9 to 3 multiplex chips?

[mbeals 74]

I have a piece of equipment in my lab that uses rs485 for communication (master with single slave). The issue is that we have several interface cards, each with its own pin out. I'm contemplating building an auto sensing translator with a pair of 9 to 3 mux/demux chips with a micro that will run voltage comparisons across all pin pairs to map the pin out and configure the mux/demux with the correct mapping.

 

I know there will be challenges with line level conversion but does this seem like a reasonable approach? Can anyone recommend a 9 to 3 mux chip?

[nemui-kuma 8]

There is a 7400 series 16 to 4 mux chips, but i don't really know your requirements.

so If you need anything like this be sure to check out this list : http://en.wikipedia.org/wiki/List_of_7400_series_integrated_circuits

[mbeals 74]

Thanks for that list. Basically what I need is a way to route 3 arbitrary pins on a db9 to 3 arbitrary connections. Imagine laying out an rs232 chip a rs485 chip and a db9 on a breadboard. Now connect either transceiver to the db9 with whatever pin out you want with jumper wires. I want to do that reconfiguration in a chip.

 

The 16 to 1 selector looks promising, but I don't think it will take the full voltage swing of rs485.

[nemui-kuma 8]

Thanks for that list. Basically what I need is a way to route 3 arbitrary pins on a db9 to 3 arbitrary connections. Imagine laying out an rs232 chip a rs485 chip and a db9 on a breadboard. Now connect either transceiver to the db9 with whatever pin out you want with jumper wires. I want to do that reconfiguration in a chip.

 

The 16 to 1 selector looks promising, but I don't think it will take the full voltage swing of rs485.

 

the 4067 can be used with 15V supply max, there are specialized analog switches that has higher voltage swing, although the are very expensive, but you can always use a resistor divider before and an amp after.

The other solution is to use tiny relays, there are 3.3v actuation voltage telecommunication relays.

 

The problem is that most of today's digital logic ICs don't work above 5V, so you can either use very expensive specialized chips , use relays, or alter the signal in a way that you can easily handle.

[mbeals 74]

Looking at the spec, I believe I can drive the signals at 3V (or possibly 5) and not get lost in the noise floor, so I might not need to amp the signal.

 

So I guess the question becomes the best way to clamp the voltage down to between +-3V and how an analog mux will handle -3V. Are there any multiple channel voltage clamps in a single IC?

[nemui-kuma 8]

For clamping , just use diodes.(just google diode clamping).

A 3V signal only gets lost in the noise if there is a serious flaw in the system.

 

The 4067 has a digital ground, and an analog negative supply, it won't have any problems with negative voltage , as long as you supply a negative voltage rail to the IC.