Remote Controlling

[headcracker]

hey friends...

i am a telecomm student. i don't have much idea about latest technologies used in remote comtrolling.

i wanted to know, if sending a sms to a remote device like a robot, can be used to control it. i mean its motion n all. can it be controlled by sending sms to that device

 

[Papabravo]

Anything that can be controlled with a text string can be controlled with an SMS message. You might be shocked at the quantity one price for a cellphone module that you can experiment with. Unless there is a cheap cellphone with a serial interface you can get your hands on, or they start making cellphones with general purpose I/O on them, your going to have to be adaptable and resourceful.

 

[headcracker]

hey..thanks for that

but how to control things with text strings....i mean i don't know

 

[Papabravo]

You can start with a program that associates actions with individual characters. For example, lets say we want a program to control a PWM(Pulse Width Modulation) scheme. If our CONTROL_VARIABLE is a number in the range 0 to 100 and the characters '+' and '-' are used to change that number then we might have a program like the following.

while(1) /* Do Forever */
{
unsigned char c ;

  while(NO_CHARACTER_PRESENT) ; /* Wait for a character to show up */

  c = SERIAL_PORT_DATA_REGISTER ;
  {
    if( c == '+')
    {
      if(CONTROL_VARIABLE < 100)
      {
        ++CONTROL_VARIABLE ;
      }
    }
    else if( c == '-')
    {
      if(CONTROL_VARIABLE > 0)
      {
        --CONTROL_VARIABLE ;
      }
    }
    else ; /*Do nothing -- throw the character on the floor */
  }

}  /* End while(1)  */

Naturally this code fragment would be included in some function and there would be some initialization that is not shown, but this should give you an idea. From single characters it's not much of a stretch, to work with longer strings. Programs which process strings very well, are compilers and assemblers. You could learn a great deal from picking one apart.

 

[headcracker]

thanks mate....
i thought it wud be really diff.....
u made me think i can do it

 

[ThermalRunaway]

The hardest part is getting the information from the SMS module or mobile phone. If this is a one off project, it'd definately be cheaper to buy an old mobile phone which includes a serial port off Ebay and use that. I'd recommend a Nokia, but that's only because I personally find Nokia phones very user friendly and I have the command set for them to hand ;-)

Take a look at the attachment which details the Nokia command set for serial communication with it. You'll be particularly interested in the SMS commands I think

Brian

 

[adaminc]

Another problem is the fact that most carriers queue up SMS messages, so it might not be instant when trying to control, I had an idea like this once, except I was going to use series DTMF tones to control, instead of an SMS message. But I never followed through with it.

 

[ThermalRunaway]

Yes that is an issue with SMS, although generally the performance of the SMS service in terms of delivery times is pretty good provided that both the sending and receiving end have good signal. You do get the odd occasion where a message gets held up in processing, so as you say if the delivery time is critical then SMS is not good enough for this application.

Adaminc mentions DTMF though - this could be used instead to carry messages I guess. There aren't enough DTMF codes for the full alphabet (I think there's 15?) but I suppose you could use each key three times much in the same way that text messaging actually works. One DTMF key gives the letter A, two of that same DTMF keys gives letter B and so on. I think that sort of project would have to be microprocessor controlled, and there'd be quite a bit of program planning to get it done, but sounds like an exciting project to me!

Brian

 

[Paul Obrien]

If the robot is close enough <100m you could try Bluetooth, there are some cheap bluetooth moudles around and the output is serial.
DTMF decoders usually require 40mS of valid tone with a 40mS interdigital pause or 4bits/80mS a tone being 1 of 16. Two digits make 8bits or 160mS for 8bits of data.