Guest analouge Posted September 22, 2005 Report Share Posted September 22, 2005 Hi all u guys!I know this is probably a VERY lame question to ask, but I'm gonna do it anyway :D.I am no expert with electronic design or something, but I have experience with building both pretty complicated stuff (from schematics) and less complicated things that I designed myself..But as I read through these pages I constantly run into the word "pull-up resistor". Here's the deal. I think I understand why they need to be there, but I have never heard the word before... So... The lame question... I just wondered if a pull-up resistor is exactly the same thing as an ordinary resistor (I mean - the same component)...? Or is it a different component? If so, can someone tell me a little about it?Hey, I know it's a lame question - but if you can't ask, you won't learn... ;)Have FunIngebret Quote Link to comment Share on other sites More sharing options...
kokoon Posted September 22, 2005 Report Share Posted September 22, 2005 http://www.google.com/search?q=pull-up+resistor Quote Link to comment Share on other sites More sharing options...
Guest analouge Posted September 22, 2005 Report Share Posted September 22, 2005 Thanks...!I thought I knew a little something about electronic design, but I admit I ran into a corner and stood there and blushed when I saw the title on the site I found: "Very basic circuits" ;D HAHA.Anyway - thanks for the assistance. I'm the type of guy that needs to understand everything completely before I'm satisfied :). But when I think of it I should really understood it by looking at the pages around this site and I should at least understand it when I saw the schematics :P.Have Fun! Quote Link to comment Share on other sites More sharing options...
kokoon Posted September 22, 2005 Report Share Posted September 22, 2005 well... to be honest - i dont understand 99% of how any of these work. electronically-wise. but it's so well-documented that it's really easy to build so i'm getting somewhere already. but i'm that type of person that's used to searching for general topics info on the net and i guess that helps me quite a bit. and i've learned many things about electronic circuits so far (starting from ZERO)so - all's good and we'll all build midiboxes and have fun during the process. AND when they're finished ;) Quote Link to comment Share on other sites More sharing options...
Guest analouge Posted September 23, 2005 Report Share Posted September 23, 2005 Yeah - it's very well documented, but sometimes I tend to fall off and don't understand certain things that I feel I need to understand. Like the pull-up resistor stuff.But when I google'd for it like you said, I did find a REALLY nice page with some examples of really simple circuits with a OPAmp (or single transistor to make it easier to understand) and a pull-up resistor. I think I understand the thing now... The OPAmp or CMOS can't be floating, coz that's bad :P... So the pull-up resistor's task is to keep it steady (not floating) - I mean - deliver power to the circuit without short-circuit... Am I on the right way here...?Before I found this page I had ZERO experience with digital stuff... My first project was a FM sender... That's like 10-15 years ago. Me and some friends had a LOT of fun with it until the cops came around and told us not to use it :P. My latest project was half mine. I rebuilt a Nokia car charger. Coz my electrical system in the old car of mine is really crappy, so it tends to deliver very unstable current, so the chargers I had didn't survive. So I built a new charger (from the old one) with a voltage regualting cuircut on it, and some caps to make the whole thing even more stable... I also included some diodes so that it couldn't be wired incorrectly + and - then burn. I did that too once with a CD changer - I wasn't very happy! But one of my poor friends did that to a pocket pc when he tried to modify the car charger. He burnt the whole thing. I still don't understand why there wasn't a protecting circuit inside the computer!!!Else I have built some simple lighting chasers... Not much really, so this site is my first encounter with digital circuits. So I am VERY eager to learn everything about it! I'm actually a carpenter, but If I was a little better in maths and could go to school again I would attend some electronic stuff! :PWhat I don't understand - or I don't think I understand - is the difference between a pull-up and a pull-down. The only thing I could make out from the examples on the webpage I found was that on the pull-up setup the resistor was wired to the 5V, and in the pull-down example the resistor was wired to the ground. Is this right? And is this the only difference...?Thanks for all tips!Eager to learn,Ingebret Quote Link to comment Share on other sites More sharing options...
illogik Posted September 23, 2005 Report Share Posted September 23, 2005 hiWhat I don't understand - or I don't think I understand - is the difference between a pull-up and a pull-down. The only thing I could make out from the examples on the webpage I found was that on the pull-up setup the resistor was wired to the 5V, and in the pull-down example the resistor was wired to the ground. Is this right? And is this the only difference...?think it's the only difference yeah; since ground is the point with the lowest voltage (in a unipolar, no negative voltage circuit) and V+ is the point with the highest voltage, hence pull-down and pull-upcheers, marcel Quote Link to comment Share on other sites More sharing options...
kokoon Posted September 23, 2005 Report Share Posted September 23, 2005 well the thing I dont understand is how a resistor can LIMIT current. (pull-down if i understood that correctly) Quote Link to comment Share on other sites More sharing options...
illogik Posted September 23, 2005 Report Share Posted September 23, 2005 hi, i vaguely remember from school ;); V= I x R or voltage= current x resistancesince the voltage is stable (you get 9v from a 9v adapter regardless of the circuit connected to it, theoretically), with a resistor added you get lower current ???, buti think thats not what it's there for; it fixes/stabilises the voltage on that point, otherwise the voltage would float too much and the app/pic thinks that something is happening.cheers, marcel Quote Link to comment Share on other sites More sharing options...
kokoon Posted September 24, 2005 Report Share Posted September 24, 2005 yeah U=R*I - ohm's law.but what you're describing about "floating"... i think the capacitors are better at eliminating that. Quote Link to comment Share on other sites More sharing options...
Dave_Wheeler Posted September 24, 2005 Report Share Posted September 24, 2005 In this context, think of logic levels as being +5V and 0V. A logic input that is not pulled up (or down) is in an unknown state so if there is a pull up, the input is pulled to the +V rail, if there is a pull down the input is pulled to 0V. The value of the resistor determines the current when the input is pulled to the other state. For example, a 10K pull up to 5V----connect input to 0V---current is 5/10000 Ampere (not including any current that the input pulls)Dave Quote Link to comment Share on other sites More sharing options...
Guest analouge Posted October 5, 2005 Report Share Posted October 5, 2005 OK. I maybe don't understand this at all, but I'll sum everything I have picked up from the forum and doing some google research. It's a long shot - since I really have no idea at all how the pic works at all, but I'll try to come up with an example here to show what I think - and please - if someone knows I'm totally - or just a little bit - from - please correct me :)OK. Say you have a MIDI input. And you want to send data to the PIC. And you want the MIDI data to be correctly "read" by the PIC, and you want only the data you choose to send to reach the PIC, and not some random data.I don't know if random data is only read by the PIC when you don't send data to it, or if random data blends in with the data you send...?But anyway - You need to find some way to eliminate the random data transmissions to the PIC. As I understand it - random data is caused by current to the pic that shouldn't be there.So to get the data to the PIC - and to keep the PIC from thinking that there is data when there isn't any - you need to limit the current with a pull-up resistor - not too much, and not too little.That way the PIC gets only the data it was meant to recieve.OK - am I totally wrong here, or is this somehow close to the truth? If it is I am very impressed by myself ;DI am still very confused about this, since I have never worked with digital circuits before - still haven't - but as I have mentioned earlier - I am a person that needs to understand "everything". For me, building a MIDIbox isn't just to satisfy me screaming need for a VST controller, but much more to learn about electronics... Of course I could build a MIDIbox from the schematics laying around this site, but if I can't understand it - 95% of the joy of building it disappears :PSo - as I understand it - the components who doesn't appreciate to be floating, you add a pull-up or pull-down. But I'm still also very confused when to use pull-ups or pull-downs... Somewhere along the road I thought that it didn't matter what design you used, but now I'm not very sure about that...Have fun,Ingebret Quote Link to comment Share on other sites More sharing options...
ImAlive Posted October 5, 2005 Report Share Posted October 5, 2005 Pull-up-resistors are mounted between your logic "high" supply (e.g. +5V) and the pin you want to "pull up". This puts the pin at potential +5V and ensures a defined "high" signal. You want to keep the resistors at high values to have only small currents go through them, so that your supply won't drop in voltage.Same goes for pulldown resistors, just that they connect the signal pin to ground (0V). For analog inputs like on the AIN, as well as the multiplexed lines to the pic, you just clamp unneeded inputs to 0V since there won't be no current to worry about, it's just that they stay at 0%.So, if you want something to be always "high" (inside the defined high voltage), you add a pull-up, at least that's what I think. Quote Link to comment Share on other sites More sharing options...
Guest analouge Posted October 6, 2005 Report Share Posted October 6, 2005 Thanks for info, I'm really impressed how much knowledge this forum can provide. Seems to be a LOT of smart people around :). A great place!!ImAlive: I think I understand what you say. It's pretty logical for me now what the difference between pull-up and pull-down... But I'm still very confused when to use what... But on the other hand, this may be too much for me at the moment... ;DAs I mentioned earlier I've never actually worked with digital circuits. I'm trying to understand the stuff. My electronical skills are not very much to brag about. So I realize that I gotta learn more about how the circuits work before I can understand why and when to use pull-ups or pulldowns. I understand what they do now, but I don't understand why they have to do what they do, or what components that needs to have a pull-up/down resistor attached. I gathered after some google'ing that some components have built in resistors to take care of it - I think it was OpAmps I was looking into... Hell, I don't even know what an OpAmp is good for yet ;DSo I gather I should learn more about the actual components - what they are, and what they do, where to use it etc. before I can understand what components are needed in addition to the logics ;D.So if any have some tips for info on the web about stuff like that, it would be MOST welcome! Right now I'm especially interested in OpAmps... They seem to be a widely used component that I need to learn about... But if anyone think I'm starting the wrong place, you're welcome to yell at me and tell me what to do ;DHave fun. Quote Link to comment Share on other sites More sharing options...
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