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• Rev2 Final Calibration

  Marek • 04/14/2024 at 03:52 • 0 comments

  I have completed the final calibration for the second revision. The data is as follows:

  Voltage:
  Meter, Fluke 101
  -60.28, -60.4
  -54.70, -54.81
  -49.86, -49.90
  -44.88, -44.97
  -39.86, -39.93
  -34.93, -35.00
  -29.89, -29.94
  -24.90, -24.94
  -19.92, -19.95
  -14.94, -14.96
  -9.956, -9.97
  -4.972, -4.978
  -0.987, -0.989
  0.001, 0.000
  0.989, 0.989 
  4.975, 4.984
  9.960, 9.97
  14.94, 14.97
  19.92, 19.96
  24.90, 24.95
  29.89, 29.95
  34.81, 34.87
  40.00, 40.08
  44.80, 44.88
  49.90, 50.03
  54.97, 55.11
  61.04, 61.1
  
  Resistance:
  Meter, Range, Fluke 101
  29.57, 1, 31.7, 
  98.33, 1, 103.3
  332.3, 1, 332.8
  1081, 1, 1044
  10730, 2, 10520 
  21930, 2, 21410 
  100500, 2, 97300
  339800, 2, 315200
  530000, 2, 484000
  
  Capacitance:
  Meter, Range, Fluke 101
  50.88n, 2, 49.2n
  96.73n, 2, 96.6n
  1.006u, 2, 1.009u
  10.03u, 1, 9.92u
  45.57u, 1, 47.32u
  

  This works out to 0.3% relative accuracy for voltage, 10% for resistance, and 5% for capacitance.
  

• Rev2 PCB Assembly and Bring Up

  Marek • 03/22/2024 at 06:34 • 0 comments

  I have assembled and brought up the revision 2 PCB to the point where it reads voltage. Additional firmware is needed for mode switching and calibration is also needed.

• Rev1 Enclosure

  Marek • 03/20/2024 at 03:57 • 0 comments

  I have mounted the first revision into an aluminum sheet metal enclosure with some holes cut in it. The first revision has been repurposed into just a voltmeter because there are some problems with the switching circuit.
  

• Rev1 Voltage Test

  Marek • 03/14/2024 at 03:44 • 0 comments

  I did another test with the rev1 prototype, this time only measuring voltage, and bringing it all the way to the maximum voltage of 60V. Again I am doing calibration and comparison to my Fluke 101 Multimeter. This has a problem as the Fluke 101 does not have more digits than this multimeter, however, I am ignoring this for now. I was able to stay under 1% error for all measurements, and I think this could be improved with a better calibration procedure. Here are the results:

  Voltage(V), Error(%)
  0.989, 0.0
  4.982, 0.71
  9.97, 0.76
  14.96, 0.81
  19.95, 0.86
  24.94, 0.85
  29.94, 0.88
  34.99, 0.86
  40.03, 0.83
  44.9, 0.81
  49.89, 0.85
  54.84, 0.9
  59.8, 0.71
  

• Rev1 Display Bodge

  Marek • 03/13/2024 at 00:45 • 0 comments

  To make the display work on revision 1, I bypassed the display driver and wired the pico IO pins strait to the segment LEDs. It is a little faint, as the display driver circuit worked completely differently, but it works to test the display.
  

• Rev1 Preliminary Accuracy and Precision Test

  Marek • 03/10/2024 at 05:41 • 0 comments

  As the title says, this is a preliminary test of the first version of the multimeter. Before the test, I basically calibrated it using my Fluke 101 as a reference. The results of the test are as follows:

  2.5V
  Error: 0.569, Coeff of Var: 0.0102
  
  5V
  Error: 0.2342, Coeff of Var: 0.001
  
  7.5V
  Error: 0.2404, Coeff of Var: 0.0019
  
  10V
  Error: 0.0671, Coeff of Var: 0.0006
  
  10ohm
  Error: 48.5352, Coeff of Var: 0.0
  
  100ohm
  Error: 8.2285, Coeff of Var: 0.0
  
  1000ohm
  Error: 0.0443, Coeff of Var: 0.0
  
  10000ohm
  Error: 1.9391, Coeff of Var: 0.0
  
  40000ohm
  Error: 5.2247, Coeff of Var: 0.1246

  As can be observed, the error is fairly low for all the tested voltages. For resistance, the error is higher especially at the low and high ends. It basically isn't accurate at all at 10 ohms. I also did a test of capacitance and for 100nF it measured 579nF, so basically order of magnitude. For 10uF it measured 11.78uF, so close. I may be able to make capacitance better  (for 100nF) by increasing the sample rate.
  

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