 Notice. New forum software under development. It's going to miss a few functions and look a bit ugly for a while, but I'm working on it full time now as the old forum was too unstable. Couple days, all good. If you notice any issues, please contact me. |
Forum Index : Microcontroller and PC projects : 8-Station intercom for $29....
| Author | Message | ||||
Grogster Admin Group  Joined: 31/12/2012 Location: New ZealandPosts: 9610 |
Well, this is really a PABX, but when I went looking for a simple intercom that could have about five stations on it, it was FAR cheaper to just install a basic PABX and use bog-standard phones for ten bucks a piece(or so).   $30 8-Station PABX I should like to state at this point that this unit will NOT be Telepermitted for use on the New Zealand(Telecom) telephone network, nor the Australian(Austel) network either I would think. Having said that, and provided you don't bother connecting a trunk line to it(an outside phone line) and just use it as an intercom, the price is just too good to NOT get one to play with - so I have.  It seems to have a quite good feature-set too, for that thirty bucks. Amazing. The unit does not state what voltage it wants, so I asked them, and it is a 220v AC powered unit. Naturally, one of the first things I will be doing with it, is cracking it open to examine it for compliance before I use it for anything. Intercoms tend to be a party-line arrangement, meaning only two stations can be talking to each other at any one time, whereas with a PABX, you could have a couple of different stations talking to other stations all at the same time. This company also does much bigger PABX boxes, this is just their little baby. I was about to spend up to a couple of hundred bucks to make a five-station intercom, but hell.....for this price...... Smoke makes things work. When the smoke gets out, it stops! |
||||
MicroBlocks Guru  Joined: 12/05/2012 Location: ThailandPosts: 2209 |
For $30 it is even a good deal to rip out everything except aybe the power supply and use it as enclosure for home automation. I am curious how it looks on the inside. Microblocks. Build with logic. |
||||
| Grogster Admin Group Joined: 31/12/2012 Location: New ZealandPosts: 9610 |
I will post photos and a electrical compliance report as soon as I get my hands on it. I selected AliExpress Standard Shipping, which normally gets to me in just over one week, so watch this space.(thread!) I can't get over the price. As I say - this company does a whole heap of other PABX's up to about 64-extension, so they obviously know what they are doing in that respect and are not just a one-off type thing. Life expectancy on a $30 PABX will probably come into question, but still - can't get over the price.  Smoke makes things work. When the smoke gets out, it stops! |
||||
| Volhout Guru Joined: 05/03/2018 Location: NetherlandsPosts: 5089 |
It is an absolute bargain for that price !! Still when adding the 5 pieces of 10 dollar phone..... I had something similar to THIS in my house for years. small box with speaker (that also acts as microphone) and button  You don't need to ring first, just say the word.. and you are heard everywhere in the house. Volhout PicomiteVGA PETSCII ROBOTS |
||||
| Grogster Admin Group Joined: 31/12/2012 Location: New ZealandPosts: 9610 |
I hear you on the cost of the phones, but I dear-say I can rustle up five or six old spare phones that still work from the workshop mess, then I won't even need to buy cheap phones. ..... A quick look in the other messy workshop room has revealed two phones with cords wrapped around them, and two new phones still in boxes(cheap ones). I only need to find one more. Smoke makes things work. When the smoke gets out, it stops! |
||||
CaptainBoing Guru Joined: 07/09/2016 Location: United KingdomPosts: 2170 |
A bog standard PABX using PSTN (copper wires with one speech path per pair) can be made compatible with any nation by using them with a PSTN to VoIP converter module (and having a VoIP supply) then routing calls over the internet. Something like an OBi110 would convert this a treat but there are many others. |
||||
| Grogster Admin Group Joined: 31/12/2012 Location: New ZealandPosts: 9610 |
Photos of inside and outside:     Transformer based PSU, which is interesting these days. Green-Black-Green winding is 25v CT White-White winding is 82v, which is a little higher then I was expecting to see(around 50v or so) for what I expect is the line voltage. Switch it on, and it worked with no explosion, so that is a good sign. I will hook up some phones to it later. Right now, I need to be somewhere else. Smoke makes things work. When the smoke gets out, it stops! |
||||
Andrew-L Newbie  Joined: 30/11/2017 Location: AustraliaPosts: 4 |
It's likely that the 82V @ 50Hz is being used as the ring signal. This would explain why they aren't using the expected switch mode power supply as they want the 50Hz mains frequency. Also typical of low cost devices is that they use a lower line voltage anything from 12 to 24V DC where as the PSTN uses a 48V DC (Nominal) voltage. If you have time can you measure the line voltage and the ring voltage on one of the lines without a phone connected. I would be interested to know what you find. When a phone is off hook, the voltage is typically around 8V for an electronic phone and 4V for an old rotary dial phone. I expect that the PABX will not work with old rotary dial phones as it will only decode DTMF signals. This should not be a problem as most people don't want to use old rotary dial phones unless they are a telephone collector. The ring frequency of PABX systems was typically 20 to 25 Hz. It looks like excellent value for money. Do it once and do it right. |
||||
| Grogster Admin Group Joined: 31/12/2012 Location: New ZealandPosts: 9610 |
Finally got around to playing with this PABX a little. Yes, this PABX is DTMF only so says the manual. I fully expected as much. Voltage on ext 601 with no phone connected is 31.9v DC, rises to about 65v AC when the ring voltage is on the line. This is measured with my multimeter, which might not be giving accurate readings for the ring voltage, as it is only there for about one second. This PABX has a two-ring alerting as here in NZ, Australia, England etc. It is not single-long ring like America. EDIT: Oh, and I forgot to mention - the line voltage drops to 7.7v when the line is looped by the phone(off-hook). Smoke makes things work. When the smoke gets out, it stops! |
||||
 Print this page |
 |
The Back Shed's forum code is written, and hosted, in Australia. | © JAQ Software 2025 |
