This part came off a different board I had. The board below.
This Aleph security system board can be connected to a phone line and controlled by DTMF tones. It also has an R6501Q just like this SBC on tindie and a digitalker that one day I’ll get going. The DTMF tones were received by the Mitel MT8870CE and not intending to use this board whole I decided to spin it off onto its own standalone board.
This board combines some of the parts from the Aleph board, some information from the schematic for the example circuit, and some of my own labeling and breakout pins. I haven’t actually gotten to test the ting yet, but if anyone needs a design I think this will work for connecting to a phone line directly.
This is another example circuit with values for connecting this chip to a phone line. It’s still useful considering these chips are available at the electronic goldmine to this day. Not the same package, but changing the footprint on the board is no big deal. There’s also something else interesting about this one.
This one’s been decapped! From Reddit, Lord_Nightmare says: It makes sense that the chip is split into two halves like this: the MT8870 is a combination of two earlier chips used as a pair (used, among other places, in the DECTalk DTC-01): the MT8860 DTMF Decoder (presumably equivalent to what’s on the left side of the MT8870 decap) and the MT8865 DTMF Filter (presumably equivalent to what’s on the right side of the MT8870 decap).
That’s it for now, the board is up on github here and if I get around to using it I’ll post something on this blog.
Evan's Techie-Blog 
January 1, 2024 at 5:19 pm |
Interesting! I used to work for telecom companies.
Dumb question: It’s a little hard for me to tell (vision issues) but it looks like you went mostly vertical with your resistor/diode mounting. Just a S/W dummy (that is, S/W engr) here thinking about getting into H/W and PCBs, but is there a good reason to mount vertically? I mean, it seems like there’s space for horizontal and wouldn’t this be safer? Maybe for heat dissipation?
Only other thought is on the phone connection. This is, of course, application dependent, but pass-thru maybe? Otherwise it ends here (analog anyway, you have the digital interpretation to continue on).
January 3, 2024 at 1:10 am |
The mounting was mostly arbitrary, I tried a bit to make the board smaller and to have more allowance for different sized parts to be fitted. A pass-through is a good idea since this does end the cable how it’s designed. I didn’t really push the boundaries with this design like I did with the z80 plcc adapter, it was just to get the components on the board in a way that would work. At this size the boards all cost the same (or nearly so).
January 16, 2024 at 10:19 am |
[…] The board is on GitHub here and more in the blog post. […]
March 21, 2024 at 9:14 pm |
I am wondering if you ever got to use this board. I was thinking about making one of your boards for a dial in phone synth project.
March 21, 2024 at 8:20 pm |
I did not, but I can probably test it tomorrow and let you know how it works. And don’t have boards made, let me send you one of my spares
March 23, 2024 at 11:45 am
WordPress is making it hard for me to comment btw. I no longer have a wordpress.com account but forces me to try and login with a closed account.
So if you are able to see the email address in my first comment please reach out and I will get back with you on Monday.
March 23, 2024 at 3:11 pm |
[…] while back I showed off this board, but I never got around to testing it. Now I have and it works great. There are a couple things to […]