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Thread: RC help

  1. #1
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    Default RC help

    hi there...

    for someone trying to make his first robot, with endless things to buy, a rf data link for 40 bucks sounds great..
    but being a very very new "newbie" and a mech student means that all that goes tangent.... can anyone help me and translate it for dummies like me?
    a tutorial would be really nice... can anyone tell me how u manage to send info on one freq ..(what i cant understand is that once freq of a signal is fixed u can only change its amplitude.. so how u can send info abt many more things???)

    and btw.. i also found this link.. tell what u ppl think of it..
    http://www.rentron.com/ruf-bot.htm

    mandar

  2. #2
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    Default

    hii mandar

    Facing much of same problem; being a mechie really makes ur going tough when it comes to makin your machine wireless. :?really dont know whether i can use FM modulation for controlling my machine as i have to transfer data from my PC(for controlling left and right motors) and not simple signals. RF modules are pretty costly!!

    really looking for someone who can come up with a solution that can really help ......

    regards

    mexx

  3. #3

    Default

    I shall try to give you a brief idea.

    I assume you are familier with, how digital data is transmitted betn two devices serially. Offcourse it's bit-by-bit, ie the transmitter sends 1st_bit, 2nd_bit, 3rd_bit...... last_bit. The tramsmitter needs to transmit only one bit of information at a time.

    mandar, you're right, if you fix the frequency you can do 2 things. 1) Change the amplitude between a high level and a low level or 2) Turn on signal and off. While doing this you are actually transmitting binary data in bit-by-bit.

    FSK(Frequency shift keying), ASK(Amplitude shift keying), OOK(On-Off keying) are the 3 main methods of transmitting digital data.

    In FSK 2 different carrier frequencies are used, one frequency to represent the binary ONE(called mark) and the other to represent binary ZERO(called space). Transmitter outputs these 2 frequencies according to the binary value to be transmitted.

    In ASK the frequency of the carrier is kept constant, while its amplitude is changed. A high amplitude carrier indicates a binary ONE and a low amplitude carrier indicates a binary ZERO.

    OOK is a type of ASK, in which the the presence and absence of the carrier is used to represent a binary ONE and ZERO respectively.

    Tell me if it's clear and then we'll see how to control the bot.

    Regds

    happy_99

  4. #4
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    Default

    i did get what u wrote...
    but guess that this is the easiest part of all...
    just one doubt.. not so imp i guess... suppose u have 2 consecutive high signals... how do u know its not a 1 high .. do u fix a time frame for each bit or do u revert back to some base freq or base state and then proceed?

    mandar

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    Administrator T-1000 vikas's Avatar
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    Default well

    There is a sync part sent before the singnal or datapacket ( like UART ) . i mean that you will be sending a 8 bit synchorinzaion signal before the message the sync part is mainly 0101010101 kind of signal . The uC then calculates the timing from this sync part and appropiately checks the messages at vaious points .. Simple right !!!

  6. #6
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    Default

    hii guys

    thanks for that nice tutorial.but the problem still prevails.....how to go for makin your bot wireless....and that too cheaply!!whether to use RF or FM?is it possible to use FM and still control both the motors of ur bot?how to interface tx/rx with comp. and bot??
    please do come up with a solution.....

    regards
    mexx.

  7. #7

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    mandar, you guess is right. For a particular baud rate there's a definite time frame(bit period) for each bit. The microcontroller scans each bit at the middle of this time frame. Some micros such as Microchip PIC, scan 3 times in this bit period and a majority detector circuit takes the value which is repeated twice or more.

    mexx, I guess, by RF u mean those readymade RF modules and by FM, those simple FM transmitter/reciever circuits. Both are basically same, but the readymade RF modules are tuned for perfect operation and are capeable of transmitting digital data. To interface these modules with computer, you jst require an IC (MAX232) and a few caps and offcourse you've to use a micro at the robot end. But if you jst need to turn on/off your motor(s), you can use some simple FM transmitter circuits coupled with DTMF IC, which's capeable of controlling 16 lines. A lot of such circuits are published in 'Electronics For You'. But if your robo has got some sensors and you want that data to be send to pc, definitely you require the RF modules. Vikas has suggested a circuit to do it urself, for < Rs.100, but I think it's not suited for newbies as it requires tuning, adjustments and all. My suggestion is, go for readymade RF modules, will not be as cheap, but you can use it for all your future robos(plug 'n play ;-))

    REgds

    happy_99

  8. #8
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    Default

    thanks a lot there... that puts things a bit better...
    but i still have my question unanswered.. . how do u make those ckts...
    ripping them off from somewhere is a way out but then there is no fun..
    is there nething u think i shud read up before i shud look to understand.. might make it easier for u ppl too..

    mandar

  9. #9
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    Default

    hii guys

    i think what mandar is asking is right......there must be some tutorials so that we do what we know and undrstand.....there is no fun in doing it blindly
    n happy,what if i dunno send any data from my bot....and just control the speed of both the motors in my bot by sending different pulses from my comp.

    regards
    mexx

  10. #10
    Administrator T-1000 vikas's Avatar
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    Default well

    In india we dont have many poeple using Rx/Tx modules so we usally have to improvise . FM is a good choice but requires a little tweaking with the circuit . I think ill write a short tutorial on this

    for building a custom rx/tx here is a nice link

    http://jap.hu/electronic/rf.html

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