Adjusting EKG shield gain to read up to 10 mV

[chunkers44]

Hi,

I am doing a project where I'm using your EKG shield to measure voltages up to 10 mV. I am using the shield on the 5 V setting with the Arduino Uno. From my understanding, I can adjust the trimmer to adjust the overall gain. However, I've been looking and cannot find any info specifically on how to adjust the trimmer. Any advice?

Thank you!

[LubOlimex]

You can increase the gain by manipulating the trimmer. The trimmer is a blue piece of electronics with metallic head pointing sideways – this metallic part can be rotated with a sharp object. In our calculations there is an estimate for G2 used ("~80") – it represents the typical value of this part of the circuit (G2) after assembly. This value can be increased or decreased by rotating the trimmer. Still the maximum value for this trimmer is 101.

In order to calculate the exact amplification you'd need to measure the value of the same trimmer TR1, using a multimeter tool. There is just one value that is not known since each person might rotate the resistive trimmer differently, so the value of TR1 is unknown and you should measure the resistance between pins 1 and 2 of TR1 with a multimeter tool. All other values are known and visible in the schematic. The unknown TR1 value is used in this formula G2=1+R12/(TR1+R11). Make sure to refer to the schematics for more information on formulas: https://www.olimex.com/Products/Duino/Shields/SHIELD-EKG-EMG/resources/SHIELD-EKG-EMG-REV-B-SCHEMATIC.pdf