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CD4051B: Readout from two different sources and multiplexing to an Arduino Nano

Part Number: CD4051B

Hi TI-Community,

Right now I have a CD4051B on hand and I am not sure if I can use it as I intend. I have in total 6 inputs from two different sources. 4 inputs are from a laser diode driver and 2 from a temperature controller (TEC). The range from both components is between 0-5V. The laser diode driver needs at least a 1MegOhm load and the TEC 500kOhm to have rated output. The data will then be processed by an Arduino Nano at a relatively slow pace (only check the temperature occasionally).

Also, one input uses the voltage of VCC (5V) by using a voltage divider, about 1V. For this input, I may need to use a current limiting circuit to protect my multiplexer?

Best regards,

Martin

  • Martin,

    The CD4051B device can be operated with a 5V supply and pass 5V signals.  This device is an 8:1 mux and will be able to accommodate the 6 signals in your system.  The series on-state resistance of the signal path in this case will be ~500ohms which you should take into consideration.  

    I don't understand your comment about the voltage divider.  This device will not need a voltage divider on the signal path if Vdd is operated at 5V it will pass signals 0-5V

    Thank you,

    Adam

      

  • Hi Adam,

    First, thank you for your fast reply. Sorry for my vague wording. As showed in Fig. 1 what intend to do is read 6 analog inputs. 2 of the 6 values are from a temperature controller and the rest from a laser diode driver. The range all values is between 0-5V. To read the inputs from the laser diode driver, ILDSET, ILDACT, TSETLD, and TACTLD, I need at least a 1MegOhm load resistor, specified by the manufacturer of der laser diode driver.

    The manufacturer of the other component (temperature controller) told me the temperature controller has an input impedance of 1MegOhm. So I am not sure if the 1MegOhm input impedance may draw too much current and may damage the multiplexer because it can't handle it. Especially, I am concerned about TSETPD. TSETPD is derived from the voltage divider (framed in blue) and from VDD (VCC5V 12VA Power). VCC5V is of course VDD. The technical support suggests me to use a voltage reference instead of the voltage divider for a more precise control of this pin. But the current problem stays.

    Fig. 1 Multiplexer schematic

    Best regards,

    Martin

  • Martin,

    The CD4051B device will support up to 10mA per signal path.  The current from Vcc 5V through R_VDD 18k ohm in series with RL 1M ohm will be in the uA range. 5V / (18k +1M) = 4.9 uA.  This small current will not be an issue. 

    Thank you,

    Adam

  • Thank you very much. Then I'll try it out. Have a nice weekend!

    Best regards,
    Martin