Quad Sum and Difference Amplifier

Comments

• Beau Schwabe Posts: 6,547

  2009-08-21 13:40 edited 2009-08-21 13:40

  Tim,
  
  It looks like you will need to level-shift your voltages from +/-15V down to +5V/0V ... You will need to do this at least three times for each output. Once you have done that, the Stamp would be able to read the signal through an ADC.
  
  www.parallax.com/StoreSearchResults/tabid/768/txtSearch/ADC/List/0/SortField/4/ProductID/574/Default.aspx
  
  I'm about ready to board a plane, or else I would show you how to do the level-shift. If I don't see a reply, I will try to provide one later tonight.
  
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  Beau Schwabe
  
  IC Layout Engineer
  Parallax, Inc.
  
• WhatamINuts Posts: 6

  2009-08-21 16:14 edited 2009-08-21 16:14

  Thanks looking forward to your voltage shifter
  
  ·hope you had a good flight
  
  ·· Have Fun
  
  ····· Tim
• Tracy Allen Posts: 6,657

  2009-08-22 16:54 edited 2009-08-22 16:54

  Tim,
  
  Maybe Beau is at UPENE?
  
  One option would be to use the MAX1270 analog to digital converter, which accepts inputs in the range of +/- 10 volts even when operating on a single 5 volt power supply. Parallax sells the MAX1270 for use with the StampPLC. The QP154-Q-HVSD outputs swing to within 3 volts of the rails, so with a +/-12 V supply for the QP154-Q-HVSD, you would have +/-9 volts into the ADC.
  
  The MAX1270 uses a simple scheme at the inputs to extend the range beyond the +5 volt level. You can use the same technique with a different ADC.
  

                                               12.5k            8.67k
         signal +/- 10 volts   -------/\/\---o------/\/\------ Vss common
                                                         |
                                                         o----/\/\------- Vref 4.096 Volts
                                                         |    5.12k        
                                                         `----------------ADC input 0 to 4.096 Volts
  
  

  
  
  
  The way this work is, yes, a voltage divider. When the input is at -10 Volts, the ADC sees 0 Volts. When the input is +10 volts, the ADC sees 4.096 Volts. And it is linear in between those limits. Those are the same resistor values that are used by the MAX1270, and I verified for myself that the math does work out with those ratios.
  
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  Tracy Allen
  www.emesystems.com
• Beau Schwabe Posts: 6,547

  2009-08-26 05:45 edited 2009-08-26 05:45

  Yes Tracy you were correct... I was at the UPENE with Chip, Jeff, and many forum friends along the way.
  
  
  WhatamINuts,
  
  Sorry I did not get back to you sooner. The method that Tracy posted was what I had in mind, but the values should be re-calculated for +/- 15V
  
  ▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔
  Beau Schwabe
  
  IC Layout Engineer
  Parallax, Inc.
  
• WhatamINuts Posts: 6

  2009-08-26 12:37 edited 2009-08-26 12:37

  Guys
  · Thanks for· the help.
  ·· I think I wil use the Max1270 with a +/- 12 Volt supply as suggested by Tracy.
  · less wires.
  ·· For the appllication see Space elevator Blues here.
  http://www.spaceelevatorgames.org/
  · Page down to the article on NSS space elevator.· We are building the tracking system for the mirror in the video
  ·· Have Fun
  ········ Tim