texts:
I constructed this circuit as shown for use as a simple headphone amplifier. I was so happy with myself that I made a second one for stereo, as well as using a 3915 to make a very simple volume visualizer.

The circuit uses a uA/LM741 as a "preamp" for the 386 audio amplifier. Through my reading, I learned there are much better op-amps to use for audio applications than a 741, such as the TL071. So, imagine my gaiety when I discovered a set of TL071s in my parts box. Well, I'll just plug them in (swapping the TL071 in where the 741 is without changing the circuit otherwise) and...

No dice. I have to change the bias on pin 3 (the noninverting input) so that it's biased at Vcc/2, which ends up limiting the amount of "volume" I can get out as well.

My question is, why can the 741 have its NI input hooked to ground and still function fine, but the TL071 needs a "typical" mid-supply bias?

I know that the 741 is a BJT-based design and the TL071 is a JFET op-amp, and you'll have to excuse me but I'm still just learning about FETs at the moment. Is this because of the larger offset voltage in the TL071 because it's harder to match device parameters in a FET?


texts:
I have to design a PID controller for a differential drive robot.

The hardware board consists of a AVR atmega168 running at 16mhz.
Driven by two 24v scooter motors with 256 CPR encoders
The motors spin roughly at about 4700 RPM and has a 51.56:1 gear ratio

So far I can read the encoder direction and the tick count. But I have no idea how to convert this to speed. And eventually a PID controller. I also want to be able to rotate the robot at a given angle. Can someone please help me to get started ?

Currently I am having problems figuring out a suitable timer calculation for this.


texts:
I know that the standard form of a second-order transfer function is as follows,
$$ T(S) = \frac{\omega_n^2}{S^2+2\zeta\omega_nS+\omega_n^2} $$
Now I have two transfer functions
$$ F(S) = \frac{25}{S^2+2S+25} $$
$$ G(S) = \frac{25+3S}{S^2+5S+25} $$
F(S) is clearly 2nd order and I can calculate natural frequency and damping ration by comparing it with standard form. But is G(S) second order? If yes, How can I calculate the damping ratio and natural frequency of it?


texts: EMC testing of polarity detecting circuit

texts: I am in the process of building a prototype and need advice on best way to ensure passing EMC testing the first time.  I am what most would consider a hobbyist and I am doing this project on a shoestring and I really can't afford to go through the testing process more than once. It seems from what I have been reading that EMI seems to be more of an issue at the kHz to MHz range. My device is very simple, consisting of 2 identical, polarity checking circuits in a plastic enclosure.  These circuits consist mainly of diodes but I have incorporated a LED that flashes at 2 Hz. There is also a 4 kHz piezo buzzer hooked up in parallel so that the "alarm" is in sync with the flashing. I don't imagine that the 2 Hz flashing would be an issue, but I am concerned about the 4 kHz buzzer. This is a simple DC circuit. Any advice offered would be greatly appreciated.


texts: Switching between a solar cell and battery?

texts:
What would be the best method of switching between a solar cell and a battery, I'm currently implementing a system that is functional so long as the solar cell outputs a voltage between around 2V to 7V (7V is the max voltage the panel can output). However, once the panel output dips below 2V the system won't be able to function correctly.

What would be the best way of implementing a battery backup system of some sort so that once the panel output drops below 2V the battery will take over and provide a steady 5V for example, and once the panel goes back to producing above 2V the system switches back to being solar powered.

Since posting, I have been looking into Relays - what would be the advantages and disadvantages of using a Relay Module controlled by an arduino? A relay module such as the 'Parallax 27115' looks like it'd do the trick. That way I could electronically control when to switch between power sources using the arduino? Is this a good solution?


texts:
I wanted to know exactly how does bluetooth sniff mode work.
Is this special mode going to affect data rates?

Is it used in active transmissions or in idle mode? I am a bit confused.


texts: Transformer drawing 29x more current than it needs

texts: I have an old transformer (20+ yrs) in a building I manage (GE Model 9T23B3872), it takes 277V 3-phase and converts it to 120V 3-phase.  It seems very wasteful.  It is drawing a combined 8.7 A @ 277 V or 2409.9 W from the breakers that feed it, but it only needs to be drawing 0.7 A @ 120 V or 84 W (the total current being drawn by all 120v lines in the breaker box that it feeds).  How can there be such a discrepancy between the load on the transformer and the current that the transformer is drawing?  There's almost a 29-fold difference here!  Is this par for the course in terms of transformers?


texts: How to use a CSV file from an oscilloscope for further analysis

texts:
I saved and opened this data from my oscilloscope:

How to plot the real scale waveform data? Do I have to multiply it with vertical scale?
And what about the time? What to do if I want to plot the waveform data in the time domain? Since there's no time data and all I have is the sample period, horizontal scale and position.
here's the waveform from the oscilloscope display

Thanks!!


texts: Which tool do I have to use for wire connector?

texts: I want to make the wire connector as the screen below. What tool do I need to use and how can I make it?


texts:
What does short circuit and open circuit mean ?
I mean practically what does short circuit & open circuit means?


texts: 5V and 1.4V switching circuit for a sensor

texts: Why this circuit provides only 2V on the load (33 ohms resistor) when the switch to the gate of the MOSFET is closed ? I was expecting it to switch between 1.4V (caused by the 85 ohms resistor) and 5V (when the MOSFET gate is on). I'm using the MOSFET 2N7000. Is there any way to solve this to provide 1.4V and 5V when the gate of the MOSFET is on ?


texts: Why do oscilloscopes have such high sampling rates when the bandwidth is low?

texts:
Lets say we have an oscilloscope with Bandwidth:70MHz and Sample Rate:2.5GSample/s.
Since we can capture adequately signals of frequency 14MHz (1/5 of bandwidth rule of thumb,) why do we need such a huge sample rate?


texts: Can a Magnet power a fan for a wind and electricity output?

texts: can it really be possible to power a ceiling fan with the use of magnets and could give you a wind and electricity output? how to do it? (For Remote Areas Without Electricity).


texts:
simulate this circuit – Schematic created using CircuitLab

I am working on a battery charger with indicator. I am using a LM358 to compare the voltage of my battery with a reference voltage of 8V from 7808. My input supply is 12V. The battery is connected to pin 2 (inverting input) and 7808 output is connected to pin 3 (non inverting input) of LM358. The Comparator is connected to 12V VCC through a 4.7k Resistor. Indicator LED is connected on pin 1 of LM358.

The expected output is that once the battery crosses 8V, the output of the comparator must swing low and LED will turn OFF. Initially, the output is high and LED glows as expected. But when the inverting pin crosses 8V, the output doesn't swing (High to low). However, when I touch any metal part to any component (lead of the component), the output swings low (from High) and LED goes OFF. But this doesn't happen automatically, every time I touch a metal I see the swing.I want this to happen automatically.

And if the battery is above 8V, and when I connect it for charging, the LED does not glow; which is correct. It is just the transition from High to Low I need. Can anyone help/suggest me what am I missing here?

Note: LM358 is used in open loop configuration and no feedback is given.

P.S.: I have inserted the schematic. Sorry if it is not clear, I am new to the interface.
Thanks in advance.


texts: Dangers in using parallel or series resistors for buck feedback divider

texts:
I have multiple adjustable DC/DC buck converters in a design and I'm looking to save lines in the BOM for assembly. Is there any significant drawback to using more than two resistors in a feedback network?

For example, if I need R1 to be 300k and R2 to be 150k can I replace a single 300k R1 resistor with 2 150k's in series? Assuming I use high precision resistors and can tolerate an increased ±% output tolerance what other negatives might I encounter?

Same question applies for resistors in parallel.


texts:
I am really confused with the above problem. I doubt the solution.

According to me,

Sampling Frequency of x(t) = HCF(5,12.5) = HCF(5,25)/LCM(1,2) = 5/2 = 2.5Hz

Sampling Frequency of y(t) = 3x2.5 = 7.5Hz

Nyquist Sampling Rate = 2 * 7.5 = 15Hz

Where I am doing the mistake? Please help me with this problem.

EDIT: I got confused because I was taught the following example in class and I tried to use the same here.

Q Find the fundamental time period for

x(t) = sin(22pit)+sin(7pit+30)

f = HCF(11,7/2) = HCF(11,7)/LCM(1,2) = 1/2

T = LCM(1/11,2/7) = LCM(1,2)/HCF(11,7) = 2

So, Fundamental Time Period = 2 using either of the above methods.

Is there a difference between sampling frequency and the fundamental frequency ?


texts: Controlling output voltage (12v to 0-12v 5a)

texts: I'm having a problem finding the right circuit/device for a circuit I need to make (I'm quite a noob). It doesn't matter what the input voltage is, but I need an output voltage which I can digitally change from 0 (or at least the lowest possible) to 12 volts. It needs to be able to handle 5 amps and sudden changes in the output voltage. Since I don't know how such a circuit is called, I have no idea if it has been asked before. Please tell me how I can make this or at least how this sort of thing is called.


texts: Simulation vs theory in 50 Ohm matched impedance clock lines

texts:
simulate this circuit – Schematic created using CircuitLab

I'm routing an aquisition system based on 3 high speed ADCs.

To trigger the conversion at the same time I planned use a clock buffer to split the master clock triggering to the 3 ADCs, so the Ds says routing clock lines with 50 ohm matched impedance. Ok well, my manufacturer (Eurocircuits) gives me track width acording prepeg height,Er and dissipation factor, also Altium gives me a similar width (0.2 mm TOP/BOT = 51 Ohms).

I used Altium SI to simulate these tracks.

With 51R series resistor termination:

Without series resistor:

With series term, looks very good in terms of overshooting/overvoltage. The clock buffer is LMK00105, the datasheet indicates: Rs = Zo - Ro, but I'm confused because transmission line Zo = 50R and output impedance Ro=50R gives me 0R, so why does the signal "look better" when I put in the 51R resistor?


texts: How do you find the equivalent resistance for the following question?

texts:
In the given circuit, i need to find the current flowing in the circuit when the switch is closed and for this i need to calculate the equivalent resistance between the terminals of the cell. How would you calculate the equivalent resistance between the terminals of the cell?

I calculated the equivalent resistance to be by taking 6 ohms and 3 ohms resistors in parallel and the equivalent resistance of these two in series with the 10 ohms resistor. The equivalent resistance between the terminals of the cell comes out to be 2 ohms and the current hence comes out to be 5/6 A which is not present in the options. (The options are-:2 A, 1 A, 3 A and 0 A.)


texts:
What type of a connector is the white one in the middle of the photo. It has pins on both sides and connects to the underside of a laptop motherboard.

I'd like to find an extender for it so that I don't have the two circuit boards directly and I can reduce the footprint.


texts: How scroll led in dot matrix without using microcontroller?

texts: I can turn ON my desired led in dot matrix. And given that i know about the trick of persistence of vision, help me.


texts:
I'm building an 8 stage coil gun for a physics project, and I want to verify this circuit as I've never used a phototransistor before and I'm still pretty new to mosfets. Here is a schematic:

The idea is that when the projectile (a penny in this case) crosses between the ir led and the phototransistor, the coil triggers until the penny exits the photogate. It will also light the 6 2v red LED's for the duration. I'm not sure that Iwired the mosfets to the phototransistor properly. I know that the load should be attached between v+ and the collector of the phototransistor, but that would require routing the potentially 100 amps of coil current through the phototransistor and remove the purpose of even having the mosfet there. would putting a pullup resistor between the collector and 5v and attaching the Mosfets' gates to the emitter work as intended?

As a side note, the coil will only be on for a tiny fraction of a second. If I hook up the red LED's to the red channel of rgb LED's that have blue on constantly, will a purple wave travelling down the stages be visible, or will I need to extend the red channel pulse? I could use a capacitor charging circuit between two NAND gates I guess, but I want to minimize unnecessary circuitry so it can all fit in a small-ish package.

Thanks for the help; I'll probably be back shortly with some troubleshooting for the actual coils haha.

EDIT: this is the phototransistor I'm using: https://www.sparkfun.com/datasheets/Components/LTR-301.pdf

EDIT 2: could I hook up 12 v to the phototransistor, or would I risk overvolting the mosfet? I need to break the mosfet's activation voltage, which the pullup resistor might prevent from happening.... Also not having to route a 5v line helps.


texts:
Trying to find what is the clock-to-output delay for registers inside EP4CE6E22C6.

Have looked through the 3 Cyclone IV handbooks searching by delay but have not found any values specified. All the delays specified appear to be input/output delays, not internal delays.

If with a 100MHz clock I'm latching data into a reg at the falling edge will this input register on the output 5ns later on the rising edge?

//clk - 100MHz
reg r1;
reg r2;

always @(negedge clk or posedge clk)
begin
  r1 <= in_data;
  r2 <= r1;
end


texts:
[![enter image description here][2]][2]USB C —————- Battery charge IC
Nominal 5.0V voltage delivers from usb C to Battery charge IC.
For ESD protection, I plan to add tvs diode between them.
SD05.TCT is with Vrwm of 5V , Vbr of 6V and Vc of 9.8V.
USB C PD is not supported for my project.
I think that chosen tvs diode seems tight..
Please let me know if there are better diode with same package size.
https://pdf1.alldatasheet.co.kr/datasheet-pdf/view/516632/SAMTEC/SD05.TCT.html


texts: Is it safe to use this relay with mains voltage?

texts:
I'm new to electronics and have recently fallen in love with it, after buying a few NodeMCUs to play around with. I currently have a load of them around my house monitoring things like temperature and humidity, but would like to further extend their use to garage door controllers and maybe even control mains voltage, which is what my question below relates to.

I have two questions both of which relating to this relay module:

I understand that the NodeMCU voltage out is 3.3V, however, the relay advertises itself as 3V. Does this small difference have any effect? (i.e. will it still work with a NodeMCU?)
Whilst I am new to electronics, I do fully understand the risks related to mains power and will take every precaution when dealing with it, including having one of my friends who is a qualified electrical engineer watching over me. The question is: Can the relay module specified above handle European outlet power? (I.e. could this be plugged directly into the side of the relay which is being controlled and have the NodeMCU control it on/off or is the voltage/current etc. too high to work with the relay module linked; either causing a hazard or frying the relay module/NodeMCU?)

I would really appreciate any guidance people can give me, as I am just in the research phase of a possible new project and would like to have a better overall idea of what is/isn't possible specifically with these relay modules. I have been unable to find concrete information on the Amazon page and have instead been told "One Channel 3V Relay interface board, be able to control various appliances, and equipments with large current" and "Optical coupling isolation, input and output power optional independent control ( DC 3V )".

Thank you in advance for any help.


texts: SPI to USB converter Question (for STM32F105)

texts:
I have a question regarding which SPI to USB connector to choose and what the main difference is between them. All i want to to is monitor the SPI activity going on which is possible through an SPI port connection on my board.

There are two USB to SPI convertors I have seen:

One at sparkfun and
the other at totalphase

Why is the price difference so big between them?


texts: Why don't capacitor's plates stick together?

texts: When capacitor plates carry opposite charges, then why don't they stick together due to attraction? They must stick since the plates have opposite charges.


texts: Trying to identify SMD component from a Ps2 Slimline

texts:
(English isn't my first language) I'm trying to fix an old Playstation 2 Slim my cousin had that was turning off by itself after 5 minutes playing. After some search on the internet, I found that it was a common overheating problem coused by the cooler fan not spinning, wich could be caused by two things: 1) The cooler is broken; 2) There's a sacrificial SMD component in the motherboard tagged PS17 that burned.
After quite some time I was able to fix and test the cooler, but it still wasn't spinning when plugged in the console, so I knew it had to be the SMD component. I tested it with a multimeter, and indeed it failed the continuity test. I saw in a video someone saying it was a "fusible resistor". I'm trying to identify it so I can search for some scrap component that could replace it or perhaps buy another one, but I wasn't able to find anything useful in the internet. It appears have a width between 1mm and 2mm.
The Ps2 is a 9000X series and I wasn't able to find any service manuals. I have a pretty amateur knowledge in electronics and this is getting me frustrated. I wonder if someone can help me.
(07/07/2020) Edit: I did more research and also ended up in this post: Please help me identify the SMD component in the picture (or help me fix my Wacom). So it's probably a SMD Fuse marked "MD". I still wasn't able to identify it.


texts: How difficult is building an op amp circuit with datasheet performance?

texts:
I want to build a simple voltage follower to buffer headphones with the OPA1688.
It will just be built on protoboard, considering how simple the circuit is I think it should still be possible to achieve close to the advertised ultra low distortion.
I will just follow basic, good design principles that you will find in nearly all op amp datasheets: Tying the output and inverting input pins directly together to keep feedback loop as small as possible. Adding ceramic bypass caps directly to the power pins. Adding individual ground wires from the power supply for audio inputs, audio outputs and bypass caps.
I can not test how well it performs or even if the circuit will be stable, but surely following those steps there shouldn't be any problem?


texts:
I need to build a box with 12 momentary push button switches for 12 separate lighting sources. I plan to plug 12 fluorescent lights into the box, then I'd like to control the lights with the push buttons (so I can turn them on and off along with music). This will accompany a theatrical performance.

Here's what I'm thinking:
Start with a 12-outlet surge protector power strip. Disassemble it and splice a push-button switch over each outlet's black wire. House the whole thing in a box with the switches on one side (so I can operate them easily).

I need help with the following:

Finding the right switch: would a Momentary SPST NO Push Button Switch AC 6A/125V 3A/250V work for my needs?
Finding the right housing: From what I'm reading online, a metal housing would be best to help ground the switches. But, I don't have a metalworking shop so I won't be able to custom-build a metal case. My original thought was to use a thick plastic box, which would be easier to drill and cut holes into. If I really should use a metal box, would a metal lunchbox work? What tools would I need to drill and cut into it?

Please let me know if there are any other considerations for my project, as this is my first project of this kind. Thanks!

If it helps, I'm using these lights:
http://www.homedepot.com/p/GE-Slim-Line-23-in-Fluorescent-Light-Fixture-10169/202024437 -- I may need to string two of these lights together (they can connect to each other)


texts: Velocity control system is stable even though CLTF has a pole at s=0?

texts:
I was reading about steady error calculation for system with H(s) having Nth order Zero at s=0.
In book it is written that steady error calculation is meaningless when closed loop transfer function(CLTF) M(s) is unstable(And it turns out same is the case here due to pole at origin in CLTF M(s)).
But in this example despite having pole at s=0. He is finding the value of steady state error (ess) for unit step input i.e,(R(s)=1/s). But i am not able to understand the justification he gave in the statement saying "The velocity control system is stable, Although M(s) has a pole at s=0, because objective is to control velocity with step input"
Also i don't get the meaning of the statement in last line that "if H(s) were constant for this type 2 system, the close loop system would be unstable. So,the derivative control in the feedback path also has a stabilizing effect".
I hope you all get the context so i am also telling the name of the book it is "Automatic Control Systems" By Farid Golnaraghi and Benjamin C. Kuo. And this problem is in the Chapter 5: Time domain analysis of control systems.
In Gist below paragraph is main source of problem: I think i am not understanding the term "Velocity control system" and how in this kind of system step input is used to control system output that contains ramp in steady state(figure is also attached for this statement)

Sorry for such a long post but if you please clear my concept with reference to steady state error chapter i would be very thankful to you.


texts: Why would an STM32 flight controller need programming interfaces other than USB?

texts: I am new to STM32 chips. I am currently working on a self driving airplane and I have realized that the processing power of an Arduino is not enough so I decided to try to create a custom PCB as a flight controller that will have a STM32F756NGH6 as the main processor. While designing the PCB I read that I should not use USB for programming but SWD interface. After googling I could not find anything that could explain why I should not use USB. USB would be a much simpler and cheaper solution. The datasheet also says the this chip is capable of USB communication so I really do not see any reason not to use it.


texts: Bare-metal start-up code for Cortex M3 .bss region initialization

texts:
I have developed inspired from here a bare metal start-up code for arm cortex M3. However, I encounter the following problem: suppose I declare an uninitialized global variable, say of type unsigned char in main.c

#include ...
unsigned char var;
...
int main()
{
 ...
}

this makes the .bss region in STM32 f103 starting at _BSS_START=0x20000000 and ending at _BSS_END = 0x20000001. Now, the start up code

    unsigned int * bss_start_p = &_BSS_START;
    unsigned int * bss_end_p = &_BSS_END;

    while(bss_start_p != bss_end_p)
    {
        *bss_start_p = 0;
        bss_start_p++;
    }

tries to initialize to zero the whole .bss region. However, inside that while loop the pointer increases with 4 bytes, therefore after one step bss_start_p = 0x20000004 hence it will always be different than bss_end_p which leads to an infinite loop etc.

Is there any standard solution to this? Am I suppose to "force" somehow the dimension of the .bss region to be a multiple of 4? Or should I use a pointer to unsigned char to walk through .bss region? Perhaps something like:

    unsigned char * bss_start_p = (unsigned char *)(&_BSS_START);
    unsigned char * bss_end_p = (unsigned char *)(&_BSS_END);

    while(bss_start_p != bss_end_p)
    {
        *bss_start_p = 0;
        bss_start_p++;
    }
```


texts: Split AC current from one wire into two wires (+ and - DC wires) using bridge rectifier

texts:
I am new and a novice. I apologize if this is a ridiculous question. I have a ground/bond wire coming from the Cable TV intersystem bonding bus bar that is carrying current and a lot of "noise" on it. It is contaminating the ground rod and traveling backing into the home. I want to filter the noise out before it touches the ground rod.

In addition to using clamp-on ferrite beads, I am wondering if I could take that Cable TV bond wire current and split it into two wires using a full wave bridge rectifier creating a DC black negative wire and red positive wire so I could wire EMI filters to it?

I have heard one could attach capacitors to lower the noise or pay for various EMI filters. If there is only one wire, I am not sure how to wire the filters or capacitors that have positive and negative terminals. I have thought about using the house ground rod as the negative and the Cable TV as the positive but don't want to cut the ground rod connection.

I am most interested, curious, if it is possible to create two DC wires (one red positive and one black negative) from the one AC bond wire using a full wave bridge rectifier and capacitor. Is this ridiculous? Thoughts or suggestions? Thank you for your patience!


texts:
A friend asked me to make a simple regulator for a high current load: a 13.8+-15% V, 20 A (a radio). The input is a 13.5-16.8 V LiPo 4S pack. Obviously, the pack cannot be discharged completely. Still, a LiPo buzzer will be used to notify low charge.

I chose the components that I had available and I designed this circuit. I placed only one MOSFET, I plan to have two in parallel for better heat dissipation.

I tried to simulate it with CircuitLab, to ensure that no power-up transient would damage the radio, and the output voltage seems never to go beyond the set voltage.

Are there other potential issues in this circuit that I may have overlooked? I wouldn't like to the radio to get damaged.

For example, in CircuitLab I notice that there is a resonance at about 250 kHz where little PSRR is achieved. Can it be improved? In fact, the input voltage is very stable, only the load can be variable due to intermittent transmission. I'm not sure that frequency analysis is relevant in my case.

Edit: by using time domain analysis I noticed that this circuit is oscillating quite a lot. I guess such a simple circuit cannot be reliably used.

simulate this circuit – Schematic created using CircuitLab


texts: Postive input ==> Positive and Negative output

texts:
I was watching some tutorials on thesignalpath.com and came across something that I didn't quite understand (even after it was explained).

toddrharrison
August 21, 2011 at 6:29 PM
Answer to first op-amp: You are using it as a high impedance voltage follower to split your single power supply into a plus and minus dual source.
Details: Your single power supply source will be feed into a 50/50 voltage divider circuit with relatively high resistance to keep the voltage divider’s current to a minim. Then this divided voltage is feed into the first op-amp’s non-inverting terminal. The out of this op-amp is feed back into the inverting terminal with a short creating wait is called a voltage follower. The output of this op-amp then becomes your new common for the other three op-amps.
Results: This makes the single source power supply’s ground look like a minus voltage supply and the positive looks like 1/2 the original positive supply to the part of the circuit using the voltage follower’s output as common. From this you can power your other op-amps with equal + and – power rails. What do I win?

http://thesignalpath.com/blogs/2011/08/21/op-amps-pwm-and-ignition-coils-tutorial/#comment-71

Is this a matter of connecting Vout of the voltage divider to the Vin of the voltage follower?
So the voltage follower Vout is -1/2 voltage divider Vout, yes?
Would I have a 2nd output on the voltage divider between R2 and GND for my +V rail?
I hope this is not confusing.


texts:
I am working on an adjustable current source.   In a thread awhile back, various circuits were discussed:

simple adjustable current source for LED string

... but as I have settled on one option, and it's not working correctly, I'm starting a new thread to focus on my conundrum.

Here is the circuit:

The resistor divider (30K resistor and potentiometer) provide a reference voltage on 'set' (the DC sweep of v1 just rotates the pot shaft).  The opamp should servo 'gate' so that 'sense' equals 'set', and thus the current (in milliamps) pulled through the load 'Rload' equals the voltage of 'set' (in millivolts).   Simple as that.

The 12v supply which powers the 'set' circuit and the opamp is a 7812 powered off the 24v supply.   And the mosfet is actually a FQP10N20C (a fairly vanilla power nfet).

I've simulated with LTspice and it behaves as I'd expect. But on the breadboard, as 'set' is increased from 0 to about 400mV, 'sense' tracks 'set' less and less well.    At one point I'm seeing 257mV on 'set' but only 226mV on 'sense'; so only 226mA is flowing through Rload and R1.   'Gate' is at 3.53V and 'down' is at 11.7V.   If one just examines the opamp in isolation, it seems that 'gate' should be driven higher (until, presumably, at some point enough current flows that 'sense' equals 257mV).

The opamp is meant to be used with a single-ended supply, and should easily be able to drive its output above 3.53V (with a 12V supply voltage).   The gate of the FET should not be sinking any current (verified with meter).

I'm stumped.

Datasheet for the opamp (LT1006)


texts:
I am trying to install a photo eye to use for a lay down bottle sensor.
I wired in the power, it turns on the light on the sensor flags when triggered.
But I’m not abel to trace where the signal is happening on the wiring. It’s a 4 pin and below is the schematic . Someone told me they had to use a relay to get it working something about separate power. But the photo eye should be self contained. So I don’t know why they needed to add extra stuff to get it to work.
Below is the schematic it comes with. Any help in understanding would be greatly appreciated. I can get it to work with the relay. Like the other person suggested I’m just not sure why.
Thank you


texts: The ideal op-amp in open loop, has a frequency response with infinite bandwidth. What about an ideal op amp in closed loop (inverting, non-inverting etc.) configuration? Does it (still being an ideal op amp although now in closed loop) also have a frequency response with infinite bandwidth?


texts: How to find True power dissipated and apparent power?

texts: I have to find the true power dissipated and apparent power for this RLC AC circuit. I've already found the impedance, the current from the supply and the current from each branch but I've forgotten how to find the true power dissipated and apparent power. Help would be appreciated. Sorry for the rough circuit.


texts: CAN bus communication. Issue with two slaves having same CAN ID

texts: Does anyone know if it is possible to have CAN offsetting in case two slaves in same circuit transmits different data in same ID?? I have two slaves with same CAN ID transmitting data and I cannot change the IDs but I need to capture both data for further processing. I heard something about offsetting the CAN ID of one to get both data for post-processing but could not find much material. Thank you


texts: How to pick right value of capacitor while switching DC source

texts:
I have two loads consuming 0.5A,12V and 0.6A,5V. Load demanding 12v is powered through boost converter and 5v Dc source. And load demanding 5v is connected directly to 5v dc source. By design, whenever dc power source switch goes from one source to another there is a black out for 1second.
I read somewhere a capacitor can solve my problem. Can someone please help me calculate a capacitor value for above load for a second?


texts: Watchdog with long on and off periods for microcontroller

texts:
I have a microcontroller (Arduino-like IoT device) and would like to connect a low power external hardware watchdog to be able to recover from failures. I know that a software watchdog is already incorporated, but it's just not sufficient in this case.

The requirements are:

WD's output to start on "on" state and be able to stay in this state for at least one day in the absence of external trigger.
If it receives a high signal from the microcontroller, it should reset (i.e. extend the "on" state for another day).
If it doesn't receive a high signal from the microcontroller within the predefined time period (e.g. one day), it should timeout and switch its output to "off" for at least 10 seconds.
It would be nice if the on and off periods are configurable (hardware-wise, e.g. through a potentiometer).
Operation voltages 2-6V.
Price does matter, as it's for a relatively cheap IoT microcontroller.

To give an example of what I'm trying to achieve, the best solution that I've come across that should cover my needs is this one: https://www.ebay.com/itm/DC-3V-24V-automatic-re-trigger-cycle-delay-time-timer-switch-module-max-20days/303098128782 (unfortunately, it exhibits instabilities and even worse the IC on it is not labeled).


texts:
I've read about it, checked a few youtube videos about the subject but I still can't understand the process.

What is it that makes high voltage + AC current a better process to transport energy? I have seen formulas, but I need to understand how it works conceptually first.

If we use High Voltage (to cope with the resistance over a long distance) together with DC current a lot of energy is lost due to the continues resistance and the same happens with AC, so how is that one is better that the other one?

The only difference I can see, is the relief on the cables because of the polarity switch, is that why AC is better to transport electricity over long distances? Please don't use formulas to explain it, I need to understand how it all works first.

And if the voltage is higher how can the current be lower? I mean, there's a stronger force to push the electrons, so shouldn't it be the opposite?


texts: Class C Amplifier: Calculating the base resistor

texts:
I've built a Class C amplifier for educational purposes and believe I understand the major concepts on how it works. The only piece I'm struggling with is how to calculate for the base resistor. From the resources I can find, they authors talk about calculating the RC base network for 10 times the input signal time. My experience is quite different.
The circuit below has the following:
Input signal: 11.628 kHz (tuned to the tank circuit) @ 2v p-p
Tank circuit: C3 = 213nf, L1 = 877mH
Base clamping circuit:
C1 = 100uf
R = is a variable resistor. I've dialed it to 1.1K ohms, which produces the optimal output p-p signal. The circuit works as expected, but just lost on getting the right math.
My question is: what is the formula to correctly choose the base resistor? Any good resources on negative clamping circuit calculations?


texts:
How would someone test Vih, Vil of an input pin (Or VoH, VoL of output pin) of a SoC. With an inverter, you could easily see the results but with a microcontroller/SoC, it seems difficult without the device being used in a circuit.

https://www.arrow.com/en/products/am79c874vd/amd#page-2 For Example

Picking any input pin on the device, how would I test ViH, ViL?


texts:
I got some high lumen LEDs. When I power them singularly they are indeed very bright.
I connected 52 of them in parallel in parallel and plugged to the same power source and the brightness dropped significantly.
The LEDs are 3.2v,1W. The battery pack (a controller for christmas lights) has 3 AA batteries. How can I fix the issue? Shall I add more batteries in parallel?
These are the specs given on the shop:

Matériel: Base d'alliage d'aluminium
Type: Perles de LED, SMD
Couleur de la lumière: blanc chaud, blanc (facultatif)
Longueur d'onde: 380 ~ 840nm
Puissance: 3W
Température de couleur: 3000 ~ 3200K, 6000 ~ 6500K
Tension: 3.2 ~ 3.4 V
Courant: 350mA
Luminosité: 100 ~ 110lm


texts:
I am building a controller for RGB LED strip (12V 5m 5050 LED RGB strip with common anode). My current solution uses Arduino Uno with 3x IRFZ44N MOSFETs to power the strip. The solution is partially inspired from this site.

The problem is PWM resolution where 256 levels are not enough to have smooth "true color", especially for lower brightness, because eye's light perception is exponential. There is a way to adjust levels so that brightness would be linear but changes at low light intensity will still be "jumpy".

From what I've read it is possible to use Timer1 to produce 10bit PWM at two pins. Unfortunately I am missing the solution for the third pin.

I've read some articles about TLC5940 but found no good solution for as high current as I need.

Is there any relatively simple solution to have Arduino (or AVR) controlling 10bit (or better 12bit) PWM which I could use it as input to MOSFET transistor to use with 12V and current > 1A?


texts: Opamp input fault current limit vs fault duration

texts:
A usual datasheet rating for maximum allowed input current into opamps is 10 mA. Initially I thought that this is some kind of DC limit of what the clamping diodes could handle before thermal destruction. I thought that this can be exceeded if the fault is short e.g. a few ms.
However then I learned that silicon latch-up could be the issue if the input current (and thus voltage) reaches a critical level even momentarily.
But during ESD the input current can be much higher without causing permanent damage. At least this is what I assume if opamps claim an ESD rating in their datasheet.
So the question is: can the input current be exceeded for
transients? And if so for what approximate duration?
Edit: I am specifically interested in bipolar and JFET input opamps. And in precision application where a series resistor is sometimes not an option.


texts: What is the truth about 1.5 V "lithium" cells?

texts:
At least one manufacturer out there is marketing "Lithium" cells in familiar AA and AAA sizes, as direct replacements for those standard 1.5 V sizes, boasting the typically better than alkaline longevity you'd expect from lithium.

But we all know the range of lithium technology cell voltage is expected to be 3 V for single use cells, up to a max of around 4.2 for li-Ion variations of rechargeable at max charge. All my attempts to research what the truth is (short of buying and cutting one open) have resulted in little more than manufacturers hype. Can anyone shed light on what is going on with these? A stretch to think perhaps they actually have embedded buck converters under the hood? Or has a genuine 1.5 V lithium technology actually been invented?

I've included one manufacturer's photo as a reference


texts: How to mount a narrow component on breadboard?

texts:
I have a narrow component with two rows of pins. The pins have the right pitch but the rows are too close together to be placed over the non-conducting gap between E and F rows of the breadboard. The distance between rows is only 3.2 mm. There are 5 positions on each side (1 pin, a gap, and then 3 more pins). It is Axicom minature relay.

What is the best, recommended practice to mount such a component? I consider:

Solder extensions to the relay contacts. This would be a rather delicate work with the 2.54 mm spacing.
Bend the pins, but they may get too short and do not go into the board deep enough.
Try to disassemble the breadbord and have the two rows separated. I would like to know if possible at all before ripping it apart.
Try some connector (which one?).
Order another component for prototyping. But we will use this one in production.

Drawing of the relay I need to integrate can be found here.

Any other ideas? I would like to know how it is typically done with such components.


texts: How do I know what the right signal amplifier to use is in order to program a hall-effect sensor?

texts:
I am trying to look for a signal amplifier in order to program the sensitivity and offset of the A1362 Hall-Effect sensor.

Doing a simple google search reveals:

http://www.amazon.com/RDL-ST-VCA3-Voltage-Controlled-Amplifier/dp/B0051V1JRG

But I feel like this is overkill for the hall-effect sensor.

In order to program the hall-effect sensor data sheet I need approximately 27V to send a high pulse, 15V for a mid, and less than 5V for a low pulse.

I would appreciate it if someone could point me in the right direction with regards to the bare minimum voltage / signal amplifier needed to program the hall-effect sensor.


texts:
There are 3 stages that every VHDL program undergoes: parsing, analysis and elaboration. Elaboration is circuit instantiation once top entity is specified. Analysis is something that determines available entities. What is it actually?

It is probably applied computer science question, but I see the vhdl tag specified here.


texts:
Im using a 3.7V 18650 Li-ion battery (Ultrafire) and the circuit calls for a 27 ohm resistor. But one battery tested at 4V and the other 3.7V.

Is the resistor too low now? Which rating should my circuit be based on, the 3.7V battery rating or the 4V actual rating?

http://s29.postimg.org/rxgzi0kzb/LED_schematic7.jpg


texts: Converting raw temperature data to Celcius L3GD20

texts:
I have an L3GD20, which is an accelerometer with a temperature sensor built in, and I want to make sure my math isn't funky regarding the temperature.  I'm not exactly experienced with embedded hardware.

I've been playing around with the temperature sensor on the L3GD20.  According to the datasheet, the temperature is represented in 8 bit 2's complement, so it goes from -128 to 127.  However, the datasheet includes this little snipp:

So, if I'm understanding the datasheet, the temperature sensor will deliver a temperature range of -40c to +85c in 8 bit 2's complement.  So, a raw value of 127 (0x7F) from the sensor would correspond to +85c, and a raw value of -128 (0x80) would correspond to -40c.  Therefore, the spacing between consecutive readings (for example, 0x00 and 0x01) is approximately 0.5c.  I came to this conclusion by taking the temperature range and dividing it by the output range of the sensor: (85 - (-40)) / (127 - (-128)).

But then here's the part where my math gets fuzzy.  If the temperature range remained the same (125c from smallest to largest), but was centered on 0, it would go from -62.5 to +62.5).  But it doesn't.  It goes from -40 to 85c.  Therefore, the temperature range has a positive offset of 22.5c. But since there's approximately 2 codes from the temperature sensor for every degree Celsius, a raw value of 0x00 from the sensor would correspond to 11.25c, correct?

TL;DR version:  I have a temperature sensor that ranges from -40c to +85c, and gives the reading back in 8 bit 2's complement.  In order to get the actual temperature in degrees Celsius, I believe I need to add 11.25 (or just 11 to keep things simple) to the sensor output.  Is this correct?


texts: What does it mean for a signal to have an amplitude below 0 dB?

texts:
I am a software developer (using high level languages like .NET,C,C++ etc) trying to understand how computers work at a lower level.

I understand that amplitude is always positive because it is calculated by (top-bottom)/2.  However, I don't understand what a negative amplitude actually is i.e. what does it mean if the wave falls below the equilibrium (0).

The negative values that appear confusing are given in decibels (dB).

This is probably more of a physics question but I am trying to understand analogue circuits.


texts: How to power a lower-power circuit and an audio amplifier off the same source efficiently?

texts:
I want to create an audio amplifier that powers itself one when it detects audio coming in. I've found a low power IC that can signal when audio is present: NJM2072.

I figure I could use that switch to throw a relay or similar to send power to the amp.

The trick is that the amp designs I've been looking at require ~12 volts and will generally suck a lot of power. The NJM2072 takes 7V max and I'd like it to consume as little power as possible. Ideally, however, I'd like them both powered from the same wall-wart.

I could use a step down converter to convert the 12V line to something lower, I presume. However, it is my understanding that voltage regulators like that aren't known for being efficient. It defeats the purpose of powering down the amp if the audio detector is going to suck a lot of energy.

I should note that I am a circuitry enthusiast with only modest knowledge. I still don't have a firm grasp of power, efficiency, and voltage stepping.

Edit: Since folks are curious, I am thinking of an amp along the lines of https://www.sparkfun.com/products/9612, though I am by no means settled on that. It will be a modest power amp either way.


texts: Best way to power a microcontroller, SMPS vs Linear Regulator

texts:
I'm using a 12V adapter and a 2S 7.4V Li-ion battery to power my electronics, and I would also like to power my MCU with it. To switch between the adapter and battery I'm using a BQ24133 from TI.

I will use an STM32L4 MCU and some other components that use 3.3V on a custom PCB. Everything together on 3V3 uses up to 150 mA when in full operation mode.

I'm searching for the best/cheapest solution.

1. What is the difference of using buck converter vs linear linear regulator to power an MCU?

2. Would a linear regulator (small packages) be a bad idea because it would heat up a lot because there is a big difference in voltage (12-3.3=8.7, 8.7*0.15=1.3W) ?

3. Would the frequency of switching, or output voltage ripple (noise) be a big influence on the normal operation of an MCU?

4. Conclusion, what is the best way to power it with the input voltages between 6V and 12V?

Thank you for you patience and your answers.

Thank you for all your answers. You all were very helpful. Up until now I used linear for my projects, but I think now I might go buck. If you wanna follow up the reason I asked this, and see what I am making, follow this link


texts:
I try to understand inductors and inductance.

I create a multi-layer circular coil with 35 turns of enamelled copper wire ~21AWG (0.75mm precisely) with a diameter of 8.5cm.

    Maths results:
        MULTILAYER CIRCULAR COIL
        -------------------------

    Inductance          : 0.16mH/160.45μH
    Number of Turns     : 35
    Coil Inner Diameter : 8.5cm
    Wire Length         : 934.62cm/9.35m
    Turns per Layer     : 20
    Number of Layers    : 1.75
    Coil Length         : 1.5cm
    Thickness           : 0.375cm
    Coil Outer Diameter : 9.25cm

Then I realize an inductance meter from this tutorial using my arduino and the LM239N comparator instead of the LM339 and a 100nF capacitor instead of 2μf. This counter inductance returns me 171.23μH. Here, I am very close to 160.45μH.

But ,I create a multi-layer rectangular antenna of 105 turns of enamelled copper wire ~21AWG (0.75mm precisely).

Maths results:
    MULTILAYER RECTANGULAR COIL
    ---------------------------

Inductance          : 0.923mH/923.272μH
Number of Turns     : 105
Width               : 4.589cm
Length              : 5cm
Wire Length         : 2013.69cm/20.14m
Turns per Layer     : 16.67 *
Number of Layers    : 6.3   *
Thickness           : 1.4cm
Coil Length         : 1.25cm

  .--------------------.
  |          ↕b        |⋱↘h
  |  +--------------+  | '
  |  |\_____________|  | |
  |  ||             X  | |
  |  ||             |  | |
  |  +-------Y------+  | |
  |                    | |
  .--------------------. |
   ⋱___________________⋱,

   X: 4.589cm
   Y: 5cm
   b: 1.4cm
   h: 1.25cm

 * I use 10 turns per layers.

The inductance meter returns me also 171.23μH for this coil (yes exactly the same value of first circular coil).
I don't understand why my second coil is so far of ~1mH (my second coil maths calculation) and the same as my first circular coil result.

The LM239N have the same LM339's response time used in the inductance meter tutorial.

The range of inductance meters is given for : 80μH to 30mH.

How to correctly mesure inductance please. Thank you for your help.


texts: Voltage on the secondary of current transformer

texts:
We know that current transformer is used to step down the current of the primary side. So basically it is a STEP UP transformer. Also we say that current transformer basically works on close to short circuit mode.

So if \$ {V1\over V2} = {I2\over I1} = {N1\over N2} \$ and N2 >> N1 so V2 should be also very much high than V1. So if we are trying to short circuit this large voltage, how it is going to work as large current will flow in the secondary also. Don't you think it is going fundamentally wrong?


texts: Simplify this CAN to CAN transceiver circuit?

texts:
I currently have a circuit that does this, is there a way to simplify this circuit, ossibly with isolation?
Do I need the BJTs? or can I just connect RX to TX and TX to RX then have a CAN to CAN bus isolator?


texts:
I got a mess of components at an auction a couple weeks ago, including an unmarked box of unmarked bridge rectifiers. They're about 1" square & 1/4" high if that makes a difference in terms of an input voltage for testing. I don't know if there are ANY inferences that can be made from size, shape or color. The bottom has the typical one blade that's oriented perpendicular to the other three.

What is the best way to figure out what I've got? I'm not a big fan of the "if it smokes, that's too much voltage...back off a titch and see if the next one smokes" method.

UPDATE: I found a scribbled note in a box of capacitors marked "40/50v Rect", and sure enough, they all test in that range. Now I've just gotta figure out what to do with 'em. Amperage experiments coming up next, but I'm at least confident that I'm starting from a place where nothing will explode. Too much. :)


texts: Impedance matching network for a varying load

texts:
A good impedance matching network should match a load to within a maximum SWR (typically less than 2?).

But with a varying load (i.e. Antenna in varying surroundings), are there any techniques that match a widely varying load to a less widely varying match?

In other words, if the plotted range of a given antenn's loads on a Smith chart were the size, so to speak, of an SWR circle of 3.5, is there a matching technique that results in a matched impedance that is always less than 2?

UPDATE
In my particular case, I'm working with a Maxim 7044 transmitter at 320MHz in a wireless sensor. So large SWR voltages aren't the problem. I want to maintain an SWR < 2 under all conditions, with an antenna that occupies most of a quadrant of the Smith chart.


texts: Best way to handle 100 GPIO on AT32UC3C0128C

texts:
I want to monitor 100 GPIO pins on the AT32UC3C0128C and indicate the changes on the USART (RS-485 transceiver).

In the code snippet below, I have set one of the pins as an input with the internal pull up activated.

#include <asf.h>
#include <gpio.h>
#include "PinDefine.h"
int temp;
int main (void)
{
    /* Insert system clock initialization code here (sysclk_init()). */

    board_init();
    gpio_enable_pin_pull_up(AVR32_PIN_PA04);
    GPIO_DIR_INPUT(AVR32_PIN_PA04);

    gpio_enable_pin_pull_up(AVR32_PIN_PA05);
    GPIO_DIR_INPUT(AVR32_PIN_PA06);

    if (gpio_get_pin_value(AVR32_PIN_PA00) == true)
    {

    }

    /* Insert application code here, after the board has been initialized. */
}

I understand that I need to configure each pin (copy and paste exercise). What is best way for me to monitor the GPIO, without having 100 if {} statements? Haven't figured out the USART yet.

Any suggestions will be appreciated. Thanks. (new to coding)


texts: Simple \$12V_{AC}\$ to \$12V_{DC}\$ Rectifier

texts:
I want to convert a \$12V_{AC}\$ power supply output to use \$12V_{DC}\$ to power some outdoor LEDs.

The power supply as it stands will light the LEDs (with a slight flicker from the reverse polarity portion of the AC) but I have been told this may reduce the life of the LEDs having them reverse polarity for a long time.

So can someone suggest a simple rectifier circuit I could build or point me in the right direction of which one of these Maplin rectifiers is suitable (I'm not sure what the specifications refer to exactly)?


texts: Measuring the phase difference between two signals

texts:
I'm looking for an analog method of measuring the phase difference between two signals operating at frequencies in the range from (0 - 20 MHz). I'm wondering if there's an IC that does that or a specific circuit that converts the phase difference into a voltage signal.

Thank you very much


texts:
I don't want to damage the pins on my Arduino Uno, and I'm especially cautious of drawing too much current.  I'm experimenting with a small servo motor (similar to this one), and have connected the power line to the Vin pin on my Arduino.  (I'm powering the Arduino via a 9v battery connected to the DC jack).

I know the current limits for the digital ports (which are covered in this question), but I haven't been able to find any current draw limit for the Vin pin.  Is there a limit determined by the Arduino hardware?


texts: Modifying a N64 controller to connect to a switch

texts:
I am trying to make a game, and I need to turn my N64 controller on and off from a micro controller (STM32F4). My microcontroller has an output pin that outputs approximately 5V, for testing reasons I have currently kept this pin high at 5V. To create this switch I cut the cord connected to my N64 controller (that connects the N64 to the controller) in the middle. I have 3 wires (red-3.3V, black-grd, white-data), which is information I got from online.

However if I disconnect the power (3.3V) for some reason the controller works only the joystick does not. The only way the controller completely stops from working is by disconnecting the ground. Therefore as shown in my circuit below. I connected the microcontroller 5V output to the base of the NPN. I then connected the ground output from my controller to the collector of the NPN, and the ground from the N64 to the emitter of the NPN transistor. I tried the transistor with an LED and it works, so I know my microcontroller and my wiring is not bad. However for some reason if I connect the controller with this setup and turn on the 5V from the microcontroller nothing happens (it remains disconnected). Anyone have any advice or other circuit designs to help me out please?

simulate this circuit – Schematic created using CircuitLab


texts: LED driver does not give constant current with a load

texts:
I'm working with an AL5810Q, which is a linear LED driver where the current can be set with only one external resistor following $$I_{LED}=\frac{750}{R_{SET}}.$$
With that, since I need a current of 10mA I calculated an external resistor of 75kΩ. (Vin = 12V)
I did a simple test following the schematics provided in the datasheet, which are the following

So far, so good. 10mA Sharp.
However, the application I have in mind considers a very high line impedance (≈100Ω/mm) so I wanted to model that impedance by means of a resistor of 330Ω, which would leave the previous schemes like this:

by implementing these resistors the current is no longer constant and becomes a ratio to the voltage.
To be honest, I was not expecting this behavior, but it doesn't surprise me. The block diagram is as follows (with resistors)

can anyone shed some light on what might be happening and what I can do to fix this.


texts:
The HCPL3700 seems to be a wonderful IC for sensing all kinds of input voltages, however it is a bit pricey so I was looking for alternatives. Alternatives I'm looking for should not contain components like transformers or other not widely used or large components. Isolation is preferable.
One alternative I found is using X2 capacitors combined with a Z-diode, resistors and an optocoupler, however X2 capacitors have a pretty huge footprint and the circuit is not made for sensing DC voltages.


texts:
I'm working on a simple alarm project and would like to build a circuit which gives a short tone when the alarm is armed and also a again once disarmed.can I do this with a 555? I am a begginer so am trying to keep things simple, And also what would the name of this type of circuit be called?
Any help would be appreciated.


texts: What is the maximum physical current that can pass through a standard USB cable?

texts: I am looking at hi-jacking an USB cable to supply to supply > 2.1A to the target.  What is the physical current limitations of a standard USB cable?


texts:
I'm working on a sensor which purpose is to measure the water level of a sinkhole without getting in touch with the wastewater.
The Sensor is mounted beneath the manhole cover --> The underside is formed like a rhomb and the sensor fits perfectly in the center bulge --> something like this --> similar Manhole Cover.  The whole system is attached to the Manhole cover with strong magnets.
The heart of the sensor is an ESP8266-12F. The whole system runs on 3,6 Volt.

An ESP8266-12F measures the distance between manhole cover and waterline via ultrasound (HC-SR04) uploads the measurement to Thingspeak if its able to locate a known WiFi nearby and additionally transmits the measurement via 433 MHz to a Receiving Unit.
The receiving Unit uses and Arduino micro, a RTC modul and a 433 MHz receiving unit.

433 MHz transmitting and receiving unit are equipped with those antennas AntennaP  Picture
This are the 433 MHz Receiving and transmitting Units: 433 MHz Superheteodyn
I want to achieve approximately 10 Meters transmitting distance from the manhole cover to the receiving unit.

I tested the system in my flat and on numerous distances without any problems and was really confident that an obstacle like the Manhole Cover + 10 Meters Air wouldn't be any problems.
I knew that getting the signal out of the sink would be the tricky part because of all concrete and steel and I've got pretty much no experience with radio frequencies and the way they behave.

Today I was able to test the whole system --> The upload to ThingsPeak works like a charm. The WiFi has to be within 10 Meters from the manhole cover so that the ESP8266-12F is able to establish the connection.
The 433MHz connection however fails.
I need to be within 2 Meters of the manhole cover to get it to work.

Question:
What could be the reason for this bad 433 MHz result. Why is the 2,4GHz Signal so much better than the 433 MHz signal ---> I thought when it comes to obstacles a lower frequency is better?
Are the antennas bad? Can I improve them? Would it be better to use a long Cable with 17 cm? (Lambda/4)
Would it work better with higher VCC than 3,6 V. As far as I know the transmitting unit isn't supposed to go over 3,8 V. The receiving unit runs on 5 Volt from the arduino micro?


texts: Advantage of PWMs over an Oscillator based Induction Motor Drive

texts: Variable Frequncy Drives commonly use pulse width modulation to generate frequencies for driving induction motors via the use of microcontrollers. Is there any advantage to using MC based PWM signals instead of an oscillator circuit (Wein Bridge?) to generate frequencies?


texts:
I want to listen TV channels without display (terrestrial) just like FM Radio
channels. There are lots of FM receiver circuits on the web but I couldn't find for TV channels. Is such a thing possbile for beginners or it is just an advanved topic?


texts: As servos use PWM and duration pulse determines the angle, the way to control a servo is via programming or an IC component is required?


texts: Led driver interference on lcd screen but only when with 1 power source

texts: I have a few lcd open panel screens I've modified with higher powered led strips instead of ccfl. In doing this I needed to add led drivers for voltage and current regulation. When utilizing the same power source there is so much noise and static and interference that the screen shuts down. When not changing anything except running the power to the drivers via a seperste power source (even non-grounded AC/dc) I get no interference at all. I built an LC filter which helped a bit but these are still unusable. I need to use them off the same power source because they are portable. I can't seem to figure out how to reduce the interference. Any ideas?


texts:
I loaded up the example sketch for the itead Motomama on my Arduino Mega ADK and I see the green led's in the middle of the board slowly going on and off as expected from the sketch. The problem is, as soon as I connect a motor, well, nothing happens and the LED's don't do anything either (on the side that I connect the motor . . . the other side works fine). I use the same motors on the official Arduino Motor Shield and it works fine (using a 12V input).

When I check the voltages comming off the screw terminals I see it going from about -6 volts to 6 volts . . . much like when I check the volts on any PWM pins.

I tried connecting the power directly to the Vin/Ground pins on the shield and got the same result.

And, I connected a BTBee to the XBee socket and added a bit of sample code to send text from the Arduino through BT back to my phone (using a test app) and that part works fine too.

There are a couple of jumpers on the other side of the screw terminals and I can't help but wonder what they do but haven't seen anything in the (sparse) docs about them.

Any ideas?


texts: Can you run an x86 class processor ramless?

texts:
Modern x86 processors have at least 512K of L2 cache. There are applications which would fit entirely into this amount of memory. Can you run these chips with no RAM attached? If so, is there a way to do it that eliminates the writeback timing penalty when the CPU attempts to maintain RAM coherency?

I don't have a specific application in mind, it's just idle curiosity. I'm certain that somewhere there is a niche application where this would be useful though.


texts: Switching 12 Volt Relay with 5 volt Arduino Output

texts:
I want to use use an Arduino that is powered by 12 V to switch this relay:

The Arduino pins only give 5 V, so I want to try to design something that will give 12 volts to the relay coil when the Arduino output is at +5 out and then drop to zero volts when Arduino gives out 0.  What I had in mind is here (where I am only modeling the relay portion with the coil (not sure what the actual inductance is either)

simulate this circuit – Schematic created using CircuitLab

Will this work?


texts: LED_INTENSITY - controlling a led by a RF transmitter

texts:
More precisely this transmitter: http://www.mouser.com/ds/2/368/Si4012-35123.pdf

On page 34 there is

> 5.2.3. PROPERTY: LED_INTENSITY Purpose: LED current drive strength
> Property: 0x11
> Default: 0x00
> Fields: LedIntensity [1:0]—LED intensity
> 00: LED off
> 01: 0.37 mA
> 10: 0.60 mA
> 11: 0.97 mA

Page 8 (Typical Application Schematic) shows how they connect the LED to the appropriate pin - no resistor (!)

I think I am missing a few things;

first there is the Ampere stepping for led intensity - should it not be a Volt scale ?
secondly 0.xx mA seems quite low. I was unable to find any LEDs working at that sort of amperage. Perhaps there is an error and they meant 37 / 60 / 97 mA ?

How do these led drivers work really ?


texts:
I have a small doubt in a one way wireless communication. If I am using a receiver chip to demodulate an FSK signal. How does the receiver understands, which frequency to listen to? For example, I have a central frequency of 2.4 GHz and my FSK operates at "2.4Ghz + X Hz" and "2.4Ghz - X Hz". How does the receiver now knows that it has to demodulate "2.4Ghz + X Hz" and not some "2.4Ghz + Y Hz" or "2.4Ghz + Z Hz"?
Similar doubt in OOK modulation as for a "1" I can send 10 pulses or 50 pulses. How will the receiver know that it is representing "1" and not "11111"?


texts: Ripple carry adder, analysis of error propagation

texts:
In section 5.3. of the following book an analysis of carry propagation in the ripple carry adder is performed. However the statistical analysis doesn't particularly convince me. Specifically at the beginning of page 81 it is stated that "The probability that a carry generated at position i will propagate up to and including position (j - 1) and sto at position  \$j(j > i)\$ is \$2^{-(j-1-i)}*1/2 = 2^{-(j-i)}\$ ".

However, assuming j > i, my modeling gives me instead of a factor 1/2, a factor \$(1/2^4)\$. I would like to understand how the result of the book is derived, does anybody have a clue?

Update, based on the comments:

Basically "assuming at position \$i\$ a carry has been generated (let's call this event \$g_i\$) then this would propagate through the position \$i+1,i+2,...j-1\$, let's call such events  \$p_{i+1},\ldots,p_{j-1}\$, such propagation will stop at position \$j\$ if the propagated bit is both "annihilated" (event \$a_{j}\$) or there's a further carry generation in position \$j\$, \$g_j\$. So the whole probability can be expressed as
$$Pr(g_j \vee a_j,p_{j-1},\ldots p_{i+1} \;|\; g_i) = Pr(g_j \vee a_j,p_{j-1},\ldots p_{i+1})= \prod_{k=i+1}^{j-1} Pr(p_k) \left( Pr(g_j) + Pr(a_j)\right) = 2^{j-i-1}\times \left( \frac{1}{4} + \frac{1}{4}\right) = 2^{j-i-1} \times \frac{1}{2} = 2^{j-i}.$$

In the equation I wrote I'm considering that all the events $$g_j,a_j,p_{j-1} \ldots p_{i+1} , g_i $$ are all disjointed.


texts: Arduino UNO: How to connect 2 way power for DC Motor?

texts:
Currently I'm using Arduino UNO R3 board.
I want to drive small DC Motor using same power source as the    arduino is  using.
My motor driver is TB6612FNG and it works well.

I have two  motors.
One is 5V the other is 12V.

So I connect arduino's VIN pin to TB6612FNG's VM(Motor Power) Pins for more voltage to supply 12V motor.
It works good.

But when I connect USB power for 5V motor
then VM voltage is measured under 5V (around 4.4V).

How can I fix it?Is there too much current draw pulling V down to 4.4
Why this voltage appears on VM, and which path is using this voltage?

Any comment appreciated
Thanks


texts:
Which equation defines maximum current sink by Q1 in this circuit ?
Which equation define maximum voltage at V2 at which  Q1  enter linear mode of operation ( f.e.  VCE ~ 0.5V)  ?

simulate this circuit – Schematic created using CircuitLab

If I consider circuit without the resistor and voltage at collector I can write:

Ic ~ Ie= Ve/R4

When I ignore base current then I get :

Ve = Vb - Ube = R1/(R1+R5)*(5V - UfD1) +UfD1 -Ube

Then with first equation I get:

Ie Re  = R1/(R1+R5)(5V - UfD1) +UfD1 -Ube

How to solve these equation in order to get value of sink current by current source ?


texts: Installing Samsung electric range oven on 110V

texts:
I just purchased a Samsung electric range oven, NE59M4320SS.

It has a connector cable,

https://www.bestbuy.com/site/smart-choice-6-range-cord/8929671.p?skuId=8929671

As you can see the cord has 3-wire, and is for 220V.

My apartment does only have 110V normal US outlets.

I tried to search for adapters/voltage converters, but this special crowfoot 3-wire connector is called somehow Australian.

I cannot find an adapter that would be the same shape as this crowfoot 3-wire connector, and would convert it to the normal US 110V connector.

Question:

Is there any adapter (or voltage converter), that I could use to just convert the voltage, and connect the electric range to the 110V outlet?
Or do I need an electrician?


texts: Using Digital Clock Manager with Verilog to generate 25Mhz clock from 32Mhz internal clock

texts:
I am writing a VGA driver program in Verilog on a Spartan 3E (FPGA board Papilio one- 500k bundled with LogicStart MegaWIng). The frequency of the internal clock of Spartan 3E is 32MHz. But I need to generate 25Mhz clock to send Vsync and Hsync singnals. I tried to use the Digital Clock Manager (available in Xilinx Papilio boards) by following the tutorial at...

http://www.gadgetfactory.net/2010/08/dcm-digital-clock-manager-tutorial/

However, the tutorial explains by generating a code in VHDL. I followed the same steps with the only change that, I opted for "Verilog" while choosing the language of the code. However the code generated in my case is structurally different from that in tutorial and I am unable to generate a 25 Mhz clock.

I need to know how to use the DCM feature of Xilinx Papilio boards with Verilog to generate 25 Mh clock from internal 32Mhz clock. How to generate the instantiation code and then how to use it in your .v file containing the code that uses the 25Mhz clock?

Addition

I am using ISE Design Suite 14.7. The code that gets generated with the DCM feature used with Verilog is as follows.

// Instantiate the module
DCM32to50 instance_name (
    .CLKIN_IN(CLKIN_IN),
    .CLKFX_OUT(CLKFX_OUT),
    .CLKIN_IBUFG_OUT(CLKIN_IBUFG_OUT),
    .CLK0_OUT(CLK0_OUT)
);

I don't know how to use this in my code and that 25Mhz is produced at which pin.


texts:
I am not really sure what is wrong with my code bellow for a vga.  All I want the program to do is display a solid color on the monitor.   I want to use the switches on my card to change the color displayed.  I ran the simulation and all the hsync and vsync signals seem to be as expected.  When I flick the switches I get a short pulse of color on the display and then it goes black.  Anyone know what is wrong with this code?

module vga(output reg [3:0] red, green, blue,
           input [15:0] sw,
           output hsync, vsync,
           input clk);
    wire vga_clk; //25.203 Mhz
    vga_clk_gen gen(.clk_in1(clk), .clk_out1(vga_clk));

    reg [9:0] hpx = 0, vpx = 0;
    reg [9:0] next_hpx, next_vpx;
    reg [3:0] next_red, next_green, next_blue;

    assign hsync = !(hpx >= 660 && hpx <= 756);
    assign vsync = !(vpx >= 494 && vpx <= 495);

    always @(posedge vga_clk) begin
        hpx <= next_hpx;
        vpx <= next_vpx;
        red <= next_red;
        green <= next_green;
        blue <= next_blue;
    end

    always @* begin
        next_red = sw[3:0];
        next_blue = sw[7:4];
        next_green = sw[11:8];
        next_vpx = vpx;

        if(hpx == 800) begin
            next_hpx = 0;
            if(vpx == 525)
                next_vpx = 0;
            else
                next_vpx = vpx + 1;
        end else begin
            next_hpx = hpx + 1;
        end
    end
endmodule


texts:
I was trying to design a driver of a proportional valve. My driver has ±10VDC input and ±100mA output (Load: 200 ohm, 0.5 H, Series RL) I have two supplies which are 28±4VDC and -28±4VDC. I applied this circuit and simulated. I take ±100mA when i applied ±32VDC to opamps supplies however i took ±90mA for ±28VDC and ±75mA for ±24VDC. It was fixed to 100mA when i applied bigger supplies than ±32VDC. Also there is some problem about load, the output current should be independent from load resistor but values bigger than 200 ohm, the current was influenced. I have included the circuit.

I investigated some proportional valve models and i realised that they can give almost 3A. Do you know that how that circuits can give those currents? My circuit is limited at some values for some reasons but i couldn't find it.

This is a commercial circuit example for proportional valve: http://agsotomasyon.com.tr/content/ags-pv02-2-kanal-oransal-valf-kontrol-karti


texts: What does "full array operation" mean for EEPROM?

texts: What is full array operation as shown in data sheet of AT24C08B: Two-wire Serial EEPROM (page3)? What is application of that full array operation? Please help to clarify.


texts: What is the difference between Commercial and Industrial temperature range IC physical parts?

texts:
If I buy the Industrial and Commercial variants of the same IC, besides the markings what differences are there in the actual parts?

Seems like they must use the same die, so is it different formations in the packaging material?  Different types of bond-out wires?

Or is it a matter of binning where the higher grade parts have been tested and found to work at the wider temperature range?


texts:
Take as an example this circuit: this question is in fact related to a previous one.

When considering a variable, decreasing load \$ R_L \$,

$$ R_L I_L = R_L (I_S - I_Z) = V_Z $$

can be constant as far as the Zener diode balances the reduction of \$ R_L \$ by decreasing \$ I_Z \$, so: the Zener diode regulates the voltage. When \$ I_Z = 0 \$, the diode is useless and the resistances \$ R_S, R_L \$ determine the voltage across it, so they "regulate" this voltage. It seems that the Zener diode needs an external circuit (like the one composed by \$V_S, R_S, R_L \$) which can put it in reverse bias, and it can become a regulator only after this condition is reached. Otherwise, it is useless and its voltage is determined by the remaining part of the circuit.

Then, who is the actual regulator in this circuit? The diode or the resistances?


texts:
I have an audio mixing desk that I need a power supply for.

The output required is 16.8VAC 1.4 amperes. The original is discontinued but I have found one for sale that is rated 17VAC 1.2 amperes and one that is 18 VAC 2.0 amperes. Is the lower current rating a problem with the first and is the extra voltage a problem with the second?


texts: PWM-stimulated N-channel MOSFET unexpectedly always on

texts:
Electronics!

I would appreciate help with the following problem:

Goal:
Get 12V PWM-modulated from a microcontroller-generated 5V PWM.

Elements:
• IRLML2502, n-channel FET  - Datasheet
• Resistors R1 (56 Ohm) and R2 (6K8 Ohm)

Reduced schematics:

Problem:
Drain is always around 12V (100% duty cycle) - independent of gate duty-cycle.
All my IRLML2502 show the same behaviour.

What I checked:
• Scope shows correct duty cycle(s) on gate.
• Gate voltage either 0V or 5V.
• Source voltage is 12V as expected.
• Checked pin-correctness various times.

My Request:
Please tell me, if you see any obvious problems.
Please point me in a direction to perform further checks.
Please be kind, i am no native electronics guy :)

Thank you very much for your help!

Best regards,
R2D2


texts: Long lines: whether or not to treat PCB traces as RF lines

texts:
My setup: 53 x 28 mm PCB, uC will run somewhere between 1 MHz and 8MHz. Dual layer PCB design.

From the info I gathered on this site it seems there are two aspects to consider in deciding how to treat the PCB traces:

1) Maximum sinusoidal frequency of the digital (square) signals running on the board. For this one I understand that the 3rd harmonic is a good maximum frequency to be weighed in.

2) Rising / falling edges of such digital signals. For this point I do not know what frequencies needs to be considered or how to determine them. Or how to manipulate (?) them either.

I am not sure whether or not my understanding is flawed. All I could find in the datasheet of the ATMega168 uC is that for some pins used in some modes (such as TWI) the hardware switches to a special mode that won't consider glitches shorter than 50 ns and that it slows down its the slew rate on those pins.

Help!


texts:
simulate this circuit – Schematic created using CircuitLab

-Suppose that the distance between "D1" and "D2" is too large.

-Does "D2" give a delayed response compared to "D1"?


texts:
I've been looking at input protection circuits and I came across to some circuits that look like this one. Which is just based on the series resistor R1 to limit the current that flows through the MCU pin and also uses the Diodes D1 and D2 (D1 in this case) to release the excessive voltage to the power rail V1.

The question is about permanent voltage levels at 24V not transient effects or more higher than MCU pin levels.

Wouldn't that hurt the power rail (V1)? Even if diodes were omitted it would somehow hurt the power rail through MCU internal diodes. Wouldn't that make LDOs or DC to DC power supplies stop supplying power to the system due to the excessive voltage level and cause damage to the circuit?

I would lower the input voltage at a normal level and wouldn't use such circuit as a voltage translation.

Many other designs just suggest the same, a series resistor with a pair of diodes to both power rails. Some others just add a pull-up to MCU positive rail. And my understanding is that circuits like that are not meant to be used for voltage translation but only for ESD protection or transient responses.
Am I missing something regarding to similar designs that could be found online?

simulate this circuit – Schematic created using CircuitLab

Image 1


texts:
I want to read MIDI data with an arduino (specifically an ATtiny85) for use in a synthesizer. The only method I'm aware of involves using an optocoupler such as the 6N138 found on this Instructable. It seems quite practical but unfortunately I don't have one on hand right now and shipping might take too long for my project. I was wondering if it would be possible to configure a 555 timer to do the same task instead. I quickly threw together this circuit of what I'm working with.

The circuit should compare the voltage difference between the relevant MIDI pins and reproduce this difference as a logic level at the output. My setup as a whole is not working but without an oscilloscope nearby I can't confirm that this is the buggy part (the other option being the code I'm using). Is my circuit a valid alternative to an optocoupler?

EDIT: Removed "Isolator" from title.


texts:
Could someone tell me the specification of this plug?
The plug is from the camera and microphone unit of my laptop lenovo u330 touch. I damaged it and want to replace it. i hope to find a replacement including wires, with i could link to the wires of the old cable after cutting off the old plug.
thank you for your quick replies so far!
I added a new picture of the back, and i measured the distance: 4 mm between 5 contacts, leeding to a distance of 0.8 mm between the contacts.
still hoping to find an solution


texts: Does the remote car door keyfob in today's automobiles change its code with every use?

texts:
I am just wondering why other keyfobs do not open my car door and thought every signal would have to be unique.

So I did some research and they use a rolling code so in fact the code changes with each use  Why would this be anymore secure than having a unique transmitter and receiver for each car since with a rolling code change the keyfob needs to do it every time?

If I loose my fob  and get my spare how does my spare then know what the code was?

I did my research on "How Stuff Works" but it raised more questions to me than it answered.


texts: What is this component attached to electric pole

texts: I have noticed the following component attached to an electric pole, I wonder what that is.


texts: Wiring L298n H-Bridge Using 24V Power Supply

texts:
Need you help, re: correct Wiring of my L298N H-Bridge Driver Using 25V power supply to run two 24 DC Motors (Takanawa). I have a separate 9V Power Supply for my Arduino Board which my Bread Board gets 5V power supply, My bread board supplies power to 1 Remote Wireless Control Key and 1 relay for my Solenoid.
My Question; can I get 5V supply from my bread board to L298N  driver and at the same time connect the negative wire(GND) from breadboard to middle GND of L298N driver?
Thanks for your help.
Rod


texts: P Channel MOSFET is not behaving with another MOSFET

texts:
This is a very simple (or so I thought) power switching circuit I made for an extremely low, power consumptive device.

The device normally runs on a 3.6v lithium, but occasionally a user will plug it into a computer to grab/program data. When plugging into computer, I want to kill power from the battery and solely power from USB interface. When USB is disconnected, MOSFETs make the switch back to battery.

Both MOSFETs are P Channel.

When I first built the circuit, I left Q2 out to check if Q1 was working as expected. It was. When the USB is not plugged in, Q1 gate is 0v, and source is 3.6V. Negative 3.6V fully turns on the MOSFET. When I plug in USB, interface IC turns on, and drives Q1's gate to 3.3v which turns it off just fine.

But when I added Q2 (with no USB power), Q2 doesn't want to turn off. The VGs should be +3.6v, so it should drive it hard off! Instead, it seems like it's partially on, back feeding the voltage regulator; I'm reading 2V on the reg's input. Then when I plug in USB, now Q1 wont turn off!

Here's my thought's on what should happen:

With a battery, but no USB power, Q1 Vgs should be -3.6v which turns on Q1. When Q1 is on, it feeds the gate of Q2 with +3.6v while the source is 0v because theres no USB power. So Q2 should be off.

When USB power is added, Q1's gate is driven high by the USB IC which brings the Vgs to -0.3v which is plenty to keep Q1 off (confirmed through testing). When Q1 turns off, Q2's gate is 0v and the source is +3.3v. This gives Vgs -3.3v which should be driven fully on.

Any help would be awesome. Thanks guys!
MOSFETs data sheet


texts: How do I troubleshoot this high-frequency PWM fan control circuit?

texts:
I have a 230 Volts fan from EBM papst. It is a fan that can be controlled through a PWM signal (between 1 and 10 kHz). I have built the circuit that is in the manual (see image)

I did get this working using a 5.0 Volt arduino clone. I have been able to change one of the timers, so I am able to get a clean 4 kHz pwm signal on digitalOut 4. The fan responds nicely.

But I would like to get it working on another arduino clone that runs on 3.3 volt, currently I am getting no response at all from the 3.3V circuit.

The only thing I can think of that is different is the PWM voltage. The 3.3 volt arduino clone only makes 3.3 volt peak-to-peak, whereas the other arduino does to at 5.0 volt.

My question, can this be solved by choosing a different transistor? And if so, what specifications should I look for?

And otherwise, what other information is useful to know? I have some basic measurement equipment including a simple oscilloscope, but I don't know what to look for.

Edit: http://datasheet.octopart.com/R3G310-AI01-81-EBM-Papst-datasheet-15198448.pdf

Page 4, not the exact same fan, but the same schematic, could not find the correct one at the moment.


texts: Improve protection of device that got damaged by a primary side short

texts:
Today I swapped one of our devices that got damaged by the customer during installation. The device consists of a base board with several modules (power supply, IO cards, processor board, display+USB, ...).

The device was specced with 230V AC supply that basically consists of a daughterboard with two off-the-shelf potted SMPS modules, two fuses and a board-to-board connector for the secondary side. Primary side is connected on the power supply module. The customer seems to have removed the PS module while it was still connected to mains and appears to have shorted the solder connections of the input to the chassis of our device via one of the standoffs that the PS module is mounted with.

This blew the primary fuse and blew several inches of PE copper track off the base board. The device was earthed via the PCB mounting screws to the aluminum case and from there to the machine it was mounted to.
After replacing the fuse (and later attempting to bridge the blown PE track), the device came back on (processor was running, customer could configure it via the display/buttons), however the device did not switch any of it's relays, nor was the customer able to connect it to his laptop via the onboard FTDI + USB jack.

The relay issue is related to the relay driver IC (PCF8574), which sits directly below the power supply module and had a burnt pin. The USB issue is probably because the CPU (STM32F407) and/or the FT232RL were damaged as well. I will test this tomorrow.

What would be best practice protection circuitry in order to avoid damaging the device in a case like this?

There's a primary side fuse as mentioned, two secondary fuses (one per SMPS) and some local 5V and 3.3V regulation going on right now. Since there are also DC power supply options, there is a reverse protection diode on those supply modules, before the dc-dc module (also off-the-shelf on custom daughterboard).

Would MOVs/diode clamping/TVS diodes improve the situation? Would I add those to the base board or to each daughterboard that has it's own regulation? What about polyfuses? Other suggestions?

The device is used in rough industrial environments, protected by a die-cast aluminum case (with crimped-on earth connection for the case and the lid).


texts: where should I place the terminations resistors for RS485?

texts:
I want to add termination resistors in RS485 bus .
My systems is Multi-point ( the MCU can send to/receive from 3 external devices) I found out from this RS-485 CABLE SPECIFICATION GUIDE.
that I need termination resistors at both ends of the cable because data is sent bidirectionally.
but I get confused where I should place them.Can someone check if this is correct


texts: How can I increase the distance of a photodiode

texts:
simulate this circuit – Schematic created using CircuitLab

I wanted to make a fire detection system using a photodiode, comparator with potentiometer to adjust sensitivity, and an alarm circuit after that. My question is, how can I increase the range of a photodiode so that I can detect a fire about 20 feets away or more? Is this possible? Thank you.


texts:
I need to power a 5V LCD display from a 3.3V microcontroller. On my breadboard I used 74AHCT125 level shifters powered at 5V. This worked fine.

For the PCB version I have - mistakenly - ordered 74LVC125 chips. With a 5V power rail can I still use them (the data sheet seems to me ambiguous)?


texts:
I've been trying to get into some low level electronics to explore to "Internet of Things" and still struggling a little with MOSFETS.

I'm trying to make a single push button act as a latching power switch for a microcontroller, then act as an input button when the mc has powered up
 (further details in my previous question).

Following the suggestion to use a BSS84, I discovered the mircocontroller I'm using (ESP8266 ESP-12) draws a current of around 300mA and, looking at the datasheet for the BSS84, I saw the continuous current draw is -0.13A?

This is where I get confused a little. I understand the continuous draw needs to be adequate (130mA is too low) but why is it +/-?

Does the current not flow from Drain to Source? If so how can there be +/- voltages? (I realise I may have a very poor understanding of FETS)

Goal

I'm aiming to use a logic level mosfet to provide at least 300mA when the gate is connected to ground. Would something like the IRLML5103TRPBF work or are there better options?

Thanks in advance for your help. Apologies if I've got entirely the wrong idea and sounds like a crazy person ha!


texts: Determining current through a short circuit

texts:
Edit: So I have to calculate the current through the short circuit and what I thought of is:
Applying current divider across 4kohm and then the 2kohm resistor right below to get their respective currents and then subtracting them to get the current through the short circuit. Is this method reasonable?
Edit: For the current through 4kohm resistor, applying CDR as:
2/(2+4) * 1mA = 0.33mA
I'm very new to all these concepts so any help is appreciated!


texts: Which Shottky diode do I need for redundant power to a Raspberry Pi Pico

texts:
I'm working on a project which involves setting the clock on a Pi Pico over USB and then seamlessly switching over to battery power when the USB connection is removed. How to accomplish this is documented in the PDF for the Pi Pico, with the following diagram:

Try as I might, I can't find or figure out what Schottky diode to use. I'm thinking that the battery supply voltage will be around 3 - 4.8V (3xAAA or 4xAAA NiMh cells). The maths involved in calculating which diode is just a bit beyond me.
PDF source, section 4.5.


texts: Communicating via USART with an AVR - Input Buffer?

texts:
I am currently building a robot (as some of you may know from my previous questions). The current task I a dealing with is that of communication. To keep things simple, assume I have 5 commands to deliver from my ground station to my robot:

Drive forward
Drive reverse
Activate servo 1
Activate servo 2
Motor speed

Now, I am sending these commands from my computer to a USB to Serial adapter and then over an RF link. But this is not important, as far as I know, to my question.

So my question is, how does communication work in general? My idea is that I will have five different 8 bit data packets (one for each command) which I will continuously send from my computer. So I will keep an infinite loop going which will check, say, the position of an analog joystick. If it is pointing upward, command 1 will carry the drive forward message. If it is pointing downward, command 2 will carry the message, etc. Depending on how far the joystick is in the up/down position will dictate the contents of command 5. And the state of some keys on the keyboard will dictate whether commands 4 and 5 contain info to actuate servos.

So, again, I plan on having a continuous loop which will check each of the 5 states and send the appropriate commands over the USART from the computer's side.

The problem I am having, conceptually at least, is that what if there is a lag on the robot's end to process the data coming through the USART? As I understand, to ensure data isn't lost, the data is stored in a buffer on the MCU. Essentially, I want a "last in first out" system on my robot, so even if I miss the older commands for whatever reason, the robot is doing what I want it to do now, not what I wanted 2 seconds ago. But with this methodology, I'm also afraid that I will skip data packets of commands 1-4 because it will just keep reading the last data packet (i.e. command 5).

I came up with this communication "roadmap" on my own, so I'm sure there are much better ways to accomplish what I want. But I hope you understand what I mean. Also, I am using an ATmega328 on my robot, if it matters.

I would appreciate any advice pertaining to this situation.


texts: Optimizing a "stop light" circuit to run on lower voltage

texts:
I am specifically talking about the circuit found here.

I want to make this same circuit but make it run on much lower voltage, preferably a coin cell or two. Longevity is not important.


texts: LED to mount securely in little space (< 5mm)?

texts:
The picture shows a 2mm wooden board, 4.63mm deep and 9.86mm wide. Below the board there is 3mm clearance for wires. Above the board, there is 5mm of free "air space". Behind the wooden board is a 2×7mm aluminum plate. The board is suspended on the left and right (cut off for visualization) by 3mm aluminum plates.

I would like to mount an LED somewhere on the board or the aluminum plate behind. I could also mill into the suspending aluminum on the left side, if that helps with mounting.

What is a good mounting option?

Already, I looked at the Mouser EU catalog, but close to 40,000 LED products is overwhelming, and unfortunately for many products pictures are bad or missing. I was thinking about a classic dome shaped through-hole LED, but I don't think I can securely fasten this. It should be safe to touch.

Nice to have, but not mandatory:

Multi-color LED, e.g. an RGB one.
Replaceable LED.

Brightness should be that of a typical keyboard status LED, i.e. not super bright.


texts: Using Octave instead of Matlab in control engineering

texts: I would like to know if in a first course in control systems at the undergraduate level I would miss much by using Octave instead of Matlab? I understand that Matlab has simulink but regarding basic control system design, is Octave enough?


texts: Where to buy part with specific package marking

texts:
Hi fellow electronicians,
I am looking to buy this Toshiba HDMI-CSI2 bridge chipset and the datasheet states that it comes in two versions:

HAL - with HDCP keys
HNL - without HDCP keys

I have looked around on electronics websites and they simply list the component as TC358743XBG and do not mention the package marking.

How can I find a distributor with this specific version? Is there a better solution than contacting all the websites individually?


texts: Can someone explain this part of circuit from BQ500212A?

texts:
As the title says, I am struggling to understand what this part of a circuit does. It's part of this evaluation module.

Is there any chance the BSS138 transistors will activate without the SNOOZE/SLEEP input? If so, how?


texts: AC/DC Converters in Series with the Same AC Source

texts: Would it be safe to connect two identical AC/DC converters in series if they share the same AC source? My concern is that the negative DC output is grounded somewhere in the converters causing the second AC/DC converter to be shorted.


texts:
I'm developing on a PC/104 stack which aparently has an I2C interface. However, on further investigation it is actually an SMBus interface but says the two are interchangable up to 400kHz.
However, the only way I can access it is through a DLL provided by the vendor. The DLL only has SMBus specific commands but reading up on SMBus I can see that the read_byte functionality seems to be the same as that for I2C.

The DLL shows the interface for read_byte as:

//
// Call this function to reads a byte on the SMBus. This function
// requires the proper values to be setup in the SMB_REQUEST structure.
// This call is valid after a successful OPEN call has been made.
//
// Parameters: handle - Handle to open SMBus API
//      request - input SMB_REQUEST structure
//
// Returns: 0=SUCCESS, non-zero = FAIL
//
SMBUS_API int SmBusReadByte( SMBUS_HANDLE handle, SMB_REQUEST *request );

....defining the SMB_REQUEST struct as

typedef struct _SMB_REQUEST
{
 unsigned char Address;
 unsigned char Command;
 unsigned char BlockLength;
 unsigned char Data[SMB_MAX_DATA_SIZE];
} SMB_REQUEST;

Relating this to I2C I'm thinking that:
Address is the address of the I2C device
Command is the register to read from
BlockLength the amount of bytes to read
Data is the memory buffer used to give back the result.

However, using it like this doesn't seem to work. There is also a SmReceiveReadByte() function with the same interface so I'm not sure whether I'm supposed to be using that or this funcion.
There is also a SmBusReadWord() function with the same interface so that leads me to beleive that I have the wrong idea about BlockLength above. What else could it be?
I'm probably not using this correctly at all.
Would anyone be able to shed some light on this for me?

Thanks


texts: Doubt on ground reference of Isolation transformer

texts:
I studies the posts on this blog regarding isolation transformer and its working. But I don't understand that when there is no ground reference in the secondary winding of the isolation transformer, then how is the current able to circulate in it. I mean as per my knowledge, we need some reference with respect to which the current can flow, like ground in general cases. If there is no reference in isolation transformer secondary, how is the current able to flow through any load that I connect to its secondary side ?

Could someone tell me some detailed explanations regarding my doubts?


texts: How to apply a rule to only one component in altium?

texts: I would leave the insulation of copper with 0.35 mm across the board except in a microcontroller. It requires that the insulation allowed is 0.2 mm because of the distances between the pad. How to make a rule unique to this component?