XBee (S2) and Texecom Premier 24 Digi Ouput Pins

[ilnli]

Hi,

I have an XBee Series 2 and I was trying to detect an input from a signal which was 12v, so I used a voltage divider with R1=220k and R2=24k, I checked the output voltage with multipmeter and it was 1.2v, which is what XBee S2 input pin is meant to get, however the XBee was not able to detect that input, could you please tell me why was it? could it be because the output current (Io) from the voltage divider was so low that it couldn't detect it? if so what register values should I use.

Also my second question is what if I want to power XBee from the output of that voltage divider, what register values should I used if I am to power it from the same voltage divider?

Basically I want to use XBee (S2) to get power from a Texecom Premier 24 alarm system, and also want it to read the status of the output pins (digi output) and send signals to a remote server wirelessly, but since XBee data input pins cannot read 12v signal which is why I had to use a voltage divider but still it was not been able to detect the signal, which is why I'm thinking may be the register values I used were not the correct ones for this setup.

I'll really appreciate if someone could help me with this, as I seem to be getting no where on my own because of having very limited knowledge of electronics

Thanks

 

[secureiam]

Not familiar with the device, have you tried there support forums, someone on here may be familiar with this unit, but there are support forums specifically for the device your trying to use?

You say the voltage is correct, and what happens when you activate the Output?

The input has 1.2V to it, but it will only do something once the state changes, so does the state change need to be?

does the unit have enough power to power it.

 

[bernardgreen]

VIL Input Low Voltage All Digital Inputs - - 0.35 * VCC V
VIH Input High Voltage All Digital Inputs 0.7 * VCC - - V

If the supply voltage ( VCC ) was 1.7 volts then an input voltage of 1.2 volts would be correct ( 1.2 = 1.7 x 0.7 )

With a supply voltage of 2.8 volts the minimum high input voltage is 0.7 * 2.8 = 1.96

 

[ilnli]

hi

Does VIL mean that if the input receives voltage between that range then it would be considered as zero and similarly from VIH does it mean that if the voltage received on that input are in that range then it would consider them as high?

From VCC does it mean the required voltage on which XBee normally runs? XBee runs on 3.3 volts.

What is source impedance and do I have to worry about that?

Thanks

 

[bernardgreen]

Any voltage below VIL will be read as logic Low

Any voltage above VIH will be read as logic High.

Inputs should not be taken below 0v or above Vcc

Input impedance is normally very high, the input current is unlikely to be more than a few micro-amps.

 

[ilnli]

Hi,

Then it sounds like the voltage divider set-up I had should work, but it didn't, I'm completely lost, why it won't work.

Thanks,

 

[bernardgreen]

You said the voltage divider was producing 1.2 volts.

The minimum voltage for an input to be read as High is 0.7 Vcc

If Vcc is 3.3 volts then minimum voltage for a High input is 2.31

Then add 10% to avoid noise related problems so change the voltage divider to put a 2.5 volt signal to the input.

 

[ilnli]

Hi,

Thanks, this is really helpful, I feel that I'm now equipped with the information I was missing before, I'll give it another try thanks.