Comparator Inputs ?

On the two inputs of a standard comparator op amp (say for example  LM741)  they usually  connect resistors from both the positive and negative voltage rails .Why do they do this and how does this work . This has been on my mind for a really long time . Could someone give me a really detailed explanation maybe with images if possible , cause this would be really helpful in the building of my next project .Most of the tutorial videos out there , i don't understand either. Thank you in advance  

Question by Strontium   |  last reply

Simple Comparator with a LM339N

Hello, I am trying to make a simple comparator with a LM339N. I don't understand what is wrong with the circuit. The output is always low, even when the inputs are reversed. The schematic is attached--the schematic doesn't include the two 100k ohm pull-down resistors on the inputs.  Thank you.

Question by dboone628   |  last reply

cooler lid off cooler lid on both with ice which soda will be colder?

We have 2 coolers both with ice with cans of soda in each. Bothin the shade One has lid on one has lid off which soda will stay and be colder?

Question by    |  last reply


I just bought craploads of knex so i can build loads now. If you want to see how much here is the like to what i bought:

Topic by Millawi Legend   |  last reply

Headphone showdown

I'm currently in a dilemma over the next pair of headphones I'm buying. Does anyone have anything bad to say about certain ones? (Or better yet good things). The three I've narrowed down to are: - Solo HD's  from beats     - These are a tad more expensive, but I personally like them and have heard great things.     - Detachable cord     - Great sound     - Most expensive (119USD) - Skullcandy Lowriders    - I've gotten mixed reviews here, some say that they are crap yet I personally know someone who had a pair of these for 3 years and they were still in one piece.   - A little uncomfortable, but durable.   - Decent sound   - Also the cheapest (40USD) - Ifrogz Vertex    - I have a pair of these which are broken, the cord is a tad cheap but the quality is fairly good otherwise.    - Decent sound    - Mid priced (50USD) Thank You - Nerdman

Topic by ry25920   |  last reply

Mac VS PC?

I'm posting this to share my experience and opinion of Mac's VS PC's. I welcome you to read and share your story. For many years I was a PC. I believed whole-heartedly that I needed Windows, and I needed Microsoft. Then I bought my last laptop. It wasn't cheap. I used it everyday for work and therefore it was important that it ran efficiently. Like many of you, I suffered from "blue screens" and on occasion a "crash". There were viruses and trojans and attacks from all places, you'd think I was engaged in war! Then the proverbial "last straw" occurred. I needed to upgrade into some new software, and I received a simple message that I needed to also upgrade the Windows Service Pack. Hmmm.... Seemed easy enough. (Been there. Done that.) So, off I went to download the SP (from a reputable source) and then "Success!"... I got a message that said "Successfully installed. Windows must restart to complete process". Hmmm... Ok... I pressed through the process to restart my machine and there it began.... The long and never ending cycle had started! My laptop shut down, started to boot and then upon seeing the (dare I say it?) Vista Start Up Screen, my laptop promptly repeated itself and began to reboot... o_0 ??? This went on for sometime... *anger growing*... NOTHING I did would stop this, or should I say NOTHING would START my laptop. It was forever entangled into a mysterious vortex of computer "Neverland". I was NOT impressed. I had to borrow another computer to do some research and found very little at the time to explain this conundrum. Then I tried Microsoft. I used their "so-called" online customer service department and was put in touch with someone who was younger than my oldest pair of shoes. He also couldn't speak English very well, so without being incredibly rude I requested another agent. Upon conversing with agent #2, I knew I was in trouble... (Was Agent #2 related to Agent #1???) ... o_0 ??? *shakes head* I will give credit to Agent #2. He was nice. He tried his hardest to suggest everything under the sun, but alas, we both concluded it was hopeless. The final bluescreen error number confirmed the toe tag on my machine. So I was left with having to reinstall the entire system and lose EVERYTHING on my laptop. *fuming mad now* Then it occurred to me that "Windon'ts" (as I affectionately call them now), opted not to provide me with necessary disks to reinstall their OS during my purchase. It seems that the cost of a CD has become so expensive for Microsoft that they are forced to leave it up to the consumer to fend for themselves. Clearly, they are suffering financially, No? When I rationalized this logic with Agent #2, he suggested that I purchase Windows 7 as it had just come out and was much better than Vista (No kidding.... *rolls eyes*). But why? Why prey-tell should I have to purchase anything? My laptop was only 14 months old (conveniently out of warranty) and may as well have been a pre-historic dinosaur as far as Agent #2 was concerned. So where did me and Agent #2 leave off? He suggested I "borrow" an installation disk from someone and reinstall windows vista and start over... *tics forming now...* He assured me that my "service call to Microsoft" would remain as "unsolved". (Oh btw, at this point we were regulars on the telephone). So my ONE LAST QUESTION to him was: "What assurance do I have, after reinstalling Vista and then the SP I need, that this problem won't just start again?" - His reply was, "Well, it shouldn't"... Straw officially broken. Now we come to my life with my new MacBook. Clearly much more expensive than a Windon'ts PC, but wait... Is it? Let's review. There are more "open-source apps" available to a Mac (meaning you get them for free), and in most cases I find they are the same if not better than the paid for MS version. The critical applications that I use everyday for work, installed fine and without issue. I also received "DISKS" from Apple. Apparently they can afford to give customers what they pay for.... Upon opening the box, I was running my new laptop within 5 minutes. Easy Peasy... The time alone that I save from all that aggravation is money in the bank. Do I miss anything? Yes, actually I do (or maybe I don't). What I miss out on are bluescreens, viruses, trojans, attacks, intrusions, crashes and all the other fun stuff I got to know and expect with a PC. So why tell all of you about this now? Well yesterday I noticed that the bottom of my MacBook had a slight bulge in the case. *Heart skipped a beat*. Then after some mild panic, with visions of my last ordeal swirling in my head, I went online in search of why, and found the answer within 5 minutes. Apparently this was something Apple became aware of and had a simple solution. Fill out a contact information form along with my serial number and I got a confirmation message. Not only would I receive an ENTIRELY NEW bottom to my MacBook, I would receive a full set of screws AND a screwdriver!!! All FREE OF CHARGE. NO SHIPPING FEES. COST ME NOTHING!!! *shocked* Now I was beaming. *ear to ear grin* I felt validated for my departure from PC. Then in some kind of absurd customer service universe, I received a knock at the door. My replacement parts had arrived!!! - Less than 24 hours later... *mouth gaping and eyes wide* So I thank you for reading this. I encourage you to share your opinions. If you don't know who I am. I am canucksgirl. I'm a Mac. Not a PC.

Topic by canucksgirl   |  last reply

Comparator doesn't work as expected? Answered

Hello, I'm having a strange problem with the LT1016 ( When the -input is at 0.630V, and the +input is at 0.555V, and the comparator is fed with 5V, the outputs are because of some reason Q(inverted) = 2.10V and Q = 2.67V 2.67V for Q is just out of specifications (minimum High voltage of the pin should be 2.7V). 2.10V for Q(inverted) is not good as it should be less than 0.3V in it's low state. The "latch enable" pin is grounded. Both output pins are not connected. Why doesn't Q(inverted) go to 0.3V and Q to 3V, as the datasheet suggests? I tested this with another (also new) comparator; also an LT1016, and it behaves exactly the same. Pins: 1 V+ 5V 2 +IN 0.555V 3 -IN 0.630V 4 V- 0V 5 Latch Enable 0V 6 GND 0V 7 Qout 2.67V 8 Qout(inverted) 2.10V Any ideas?

Question by DELETED_Electorials   |  last reply

op amp as comparator basics? Answered

Well... I'm making this battery charger cum level indicator, which should turn off the battery supply when its voltage drops below 10V. Im using an opamp as a comparator to do that. I have been scratching my head for 3 days but cant get this sorted. From what I have been experiencing for years, on an op amp if the potential on the in+ pin is higher than that on the in- pin, then the output pin goes high, else low. Right?  Now in this particular case (and the first time in my life) the ic gives 4.xx Volts on the output pin when in+ is higher than in- and 11.xx volts when in- is higher. Vcc is 12V.  Im bugged... I have attached the part of the Schematic that shows the IC and its connections. Please have a look. I haven't changed the IC yet, im doing that in a minute anyway. I'll mark this solved if the new IC does the trick. :)

Question by pro2xy   |  last reply

how do i match gears that will work together by gear tooth/ spur sizes, i have no clue? Answered

Hello, i recently bought some shaft gears for the motors for my r/c tank project, in case you don't know, a shaft gear is the spur gear that goes onto the motor! anyway, i am back to start working on my tank again, and am searching for some large gears , but i have no idea aside from physically comparing the two, of what gear is the correct size for my gear. how do i figure out if two spur gears are compatible or not? someone please help!

Question by oldmanbeefjerky   |  last reply

What - besides rulers - can I put in my photos to indicate scale? What things are the same size all over the world? Answered

 I'd like to include scale-indicator objects in some of my photos; but rulers are boring, and dollar bills or US coins seem kind of US-centric. What small, preferably common-household-type, objects are the same size all over the world?

Question by Gorfram   |  last reply

I am saving up for a xbox 360 and was wondering if it would be better to buy a used one or buy one on ebay with the RROD Answered

I don't have a job yet and i just turned 16 and i am looking for one. so i am either going to save up for a used xbox 360 from gamestop or buy one from ebay with the RROD and fix it I know how to fix the RROD and have done it on a friends xbox so repairing it is not much of a prolblem

Question by maxpower49   |  last reply

I need some help with comparators. Answered

Upfront I apologize if this seems like a dumb question, but both Instructables and google have turned up nothing useful for me. I have a need for a resistance comparing switch circuit. I can't find anything about resistance comparators anywhere except articles that you have to pay to read. I need something that will compare a set resistance to a resistance that will vary, I want it to switch off when the tested resistance is higher then the set one and off when its the reverse. I have no clue what to do.

Question by The Ideanator   |  last reply

Simple comparator problems. (Outputting sine wave)

I just got a couple of LM2903N comparators off of an old board, and decided to do something with them. I have it running on +/- 5V, with the (-) input on 0V, and the voltage on the (+) input varied between +/- 5V on a 100K pot. If it is left like that, a sine wave of about 1.5V and 100Hz is generated when the (+) input is above 0V, and outputs 0V when the input is below 0V. With the output connected to +5V via a 33K resistor, the amplitude of the sine wave is significantly reduced, to about 0.1V Also, as the input voltage passes through 0V, the output will jump to 1.5V above or below 0V, and slowly return to 0V over about a second. The same is seen for both constant output voltage, and for the sine wave. (Tried this with both chips, and both give the same result) Thanks in advance for the help.

Question by The Skinnerz 

AVR ATmega32U4 Timer compare interrupt not triggering?

I tried to create a CTC timer interrupt on my ATmega32U4 leonardo board. When I continuously check the value of OCF1A I have no problem detecting when the output reaches the desired value, however once I move the code into an interrupt, the interrupt never triggers. Here is the atmega32u4 datesheet Timer setup: #include void setupTimer() {     TCCR1B |= (1 << WGM12); // CTC mode     TCCR1B |= ((0 << CS10) | (0 << CS11) | (1 << CS12)); // set up prescaler     OCR1A = 6249; // 100 ms set up output compare value for interrupt     TIMSK1 |= (1 << OCIE1A); // enable interrupt on clock compare } The loop that works: setupTimer(); for (;;) {     if (TIFR1 & (1 << OCF1A)) {         PORTC ^= (1 << PORTC7);         TIFR1 = (1 << OCF1A);     } } The interrupt that does not work: #include ISR(TIMER1_COMPA_vect) {     PORTC ^= (1 << PORTC7); } I must be missing something as from what I have seen in the tutorials the above code should work. One interesting observation here is that if I have both the loop and the interrupt in my code at once if I call sei(), the LED does not blink as if the OCF1A register was cleared prematurely. I'm pretty sure it is irrelevant in this case but the fuses are as follows: E:CB, H:D8, L:FF. I use avr-g++ to compile and the code is spread out between several files.

Question by DELETED_MakiY2   |  last reply

How strong is JB weld compared to real welding? Answered

I want to build a recumbent bike, but I can't weld. Any other ways to build one. Mabye make one from hockey sticks.

Question by ANDY!   |  last reply

Comparative Environmental Friendliness of Internal Combustion and Electric Vehicles

I would like to know which type of vehicle is more environmentally friendly. Electric and hybrid vehicles are gaining in popularity and they are touted as green, but they clearly require more energy and resources in their manufacture due to their battery packs, rare earth metals and electric motors. On the other hand, traditional internal combustion vehicles require fewer resources to manufacture. However, I imagine that it converts fossil fuels to energy less efficiently than electrics because the conversion process is smaller, unlike in large scale power plants (not sure if this is true). Electric === More resources to create (-) Power Plant (Generates energy efficiently?) (+) -> Power Lines (A: energy loss) (-) -> Motion +,-,- Gas === Fewer Resources to create (+) Combustion Motor (Generates energy inefficiently? B: energy loss) (-) -> Motion +,- I'm pretty terrible at explaining this, but is the energy loss at A or B worse when comparing the two systems? For electrics to be viable, it must offset the higher creation cost. Just wondering which one is actually more "green" when you factor in production (disregard cost of transporting fossil fuels to gas stations and power plants).

Topic by crestind   |  last reply

I have a quad comparator, what should i use it for?

Its the LM339, i know a quad comparator compares 4 different voltages, but thats about it. what kind of application could this have? ideas?

Question by zack247   |  last reply

How does the taste compare in Flourless versus Flour recipes? Answered

I see recipes once in a while, like this one, where they don't use flour.  I know it is easier, but does anyone know the taste difference in flourless recipes?  Is it not worth it to do flourless?

Question by Penolopy Bulnick   |  last reply

can ducted propeller produce twice lift compared to opened propeller ?

Can ducted propeller produce twice lift compared to opened propeller ? for example if there is an opened propeller with low rpm producing some amount of lift. If we ducted that opened propeller and provide same rpm and power as opened propeller to it will it produce twice lift compared to opened propeller with same rpm and power ?

Question by MuhammadK19   |  last reply

what is the energy saving in LED street-lightings compared to HSVP/ HID ???

Compared to old lamps, energy savings , maintenance costs,,,etc

Question by sunsolaristech   |  last reply

How strong is JB weld compared to cast aluminium by a tensile force?

Hello. How strong is JB weld compared to cast aluminium? A broken lever from the quick snap from a "Supercut 2 Q" oscillating tool from "Fein".

Question by tobias.claren.9   |  last reply

is it possible to determine the direction a motor is spining by attaching a comparator to both leads?

The motor is not being powered with electricity it is being spun by hand. and if it is possible how can I determine the speed.

Question by evilmadscientistman   |  last reply

Help with OP amps Answered

I'm making an instructable about this circuit, it's a heartbeat detector, it's supposed to beep when a heartbeat is detected. Something weird is going on with the comparator, first of all, the input signal to the comparator seems to get "stuck" at the level of the comparator, like it is an invisible barrier that doesn't allows the signal to cross it easily, this seems to happen with and without the buzzer. Secondly, the comparator "rings", it doesn't displays a clean square signal when the threshold is reached, instead, at the end of the square pulse "ringing" appears. Removing the buzzer or speaker solves the ringing problem.  I tried replacing the buzzer by a 8 ohm speaker, but the problem persists. Then I tried changing the 1k resistor of the transistor by a 10k, but the problem is still the same. I don't know what could be causing this, bad design? A faulty chip? In the second picture it can be seen how the signal "bumps" an invisible barrier when reaches the comparator level, in the third the "ringing" can be seen, the fourth and last picture is how the (previous) comparator signal looks when the load is removed, the problem disappears. Thanks in advance,

Question by Victor805   |  last reply

How much more messier is your room/house/workshop compared to mine?

I was just wondering how much messier is your room/house/workshop compared to mine, If so how much messier, Post a pic to show us if possible

Topic by thermoelectric   |  last reply

Is there a cheaper alternative to arduino? Answered

What is the alternative, and what are the pros and cons compared to the arduino

Question by sunny342   |  last reply

View counter not matching with stats

Hello I guess i'm not the only one here who likes graphs and data. But If I compare the view count on an instructable and compare it with the stats view. The values don't match up not even close. For the screenshots please check this link because I've trouble uploading the pictures. 

Topic by geo bruce   |  last reply

how to compare two stepper motors with the same torque based on other parameters like current, inductance etc? Answered

I am looking for NM 23, 425 oz-in stepper. I found two in eBay for the same price one from wantai and another from OSM, with different current, inductance, resistance and weight. I need guidance to select.

Question by saaddition   |  last reply

Help with battery charger circuit

I have a slot machine with a 3.6v rechargable lithium battery on motherboard. The problem is the battery goes dead after about a week and the settings are lost. I want to attach a solar battery charger to it so I do not have to leave it plugged in. Could I run the output of the solar charger through a comparator and then to the battery while it is still in the circuit? The panel puts out around 3v in the room I want to use it. Would this be enough to power an op amp? Then when the battery reaches a certain voltage the comparator changes output and stops charging.  If so, would this work? Any advice on how to build the circuit?

Topic by aballworth   |  last reply


So TheDunkis gave me the idea to build the AN94... so here it is! It's pretty good but I fail so damn hard at (front) barrels. As you can see it don't look very great, and the worse it doesn't look like the front part of the real gun. I'll change it, and maybe post it when I chgned it, but it's such an annoying thing to build. Pictures: -To compare, compare picure 2 and 5.-

Topic by mahmel   |  last reply

Compare the older posts of Magnet generators "instructable-type" to the current posts - Is this way still competitive?

I love you guys - keep it up!  I am the Hippie often referred to, according to my little brother, Dirt. (I'm older than Dirt...) Over a year ago I studied this fellow while recovering from being run down on my bike by a hit and run car doing 65MPH. The thing that keeps coming back to me is that I always see a multitude of ceiling fans for practically free. Also he addresses the over speed topic very well too. HTTP://

Question by miscexpert   |  last reply

Can We Compare IT Sector with Public Sector Undertaking (PSU), Indian Engineering Services (IES)?

Now a days electronics engineering students have a big problem to select a job in private sector just like a IT SECTOR or in a government sector for example IES or PSU. In my point of view all the above job have good future and good respect and there are some limitation for every sector. If someone ask me this question and i don't have a any choice then my answer is ....... I think we can not compare government sector with IT sector at this stage. Because in govt sector for example IES . Indian Engineering services will give you a huge respect in every sector, promotion, good environment, peaceful life, safety of family etc. When we talk about Public Sector Undertaking (PSU) this will also give you more work experience than IES and promotion, good environment, peaceful life, safety of family etc. Now at last in IT sector this will give you a lot of its depend on your strength. In some cases if you have a potential then you can achieve in few years but in case you are a lazy person then IT sector or private sector will give you nothing and give you a lot of pressure. Finally i conclude this remove your confusion please select your future with your interest, every sector have good scope. Please improve my question and answer with your comment ?

Topic by Abhishek Upadhyay   |  last reply

What do you think about sharing craft tutorials online compared to learning in a classroom?

Hi can you please complete this questionnaire for my dissertation? It would be a massive help, the subject is about online how to's in terms of craft and the social community and whether or not people prefer this to learning in a classroom. If you could fill out the questionnaire or leave a comment below with your thoughts, that would be amazing. The questionnaire is anonomous! Also I am designing a dressing table so ladies, if you could complete this short one too that would be amazing! Thankyou for your time =)

Question by katrina789   |  last reply

beetle bike

I want to build a beetle bike but i need some info on power on hp of bikes compared to the beetle

Topic by abadfart   |  last reply

decoder and encoder

What the mathematics for base64 compared to our base10 system and for writing a base64decoder and encoder with perl that dosent olny work for numbers but also text

Topic by cris1133   |  last reply

arduino uno programe

I am new to arduino programing and have below query. i am getting below content in abc and wanted to parse and compare with current time. char abc[128] = Fajr5,04:40 Sunrise6,06:03 Dhuhr13,12:39 Asr17,17:16 Sunset19,19:15 Maghrib19,19:15 Isha21,20:37 ; how do we parse and get something     String time[] = 04:40 06:03 12:39 17:16 19:15 20:37 ; and then split and compare with current time. i am getting time from ds3231, hh=hour and mm=minute then compare like below     int h = time.Split(' ')[0].Split(':')[0]; // this is 04     int m = time.Split(' ')[0].Split(':')[1]; //this is 40     if(hh== h && mm==m)     {         Serial.print("Fajr");     }

Topic by sayedfar 


I just made the EV3 rubiks cube solver and i am wondering why mine takes a long time to scan compared to

Question by ben2000   |  last reply

Nst transformer?

How do I find out how much current my transformer can drive? How do I compare the drive of my transformer, and what's the purpose?

Question by wiccakingkamui   |  last reply

Creating an Invention and Instructable Mixing Software or Website

I was wondering if we could create a new website device, we could call it the Invention Mixer Software.It would basically be a large database of practical or groundbreaking inventions, and maybe many of the instructables here.We could arrange it according to use (Renewable Energy, Agricultural, Games, etc) and we could arrange it like a shopping cart selection. Each item would contain Name of Invention, Its basic use and advantage over common inventions, and the link to the manufacturer or institution doing the research.With the shopping cart, you can choose the inventions and instructables you like and store them in the website, or copy and paste to your friends to discuss,compare or talk over.It would be more than hobbyists website. People making new inventions could compare with the products now in the market, and compare it to instructables that can make similar inventions.It would be like a cheap, low cost utility compared to the very powerful but expensive invention making machines like:INVENTION MACHINE Software stuff like this:CREAX Invention Software would be the every man's invention software on a website.

Topic by mikedu   |  last reply

How does Smooth-On's Feather Lite urethane resin compare to their Smooth-Cast 300 resin?

I want to cast my original horse sculptures, but since I don't have a roto-cast machine, I'll have to solid-cast the models. I'm a fan of draft horses, so my 1:9 scale horses will be rather large and bulky. This would be heavy if I did a solid-cast with normal resin, which would make shipping prices escalate, so I'm thinking the feather-lite would be a better choice. I'm worried about its ability to replicate fine details, and in the model horse hobby, it's all about the fine details and the quality of the cast. What is the quality of the resin like compared to their other resins, and how well does it replicate the original sculpt? Any help is appreciated! Thanks in advance!

Question by Ayedeas   |  last reply

Do you guys think about this PCB design?

Here is revision 1 of my PCB. Also is a link to the schematic that is on the PCB design.|vUO60iAua It is a flyback driver based on the LM339 comparator. What is important is that the MOSFET is switched on and off very hard, very fast. audio is AC coupled into the second comparator which sets the PWM duty cycle. Is there any issue with stray inductance or other parasitic bad stuff in the PCB layout? Or any misteaks in the schematic?

Question by -max-   |  last reply

Converting sounds into motion without a microcontroller

I want to build a circuit which converts 3 specific frequencies into a voltage, then to be used by 3 different servos, I don't need to use a microcontroller!! what should I use other than microphone, op amp, 555 timer, servo and comparator for this circuit?  Which one is better LM567 OR LM2907 to convert the frequencies? Thank you in advance!! Waiting for your reply ASAP :) Joe,)

Question by joee1   |  last reply

Prophecies for Future Research

800 years from now, archeologists will conduct research on landfills and compare international findings concerning the wealth of an ancient culture based on the amount on disposable diapers found. Share your own.  

Topic by AngryRedhead   |  last reply

is a coilgun (gaussgun) better than a railgun? Answered

I am writing an essay comparing and contrasting a coilgun and a railgun. i know the differences between the two but i am in need of outside opinions on what is a more effective tool.

Question by BrendenK2   |  last reply

How can I make a PSPICE model of LM3915???

I am aware that the IC LM3915 is made up of about 10 comparators...but how do i represent them in my PSPICE program???

Question by Yashknowsbetter   |  last reply