Universal Telephone Interface with C8PDF

[lowrybt1]

You are correct. The person I tracked down is Kevin Horton. He was very much into the Votrax Speech System and was the person who obtained the VSL from an OSI 567 Board.

[lowrybt1]

One further request for assistance checking out functionality of a OSI 567 board....

When I received the board, one socket (U1A) that is supposed to be populated with a 7407 was empty. I found a spare 7407N and plugged it in. I gather there are different varieties of 7407. Based on the attached schematic, is there anyway to tell if 7407N is not a reasonable replacement. I can tell that the 7407 is in the vicinity of the DTMF generators and decoders.

Thanks for any insight.

OSI UTI-Votrax Manual March 1980_compressed_1.pdf

(213.71 KiB) Downloaded 621 times

[bxdanny]

But what you attached was not a schematic at all, just the parts-placement guide. The 7407N chips have "open-collector high-voltage outputs" (I looked that up). So they need pull-up resistors on all outputs. Without them, it isn't going to work right.

[Mark]

Looking at the full schematics you posted earlier, the 7407 is being used as an open collector driver for a couple of digital signals to the Honeywell DAA. I wasn't able to quickly locate any spec for that DAA, but the main difference I can see is some 7407 work with voltages up to at least 30V and other 15V. You could check the pull-up voltage on the DAA pins to see what yours needs, but if powered by +24V you probably need the higher breakdown voltage version. Open collector drivers pull the signal to ground and are passively pulled high, allowing interfacing between different logic levels or used in a multisource wired-OR configurations like the IRQ line in 6502 based computers.

[lowrybt1]

Thanks Mark. This is helpful. I wish I had taken electrical engineering in college. The DAA runs on +24V so if I understand correctly, I want to use a 7407 with high voltage open collector outputs.

[Mark]

Yes.
It looks like most of the plain 7407 should have a +30v tolerance so if you have one it should be fine. Otherwise here are two random sources:
https://www.jameco.com/z/7407-Major-Bra ... 49120.html
https://www.digikey.com/en/products/det ... 7407N/2960

[Mark]

I came across an interesting way to do modem-modem hookup via two Cisco SPA122 (or equivalent) VOIP devices. I'm actually using one for my home VOIP, and picked up another at a thrift store for less than $5 as a backup.

https://gekk.info/articles/ata-config.html

[lowrybt1]

Thanks for this. Very straightforward.

I'm getting close to another comprehensive test of the 567 board. After careful examination, I discovered that I had cross-wired two of terminals on the CBT connected to the 567. That's what I get for using the same color wire for 2 of the lines between the 567 and the CBT. I've got the right 7407 installed.