sundance-communications.com/forum Forums Other TDM Phone Systems 1A2 and Comkey Telephones & Systems Ooma home system

I bought an Ooma Telo for home use. It's currently connected to line 2 of my modified 1A2 system. It no longer uses K400E cards, instead I made my own circuit for line status and hold to I can accommodate standard non-A lead phones. The receive level of the Ooma is way too loud - about double of what my telco line is. I wonder if anyone else uses that system and has experienced that. Also - I can't access my Verizon cellphone voicemail remotely. No DTMF is recognized. If I call into my office from the Ooma line and obtain PBX dial tone, then call the cellphone voicemail I can access it. That tells me the transmit level is high as well. I can access other voicemail systems remotely directly from the Ooma line. I was thinking of making a pad, or attenuator of some sort. It would be with resistors in series with T & R, then some resistance in parallel. I'll have to experiment, of course the parallel resistance can't be too low otherwise it'll keep the line off hook, and series resistance must still allow sufficient current to the phone. I have a ticket open with Ooma, but don't suspect anything will be done based on my experience with the customer support chat session I had.

I made a simple circuit to get the audio level down a bit. Two 383 ohm resistors, each in series with tip and ring and 4.7k ohms in parallel toward the station side. There's enough current to operate 500 type network phones as well as modern AT&T speakerphones with electronic networks. The series resistors are from a Rolm 8000 line card. I still can't access the cellphone voicemail remotely.

By trying to re-invent the wheel, or in this case the 400-type line card, you have inadvertently introduced (I suspect) an impedance mis-match.

Why not use standard line cards, and make some electronic accommodation for the non- A-lead phones? It would seem to be easier that way, and you would them keep the 1A2 system prototypical.

One thing to remember with voip is dtmf tones aren't handled the same way they are on an analog pots line. The tones are not transmitted inband, they are sent in the sip channel and reproduced on the other end. I know with my sipura devices I can set the dtmf playback length. Sometimes they are played for such a short time (10ms) that equipment can't read them. I had to up the playback length on one of my sipuras connected to my valcom 1A2 intercom, so it could be accessed by users of the collectors network. It didn't like the real short tones. I currently have two OOMA telo's and I haven't had any issue with them, but they are a locked device and most settings cannot be accessed. I did finally figure out how to get precise dial tone out of them instead of their dopey musical DT they come with. As far as the line cards, I have had excellent luck with both ITT's 400E cards and Western's 400D cards. There is a modification that is easy to make on the 400D cards so they will ring up on bridged ringing such as comes from Voip devices. A simple loop current relay from sandman is all you need for a lead control on phones you can't modify. Sandman part #CID2N. Click here.

I used the lower resistance of the 400 line card relay which I think is about 40 ohms, and even put resistor across that to bring it down more while allowing the relay to close. So, the slight resistance on the tip side of the line is negligible. Formerly I made a circuit with an opto-isolator which when the line was idle, the high voltage put a negative bias on a NPN transistor keeping it turned off. When going off hook, the normal + bias in place turned it on activating the lamp relay. Unfortunately a lightning storm this summer took that circuit out. Also the hold circuit I use is unconventional, but practical. One of these days I may post the schematic for that. I no longer use the Elgin power supply, but that's a whole different subject.

The issue with not being able to access Verizon voicemail was resolved by Ooma, they had a tech from Brighlink, a VOIP carrier they use, call me and I explained the trouble. I knew the DTMF was regenerated, when I called the cellphone and pressed and held a digit from my home phone, I wouldn't hear the DTMF digit until I released the digit, and it would only be repeated for a specific duration.