Confusion on whom to get letter of recommendation from
If your ability in developing circuits for electrochemical studies sheds light on how good you would be designing circuits for mechatronics (and I suspect it does), definitely get a letter from them.
If all the professor can say that addresses your ability in mechatronics is &quot;he was smart, diligent, and careful,&quot; then that's certainly better than no letter, but you might be better off with a letter from somebody closer to your field, even if you haven't worked directly with them.