RS422 - 24V digital I/0 problem

[Churchie1]

Can any one help. I need to make a one-way Digital I/O connection between to devices. The output signal from device A is 24V (high). However The input device can only be configured to recieve TTL or RS422. TTL is 5V max(right?). Rs422 is 6V max (right?). If thse assumptions are right then I can't connect them directly (right?). What can I use as an interface between the two?
Thanks in advance, Churchie1

 

[geekEE]

Are you just detecting the presence or absence of the 24V signal How about a resistor divider? It doesn't get easier than that.

 

[Churchie1]

Thanks for the reply GeekEE. Makes sense but you will have to excuse my ignorance. I understand that I can select a (for example) 4K and 1K resistor and that I will then (with a 24V supply) get 4.8V ish across the 1K resistor. So as long as I keep the value of these two resistors high (at least 1K) then the effect on the current will be negligible -right?

 

[itsmoked]

Yes. Thats got it. Gotta be careful though, one slip and... or



Keith Cress
Flamin Systems, Inc.-

http://www.flaminsystems.com

 

[Comcokid]

I would also put in parallel with that 1K resistor a zener diode of 4.7 or 5.1 volts to give a little piece-of-mind. Something like a 1N5230B, 1N5231B . This will provide some protection on the TTL input.

 

[nbucska]

The TTL needs only 2V to sense HIGH-- I would design it for 3.5 ( midway between 2 and 5 ) and clamp it with a
4 to 4.5 V Zener and with a reversed Shottky to GND.

What is your input device ?(this determines the current and R values)


Plesae read FAQ240-1032
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