sim900A dtmf tone detection

I Have sim 900A uart modem previously I used this model for project to send sms with Arduino. Currently I am trying to use this sim 900A uart model in my latest project where I want to detect dtmf tones but as far as I can see in the documentation there is no command to detect dtmf tones but to there is command to generate dtmf tones.

Is it possible to detecting dtmf tone in this model (sim 900a uart). Or I have to buy another device for this or I need to update framework of sim900a if so then how. How can I detect the current framework version.

Can I use 4g sim with this model as I only tested it with 2g till now?

well when i used to play around with the DTMF i used an ic called as “MT8870-1” , now i can see you want to do something based on tones, well you can simply connect the Audio output of the SIM900a, to the input of this dtmf decoder. (Im not sure if practically that would work, as we used the nokia phones) and then you can do what you want based on the output of it.
Ofcourse, you still need to connect the arduino through usart to the sim900A to answer the incoming call.

now to answer your another question,
Most of the 4G sims work , when i say most, i do not include the JiO simcard, as it doesn’t use the actual old school calling technology, it simply is more like a 4g internet and through internet the calls are routed. so, Vodafone, Idea, Airtel, Docomo, Aircel should work just fine.


Thanks parth,

i have used the ic method to detect the dtmf tones. but when we can detect the tone through sim900 module why use extra ic for same and connect audio jack.

for now what i understood reading from this site is i need to update my sim900a module framework as ideally it will be able to use AT+DDET command. i will try to update the framemwork and test it out.

thanks for the reply but i think i was not clear in my last post. i wanted to know if i place
a 4g sim in sim900a module then will i use the 4g network to connect or will it use 2g network to connect the mobile network.

thanks again


well i have not really looked into updating the gsm firmware, maybe @RaviPujar can guide you more better , but i always recommend people to first google thoroughly and then ask questions. you can give it a try and see if things are working according to the plan.

to answer your second question, no, your sim900 wont use the 4g data, it will still use the 2g data as that’s what it is only capable for. if you want to use the 4g data you may have to plan to upgrade the module to maybe sim7600 or some other variants.

Parth Temkar

I have video on my youtube channel on firmware update for SIM900, you can check it out. Try updating firmware only if you get error for the DTMF enable command.