I have an input voltage of 12V from my power supply and i need 6V to feed into the ESP8622. I was giving it all the 12V but the wifi module becomes increasingly hot with time and so i decided to have a limited voltage feed into it.  Am not getting it to fire up however. It still stays blank.  I tested providing the 6V from the power supply and got positive results.  My resistors are both 100 ohms and when i probe the interconnection rail of the resistors on the breadboard, i can see that 6V is there. But when i feed the link into the ESP8266, it doesn't light up. It only does when the 6V are coming from the power supply.  Here is a pic of my circuit
122783
I'm making a voltmeter for the college senior project, and the problem is that voltage divider should equally split 17V into two 9V(nominal value of the batteries. As of now, an actual voltage is 8.5V and eventually will go down as the batteries die, so don't freak out too much by my round errors.) sources, but as soon as I connect Arduino board to the circuit, voltage( across the resistor it's connected to) drops to 2-3 Volts. Which is apparently enough to power the micro controller, but not enough to light the display up. (it's also enough to use the other resistor as a space heater with 14 Volts across it).    Please feel free to look at the schematic of the device provided above. (either models, or specs of the components are written on the schematic)  Now I'll explain the design thoroughly: The idea is to use piezoelectric element (thin laminated  flexible piezoelectric beam), place it into a fluid flow (air) and rectify the outgoing AC signal with a full wave bridge. The next step is to amplify the signal, because it has very low magnitude and arduino analog pin can't register it without amplification.   Amplifier needs at least +-7V supply, so it's provided to it from the two 9V batteries, that are connected to a voltage divider. Therefore, the virtual ground of the circuit is in between the two batteries.   At the same time I want the arduino board (Actually it's not arduino, it's arduino compatible board dubbed Pro Micro 5V) to be powered from the same two batteries.  The whole thing works fine from USB, but from the batteries it works as it pleases!  Here are the design constraints of the device:   The entire device shall hang somewhere in a remote location, so it has to be powered from an autonomous power supply (two 9V batteries in my solution). The device should be as light, and as small, as possible. (solutions like adding another battery are not desirable). Arduino board have to have 5V on it to light the display.   Additionally I'd like to learn why micro controller has variable input resistance and what it depends on.  I've tried to figure out what is the resistance across the arduino's ground and RAW by assuming that the resistor of the voltage divider and the arduino are connected in parralel. In three different setups I've got the arduino's resistance to be equal to 221.93, 527.73 and 743.4 Ohm.  As I understand, the board has some kind of reducer at the voltage input that prevents the board from burning at supplied voltages above 5V and below 12V, but why it drops the supplied voltage from 8V to 2-3V?
101840
Have set up a voltage divider inputting 1 volt into a LM741 op amp to act as a voltage follower. For some reason I get 2 volts at the output. Have checked everything I can think of and can’t figure out why.
55034
I'm designing a project that controls 110VAC (plug in, socket out), and also has a microprocessor inside.  I'd really like this project to not need a wall wart to get it's 5V, so I want to include a small DC power supply inside.    Apple's USB power adapter looks like a great small design that I can fit inside my case.  I'm guessing this is a switching power supply but I can't find any teardowns or schematics anywhere.  Does anyone know how this thing works?  I know I could make my own 110V->5VDC supply from a bridge rectifier and some caps, but I'd like to also be super safe.  What's in the Apple brick?
32000
I am replacing a power receptacle at my apartment. It has the standard four wires, with one of the two reds going to a nearby toggle switch.  I am concerned because when the toggle switch is off, I measure 16V between one of the red wires and a white. (The other red wire always measures 0 V, so I assume it doesn't go to anything.)  I don't want to wire up the red if it's going to sit at 16 V when it's supposed to be off. Any ideas why this is happening or what I can do? Or is 16 sufficiently close to 0?
32088
Once again I need your help in my project. I have a 4,5v powered circuit. I put a voltage divider with 2 resistors in series to reduce my initial voltage of 4.5 V to 3.4 V (to feed an XBee module).  The issue is that if I do not connect the xbee, the voltage divider reduces the input voltage to the desired voltage(3.4 V), but when I connect the XBee module, the resulting voltage divider voltage drops to a value very low (0.85 V), making the XBee malfunction. Surely it is a basic mistake, I am asking something that is very clear, but I'm newbies.   Basic Circuit:  Vin(4.5 V)-----R2(10 kΩ)---------R1(33 kΩ)--------GROUND                        |                        |                  Vout desired (3.4 V)                        |                        |                       XBee
109513
Based on my , since there supposed to be zero voltage (V=IR) drop across a 0&nbsp;Ω resistor, how do we select the  of such a component?  For example, let's say I were to connect a zero-ohm resistor in between 5&nbsp;V power source and a load (circuit variant) which take current ranges from 20-200&nbsp;mA. What is the power rating of the 0&nbsp;Ω resistor I should select?
107643
I asked a similar question  about this, but I still don't  quite understand.  Say I grab onto two wires from a standard 120V 20A wall socket. I would fry. I would have 20A at 120 forced on my body.  But, when speaking in terms of circuits, as in my linked question, if I have a power supply outputting 100mA maximum at 5v, for some reason my device only gets exactly what it needs? Why is this?  Most things flow from an area of high concentration to low concentration, taking the path of least resistence. If you connect two wires to a power supply, why don't the maximum number of electrons want to go through your circuit?  If current behaves this way...why do you have to regulate voltage?
113023
I've been working on a data logging device that will eventually go into my personal vehicle.  I've scoured the interwebs and built what, in theory, should be a fairly stout power supply capable to handle fast transients and undervoltage and the fabled load dump.  My problem is, though... I want to actually test the power supply.  In previous questions that I've asked related to the design of the power supply portion, I've been told that the "right way" to simulate a load dump is with a proper, preofessional testing device.  I'm curious, though... what's stopping me from rigging up something that is "close enough"?  My idea is simply this: get a low-voltage DC power source, such as an old PC power supply.  Get a DC-DC converter to step that 12V up to something in the 80V range.  Assemble a bank of capacitors to get me in the neighborhood of a theoretical 12V load dump..  which from what I can tell is in the hundreds of joules range.  Once charged, simply connect it to the battery input of the device - which wouldn't be connected to an actual power source lest I want to potentially screw that power source up - and see if explodes, and if not, see if it works normally afterwards.  Does this sound like the dumbest idea you've ever heard?  Is it a somewhat decent idea that simply needs a lot of planning and number checking to in order to work roughly as intended?
102039
Question:  1.3  1.4  How would I calculate the input impedance in the diagrams above?  This is what I have tried in my exam, however I got this wrong, and my teacher had told me not to take into account the 2 10k resistors.
117600
I'm using a repurposed ATX power supply for my hobby projects since it's got 3.3/±5/±12 outputs, all of which are really convenient. But one thing I didn't really think about until I slipped my probes across the pins of an opamp, since I've always dealt with commercial/proper lab power supplies in my school labs, was that an ATX power supply will gladly deliver lots of current if that 12V line (or any other) is shorted to ground. The poor LM318 didn't stand a chance. My meter and supply survived, but in the interest of not killing anything in the future, myself included, I was wondering what the best option was for short/overcurrent protection?  I was thinking of sticking some high wattage resistors at the output of the supply before connecting them to the rails of my project breadboard (I use a separate breadboard with terminal blocks for power, which the ATX supply connects to). The problem is if I'm drawing a lot of current (LEDs etc) this will sag the voltage on the line. And, for example, if I use a 1W 200ohm resistor on the 12V line, it limits my current to only 60mA - if I want more, I need some really beefy wattage resistors. I can probably work around the voltage sagging by using a voltage regulator (eg at 10V), but this all doesn't seem like the best way to go about doing things.   I'd appreciate some input from someone more experienced than I am.
86962
I have 16 meters of  LED Strips . The strips have 60 LED/s per meter and run on 5 volts. They come in 4 meter reels.  I know how i want to control them but i am unsure about how to hook them up safely and so that they draw enough power. I know that i cannot just hook up a power supply to one end and expect the entire 16 meters to be powered. I read online that for the non-addressable ones that run on 12volts you need to hook up the power supply in multiple places, is this the same case with the 5Volts?   Also how do i know what kind of power supply i need and how do i hook it up so that all the LEDs are fully powered? Will i need more than one power supply or should one be enough?
41149
I've lost my original power adapter, and I can't find the proper one in any of the stores currently available.  I've HP Compaq 6730b, and as per  it outputs 18.5V 3.5A. However, I've found an older power adapter I have which outputs 19.5V 4.62 A.  So, my question is: how much of a difference between those two it really is, and more importantly, how much of a risk would it be if I tried the power adapter I already have.  P.S. I know pretty much nothing about electricity/electronics.
116595
I am trying to put a server together to install Ubuntu. I bought an Intel S1200v3RPS motherboard and plugged an Intel Xeon E3 processor into it. I purchased a 1U chassis from Supermicro with a power supply.  The power supply does not have a 5-pin cable to the motherboard's Auxiliary Power Supply socket. A bit of research did not give any definite answer on the need for the 5-pin connection. The motherboard does not power on and the CPU fan is off. I tested the power supply on a desktop Intel motherboard and it works fine.   I would like to buy a new power supply but could not find one which expressly stated that it comes with the 5-pin aux power supply cable. Any recommendations on a power supply unit for this motherboard would be helpful. Any comments on the problem would be greatly appreciated.
66381
I just received the following breadboard in a electronics starter pack I purchased.    I am a little confused in how I would go about prototyping on this board, all the tutorials I have read state that the breadboard should have a positive and negative  input on it. But it appears this one doesn't.  Could anyone help clear my confusion?
121881
of the 24LC256 EEPROM states that:     The SDA bus requires a pull-up resistor to VCC (typical 10 kΩ for 100 kHz, 2 kΩ for 400 kHz and 1 MHz).   I thought that any resistor with a kΩ value would do the job (and it seems that my EEPROM works fine at different frequencies with a 10 kΩ resistor).  My questions are:   is there a correct value for pull-up resistors ? is there a law/rule to determine this value ? how do different resistance values affect the I²C data bus ?
119426
I'm building a device that has a mains power component, which I need to prototype before building to make sure everything works. I know I need to make sure wiring—and insulation!—is thick enough to cope with the higher current, and that I need to make sure there's enough space between exposed components so there's no arcing. I'll also be stashing whatever I prototype in a nice, insulated box before applying power, and I'll be include a small-value (250mA) fuse just in case. I'll be considering everything double-insulated rather than earthed (plastic enclosure, and there's nothing I'll need to touch while it's operating).  My plan is to solder (through-hole) components directly to each other, then insulate everything (with heatshrink tubing or electrical tape) as much as possible, then use screw-type cable joiners to connect the power cable.  I know I can't use traditional prototyping tools such as breadboards and stripboard for mains voltages, but what can I use to make prototyping at mains voltages easier?  (To be clear, 'mains voltage' in my area means 230V AC +10/-6% at 50Hz; GPOs are generally rated at 10A.)
113860
Can I use a 12 V power supply as the source of electricity for this circuit? And where do I connect the positive/negative of my power supply?  I'm a bit new to this so please understand, thank you.