texts: Understanding a debit card reader through RFID

texts:
I work in the bus industry and today I went to a meeting that gave me an idea for a project. In order to start the project, I need to gather a technical perspective of how the product that I saw in the meeting worked.

The device I was shown worked as follows (pseudo terms):

Place a contactless debit card against the device
The device reads the card data and then sends the card information to a server over a secure TLS connection (with all the information required to make a payment using the card, the number, CSC etc). This was known as "touching on"
Touch the device again to "touch off"

Then, the server calculated the difference in seconds between when you touched on and when you touched off, and created and performed a transaction for seconds * £0.01.

To be clear, the transaction was made on the server not from the device. This means that the device must have sent card information to the server.

My goal of posting on this site is to try and understand further how the card information was read and then eventually decrypted. I already fully understand how to use a merchant gateway to make a payment securely, how to send data using a SIM etc.

What I know so far:

So to start off, there's gotta be a board in there running something. My guess is it'll be running a Linux distro. I believe that in order to access the data within the debit card (the number, csc etc) an RFID reader must have been used. This would then interact with the Linux distro when the debit card was placed near.

Here's where I get stuck. After they waved the card, they showed us that the card information was then in their server's database. Where have they read the data and decrypted its contents? Did they send encrypted bits and then decrypt them on the server, or did they decrypt the data using the RFID reader and then send the debit card number, expiry, csc etc over the connection. It's this bit I can't get my head around.

I appreciate I have very little knowledge here but if anyone could lighten this up for me I'd really appreciate it. I am primarily a software developer so I'm new to hardware, but I'd love a bit of an insight into what's going on here.


texts: Many-year-old laptop batteries: safe in my closet? For how long?

texts:
I have laptop batteries that are a few years old and lost their charges, but which I've still kept "just in case"*. However, I've heard that letting them lose all of their charges can be dangerous. Does this mean they could burst into flames one day?
How much longer can I keep them around?

*Note: Yes, I do realize they probably won't hold charge anymore, but that's not my quesiton. I'm only asking about their safety, not usefulness.


texts:
Here I solved most of my doubts from this site.Thanks to you all and cos of that I come this far.

1 . I wanna cycle through the various color LEDs using clap .

2 . I use a switch to cycle through the effects of LED so I used another 4017 to switch the power supply through 555 and the output of the 555 is amplified using bc547. I hope so.

I made the exact same connection.  8 and 13 to ground and 16 to +ve source. That's it. but LED randomly started glowing . If i apply ground to LED's ground it acts pretty normal but it automatically cycles through various pins.
and each pins contains 3 LED in series . incl rainbow LED.  I'm using 9v 6f22 battery.


texts: How is this board switching a 24V DC relay via AC Mains voltage?

texts:
A while ago, I bought a wireless switch (similar to this) for a wall outlet. It has recently failed so I opened it to see if there was a simple fix. It is a two part system (the transmitter which sticks to the wall, and the receiver/relay which plugs into the outlet) - but since the receiver gets knocked around a lot and has the relay, I figured I'd start there.

I don't have much experience working with relays, but the circuit I found seems to defy logic.

First, an image of the board - note, the image of the bottom was taken against the white screen of my monitor, so that the profile of the relay is visible (making its pinout clear).

On the left edge, you'll see prongs for an outlet. So, this module plugs into an outlet and is suppose to switch the outlet power to the black socket (bottom-left) where some other appliance would be plugged in (a desk lamp, in my case).

The module receives signals from an RF transmitter which acts as a switch on a wall - the RF receiver circuitry is clearly the mess on the bottom right of the board. When a signal is received, the board is supposed to activate the relay, and connect power to the output socket.

Now to the point: What's got me confused is that, when tracing out the front-end, I find that the circuit is (or at least, "was") somehow activating the 24 VDC relay coil via the mains. Here's what I see:

(Note: I realize that I drew the relay a little unorthodox. I did it that way to mimic the symbol as it is presented in the datasheet.)

This must be possible, since it was working for a couple of years, but how? From the image you can clearly see that the top of the HRS4H-S-DC24V relay coil (bottom-left pin of the relay, as shown in the image) is connected to a mains prong. The bottom of the coil then goes to the collector of a C945 NPN transistor - which could never drop 120 VAC, so I assume there must be some weird biasing going on.

Q: How is it possible that the circuit is activating the switch, using the mains as a driver for the coil, when the coil is clearly defined for use with 24 VDC?

I feel like I've missed something very obvious.

Here's the top view:


texts:
I am new to electronics and have a limited knowledge. I tried calculating the values for a series transistor regulator to simulate in Multisim but still could not figure out a way to do this.
The two transistors are TIP122G and BC182. Please help me to calculate the zener value and the values for the resistors to get an output of 5.6V. The input is 10V
The BE drop of the TIP122 is considered as 1.2V and of the BC182 0.75V
I tried with some formulas and still could not get the simulation right. Please help me.
Edit-
Apart from all the above details the output current spec was given. It is 10mA nominal.


texts: Updating Schematic Component/Footprint in Altium Designer 15.0

texts: I am building a library for Altium Designer version 15.0 and have a schematic component as well as a PCB footprint. The footprint is linked to the schematic through the dialog opened when I double-click the component in the schematic library and add the footprint there. If I then edit the footprint later on, do I need to re-add it to the component through the schematic library, or is it updated automatically? I'm leaning towards the latter but want to be certain.


texts: Why do we short the input when calculating the output impedance?

texts:
I believe the title says everything about the question. My issue has to to do with the following: Consider a two-port given by:

$$V_1 = Z_{11}I_1 + Z_{12}I_2$$
$$V_2 = Z_{21}I_1 + Z_{22}I_2$$

Cleary by the equations above, one would expect that the measurement of the \$Z_{ij}\$ parameters to be performed while keeping one port at a time in open loop configuration to guarantee \$I = 0\$ for the "unwanted" current. However this seems not to be the case, as can be seen for instance in the derivation of the of the output resistance of a simple CE amplifier where the input is shorted to determine the output resistance. What am I missing here?


texts: How to apply heat to Lithium ion batteries without damaging them

texts:
I am making these batteries into a battery pack, and want to put heat shrink tubing around my batteries for a more professional look. Would the heat that it takes to shrink the my PVC heat shrink tubing (walmart.com) be damaging to the batteries in any way?
If so, do you suggest any other methods of heating / types of heat shrink tubing that would be better to use instead?
How would I apply the necessary temperature to shrink PVC heat shrink-tubing (80℃) to a pack of Li-ion batteries without damaging them?


texts: Are there any interesting present-day or historical uses of "resistor priority" logic?

texts:
In many digital logic applications, it's necessary to have an output which will be derived from one signal under certain conditions, and from another signal under other conditions, etc.  Sometimes the conditions may have a priority relationship.

Although it would be possible to use nested multiplexers to implement a priority relationship, a simple means of achieving such a thing is to have three-state outputs connected to a bus via differently-sized resistors.  For example, for a slow-speed bus, if power dissipation wasn't a particular concern, one might have four devices on a bus--one connected with 100K resistors, one with 10K's, one with 1K's, and one with no resistors.  If the device with no resistors decides to output, and is capable of sinking or sourcing 5.6mA, it will "win" rather decisively even if all other devices want to drive the other state.  Otherwise, if the device with 1K resistors wants to output, it will "win".  Otherwise the device with 10K's.  Otherwise the device with 100K's.

To be sure, such an approach could waste massive amounts of power, especially if the 1K- and resistorless devices often want to drive opposite bus states.  On the other hand, it has the advantage of being electrically very simple.

This approach is sometimes used, in a sense, with buses that have pull-ups, pull-downs, or some combination thereof to select an idle-bus condition.  A somewhat nicer application exists with bus-keeper circuits, which pulls an idle bus toward whichever real is nearer.  Has anyone seen or used a "deeper" multiplexing scenario, in either present-day or historical circuits?  As noted, the power dissipation is nasty, but for low-speed applications it would seem that it should be possible to cascade at least four devices reliably (one probably wouldn't need a full 10:1 resistor ratio; values of 1K, 6.8K, 33K might be workable.)


texts: Is USB Vendor ID needed to sell custom USB-hub based on IC?

texts:
I'm about to make a hobby project - build custom USB hub fitting required physical/package dimensions and port positions. The main IC would be TI TUSB4041I, which is is 4-port 2.0 USB HUB (I don't dare to go to USB 3.0 level with my very limited skills).

After a successful prototype, I 'm considering to have the device upgraded to 3.0, and manufactured professionally, in some higher quantity, and to sell it.

If I was about to sell custom USB hub device, which is based on IC like TI TUSB4041I, then do I need to register custom Vendor ID?

would it be legal to sell device without Vendor ID and Product ID?
would it be functional? (I guess yes, as it depends on device class, subclass, and protocol)


texts: CE Amplifier voltage gain is not as calculated

texts:
Am trying to learn from what i read by simulating a common-emitter-amplifier using 2N3055A that has Bdc(DC Current Gain) of 20 - 70. I fallowed the steps below but the Voltage gain is not even close to what i calculated 144 and what the oscilloscope showed 44.3. What am i missing or doing wrong.

The setup was to have IE=0.02A.

Step 1: DC calculations

VE = 0.1VCC = 0.9V
RE = VE / IE = 0.9/0.02 = 45
RC = 4*RE = 180
R2 < Bdc*0.01*RE => R2 = 9
V2 = VE + 0.7 = 1.6V
V1 = VCC - V2 = 7.4V
R1 = R2*(V1/V2) = 42

Step 2: Capacitor calculations

CE < 0.1*RE = 4.5 => CE=1/(2*PI*4.5*F) =35.3uf
CB < 0.1*R1||R2 = 0.74 => CB =1/(2*PI*0.74*F) =215uf
CC < 0.1*RLoad = 1000=> CC = 1/(2*PI*1000*F) = 159nf

Step 3: Voltage Gain calculations

r'e = 25mV/ IE = 1.25
rc = RC || RLoad = 177
Av(voltage gain) = rc/ r'e = 141

Thank you for the help


texts: Timing a circuit's 'on-cycle' after a push button switch is pressed

texts:
First off, thank you for reading all of this - you are the part of the internet that gives me hope for mankind. I’m looking for a circuit that I would think is relatively straightforward, but has a few important nuances.

The end goal is to turn on a user to have the ability to hit a push button switch, which sends power an electromagnet. The electromagnet will be on for a period of one hour. I would like to be able to easily switch the design to two hours, but the PCB itself will have a single predetermined time period.

After the hour is up, the electromagnet turns off and stays off until the next button press.

During it’s ‘off’ phase, I need minimum power drain – I would like a long shelf life
The circuit is being run off of 2 AA batteries. With the batteries hooked up directly to the electromagnet, the 3v results in approximately 30ma is being drawn from the electromagnet, scaling down as the batteries drain (alkaline batteries).
A cheap solution is necessary – this is going into a product with pretty low margins. Hoping for less than $2 for the PCB fabrication & assembly.
If anything goes wrong (eg soldering crack, etc) it is important that the electromagnet is off.

Thus far, we have been experimenting with the TI5111 nanotimer in ‘one-shot’ mode. http://www.ti.com/product/TPL5111. We have ran into a few hiccups using this (eg voltage drop of npn transistor)

I'm looking into micro controllers, such as https://www.microchip.com/wwwproducts/en/PIC10F200#additional-features but the datasheet blows my mind.

I'm basically just looking for something I can put between the batteries and electromagnet that results in a button press allowing the 3V to go through to the electromagnet, then shutting it off after an hour or two.

oooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooo

on a side note:

I've had a lot of people comment on the amount of button presses given I'm only using 2 AA. The electromagnet can hold what I need as long as the current is above 15ma. I'm purposefully drawing 30ma to begin, knowing that the alkaline batteries I'm using will lose voltage as they are used. Based on spec sheets, I expect 2500maH before the voltage drops from 1.5v per battery to .8, which would cut my current from 30ma to right around 15ma. Given this logic, and drawing around 25ma on average, I would expect around 100 hours of 'on-time'. I only need this to last 60ish hours, so I'm good on that aspect.

But if there is a large significant voltage drop between the batteries and electromagnet due to the timing solution, I can get into some trouble because there isn't a ton of room for the voltage to decay. Eg we used a npn transistor with the ti5111 timer and it resulted in a .7V drop between drain and source (we are trying to work around this), so my electromagnet was only receiving 2.3V on a 3V battery, which would drop the number of uses significantly as the batteries drained.
ooooooooooooooooooooooooooooooooooooooooooooooooooooooo

Any suggestions on whether you would use a microcontroller or something like the TI5111 timer? I'm not an engineer, so this is all new to me. We are looking to implement this in a consumer product, so the less than $2 per for the electronics is on a relatively large order (1000-5000).

Any help is very much appreciated - let me know if you have any questions!!


texts: Power on configuration for MCU using CPLD and pin multiplexing

texts:
simulate this circuit – Schematic created using CircuitLab

Suppose we have simple same here. The logic behind this is very simple. During MCU boot it tests pins CONF1 and CONF2 for data on it (LOW or HIGH) and configures its internals based on this. Also during the startup sequence it holds BOOT_COMPLATE HIGH for example. After MCU goes into ready state it drives BOOT_COMPLATE in the opposite direction (LOW in this example). After that pin on the MCU are used for DATA1 and DATA2 functionality. Vendor of MCU advises to use CPLD for this kind of work. But provide no shame for free.
My thoughts about how this should work and looks like all together:

simulate this circuit

Power up CPLD first (assume we have the proper program already set up in it)
Drive IO2 and IO3 LOW or HIGH as needed by config
Test signal level on IO1 and wait for LOW in this example (indicates MCU boot complete)
Set IO2 and IO3 tri-stated (floating)
Done? Or am I missing something?

Also it would be nice to have VHDL or SystemVerilog example for this simple situation


texts: Is there a practical difference to connecting batteries in series or parallel when routed through switched/regulated output?

texts:
I'm building a battery pack that will be hooked up to a buck converter for switched output.  To increase the pack's mAh capacity, I can hookup a second array of similar cells in parallel to the converter's input.  However, since the cell output is passing through a switch-mode regulator, can I accomplish the same increase in capacity by connecting all the cells in series?

Conceptually, the regulator will switch on half as often (when the input voltage doubles), so the cells should discharge at the slower rate.  I may be able to simplify some of my connections and packaging by using the series connection, and thus I'm wondering if there is any practical difference to connecting the cell arrays in series or parallel.


texts: Tachometer IC that does not require zero-crossings?

texts:
I recently built the basic tachometer circuit in this LM2917/LM2907 Datasheet shown below using the 8-Pin version of the device. I realize this circuit requires a VR pickup sensor, and so the LM2907/LM2917 must rely on triggering off of zero-crossings. But what if I have a square, 0-5V TTL input waveform? Can this IC even trigger off of a non-VR input frequency, or do I need to find another tachometer?

I can only think to use an op-amp to convert the 0 to 5 V TTL square wave to a -5 to 5 V. But that requires a negative voltage supply to the -Vcc rail of the op-amp, which I will not have access to.
Upon further reading of the datasheet, it talks about triggering off of a differential input using the 14-pin version of the device, and further explains this in section 10.1 paragraph 2 (page 13). Perhaps this is what I need? If so, how do you adjust the threshold to which it will trigger off of?


texts:
I'm trying to simulate the workings of smoothing capacitors in TINA-TI. I have a varying voltage source (sine wave varying from 4.5-5.5V) and 2 capacitors (1uF and 100uF) connected. The load is a 1000 ohm resistor, and VF1 is the test point. After testing with various capacitor values, I'm finding that there's no change at all to the output waveform compared to the input. See the image below:

Basically, why would this occur? Is it because these capacitor values are not suitable for smoothing, or is it just a problem with my simulation?


texts:
I’ve been doing some experiments recently with metal powders and I’m wondering if someone can help me interpret the results and give me some advice.
I wanted to test how the metal powder would work in a circuit. I tested some graphite powder and some nichrome powder.
I made a circuit using two AAA 1.5 V batteries in series and some PVC insulated solid core 1.5 mm diameter copper wire. I pulled some of the PVC insulation off the copper wire a little and then packed some metal powder into the tube. Next I pushed another copper wire into the tube.  This made two pieces of copper wire connected by some densely packed powder.  I then tested the amps running through the circuit using a multimeter.
The results were -
Control circuit (using only copper wire - no powder) 400 micro amps
Graphite circuit 10 micro amps
Nichrome circuit 0 micro amps
What happened here? Obviously the graphite has a much higher conductivity than the nichrome. Is the nichrome acting as a resistor in my circuit?
How can I get my circuit to run using the nichrome powder?  Do I need to increase the amps with the batteries in parallel, or the volts with the batteries in series?
I know the conductivity of the nichrome in relation to the graphite - can I calculate how much more power is needed in the circuit based on a comparison of the conductivity of the two materials?


texts: IMU axis rotation, calculate values with respect to Earth plane

texts:
I'm building a project that uses an IMU (Inertial Measurement Unit). The project involves the device to be mounted inside a vehicle and I should provide the acceleration, angular velocity and Euler angles of the vehicle (and not the device).
After a few reading I understand that I must rotate the 3D axis of acceleration from the device frame (reference frame) into the Earth frame. To do this I can use quaternion rotation as described here (SO Question). But what about angular velocity? Can the gyroscope axis rotations also be rotated using quaternions?
And as I'm a bit confused, once I rotate the axes, I can calculate the Euler angles from the quaternions. Am I right?
I have come across many algorithms that calculate the quaterions (Madwick's Algo). After the calculation of the quaternions can I use "SO question"'s approach to rotate the device frame into Earth frame?

In brief:
I need to get accelerometer, gyroscope, Euler angle data for the earth plane. I'm a bit confused and so this question is just to understand the best approach for this problem.


texts: Bare metal timer interrupts on stm32f103 "bluepill"

texts:
I am trying to implement a simple interrupt routine, blinky led using a timer on the stm32f103 "blue pill" board.
I have been reading the datasheet, reference manual, timer cookbooks and all but I'm not able to figure this part out.
I'm using the gnu-arm cross compiler and was successful in getting a timer a started and was able to blink an led by continuously checking the 'update event'  bit inside the TIMx_SR register.
Up till now, I had a look at the NVIC section in reference manual but I can't figure out exactly how to work with the vector table...
Any suggestions or resources are welcome.


texts: Overcurrent protection in lab bench power supplies

texts: In my school we used lab bench power supplies all the time as it is an electrical engineering school. Can someone point me in the direction of an implementation of an overcurrent protection found in such supplies?


texts: Does voltage matter when using constant current PSU?

texts: Let's say I have 90W RGB LED module/plate (10 Series and 9 in Parallel internally). It has Voltages: R: 20~22V; G: 32~34V; B: 32~34V; Can I power all colors with 3 identical 30W constant current driver that has voltage of 30~36V? To what extent does voltage matter/not matter when using constant current psu?


texts: Rx buffer overwrites Tx buffer in spidev xfer2

texts:
I'm setting up a comms link between an STM32F407 MCU and the Pi3B+. The code shown below works but when the data is printed out, it looks like the RX buffer overwrites the TX one. How do I stop that? The console output is shown below the code.
import spidev
from time import sleep
from tabulate import tabulate  # pip3 install tabulate

ARRAY_SIZE = 56

spi = spidev.SpiDev()
spi.open(0, 0)
spi.mode = 0
spi.max_speed_hz = 10000000
spi.bits_per_word = 8

tx1 = [0xCA, 0xFE, 0x00, 0x00, 0x00,
       0x00, 0x00, 0x00, 0x00, 0x00,
       0x00, 0x00, 0x00, 0x00, 0x00,
       0x00, 0x00, 0x00, 0x00, 0x00,
       0x00, 0x00, 0x00, 0x00, 0xff,
       0xff, 0x00, 0x00, 0xff, 0x00,
       0x00, 0x00, 0x00, 0x00, 0x00,
       0x00, 0x00, 0x00, 0x00, 0x00,
       0x00, 0x00, 0x00, 0x00, 0x00,
       0x00, 0x00, 0x00, 0x00, 0x00,
       0x00, 0x00, 0x00, 0x00, 0x00,
       0x00]

# Do an SPI transaction
# rx1 is the receive buffer
rx1 = spi.xfer2(tx1)

# Print the RX and TX arrays
headers = ['array #', 'TX', 'RX']
idx = range(0, ARRAY_SIZE, 1)
table = zip(idx, tx1, rx1)

print(tabulate(table, headers=headers))

# close the SPI port
spi.close()

The console output looks like this,
  array #    TX    RX
---------  ----  ----
        0     0     0
        1     0     0
        2     0     0
        3     0     0
        4     0     0
        5     0     0
        6     0     0
        7     0     0
        8     0     0
        9     0     0
       10     0     0
       11     0     0
       12     0     0
       13     0     0
       14     0     0
       15     0     0
       16     0     0
       17     0     0
       18     0     0
       19     0     0
       20     0     0
       21     0     0
       22     0     0
       23     0     0
       24     0     0
       25     0     0
       26     0     0
       27     0     0
       28     0     0
       29   254   254
       30   255   255
       31   134   134
       32   254   254
       33   204   204
       34   254   254
       35   253   253
       36     0     0
       37     0     0
       38     0     0
       39     0     0
       40     0     0
       41     0     0
       42     0     0
       43     0     0
       44     0     0
       45     0     0
       46     0     0
       47    54    54
       48    84    84
       49    52    52
       50   108   108
       51     0     0
       52     0     0
       53     0     0
       54     0     0
       55     0     *0

EDIT: Solved here. Didn't make much headway with spidev but was guided on how to use an alternative library.


texts: Can sampling I2C influence transmission?

texts:
I have 200 kHz I2C communication and I am monitoring it with Logic Analyzer that has 100 kOhm input impedance. When I set sampling rate at 2 Mhz everything looks good on the time diagram. On the other hand, when I set sampling rate at 16 MHz something weird is happening. During start condition my analyzer samples SDA as '0' and SCL as '0' but in next sample it detects SCL as '1'. Everyting looks like there was no start condition and I am not able to debugg my communication.
One more thing I can't understand happens when I set 2 MHz sampling. After end condition my analyzer detects adjacent start condition, end conditon that happens on next sample. I cant fiugre out where it comes from because it doesn't happen at all packets.
There is cleary something wrong with my communication but I am not able to understand what. I2C master is implemented on FPGA (simulating in ISE Simulator has shown that it works properly). On I2C bus I got FPGA, ADAU1772 audio codec (that I am talking to), Atmel EEPROM and equivalent of Saleae Logic Analyzer (used to sample transmission).
I have spent 3 days discovering what is going on and now it is just a big headache.


texts:
I know this question title is not the best, but it describes the question well.
I am confused with one thing. Why does this circuit work:

simulate this circuit – Schematic created using CircuitLab

By work I mean turn the 12V relay on. And this doesn't.

simulate this circuit

I have tested it out on a breadboard. The first one is able to run the Relay and the second one can't.

Why is that so? What difference does it make if the load is before or after the transistor.

PS: I am using BD435 transistor. And a motor instead of relay.


texts:
Has anyone managed to get a TI Launchpad doing serial comms via the onboard USB chip (TUSB3410) to OSX?

I have mspdebug working for uploading code. But to get serial I'm having to plug an FTDI chip into the serial lines on the MSP430.

Does anybody have instructions for making the TUSB3410 work properly in OSX?

They claim to have drivers, but I can't make them work.

MSP430 LaunchPad Mac OS X


texts: Sequencing modes for FCC "Intentional Radiator" test

texts:
I'm FCC certifying as an "intentional radiator" a product that uses a custom antenna and off the shelf Broadcom WiFi module.  The module has an antenna port, so single-modular and limited single-modular certification are out of the question.  I have manual transmitter control, through specialized vendor firmware.

My FCC lab is shuddering at the number of test passes, which are some combinations of:

Two bands (2.4Ghz and 5Ghz)
Eight protocols (802.11a, 802.11b, 802.11g, 802.11n, 802.11ac, Bluetooth, BTLE)
Six modulation techniques (FHSS DSSS OFDM HR-DSSS 256-QUAM CKM) at various data rates from 1 to 54 Mbps.
Two channel pairings (20 Mhz, 40 Mhz)
Three regulatory regions (US/Canada, Japan, Europe).
Bluetooth in three modes.
DFS (Dynamic Frequency Selection) in the 5Ghz band to avoid radar.

Each test takes about two minutes of stunningly boring waiting, then manual set up of the next band/speed combination.

Is it permissible to use software to sweep each of the data rates (say at one rate per second) and check for out of band exceedances during that time period?

Are there other techniques to speed this process up? See also How do I cycle a WiFi transmitter through all modes, for FCC intentional radiator EMC testing?


texts: Can I Use an Isolated DC/DC Converter to Step Down a Switching Dynamic Signal?

texts:
I have a 24V device that takes a signal of either of 36V or 72V that will switch on and off at around 2Hz. This signal needs to be converted to 24V and I'm considering this isolated DC/DC converter which can convert 18-75V to 24V. The problem is that I don't know if the device is capable of consistant switching since these are normally used for providing constant power. I looked on the datasheet and it doesn't say anything about switching lifespan or capable number of power-ons. My concerns are about activation time, reduced lifespan, start-up delay, start-up voltage jump, etc.

Is this a viable use of the converter or should I use another device or configuration?

Edit: For clarification, the input signal can come in as either 0V, 36V, or 72V (DC). The output is either 0V and 24V (DC). A 36V and 72V input must translate into a 24V output, and a 0V input must translate to a 0V output.


texts:
I am running a 3.3V 20MHz clock signal for LED drivers over 10 PCBs that are connected to each other over short cables. Overall, the clock signal must travel 1m.

Is this even possible with a 20MHz clock signal without using a buffer on each board? Will I run into EMI issues even if I route the clock signal carefully (e.g. applied best-practice PCB design rules for routing clocks)?


texts: Why is every address in a micro-controller only 8 bits in size?

texts: I have seen that, in 32-bit microcontroller, each address of memory holds only 8 bits of data; it is the same for a 16 bit MC as well. For 32-bit data, it uses a combination of 4 addresses. Why can't an address made to hold 32-bit data directly (making it 32 bits or 16 each instead of 8)?


texts: How can I objectively compare TCXO performance?

texts:
I would like to evaluate an alternate TCXO used in a GPS receiver circuit. Our current TCXO works good but I'm looking to test a lower cost alternate.

The alternate part is Epson TG - 5035CJ / CG / CE (datasheet).

Import specifications like voltage, frequency tolerance, aging..., current consumption, and package size are acceptable according to our GNSS chipset manufacturer's recommendation.

I've done some basic GPS testing including Time To First Fix (TTFF) and Top 4 satellite CNo number comparison, as well as overall GPS performance. All of the tests I've done so far have been at room temperature.

I have access to a temp chamber, GNSS simulator, Vector network signal generator, and a decent Tektronix Oscilloscope. Our network analyzer is currently out of shop.

I do not have a test jig but I'm hoping to somehow objectively measure performance differences between our existing and new part.

EDIT

What specific tests can be done on both TCXOs in-circuit or out-of-circuit with the equipment I have available? Is it possible to measure jitter or are there any other performance characteristics that would be useful to measure?


texts: Difference between the two Ethernet magnetic topologies

texts:
Background
Hello, I'm building up a PCB for a PoE module based on Microchip LAN8720 IC. The recommended schematic is shown in the following figure.

I built up a prototype based on the Waveshare LAN8720 board. This Waveshare board uses an RJ-45 jack with magnetics integrated. The jack they used has a wiring as shown in the following figure. Obviously it doesn't support Power over Ethernet (PoE) with all the spare pins tight together, I had to pick a jack that supports PoE. So I made a decision to use an RJ-45 jack without magnetics and have the magnetics on the outside.
However, I made a mistake in the schematic by not connecting one of the center tap coils (ones next to the common-mode choke) together. (elaborating more on this: the two center taps should be connected to a 75 Ohm resistor each and ground through a 1000pF 3kV capacitor according to the recommended schematic in the figure above. This was the same setup the RJ45 jack with integrated magnetics have. Instead, I omitted this part by mistake and only connected them to the diode bridge for PoE). So the prototype does not work.

Question
I noticed this mistake while I was debugging the circuit and I found several RJ45 jacks with PoE enabled magnetics integrated. (Was too late..) However, I saw a difference in the wiring between PoE enabled jacks and the normal ones. The figure below is a jack with PoE capability and the center taps are first connected to capacitors and then to 75 Ohm resistors (C first then R). This is quiet different from the recommended (R first then C) layout.

My question is, is there a difference between these two topologies (C first then R) and (R first then C).
Intuitively (R first then C) topology used by the normal topology (without PoE) creates a conductive path between the two taps. Is this something to do with power delivery?
-- Update
Question in summary
What could be the difference in these two topologies marked with red boxes? Is there any underlying theory behind the difference? (Thanks @Jason for the insight on power wastage if the PoE topology had resistors connected creating a DC path)


texts: What is the core concept of SINR or SNR model?

texts:
As we all know, there is a relationship between SINR or SNR and BER. Specifically, when SINR/SNR is higher, the BER is lower. And there are lots of work on modeling the complex SINR/SNR.

SNR

  Signal-to-noise ratio (abbreviated SNR or S/N) is a measure used in science and engineering that compares the level of a desired signal to the level of background noise. It is defined as the ratio of signal power to the noise power, often expressed in decibels. A ratio higher than 1:1 (greater than 0 dB) indicates more signal than noise. While SNR is commonly quoted for electrical signals, it can be applied to any form of signal (such as isotope levels in an ice core or biochemical signaling between cells).

SINR

  Analogous to the SNR used often in wired communications systems, the SINR is defined as the power of a certain signal of interest divided by the sum of the interference power (from all the other interfering signals) and the power of some background noise. If the power of noise term is zero, then the SINR reduces to the signal-to-interference ratio (SIR).

two of them are from the wiki.

While, there is still a question that
"What is the core concept of SINR/SNR?"

It is clear that when the signal is higher than the interference plus the noise, the probability of decoding signal successfully is higher. But, what is the root component that supports this?

Until now, the "Capture Effect" is the only concept that I found can explain this.

  The capture effect is defined as the complete suppression of the weaker signal at the receiver limiter (if it has one) where the weaker signal is not amplified, but attenuated. When both signals are nearly equal in strength, or are fading independently, the receiver may switch from one to the other and exhibit picket fencing.

This is the description from the wiki. Capture effect
Specifically, the limiter at receiver works for it and it can explain the SINR/SNR to BER correspondingly.

But I am not sure whether it is the exact reason  for the SINR/SNR model.

well, there is another question in my mind just now:
what is the basic/general  technology for wireless system to combat the interference? Besides the SINR/SNR model (or the relative power model)?

Summarize:

1.What is the core concept of SINR/SNR?

2.what is the basic/general  technology for wireless system to combat the interference?

Thanks!


texts:
I would like to get an idea of how fast SDRAM accesses should be.
If I have a 32-bit ARM based processor running at 500MHz accessing an SDR sdram device clocked at 166MHz, what sort of read/write access rates would you expect?
And what difference to these numbers would running with and without a cache make?
I'm not sure how easy this is, as I know there are many factors involved, but ideally I'm looking for the kind of numbers one would expect in a typical scenario and in a best-case scenario.
Many thanks for any help.


texts:
How do you unit test your assembly code?

I'm working on a serial servo controller as part of a hexapod robot project and the code has got to the point where it's becoming complicated ;) Anyway, I'm used to using unit tests in my day job as a C++ server developer and so have been trying to apply the same kinds of testing to my AVR assembly code. I've worked out a way that works OK for me (see here) but I'm interested if there are any standard tools or techniques that I'm missing.

Updated: For those of you that are interested the full source to the servo controller and the unit tests are now available here.


texts: selecting the footprint size of ceramic capacitor for MCUs

texts:
I have noticed there are different sized(SMT foot print size) ceramics capacitor with same voltage and capacitance ratings. I have been told that smaller the footprint, smaller the parasitic inductance and parasitic resistance a capacitor would have.. does this means I should select the smallest possible capacitor available?
I'm gonna use this capacitors as bypass capacitors for MCUs.
Available foot print sizes {C0402, C0603, C0805, C1206, C1812}
capacitance needed - 100nf, 27pf.
and also, should I use a 1uf ceramic cap, parallel to 100nf bypass capacitors, just in case?


texts: Selecting temperature probe for home use with long cable / low power

texts:
I would like to monitor the temperature outside my home. The sensor has to be located at least 20m cable length from the display unit. Whole system should be powered by a battery (doesn't matter which) and should have a decent display.

I would like to have an accuracy of <=0.5°C but it's ok if it's not as good. I would like to create a display unit myself (as fun project). But it's also OK if there is an off-the-shelf component.

All components should be obtainable from cheap online shops from china and should be cheap.

Which sensor should I select? Digital? Analog?
How much resistance is acceptable per 'm of the cable?
Can arduino nano handle displaying part? Would it be possible to log temperatures using arduino?

I've never done anything like this, I've tried a little research, but I know there are people here who can answer this without to much effort. Great, thanks a lot.

so i found this sensor: and I guess there is some info about it here

Still remains question of cable type/dimension.


texts: How do I make a CPE (constant phase element) with Simscape language?

texts:
I want to use a CPE in my circuit, but I can't find a CPE in the Simscape library, so I want to make a CEP with the Simscape language. What can I do?
I just want to build this circuit,like the picture,the impedacne is a complex number,I can't express it's imaginary part.


texts: Error when compiling start-up file on STM32

texts:
I am attempting to provide custom interrupt handlers for my Cortex M3 (reference manual here). ST kindly provides a standard library, which has various startup files all called "startup_stm32f2xx.s". Each is in a different folder according to IDE.

Now I do not use an IDE (I compile directly with Yagarto, a modified version of the gcc toolchain). I have already asked which of the start-up to use. However, having now tried all the available startup files, I always get the same error:

  /startup_stm32f2xx.s:1:0: error: target CPU does not support ARM mode

A quick Google search reveals that this probably means that the assembler code has instructions that my ARM cannot understand, which is surprising given that the code was provided for my board.

How can I compile the startup file that defines the interrupt vector on my STM32?

Edit: In each of the files, startup_stm32f2xx.s:1:0 is the beginning of a comment. Also, I'm using the flag -mcpu=cortex-m3. Here is the complete error message:

$ make all
arm-none-eabi-gcc -x assembler-with-cpp -c -g -mcpu=cortex-m3 -gdwarf-2 -Wa,-amhls=startup_stm32f2xx.lst   startup_stm32f2xx.s -o startup_stm32f2xx.o
startup_stm32f2xx.s:1:0: error: target CPU does not support ARM mode
makefile:46: recipe for target `startup_stm32f2xx.o' failed
make: *** [startup_stm32f2xx.o] Error 1


texts: How can the current change suddenly in an RC circuit?

texts:
I was trying to simulate a circuit where a capacitor is being charged then discharged. I used an oscilloscope to measure the voltage and the current. I've noticed that when I switch the state of the capacitor from charging to discharging or from discharging to charging, the current suddenly changes to a different value.
I can understand that the voltage can change immediately, but the current? Shouldn't it have a smooth curve?
What is the explanation of what's happened with me?
What happened with me:

Voltage and current measurement in an RC circuit on YouTube


texts: Where I am confused is that the signal coming to the opamp should be superimposed on dc, or could it only consist of ac? Because when we want to make a filter consisting of a few transistors, we need to superimpose the input signal to dc. Is there the same thing here?I am confused here because while analyzing, for example, we are analyzing differential amplifer as large signal and small signal, but here I do not fully understand what the large and small signal is based on.So how should the input signal be, what is the analysis based on, you can explain it, I would appreciate it.


texts: When I connect the 5v power supply of my arduino to my h-bridge the usb connection is dropped and the on LED dims. What is causing this?


texts:
I'm a beginner in electronics. I tried making a hovercraft that looks like this:

The bottom looks like this:

And the battery used is this:

I have used a 9v motor, a 9v battery and a dual blade propeller. For now, I just temporarily connect the wires to the motor to see how it works. As soon as I connect the wires, the motor turns on and the propeller spins with a high speed. However, the entire craft just vibrates(not vigorously) and stays in its place. Sometimes, it displaces very slightly due to the vibration. Moreover, the speed of the motor decreases after a minute or so. Note that I'm not placing the battery on the hovercraft. I hold it while it is connected and try to move along with it when it moves. But the movement is too feeble.

1) Is the battery not good enough?

2) Is the skirt not well shaped?

3) Is the motor to heavy?

4) Is the air intake not properly designed?

What am I doing wrong here?


texts:
I've been playing around with a sample and hold adder circuit. Essentially, I am trying to sample a sine wave with a sample and hold circuit. I want to take that sample and add it back to the sine wave to set its DC value. This is what I've come up with but its not happening the wave I imagined it. What is going wrong here?

simulate this circuit – Schematic created using CircuitLab

Red = Sine Wave
Blue = Sample
Green = Summing Amp

I know I am forgetting a fundamental concept here. Can someone explain to me what's going wrong here?


texts: Can anybody identify this connector? The inside diameter is about 5mm and there is a thread around the outside. I need to get the opposite connector to plug it into.


texts: Reducing IR proximity sensor module power consumption

texts:
I have built a rechargeable automatic hand sanitiser using an IR proximity sensor(HW 201.) It consists of an IR proximity sensor module, TIP 32 transistor, 3-6 V DC pump, TP4056 charging module and a 3.7 V Li-Ion 3800 mAh rechargeable battery.
I'm facing an issue with power consumption.
The battery drains too fast - it is empty after 1 or 2 days.
The IR sensor consumes about 20mA even during idle state (when not sensing hand.)
Is there any option to reduce the power consumption using 555 timer IC or any other programmable MCU (no Arduino?)
How can I make a low power consuming IR proximity sensor circuit?


texts: How to add Gaussian noise or any other noise to a sine wave (using VHDL)?

texts:
We need a noisy sine wave signal. We have generated the sine wave (using VHDL), but we can't figure out how to add noise to it. We are including the code for sine wave generation. Kindly mention how to add Gaussian or any other noise to it.

library IEEE;
use IEEE.STD_LOGIC_1164.ALL;
use IEEE.NUMERIC_STD.ALL;  --try to use this library as much as possible.

entity sine_wave is
port (clk :in  std_logic;
      data_out : out STD_LOGIC_VECTOR(7 downto 0)
      );
end sine_wave;

architecture Behavioral of sine_wave is
signal i : integer range 0 to 29:=0;
--type memory_type is array (0 to 29) of integer;
type memory_type is array (0 to 29) of std_logic_vector(7 downto 0);
--ROM for storing the sine values generated by MATLAB.
signal sine : memory_type :=("01001101","01011101","01101100","01111010","10000111","10010000","10010111","10011010","10011010","10010111","10010000","10000111","01111010","01101100","01011101","01001101",
"00111101","00101110","00100000","00010011","00001010","00000011","00000000","00000000","00000011","00001010","00010011","00100000","00101110","00111101");
--hi
begin

process(clk)
begin
  --to check the rising edge of the clock signal
if(rising_edge(clk)) then
data_out <= sine(i);
i <= i+ 1;
if(i = 29) then
i <= 0;
end if;
end if;
end process;

end Behavioral;


texts:
I'm trying to make my 82C55 function as three sets of 8-bit latches where I can choose one of them by applying the appropriate logic to A0 and A1 and lowering the WR signal to apply the data from input to desired output port.

I read online that this chip has 4 modes of operation, but I want to configure it as three addressable byte latches as I have explained.

Is it possible I can use it like that without specifically programming the chip in advance even though sources tell me data is in groups of 12 bits?


texts: Inverter Design - High Side MOSFET Switch-off Issue

texts:
I've been chasing an issue in a 3-Phase BLDC inverter for some time now. The problem manifests itself as high current and voltage sense noise at high DC bus voltages, irrespective of the load on the inverter.

I've broken the design down into its smallest elements and from what I can tell, the voltage at the switching node (source of high side MOSFET) remains at the DC Bus voltage long after the high side MOSFET is off. This measured voltage is most likely stored energy in a bootstrap capacitor on my driver or the capacitance of the MOSFET.

When the low side MOSFET is switched on, I get fairly large oscillations at the low side gate and drain. This also appears as large currents in the current measurement system.

About the design:

3-Phase BLDC Inverter, capable of 310V DC Bus, however for this exercise testing at 24VDC.
MOSFETS are STF10N60DM2
Gate Driver is 6EDL04N06PT
PWM Control, etc is generated from TMS320F28069F MCU

I've prepared an example schematic showing a a single pair of MOSFETS as per the image below, and I've annotated the colors of the scope measurement channels.

I've captured the relevant issue on the scope in the image below, however there are a few things to note.

Blue = Upper Gate measured at the MOSFET
Green = Upper Source Measured at the MOSFET
Pink = Lower Gate, Measured at the MOSFET
Yellow = Switching Node (Identical to Green but overlaid on Blue)
D4 = High side PWM Signal from MCU, D5 = low Side.

In this capture there is NO LOAD connected to the design, and the PWM is operating in open loop control mode.  I have very similar waveforms, irrespective of whether I have No Load, a Resistive Load or an Inductive Load connected.

There is a ~500ns propagation delay through the driver, the PWM dead-band is at 800ns and I've annotated with grey lines the PWM input versus MOSFET switching edge.

As for the probing techniques, I have SMA connectors on the hardware at the appropriate measurement points. Even if I use a standard scope probe and 100mm ground clip, I still get the same measurement. Using these two diverse measurement methods, and achieving the same measurements I'm certain the noise is present in the circuit and not a measurement artefact.

What I have tried:

Ferrite beads in the gate drive path.
Various combinations of Gate slew control resistors
1K resistor between GS on each FET
100nF to 10uF bootstrap capacitors
Different types of MOSFETS

My Questions:

Is what I am seeing on the Yellow Trace (Switching Node) correct? I think I should see the yellow trace go low after upper MOSFET is off.
When the lower MOSFET switches on (Pink Trace) I get a lot of disturbance, (this is actually massive at 310VDC). What is the cause of this?

Any help would be greatly appreciated.

Update 1, 2018-07-25:

Top Layer Image showing gate driver, low side gate trace (its a 0.8mm track, ~35mm long). Pink and Yellow measurement points shown. Red triangles are gate driver GND attach points.

Bottom layer image showing FET's, DC Bus, GND and decoupling caps. Please note there are additional layers of copper in this design where GND and DC_BUS are duplicated, hence the via stitching.

Note:
In this design we are using our own current sense resistors on each phase, and NOT using the current trip feature of the gate driver. This means that Pin 12 and Pin 13 (VSS and COM) are linked together.


texts: Why could my electrolytic capacitor have current but not my parallel plate capacitor?

texts:
This is for a science project. I have built my own electrolytic capacitor with aluminum foil and paper dielectric soaked in salt water solution. My parallel plate capacitor is simply aluminum foil with a paper dielectric.
While they both have voltage when measured with a multimeter, only the electrolytic capacitor has current. Why might only the electrolytic capacitor be measuring current?


texts:
I just burned my arduino and want to understand what happened.
I tried to control 12V 4A DC motor with 5V Arduino Pro Mini, here is a PCB I made for this:

In the bottom part you can see arduino pins, I used Raw input to power my arduino with 12V and PWM pin 11 to control the motor.

I used IRF3205 N-channel Mosfet and 1N5817 Diode in my circuit.
R1 resistor is 220 Ohms, R2 1KOhm
The circuit I tried to build is something like this (picture from google):

When I turned it on my arduino smoked in 3 seconds (I believe somewhere near "Raw" pin, maybe in was built-in regulator).
Are there any obvious mistakes I made?
UPD: some pictures of my assembly: link to imgur.com


texts:
simulate this circuit – Schematic created using CircuitLab

I made a RC car with an Arduino board, using an H-bridge to operate the motors. I connect them through a capacitor and a diode to the +5 V pin of the Arduino board to avoid damages on the board. I wrote a simple program. I am using an ultrasonic sensor to avoid objects. The idea is when I don't have an object in front of me, then a command to move forward must be turned on. When there is an object, the motors must go in reverse, move for a while, then go forward and turn right. I use 2 DC motors, one for reverse and forward drive, and one for right and left (steering).

The problem is this: if I connect the board to the computer through the USB cable, and at the same time I turn on the car then the code is executed normally, but if I remove the USB cable and I turn on the car (using the ~ 5.4 V from BAT1 through D1) then the car doesn't move forward, it goes back, stays, goes forward, and turns right - this is repeated twice and after that the program starts to function normally.

Here is the code :

int forward = 11;
int reverse = 10;
int left = 9;
int right = 8;

#define ECHOPIN 3
#define TRIGPIN 2

void setup() {

  Serial.begin(9600);

   pinMode(forward, OUTPUT);
   pinMode(reverse, OUTPUT);
   pinMode(left, OUTPUT);
   pinMode(right, OUTPUT);

   pinMode(ECHOPIN, INPUT);
   pinMode(TRIGPIN, OUTPUT);

  }

   void loop() {

    digitalWrite(TRIGPIN, LOW);
    delayMicroseconds(2);
    digitalWrite(TRIGPIN, HIGH);
    delayMicroseconds(10);
    digitalWrite(TRIGPIN, LOW);
      // Compute distance
    float distance = pulseIn(ECHOPIN, HIGH);
    distance= distance/58;
    Serial.println(distance);

     delay(200);

      if ( distance < 12.50) {

      analogWrite(forward,0);
      delay(1000);

      analogWrite(reverse,100);
      delay(1000);

       analogWrite(reverse,0);
       delay(1000);

       analogWrite(forward,100);
       digitalWrite(right,HIGH);
       delay(1500);
       digitalWrite(right,LOW);
       delay(500);

     }

      if ( distance > 12.50) {
      analogWrite(forward,100);
      delay(1000);
      }

    }


texts: Computer inside aluminum plated wooden box

texts:
I have a wooden box and the outside is plated with aluminum. I'm trying to install a computer (the components) inside this box, but I'm worried about the earthing. Usually the screw holes in the motherboard has big dabs of solder around them, as if to earth the case, but this wouldn't be possible in a wooden box, of course. I'm wondering if there is a problem with the aluminum plating, and if it in some way would interfere. Would I have to wire the motherboard earth to the aluminum plates?

Thanks for any help.


texts: How to calculate the zero crossing offset in a capacitive transformerless power supply

texts:
I'm working on a circuit powered by a capacitive transformerless power supply, that is a microcontroller based triac-switching project for resistive loads.

I've taken the basic design of the power supply from Microchip's Application Note AN954:

I'm using 1uF for C1 and 5.6V for D1, as they allow for a slightly increased load. I'm also in the UK so it's powered by 240v @ 50Hz.

I've attached an interrupt pin on the microcontroller to the point circled in red on the schematic via a 100K resistor, to give me the ability to detect the zero crossing. However, as this is a capacitive power supply, the zero crossing point detected is out of phase with the real zero crossing.

If I simulate the circuit, I can see that it's approximately 270° out of phase, however I'm not sure if this is just by chance based on the component values I've chosen, or if this circuit would always produce a zero cross exactly 270° out.

Is there a way to calculate mathematically (not too advanced!!) exactly what the offset is, so that I can accurately compensate for it in the firmware?


texts: STM32F401RE Nucleo failing to read DHT22 sensor

texts:
This is my first project and I am trying to read the temperature readings from a DHT22 sensor using a STM32F401RE-NUCLEO board.

My code is failing at reading the input from the DHT22 sensor when I use the CCR1 command. I have verified my circuit is working as I previously tested it using the MBED compiler.

I set up the timer to use TIM_CHANNEL_1 and TIM3 instance, which according to the STM32CubeMX GUI corresponds to STM32 pin PA6.

My DHT22 structure looks like the following:

typedef struct{
    uint8_t             bitsRX[5];
    float               temp;
    float               hum;
    uint8_t             crcErrorFlag;
    DHT22_STATE         state;
    TIM_HandleTypeDef   timHandle;
    TIM_IC_InitTypeDef  timICHandle;
    uint32_t            timChannel;
    uint16_t            gpioPin;
    GPIO_TypeDef*       gpioPort;
    int                 bitPos;
    IRQn_Type           timerIRQn;
    uint32_t            gpioAlternateFunction;
    uint16_t            lastVal;
    void                (*errorCallback)(DHT22_RESULT);
}

I set up my DHT object as the following:

dht.gpioPin = GPIO_PIN_6;
dht.gpioPort = GPIOA;
dht.timChannel = TIM_CHANNEL_1;
dht.gpioAlternateFunction = GPIO_AF2_TIM3;
dht.timHandle.Instance = TIM3;

I am running the following command to try and capture the value:

uint16_t val = HAL_TIM_ReadCapturedValue(&dht->timHandle, dht->timChannel);

Where the function is defined as the following (snipped off the later parts since I only care about channel 1):

uint32_t HAL_TIM_ReadCapturedValue(TIM_HandleTypeDef *htim, uint32_t Channel)
{
uint32_t tmpreg = 0U;

__HAL_LOCK(htim);
switch (Channel)
{
case TIM_CHANNEL_1:
{
  /* Check the parameters */
  assert_param(IS_TIM_CC1_INSTANCE(htim->Instance));
  /* Return the capture 1 value */

  tmpreg = htim->Instance->CCR1; // This line is giving me the problem

  break;
}

The tmpreg = htim->Instance->CCR1 is always returning 0.

Any solutions or pointers that may help me?


texts: When wiring an anlogue switch to grounded button, which goes to Y and Z?

texts:
I'm wiring an analogue switch (74HCT4066N) to throw a grounded switch. The datasheet says that the recommended Vsw value should be between GND and Vcc. This means that it's important which of Y or Z I should connect to ground. Which (Y or Z) should I connect to ground to ensure that my voltage stays positive? (The other end of my switch has a positive voltage relative to ground)

Thanks!


texts: How can I add two limit switches in this circuit?

texts:
Here is schematic for control of rotating direction of DC motor using two relays:

How can I add two limit switches here?
When limit is reached I want to stop motor and of course to be able to move it in opposite direction :)


texts:
I am working on an indoor positioning system where I need to:

Compute distance based on RSSI (I understand this won't be 100% accurate)
Then do trilateration to pinpoint the location of the wifi signal. This part might be solved via this solution: Trilateration using 3 latitude and longitude points, and 3 distances

I am stuck with (1).

The relationship b/w RSSI and Distance is (source PPT):

Where:

Fm = Fade Margin - ??
N = Path-Loss Exponent, ranges from 2.7 to 4.3
Po = Signal power (dBm) at zero distance - Get this value by testing
Pr = Signal power (dBm) at distance - Get this value by testing
F = signal frequency in MHz - 2412~2483.5 MHz for Ralink 5370

But I am not able to figure out how to calculate the fade margin.
Based on some findings, fade margin = sensitivity of receiver - received signal
But then again, how do I get sensitivity of the receiver?

I have an Ralink RT5370 chipset wifi dongle with this specification: Ralink 5370 spec

Any suggestions will help!

Notes from: http://www.tp-link.sg/support/calculator/ suggest that fade margin varies from 14dB to 22dB

Excellent: Link should work with high reliability, ideal for applications demanding high link quality. Fade Margin level is more than 22dB.
Good: Link should give you a good surfing experience. Fade Margin level is 14~22dB.
Normal: Link would not be stable all the time, but should work properly. Fade Margin level is 14dB or lower


texts: Measurements with multimeter giving paradoxical values

texts:
I study civil engineering (majoring in electrical engineering) and part of the program in my university is a design project. For this project my team developed a PCB and naturally it was full of bugs.
This week we were debugging it and we got a few strange values. After applying a voltage we checked a few lines to see if they had logical voltages on them (referenced to the ground). 2 were really strange. Point 1 had 0 voltage between it and the ground, point 2 had 23 V between it and the ground, measuring the voltage between 1 and 2 with the meter resulted in a difference of 0V. How is this possible?

The issue is already resolved. There was a resistor that was not soldered properly, so the point was floating (as in not connected to anything). After connecting it, the multimeter gave expected values.

To reiterate: how can a badly connected circuit cause a multimeter to contradict itself?


texts: MOSFET current source / current limiter request for review

texts:
I need a small (somewhat) voltage independent current (about 10 mA), with a voltage range of 3-30V. I came  up with the following circuit.

simulate this circuit – Schematic created using CircuitLab

I drew the resistor U/I characteristic in the Id-Vgs characteristic of the MOSFET:

The idea is the circuit will quiesce at the intersection of both characteristics.

The MOSFET is a depletion mode N channel type. Circuitlab doesn't seem to have distinctive symbols for enhancement and depletion mode.

I choose a type that can handle over 1W of power to keep well away from SOA limits.

I am aware that a similar solution exists for JFET's, but I could not find a JFET type that can handle the voltage requirement. Also I know similar devices with JFET's exist as discrete components (constant current diodes), but these are rather expensive ($5 or more. The aim is to both keep component count and price low. A Widlar source is not an option, because it needs a reference current, which is not available.

Current constancy is less of an issue, it is meant to limit the current of an unknown voltage, supplied to a low resistance (20-50 ohm), 10 - 20 mA is fine. Neither are response times very important.

I don't feel really comfortable working at the lower end of the characteristic. Does anyone see a problem with this setup, something I overlooked, thermal stability issues, and maybe points for improvement? Maybe I am too much reliant on constancy of performance of individual devices?


texts:
So I just put my first complicated circuit together and of coarse it doesn't work, good news is I found the problem.

Given a LA5752 voltage regulator I assumed the hookup was pin1->Vin, pin3->GND and pin5->5 Volts. For some reason I'm only getting .8-1.1V on pin 5... Do I need any other pins hooked up? Could someone help me out?


texts: Wiring RS485/422 to RS232 converter to a given device pins

texts:
I'm trying to establish a full-duplex and then a half duplex communication and need to wire a device output to an RS485/422 to RS232 converter.

Here is the device output pins for full and half duplex modes:

And here is the RS485/422 to RS232 converter screw pins(DATA+ DATA- are for RS485 rest TXs and RXs are for RS422 manual says):

I have 3 questions here.

1-) Is my wiring below from the converter to the device correct for full-duplex?

RS422(FULL DUPLEX)

TX+ <-----> RXD+

TX- <-----> RXD-

RX+ <-----> TXD+

RX- <-----> TXD-

2-) Here is most confusion at half-duplex wiring. Converter shows D for RS485, device shows another notation such as TXD. Here I don't get why they use TXD-/RXD- format for half-duplex. Why both shown?
Anyway is my wiring below from the converter to the device correct for half-duplex?

RS485(HALF DUPLEX)

D1+ <-----> TXD+

D1- <-----> TXD-

3-) And finally can I use the half-duplex mode with RS422 full-duplex wiring without wiring back for RS485?

manuals are here:
device and
converter


texts: What is the principal challenge to making an incandescent-like dimmable LED lightbulb?

texts:
Although exhibiting better dimming performance than CFLs, commercially available LED lightbulbs seem to exhibit poor linearity compared with incandescents (especially in the bottom 20% of the dimming range).

On the workbench, I've seen that it's possible to dim LEDs to very low effective outputs using pulse width modulation. It's also reasonably straightforward to envision using comparators and zero-crossing detectors (or something more complex, like a microcontroller with an A/D converter) to analyze the AC input coming from a triac/thyristor, and generate an appropriate pulse train.

So what is the big challenge here? Why does it seem that all commercially available dimmable LED bulbs have poor linearity (especially at the low end) compared to incandescents? What am I missing here? Is it the voltage drop across the LEDs that's "offsetting" the linearity?


texts: Impedance of microcontroller pins with no power supplied?

texts:
I have a serial flash chip connected to an ARM microcontroller (AT91SAM9G20). I'd like to be able to program the serial flash after both chips are soldered on to the PCB. For each of the serial flash lines, I can add vias that I can hit with pogo pins pretty easily.

Do I also need to disconnect the serial flash pins from the microcontroller with jumpers? What is the impedance of microcontroller pins when the micro is not powered?

(I have measured the impedance of the pins to ground on the microcontroller in parallel with the flash at around 2 MΩ with a multimeter, but I don't trust that sort of measurement when operating in the presence of diodes.)


texts: I have a HBLED driver that for some reason, uses a 5V-0V linear control voltage. The driver has the LED OFF at 5V and full on a 0V.  Id like to be able to use the drivers with a 0v-5v signal. Im pretty sure this can be done with a microprocessor, but the LED driver uses an Analog voltage, not PWM and a linear analog voltage is required.  I did look through the similar answers, but could not extrapolate to what I needed. Im disabled now and I wish my brain worked as it did earlier in life.   SUMMING it up, I need what I think should be a an OP Amp with negative gain value, taking 0-5VDC and returning linear 5V to 0V signal.


texts: Buck boost converter output voltage dropping over time

texts:
I have a TPS61222 Buck boost voltage converter, in a circuit intended to boost a 3.7V battery source to 5V. The output voltage however, is consistently less than 5V - scoping shows a 4V signal with spikes up to 6v at about 90kHz, low duty cycle.

The current draw is 56mA nominal (into the converter).  The converter powers a charge pump inverter, to generate -5V, along with a number of other devices. The feedback pin voltage should be o.5V, with about 13mV tolerance (as per data sheet) - the value it is showing is more like 0.35-0.42V.

Full schematic and PCB layout are here


texts: Solving circuit with voltage and current sources in series

texts:
simulate this circuit – Schematic created using CircuitLab

The only method I know I can solve with is superposition but that takes too long! Can you suggest some other methods that would be faster?

I need to know the currents entering the node between the 1 amp and the 3 resistors.


texts: How should unidentifiable breakers and fuses be represented in arc flash studies?

texts:
When analyzing arc flash hazards in industrial power systems, I have encountered situations in which visual inspection reveals the manufacturer and the trip rating only. The breaker or fuse model cannot be determined from documentation or visual inspection.

Since the IEEE 1584 method of analyzing arc flash hazards depends on the protective device's response time--which varies according to the device's TCC curve--lacking the full product information poses a dilemma. Should the devices be modeled as switches and yield overly conservative results? Should the model information be guessed or assumed?

How should unidentifiable protective devices be represented in arc flash studies?


texts: What does 'W/DIO' mean when used for MOSFET descriptions?

texts:
For example on Farnell: VISHAY SILICONIX SIHP18N50C-E3 MOSFET,N CH,W DIO,500V,18A,TO220AB

I've googled it in various forms but all it returns is other listings for MOSFETs with that in the title.

I also checked through a load of data sheets but couldn't see what it was referring to.

Thanks


texts: Why does a PMDC motor refuse to rotate on half wave rectified AC?

texts:
I tried to make a PMDC motor rotate through a step down transformer. Obviously I needed DC. So, I added a 1N4007 general purpose diode in two ways to have a half wave rectified input for the motor.

Case-1:-The motor rotates.

Case-2:-The motor pulsates (vibrates in to and fro motion) as if there is AC input across the motor.

Case-2 does not make sense to me as in both cases the diode rectifies the power supply.


texts: Calculating omega (ω) in a separately excited DC motor

texts:
I'm currently struggling here so perhaps you can help out. I'm given "three basic equations":

Magnetic flux of the field winding is given by:

ϕ = Kf(shunt)If

Torque is given by
T = ϕKaIa

EMF developed by the armature is given by:
E = ϕKaω

I'm now expected to extract an equation for E in terms of Va and Ia. Then rearrange the equations above to express Ia in terms of T and ω in terms of E. THEN I'm supposed to write w in terms of T and Va only. Finally I should then eliminate ϕ from the omega question to get a crazy equation. Attached is some images to help you guys understand. Any help would be appreciated as I've spent hours attempting these questions (as seen in the image) but I have no idea if they're correct or how to even answer the final question.


texts:
First of all, I'm sorry if this question turns out as a duplicate (since I absolutely have no idea about the keyword I should used).

I am trying to recreate a power supply (DC) which can have multiple output level. My model is Lex Solar Power Module (sadly its broken now, thus why I am trying to create my own)

Description about the module :
It supplied with 12V 2A adaptor, and able to deliver single 1-12V output with 0.5V increment/decrement based on the input ('+' or '-').
At first, I though it was only analog, but turns out its using STM32 as main controller.

So, my question is, what should I look for? What is the technical terms of this type of power supply, and perhaps along with an example of IC used.

EDIT------------
I forgot to mention one thing about the module characteristics, when constant load is used (i.e. 1K resistor), when the output is 1V, the current is 1mA, so does when the output is 5,6,7,8 V, the current is 5mA, 6mA, 7mA and 8mA. In short, current raise as the voltage raise.

If there any disambiguation about my question please ask, I will try to fix it. Thanks


texts: Configure Pin Swapping in Altium for a library component?

texts:
I was wondering if someone knew if there was a way to configure pin swap groups on a library component in Altium, rather than from the schematic, so I didn't have to do it every time I put down a large memory or FPGA.

Thanks!


texts: Can I use staples to hold down electric wire?

texts:
I'm building a very small game for my brother. I am moving it from the original, ready-printed motherboard to a sheet of metal. The metal doesn't have holes punched in it, and I need a different way to attach my wire to the sheet of metal. Could I possibly use staples to hold down wire to the metal? I've heard that staples are conductive, and I worry about messing something up. I will look into what kind of metal the metal sheet is, but I don't currently know. If staples would mess anything up, what else could I use?

A note: This is my first post on here, and I haven't read through the scope etc. yet. If I did something wrong, notify me and I'll take note on your comments.


texts: 36V DC charger with 12V DC charger and multiplier circuit?

texts: Could I use a 12 V DC charger and and a voltage multiplier to achieve 36 volts? Are there any issues I might come across?


texts: What would be the cheapest way to get video signal?

texts:
I have an OSD that I would fiddle around with till I'll get new camera. For OSD to work, I need PAL video signal, it may be anything, like black only.
I was thinking may be test video signal generator would help, but those things are way too expensive for such task, may be it is possible to make something simple using arduino?
I don't have any analog video source at home, like VCR, my notebook does not provide S-Video.


texts: How to prevent LEDs from flashing when turned ON

texts:
I have a custom board to control multiple high-brightness strip LED (ON/OFF and dimming through a potentiometer).
Into this board, I have some strip LED that are continuously ON (only dimmable) and some other strip LED that are dimmable AND ON/OFF controlable via panel mount selectors.
The dimming through the potentiometer affects all strip LED.
I have this issue where when my LEDs are dimmed (< 50%), when I turn ON my board, they are fully bright for like few milliseconds before returning to their luminosity controlled by the potentiometer.
The same way, when I move a selector, all my LEDs are fully bright for few milliseconds then return to their luminosity controlled by the potentiometer. And this phenomenon affects all my LEDs, not only those which are affected by the selector.
Here is an example (simplified) of how I control the state (ON/OFF) and the brightness of my LEDs. The LEDs that are only dimmable doesn't have the P-MOSFET part (not shown here).

SIG_LED1 is connected to a switch that pulls the signal to ground to turn ON the P-MOSFET Q19 when switched.
SIG_LED2 is connected to another switch that pulls the signal to ground to turn ON the P-MOSFET Q21 when switched.
V_POT is connected to the wiper of a 10K potentiometer and its value ranges from 0V to 1.8V.
The TEST signal is used to turn ON all LED independantly of the panel mount selectors state.

My board is power supplied with 28VDC (I use an AC/DC converter to generate the 28VDC).
The 28VDC is used to generate 3.3V and 1.8V through LDO. The 3.3V is used to power supply OP AMP. The 1.8V is used for the potentiometer.
The phenomenon is very brief but higly annoying. Do you have an idea on how I could prevent this? What am I doing wrong here?
Thanks!


texts: I am looking for a solution for shifting signal in 0V to 5V range to -2,5V - 2,5V range. I can design a solution for AC with filter - where I remove the DC offset by a RC filter and add amplification (compensation). But I need a DC solution. Any tips?


texts: Antenna Length for Low Frequency Radio Signals - Why so long?

texts:
I know that when you want to pick up low frequency radio signals, the longer the wavelength, the longer the antenna needs to be. Why is that?

mj


texts: Can a dead phone still be pinged? I was watching a news clip recently of someone lost in the woods with a dead phone that still managed to be pinged. How it this possible? I'd imagine it's some sort of analog response to a targeted scan by a tower or satellite? My understanding was that this is not possible.


texts: Choosing LEDs/resistors to drive directly from 3v3 HC CMOS logic

texts:
I'm building a home-brew CPU and I would like to add some blinkenlights, to show the logic state of various signals.  (It will run at 1Hz - 100kHz.)

Can I directly drive an LED from a 3v3 74HCxxx output (with a fanout of 1-3)?

If so, what can I get away with regarding LED colours and current-limiting resistors?


texts: Substituting Arduino for ESP8266 in a (Yet Another!) Garage Door Controller

texts:
I have a garage door opener with two leads that will activate the motor if the leads are shorted.  I hooked my multimeter into the leads and measured ~24VDC and triggered the motor ~50mA.

Using an Arduino Nano v3 as a power supply, I wired a simple push button to short the 3v3 output through a 100 Ohm resistor (R1) to the emitter side of the an H11AA1M optoisolator.  The Arduino's ground goes to the other input of the emitter side of the optoisolator.

On the detector side of the optoisolator, I hooked the leads from the garage door opener through another 100 Ohm resistor (R2), and when I press the button, I can successfully control the garage door opener.  I could be remembering things incorrectly, but I'm fairly certain I measured between 20-30mA across R2 when the door activates.

When I swap the Arduino for an implementation of the ESP8266 and swap the button for one of the ESP8266's GPIO, I cannot activate the garage door opener when I push gpio.HIGH across the connect GPIO.  I also measured 20-30mA across R2.

If I toggle R1 or R2, I see different current values across R2, but if I'm fairly confident that I'm within tolerance for the necessary current to trigger the garage door opener.  I ultimately want to drive my custom controller using the GPIO, and as far as I'm aware, I just need to activate the optoisolator's emitter to drive the transistor on the optoisolator's detector side into saturation.

What's going wrong?  I'd love to know how to best diagnose my problem.  I have a feeling that I'm not calculating something correctly based on the optoisolator's specs, but Googling hasn't led me to tutorial that hasn't made my head swim.  I'm love some more insight into how to best read the optoisolator's specs and how they apply to my current and future projects.

(Please don't suggest I swap out the optoisolator for a relay.  I realize that relays will probably be less finicky, but at this point, I'm more interested in the why than how.)

EDIT: I removed R2 and confirmed with the multimeter that >30mA run across garage door opener's leads, and now, the garage door opener is properly triggered!


texts: Battery power required for a 2HP Motor AC at 1800 rpm, 56Hz?

texts:
So I will be using an Inverter to convert DC(12V) to AC(220v)(50Hz).

The 2HP*(746w) = 2.3 kW / .85 power factor = 2.7 kW / 220V = 12.27A

If I want it to run for 5 hours that's 62 Ah.

Can I use a single 100 Ah battery or even a 50 Ah batter rated at 12V?


texts: How does an AM radio filter out only the desired frequency?

texts:
I understand that electromagnetic waves in the air induce an alternating current in the antenna. I also understand how, once you filter the signal to obtain the desired frequency, you can get the envelope of the signal and drive a speaker.

What I don't understand is the bit in the middle, where the radio takes the signal from the antenna and filters out just the desired frequency. Say it's a very simple radio that only cares about a single frequency. Can you explain how this works in electronics, and how this would work if you were trying to write a radio in software based on discretely sampled data?


texts: I am new to analog electronics and I am still learning about op amps. I am driving an 8ohm 15 watt speaker with just an op amp and my phone. What I do not understand is that I have a dual supply, 10V and -10V, more than enough voltage to handle audio being doubled from a cell phone. If the speaker is 15 watts, and there is sufficient supply voltages on both ends. How is there distortion when I turn up the volume or heavy bass occurs? When I run a sine wave from my function generator through the circuit I have no problems at all, I can turn up the amplitude until the output is clipped by the supply voltage. Does anyone know what is happening with my phone input/output though?


texts: Wattmeter Required for Transfomer Characterization?

texts:
I have to characterize and test a small 6VA 230VAC Transformer.
Seems like I will do

1) Winding Resistance Test - DC Test

2) Open Circuit Test

3) Short Circuit Test

I do not have a wattmeter, but I do have two multimeters.
Wherever a wattage is required, I can just measure the Amps and multiply it with the Voltage, right?

Example Procedure: http://iitkgp.vlab.co.in/?sub=39&brch=124&sim=924&cnt=2

Thanks guys!


texts: The drawings below are controlled power switches. I already tried them both and seems to work. Can someone tell me please which is better to use? Any advantage and disadvantage.


texts: How to design electronics to last 40 years or more?

texts:
I've been reading about the Voyager space probes and am very curious about how you design electronics and instrumentation for a very long life (40+ years) without any physical maintenance.

My guesses so far include:

Physical protection for components (sturdy metal box and potting compound)
environmental protection, keeping electronics warm and dry.
Redundancy (i.e. duplicates) where possible.

But what about the individual components themselves? How do you ensure a diode/transistor/capacitor actually lasts for that long? Or even harder, what about the (albeit primitive) microprocessors?

I guess under-rating components might help (i.e. using a 12 V capacitor in a 5 V circuit, or running a 8 MHz processor at 4 MHz, or using a 100 mA cable for a 1 mA current).

But there's got to be more to it than that? Or is this all part of the miracle of the probes, the fact that they're still working now?


texts: Using 566 or 555 IC timer I can create voltage controlled oscillator, but this oscillator can produce square and triangular wave only, but how can I obtain controlled sinusoidal oscillator of frequency range (1Hz to 100Hz).


texts: Using a Zener diode as voltage reference

texts:
I want to use a zener diode as a voltage reference to the the PIC18F2550, as the analog V+ reference. I am planning to use this zener diode, but I am not sure how to calculate its values. I am planning to have a 4.7V voltage reference, by just using a simple circuit as Vcc->Resistor->Zener->GND (using a reversed zener and gettitng its zener voltage).

looking at the zener's datasheet I cant see the zener curve on it, just the positive, foward voltage graph...why?
And I can only see a table with just the values for a 5mA current. I was planning to use a 10K resistor, but by some simulations I am not getting 4.7V, which is probably because I am not giving it 5mA, but how may I calculate this? How may I know how much voltage will it output with a 10K resistor?


texts: ripping layers off a board can it causes a short

texts:
I was watching a video on laptop motherboard repai.

There was a section of the motherboard that was shorted to gnd.
but the copper was completey ripped off the board by a previous repair tech. The repair tech said ripping layers off a board can cause shorts why?


texts:
I have a mobile headset setup which could be summed up like this:

phone→30cm cable→aluminum box→ 100cm cable → headset

The aluminum box is 50x50x20mm and contains one potentiometer and 2x 3.5mm female plugs to separate the mic and audio signals at will.

I want to place a ferrite bead to reduce EMI coming from the mobile phone.

It would be a lot more convenient for me to have the ferrite bead inside the aluminum box instead of outside...

Is there any reason important enough regarding sound quality or EMI removal to convince me not to place the ferrite bead inside the aluminum box (instead of outside- on the 30cm cable)?

Should the aluminum box be grounded in any case?


texts: I have a 4V 1.5A battery using it for led lights. What time it will take to charge full? Or on what factor this charging time depends? And how to calculate this


texts: Programming blank atmega328 microcontroller

texts:
I bought couple ATMEGA328P-PU as a replacement for my Arduino Uno. The problem is that I don't have any cables to program to 328 directly and I'm trying to avoid using Arduino and it's bootloader. I want to write code in C, but I don't know where to start..

I'm trying to figure out two things:

  How to build my own USB cable to write bootloader & code to the ATMEGA328P-PU?
  What software do I use to get started with the bootloader (Linux)?

Any help would be much appreciated, thanks!


texts:
Hi People... I`m working on a Project to create a Colling controled box using peltier elements..

The circuit above works as a voltage follower, dropping DC voltage on the peltier. Allthough its working, when i reach 5Vdc at the input The peltier cell(2 in parallel) only drives 5amps. Even when i increase the dc input tô 6 or 8 volts, mosfet is still delivering 5amps at Max(remember its 2 cell in parallel) . Why is that? I wish i could work at full power these cells...

Here it is a test
I was able tô reach 8 degress celsius


texts: MP1584 DC/DC step down converter cause whine in audio, how to avoid?

texts:
Short story

I use the MP1584 to step down 5VDC to 1.5VDC to power an audio equalizer taken from a Panasonic walkman (RQ-P255) from the nineties. However this is working great, sound is great, it introduces a heavy whine and don't know how to avoid this. See also the schematic below of the device I have build. What can I do to remove the whine?

Long Story

I have build/want to build a Micro Portable Stereo Amplifier With Battery, Equalizer, BlueTooth And Line-In/Line-Out (in a small candy case) so you can connect any speaker you want (nice to use outside in the garden/party) and you can use it as a BlueTooth Walkman. I have added an equalizer taken from an old walkman of the nineties, the Panasonic RQ-P255. This because most bluetooth transmitters don't support an equalizer and, some bluetooth speakers supports only EQ with presets (hate it).

Figure out how the equalizer works and it was very straight forward but requires only 1.5VDC input (the whole device, all other parts, operates on 5VDC). Because of positive reviews of the MP1584, I use this little device to step down 5VDC to 1.5VDC. This is working great except the whine it produces, very annoying. The device has an equalizer on/off switch and when I turn it off, the whine is gone.

What can I do to remove the whine?

The whine i'm talking about

This is recorded with a microphone of a Tascam DR07 nearby speaker. The picture below is the waveform 1600% amplified.

To hear the whine 800% amplified:
https://drive.google.com/file/d/0B2l-eQoHefcVaVd3ZVNZMXJYcXM/view?usp=sharing
To hear the whine - whine original:
https://drive.google.com/file/d/0B2l-eQoHefcVb2NMS3dINDU3SFU/view?usp=sharing

Notice: I don't have an oscilloscope.

Schematic of the device

Notice: I'm not a hardware designer or schematic professional, so maybe the schematic is not as it should but I think it is very clear what goal I want to achieve. The headphones connection is not in the schematic.
EDIT: 200K must be 200 Ohms

Setup of the device

Here some drawings how the device must be set up

What I got so far

BlueTooth module and switch and headphone jack not implemented yet.

What it should look like when finished ;-)

Used parts/devices in current setup:

Battery charger / DC converter taken from this product: http://www.mrhandsfree.com/en/shop/7318-portable-power-chargers/product/7320-portable-power-charger-2600-mah
Step down converter: http://artofcircuits.com/product/mp1584-buck-step-down-3a-adjustable-regulator-module
Equalizer taken from this product from the past: http://img19.staticclassifieds.com/images_slandokz/91858292_1_644x461_kassetnyy-audiopleyer-panasonic-rq-p255-pavlodar.jpg
Amplifier: http://www.diodes.com/_files/datasheets/PAM8403.pdf


texts: relative price of a transistor and a capacitor

texts: DRAMs achieve high memory density by storing each bit of information with one transistor and one capacitor. That got me wondering, how expensive is a capacitor relative to a transistor?


texts: Can a 12v dry relay be able to handle 24v load with its own PSU?

texts:
i have this door access controller

https://zktecousa.com/product/c3-200-access-control-panel/#section-3

and on the DOOR CONTROLLER terminals where the relay works on, I wanted to attach a 24v light on it instead of a magnetic lock. I will be supplying separate 24v power to the light (power wont come from the access control board's 12v psu)

So technically i'll just be using the NO and COM terminals to trigger my lights.

Is this alright? or will i blow out the relay or board?

pretty much looks like this


texts: What's the phase relation between the sine wave and the sync output from a function generator?

texts:
I'm using a function generator to generate a sine wave, and am trying to use the sync (TTL) output to flash an LED at the beginning of each wave pulse. However, when I compare the sin wave and the sync pulse on a function generator, I notice that while both have the same frequency, there's a phase difference between the two.
In particular, for a 2 V peak-to-peak signal, I would expect the square pulse from the sync to go from low to high when the sine wave is at minimum (0 volts, or ) or maximum amplitude (+- 1 volt) but instead the sync wave goes from low-to-high when the sine wave hits around 0.4 V (or in general, around 40% of the amplitude).
This number seems arbitrary to me, but I've checked two function generators and both seem to trigger around this point. It's also worth noting that when I generate a square wave, it overlaps with the trigger pulse exactly.
Why does the TTL pulse trigger at this point, rather than at the minimum or maximum? Additionally, do most function generators have a way to change the phase of the sync pulse?


texts:
The circuit below is an oscillator. When I simulate it with ltspice, it does indeed generate a waveform (although it doesn't seem to be a very pure sine wave).

What I fail to understand is why it oscillates.

All the basic literature I have read so far on oscillators (Colpitts, Clapp, Hartley, etc ...) seem to indicate that oscillator circuits need to have both capacitors and inductors in the "tank" part of the circuit.

Also, if you look at the theory, it seems like you need to have both caps and coils to make a tank that has a proper resonant frequency (the 1/Sqrt[LC] formula), but this circuit's "tank" is only made from resistors and capacitors.

When I compute impedances for the tank of that circuit using H-topology formulas, it seem to be tuned to look like one big capacitor (except of course for the short to ground in the middle of it),

If anyone could explain why this circuit oscillates, and how, I would really appreciate it (both intuitive/practical and theoretical explanations are very welcome).

simulate this circuit – Schematic created using CircuitLab


texts: Li-ion battery and arduinos custom circuitry

texts:
So i have to design a board around a dialog SOC (DA14681).
The dialog part supports li-ion batteries, it has a charger and fuel gauge and USB detection (to power device in case both usb and dc voltage/li-ion  connected at the same time).
As part of the requirements, my board should be compatible with an arduino shield (so i need headers that are identical to arduino uno).

This then means i need to add the Vin pin present on an arduino.
I will also need to generate the 3v3 and 5V rails. The dialog part generates a 3v3 rail but this is limited to 100mA so will have to generate the rails externally to the chip.

Could i boost the li-ion battery to 9V and treat it as the DC Jack voltage (connected to Vin through a diode?). Leave the rest of the circuitry as would be present on an arduino?
Would this circuit work?
My concern is that if li-ion is turned on, it will disconnect the USB voltage to the rails (the pfet) but the VBUS voltage will still be present. So the dialog part will be turned on by VBUS (USB) whilst the rails will be turned on by the li-ion.

Would i need protection circuitry for the li-ion (considering there is protection in the dialog part)?

Is there an easier way of doing this?

Sorry for the long question, i will be so grateful for the help or push in the right direction.

Having three voltage sources (li-ion, usb and Vin) complicates things here.


texts:
I have connected three N channel MOSFETS in parallel (Nexperia PSMN1R2-25YLC) but when power is applied they conduct regardless of the gate voltage. The gates are just connected directly together and there is no capacitor to ground either. I have run out of components and need to understand this a bit better before ordering more. What might be causing them to conduct regardless of the gate voltage? The circuit being switched is at 24v and it doesn't need to switch quickly, this is just for powering up/down an external device - switching is likely to happen very infrequently (hours, days). I need it to support 24v at 5A = 120W with passive cooling, hence the parallel arrangement.

This is the current schematic:

I've changed the schematic so the gates are separated with resistors and each has a stabilising capacitor. My question is whether this seems like a sane way to do it. The MOSFETS are logic level, the datasheet specifies a gate threshold voltage of about 1.2v, I'm giving it 3.3v. The circuit being switched is at 24v.


texts: Mechanism to temporarily connect different pitch stake pins (2.54mm and 1.27mm)?

texts:
I'm working with boards that have a mix of pin pitch and occasionally I need to connect a 2.54mm pin to a 1.27mm pin.  The most recent example was to get access to UART output that was being provided via 1.27mm but my USB-to-UART adapter has 2.54mm.  Soldering would work but I'd prefer something more temporary that I can quickly connect/disconnect.

(This is my first post to this community so feel free to edit the post/tags and give me a nudge in a better direction if I'm off track.)


texts: Problems while using accelerometer as a motion switch

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I am using an accelerometer ADXL206 and a microcontroller PIC16F917 to determine the relative linear motion of a device that functions according to this motion.

I can read data from the accelerometer:

It gives an output of 2.5 @ no Motion
It gives an output of 2.5 + 0.312 Volts per 1g Right
It gives an output of 2.5 + 0.312 Volts per 1g Left

I have a device with 2 LEDs to determine direction of motion.  It should work like this:

start of the program: LEDs off
right motion: red LED on and stays so. Blue LED off. even when the device stops motion
left motion: blue LED ON and stays on. Red LED off. even when the device stops motion

The real results I get is when the device moves, it blinks the LED only during motion then they are OFF during no motion.

I cannot get the direction from the Accelerometer and stay in a stable state.

Is the problem in reading the values from the accelerometer or in the algorithm?


texts: Can I connect 24V direct to optocoupler?

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I would like to check sensor signal on MCU. Sensor signal is 24V. Therefore, i want to use optocoupler as an interface between MCU and sensor. NC1 is going to MCU pin. My question is if i can connect 24V direct like this. There are total 4 inputs exactly same.(24V to 5V)
I have simulated this on tinkercad and it shows 11mA current flows over diode and it works without any problem. However, i don't think it is reliable to connect it like this so i want to ask how should i connect this for proper and reliable operation?


texts:
I developed a circuit to read a temperature value [30,60] with a PT100 using a PIC32.The circuit has a 1mA current source connected to the PT100.The PT100 is then connected to a differential op amp to accommodate de voltage to the 3.3V Range of the ADC.The other input is the value of V in the PT100 for my minimum temperature (30Degrees)(Since V=RI I calculated the PT100 Resistance at 30º with the Callendar-van Dusen Eq and multiplied it by 1mA).So I Have Vo=(Gain*(PT-PTmin)).
The question is now that my output is [0,3.3]V can I calculate the temperature in the PIC by just linearizing the ADC value (something like 1023-60 and 0-30) or do I still need to calculate the Resistance in the PT100 and from that get the temperature?Im trying to get at least a 1º accuracy in the readings if that makes a difference.
Thanks


texts:
I'm building a circuit that stays powered for some time after an additional power source is switched off.

+5V is always enabled but I only want LOAD to be powered when VCC (12V) is enabled and for some time (around 5 mins) after it is disabled. To achieve this I'm using a capacitor C1 which keeps NMOS open.
There are some questions:

Is this circuit looks good enough or are there some issues here?
R1 + R2 defines how fast the C1 discharges (and given the desired time, defines C1 capacitance). How big resistance can I choose for R1? I don't really care about how fast it works but my guess is that with too big value it may fail.

Appreciate any help.


texts: How to find the right battery for my project

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I am working on a project that requires 12v 12A of power. But I can't find the right battery. I have been looking at a few online tutorials about choosing batteries but they have not been very helpful.
The battery I am requiring is 12v 12A DC. and it needs to be rechargeable. It also needs to be less than 2.5 inches tall, since there is not much clearance space in my robot. Any help I can get would be greatly appreciated.


texts: Design a 3-Bit Up Synchronous Counter Using JK Flip Flop (odd vs even numbers)

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I have to design 3-Bit Up Synchronous Counter Using JK Flip Flop counters.

The first one should count even numbers: 0-2-4-6-0

The second one should count odd numbers: 1-3-5-7-1

Execution Table For JK Flip Flop:

Q(n) Q(n+1) J K
---------------
0    0      0 X
0    1      1 X
1    0      X 1
1    1      X 0

First Question: Design a negative-edge-triggered synchronous counter with the form of operation: 0-2-4-6-0

My Design:

Second Question: Design a negative-edge-triggered synchronous counter with the form of operation: 1-3-5-7-1

My Design:

Main Question: I made two designs like the pictures above. But as you can see, the JK output is the same. That's weird! In both designs (even and odd) the J(C) output = Q(B) and K(C) output = Q(B). And in this case, will this odd-number circuit count by two-by-two?

Why the results are the same? Where exactly am I making a mistake?

Hint:

In the first even-counter circuit, the value of the K(A) can take 1 or 0.

In the second odd-counter circuit, the value of the J(A) can take 1 or 0.


texts: signal generator and clock synchronization with FPGA

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I am just a beginner in electronics, so please bear with me.

I am using a signal generator to get two channel output which are then fed to a FPGA based Mojo. The mojo is then connected to a computer which has a GUI, which shows me counts on two channels. The mojo has a 50 MHz clock cycle.
The way it works is:

"The external signal from the signal generator is connected via BNC to 4 I/O pins on the FPGA. The signals that are captured are then digitized by Pulse Replicator Modules, which I think is also supposed to help in synchronization of external signal with the FPGA clock. The output signal is then sent to a comparator module which is like a 4-way AND gate;when the input is connected to the top-level Pin Register, an OR mask is used to hold a “1” on the channels the user wishes to ignore. "

Now, the problem is if I set my channel A to 10 MHz, my GUI shows that at least 100 counts are lost. Same for channel B. But, when it is a low frequency signal like let's say 5KHz, it shows 4999 and fluctuates around that value.
What could possibly be the problem that I am losing counts? Is it because the clock cycles of the FPGA in the mojo and the signal generator asynchronous?

Edit: I have added how the signal is processed by the FPGA.


texts:
I'm working on a design using a Spartan6 FPGA, I recently made a change that added a PLL to the design to allow for faster clock speeds, however this caused a problem during the "map" command:

    The following 1 components are required to be placed in a specific relative placement form.
    The required relative coordinates in the RPM grid (that can be seen in the FPGA Editor)
    are shown in brackets next to the component names. Due to placement constraints it is impossible
    to place the components in the required form.

    PLL XLXI_52/PLL_ADV (0, 0)               locked to site PLL_ADV_X0Y0

What would cause PLL_ADV to be locked to this specific location (which I assume is being occupied by a different PLL), when there are three other possible locations for it. I have made no changes to the default configuration of the PLL element