max wire lengths

[spazmatron]

Is there a maximum length for the wires from either the din module to the core, or from the inputs (buttons/encoders) to the din module.

I want to have some inputs in a seperate case 5 to 10 feet from my main case.

Sorry if this has been asked before, I couldn't find it in the forum.

Thanks.

[pay_c]

Not really, the DIN just switched between 0 and 5 Volts, so the wire length is not so critical (it´s something different if we talked about AIN). *IF* you do get probs, you can either shield the cables and/or use a lower resistor value on the DIN (e.g. 4,7 k instead of the standard 10k ones). But as long as you are below 5 meters (=15 feets) you should be just well!

Greetz!

[Synapsys]

Hi,

I believe that you would have better success if you ran the wires for the buttons/encoders to the remote location rather than the connections between the core and the DIN module. MIOS scans the DIN shift registers at a relatively high frequencey (ca. 75 usec for all 128 inputs). As the length of the wires between the core and the DIN module increases so does the capacitance. The increasing capacitance degrades the signals and at some point the signals will no longer be reliable.

I agree with pay_c about lowering the value of the pullup resistors. The are two benefits to this. One, lower resistance  improves the signals as capacitance rises (i.e. improves the rise time due to a lower RC time constant). Second, lower resistance values help reduce interference from external electrical noise. The 74HC595 shift register chips can sink 25 ma which means you could lower the resistance down to about 200 ohms  without endangering the chips.

Shielded cable would also be advisable with the shield connected to ground at the DIN module end of things.

As is always the case, however, the best thing to do is just try it :)

Regards,

Synapsys

[spazmatron]

Thanks for the tips.

About the resistors, Synapsys says to lower by 200 ohms.  So that would be 9800 ohms I guess?

Pay c says 4,7 k.  Is that supposed to be 4.7, or 4 or 7 k.

I understand the concept behind lowering the value, but I don't want to fry anything.  I don't know much about the math of electronics, so any help is much appreciated.

Thanks for your time

[illogik]

hi,

About the resistors, Synapsys says to lower by 200 ohms.  So that would be 9800 ohms I guess?

no, synapsys says that you could go down to 200 ohms resistors without frying the shift registers, but this is just to indicate the lowest value you can take

Pay c says 4,7 k.  Is that supposed to be 4.7, or 4 or 7 k.

4,7k  is the same as  4.7k  (you say "." i say "," ;)) or to be exact >> 4700 ohm, another way to write it is 4k7

these values ar (i think) not calculated; so it doesn't really matter as long as they are above 200 ohm you can try out which works for you

but again only try this IF you have problems like pay-c said, maybe you don't have to change anything

cheers, marcel