I am using a SC2345 &SCCAI04, where can I get the +5V for my sensors?

[Druesedow]

I need to get +5V for a pressure sensor and infrared sensor, but I am unsure of where to get this power on the SC 2345 or the SCC AI04.  Both sensors have 3 wires, voltage input, voltage output and ground.  Can anyone explain to me how to connect these correctly to the SCC AI04?

Thanks,

[Raajit_Lall]

Hi,

Could you tell me what kind of sensor this is.  I am not able to understand whether you want to output 5V to the sensor (like an excitation voltage?) or if the sensor has a 5V output and you want to read that.  The Vout and Ground should be easy enough to connect to the modules.  However, is the voltage out where the excitation voltage need to be provided?  If you could give us a data sheet or what the vendor of the sensor is, that would help.

Thank you,


Message Edited by Raajit L on 03-21-2008 12:29 PM

[Druesedow]

I attached the PDF for the Infrared sensor.  The Pressure sensor has the same wire configuration.  You are right that the Vout and ground are easy enough to connect to the module.  I just have another seperate wire that needs and +5V excitation voltage.  I found a +5V supply on the SC 2345 connector block (terminal 14), but I need another +5V for the pressure sensor.  If I put both sensors on the same +5V excitation voltage the error in the signals increases dramatically.

Thanks,

[Raajit_Lall]

Inherintly, the AI04 will not be able to provide an excitation voltage.  The +5V pin that you see on the 2345 is a constant supply of 5V and not an excitation voltage. 

You mentioned

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If I put both sensors on the same +5V excitation voltage the error in the signals increases dramatically.

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Does this mean that if you use just one sensor, it seems to be working fine?  If that is the case, there might be a division of the voltage taking place from the 5V pin.  I see a Vcc Vo and a GND pin on the sensor data sheet.  I could not find anything that says it is an actual excitation voltage.
 
This might be why that 5V pin works if you are using just one sensor.  How are you connecting both the sensors to the 5V pin?  I suspect some kind of grounding issues.  If you use an external power supply and connect that to the 5V pin of the other sensor, does that make any kind of difference?

Regards,

[Druesedow]

Raajit,
I think I am confused on excitation voltage and Vcc.  I think what I need is a constant +5V to the then sensor, I don't know if I should call it excitiation or Vcc, Vcc I guess. 

Yes, when I have one sensor hooked up to the +5V it works fine, i.e. the signal noise is low.  I can use an external power supply, in fact that is what I am doing right now, but it just seems weird to me that the SC 2345 has only one +5V power source.  I see that the sockets on pin 9 have a +5V and I could use that, but that seems very crude to me. 

For now I am using the +5V on the connector block for the IR sensor and an external power source for my pressure sensor, and it is working fine.  If you have any suggestion on how to get rid of the external power supply let me know.

Thanks,
Charlie

[Raajit_Lall]

Depending on what your actual data acquisition device is, the current output on that 5V pin can range any where from 250mA to 1A.  When you are dividing this between two sensors, although the voltage might be the same, the current is getting divided, which is probably what is causing the noisy readings etc.  You could use a DMM to find out exactly how much current is being drawn by each of the sensors, and match it with the sensor specifications.  You could try some configuration where you could output some current (again depending on what type of board you have), or buy another board that could supply that amount of power to the sensor.  It does not look like only 1 5V pin is able to provide that much power to the sensor right now.

We have boards that can output some amount of current.  From your datasheet it looks like 50mA is the amount of current that needs to be supplied.  Here are some of the boards that can output current.  Could you tell me what board the 2345 is connected to so that we can take a look at how much current is being supplied on the 5V pin.  Although, since you are already seeing noise when you connect two sensors, it looks like the board itself will not be able to provide the current.  This is something that needs to be confirmed.

Hope that helps.

Regards,