Anyone know about the UK telephone system? - Page 1
Forum section: electronics / general

author: icon
author_rank: Regular Contributor
timestamp: August 09, 2013, 08:04:06 pm
content: HiI want to connect a 'real' bell to the phone system so that it acts as a ringer. I have a bell to hand, but it turns out that it's actually intended for DC operation. It's this onehttp://www.samhallas.co.uk/repository/n_diagrams/0000/N656.pdf. I'm wondering if I can modify it in some way to operate with AC? I'm hampered (apart from by my general ignorance) by the fact that I don't know exactly how ringers operate on phone systems. I've gleaned that it expects the ringer to be 4kohms and this one (with the coils in series) is 2k.Am I on a hiding to nothing, and I'd be better off getting a different bell?CheersJohn

author: SeanB
author_rank: Super Contributor
timestamp: August 10, 2013, 08:14:06 am
content: Connect it as shown in the diagram for single stroke series operation ( bottom connection of terminals 2 and 3 and the optional wire in the diagram) and then connect it to the phone line with a series capacitor of 0.47uF to 1uF with a voltage rating of 250V. Capacitor must be a film unit, polyester or polycarbonate.This is not really allowed but most central office lines ( not a PBX or a fibre adaptor as they often do not have the drive capability) will drive it with no problem. It will appear to the phone company as a 2 REN ringer, and they will allow up to 4 ringers anyway, and most modern ones are 0.1 anyhow.

author: icon
author_rank: Regular Contributor
timestamp: August 10, 2013, 08:37:16 am
content: Brilliant! Thanks for that - I'll have a root through the capacitor box.John

author: djsb
author_rank: Super Contributor
timestamp: August 10, 2013, 09:10:41 am
content: Join this yahoo group (Remote Access Terminal using PIC micro's)http://tech.groups.yahoo.com/group/rat_ring/It has details of how to connect to the UK network in the files section.The group is inactive but the information might be useful.David.

author: icon
author_rank: Regular Contributor
timestamp: August 11, 2013, 08:50:09 pm
content: Quote from: SeanB on August 10, 2013, 08:14:06 amHmm. How critical is the capacitor value? I could only muster 2x 220nF which I wired in parallel (making .44uF?). I can see the clapper arm twitch, but it doesn't have enough oomph to reach the bell. Would a bigger capacitor help? I had a look in an old dial phone with a bell - that has a whacking great 1.8uF capacitor.CheersJohn

author: digsys
author_rank: Unknown
timestamp: August 11, 2013, 10:50:21 pm
content: Quote from: iconYes, doubling the capacitance will help, but if that doesn't work you may just have too much loss or load. As Shawn said,don't go over 0.1uF. A much safer method is to use an AC opto-coupler (or make one with 2 back-back DC ones). Naturally,limit the LED current to a few mA and add a protection mov. Then on the Transistor side, use a plug pack for power and anyringer / lamp etc you want. No limits then to what you can do.

author: richard.cs
author_rank: Super Contributor
timestamp: August 12, 2013, 12:12:49 pm
content: They make bells with an a.c. coil of the right impedance for direct connection and mechanically resonant at the ringing voltage. They're intended for this application and I'm pretty sure you should be able to pick one up from ebay or similar.