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Help me , running long cables ...

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rishi254

New Member
Hello Sir

I have a project to log the keypresses from an hall of 60m X 50m area. There are around 500 switches in this area(actually there r 500 users sitting in this hall, each table has one toggle switch,reset switch).

Tables are arranged as 10cols X 50 rows.

I was thinking for a simple matrix logic as its extremely simple and would be cost effective in terms of cabling costs as well as other hardware required.

I have a requirement of running 60 m cables with ttl signals.Is it possible with using BUS Buffers/transreceivers?

ON the computer end i will use 60 bit digital I/O board and write the software which will scan

rows and columns continuosly.

Will be feasible or there is any better alternative...

Please , can u suggest me on this.

Thanks alot
Best Regards
Rishi Bhanot
 

Nigel Goodwin

Super Moderator
Most Helpful Member
rishi254 said:
Hello Sir

I have a project to log the keypresses from an hall of 60m X 50m area. There are around 500 switches in this area(actually there r 500 users sitting in this hall, each table has one toggle switch,reset switch).

Tables are arranged as 10cols X 50 rows.

Please , can u suggest me on this.

Thanks alot
Best Regards
Rishi Bhanot

How about using micro-controllers?, personally I would use PIC's, but any would do just as well. Use one PIC per row (50 in all) scanning the 10 desks in one column. Each PIC would need a serial input and a serial output - link the first PIC serial input to the serial output of your computer, and the output of that one to the input of the next. Chain all the PIC's together like this until the last one, connect that one's output to the serial input on the PC. Each PIC would have it's own unique address, 1-50 would seen nice and simple - to interrogate a column send a data packet from the computer including the address of the PIC - the first PIC reads the command, checks if it includes it's own address and otherwise passes the whole data packet down the chain to the next PIC. This continues down the chain of PIC's until the one with the correct address receives it. This PIC then reads all it's keys, assembles it's own data packet with the results (including it's own address) and sends it on down the chain until it reaches the PC.

This keeps all long wires at RS232 levels, so should be OK, it sounds fraught with difficulties running all those long wires from a TTL port, even with buffers.

Depending on how you need to run cables the costs could even be lower than your first thought, and you wouldn't need any extra board in the PC.
 

kinjalgp

Active Member
Nigel Goodwin said:
This keeps all long wires at RS232 levels, so should be OK, it sounds fraught with difficulties running all those long wires from a TTL port, even with buffers.
I would like to clear one point. RS232 is documented to work properly upt 15m only. At low baud rates distance can be increased but I don't think it will go upto 50-60m. Use RS485 for longer distances upto 1.2km
 
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