Milliohm Meter

MilliOhm Meter Display 0.025ohmThe Milliohm Meter Project

I built this mil­liohm meter sev­er­al months ago which is based on a project by Scullcom Hobby Electronics and pre­sent­ed on YouTube.

Louis at Scullcom Hobby Electronics has a new video updat­ing the mil­liohm meter, and fea­tures the board I pro­duced in this post.
NEW Link to updat­ed video on YouTube
NEW Version 1.5 board avail­able at OSH Park requires addi­tion­al 0.01 uF ceram­ic capac­i­tor, 2 pin head­er, and 250 mA PTC fuse.
NEW Updated project post with Milliohm Meter ver­sion 1.5 board.

It uses a 4 wire kelvin mea­sure­ment sys­tem that sup­plies a pre­cise 100 mA cur­rent to the device under test using one pair of leads, and then mea­sures the volt­age drop across the device under test using a sec­ond pair of leads.
As designed it can be used to mea­sure low resis­tances of under 2 ohms (Ω).   Some of the design changes I made to fit my needs were:

  • Change the num­ber of resis­tors need­ed in the cur­rent source circuit
  • Use high­er pre­ci­sion resis­tors with a low tem­per­a­ture coefficient
  • Add sep­a­ra­tion and shield­ing between input, out­put, and sup­ply circuits
  • Use low­er ESR and high­er val­ue capac­i­tors for the MAX680 pow­er supply
  • Add addi­tion­al decou­pling capac­i­tors on the INA106, and MAX680 IC’s
  • Change the volt­age reg­u­la­tor from a TO220 pack­age to a SOT-223 package

Continue read­ing “Milliohm Meter”

Millivolt Meter

The Millivolt Meter Project

This is a DIY mil­li­volt meter that was orig­i­nal­ly designed by
Scullcom Hobby Electronics and pre­sent­ed on Youtube.
Definitely take the time to watch the videos (4 parts) as they are very well done and pre­sent­ed in a way that’s easy to fol­low and learn from.

I was in need of a meter that I could ded­i­cate to low volt­age pre­ci­sion read­ings, and could be done for a rea­son­able cost. So this project seemed like a per­fect fit. As usu­al after view­ing the video I saw many areas that the meter could be mod­i­fied and improved for my spe­cif­ic use, and quick­ly began design­ing my own ver­sion of it using Eagle CAD V7.5. Continue read­ing “Millivolt Meter”