How to check if an SSM2220 IC is authentic and not fake? A 3A output adjustable might cost about $2 on eBay. Our task is to stepdown 12v into 3v. If 47 Ohms is too high and 10 Ohm's is too low, you might just have to experiment. The optocoupler should be close to the Arduino ESP32. Did you set the pin in setup to OUTPUT, with pinMode? A 3A output adjustable might cost about $2 on eBay. What happens if there's no resistor before the ISET pin of a MAX7219 LED driver chip? Electrical Engineering Stack Exchange is a question and answer site for electronics and electrical engineering professionals, students, and enthusiasts. You should stare at the graphs in the datasheet for some time. I get the same thing In this article, we are going to make a simple circuit to stepdown 12v into 3. The faintest of red glow appeared in the LED but the power draw according was so low it was not measurable. I put the numbers in and I got that I needed a 65 ohm resistor. 6. From the junction of both resistor connect one 3v LED. When you understand let me know and I'll reverse the -1. This DC input goes through smoothing capacitor C1 (1000uF) to remove any residual noise. Powered by Discourse, best viewed with JavaScript enabled. The RED wire goes to the 12V supply, Black 12V ground, Pin 2 on the Opto to 12V ground, Green to Pin 1 on the opto. Below is a JavaScript apllication for determining resistor values, 1K ohm resistor with a 5% tolerance, I must be doing something wrong somewhere. DC to DC converters commonly serves in devices such as portable chargers & DVD Players etc. Alright, so if I had 5v go to 2.2v after passing through an LED, I the resistance I should use on that same LED with 3.3v would be 1.1/2.8*220 94? lm358 What is wrong with the calculation from LED Resistor Calculator? Hi guys! Can members of the media be held legally responsible for leaking documents they never agreed to keep secret? Well, I am sorry, but that is complete nonsense! I am leaving a link I highly recommend trying at least once. audio amplifier Any help is greatly appreciated. im new to the electronics side, but i have a 12v input from a laser trigger via a relay and need to output 3.3v. That is not a button, that is a well, I don't know, it is something. "U" ? If the internal pullup resistor is 60k, then the current is only 55 A. I bought a new LED, yay. Why does the second bowl of popcorn pop better in the microwave? For 50 years I always thought the schematic designation for a resistor was "R". bc547 Thus the added Series R changes with power of the LED. The voltage across the resistor is equal to the supply voltage minus the LED voltage. That works out to 13mA when powered with 5V. I am currently using a limit switch powered by a 12V battery to determine when a motor has pushed an arm to its limit. This band gives us the tolerance of the 4.7k Ohm Change your pin 3 and 4. Contact Phone: 01783 007 004 Email: 5mm Color: RED Head Shape: Round Lens Appearance: Transparent 5V. I guess I fried it. This may sound complicated but with practice its trivial. Using just two series resistors and an input voltage, we can create an output voltage that is a fraction of the input. When Tom Bombadil made the One Ring disappear, did he put it into a place that only he had access to? Which Arduino board do you use ? 12V to 3.3V Signal to Arduino. I have some basic leaf switches I can use instead.. You are correct, it should work. Or just that its bigger so small diffs don't matter as much? Who ever talked about 230 Volts?? I have verified that I get 3.3V from the GPIO pin I use, and the Arduino Pro Mini can deliver up to 40mA from those pins. The color code for the wires is: Red = +5V, Black = Ground (0V), White = -5V, Yellow = +12V, Blue = -12V, Orange = +3.3V, Purple = +5V Standby (not used), Gray = power is on (output), and Green = PS_ON# (turn DC on by shorting to ground). Define safely. More than the LED wants so I only let it happen for a second. If I measure voltage between the two legs of the LED while using the 47 ohm resistor I get 1.6V. MathJax reference. I am running it off a GPIO pin of my Arduino Pro Mini (3.3V) triac in search tab above type or paste user:"Tony Stewart" LED ESR R I checked the LED with a tester and it also reported 2V forward voltage. WebGraphical Resistor Calculator. Not really. Damn troll of a LED. They If a resistor does not have a tolerance band, start from the band start at the opposite side of the GOLD tolerance Did you make this project? Leo.. Wawa: That is still way above the dark current, but 55 A is such a tiny current ! so, we are going to use 1k ohm resistor and 330-ohm resistor. Best used with white, blue and green LEDs at 5V. To bias a transistor we have to supply current to the base pin, this current (IB) should be limited to 1/10th of the collector current, and the voltage across the base-emitter pin should be 5V maximum. Is the amplitude of a wave affected by the Doppler effect? I never want my LEDs so bright that they would light the room. Price BDT 1,100 Can I safely power a LED with 3.3 V without a resistor? By clicking Post Your Answer, you agree to our terms of service, privacy policy and cookie policy. I came up with the idea to post this mini project because my roommate needed a power supply to power leds and also 12v fans. Yeah when I wrote "I have verified that I get 3.3V from the GPIO pin I use" I meant that I had verified it by measuring : ) Free shipping for many products! If you search my answers in the window at the top of this page you will find I have written dozens of examples on this topic. The total series resistance you would need to drop from 3.3 V just depends on the LED curve ESR plus the series resistance to get exact desired current with reasonable tolerances. N Channel MOSFET A voltage divider is a simple circuit which turns a large voltage into a smaller one. band to the right of the 2nd before you multiply by the corresponding number of Can a rotating object accelerate by changing shape? See my page here that shows how to choose a resistor value for different LEDs on an Arduino. Turns out you were 100% correct! A voltage divider is a simple circuit which turns a large voltage into a smaller one. I wouldn't expect the full 3.3V and it's probably quite a bit less. Notice in the calculator for both 5V and 3.3V supply voltage the "power consumed by LED" remains the same. Making statements based on opinion; back them up with references or personal experience. Capiche? Input should be high. 100 Ohm Resistor Color Code (5-Band) (Image credit: Tom's Hardware) The 100 Ohm resistor is commonly used for LED protection. With your 47-ohm resistor in place, and the LED turned on, what is the voltage at the GPIO pin, and at the connection point between the resistor and the LED? Refresh your browser window to try again. The input protection diodes clamp the input voltage to VCC+0.65volt, so no 12volt on the input. Share it with us! GRAPHICAL RESISTANCE CALCULATOR in JAVASCRIPT Version 2.0, Copyright 1999-2023 the12volt.com, All Rights Reserved. 20Pcs Pre Wired 3mm Warm White Led If the current through the LED remains the same so does the ESR. New replies are no longer allowed. Free shipping for many products! If it does not work, there is obviously a mistake in the wiring or a damaged component. diode Powered by Discourse, best viewed with JavaScript enabled. power transistor Did you set the pin in setup to OUTPUT, with pinMode? SteveMann: voltage regulator Using Arduino Project Guidance. The regulated 3V DC signal goes through the smoothing capacitor C3 (100uF), before moving on towards the output. You need to control the LED current. Let me say thanks, i like your answers and tonight i'm lucky to see you twice during my nightly researches. No it isnt. ESR? This Atmel application document connects 230volt AC on an input pin through a current limiting resistor. Obviously this is not enough for the LED to shine. Perhaps, that is part of the problem. : ). power amplifier More amps, more cost. (if that is the case, then jremington's solution would be preferable). If not you should get one. 7. To verify Connect multimeter to the junction and measure the output voltage Something went wrong. I switched out the PC817 for another one and everything worked. Can you add a extra external pullup resistor of 4k7 (2k2 to 10k or so) ? WebResistor Colour Code Calculator Select # of Bands: Four Five Six Band #1: None 0 - Black 1 - Brown 2 - Red 3 - Orange 4 - Yellow 5 - Green 6 - Blue 7 - Violet 8 - Grey 9 - White WebThe 150 ohm Resistor color code for 4-band resistor is as shown in the image below: [Brown, Green, Brown, Gold] 150 ohm resistor color code for 4-band is calculated as: (1st digit) = Brown = 1 (2nd digit) = Green = 5 (multiplier) = Brown = 1 = 10^1 = 10 (tolerance) = Gold= 5% 15105% > 150 ohms > 150 The DC signal then goes through a Zener diode producing a regulated 3V. courtesy of Danny Goodman. Forward voltage 2V WebResistor Colour Code Calculator Select # of Bands: Four Five Six Band #1: None 0 - Black 1 - Brown 2 - Red 3 - Orange 4 - Yellow 5 - Green 6 - Blue 7 - Violet 8 - Grey 9 - White zener diode. Wawa: So the two questions are: remove the button). Why is Noether's theorem not guaranteed by calculus? Now, if your 5 volt rose to 5.1 volts, the 100 mA would rise to no more than 1.8 volts / 17 ohm = 106 mA. The resistor value is 7.5 for 60 mA and a 2.85 Vf powered by a 3.3V source, Source: Hobby Hour LED Series Resistor Calculator, A red indicator LED with a 220 resistor draws about 13 mA at 5V. And how to capitalize on that? That is the convention, however in reality it is arbitrary. The voltage divider is basic and easiest circuit to stepdown any DC supply. Copyright 2023 ec Estudio Integral. cmos You got it. My roommate went to a local electronics supplier and recently paid 90 dollars for a 7amp 12v DC power supply. So, in this project, we are going to build a simple 12V to 3V Converter circuit using a Zener diode & a BD139 NPN Transistor. 2. This topic was automatically closed 120 days after the last reply. (adsbygoogle = window.adsbygoogle || []).push({}); 2n3904 i.e. But that is not the case with a properly working LED which draws no (meaningful - beyond nanoamps/ picoamps; it is specified) current below the threshold voltage, so any resistor you put in series will cause it to draw some current and light as long as the applied voltage is higher than the threshold. arduinoaleman: Right now I am using the PC817 and on the LED side I have a 3.9K resistor connected to pin 1, pin 2 connected to ground, pin 3 connected to INPUT_PULLUP and pin 4 connected to Arduino ground. Why don't objects get brighter when I reflect their light back at them? Is there a general rule on what resistor should be used given the voltage? 4000mcd. I typically use 1K for my LEDs. I think he was using it to make the point that you can put a much larger voltage on an input pin without damaging it. I was reading that using an optocoupler would be a good choice; however, I am having some issues getting it to work. You can easily step down any DC supply by just using 2 resistors. From the junction of both resistor connect one 3v LED. DVDdoug: Here, the BD139 transistor increases the output current of the circuit to operate high-current devices. That resistor minimizes the impact. Today most new white LEDs driven at less than maximum (e.g. If you were using to 220 ohms from 5 V and you drop the supply to 3.3 for a 2.1V RED then 5-2.1=2.9 or R reduces to 2.9/220*R=1.2V difference. Should work as is but slowing it down might be wise. Now multiply that number (you should have 10) by the corresponding I continue to wonder what the GPIO voltage is when the LED is on using the 47R resistor. From the MCU datasheet: V IL: -0.3V min, 0.99V max (0.3 x V DDIO) V IH: 2.31V min (0.7 x V DDIO), 3.6V max (V DDIO + 0.3) V hys: 150mV min, 500mV max V IL leakage current: 5nA typ @ T A = 25C, 30nA max @ T A = 85C V IH leakage current: 2nA typ @ T A = 25C, 18nA max @ T A = 85C There's also an on-die series termination Thanks for the down vote. temperature sensor that include a tolerance band, ignore this column and go straight to the multiplier. jontaa: The LED resistance is I have found inverse to its power rating so a 1/16W is ~ 16 ohms , a 1 W is approximately 1 ohms or less. operational amplifier Eventually, I would like to add an LED on the 12V side just to show when the limit switch is hit, but I want to get this working first. 8. NextPCB is one of the best PCB manufacturers having amazing quality and the best prices for beginners and students. I am leaving a link I highly The 90%Vf is an estimate but is better obtained from datasheet. I don't see any need to connect it to VCC as the voltage output of the GPIO seems to be correct. ESR will remain exactly the same at 13mA no matter what the supply voltage is. Pc power supplies are generally reliable , handle 15 to 40 amps DC and are 1/5 the price. Some 10W LEDs are 2.85V at 350mA may be Vt=2.6V with ESR = 100 m +0/-50% and Li-Ion ESR may be 50 m +/- xx % per cell. And I know R is the first letter in resistor. Additionally, I have push-buttons that I typically pull-down with 10 k resistors when using 5 V. What resistor should I use in this case? The faintest of red glow appeared in the LED but the power draw according was so low it was not measurable. If the LED was bright with a 10 Ohm resistor, it would be only a little less bright with 47 Ohms. Here, the BD139 transistor increases the output current of the circuit to operate high-current devices. However, the voltage bounds will change over time. Current: 20mA Resistors are color coded. This JavaScript-based web app comes from my JavaScript Bible books (dating back to the very first edition with a few upgrades a long time ago). I want to see the maximum brightness of it to see if it fits into one of my projects. But the result of the calculator is a too high resistor, not too low. what youre really doing is pull an input pin up to a 12v rail which would most likely break something!!! By clicking Accept all cookies, you agree Stack Exchange can store cookies on your device and disclose information in accordance with our Cookie Policy. color chart below for the 1st color band (BROWN). switch Please try again. 3V would be fine. 3. Our task is to stepdown 12v into 3v. so, we are going to use 1k ohm resistor and 330-ohm resistor.Connect one end of 1K ohm resistor to 12v supp power MOSFET jontaa: Just select the color for each band and You could use a 10k resistor to directly connect to an input pin, the 10k is probably enough resistance to Why hasn't the Attorney General investigated Justice Thomas? Does Chain Lightning deal damage to its original target first? Or am I doing something wrong? I've added my new schematic and code. New external SSD acting up, no eject option. At maximum current about 3.1V. 3.3V Vout is at light loads. A buck converter down to 4V and then into the HT would be clean and cool. To use the calculator, enter any three known values and press "Calculate" to solve for the others. 12V to 3V Converter (DC-DC) is a common preference of electronic hobbyists and enthusiasts for small/low-end electronic projects. Should the alternative hypothesis always be the research hypothesis? Write down the corresponding number from the Adjustable Regulator See my page here that shows how to choose a resistor value for different LEDs on an Arduino. resistors only. The original circuit using a 3.9K resistor to the optocoupler LED and INPUT_PULLUP on the Arduino ESP32 was perfectly correct. EPROM Red Vf=2.1 Vcc=3.3 new difference = 1.2 old difference was 2.9 . You can also try the LED & resistor directly to the 3.3V power supply, but with 47 Ohm's you'll be exceeding the "recommended" 20mA. You likely don't need U14 to be 4.7k. Anyway, 15-3 gives a 12V drop across the resistor, and he wants 20mA to flow, so it's V=I*R, 12=0.02*R, R=12/0.02 = 600 ohms, How to Send Your Tinkercad Design to Fusion 360, LEVITATING BANANA - Electromagnetic Levitation, ECLIPSE - the Ring Lamp With Progressive Lighting, IR Controlled, DIY Arduino Camera Robot (Motorized Pan Tilt Head). parts that should have a section in the installer's parts bin. LDR Then I changed the 5V supply voltage to 3.3 leaving the 13 mA. The assumption is wrong and I indicated why. Two characteristics of the LED need to be known to calculate the resistor. The forward voltage over the led is about 1 V. E.g. The delay is because the loop is going a full speed. Commonly used in applications such as increasing or decreasing DC voltage for different applications. Also used for industrial processes such as load matching in power industries. arduino uno Do you see how adding a resistor protects your LED from over-current? I think it has something to do with the forward current required to drive the LED; however, I thought 3.9K would do the trick. I also found online that some people are using a transistor on the Arduino GND side. The CTR tells that at 2.8 mA, the ratio is about 6.5 times. We watched the EZ-box video and intended to build that movie videos Hello Friend, Oh so long i never posted a project, well after my first posted project in here about My new and improved ARC Talk Servo with the Arduino Arc software, dangerousprototypes.com/docs/ATX_Breakout_Board. Your robot can be more than a simple automated machine with the power of ARC Pro! I'll try out some of these suggestions. Is the 3.3V just needed for a logic level input (in which case a voltage divider will suffice), or are you using it to power something? Why would 5V be better? bridge rectifier closest to a lead. finding the right resistor for a LED Using Arduino General Electronics jontaa January 28, 2021, 9:56pm #1 I bought a new LED, yay. The calculator assumes that you want the full brightness of the LED. If you want to pull much current at 3.3V from 12V, get a 90+% efficient DC-DC buck converter rated for twice what you want. The specs are Very accurate method which I use to estimate R and determine the voltage threshold for dim at 10% Imax which is often 10% below the rated forward voltage . You need to know that that IV curve is going to change and do something to minimize the impact. ShermanP: for the fact that he's got 20 mA LEDs at 3V (sounds kinda high for voltage, but maybe some new white LED or something). I am still not seeing a HIGH/LOW toggle from the optopcoupler in code. Model Light*10 Model Lamp Resistor*10 Single Head 3V DC Or AC Height:5.5cm. MatheusGarbelini 3 yr. ago HT7333-A Yes, I have seen a lot of this hybrid usage of buck + linear. More amps, more cost. So I understand that the forward voltage is something that needs to be exceeded in order for the LED to shine, and I assume that I don't reach that. So I was a bit lazy and I went here: LED Resistor Calculator I plugged it in and almost nothing happened. A very common current for LEDs used in lighting is 65mA. For an example let's use 60 mA as the target current and an LED with a 2.85V Vf. I calculated R based on the 1.2V @ 20mA and came up with 540ohm (12V - 1.2V/20ma). To read the color code of a common 4 band Designed by, INVERSORES! "Is there a general rule on what resistor should be used given the voltage?" Find many great new & used options and get the best deals for Motorcycle 6V-12V 8W 2 Pin Flasher Turn Signal LED Blinker Inbuilt Resistor at the best online prices at eBay! pnp transistor View cart for details. Find many great new & used options and get the best deals for Model Light*10 Model Lamp Resistor*10 Single Head 3V DC Or AC Height:5.5cm at the best online prices at eBay! WebDC 3V-36V 15A Dual H-Bridge DC Motor Driver Robotics Bangladesh. I only need desired current and forward voltage at that current. With more voltage across the resistor the LED voltage matters less. If your LED takes 100 mA at 3.3 volts (for instance) you would need to drop 1.7 volts from 5 volts with a resistor. Pin 3 is Arduino GND and pin 4 is the open collector output to a digital input (preferably with a external pullup resistors to 3.3V). I never want my LEDs so bright that they would light the room. If you do not need your circuit to supply much current, then you could use a simple voltage divider. I didn't have a 65 ohm so I took a 47 ohm one instead. Because the whole calculation relies on the voltage drop across the resistor. jfet WebThis calculator is based on the Ohms Law Calculator, but takes into consideration the voltage drop from the LED. The math is not that difficult. should i be using something else to instead of or as well as to get the voltage down to 3.3? Just to test I put in a 10 ohm resistor instead. LOTE EN VA PARQUE SIQUIMAN A 2 CUADRAS DE LAGO SAN ROQUE. Vcc IR+ Vf = I*94 +2.1V= 3.3V so If13 mA, which is ok? Voltage Source (V S) Volts (V) Voltage drop from LED (V LED) Volts (V) Current through the LED (I LED) Resistance (R) LED Power (P) You don't need a super precision one, just enough to measure voltages and likely ohms. Smaller sizes than expected but ok, cheers. Where did you get lost?? Did it light-up with the tester? Fast Recovery Diode With 12V you could "assume" all of the voltage is dropped across the resistor and get a "close enough" current calculation without even considering the ~2V drop across the LED. Max_Rush 3 yr. ago Quora - A place to share knowledge and better understand the world Thanks for contributing an answer to Electrical Engineering Stack Exchange! They tell a lot. Delivery times may vary, especially during peak periods. Is there a way to use any communication without a CPU? These calculators have innacuracies based on user input of 2.1 @ 13mA which is incorrect, It should be reduced 7mA *ESR. rev2023.4.17.43393. origin ZIP Code, destination ZIP Code and time of acceptance and will depend on shipping service selected and receipt of cleared Now the LED glows bright and my multimeter says it uses 27mA. WebThe HT7333-A won't be low heat running an ESP from 12V though. darlington transisor Voltage dividers are one of the most fundamental circuits in electronics. An LED has a point where the terminal voltage applied causes a significant rise in the current taken and if you increase that voltage by even as little as 0.1 volts, the current taken by the LED could be beyond its operational rating. This is why we put a current limit resistor in series. Resistor Color Code | Resistor Standards and Codes | Resistor Guide Please note, this is for 4 band It only takes a minute to sign up. 2. A voltage divider is a simple circuit which turns a large voltage into a smaller one. Using just two series resistors and an input voltage, we c arduino Then you can look at the transfer ratio or saturation voltage vs forward current. Yeah it lit up with the tester 20Pcs Pre Wired 3mm Warm White Led Lamp Light Set 12V-18V AC/DC For Train Layout. The resistance should be high enough to not use excessive current, and low enough that EMI and other disturbances won't trigger spurious button presses. Who ever talked about 230 Volts?? @TonyStewartolderthandirt OP said 5V with 220 resistor. Stack Exchange network consists of 181 Q&A communities including Stack Overflow, the largest, most trusted online community for developers to learn, share their knowledge, and build their careers. I would assume that if the calculator wanted the full brightness it would hover near the max instead of the min. ( 12V - 1V ) / 3k9 = 2.8 mA The regulated 3V DC signal goes through And when you follow the link, you will end up with a discription of a Zero-Crossing-Detection device. Copyright 1995-2023 eBay Inc. All Rights Reserved. cd4017 5. Connect 12v supply The higher the value of resistance (measured in ohms) This topic was automatically closed 120 days after the last reply. If you need a resistor you select your desired current which must be equal to or less than the LED's maximum current. Things are a LOT easier and more predictable if you have 5V to work with. I can put that into a ratio formula for scaling know R values or you can try to follow my general rule in answer for any situation. For pull-down resistors on switches you need to ensure that if there is a wetting current requirement to be met, the resistor is low enough to allow that current to flow. 13 mA at 3.3V would use a 91.3 (1%) or 100 (5% 12mA) resistor Share Cite Follow edited May 8, 2018 at 22:12 answered May 8, 2018 at 20:07 Misunderstood ldo To the right of that number, write the corresponding number for the 2nd band You can probably get by with a 10K or by enabling the internal pullup. For users wanting to check self, enter "user:me" . key words. The calculated resistance value is then 92.3. cleared payment - opens in a new window or tab, Report this item - opens in new window or tab. If the supply voltage is 12v and the LED voltage is 3v the resistor voltage is 12v - 3v = 9v Note: The sum of the voltage drops in your circuit must add up to the supply high voltage Both the schematic in post 3 and 8 should be a slam dunk. Input Voltage (recommended) : 7-12V. So I went about it a different way. LEDs have a dynamic ESR based on the current. When dropped below this the LED stops shining altogether. The general rule depends on the LED specifications. Divider or regulator is the way to go depending why youre needing the 3.3. dcrash36: I'm using an ESP32 HUZZAH from Adafruit. I have some LEDs that I typically power with 5 V and a 220 resistor, but I can only supply 3.3 V at the moment. BD139 NPN Medium Power transistor has a gain value of 40 to 160, this value determines the amplification capacity of the transistor. Hopefully this does the trick. These low-end DC-DC converters provide a simple, easy & cheap way of building your own test supply for projects. 2n4401 Digital I/O Pins : 14 (of which 6 provide PWM output). WebHelpful Tips for Using Resistor Color Codes: 1) Start by identifying the last band first. Can dialogue be put in the same paragraph as action text? Check the actual Arduino output voltage with the LED & resistor connected. Or, the "12V" can vary by one volt and the LED brightness will hardly vary at all. multiplier number of the 3rd band (RED)(100). It depends on the LED. It's that easy. Then in fancier high power methods current can be sensed on the low side and regulated with a comparator or difference amplifier. How are you calculating the value? A 12V DC input is received at the input. On four and five band resistors, the last band is usually gold or silver and should be separated from the other bands by a small gap. the value will automatically be displayed. I would add a delay in your loop. Some LEDs won't even light at 3.3V. You can get the best of both worlds and still do it on budget. So minor corrections mean Vf might be 2.0V with same If=13mA, {R+ESR}=(3.3-2.0)V/13mA= 100 Ohms = R+ESR so. You may learn how to do this or not is your choice. system Closed May 6, 2021, 2:02am 11. Find many great new & used options and get the best deals for Model Light*10 Model Lamp Resistor*10 Single Head 3V DC Or AC Height:5.5cm at the best online prices at eBay! IDEAL OPORTUNIDAD DE INVERSION, CODIGO 4803 OPORTUNIDAD!! Should work as is but slowing it down might be wise. Something isn't "adding up". Buy IP67 Waterproof LED Metal Warning Indicator Light 6mm Pilot Signal Lamp 3V 5V 6V 12V 24V 220v Red Yellow Blue Green White - (Color: 6MM, Voltage: 3V, Size: Red LED, Standard: Flat head): Indicator Lights - Amazon.com FREE DELIVERY possible on eligible purchases The calculator assumes that you want the full brightness of the LED. It should not make a difference but a delay is easy to do. And when you follow the link, you will end up with a discription of a Zero-Crossing-Detection device. Mind you, it was actually true for a batch of really cheap, known faulty LEDs I bought some years ago, a couple of which still illuminate my doorbell push. czu001 June 30, 2021, 8:58pm 1. we can create any small voltage respect to supply voltage by adjusting only one resistance. Use MathJax to format equations. If the above shows the correct output, I would short pin 12 to ground to verify the state changes. limit the protection-diode current on the pin to a safe level, else use a 10k/3k3 divider (about 1/4), Def dont use a resistor between 12v and an input pin rated for only 3.3 or 5v.sure it limits current but what youre really doing is pull an input pin up to a 12v rail which would most likely break something!!! "can I safely power a LED with 3.3v without a resistor?" Something was clearly incorrect - perhaps a 47k resistor. If it doesn't light fully at that, then your rail Voltage is dipping on load. Connect one end of 1K ohm resistor to 12v supply and second to any other hole of breadboard. NextPCB is one of the best PCB manufacturers having amazing quality and the best prices for beginners and students. If it's near 3.3V, and there's almost no light from the LED, then the resistor is actually some other value. Capacitors in psu can pop you pretty hard so avoid touching internals of a pc psu even when its not plugged in. I am a little confused as to where you got the 1.2V in 2.9/220*R=1.2V. Frome same hole connects one end of 330-ohm resistance and another end to the ground.
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