I am planning to built a robot which can be controlled wirelessly. The robot should send data (temperature,photographs of places,etc) back to me which can be monitored on a computer. Can I use DTMF to achieve the purpose since GSM module is relatively expensive? If DTMF can be used then why GSM are more expensive.

 

If DTMF can be used then why GSM are more expensive.

GSM costs more becuse:
it has the RF section already built in
it can transmit at much higher bit rates than DTMF can


With DTMF you can transmit 4bits at a time, and I think transmitting 5 symbols per second is optimistic. That gives you 20 bits per second at most. that is 2.5 bytes per second, how long do you think transmitting a phtograph will take? For example a 640*480 image from a webcam could have 15-30kB with serious compression, that is 100-200 minutes to transmit one image.

 

Cant you use wifi?

I made a wifi remote control car using a FON.
I sent data through serial.

 

Is rf technology a better and economical option than DTMF? Which is better and why?

 

Depends how much data you need to transfer. If you need to send 10 digits of a phone number, dtmf is enough. For higher transmit speeds you need better technology.

 

do a search on MiWi, and ZigBee too, just some other options other than WiFi...