Verification of circuit before I order parts!

Discussion in 'General Electronics Chat' started by gdallas, Apr 27, 2012.

  1. gdallas

    Thread Starter Member

    Apr 25, 2012
    74
    0
    Hi,
    I’m trying to develop a basic 4 port AO/DO test box so I can interface with my DAQ to simulate instrument signals; 4No. 1-5V 4-20mA AO, and 4 No. 5V discrete outputs
    Under no power conditions, my DAQs input impedance is 140k, however on power up its goes very high impedance, but I’ve used 140K worst case as my simulated loads
    I’ve selected 2.5K pots at 10% tolerance to ensure I mange to sweep the who 1-5 range. Originally i had 1K pots selected, but wasn’t convinced id be able to get as low as 1V.
    I’ve used 10k pull down resistors for my DO’s, and added status LEDs (don’t pay attention to the model on my schem) I’ve selected LED resistors based on an LED with a forward current of 20mA at 5V.
    Any concerns or suggestions?
    Many thanks
     
  2. praondevou

    AAC Fanatic!

    Jul 9, 2011
    2,936
    488
    What DAQ is it?

    Why is there a short on the resistor/LED combination? What are the 100Ohm and 10k resistors for? What is the maximum specified output current of the DAQ?
     
  3. gdallas

    Thread Starter Member

    Apr 25, 2012
    74
    0
    Hi,

    NI USB 6008

    I concede, the LED should probably be tied direct to ground.

    the 10K resistor is a pull down to prevent the input to the DAQ floating.
    the 100ohm is in case anyone accidentally attempts to wire it up wrong, i.e. input and output. the 100 Ohm resistor will prevent a short circuit

    I have no requirement for outputs from the DAQ.

    Many thanks
     
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