texts: Kvaser Leaf Light CAN BUS Simulator problems

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I'm learning to use this tool Kvaser Leaf Light V2 with CAN-BUS. I'm stuck with some problems. I can read the packets around the CAN-BUS line from the car, I can save it in a text file, but when I want to resend this on my "Own CAN-BUS" that's connected to my instrument cluster, the instrument cluster doesnt do anything (it just turns on the digital clock)... is there any "Ignition" or "Turn on" packet that I'm missing?

Info:
Car: Fiat Stilo 1.8 petrol
Baud rate: 50k

Update 1(17/01/2015):

Info about how I'm using CANKing:

1st way, "Custom messaging" on my own CANBUS Trunk:
I click on Messages>Universal>Universal and I write my message in the field:
For example I want to manipulate RPMs I send
7E8 | 0x04 | 0x41 | 0x0C | 0x0D | 0x50 | 0x00 | 0x00 | 0x00
(What's supposed to be what car sends to nodes informating about RPM)
But Instrument cluster doesnt do anything and I get Error frame message.

2nd Way, Logged file messages:
Well, I dont know if it should be working, but I tried also with no success;
I sniffed data from the car (Fiat Stilo 1.8i) and logged to a file, with some variants (Turn on ignition, turn off, accelerating, etc. All while recording it)

Once I recorded, I did use:
View>History List>Load..[I load here my recorded file]>Send All

I think this should simulate the car system and the Instrument cluster should replicate what I was seeing in the car or I'm wrong?

Update 1.1(17/01/2015):
I will change resistances also, I misunderstanded the concept, I will get 120Ohm ones and feedback with it, someone that's helping me, told me that I'm missing Ground Kvaser to Ground Inst. Cluster.

**Update 2.0 (18/01/2015):
I changed resistances to 120Ohm, wired Kvaser GND to Instrument tool GND, and I managed to light up my Speedometer with the RPM gauge (Fault was that speedometer box got more than one 12V+ in, as it has different modules). But I can't manage to work it.
I want to control RPM and Speedometer gauges, but when i send any message, i get like 700~ error frame messages... the same when I start sending text file with all the traffic I recorded...

Anyone know where can I find FIAT CAN DB or can point me in right direction? Thanks.


texts: Trouble with SO on MCP23S18 spi gpio expander

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I am unable to get a signal out of the slave out (SO) line of an MCP23S18
For those not familiar it is a slave SPI gpio expander.

Clocking in 32 bits, as it goes 16 bits set up, 8 bit opcode, 8 bit intended register address, then data...

In the attached pics you can see my scope, having only a 2 channel scope:
- the top pic blue line clock, yellow SO
- the bottom pic the blue line SI, again the yellow is SO

The odd think is the SO line looks like it is a combination of the clock and the SI data...

For giggles I tried pulling up (and down) the SO line but that just moves the same waveform up to vdd or down to ground.

I've checked and rechecked my wiring, but I suppose anything is possibly the cause.
I've tried a second MCP23S18 with the same result.

From what I understand the SO is a tri state line, that is driven from the slave so it seems to be an issue with the slave.

What I failed to get a pic of is the CS line, though I did scope it to make sure it was going low in time.  Though from the scope it does seem that the slave might not be alerted to the CS and leaving the SO at high impedance.

I'd be grateful for advise to resolve this issue


texts: Are 5V ELDC super capacitors constructed with internal balancing resistors?

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I read that the underlying technology (the dual layers) of ELDC super capacitors is limited to about 2.5 V.  Yet I see 5 V (and 3.3 V and other) supercap packages on the market.

Also, it is well known to put such capacitors in series with balancing resistors, to prevent one of the two capacitors from receiving voltages beyond their 2.5 V limit.  And there are IC's dedicated to charging series supercaps without balancing resistors, e.g. the LTC3225.

For example, the Cooper Bussman brand, part number PB-5R0H104-R.  Rated 5 V max with max ESR of 4 Ohms. That supercap appears to be two cylindrical capacitors bound together.

Does that particular model of supercap have built in balancing resistors? In general, is that the case for supercaps rated over 2.5 V?

Are there any tradeoffs to using such a supercap? As opposed to say a Cap-XX brand, a model from the "GW 2" family (having two cells in series). That model has a "balancing" pin and the mechanical drawings at the bottom of the datasheet show its use with an external balancing resistor network. (And a note "Please contact Cap-XX for further information.")  When would you want to design your own balancing resistor network, or use a dedicated IC to charge, a series supercap?


texts: FFC (Flat Flexible Cable) ZIF Connector Reliability

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I'm wondering about the long term reliability of FFC connectors, especially in environments exposed to shock and vibration.  It seems like everything with a display uses such connectors, which means they must be present and in use in automotive environments, at least in the user console, which is still exposed to shock, vibration and thermal cycling.  One major concern is fretting.  My Internet searching up to this point hasn't provided very much information.

Does anyone have any experience using these types of connectors in automotive / aerospace / military applications who can speak of the long term reliability?  I think most people think of them as being flimsy, but from my experience they seem to make a very secure connection.  Any feedback appreciated.

One thing I am aware of is that they are not meant for applications with multiple connect / disconnect cycles, but I'm speaking specifically about applications where the connectors will only be latched once, to connect boards together permanently inside a product enclosure.


texts:
I am trying to repair several reasonably expensive pieces of equipment (ABI Veriti thermocyclers) in our lab which report the same error. They were all bought at the same time and must have a bad batch of components (they failed immediately after the warranty period).

I believe I have tracked the issue down to a failed thermistor.  ABI (now ThermoFisher) will not sell me the part or tell me the specs.

The specs I have ascertained (on a good component) with a lab thermometer and multimeter are:

Radial PTC
1.1kohm @25°C
1.293 @ 76°C
Beta(k) ??
Length: 5mm
Diameter: 2.1mm
Shape: cylindrical

A slightly smaller diameter is probably OK but larger will not fit in the orifice machined into the heat sink.

I can not find anything even vaguely close to this on Mouser or a couple of other sites I have tried.

Any suggestions would be appreciated. We're a cancer research lab if that info motivates you.


texts:
I have followed the instructions in the data sheet and tried to generate PWM signal using PIC16F628A. However it seems to be not generating any output. My code is shown below. Any help appreciated regarding finding the what is wrong in my code.

Thank you.

PROCESSOR '16F628A'
INCLUDE <P16F628A.INC>
org 0x00
bcf STATUS,RP1
bsf STATUS,RP0 ; go to bank1

movlw 0xff ;255 dec
movwf PR2 ; writing to PR2 register
bcf TRISB,3 ; set RB3 as output

bcf STATUS,RP0 ; go to bank0
bcf CCP1CON,5 ; clearing bits 5 and 4
bcf CCP1CON,4

movlw 0x00
movwf CCPR1L ; set duty cycle

bcf T2CON,1
bcf T2CON,0 ; set pre-scaler to 1
bsf T2CON,2 ; enable Timer2
bsf CCP1CON,3
bsf CCP1CON,2 ; enable pwm mode
return
end


texts: Are my calculations correct for the resistors attached to this opto-isolator?

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I am creating a circuit for an automotive application which will take 3 buttons from the stalk as 3 inputs. Now I have measured these buttons and they are active low and output a constant 12v (ish) when not pressed.

I am using an STM32F4 MCU to read the button presses and I realise that I need to drop the voltage of the buttons to 5V max prior to the digital IO pins of the MCU. After looking online I came across the idea of using an opto-isolator and because of PCB constraints I wish to use one which comes ready made in a SOIC package with 3/4 channels.

Now I see there are many available and so far I have determined I will use a transistor based one as it is a good middle ground and I don't need to deal with fast switching.

But I am confused as to how to choose one exactly as there are so many available. My requirements are:

relatively low cost (up to £2)
SOIC package
triple/quad channel
suitable for automotive voltages, 12V (possibly fluctuating a bit)

I am considering using the Toshiba TLP290-4 opto-isolator, which has a min CTR of 50%.

So by following the advice here: https://electronics.stackexchange.com/a/43502/148565

And considering the schematic (Just the forward voltage scenario, if I am not mistaken, this opto-isolator can handle reverse also):

simulate this circuit – Schematic created using CircuitLab

I calculate that given a 10mA input current through R1 and D1, and the given 1.2V typical drop across D1 according to the datasheet, then R1 = VR1 / I = 1.08kΩ, so 1.2kΩ should do.

Then given the minimum CTR of 50%, at a 10mA input current, the output current would be 5mA. Therefore, assuming the 3.3V dropped across R2, R2 = VR2 / I = 330Ω.

So the question is, are my calculations correct and will the proposed circuit be safe for use under these conditions?

And as an aside, how would I go about inverting the output in terms of the switching, Do I just tie R2 to GND instead of 3.3V?


texts: Hı. I have 100W COB Led's.(I buy them from china) I need to give power to 16 of them. The Specs. says 36V 100W 3A for one. I know there are drivers for them but i have to light too many and i don't want to buy driver for every each one seperetaly. Is there any other ways to light them with budget? There is a picture of led.Thanks.


texts: How to balance between frequency and duty cycle in this circuit?

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I have this astable circuit that generate square waves with independent control of frequency and duty cycle:

For this circuit:

$$t_H=0.759\,C\,(R_f+R_y)$$
$$t_L=0.759\,C\,R_x$$
$$period = 0.759\,C\,(R_f+R_d)$$
$$frequency = \frac{1}{period}=\frac{1.32}{C\,(R_f+R_d)}$$
$$duty\; cycle =\frac{t_H}{period}=\frac{R_f+R_y}{R_f+R_d}$$

I want the duty cycle to range -at least- from 25% to 75%, and the frequency to range -at least- from 1 kHz to 10 kHz.

For these given values:

Rd is a potentiometer whose whole resistance is 50 kOhm.
Rf is a variable resistor whose maximum value is 50 kOhm.
C = 10 nF.

, here are the possible ranges:

The maximum frequency possible:
$$freqency_{max}=\frac{1.32}{C\,(R_{f,min}+R_d)}=\frac{1.32}{10^{-8}(50k+10)}=2.64\,kHz$$
where 10 Ohm is assumed as the minimum value that can be assigned to Rf, and 50 kOhm is Rd.
The minimum frequency possible:
$$freqency_{min}=\frac{1.32}{C\,(R_{f,max}+R_d)}=\frac{1.32}{10^{-8}(50k+50k)}=1.32\,kHz$$

You can see that the frequency range is very narrow.

On the other hand, calculating duty cycle and assuming that Rf is set to 50 kOhm:

The maximum duty cycle possible:
$$duty\; cycle =\frac{R_f+R_{y,max}}{R_f+R_d}=\frac{50k+50K}{50k+50k}=1$$
The minimum duty cycle possible:
$$duty\; cycle =\frac{R_f+R_{y,min}}{R_f+R_d}=\frac{50k+10}{50k+50k}=0.5$$

The maximum duty cycle possible is great but the minimum one is bad.

I can reduce the maximum value of the variable resistor Rf to improve the range of duty cycle but the range of frequencies will not improve noticeably. For example, if Rf(max) = 5 kOhm, duty cycle will range from 10% to 100%. But the frequency will range from 2.4 kHz to 2.64 kHz which is unacceptable.

Or I can reduce the whole resistance of the potentiometer Rd to improve the range of frequencies but the range of duty cycle will not improve noticeably. For example, if Rd is reduced to 5 kOhm, the maximum frequency becomes 25.9 kHz and the minimum frequency becomes 2.4 kHz. But the duty cycle will range from 90% to 100% which is so bad.

Even if I reduce both of Rf and Rd or change the value of C, I can't get to my goal.

How can I achieve the required range of frequency and duty cycle?


texts: Using MOSFET to control positive side of motor?

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I want to control the speed of a DC motor, but the chassis is connected to the negative side of the motor, making it impossible to use the MOSFET to disconnect ground.

Is there a way that I can use the MOSFET to disconnect the positive side of the motor, as in the following diagram? And does that configuration have a name, so I can read more about it?

simulate this circuit – Schematic created using CircuitLab


texts: Li-ion custom protection circuit module (PCM) design and de-rating

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I am designing a custom PCM (protection circuit module) for Li-ion cells provided by a supplier ( they offer PCMs but they do not meet our RF immunity spec ). The supplier-provided PCMs have a charge / discharge limit set for 1.7A - 4A for a 240mAh battery and a 4A - 8A limit for a 1800mAh battery. Now these limits seem huge to me, so I'm wondering what a more reasonable charge discharge current is where you could still get reasonably high instantaneous current without damaging the cells.

Since the 240mAh battery is used for a BLE (Bluetooth Low-Energy) device, I doubt it will ever see more than 50mA peak. Right now I'm thinking of setting the battery protection IC to limit charge / discharge at max ~500mA current.

For the 1800mAh hour battery, I am considering a max limit of 3A. Expected peak current from this battery would be about 2A.

Are there commonly used guidelines for the Li-ion cell capacity and charge / discharge current limits or are they totally application dependent? From my search, PCM current limits vary wildly so I am curious to know what (if any) standards exist.


texts:
The best way to protect AVR pin for me is RC filter and TVS diode but I don't know one thing. I've seen schematics where TVS diode was before RC filter like in first schematics.

simulate this circuit – Schematic created using CircuitLab

But before resistor it is larger current so TVS diode will blow faster than in situation that TVS diode would be behind RC like in second schematics.

simulate this circuit

Question is:
Which way of protecting AVR input is better, first or second?


texts: HSPLL mode freezes 18F46K20 micro controller

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COMPILER: XC8 v 1.30
micro: PIC18F46K20

I use this in CONFIG1H register to get 64MHz Fosc (and use PLL):

#pragma config FOSC = INTIO7 // 1001 = Internal oscillator block, CLKOUT
                             // function on RA6, port function on RA7
OSCON.IDLEN = 1;    // 16 MHz (HFINTOSC drives clock directly)
OSCON.IRCF = 111;
OSCON.SCS = 00; // Primary clock (determined by   CONFIG1H[FOSC<3:0>]).
OSCTUNE.PLLEN = 1;  // enable PLL for 8 and 16MHz Fosc

And then uC runs at 64MHz and I get 64/4=16MHz signal on pin RA6 (as expected)

But when I tried 'HSPLL' - as in data sheet :

 #pragma config FOSC = HSPLL // 0110 = HS oscillator, PLL enabled (Clock Frequency = 4 x FOSC1)

then it completely STALLS uC : !!! It would not even start after build and power up.

Any ideas ?


texts: 2 NO reed switch - turn on 230V water heater

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For a small home project I would like to turn on a water heater using 2 NO reed switches. Once I put a small magnet ontop of the reed switch (turn the reed switch to Close), the water heater will be activated. Once one of the small magnets is separated from the reed switch, the water heater will be off.
How can I accomplish that ?
Reed switch always needs a current and I cant just connect it to 230V power right ?
If so, How would a DC 3v powered reed switch turn on a AC 230v device ?

Also, I have no experience with arduino and such, so I would appreciate a simpler solution to my problem.

thank you in advance !


texts: Is there an IC that inverts DC==>AC at the resonant frequency of a tank connected to it? (~50V ~40A)

texts:
Assuming I used the word "tank" correctly (something that has a resonant frequency) I have been working on a circuit that has 4 leads--two for DC input and two for AC output--such that you can attach something with a resonant frequency to the AC outputs, and the device will automatically adjust the frequency of the AC current to resonate with the tank.

I actually came up with a simple design using just two n-channel mosfets, two p-channel mosfets and four diodes. The principle of operation is that whatever voltage the tank produces, the mosfets direct the DC current to counter it (assuming the tank's voltage is above the threshold of the mosfets.) However, I found it in part by a lot of trial and error, and I was wondering if there was a standard IC that does this that I missed.


texts: PA15 doesn't work as GPIO even after Enabling GPIO_Remap_SWJ_JTAGDisable

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My MCU is STM32F107. My main program works fine with using different peripherals and function. In my program a very simple task makes me crazy. I need to use PA15 as GPIO (The simplest task:) )
I enabled
    RCC_APB2PeriphClockCmd(RCC_APB2Periph_GPIOA,ENABLE);
    GPIO_PinRemapConfig(GPIO_Remap_SWJ_JTAGDisable,ENABLE);

    GPIOStruc.GPIO_Mode=GPIO_Mode_Out_PP;
    GPIOStruc.GPIO_Pin=GPIO_Pin_15;
    GPIOStruc.GPIO_Speed=GPIO_Speed_50MHz;
    GPIO_Init(GPIOA,&GPIOStruc);

but it doesn't change the pin state with Set and Reset GPIO.  Other GPIOS work fine.
what is my mistake?


texts: Designing an electronic product for the american market, need to find a DC to DC converter with FCC certification

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Can someone please explain the basics of FCC certification for electronic products, my boss has just dropped this task on me to find a fcc approved dc to dc converter for our product .

Does FCC only apply to finished products or can it also apply to individual components. I really know very little other than it is a test of the electrical emissions from a product.

Thanks for your help


texts:
Hi - I'm getting unexpected output from a MAX3232 board.  I'm trying to reimplement a baseball scoreboard controller.  The signal I'm trying to recreate is at RS232 levels (-5 to 5V) but uses a different encoding.
I've got a Raspberry Pi Zero driving a 3V GPIO (the blue trace), and the output is hooked up to a little cheap MAX3232 board with a 9 pin serial connector (the signal goes to the DIN1 pin on the 3232).  I'm getting the yellow trace output on pin3 (TX) of the RS-232 connector.  What I'm expecting is a -5 to 5V copy of the blue trace.  What I'm getting looks like the inverse of the first derivative of the signal (low on rising edge, high on falling edge) ? (the range is correct though).
Any ideas what might be happening here? I've heard of MAX3232 knockoffs...but differentiator output??  Thanks for your time!
Update - here's a picture of MAX3232 board:


texts: Relation between Signal to Noise Ratio (SNR) and Transmission Bandwidth for FM signal

texts:
I was encountered by the below question ::

The transmission bandwidth (BW) is doubled in an FM(Frequency Modulated) signal. So, the resultant SNR (Signal to Noise ratio is) ?

The answer is given as doubled -  SNR is directly proportional to (BW)^2

How can we prove this?


texts:
I know that caps do exist for 12x12mm tactile switches:

and such caps are very standard, we can find a lot.

But is it possible to fit caps on 6x6 mm or 8x8mm or 10x10mm tactile switches? (not sure if 8x8 or 10x10mm are common or not)

I'm not looking for shopping advice (I know how to order by a supplier), but to know if it's common or not to see caps on such small switches.


texts: Can a barrel shifter be done combinatorially?

texts:
I was told that 66b/64b encoding in 10Gb Ethernet (10GBASE-R) requires a one-cycle barrel stage, which adds a necessary one cycle to the theoretical terminal latency.

The Wikipedia page on barrel shifters states that

  A barrel shifter is a digital circuit that can shift a data word by a
  specified number of bits in one clock cycle.

Is "in one clock cycle" a real requirement? Can't barrel shifters be done combinatorially? Why does 66b/64b encoding have a terminal latency of one cycle?


texts:
In electrical engineering, a load profile is a graph of the variation in the electrical load versus time.

I am currently working on Smart meter data having reading an interval of 30 min i.e power consumption per 30 min. How could I plot the Load profile if I Know the sum of power consumed during 30 min not in continuous form.


texts: Is there any single-board computer/system-on-a-chip with good documentation for developing bare metal?

texts:
I always wanted to develop my own crappy operating system, but the many weird legacy quirks of the x86/PC platform kept me from doing so (e.g. real vs protected mode, only low resolutions available in VGA/VESA, etc.). Now I realized, that maybe one of the many SoCs used in smartphones would be a better platform for developing an operating system as they are all-in-one solutions without downward compability considerations and therefore better design (even though I am not the biggest fan of the ARM instruction set).

Even better: There are many single board computers, which bring SoC, RAM, USB ports for connecting mouse/keyboard and hdmi for connecting a monitor for a cheap price... a perfect platform for dabbeling into OS development I thought...

The most established of the single board computers seems to be the Raspberry Pi and I also found 2 tutorials on OS development for them online (https://hackaday.com/2018/01/19/roll-your-own-raspberry-pi-os/). I thought the tutorials would serve as a nice intro, but actually I was missing a lot of info in the tutorials so I tried to get hold of the official documentation which of there is very little... too little in order to really develop bare metal.

Some issues I ran into:

there is a peripherals documentation for the raspberry 1, but not for the raspberry 2/3, which have totally different base addresses
the RB3 for example has a wifi chip (BCM43438), but I can't find any official documentation on how it is connected to the RB3 SoC (BCM2837)
the tutorials hint at the mailbox concepts for getting a framebuffer/get output via hdmi going, but I can't find any useful information on framebuffer/mailboxes in the official documentation
same with the boot process... it is nowhere explained in the official documentation
on the official broadcom website, I can't find the BCM2837 at all!
when looking at other SoCs like the S905 (in the Odroid C2) it has ethernet directly connected to the SoC (instead of through USB like the RB has), but I can't find any information on how to program it
besides the framebuffer topic of the tutorials I didn't find any instructions on how to program the GPU (e.g. for 3D rendering). There is a architecture document describing the VisualCore GPU, but not how it has to be interfaced...

Why is the documentation/specification so bad? Is it that the SoCs aren't directly sold to endcustomers and therefore their documentation is confidential? Is it only some SoCs and there are actually some with a proper documentation?


texts: Programmable gain non inverting amplifier

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I'm a hobbyist and like to design my own tools rather than buying chinese "kits" that teach nothing.

I have been needing all sorts of amplifiers for different things and usually I would just use an op amp and a few resistors to do the job but that's time consuming and I usually end up losing the resistors afterwards XD So I decided to look into making a programmable gain amplifier.

The obvious choice was using digital pots so I had a look at a few microchip application notes in order to have some idea about accuracy and stability of different designs. This one was exactly what I was searching for: http://ww1.microchip.com/downloads/en/Appnotes/01316A.pdf

If you look at figure 6 (page 15) they show a tempco compensated, wide range amplifier which uses 2 pots. I already have a few 10K MCP4652 digital pots which are also perfect for this application, but there are 2 issues:

1) There is no easy way to calculate the gain, unlike other designs, which led me to do a basic analysis to see the range of available gains (using python).

This first graph is the gain vs R1 (I didn't know how to do a 3D graph, ideally it would be a graph of gain vs R1 vs R2):

Just wow! it's pretty obvious that a lot of gain values are repeated and multiple resistor values yield the same result. so I made another graph, this time it only includes gain values that are repeated more than once and how many times they have been repeated.

For gains of 1 and 2, there are 256 repeats since all values of the pots works, but even for really high gain values, repeated values exist.

I'm not sure how I should go about implementing the software. easiest way seems to be removing the duplicates and sorting the list, then storing it in the MCU memory, then using a lookup table to find the nearest gain to the desired value. this will also allow going through the list iteratively with a manual encoder or similar! but this will use a ton of memory. Please let me know if there are better ways of doing this.
Edit: there are a total of 39896 different gain values. if stored as floats (each takes 4 bytes), they will take 159584 bytes (almost 156KB), each of the gain values needs two resistor values and since the pot has 257 taps, they need to be int or unsigned int, tripling the memory usage (468KB)! an external EEPROM solves that but that is added cost. Calculating the next higher gain value and the resistor values needed for it seem like a good choice, but I don't think that's possible, especially since the highest resistor combination is most likely not achieved which I discussed in the next part.

2) the more important issue would be the current through R1+R2. the pot is rated for an absolute maximum of 10mA current. for an op amp powered from +/-18V (a very typical supply voltage) this can easily happen if the resistor values are too low. I think using 100K pots instead of 10K, and only saving the highest combination of resistor values for a particular gain should solve that, but again, if there is another way to limit the current, please let me know. I know op amps "can't drive much current" but they can most certainly drive 10mA with ease.

Here is a graph showing current through the resistors when minimum resistance combination is used (18V supply, 10K pots):

The maximum current is 3.5mA as you can see. Now the same graph, just using the maximum resistance combination possible:

This can exceed 400mA! the op amp can't drive that much current, but this is surely susceptible to damaging the pot. If I want to pre-compute the list, I should be careful to not choose small values.


texts: I am designing a board which needs 5V and 3.3V rails, at about 1.5A. If I used two buck converters, I would use a lot of board area. So, is there a way to create a multi-output buck converter? I tried creating one by using two inductors (each of a different value), in a circuit simulator, but it doesn't work; the output ripple is through the roof and both rails sit at 5V or 3.3V (I kind of expected this.)


texts:
I am trying to get a CD4026 IC to reset at 6 for a digital clock project. I have some 3-input AND gate IC's but there doesn't seem to any unique conditions that would work.

I do have some CD4017 and was thinking I could use them to trigger the reset of the CD4026 IC's at their count of 6, then reset together.

Is pin 5 to 15 a short? Maybe i need power on caps too?

Vs = 5V IC on top is the CD4017


texts: How does the Arduino NANO deal with simultaneous external interrupts?

texts:
I am a beginner with Arduino NANO and this is something I've been trying to figure out for a few hours now. Say, in setup(), I have the following snippet of code:
pinMode(2, INPUT_PULLUP);
attachInterrupt(digitalPinToInterrupt(2), do_this, RISING);
pinMode(3, INPUT_PULLUP);
attachInterrupt(digitalPinToInterrupt(3), do_that, RISING);

and there are two ISR functions do_this() and do_that() that are called when two push-button switches are pressed. I understand how the program is supposed to behave when the switches are pushed and released separately. But, what if the RISING action happens, hypothetically, at the same point in time? (Actually, if digital pin 2 and 3 are connected to the same push-button then the 'stimulus', so to speak, will occur at the exact same moment). Which one of the ISRs, if any, will take precedence in this case? I have checked the ATMega328 datasheet, but have not been able to come up with anything satisfactory.
Thanks in advance :)
Edit: Thanks for the detailed insights. I understand that the ISRs have priorities and even if the change is triggered at the same time, the ISRs will be executed one after another depending according to the said priority.
As for the push-button part of the question, I came to the conclusion that when the two interrupt pins are connected together through the push-button, pressing the switch does not trigger any change because one of the External Interrupt Flags gets cleared by the other. I know that's a rough conclusion and I am probably missing a lot of technical nuances but is that idea at least correct? Many thanks


texts: Confused, Is raspberry pi a real device for learning embedded linux or just for hobby?

texts:
and sorry i couldn't think of a better title, please read this so you can understand what i am asking:
I already bought the Pi, but as i see it has a fully featured pc like OS, what i'm seeking to learn is embedded Linux programming with Cortex-A to make devices similar to smart fridges smart thermostats drones etc.
In non of the above the user notices that it has Linux unless they check datasheets etc.

how can i learn to do programming like that? its just learning not doing it for hobby or only making things work. do devices like the ones i mention have an os like linux and run the app when being powered with some modifications? im not looking for bare-metal im looking for linux programming, and only experience i have in embedded is AVR and Arduino which are kind of different.

my friend already told me that these devices are just like pi with some modifications to run the app on start, but i saw on some website someone telling that raspberry pi is just embedded-PC and not good for learning!


texts:
I would like to understand this block diagram and how it relates to the formula:
g(D) = D^7 + D^4 + 1

Supposedly this helps to generate a whitening word used within bluetooth radio, the empty boxes are shift registers. I just dont understand how that formula relates to the diagram. I don't know what this type of diagram is called either.

Thanks!


texts:
I'm designing my first schematic in Eagle, with the aim of getting some PCBs produced.
Been perfboarding for a while, but new to using Eagle.

I've designed a schematic:

I know it's kind of messy, but as far as I can tell everything is matched up. Now you can probably see more than one V+ pads. The one on the far left and the one on pin 4 of the IC are V+, and that middle top one is actually VA.
When I generate the board, it gives me a pad for every instance of it, instead of just one. Is there a way round this? You can probably make out the red hatching on the bottom right two pads on the board here (power and ground)

Any help or even feedback on my schematic appreciated!


texts: Shutdown controller for Raspberry Pi (+ other components) on mains AC

texts:
Inspired by the Shutdown Controller for Raspberry Pi in a car I would like to know if it is possible to build a similar circuit working with ~230V AC instead of 12V DC.

I have a power adaptor where I connect my Raspberry Pi to 5V DC and a small audio amplifier to 12V DC. My Idea is to realise a circuit which initiates a graceful shut down of the Raspberry Pi by pressing a switch and which cuts the mains AC to the power adaptor afterwards. The reason: As a matter of principle I don't want the power adaptor to idle around and burn 2-3W while no components are connected. Pressing the switch again should restore power to the adaptor which then re-powers my Raspberry and audio amplifier.

Does this seam realisable also without any backup battery? Which modifications to the above linked answer would I have to make? Would I find appropriate relays? How to deal with the mentioned voltage divider (to 3.3V) on mains?

Other solutions for only the Raspberry Pi:

Shutdown with backup battery on power loss from 5V supply (1);
Shutdown with backup battery on power loss from 5V supply (2);
Switching the 5V supply with a MOSFET


texts: What is a good voltage regulator or voltage regulating circuit for my micro-USB battery charging needs?

texts:
I have a need for a voltage regulator such that I can use it to down-convert 5V USB to about 3.3V in order to charge a lithium battery. Ideally:

Assuming some users may have a faulty micro USB input voltage, it would be nice if it could support input voltages which range from 4V to 6V.
It would be nice if it was not greatly affected by temperature (so for example, if you're charging it outside at -40 degrees, it would be great if the battery could at least hit 3.1V of charge instead of 3.3V). UPDATE: Users have pointed out that below freezing, lithium ion batteries will start to break down because cells will start to plate, so maybe it would be best if the temperature range of the regulator starts between 0 and -20 degrees, or, that the regulator has some thermal protection on it for sub-freezing conditions, or optionally I can leave it up to the user to break his own battery by doing this. If it has an enable signal and my microcontroller comes on at about 2V, then I can warn the user at the very least that what they are doing is destructive.
No leakage current. So, for example if it is connected to the battery and the micro-USB is disconnected, it should not consume any current at all.
A small package would be very helpful since this is going into a PCB.
A feature to be able to shut it down from a microcontroller would be nice (an inverted enable signal would be great bonus, so 0 for on and 1 for off, because the microcontroller and battery could be completely dead).

The battery I am using is FDK America's ML2430-HS1.


texts: How to make the most stable low frequency down-ramp generator (60 Hz), BJT? OpAmps?

texts:
To put video onto an analog oscilloscope I have built my BJT based horizontal and vertical ramp generators here What would be the simplest BJT based *linear* ramp generator?, but there is a problem, I noticed this in all sorts of situations: fairly fast frequencies such as the 150 kHz horizontal ramp works decently, but even for rectangles I found that as soon as I go low frequency, like manual trigger, the noise becomes more of an issue.
The other problem with that BJT based ramp generator is that I want it to be negative. So I used 2 Op Amps, one voltage follower and then an inverting amplifier to make a down-ramp. And unfortunately the noise that adds makes it really bad.
The Miller Integrator, Miller integrator ramp generator?, people discouraged me from doing that. And my problem with it is the capacitor charge time is too long. I've been playing with a Darlington pair to charge the capacitor faster, but that's just going to add lots of extra components and I'll end up with noise again.
So I'm back taking suggestions about the simplest down-ramp generator with a maximum of 2 op-amp stages. Output impedance and amplitude doesn't matter much as I just drive a scope from it.
UPDATE: Of course I continue searching myself. Here is one from this "Tiny TV" project:

Since I am on the breadboard, I can change the MOSFETs 2N7002 for 2N7000 in a TO-92 package. Definitely those MOSFETs should resolve all problems I have for now getting the capacitors (dis-)charged fast enough on a quick digital pulse that I get from the Ripple Carry Output (RCO) of my pixel and line counters.
But then, that vertical ramp here is still upward-sloping, not downward as it should. Or am I mistaken and TV signals are actually organized from low to high scan lines?


texts: I recently took on a personal project that requires a vssop-8 chip:ADC081C021. In order to help me solder the pins on the pcb, I ordered a vssop-8 stencil online. But when it arrived, I found the pitches were different.  The stencil is supposed to have a .5 mm pitch while the adc has a .65 mm pitch. Which one is correct? or is there no standard for vssop?


texts:
I am currently using ZXCT1009 high side monitor for monitoring the current consumption on a bus line for an embedded system we are developing. I am currently using tek scope with Labview for automation purpose. Works good at our lab.

Now I am thinking of implementing this ZXCT1009 in the embedded design itself and somehow sensing the voltage across the output resistor.

ZXCT1009 data sheet -http://www.diodes.com/datasheets/ZXCT1009.pdf

I am not sure how to move forward along the lines of using ZXCT1009 as a battery current monitor.


texts: Will closing some hvac vents cause blower motor to use more electricity?

texts:
Question: Will closing about 50% of the hvac vents in a small apartment cause the blower motor for the air handler to use more electricity?

I live in a 700 square foot apartment. During the day I close the air vent in the bedroom then close the bedroom door.

I do the same thing for the restroom. It has got two small hvac vents. I also keep the restroom door closed.

For sure there is more resistance acting against the blower motor due to the lesser surface area of the vent opening space. I just don't know if that would translate into more electricity usage by the blower motor.

My electricity bill this year is on average about 20% higher per month than last year. The higher electricity bill started in March or when I started using my air conditioner unit.

My electricity bill for June, 2016 was $99.17. My electricity bill for June, 2017 was $121.68.

The February electricity bill was actually about 15% lower than the electricity bill for February of last year.

Thank you in advance.


texts: How to calculate battery life with a given load?

texts:
I am not very good at electricity things so any help anyone could give me would be fantastic. Here goes:

I have a battery (for power tools); it is 18v and 1500 mAh (imagine DC).
I'm trying to get it to power a tool that is designed to take 120V and 6 amp (AC).

Is there a way to calculate how long the battery would last? I read the article on "How to calculate Battery Life" and it was extremely helpful... but I have more questions. Does the AC/DC conversion have any effect on battery life? What affects do volts have on battery life? Is there an equation to calculate this?


texts:
On my understanding, a LockIn amplifier use an internal (or external) signal source, set to a given frequency, say x. The system locks into that frequency, which means only that frequency can be analyzed by the device.
Is it right, that when the device is „locked“ on that frequency x, I could measure voltage noise of an amplifier (with shorted inputs, high noise amplification) on that frequency x. To get the whole frequency noise response, (1/f + white noise) I would need the setup to do a frequency sweep?


texts: Should I shield digital sensors in close proximity to one another? If so, how?

texts:
Hi and thanks for looking!
Background
I am building a RC multicopter, the design of which has already been helped along greatly by members of this community!  Thank you.
On the underside of the aircraft, I have mounted a project enclosure box into which I am cramming a few sensors (all soldered either directly or with short leads (< 5cm) to a PCB which is run by an ATMega328), the RC receiver (2.4GHz Turnigy 9X), and the power distribution board.  The dimensions of the enclosure are approximately 8cm x 16cm x 6cm so it is a pretty tight space.
Sensors & Equipment (linked to the actual product page):

Sonar
Magnetometer
Digital Barometric Sensor
SD Card Reader
Camera module
Voltmeter
Turnigy 9X receiver
Additional transceiver for Tx/Rx of telemetry data
GPS
Angle sensor
Accelerometer

Two-Part Question:
First, should I be worried about these items causing detrimental electrical interference with one another?
If so, what is the best way to shied these items to prevent said interference?  I was thinking that--due to the small size of these sensors--I could simply cover them with a small piece of aluminum foil and then cover the foil with a small piece of electrical tape.
So, for example, the ultrasonic sensor (sonar) is mounted to the wall of the enclosure with the two transducers(?) nested in holes drilled in the enclosure wall so that it points outward away from the other components.  Should I now cover the back of this module with foil/tape?  Would heat be a problem?
Thanks in advance!


texts: What are the factors that affect delay/latency between base stations?

texts:
I am modelling a 5G network, with the uplink and downlink being decoupled and treated as separate networks.

I am exploring the integration of fog computing and how latency varies between different base stations (eNBs) and mobiles (UEs).

For example for channel gain, this is affected by fading, path loss etc. but what affects the latency?


texts: Are there any caps that have wire leads that are in the pF range?

texts:
I am an electronics hobbyist and enthusiast, and I want to build an oscillator for fun and to learn how it works.
I want to try different values of caps, such as mF, nF, etc. But I want to also try the pF range as well. What I have found is that all the caps on the market that are in the pF range are for PCBs (to my understanding). They look like this. It seems to be rather difficult to find what I need.
I don't want to get into PCBs as that subject is rather dull for me.

Basically, my requirements are:

pF range caps
That have wire leads (and not connections like in the one that I linked)
That does not require the use of PCBs (can be used without putting them on a PCB)

It would be great if all of these would be met. I am willing to create my own caps that have these requirements and if you can share any advice on how to build them or point to any resources, that would be fantastic.
I just hope I am not looking for unicorns or that I am asking for too much here.
Thank you.


texts:
I'm using a ATtiny84 and with three 74HCT595 serial to parallel converters to drive 24 LEDs. Every thing works fine, but when I try to light up more than 10 LEDs at the same time, the ATtiny84 program resets. I'm thinking a dip in voltage related to high load it causing this.

I've tried running it via a iPhone charger, PC USB but still the same issue. If I use the Arduino Uno to drive the LED's instead of the ATtiny84 it all works fine.

Any ideas on how to get around this? Do I need to add a capacitor somewhere or do I have to switch off some brown out voltage thing in the ATtiny?

Update:

I'm trying to make a clock. Two rings of 12 LEDs. The three 74HCT595 are chained using the overflow pin connected to the input of the next one. The 74HCT595 has 8 outputs so I need 3 of them for 24 LED's. The 3 digital pins of the ATtiny84 is used for clock, input and rclk.

Code: https://gist.github.com/anonymous/be75cd17bd5773f0df88


texts: Brown Out Problem in Raspberry Pi Over Power Tether Cable

texts:
I am in the middle of making my own ROV with six DC motors as the thrusters.

The main controller inside the ROV is a microcontroller that is connected to Raspberry Pi that can send and receive control command over TCP. Power and control from-and-to the surface is established using tether cable which consists of power cable  and Cat-5 cable for ethernet connection. The power transmitted is 36V with maximum current rating of 20A. Inside the ROV, the transmission voltage is converted to 12V for motor usage and 5V for other electronics (microcontrollers, Raspberry Pi, other sensors).

The problem is every time I start the motor, Raspberry Pi seems to be browning-out (flickering power indicator) and then turned off. I have tried using separate source (e.g. battery) for the 5V devices and it works seamlessly.

Do you guys have any solution to this? I have thought about using optocoupler, but then again the power came from the same source (tether cable) so I thought it will result in the same way. The best that I can think of right now is to find isolated DC-DC converter for the Raspberry Pi.

Thanks!

Edit:
I made my own driver, which consists of a single NPN transistor (TIP142) acting as a switch.
The motor will draw around 7A
To convert 36V to 12V,  I use this http://www.ebay.com/itm/DC72V-36V-48V-60V-to-12V-240W-16-20A-converter-Electric-Storage-Battery-car-/221381653107?pt=LH_DefaultDomain_0&hash=item338b5ff273.
As for the 12V to 5V converter, I 'm using Turnigy UBEC 5A


texts: how exactly pours copper at Switching node ,Buck IC and inductor component for CE_C and RE CISPR25

texts:
I am starting to update PCB layout to next version because EMC test result failed. As result of test, the designed Buck IC layout seems have the improvement room and noise is from 2.1MHz harmonic.
The designed Buck IC: LM53625LQRNLTQ1(2.1MHz
Test requirement:CISPR25 level 3
Test Voltage: 24V
Current layout: CE_C Pass, RE fail
Layer 1

Layer2

Layer3

Layer4

Layer5

Layer6

The information from co-worker, they used to pour copper under Buck IC and inductor form layer1 to layer6 and RE has a lot of improvement but CE_C became very bad
I would like to do a little bit modification based on current layout

Remove copper under C32 and R82 from layer1 to layer6

Pour copper under buck IC like layer 2 at layer3

my Question as below:

Why to remove GND copper of layer3 at current layout? do anyone have a kind of experience for this

I read some of buck Layout recommendation for reducing EMI

https://electronics.stackexchange.com/questions/503308/buck-converter-pcb-planes>
https://e2e.ti.com/support/power-management/f/196/t/538740?-DC-DC-Converter-Ground-plane-cut-below-power-inductor>
but there is no article to be discussed with how to pour copper under switching node and Buck IC.


texts: How is the output voltage of a mobile phone charger fixed to a rated value?

texts:
Here is the circuit of cellphone charger. I have seen the input voltage range for a cellphone charger to be 100-230 V but the output voltage to be fixed to the rated value(like ~4.5 V). So, my question is how the output voltage is fixed to the optimized value if I provide different mains supply voltage. Like, in India I give 220 V RMS value while in Japan I provide 100 V RMS.The grid frequency is also different in different countries as well as the RMS voltge.
I am attaching a picture of the rating of an ac adapter(cellphone charger).-


texts: Arduino inductance meter using op-amp as comparator?

texts:
I want to create an Inductance meter with an arduino nano, for that I follow
that link whose theory convinced me : tutorial

(The Diode on schematic remove analog negative voltage, Edit: I have wrong,  excuse me surely for prevent inductor negative voltage because out signal not contain diode or maybe in the comparator ?) and then the comparator
convert it into square wave based on ON/OFF DC ?
Getting wavelenght or pulse in time and then calculating resonant frequency
and finally the inductor value based on known capacitors values.

This tutorial use an LM339N comparator, but I learn an I read : op-amp can be used as comparator.

I have not a comparator but I have an TLV2462 op-amp ,can I use this
TLV2462 - Op Amp - Dual Rail-to-Rail as comparator
in place of LM329N comparator ?

My goal is to create an Inductance meter for 'nH' unit... I learn, I read but i'm confuse.
Also, I know the discharge inductor can create a big negative voltage spike.
I would not want to burn my arduino (perhaps the diode is here for that), that's why I'm always on the theoretical part.

Thank's for your help.


texts: How does pure transport delay affect the Nyquist plot, and how is it possible to find the maximum value of the delay, such that the system stays stable even after delay is introduced?


texts:
I have a device that has a 10bit parallel output that I need to get to a serial input.

Can I use a 16 bit PISO shift register and somehow ignore the 6 LSB?

How might that work?


texts:
Have a look at the diagram above.  It shows an op-amp with negative feedback.  Ignoring the feedback loop for now, the voltage (pressure) coming from the 5V battery, acting on the inverting pin, should amount to 5V.

Now, I understand that the feedback loop is adjusting the voltage on the inverting pin to make it equal to the reference (non-inverting) pin or 3.3V and you can clearly see that the output is producing a negative voltage to achieve this.  I also understand that the input pins have a very high impedance.  What's confusing me is how it actually does this (considering my rudimentary knowledge of electronics).  I considered that the output was sinking some of the current produced (by the battery) to alleviate the pressure on the input pin and bring it down to 3.3V, but clearly that isn't the case (since the 1 ohm resistor is passing 5A).  So, I'm struggling to understand how 5V of pressure from the battery results in 3.3V on the input pin.  I'd appreciate it if somebody could explain this in an intuitive way.

Much Appreciated.

Edit:

Many thanks for your all your comments and insights.  The circuit itself is a distraction.  At the heart of this is my attempt to understand op-amp and negative feedback behaviour.  I wanted to understand the following:

a) if you could apply an input voltage to the op-amp that was different to the reference voltage (more specifically that you have voltage "pressure" acting on the input pin that is higher than the reference pin). This also assumes that you have some other input other than the feedback loop.

b) if a is true (and assuming that the op-amp adjusts its output to equalize the voltage on both pins) how is this achieved?  Clearly the feedback loop plays a part and the only thing I could think of was that the output was sinking current to take the pressure off the input pin and thus explain the voltage drop between the between the higher voltage source and the voltage appearing at the input pin.  Incidentally, the question would still stand even if you had a resistor between the source voltage and the feedback loop/input pin junction.

A better circuit example is shown below (taken from http://www.electronics-tutorials.ws/opamp/opamp_2.html):

But with V1 set to some voltage other than 0V.

Final Edit (Promise!):

From the electronics tutorial article linked above:

"This negative feedback results in the inverting input terminal having a different signal on it than the actual input voltage as it will be the sum of the input voltage plus the negative feedback voltage giving it the label or term of a Summing Point."

This is exactly where my confusion lies.  As I understand it voltage is simply pressure exerted measured with respect to some reference point (usually ground).  What the paragraph above is suggesting is that at the "summing point" there's a change in voltage (pressure) because of the addition of the feedback voltage.  Intuitively, I'm thinking that the output pin "sinks" some current to reduce the voltage at the summing point.  But that sinking of current would reduce Iin (since no current flows through the inverting pin).  The result would seem to be that Vin drops.  But is this the case?


texts: Can I control commercially available zigbee switches and devices through my Xbee?

texts:
Can I control commercially available zigbee switches and devices through my Xbee, that connects to my microcontroller?

I want to design home-automation where I would like to controll Lights, fans, AC, Curtains etc. from my board. Can I use Xbee S2 module to Connect to these Lights (As they are zigbee Switches)?


texts: How to convert a device pluggable to a car lighter, changing to a regular home socket

texts:
I bought an air compressor that is powered by the car lighter in my car. It does the job when I want to inflate my car tires, but if I want to use for something else like there are 3 bikes in our house and they all have to be regularly check, it becomes a bit of a hassle.

I'd like to change the adapter of the air compressor from a car lighter to a regular adapter, but I'm not sure what should be the voltage and amperage? Or will this depend on the air compressor specs?


texts: I want to build radio/alarm clock that power itself from the wall. I live in Canada. What safety standards should I follow? And is it free to acquire the datasheet of these safety standards or does it cost money to acquire such document?


texts:
I mounted the following circuit using a LM324, where Val = 5v, Vref = 1.78v, R6=18K and R7=10K.

I measured Vu and i'm getting a very close value to Vref, why?

Edit: V- and V+ are connected to Vref when i measure Vu.
I mounted a capacitor (not shown in the schematic) of value 50nF between the power supply and ground as close as possible to the operational amplifier.

The resistors have the following values: R4=R2=8.8KOhm and R1=R3=2.2KOhm


texts:
I have a nonlinear system described by:

$$\begin{align}
 V\,\dot x_1 &= Q_1 C_1 - (Q_1+u)x_1 \\
 V\,\dot x_2 &= C_2\,u -(Q_1+u)x_2 \\
 y &= -\frac{\log{\left[(x_1-x_2)+|x_1-x_2|+4K\right]}}{2}
\end{align}$$

\$V\$, \$K\$, \$Q_1\$, \$C_1\$, \$C_2\$ are constants, \$x_1\$, \$x_2\$ are states, \$y\$ is the output, and \$u\$ is the input.

Can I perform linearization to this system as a way to control it?
I want to linearize around let's say \$y_e=7\$ but then \$x_e\$ is not zero and I cannot form the linearized model since I have to take into account the \$y-y_e\$ or \$x-x_e\$ terms. What I mean is that when you linearize around zero everything is easy and in order. But when the equilibrium point is not zero, what do we do then?

Also, what is the order here? I linearize and construct a linearized model around \$x_e\$. Then, you control it with a control law.
Then, you apply the control law to the nonlinear system. Is that correct?

Thanks for your time in advance!


texts: UHF RFID communication or something similair

texts:
I am trying to develop a proximity logger.

Basically I have 2 mobile devices (microcontrollers), when the devices are within a 1-2 meter from each other, they should exchange IDs (a simple integer value or short string). The ID should then be logged (so some serial connection). When the devices loose communication, it should again be logged (just interrupt the microcontroller).

I've done some research, effectively I'm trying do NFC but for a longer range and small data transfer.

Any suggestions on hardware I could use, or alternative research I could look into?


texts: strong noise in microphone unless usb receptacle is grounded

texts:
I installed a Banana Pro (like Raspberry Pi), plugged an usb audio stick in, and a microphone in it. I run this thing with a properly dimensioned usb power supply (tried different ones). This way, there is a constant strong humming noise in the audio signal from the microphone. This happens with two similar of those installations.

When I connect the outer part of the usb receptacle with ground, that noise disappears completely. Other parts may work as well, but usb is easily reachable.

For me this raises these questions:

Is this a typical phenomenon? What's causing it? Can I practically do something in order to avoid the cause?
If not, is it a valid workaround to actually connect it to ground? Or can that be a dangerous thing?

Added details:

The stuff is assembled this way:

230VAC---PSU---BananaPro---USB_port-*--USB_audio_stick---Microphone

It doesn't contain more (though BananaPro has some more ports). 230VAC comes from the wall socket. As PSU I tried two with 1.5A, one with 2A, both with a usb socket output. They are all 'ungrounded'. One was bundled with mobile phone, I don't know details about them, and also not about the usb audio stick. The microphone is then plugged in via typical 3.5mm TS jack.

The (*) is the place I connect to ground of the wall socket in order to make the hum disappear. To be exact (but I'm unable to paint it that detailed): The outer metal hull of the plug/socket.


texts:
Hello I will be communicating with a device using SMBus. For this, I will be using PIC18F26K83. Timing is not important for me so I m somehow free to choose any clock frequency for my MCU. Well higher, better of course. I am new to PIC so I am confused by the datasheet. I want to have I2C clock between 10 kHz and 100 kHz . (I added the picture of related register.)

In this case what is the best configuration for I2CxCLK register? (Timing is not that crucial for MCU.)
In datasheet it says I can set I2C clock to HFINTOSC and MFINTOSC. However, again datasheet says (in oscillator selection part) HFINTOSC can be 1,2,4,8,12,16,32,48,64 MHz Oscillator and MFINTOSC can be 31.25 kHz and 500 kHz Oscillator. What does that mean? Which value I2C clock takes when I choose HFINTOSC or MFINTOSC for it?
If I have 250 kHz MCU clock, if I choose I2C to be FOSC/4, in that case will it be 62.5 kHz?
Last question is can MCU clock and I2C clock be same? Would it be a problem. I ask it because in UART I remember something like: MCU freq. should be 16 times bigger than UART baudrate.


texts: digital attenuator/crossfader, how does it work

texts:
This is a schematic I extracted from the circuit of a large audio effect unit. This portion should be a digital-attenuator/crossfader between two audio sources.

In the front panel, there is a DRY/WET balance potentiometer that controls this section (not directly, but through a ADC+microcontroller that then feeds those CD4053 switches using 5 bits).

Also, not shown in the schematic, there is a simple inverting opamp used as unity gain mixer for DRY-OUT and WET-OUT signals.

At first look I thought it was pretty simple, the switches/resistors are arranged as a R2R ladder, so I understand how each signal gets attenuated..

but then I noticed two things:

1) why R40 and R61 are not at the end of the ladder (i.e. at the R38/R39 junction), but one step before?

2) how could this work as a crossfader between the two signals, if they share the same control bits on the same arrangement? This way the two signals would get attenuated at the same time, while I would expect that as one signal gets attenuated, the other would get boosted, and to get that you would need to rearrange the circuit around one pair of CD4053. Am I wrong?

I should note that I traced and checked (more than twice) this schematic from the actual unit, so there should be no errors..

obviously I am missing something


texts: Why does this BJT logic circuit only function intermittently?

texts:
In my free time I've been trying to implement some simple logic gates and circuits using BJTs only (BC547s are the ones I have lying around).

The circuit

I've successfully built inverters, NAND and NOR gates. However I ran into trouble when I tried creating some sort of "latching" circuit. Here's the logic diagram:

Both A AND B need to be HIGH in order to turn on the output, but once it's on, A can go back LOW and Q will stay HIGH until A goes back LOW.
Here's what my attempt looks like using a NAND and NOR gate, each followed by an inverter:

The base resistors are 10k and the collector resistors are 1k, VCC is 5V

The Problem

The circuit works. Sometimes. When I first tried it out, it worked like a charm. All of a sudden it stopped working. It would get stuck in the HIGH state when it should have been LOW and the other way around. I found out that if that happened, I could "flip" it into the correct state by touching resistor R8.

I'm a 2nd year EE student, I know about digital circuits (only on the logic gate level, not how they're implemented) and a bit about BJTs.

I'd greatly appreciate if somebody could shed some light on this for me.

Thanks, and a happy new year :)


texts: How can I find out which wires are the primary wires on this transformer?

texts:
About the amp:
This is from an old solid state audio amplifier with an AM/FM tuner. No digital parts or ICs were inside. It was all point to point. Unfortunately I threw out the amp and didn't write down the number and now I am trying to use the transformer to build an audio amplifier.

About the transformer:

On 'one side' the wires go as follows: White, Yellow, Brown, Orange, Red, Grey, Black

On the 'other side' the wire go as follows: Red, Red, Yellow, Grey, Yellow, Blue, Blue

My experiments to find out what the primary wires are: After reading about how to find out by measuring resistance, I found that the primary wires should be about 4-8ohms I measured all the combinations of wires on each side and applied mains to the transformer. My first thought was that the 'other side' had pairs of wires so it must be the side with the primary. To test I (very quickly) hooked up 120V to the pairs and measured the other wires with my scope. This stepped the voltage WAY up (200Vp2p was my first measurement) and buzzed a lot. Once again.. it was on for less than a second and never was remotely hot. I tried a few more wires on that side and had the same result. After doing a similar thing to the 'other side' I found that the white and grey produce approx 80Vp2p, 40Vp2p and 10Vp2p. This is the best combination I have found so far. Does this make sense? I'd like to know a little better before designing a circuit around it.

Any advice or thoughts will be very much appreciated!!!

edit: Really important detail I missed. The outside of the transformer says t52-131 on the first line and C-AS-QD7 on the second. It is a big hefty transformer weighing two or three pounds? (I'm bad at estimating weight)


texts: Rheostat replacement resistors with relays

texts:
I would like to replace a 500k rheostat with three fixed value resistors. Can I achieve this with the help of 3 sugar cube relays like I've shown in the picture? or is it bad idea?

Those relays are all powered on individually with a separate mcu interface so that I can select which resistor value I want.


texts:
I'm working with an ATTINY26(L) learning about interrupts, and discovered a problem.

I am getting a different output voltage on PORTA (half) than I am on PORTB. To simplify things, I made a program to turn on a single LED on a given pin. I've tested so far on several pins from both ports.

On PORTA, if I measure pin to ground without a load, I get 5V. If I connect the LED (3\$V_f\$) and a 100Ω resistor, the voltage drops to 2.5V, and the LED is dim (2.5V across the LED and 6mV across the resistor).

On PORTB the voltage stays 5V (3V across the LED and 2V across the resistor).

Code:

int main()
{
    DDRA = 0xFF;
    DDRB = 0xFF;

    while (1)
    {
        PORTA = (1 << PA6); // Half voltage?
        PORTB = (1 << PB6); // OK
        milli_delay(100);

        PORTA = (0 << PA6);
        PORTB = (0 << PB6);
        milli_delay(100);
    }
}

void milli_delay(int d)
{
    for (int i = 0; i < d; i++)
        _delay_ms(1);
}

Do I have a damaged microcontroller, or have I overlooked something?

Update:

I swapped out the microcontroller for an identical one, and have the same result. I think it's unlikely that two are damaged in the same way.

Update 2:

Some have requested the compiled HEX code: (Link now removed.)

Update 3:

@Jippie was kind enough to check out the ELF (decompiled) code and saw a weird change of PORTA back to input, immediately after setting it to output. What gives?

The code I pasted above isn't quite complete. There's a little extra line of code which should have been commented out, or pasted into this question:

DDRA = (0 << PA7); // input on PA7

PA7 was intended to read a switch as part of my pin change interrupt testing. I thought the line had been commented out, but it wasn't. And, if you look closely, you'll spot a problem.

It should be:

DDRA |= (0 << PA7);

Trying to set pin PA7 to 0 for input alone should be done with an OR-EQUALS operator (|=), not just EQUALS (=). As a result, the entire PORTA was set back to input.

The lesson here? A single pipe character ruined more than a whole day of learning and experimenting. A single line of code omitted from the question (or not properly commented out for testing) caused headaches.

I am always my own worst enemy when it comes to troubleshooting. It wasn't a faulty chip, a compile error, or some accidental configuration. Total newbie mistake in not thoroughly checking my own code.

Some pics:


texts: Why do some TSOP1738 have a metal cross over their window?

texts:
Why do some TSOP1738 have a metal cross over their optical window while some do not have this cover?

Does not it obscure the view and shorten the range of the sensor? Does it have some positive effects?

Compare these two:


texts:
I am trying to build a temperature controlled 555 circuit to drive a cpu fan (used for cooling my entertainment center)

I built this using slightly different diodes and MOSFET, and it works great (until you hook up the power backwards and get that distinctive pop of and poof of smoke from a blown up 555). Circuit: -

anyway, now I want to make it temperature controlled.  I have a few tmp36 sensors laying around as well as an AD592 and a AD22100, so I can use whichever will work best.  how could I go about converting this circuit to vary based on the temp?
Let's say lowest speed below 75 F and full out above 100, but I would love to learn, so if you could explain the calculations, that would be great.  I feel like this should be easy, and I am kind of just missing something, but who knows.

Thanks!


texts: Use of series inductor to control small 120v blower

texts:
I want to run the 120vac blower less agressively. Like 9ov instead.
I find that I can series install an inductor and that works well.
Q1   Would it be best to use a buck xfmr instead?
Q2   How does the inductor method affect cost of operation?
Q3   I note that the motor runs cooler either way. What is happening regarding phase shift, like EIcos theta?
Thats about it. I do plan to measure phase w analog scope but fear line isolation. I wonder if my amp clamp and fluke can give meaningful data.
I think the pf is about .86, or 30 degrees.
Just curious about how things work.
Thanks

Maybe I am wrong but this inductive blower works good at 100 vac. Do common inductor motors tend to make it to sync rpm and like lock up to line freq. within certain limits? That is what I observe. All in all I get a cool quiet blower at about 40 percent less heating. Is this believable in your opinion?


texts: Why the same sound source (low frequency, possibly infrasound) has different frequencies in different rooms of the house?

texts:
Can someone explain me why the same sound source has different frequencies in different rooms and if there is some type of correlation between the vibrating frequency and the distance between the sound source?
I am trying to locate the source of a low frequency sound that sounds like a diesel car engine or air compressor/pump, but when I record it, it has different frequencies in different rooms from the house.
I think this sound is near the infrasound range as you can also feel it as vibrations (my friends can also feel it, especially if they use foam earplugs). I am using a dual array mic from my laptop to record it (surprisingly, it detects low frequency sounds as I have tested it by rapidly closing the door at about 2-4Hz and the sound was detected).
The laptop array mics also record the 220V transformer at 50Hz and the fridge at 95 and 105Hz so I think it is working correctly.
I use Spectrum Lab app to record it.
So in one room, the frequency of the sound is ~ 16Hz and ~71Hz, while in other rooms, the same sound source (I feel the vibrations in the same way) has a frequency of 36Hz, 41Hz, 73-76Hz.
I have attached a screenshot of my recording from the 3 different rooms.


texts: Non-isolated DC power distribution for an appliance

texts:
I am building an appliance where we have a device where we need to have a +48 V/300 W DC power rail and a +24 V/300 W DC power rail. The AC (mains) should be world-compatible (both low- and high- lines) and the DC part should be isolated from the mains (double-isolation)

I am struggling to come up with the best power distribution strategy to generate those two power rails:

Two single-output AC/DC power supplies in series (mains-to-24 VDC)
with a +24 VDC mid-point and common ground.
One dual-output AC/DC power supply (Output 1: 48 VDC, Output 2: 24 VDC) with common ground.
One single-output AC/DC power supply (48 VDC) with a step-down DC/DC converter (48 VDC to 24 VDC), with common ground.
Other?

Both DC power rails should not be isolated and share a common ground to avoid ground loops.

EMC, floor area, efficiency and cost are concerns (by order of priority).

What would be the best option?


texts: Nucleo F446RE - No SPI response while transmit is working as intended

texts:
I'm trying to read some registers of an Atmel AT86RF233 transceiver via SPI with a Nucleo F446RE development board. As stated on the title, whenever I send anything through MOSI, the transceiver doesn't respond, even if the message is formatted with the exact same way specified at the datasheet. The  transceiver isn't fried (tested it on an Arduino and it worked perfectly), I've used a logic analyzer (which displayed the signal on MOSI correctly but no MISO input) and as such I've come to the conclusion that there must be a problem with SPI. Any ideas?

Register reading code:

uint8_t AT86RF2XX::reg_read(const uint8_t addr)
{
    uint8_t value;
    uint8_t readCommand = addr | AT86RF2XX_ACCESS_REG | AT86RF2XX_ACCESS_READ;  //never mind for these constants, they're correct
    HAL_GPIO_WritePin(GPIOA, GPIO_PIN_8, GPIO_PIN_RESET);
// PA8 is set as GPIO output from CubemMX, and plays the role of the SS pin, now it goes off to wake up the slave

    HAL_SPI_TransmitReceive(spi, &readCommand, &value, 1, 100);
    while(HAL_SPI_GetState(spi) != HAL_SPI_STATE_READY);

    HAL_SPI_TransmitReceive(spi, &readCommand, &value, 1, 100);
    HAL_GPIO_WritePin(GPIOA, GPIO_PIN_8, GPIO_PIN_SET);  // set it back to high to terminate the communication.

    return (uint8_t)value;
}

Thanks in advance.


texts: Why wouldn't my latching switch circuit turn off?

texts:
I built this latching switch circuit: https://www.edn.com/design/power-management/4427218/Latching-power-switch-uses-momentary-pushbutton

When I connected it to my project (~140 LEDs) I found that I could switch the circuit on but (often) not off. A more careful reading of the article told me that this is expected because "If the load impedance contains active devices such as LEDs, the load voltage at the instant Q2 turns off may be large enough to bias Q1 on via R4, thereby preventing the circuit from turning off properly. The presence of R5 pulls the OUT (+) terminal down to 0V when Q2 turns off, thus ensuring that Q1 turns off rapidly, and allowing the circuit to revert to its unlatched state in a proper manner."

I swapped out the 10K on R5 for 5K and the switch works reliably with my project, but I don't understand this explanation. What was happening when I pressed the button but the circuit didn't turn off?

Vs = approx. 4.5V from three alkaline AA batteries
Q1 = BC847C NPN transistor
Q2 = TSM2307CX P-channel mosfet
load = several strings of LEDs, in parallel. Strings are one colour of either white, blue or purple. They are different lengths (20-50 LEDs). I added a 15R to each of the longer strings because that's what I found in the original battery boxes that I removed, and a 56R to each of the shorter ones so they'd have roughly similar brightness.


texts:
I have an esp-12 soldered on this breadboard adapter. I mounted a 1117 3.3V (not adjustable ones) regulator to the board and removed the 0 Ohm jumper resistor as instructed by the manufacturer.
Using a regulated 5V power supply, I powered it up but I noticed it is getting hot. I measured the voltage on esp-12 power pins and it reads about 4.2V. I changed the regulator multiple times but the result was the same.
Any Ideas why this is happening?


texts: STM32F303 STM32CubeMX __HAL_TIM_SetCompare macro does not exist

texts:
I am using CubeMX to generate code for my NucleoF303. I am a bit confused how to set the pulse width of a timer in PWM mode.

Previously (using an F4) there has been a __HAL_TIM_SetCompare macro in the stm32fxxx_hal_tim.h file.

But that does not exist. Am I supposed to set the duty cycle in some other manner?

Of course I can just directly set the CCRx registers. That works. But if I am going to use a HAL with lots of abstraction like cube seems to be, I would at least like to know how they intend me to use it. Even if I don't.

Not really any code to go with this question.. But here is my current commit in case it is useful:
https://github.com/c-herring/Sumo2017_NucleoF303/tree/221dc57a305ccd64a4b98726df3cce02720b280b

Cheers!


texts:
I have been testing with the SSRF-240D25R to see his application on shutting down a load current that in my case is mains powered from the grid.

In order to see if the relay stops the currents flow as soon as I stop feeding the control side, I did a test where I put a LED on the load side and turned on the control side. I expect to see the LED turn on when I feed the control and turn off as soon as I turned off the control side. In the end, only one part of the experiment went as expected the LED turned on but stayed on long after a shut down the control side. I can´t see what might be the problem even though it should be something simple to resolve.

Here is an electric scheme of the montage:

In summary, the SSRelays+Detect is the 12 V that I use to feed my control side, to activate the Mosfet Q1 I apply 3.3 V (SSRelaysDrive), voltage converted from the 12 V to bias a voltage regulator and in this experiment I used my STM32 Nucleo, "MCUB", as the load.


texts: Why the Voltage in output of Buck Converter fluctuates when there is a step change in load?


texts: Help Identifying a few Molex-style Connector?

texts:
I would like to find replacements for the connectors in the below photos. They're in an arcade game called Pump it Up (think the Korean version of Dance Dance Revolution), and connect the dance pads to the main cabinet. The cabinet was likely made in the early 2000s.

I'm only interested in finding the two plugs with the female pins (red in the below photos), but the mating connectors are shown below for reference. They just connect from wire to wire. I suspect they may have been made by Molex since I've found other connectors in the cabinet that I've identified and replaced with Molex-made parts, but they could've just as easily been made by anyone else.

Any help identifying those two red connectors would be a huge help, bonus points if you can point me towards the pins I would need to get for the connectors, too.


texts:
I'm currently working on a project were I need to cascade several transformers (the core we use does not nearly work as good as it ought to..).
I'm using the equivalent circuit shown in (A), transformed it into an ideal transformer and equivalent circuit (B) by
dragging over the circuit on the secondary side, where $$\sigma_2 L_2 \rightarrow \sigma_2 L_2 N_1^2\\R_2\rightarrow R_2 N_1^2\\C_2 \rightarrow \frac{C_2}{N_1^2}$$

This works very well for a single transformer. When I use the same method for 2 cascaded equivalent circuits of transformers (C) to transform them into the e.c. (D)

the inductors, resistors and capacitors from the second e.c. transformer are modified accordingly (from C to D) :

$$\sigma_2 L_2 \rightarrow \sigma_2 L_2 N_1^2\\R_2\rightarrow R_2 N_1^2\\C_2 \rightarrow \frac{C_2}{N_1^2}\\C_3 \rightarrow \frac{C_3}{N_1^2}\\R_3\rightarrow R_3 N_1^2\\
\sigma_3 L_3 \rightarrow \sigma_3 L_3 N_1^2\\
R_{fe} \rightarrow R_{fe} N_1^2\\
L_3 \rightarrow L_3 N_1^2\\
\sigma_4 L_4 N_2^2\rightarrow \sigma_4 L_4 N_1^2 N_2^2\\
\sigma_4 R_4 N_2^2\rightarrow \sigma_4 R_4 N_1^2 N_2^2\\
\frac{C_4}{N_2^2} \rightarrow \frac{C_4}{N_1^2 N_2^2}
$$

The LTSpice simulation of (D) works as one would expect it to,
the problem is:  the LTSpice simulation of (C) does not.
It shows a decrease in amplification after the second ideal transformer in instead of an increase.

I suspect my method might be flawed, but I can't really pin it down right now.

Does anyone have an idea what could have gone wrong / where I made a mistake ?

If you can't open the schematic, I made a screenshot, hopefully that helps?
http://imgur.com/pLg1v83

Thank you!

simulate this circuit – Schematic created using CircuitLab

ASC FILES:

https://github.com/mmelchger/transformers

EDIT:

1

I'm limited by the number of turns (primary <= 10 turns) and the voltage (voltage through primary inductivity < 0.2V), but require primary inductivities > 270uH with low losses and low saturation between 0.5MHz and 1.5MHz. The transformer should have a ratio of ~ 40, which is why the number of turns on the primary side matters and I'm considering cascading multiple transformers, otherwise I won't have enough space and might run into trouble with capacitive coupling and other effects. I'm using ferrite cores (Al ~ 2700nH/[turn^2] delivers a primary inductivity of 270uH for 10 turns).
Ideally the B-H curve should be linear for my use, but that's another question.


texts:
In my latest circuit, I needed an adjustable resistance to adjust the ratio of a nearby ldr. It looks roughly like this: (btw, I'm not so sure that this schematic is correct. Feel free to fix it :)

simulate this circuit – Schematic created using CircuitLab

This is used in conjunction with an arduino. The ground and 5V come from it, and the output goes to an analog input.

As you can see, I used a potentiometer as an adjustable resistance. But it sounds like overkill, since a potentiometer has 2 inputs, and I use only one.

Something seems wrong to me in this.

Is this the right way to calibrate an ldr ?
Is it right to use a potentiometer as a variable resistance ?


texts:
My kid got a face mask with flashing eyes, but there's also some annoying sounds that comes with it. Is it totally safe to cut the white wires or could the awesome flashing lights stop working too (red and black wires)?
Do we need to see the other side of the board?
Gray wire is power. Yellow some additional connector.


texts: Drive resistor value for crystal in USB hub

texts:
I am designing a one-up two-down USB hub based on a TUSB2036 USB FS hub. I am going to use a 6MHz crystal as recommended in their datasheet:
The usage of the resistor doesn't really make sense to me with the explanation that they give. There is also a FAQ app note on this chip from TI. They say:

This explanation makes much more sense to me; the resistor is used to make sure that the crystal isn't driven with too much current. They have an example schematic that uses a 2k2 resistor value, but they also recommend a 1k5...

They explain how to use the potentiometer to "tune" the value of the resistor using a potentiometer, but they don't say how you are able to see if it is "overdriven".
So, am I safe to use a resistor of around 1k5 - 2k2? How am I to know if the crystal is being overdriven?

I assume I check the "XTAL2" node with a scope and confirm that it is oscillating at 6MHz, but I'm not positive.


texts: In a transformer, what is the phase difference b/w secondary induced voltage and current in secondary circuit for purely resistive load?

texts:
What is the phase difference between the induced emf in the secondary winding of a transformer and the current through the secondary circuit in the case where a pure resistance is connected across the secondary winding?
Or are they in phase with each other?

I have work out this much so far -
The secondary induced emf, say E2 is lagging the flux phi in the core by 90 degrees. The current I2, according to Lenz's law, should be in such a direction so as to oppose the cause producing it, i.e, the sinusoidally varying flux phi. So The current I2 will have to lag E2 by 90 degrees and also phi by 180 degrees, so that the flux phi2 produced by I2 will be lagging phi by 180 degrees as well, and phi will thus be opposed by phi2. So I think that I2 will lag E2 by 90 degrees. Am I right so far?


texts: What mathematical equation can be used to represent the output of this differential amp circuit?

texts:
My lecturer has gave my class a number of circuits to analysis and currently I'm having trouble with the following circuit:

I am familiar with how to calculate an equation for the standard differential amp but I'm struggling with this one because of the extra resistor (R1) and the one voltage source (which would make me assume that the output would be 0). It can be assumed R1 = R2 and R3 = R4, how does one derive a calculation for this?


texts: Crosstalk analysis, Altium vs. the World

texts:
I am trying to understand the real-world effect of crosstalk between nets, and I find I cannot match the data from abstract calculators (like Saturn's PCB toolkit and others) and the Altium crosstalk analysis.

For this sake I've made a dummy PCB project in Altium in which I purposedly placed the components very far away from each other and the tracks very close together (to maximize the crosstalk). See a picture of my PCB here:

It's a four-layer PCB with 1 oz. (35µm) copper on all layers, stacked like: signal, FR4 (0.3mm), GND, FR4 (0.85mm), VDD, FR4 (0.3mm), signal. VDD is 3.3V.

The analyzed tracks (SPI from MCU in the lower left corner to a memory on the upper right corner) are 0.15 mm. wide and have a 0.15 mm. gap between them.

Of course one shouldn't design boards that way. I should have so much trouble with a board like this.

So I used Saturn PCB Design's PCB Toolkit (a free tool) to calculate how bad my crosstalk should be:

Saturn PCB reports 2.64V of crosstalk for a nominal 3ns rise/fall time. My signals should be completely destroyed with such big a crosstalk.

I tried using Altium for the same analysis (a much more complete tool). I've applied the IBIS model to the CPU and generic IC (LV) models for the other two chips. Then I ran the analysis and got no errors. Here it is:

My surprise came when I generated a crosstalk analysis between the lines from the SPI group (SPI+CSEL), marking CSEL as victim and MOSI/MISO as attackers:

As you can see, Altium's analysis gives a much more optimistic data of the crosstalk, amounting to mere +/- 75 mV, instead of 2.64V I've expected.

Elsewhere I've read that Saturn PCB calculation has the wrong picture to illustrate the parameters, and the (S) parameter should be the distance between track centers and not between track edges. That would rise the distance from 0.15 mm. in my first calculation to 0.30 mm. Although the crosstalk is milder, the new data is not significantly closer to Altium's analysis:

So I am clearly missing something here. First, what would the right value for Saturn PCB's (S) parameter be? 0.15 or 0.30? And more importantly, why Altium gives us values that are orders of magnitude lower than Saturn's? What am I doing wrong?

Please find attached the Altium project and it's generated output (schematics, Gerbers, etc.) for reference.

Project and project outputs


texts: If we take a Common Base configured transistor in to consideration..Will the collector base junction break if we apply high voltage of like 7volts?if it breaks then does it give large current


texts: Switching regulator startup voltage and sag

texts:
I have designed my first voltage regulator circuit using LMR33630ADDA. When supplied with input while not loaded, it produces a very good 5V. If I have a load of ~20mA attached when input is applied, the voltage out is only 2.3V. If I then remove the load and reconnect it, the regulator picks up and continues supplying the correct voltage even with the load. However, at about 100mA load, the voltage begins to droop with increasing load.
I'm sure I have made a simple newbie mistake, but I can't figure out what. All feedback welcome.

The bottom layer in this area is solid ground plane. 8 vias under thermal pad.


texts: They look like covers at first glance but they aren't stickered on. I've never seen pads like this and searching doesn't bring up any results. Any information on these?


texts: Via drill layer static dimension in Eagle

texts:
I've had trouble finding a guide to explain PCB vias to me. Primarily, I don't understand why the drill layer (44 in eagle) is the same size for vias of differing diameters.

In the image below, I have vias with different diameters (in mm) lined up. The (white) drill layer does not vary in diameter with the vias. I've tried changing various parameters of the vias and in the DRC file, but neither seem to change the drill diameter. I'm especially confused that for the 1.4mm via, which is greater than the drill diameter. What does the drill layer tolerance represent? How can it be changed and when should it be modified?


texts: (opto)isolated PISO shift register able to "read" at 24V

texts:
I'd like to create an input module for arduino, which should read 64 digital inputs using (chained) PISO shift registers. My system voltage is 24V, so the best way will be any PISO shift register (with integrated isolation) which should be able to "read 24V inputs directly" and protect arduino from overvoltage on that inputs.

I found the only way - K847PH with CD4021, but this will make my scheme much more complicated and it will rapidly increase number of used parts and pcb size, so I am looking for (near)single-chip solution.

Thank you.


texts: TO-3 used to be a common package for power transistors, but you don't see them much anymore. It can't be just because of SMT, TO-220 is still much in use. TO-3 has a much lower thermal resistance than TO-220, so why isn't it used anymore?


texts: 74 Series Logic Power switching with Gnd? (74Hc86)

texts: I'm trying to cut power to the chip to "disable" all outputs without needing to know the input values or changing them. What happens if I use a NPN transistor to let the GND pin float and pull it to GND if the transistor switches on? Would that work? I'm trying to use a npn because my circuit has one unused channel in an ULN2003 and I'm trying to reduce my component count.


texts: Synchronizing sine waves from solar panel and grid electricity

texts:
I am new to the field of solar panel. I would like to install and use the electricity produced by the solar panels (through inverter) directly on the appliance, e.g. a fridge. In case of cloudy sky, I want to be able to withdraw electricity from the grid. I know of the sine wave difference between AC coming from the inverter and the grid.  Do you know of any equipment to synchronize them and where to buy it?
In case of power surplus from the solar panels, I wish to direct it to charge batteries instead of passing it to the grid.  Does anyone know if there is such an equipment and where to buy it?


texts:
In my AVR project, I need to measure input voltage (before buck converter), and check for power loss to quickly save some data to EEPROM.

Measuring input voltage is just to display its value, but I am considering using the same voltage divider to generate external interrupt to save data to eeprom.

Is the schematic below correct and will it do the job?

PWR_DWN goes to my INT pin(pulled down).


texts: Eagle library multiple packages in one device?

texts: So in an Eagle library, the device is created by joining schematic symbols with pcb packages.  You can have more than one symbol in a package... (a quad opamp).  Is there anyway to have multiple packages linked to one symbol?


texts:
I was wondering if you could help me out, what would be the effect of changing R1 & R2. I have looked online, but mustn't be searching in the right place!
My guess is that you would adjust them to minimise crossover distortion, are there any other effects?
your help would be greatly appreciated, thanks.
Ben

(source: electronics-tutorials.ws)


texts: How to add a LED to a Multimeter for use it with the buzzer in continuity testing?

texts:
I want to add a notification LED to my digital multimeter which i need to glow with the multimeter`s inbuilt speaker (piezo/buzzer/beeper) while in Continuity testing mode.

MM Model : DT830D

If i have no other option except to replace the speaker with the LED then also please guide.

If i have to add any additional circuit to my MM then also please guide.

To make it simple i was thinkng to built something that will be connected in parallel or series with the MM`s speaker.

or  is this possible to built a circuit that will only glow the led when the MM beeps.

Thanks in advance.


texts:
I have a telescope with a computerized mount and some additional controlling systems. The mount requires a 5-10 minute long calibration process (to track stars accurately) every time it is powered.

I use a 12V battery to power all the things (they all use 12v), and the average battery life is around 3-4 hours. Some deep sky objects require 6+ hours of observation. I can do that only when I connect the mount to AC power due to the limited power of the battery.

Usually dark sites (far away from city lights) do not provide electricity.

How can I make my system battery hot swap-able? Is keeping a low capacity battery (enough for 1-2 minutes) on the system all the time parallel to the main battery good idea (with a diode in between to prevent backup battery charging the primary battery)?


texts: What limits the modulation of digital signals?

texts:
I am trying to understand why there are different speed on different frequency bands. I see that e.g. ZigBee can do 250kb/s for both 2.4GHz and 868/915MHz, but WiFi are also 2.4GHz with much larger speeds, why are they different? How come 2.4GHz is so slow for ZigBee and so fast for WiFi when they operate in the same frequency band?

And is it possible to obtain larger speeds on lower frequency bands just by modulating the signal the same as WiFi does? Is modulation impaired by lower frequencies or is it only dependent on how good the modulating hardware is?

Thank you very much in advance!


texts: Why is there a grounding clip on this solder sucker instead of a third prong on the plug?

texts:
As most of these inexpensive tools tend to omit the ground altogether (such as in soldering irons), why would ground be added as a clip instead of a third prong?

Is there an advantage for it to be implemented this way?


texts: Correct use of Silkscreen Layer and Documentation Layer

texts:
I'm looking to understand how correctly design my board silkscreen. I usually used to draw silkscreen of exact size of my package, especially for SMD parts, to easly know their dimentions and allow me to correctly place them on my BRD.

Something like this for through hole package:

I've seen it's used, but someone use this:

My tought was, it's correct to use silk for exact size of package and doc just for placement? So in Doc I can place bigger squares for easy reading in placing moment of small SMD?


texts: Is it safe to use series polarized capacitors to form non-polarized capacitors to be used for higher rated voltage?

texts:
simulate this circuit – Schematic created using CircuitLab

It is known that we can use series capacitors to increase rated voltage. But I want to know how far we can push this feature to? Suppose, each of this capacitors are identical, 200V rated and polarized. We also know that polarized capacitors can be turned into nonpolarized by connecting their negative terminals as in the scheme above.

So, in the circuit above, can I safely say that I have formed a 25 mF - 400V rated capacitor? If I charge them up to 400V, then discharge them down to -400V, should I be expecting some problems? I suspect, over time the voltage of each capacitors will be varied and after a some point, one or two of the capacitors will be holding more than 200V (or be holding negative voltage) and blow up. If so, is there a way to prevent that and safely form a higher voltage rated, non polarized capacitors by polarized capacitors?

edit: I editted the question to be more clear. Two series polarized caps forming a nonpolarized cap has the same rated voltage.

edit2: I'm editting the question just to address the diferences between this other question on stack. Firstly, the questions are entirely different. In my question, I am aware of that we can form a non polarized capacitor out of two polarized capacitors. Secondly, I am asking for a safe design guide. I provided a schematic to demonstrate my particular problem.


texts: Basic MOSFET small signal model with no load and Rd

texts:
I've come across the most basic small signal model of the MOSFET. We have a NMOS whose drain is connected to Vdd= 5V and source is grounded. We also have biased gate with a DC 2V. Suppose the condition for saturation is met.
Now what my confusion is when we hook up a small signal voltage to the gate of NMOS, 0.01vpp sine(or any small signal to considerably affect the output swing), the output would be vds= -gm* ro*vgs (all are small signal voltages). So basically our Vout= Vds must be swinging(let's say 4V-6V) with DC at 5V. But here, our Vdd(and hence the Vds) is fixed at 5V (with no AC) as provided by the supply.
Isn't it contradicting with the small-signal model? How is KVL satisfied? Also even if we assume that Vds is swinging(from 4V to 6V), is there any drop in the connecting wires to satisfy KVL? But I'm assuming the wires have 0 resistance and are very small to avoid any resistance.


texts: What is the purpose of parallel RC network in the bridge rectifier output?

texts: Can anybody explain the necessity of the RC network shown in the figure. I found this in circuit for a logic power supply using Fly-Back converter?


texts:
I've been doing a little research online on how to make my Gameboy Color rechargeable, and I came across an instructable this guy made on how to make your GBC rechargeable using standard rechargeable batteries.

I wanted to verify that this mod would be safe and also ask, what kind of diode should I use along with the \$1\Omega\$ resistor that he used? I'm including the link to his page below.

http://nintendoage.com/forum/messageview.cfm?catid=22&threadid=122549


texts: Getting the Wrong Transfer Function for Controls Problem

texts:
Background

So admittedly, it's been about 5 years since I've dealt with any kind of circuits and now I am going back and taking a controls course. On the very first problem I am doing, my answer is not agreeing with that in the back of the book.
The controls book that I will be referencing is Control Systems Engineering, by Norman S. Nise 7th ed.

As far as I know I am doing everything exactly as described in the book (ch. 2). Anyway, here is the question (and I will show all of the work I have done as well).

  Find the transfer function, , for each network shown in Figure P2.3. [Section: 2.4].

The first step is to write out all of the associated node equations, so I convert to the S-domain by:

My next step, is to represent everything as an admittance.

Now, I solve and get the following.

Question

In the book, they seem to be getting...

Am I actually going wrong somewhere, or is there an error with the book solution?


texts: Why does atmel use 39R pull-down resistor?

texts:
I recently bought an SAM4S XPLAINED Board to get a bit experienced with ARM.
There is an external RAM on this board and there is a 39R pull-down resistor on PIN6 which is the /CS1 line of the RAM.

Complete schematic: Schematic

QUESTION:
Why 39R is the resistance of that resistor? That is quite uncommon for me. I do not see any reason why should a strong pull-down be used here. I just want to understand the logic behind that.

Based on the schematic it's connected to PC14 of the controller, but it is not actually. (missing R208)


texts: Solving for initial current for an RLC circuit with step voltage source

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I have a problem where I am asked to find \$i_L(t)\$ and \$v_c(t)\$ for a parallel RLC circuit, with a step voltage source.

The circuit diagram is this below, where the voltage source is \$5 u(t)\$, or \$V=0, t<0\$ and \$V=5, t\ge0\$.:

So far, I found \$\alpha=\dfrac{1}{2RC}=3.33 *10^5\$ rad/s, and \$\omega_o=\dfrac{1}{\sqrt{LC}}=3.16*10^5\$ rad/s.

Since \$\alpha^2 > \omega_0^2\$, it is overdamped, and thus the general solution of the DE has the form \$i_L(t)=Ae^{s_1t}+Be^{s_2t}+i_L(\infty)\$.

The roots of the characteristic equation are, \$S_1\$ and \$S_2\$ are \$ \{-2.279*10^5, -4.387*10^5\} \$.

It is known that:

\$ i_L(0^-) = 0 \$ A, since there is no source at that time.

\$ i_L(\infty) = 0.033 \$ A, since capacitor would be fully charged (no current flows), and the inductor would essentially act as a short.

The part I'm having trouble is determining what \$i_L(0^+)\$ would be. In this circuit, how would the inductor current be determined immediately after \$t = 0\$?


texts: Any good way to automatically enable an RS-485 transmitter in hardware?

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Does anyone know of a good circuit that would automatically enable the transmit on an RS-485 driver when characters are transmitted?  In our designs we currently use RTS to drive the driver transmit pin, but then the RTS signalling has to be done in software.

Note the solution would have to be quite cheap as this will be a volume product (kind of excludes using a separate microcontroller to do the job).  Also keeping the transmit enabled for any longer than necessary would be a problem, as the serial line may have to handle a lot of traffic.


texts: I'm currently making a geiger-counter and therefore I need to crank my 5VDC up to around 400 VDC, the current is very low, around 0.015-0.02 mA. What would be the best way to generate 400VDC from my 5v source?


texts: Mathematical rigour in Signal and Systems

texts:
I'm an electronics engineering student with high inclination to analysis and pure mathematics ( abstract algebra/linear algebra ... ).   I was just wondering if there was any book ( or any resource ) that treats signal and systems and signal processing with a lot of mathematics rigour ( actually doing proper complex analysis, using functional analysis and linear algebra rigorously to explain convolution, fourier, laplace and z transforms for example ).

I'm very disapointed with the books i've read ( Oppenhein, Lathi and related ) because it actually throws a lot of the beauty of analysis and algebra away, focusing on the computational side.

Thanks a lot