http://www.8051projects.net/ Learn to make simple microcontroller projects, pic, 8051, avr and arm projects. download 8051 projects, tutorials, libraries, sample codes. join the microcontroller discussion forum and ask doubts regarding electronics. the best source for 8051 over internet. en-gb 2009-01-08T08:27:59-08:00 contact@nospam.com hourly 1 2000-01-01T12:00+00:00 http://www.8051projects.net/forum-t11856.html 2009-01-08T08:27:59-08:00 I would like to use a transmitter to transmit the attendance collected by system to a remote pc instead directly using rs232 connectr.The remote computer would be almost 400-500meters away from classrooms.Will it do?If yes then which transmission protocol should i use? http://www.8051projects.net/forum-t11856.html 2009-01-08T08:27:59-08:00 say2paul RS485 . .It is successor of RS232 and can cover distance upto 1200 to 1400 meters.I request Arun Kumar to further help you on this... http://www.8051projects.net/forum-t11856.html 2009-01-08T08:27:59-08:00 shyam well i dont know ...but can RS485 be used commercially ... is it open source... i am talking about the networking protocol ahead of RS485! http://www.8051projects.net/forum-t11856.html 2009-01-08T08:27:59-08:00 say2paul Don't know buddy, but Arun recommended me the same..So lets wait for his reply! http://www.8051projects.net/forum-t11856.html 2009-01-08T08:27:59-08:00 shyam what Arun recommended u was make ur own RS485 protocol!but i want to know if RS485 protocols like siemens MODBUS etc.. are open source and can be used for commercial/hobby products!hope arun will give the exact idea... all i know is thisRS-485 is a physical layer electrical specification, not a communications protocol. RS-485 uses two wires and differential signaling (ie voltage differences across the two wires), and be multidropped to allow multiple devices on the network. Modbus-ASCII, Modbus-RTU, and Profibus-DP are three examples of protocols which use RS-485 as their physical layer.ref:http://www.rs485.com/rs485spec.html http://www.8051projects.net/forum-t11856.html 2009-01-08T08:27:59-08:00 Arun Kumar V Hello Vaibhav, your thread says "RFID" and in your post you ask " transmit wireless using RS232" ?anyway i'll brief you how its done : RFID reader reads the RF tag at particular freq. and sends it to the Micro, micro displays the Tag info on LCD and sends it to PC for database storage. there'll one RFID reader and many RF tags ( in the form of Student Ids).Now RS485 protocol which, paul was talking helps in a Multiprocessor/controller scenario (1 master and more than 2 slaves), since in you case its only one micro and one PC, RS232 can be used with help of 433Mhz RF modules ( range 300 meters in open air) for longer range ( as in your case) you have to go for Hi-power Transceiver ( 1Km range)before we go further, let me know your opinionArun http://www.8051projects.net/forum-t11856.html 2009-01-08T08:27:59-08:00 ramdasi vaibhav Sorry for the delayed post and thanks alot for earlier replies!Now, let me explain u what i would like to do:1.I want to do project RFID attendane given in download section and want to implement that for my dept.2.I want to do one modification in the given project.-Instead of storing database directly in th pc connected using rs232 i/f,i wish to transmit collected data (attendance) from uc,wirelessly to remote pc situated in the dept.3.Now,the problem is:The classrooms are quite away from my dept.To be exact-My claarooms are on groundfloor and dept is situated at around 400meters,in another building ; that too on second floor.4.If the dept and classrooms were nearby each other,i wld have used zigbee modules(i guess?...).5.So for these physical tx and rx locations,which type of transmission sceme should i be using for faithful database storage in remote pc. ( Plz do rectify my ignorance bcz i didnt have practical knowlg but wish to enhance it) http://www.8051projects.net/forum-t11856.html 2009-01-08T08:27:59-08:00 Ajay well thinking about your requirement, i would just answer for point 2,3,4well its possible to transmit data wirelessly to remote PC but distance is the problem, in your case you are considering 400 mt displacement, where as there is shift in floor too. which makes a lot of difference.zigbee modules are good, but they may be complex for this simple data transfer application. So you can look for basic wireless modules like 433Mhz, 868Mhz or 2.4Ghz all are ISM bands.your one unit is on second floor and other on 2nd floor, so depending on distance in two buildings (considering two floors parallel) and then distance between ground and second floor, so it may be possible that you need multiple wireless modules to meet these distance conditions.--> One simple solution read data on local PC where your attendance is being taken, then transfer data from that pc to other PC in second building via LAN (local area network) which is available everywhere in colleges.you can make a simple VB application in which data can be transferred from one PC to other PC. All you need is simple winsock based application. as its LAN so speed will be fast enough.I hope this solution can resolve your problem, and will make your application place independent (within the LAN). http://www.8051projects.net/forum-t11856.html 2009-01-08T08:27:59-08:00 ramdasi vaibhav Thank you ajay sir for your reply.Your suggestion of LAN is appreciable but my guide insisted me to use wireless transmission.Also my classroom hasn't got the pc and LAN is not possible in this case.Hence wireless transmission is must and it will be usp of my project.After discussing with my project guide i sorted out the problem.Now the position of tx and rx are slightly changed.THe distance between tx and rx is around 100 to 120 meters but the physical location remains same i.e. rx on second floor and tx on ground floor.I think now transmission might become easy than prev case.Stil i don't know how to implement it.Will u plz tell me how the zigbee transmission is complex. http://www.8051projects.net/forum-t11856.html 2009-01-08T08:27:59-08:00 say2paul Dear Arun, I never used RF transceivers. So I was bit curious for the security thing in RF transmission.I mean to say that is the data we transmit using RF transmitter protected by a password..?When I used RFID MIFARE Card reader/writter, the data was protected by two passwords.. http://www.8051projects.net/forum-t11856.html 2009-01-08T08:27:59-08:00 Arun Kumar V Hello vaibhav, RS232 can be used with help of 433Mhz RF modules ( range 300 meters in open air) for longer range ( as in your case) you have to go for Hi-power Transceiver ( 1Km range)the above excerpts are from my previous post, here's the Hi-Power long range(up to 1Km) 433Mhz Transceiver:its available here (cost Rs.1000):http://aplusindia.net/aplusindiauser/ProductDetailAction.apu?cat_id=52&prodno=SM-TR1100-PAArun http://www.8051projects.net/forum-t11856.html 2009-01-08T08:27:59-08:00 ramdasi vaibhav Thank u arun sir.I think 433mhz module will do for range of 120meters,won't it? http://www.8051projects.net/forum-t11856.html 2009-01-08T08:27:59-08:00 ramdasi vaibhav What is RFID MIFARE,say2paul,will u plz explain it? http://www.8051projects.net/forum-t11856.html 2009-01-08T08:27:59-08:00 say2paul To make it simple for you..MIFARE card is fundamentally just a memory storage device, where the memory is divided into segments and blocks with simple security mechanisms for access control. They have limited computational power. Their reliability and low cost, those cards are widely used for electronic wallet, access control, corporate ID cards, transportation or stadium ticketing.The MIFARE Classic 1k offers 1024 bytes of data storage, split into 16 sectors; each sector is protected by two different keys(password), called A and B. They can be programmed for operations like reading, writing. MIFARE Classic 4k offers 4096 bytes split into forty sectors, of which 32 are same size as in the 1K with eight more that are quadruple size sectors. MIFARE Classic mini offers 320 bytes split into five sectors. For each of these card types, 16 bytes per sector are reserved for the keys and access conditions and can not normally be used for user data. Each sector contains 4 blocks, out of which only 3 blocks can be used to write data. Each block can contain maximum of 16 bytes of data.The very first 16 bytes contain the serial number of the card and certain other manufacturer data and are read only. That brings the net storage capacity of these cards down to 752 bytes for Classic 1k, 3440 bytes for Classic 4k, and 224 bytes for Mini. http://www.8051projects.net/forum-t11856.html 2009-01-08T08:27:59-08:00 sashijoseph You could encrypt the data you transmit,for security.A lil extra work for the micro,that's all.We even have such a project in the download section. http://www.8051projects.net/forum-t11856.html 2009-01-08T08:27:59-08:00 Arun Kumar V @paul I mean to say that is the data we transmit using RF transmitter protected by a password..?to ensure the data transmitted is protected, we can use cipher and decipher technique, for eg: when the micro sends data thru RF Tx, we can add some special character to each byte say ascii "a" and at the Rx side we can Subtract "a" from the each byte received to get actual data. you can use different algorithms @Vaibhavsince your guide has given discount in range, you can try normal RF Modules but make sure they have proper external AntennaArun http://www.8051projects.net/forum-t11856.html 2009-01-08T08:27:59-08:00 Ajay better use a short range RFID.. you can enclose the reader in a box with appropriate distance, students have to present the card and ofcourse that will prevent errors.You can give indicators for successful/unsuccessful attendence. http://www.8051projects.net/forum-t11856.html 2009-01-08T08:27:59-08:00 ramdasi vaibhav i have some faqs regarding rfid attndance project:1. I wouid lik to know crystal clr working of circuit and the diff devices used. e.g. RFID reader, tags,real time clock ,database storage in ram,role of uC so that i can start preparing my project synopsis and initial report to be submtd to my guide.2.Possible modifications to suit todays standard or disadvantages if any to be rectified .3.Does reader detect tags around certain area of coil only?( as shown in dia). This is vital bcz i want it should detect tags of those students present in the class or sitting on benches at that instant.Bcz i want that rfid attendance should work behind the curtains ,i mean students shouldn't have to take any extra efforts to make attendance by coming in vicinity of reader,b'cz it will consume time and may create lil chaos in class. http://www.8051projects.net/forum-t11856.html 2009-01-08T08:27:59-08:00 ramdasi vaibhav 4.What if a student wears more than one tag? Should i use high power (or freq ?..plz clr this pt i 've doubt here) rfid reader for this ? thanks in advance. http://www.8051projects.net/forum-t11856.html 2009-01-08T08:27:59-08:00 ExperimenterUK RFID systems are typically short range.Usually the more secure the system, the shorter the range to preventeavesdropping.For Mifare cards 10cm is a long way I think students will have to swipe their tag past a detector to provethey attended. http://www.8051projects.net/forum-t11856.html 2009-01-08T08:27:59-08:00 ramdasi vaibhav Does reader detect tags around certain area of coil only? This is vital bcz i want it should detect tags of those students present in the class or sitting on benches at that instant.Bcz i want that rfid attendance should work behind the curtains ,i mean students shouldn't have to take any extra efforts to make attendance by coming in vicinity of reader,b'cz it will consume time and may create lil chaos in class. http://www.8051projects.net/forum-t11856.html 2009-01-08T08:27:59-08:00 Ajay well that is understandable but the thing is.. it create chances of false attendance in our language we call it proxy i hope you are getting my point.Its better to proceed with project idea instead of looking for modification in project idea..for students, little effort is not a big deal they are not so old yet hehe.. http://www.8051projects.net/forum-t11856.html 2009-01-08T08:27:59-08:00 ramdasi vaibhav Well your suggestion is good and practical too,but i want to reduce the time required to take attendance during each lecture....That means there is not any way to block proxies while using high freq reder,isn't it? http://www.8051projects.net/forum-t11856.html 2009-01-08T08:27:59-08:00 Ajay it takes not more than a second to mark successful attendance. I thnk just concentrate on your project implementation, later on you can find ways to add more advancements in it. that will be good i think. http://www.8051projects.net/forum-t11856.html 2009-01-08T08:27:59-08:00 ramdasi vaibhav Well,my project review and seminar is going to happen within few days.Plz help me . I wouid lik to know crystal clr working of circuit and the diff devices used.e.g. RFID reader, tags,real time clock ,database storage in EEprom,role of ucUse of ps2 kb,clock ic,up-down-enter-cancel switches