Forum: µC & Digital Electronics RedLab 1208LS I/O

von Sandeep Yadav (Guest)

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Hi there,

I hope everyone is doing well. I'm doing a small project using RedLab 
1208LS as IO. I have 8 digital outputs and 4 digital inputs. I have 
attached pin configuration in attachment. I'm using A0-A7 for outputs 
and B0-B3 for inputs.I have also programmed everything and it seems 
working only issue I'm having is with inputs. Further my explanation 
RedLab only works with 5V max. so if signal 2V-5V it will recognise as 
HIGH, if signal 0.8V-0V it will recognise as LOW and anything in-between 
.8V-2V will be ignored. My input signals are designed for 24V so I had 
to bring it down to 5V. I'm using 2 resistors 10k & 39k to turn 24V to 
5V but when I plug that 5V signal into B0 or B1 or B2 or B3 it won't 
show any input as once I plug that 5V signal it eats the all voltage and 
dropping it to 0. But when I use RedLab internal 5V supply as input in 
B0-B3 is shows input. So I don't know why it doesn't show when I plug my 
inputs that also has 5V (24V brought down to 5V using 10k & 39K ohm 
resistors) it won't show any input. I have tried everything but it 
doesn't seem to work and I stuck for weeks now. Anyone had similar 
problem or can help me sort out my issue will be much appreciated. I'm 
assuming low current could be the issue but don't get how it shows input 
when I use internal 5V (Redlab has 5V internal supply from pin 30) as 
input but wouldn't show when I plug in my input. I was thinking to 
attach 1208LS data sheet but I thought it would be too much to read. 
Please someone help me...Thanks in advance.

von Flemmy (Guest)

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Just a stupid idea here... But have you tried to verify your 5V "output" 
of your voltage divider? Does a scope or multimeter show 5V as well or 
is it just your theoretical value you expect?

Maybe something went wrong with your voltage divider, e.g. a short or an 
open connection.



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