Open Source SX Keyphone Project
william chan
Posts: 1,326
Sometime ago we said we wanted to develop a keyphone system based on the SX.
Here it is in ExpressPCB format. ( See attachments )
The board is now sitting on my desk. It is truly as sight to behold !
2 lines, 4 extensions only, yet more than a hundred resistors.
Any comments and ideas?
Anybody wants to help us develop the firmware for this monster?
It has to be in assembly language. ( I don't know SX/B )
How its supposed to work:-
The SX52 will sample voice from one port ( line or ext ) using software ADC and then play it on the other port on the fly using PWM.
This reference design covers
1. DTMF Detection and Generation
2. Ring Detection for lines
3. Hook and Flash Detection for Exts
4. Ring Voltage Generation
5. Power Failure bypass to Ext1 and Ext2
6. Hybrid circuits to reduce echo
7. Serial Connection to PC for Call Detail Dump
CallerID snoop not included cos we have run out of pins.
Have fun.
Here it is in ExpressPCB format. ( See attachments )
The board is now sitting on my desk. It is truly as sight to behold !
2 lines, 4 extensions only, yet more than a hundred resistors.
Any comments and ideas?
Anybody wants to help us develop the firmware for this monster?
It has to be in assembly language. ( I don't know SX/B )
How its supposed to work:-
The SX52 will sample voice from one port ( line or ext ) using software ADC and then play it on the other port on the fly using PWM.
This reference design covers
1. DTMF Detection and Generation
2. Ring Detection for lines
3. Hook and Flash Detection for Exts
4. Ring Voltage Generation
5. Power Failure bypass to Ext1 and Ext2
6. Hybrid circuits to reduce echo
7. Serial Connection to PC for Call Detail Dump
CallerID snoop not included cos we have run out of pins.
Have fun.
Comments
▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔
engineer, fireman, bowler, father, WoW addict [noparse];)[/noparse]
I normally use Eagle schematic capture and board layout (www.cadsoft.de), and Advanced Circuits in Colorado USA to do my prototypes. For a new project where I need just a few boards, I installed Express PCB and Schematic to see how it would compare, because Express PCB is cheaper than Advanced for the 4 board ProtoPro service.
Since I now have it installed, I took a look at your circuit. Pretty dense layout. [noparse]:)[/noparse]
I think you might have some issues related to no bypass caps close by the SX52 and not hooking up all the power and ground leads as well.
Perhaps this is why your SX is showing extreme sensitivity to electrical noise?
▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔
MRC
The current SX Keyphone design has failed due to a few reasons, especially
1. Sound quality is not good enough.
Even a single bit error in the software ADC causes unacceptable background noise. ( like TV without any tuned channel ).
2. Mechanical Relay sparks causing some instability in the execution of the SX processor.
We have abandoned the "record and play on the fly" concept and now have changed to a "2 analog bus" concept.
We have revised the circuit design for Version 2 and will be posting the new design in this forum very soon.
▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔
www.fd.com.my
www.mercedes.com.my
Here are the Shematic and PCB files in ExpressPCB format.
There are a lot of changes (improvements) compared to V1.
Some of the major changes are :-
1. SX52 (EOL'ed) has been replaced with SX48 and SX28. This is due to more pins required on a "bus" system.
The SX28 now acts as a "bus master", controller deciding which Ext is allowed connect to the bus.
2. Twin Analog bus design allows 2 pairs of conversation at any one time.
3. All Mechanical relays (including ring injection) have been replaced with solid state relays for better relaibility and low current consumption, except for 2 relays used for power failure switch-over.
4. Power Adapter required is now only 12V instead of 24V to save on costs. ( 12V Adapters are more common and cheaper )
5. Almost all Gnd and Pwr pins on SX48 are now connected, and closer bypass capacitor added.
6. Bottom ground plane added under both SXes in hope to improve immunity to external sparks.
7. Ring signal generation transformer is now placed off-board.
8. Six twin solid state relay ICs added for bus interfacing. One op-amp relay removed ( no longer required )
9. Hybrid Circuits removed. Board size still about the same.
Good Luck.
▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔
www.fd.com.my
www.mercedes.com.my
10. All 100K resistors are now using 0603 SMT to save board space. No silkscreen b'cos all are 100K.
11. 3 holes added for screwing / securing board to plastic casing.
12. All LEDs now aligned for better asthetics
13. Serial LCD interface (used for debugging) moved to a better location.
Anybody got any contacts in China or anywhere else cheap to make a plastic casing for the product?
▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔
www.fd.com.my
www.mercedes.com.my