CX-101-BG as current meter on LM723 supply

• CX-101-BG as current meter on LM723 supply
  Posted by MaggoT on 10 Jan, 2012 09:15
• Hello!
  I am currently attempting to build a bench power supply around a LM723 and four 2N3055 transistors.
  I have tested parts of the schematics and things seem to work great so far.
  
  However, I have two CX-101-BG panel meters from http://www.circuitspecialists.com/digital-panel-meter-cx101bg.html that I intended to use for voltage and current display. (These are the -BG ones, that should work with a common ground configuration). After a bit of frustration I managed to get one working for straight up voltage measurement using the second example from the datasheet (don't have a schematic for this, sorry), but i cannot get it to measure the voltage across a resistor properly.
  
  Here is my power supply schematic, R13 is the resistor over which i intended to measure the voltage drop, and display it on the meter.
  The "Current limit board" mentioned in the schematic is just another board that switches in various resistors in series to provide a couple of different steps for setting the current limit for the LM723.
  
  PSU schematic:
  
  
  So my question is, how do i wire the CX-101-BG up to measure the voltage drop across R13, if it is at all possible? Are any of the COM, INLO, INHI, REL pins internally connected to ground inside the meter?
  
  Here is another test i did. The circuit below shows my test setup which is roughly equivalent to what the meter will be measuring inside the PSU.
  
  The drop across R2 should be 1.66 volts in this case, and with the divide resistors the CX101 should read about 0.150 volts. However the meter reads out of range...
  
  When measuring across R2 with a multimeter i get 2.5 volts, which confirms that the meter is connecting INLO to GND. Grounding COM/RFL or leaving them floating makes no difference. Measuring across R5 with the multimeter i get 0.225 volts.
  
  I apologise if i have done some stupid mistake/assumption here, i'm having a hard time getting my head around this, and the datasheet for the meter doesn't really help much.
  Can anyone give me any tips on how to get this working?
  Ps. sorry for the long post
  
  regards
  MaggoT
• #1 Reply
  Posted by J4e8a16n on 24 Aug, 2012 13:36
• Dont forget to let us know if you find out how to make it work with a shematic.

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• #2 Reply
  Posted by Rerouter on 24 Aug, 2012 13:46
• i have 2 -bg models working in the common ground config on my own power supply, following J4e8a16n's sheet to the letter ended with it all working for me,
• #3 Reply
  Posted by J4e8a16n on 24 Aug, 2012 14:37
• Hi,
  
  The shema I seen on the blog use resistors.
  
  You did not put resistors?  Did you joined the 5678 pins?
  
  JP