Yup all good. You might be interested to know I've built and exchange based on
this one but used an Arduino Mega instead of the solid state logic. This is the third exchange I've built based on the design and I think I've just about got it right this time. It works extremely well for pulse dial GPO phones but I have also added DTMF. From top left clockwise - first board is the power supply. Have done a lot of work on this to get rid of mains hum using capacitor multipliers for a 40v for the phones and 30v feed for the logic etc using commercial VR's to reduce the voltage where required. The 40v feed uses a simple Zener diode setup for regulation. Also on this board are the ad9833 tone generation modules and relays for call progress signals. Next board has a LM386 amp to drive the speaker to monitor calls (more of a diagnostic thing really) and the circuitry to connect an external line as well as external call ring detection. Next board is the source and destination relay arrays and the feeds for lines, 8 of them. Next board is the line pick up detection optocouplers, call bridging and a/c ringing relays, source phone pulse detection and destination phone off hook detection. The final board is the DTMF detection and generation side of things along with a simple autogain amp to help with reading DTMF codes. It also uses call progress detection to monitor calls, ie to detect call hang-up, ring cadance, that kind of thing on external calls.
Top middle is a 16x2 LCD display that shows whats going on. Ignore the one by the lamp that's a different project.