controlling current using arduino.

We can control voltage in arduino usinh analogWrite and digital write, but how to control amperes. I am making a multimetre using arduino, so I have to calculate the resistance and current. Please help.

Arduino can measure a voltage using analogRead. Ohms Law says Voltage = Current x Resistance, V=IR If you apply a known voltage across 2 resistors in series, and you know the value of one, you can determine the value of the other: Vout = Vin * R2/(R1 + R2) You apply Vin, measure Vout, you know R1, solve for R2.

Same for current. V = IR, or I = V/R. Apply an unknown current across a resistor to Gnd. Measure the resulting voltage. I is then measured voltage/known resistance.