making a call blocker
by Anne Macedo
So, my dad still have a landline, in 2022. And it’s being spammed with robocalls.
It’s so annoying that I decided to use a Raspberry Pi as a call blocker. For that, I need to play with an USB modem!
Call blocking solutions
I’ll keep them out of scope to be honest, since they are their environment on their own. Links for the tool that I want to use is on [1].
To make it work, I figured out I needed:
- a Raspberry Pi
- an USB Modem (I bought a Trendnet Tfm-561U)
- a splitter
You’ll have something like this (I hope Jekyll doesn’t break it :( )
phone --------- |
|--- splitter --- my isp router
usb modem --------- |
Now that I have everything, here’s the problems.
Caller ID… doesn’t work!
In order to check if the telephone is ringing, you need a tool with a very interesting name… a name that Brazilians can’t read without laughing.
sudo apt install cu
That’s the name of the tool, cu.
Anyways, I recommend running cu on tmux, since it holds your tty. You can’t exit cu.
Also, I needed to change my user to the dialout group.
sudo usermod -aG dialout pinkiepie
And them start cu attached to /dev/ttyACM0. By making a call, it should show up the RING and the caller id, right?
cu -l /dev/ttyACM0
Connected.
RING
RING
No caller id :(
I need to figure out two things:
- does the modem support caller id?
- does it support DTMF or FSK?
- do my landline use DTMF or FSK?
I’ve bought a DTMF to FSK converter anyways. :money-with-wings:
And also need to find my modem’s chipset.
Finding the modem’s chipset
You can basically run lsusb to get the VID:PID, but you can get the chipset model from cu
cu -l /dev/ttyACM0
Connected.
ATI3
CX93001-EIS_V0.2002-V92
Found out about this on [2].
lsusb tells me it’s a Conexant. From the Trendnet Tfm-561U datasheet, it says it supports DTMF.
I tried enabling VCID, and it says OK, but nothing shows when it rings.
AT+VCID=1
OK
Dialing
On the same forum [2] someone suggested using ATDT for dialing. This guide [3] teaches how to do this.
It’s basically like this:
ATD+55yyxxxxxxxx;
OK
It says ok, but doesn’t ring my cellphone.
Ringing without DDD works!
ATDT xxxxxxxxx
It was nice messing up with this, but the DTMF/FSK converter should arrive on monday. Hopefully no one will call this weekend.
To be continued.
References
[1] Call Attendant GitHub [2] Need some guidance on setting up Caller ID Feature [3] 11. Trying Out Your Modem (Dialing Out)
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