We are producing LED programmable controler, the power supply is 5VDC. Do we need any certification (UL or similar) for the US market?
121851
I am interested in making a widget to sell, but it will probably have a small market and small volume.  At what level of complexity should I consider UL listing (or otherwise certifying) my widget?  I presume that device complexity is the range I should measure the device against to obtain a safety certification.  I understand it costs several thousand dollars for such things.  For a widget with only a few dollars in parts (off the shelf/eBay prices), and a small market or run, it doesn't make much business sense for sure.  However, in general, what level of complexity should I consider to procure some kind of safety certification?  The particular widget I am thinking of right now is a PCB with connectors and possibly a small 24V to 12V transformer (&lt;100ma).  Basically, something that was wirenutted/butt-spliced together will now be more professional looking on a board in a box.  Don't let the example distract you from the overall question though.
105516
I'm looking at a diagram and wondering if I could use just one resistor to limit the current of the LEDs instead of multiple resistors so that the cathodes are all connected to the same resistor.    JL
15576
Answers to other questions here (e.g. ) show capacitors used to drop AC voltages to levels suitable for a LED. I've seen much simpler circuits such as the one below         &ndash; Schematic created using   Assuming it's in a suitable enclosure, are there significant drawbacks or dangers to this circuit compared to others?
15508
I haven't been able to come across definitive information regarding the procedure to find out whether an electronics product (PCB) requires CE marking or not.  Since it is difficult to ask hypothetical questions, let me ask by using specific examples. Let's take  as a first example. Would this product require CE marking to be sold in Europe? (Maybe a similar question: would this product require any FCC approval/marking to be sold in the USA?)  Let's look at a . This is an A/D board. Would this product require any regulatory approvals/markings?  It would be a great help if someone with CE/FCC experience could give answers, explaining the reasoning behind those answers.
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?
32554
When I measure a 9V DC wall adapter power supply with a multimeter it shows 11.8V. When connected to my board this voltage lowers to 10V. Is this normal? Should I be afraid of toasting my  supplied board when using this adapter?  Edit: This regulator accepts up to 12V inputs. So that will be no problem. A second "9V" adapter yields 15V to the multimeter. Will this one burn my circuit?
48810
I have a light switch that switches 240v (UK) mains. Instead of using that to directly control a light, I want to use it as an input to a controller board so I can also automate the lighting. (It's low voltage LED lighting driven via a transformer although that doesn't really affect my question).  My question is what is the best and safe way to use switched 240v mains power as an input to a low voltage microcontroller circuit? It would be best to use the existing switch to switch a low voltage control signal but I can't change the wiring at at this time so the only input I have to my control is a switched 240v mains power line.  I have other power available where the controller is so I'm not intending to power this via the original light power, I just want to see if I can use it as a control line without extensive rewiring work for now.
34754
I've made a circuit to run 5V DC motor via ATmega328p  micro controller GPIO as shown below.whenever there is a connection to 5V DC motor, and if it tries to actuate the motor, micro controller will get reset.If there is no motor connection relay will get actuated properly. power supply circuit is also provided. please let me know how to resolve this.
36893
I have an application in which an RFID reader demands 200 mA of current when it attempts to read an RFID tag. For some reason the current switcher power supply either can't supply enough current or can't supply a clean enough voltage and I end up with a poor performance on the reader.   I want to use a standard LM7805CT regulator in place of the switcher, but how large of a capacitor should I use? The datasheet suggests 0.1 uF, but I'm not sure that is large enough since the reader gets turned on and off a lot.  I am regulating down from a 24 V battery (it is pushing the limit of that particular regulator, but I will add active heatskinking to it).
82874
I am new to PWM control. Is it advisable to operate a motor at higher than rated voltage with the "PWM average voltage" more than the nominal voltage specified in the datasheets? After some researching, the majority of the information that I kept seeing is that it should be OK (with a recommendation to operate at high PWM frequency). Secondly, if the "average PWM voltage" is kept less than the nominal voltage (with the supply voltage much higher) is it correct to refer to it as over-voltage operation? Or is it only when the average voltage is higher than nominal voltage?
106216
I've noticed mains voltage tends to be 120V +/- 10% for 108-132VAC.  How would you go about building a regulated AC-to-AC power supply which works off of mains and outputs 120VAC with a much lower (less than 1%) variation?  The output must be a sine wave at 120Vrms.  Edit: For those asking, the output would be fairly low, 1.5A - 2A, 2.25A max.  Circuit to be powered:  Expected input: 0V-5.5KVrms sine wave at 60Hz  Simulated output: +/- 0-100KV DC.  The objective here would be to connect components in the order:  mains --> power conditioner --> variac --> 1:46 center-tapped transformer insulated for high voltage --> Cockcroft Walton Multiplier outlined above.  To achieve a variable 0-100KV DC (effectively 0-200KV DC with both channels factored in) power supply.  I am not certain the power conditioning stage is the way to go but assumed it would be since it is much easier to stabilize low voltage (120Vrms) than it is to stabilize high voltage (5.52KVrms.)  Relatively minor ripple of 5% will grow into +/- 10% by the end of the CW stage at full power, yielding around 20KV off of the expected value - not an insignificant amount.
111896
I have a bluetooth remote control device that uses 2 AA batteries. Due to positive feedback and responses, I'm thinking to sell it to mass market. Thus I need FCC certification.  After reading many articles including all the FCC related questions in this site, I'm still confused.   There are many of wireless products in US market that don't have FCC / CE certification. Many of imported products sold in Amazon don't have the certification.  With such a high cost ($10,000-$20,000), I don't think many small company can afford to get this certification.  What is consequences if you sell the product without FCC certification? Before I apply for FCC, what are the things that I need to watch out, especially my PCB. Do I have to care about the box(enclosure)?  I mean, my product uses 2 batteries, I don't think it will cause a fire hazard or short circuit. Or if I have to watch out for fire hazard, what component should I add? The bluetooth module is already certified by FCC and CE. So I will be exempted for the Bluetooth test. But I guess they still need test the product as a whole. What if you failed for the first test, do you have to redo all over again and pay another $10,000?   Thank you.  Dan  Additional info: Q:  I’m a retailer, why should I care about FCC regulations? A:  It is illegal to import, sell, or operate covered equipment that has not undergone the required equipment authorization procedure. Illegal merchandise can be subject to forfeiture, and you may be subject to fine. Imported merchandise that does not have FCC may be held at customs. Also lack of FCC compliance means the merchandise has never been evaluated for electronic compatibility. This is a sign of bad quality. What other safety or chemical regulatory requirements might not have been evaluated?  FCC enforcement action is often levied against retailers and end users, especially where the manufacturer is located outside US jurisdiction.
82260
I want to switch ON and OFF an incandescent bulb using MCU. Please suggest an electric switch (like relay or something) for 220V 50Hz AC line which can be used here. I would prefer something very cheap to keep the total project cost minimum.  EDIT: Don't limit this to incandescent bulb. The solution should be applicable to every daily life electrical appliances.
16505
My laptop's cable broke and sadly it seems like I need to buy a new power supply.  What I wonder is, I've found that universal power supplies are much cheaper than the official HP ones. Are they really worth it?  Another question: the original supply has these specs: 65W, 18.5V, 3.5A. However the universal supplies are more powerful (90W, 100W) and come in integer voltages (17V, 18V, 19V, etc). Are they compatible? Should I set them to 18V or 19V?
48777
Does a filament lamp still have resistance when no current flows?
22406
I am supposed to come up with some control schemes for the converter before understanding the standard PWM control scheme.   Isn't it just enough if the output of the converter is compared with a fixed reference voltage to drive the output to required voltage level? Although I'm not sure there is a lot more to it, this seems to work pretty well.   I've tried simulating this circuit with L,C and R values from an example.  Schematic:    The required output voltage is 6V. S2 is a voltage controlled switch, controlled by the output of comparator.    V2(green) is the output of comparator and V1(red) is the output of buck converter.
121994
I'm wondering why, in a standard house, instead of using many low power AC-DC rectifier, there isn't a big (like 12V 20~50A) AC-DC rectifier which supplies some wall socket with a DC voltage? In the long run this should be less expensive, given the fact that AC to DC in one big apparatus is done better than in many low-quality transformers, right?  Also, modern chip DC voltage regulators have efficiency of >90%, so smaller (or even larger) voltages are still efficient and possible.  So we could use a 12V socket to charge a phone, desktop computer, laptop, radio etc... and still have an AC socket to move washing machine engine and other things that work better with an AC supply.  Why isn't this done?  edit: real question is: is it convenient, given a standard family (2 laptop, 1 desktop, 4 smarthpone, 1 big tv and some minor electonic) to do so?