Working with wire-Telephony? Here is a project that I conceived when I was working with Wire and Wireless Telephony, the Hobbyist Central Office simulator, I simply called it Hob-COS.
Design Idea
The design idea of the Hob-COS is based on FCC (Federal Communication Commissions) preferred simulator to test Part 68 rule to simulate the impedance as seen by the Telephone when connected to the Central Office (CO), see Figure 1 below
FCC rule Part 68 provide a uniform standard for the protection of the network (AT&T) from harm caused by connections of Terminal Equipment (TE). The purpose of the FCC rule is to protect telephone network from harm. Nowadays, FCC Part 68 is called EIA/TIA-IS968.
In Europe, they have harmonised standards called CTR21 (Common Terminal Regulation 21) or TBR21 (Technical Basis for Regulation 21) and TBR37 (EN301 437)- Terminal Equipment attachment requirement for Pan-Europe approval for the connection to the analogue PSTN. The updated standard is the ETSI TS103 021. Please visit www.ETSI.com
We’re not in the USA, but our Telephone System is based on USA Standards, line impedance is 600 ohms, I would say it rather complicated, I mean some network requires 900 ohms and the Caller ID, that is a challenge with different protocol from different TelCo (Telphone Company). It is very unfortunate that, I don’t have a copy of the Philippines PSTN interconnection – what I mean is, the standard for minimum requirement for interconnection to the Philippine PSTN. Please! I say please, let me have a copy in case you have or obtain one.
Central Office Services
The Central Office (CO) in the Telephone Systems provides the following basic services to the telephone subscriber :
– DC Telephone power supply
– Ringing Signal
– Dial Tone
– Busy Tone
and special services like;
– CID : Caller Identity Delivery also called CLIP (Calling Line Identity Presentation)
– CID-CW : Caller Identity Delivery on Call Waiting
– SMS : Short Messaging Systems — it is also called Text Messaging
– VMWI : Visual Message Waiting Indicator
– Metering : Also called Toll counting
The functions of each service are described shortly :
The Project Real Aim
The project real aim is not for replacing the Standard Equipment used in real R&D job or Manufacturing for Telephony, but it was designed for 2 thing with common denominator – Learning or DIY Learning in Telephone on 2 branches
(1) Telephone / Telephony hardware and software
(2) Microcontroller Programming and hardware
Again, I emphasized the DIY Learning, which simply means “Do-It-Yourself Education”, as, education institution in the Philippines which I approach do not like the idea in the name of CALASS – collaborate – avail – learn -access – share – support (well of course, if any college or University would like this idea for the Philippines, let me know), so DIY Learning – a self study and self booster is the key.
When we were studying Telephony in the University, we need to consume a lot of brain power to imagine things. I believe, with this project real-world stuff can be realized, like the DTMF – frequency and waveform or even decoding it and how it became a signalling, line current, ringing voltage, dial tone, busy tone and probably will explaiend why there is a -48Vdc on the telephone line….. maybe!
Solution
my Hob-COS is driven by an intelligent Micro Controller based on the Intel 8051 core – the standard 8051 core configuration from ATMEL, AT89S51 or AT89S52. The program was first written in Assembly Language and alter on, I port it into Basic Language.
Those are the things I can share for now, the Hob-COS indeed serves its purpose as DIY learning booster. I can think of now to design a subscriber Telephony driven by a Micro Controller – what do you think?
Cheers!