blinking and so on. Based on the values output, this happened 26 seconds after startup (plus a few more seconds for initialization). At this point I realized that the regulator is very hot, and disconnected power from the board.

After trying out some things (which included connecting power for a few seconds at a time, as I didn't realize what's going on), I noticed that 3.3V and GND are shorted. I have a jumper on the board which allows breaking the power between the regulator and the rest of the circuit, for measuring current, and with that I was able to verify that the short is on the MCU side. The regulator seems to be working fine.

I'm now worried that I've burned the MCU and it's shorting internally. However, I don't remember it getting hot to the touch during the event, and now if I connect power for a few seconds, it does not heat up, which makes me doubt that the short would be in the MCU. The regulator pulls about 700mA (!) through the short, I would imagine that much current passing through the MCU would cause quite noticeable heating?

Also, I don't understand how could turning on the DAC or GPIOA cause such destruction (some details on the circuit in the end on the post)?

My questions:

What can I do to debug this? Obviously looking for shorts in individual components is a bit difficult, since the 3.3V and GND are shorted, so measuring decoupling caps or VCC pins for example just shows that the two sides are shorted. I have measured the non-power pins of the MCU, and those do not seem to be shorted to VCC or GND.
If it is the MCU that's broken, what, if anything, can I do to verify that? I'd really hate to cut the pins on the chip and remove it only to find out that the short remains.
How could turning on the wrong devices destroy the MCU (details on the circuit in the end)? It would be even worse if I swap the MCU only to burn another one (I have exactly one spare, after which there's a week of waiting and ridiculous postage to get the part...).

Now for the promised details:

as the board is mostly unpopulated yet, there is nothing attached to any of the pins of GPIOA, except the JTAG, which shares some of them.
the Vref+ -pin on the MCU is unconnected except for the decoupling caps, as there is a external reference which is not yet soldered on the board. As I was just testing, I was under the impression that VCC would be used for Vref+ in this case (although I realize now this is probably not the case). Could this actually cause destruction of the part?

Finally, relevant parts of the schematic, sorry for the messy layout:

Fig 1: GPIOA. All the labeled connections go to unpopulated areas of the board.

Fig 2: Power. 3.3VDAC is currently unconnected, but the caps are populated.

Finally, the DAC init code:

//Set up DAC1
RCC->APB1ENR |= (uint32_t)0x20000000;//Weird bug in stm32f10x.h,
                                     //the macro constant isn't defined for XL devices
RCC->APB2ENR |= RCC_APB2ENR_IOPAEN;
DAC->CR |= DAC_CR_EN1;
DAC->DHR12R1 = 2048;

I didn't write anything to the mode configuration registers, as it looked like they should be all zeroes anyway, and this was just a very first test to see if I can get something out of the DACs. Proper init code would come later.


texts: Is the float charging voltage the same as the maximum healthy open circuit voltage?

texts:
In my case I am looking at the Hoppecke OPzV (product page) lead acid batteries. In the two page Operating Instructions (link) it says

  2.3 Maintaining the full charge (float charging)

  Devices complying with the provisions of DIN 41773 must be used.
  They are to be set so that the average cell voltage is 2.25 V ± 1%.

Ok, so to maintain the optimal full charge, the float charging voltage must be 2.25V per cell.

Let's say the charger is float charging the battery, and thus the voltage is 2.25V. Then I disconnect the charger (and nothing else is connected to the battery). Will the voltage still be exactly 2.25V?
Let's say I have a cell (or many) not connected to anything. I want to know the charge level. Is 2.25V the "optimal", ie the voltage meaning that they are fully charged and not overcharged? Or should that number be slightly below 2.25V?

(Bear with me, I am not an engineer)