dry contact reading check if ground is on pin

Forum 2005-2010 (read only) Hardware Interfacing
1

Hi There
My gsm communicator project for my alarm systemt is already working but i have problem now...
The output that gives information if the alarm is armed or not don't pass voltage, pass ground, i mean when the alarm is off that connector (out2) has ground i can measure 13v on the alarm vcc connector and with gnd on this connector, when the alarm is on the gnd is cutted from this connector. so i need to "measure if Gnd " is present.. ? how can i do this ?

small picture to see if i i can explain better what I'm saying.
thanks
I have no control on what makes the ground on/off..

720×600 64.9 KB

thanks a million.

2

Simply use a pull up resistor to 5V, then when it is a ground there will be a logic zero (LOW), no ground will be a logic one (HIGH)

3

where do i connect the resistor to ?
:-[

i'm using this code
pinMode(armpin, INPUT);
digitalWrite(armpin,HIGH);

i read that this will activate the internal 20K pullup resistors is this the same thing ?

regards

4

where do i connect the resistor to ?

From the arduino input to the 5v line.

this will activate the internal 20K pullup resistors is this the same thing ?

Basically yes

5

hi,
i only have reading of 1 if i disconnect the pin from arduino...
when my alarm system cuts the ground it continues to read 0 with ground or no ground...

strange.. i will so some debugging but i have the system already " production" so i have to do it with more attention...
now i'm always checking zones i want to check if its armed or not to ignore zone checking when disarmed (details)..

thanks

6