Mats Engstrom writes that he’s had positive experience with the ElectroDroid app. He’s had it installed in his phone for some time now finds it useful. “In addition to a lot of pinouts and lists of nice-to-have info the app also has calculators for Ohm’s law, capacitor charge timings, battery life time, voltage dividers, 555 frequency, LM317 voltage, finding the right resistors to put in series/parallel to get a specific value, and a lot of others. I highly recommend testing the free version which is basically the same as the paid PRO version ($2.49) but with displayed ads.”
Via the contact form.