0 to -10V Into 0 to +5V for Arduino Analog Input

Discussion in 'Embedded Systems and Microcontrollers' started by mlwinters, Dec 23, 2015.

  1. mlwinters

    Thread Starter New Member

    Dec 22, 2015
    2
    0
    Hi, I was just wondering if you guys could help me with something. I have an old Rank Strand lighting desk that outputs a negative voltage between 0 and -10 volt which would normally be connected to a dimmer pack. I would like to use an Arduino Mega to convert the analog signal into DMX512 (modified RS485) data so I can use the desk with modern DMX fixtures or dimmers.
    Is there a basic way of converting the 0 to -10V output into 0 to +5V for the Arduino's analog inputs? I looking for a somewhat simple converter unit that I can make using only through hole components (not good enough to solder small SMD's by hand) and ideally, would fit onto a PCB the same size and rough shape of the Arduino Mega's PCB (though PCB can be made bigger if needed (just wouldn't look as nice plugged into the Arduino if it's bigger)). The lighting desk has 12 outputs so I need to have a 12 channel converter.
    The lighting desk has two 8 pin locking DIN connectors on the back with a pin config as below.
    Socket 1
    Pin 1: Dimmer 1
    Pin 2: Dimmer 2
    Pin 3: Dimmer 3
    Pin 4: Dimmer 4
    Pin 5: Dimmer 5
    Pin 6: Dimmer 6
    Pin 7: -15V Power
    Pin 8: Dimmer Common (0V)

    Socket 2
    Pin 1: Dimmer 7
    Pin 2: Dimmer 8
    Pin 3: Dimmer 9
    Pin 4: Dimmer 10
    Pin 5: Dimmer 11
    Pin 6: Dimmer 12
    Pin 7: -15V Power
    Pin 8: Dimmer Common (0V)
    (0V output, dimmer 0% output)
    (-10V output, dimmer 100% output)

    I am more of a lighting engineer than an electronics expert but I am ok with electrics in general and so, I would just need to be pointed in the right direction e.g. use components X, Y, and Z, I should then be able to figure out the rest. I would also like to use an Arduino instead of any other microcontroller, I like the Arduino's ease of use plus I already have the code and library to control DMX from the Arduino via a MAX485.
    The lighting desk and Arduino can and ideally should use the same PSU (pre-made transformer), The lighting desk can be powered from a plug-in PSU or from a dimmer pack, in this case the pre-made PSU via the 8 pin DIN sockets on the back. Rank Strand says it needs around 16-20VDC at 300mA to run. The link below has a circuit diagram of the 3 PCB's inside the desk if you need it. Go to page 44, 45 and 47.
    http://www.theatrecrafts.com/archive/documents/lx_maintenance_1991.pdf

    I should just say that I do not want to modify to lighting desk in any way so doing anything to the desks electronics is out of the question.

    As I said I just need pointing in the right direction but if you want to attach a circuit diagram than that would be fantastic.
    Thank you very much for your time and any help you can provide.
    Take Care
    Morgan

    P.S. To everyone who celebrates it, have a great Christmas and a happy new year.
     
  2. dl324

    Distinguished Member

    Mar 30, 2015
    3,250
    626
    Your first post. Welcome to AAC!

    Use an inverting opamp with a gain of -1/2.
     
  3. MrCarlos

    Active Member

    Jan 2, 2010
    400
    134
    Hello miwinters
    .
    Have you thought about using an inverting operational amplifier That Divide by 2 ??
    You will need dual power source; +15 and - 15 Volts.
    You must select an operational amplifier that is suitable to your project.
    The circuit could be as you can see in the attached image.
     
  4. mlwinters

    Thread Starter New Member

    Dec 22, 2015
    2
    0
    Thank you both for your replies. Your suggestion for an Inverting OpAmp seem a simple and logical choice. I had a look on Rapid Electronics (the electronics company I always use) to see what OpAmps I could find. MrCarlos suggested in the picture about using a TL061, however being a single channel OpAmp I would need 12 so I had a look and found the TL064 Quad OpAmp. Would this chip be suitable for my needs? Could you also tell me why I would need a dual output PSU? Why would the chip effectively need 30VDC power or am I completely missing something? I am more than happy to buy one or make a second PCB if I need to, I just don't get why I would need to.

    Link to the TL064 on rapid that I was looking at: http://www.rapidonline.com/Electron...4CN-Bi-FET-Quad-Operational-Amplifier-82-0040

    Thank you again for your replies, I very much appreciate you taking the time to help me.
    Morgan
     
    Last edited: Dec 24, 2015
  5. MikeML

    AAC Fanatic!

    Oct 2, 2009
    5,450
    1,066
    I like simple:

    166.gif

    You lose a bit of range of the 10bit ADC, but the coding is simple.
    D1 is there to protect the Mega if you forget to turn on its power supply. (The opamp version would need that too).
    C1 provides some anti-alias filtering and satisfies the Mega's AD-input-source-impedance-requirement.
     
    Last edited: Dec 24, 2015
  6. MrCarlos

    Active Member

    Jan 2, 2010
    400
    134
    Hello miwinters
    .
    Well, most likely the Quad Op Amp TL064 is right for your project.
    .
    Dual power supply is required because it is so specified in the data sheets for that IC.
    .
    In the MAXIMUM RATINGS, data sheets section specified +/- 18 Volts.
    .
    See attached images; taken from information in the link you enclose.
    .
     
  7. MikeML

    AAC Fanatic!

    Oct 2, 2009
    5,450
    1,066
    No need for +-15V supplies if you can source a modern, low-voltage, rail-to-rail input/output opamp:

    166o.gif

    This circuit will pull the MegaAD input to within a few mV of 5.00V (1023)

    List of suitable TI OpAmps
     
    Last edited: Dec 24, 2015
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