Updated V1.5 board assembly for the Milliohm Meter Project. The Milliohm Meter board V1.41 is featured in Scullcom’s Milliohm Meter Udpdate YouTube video. I had already started on the version 1.5 board update a week earlier and was about to send the prototype files out to OSH Park for manufacturing, when I noticed a new Scullcom video thru my YouTube subscription notice. I was pleasantly surprised to see that it was an update to the original Milliohm Meter and it was featuring the V1.41 board that I had designed. Louis had made some similar updates to components, so I quickly updated the V1.5 board file to match before sending it off.
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