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• Op-Amp gain: Since the range for voltages coming out of the temperature measurement by the voltage divider is about 1.2V-1.6V in the temperature range of 15-24°C, an amplifier is needed to utilize the whole voltage range (0-3.3V) of the ADC. The configuration of the op-amp is done by external resistors. The non-inverting amplifier circuit with offset voltage is used to amplify the voltage and bring it to the right level (see also Equ. 4.3). The output is then about 0-3.3V for the already mentioned 15-24°C. The resistor values chosen are: R1, R5 = 23.7kOhm und R2, R3, R4 = 10kOhm. For the second channel the same values are used. A second configuration for the range of 5-55°C is: R1=R2=R4=10k, R5=2.7k, R3=not populated.

• Short detection: The H-Bridge driver TLE7181EM offers an integrated op-amp for current sensing including over-current or short detection, whose gain has to be defined by a resistor network. The formulas for calculation of R31-R36 can be found in the TLE7181EM datasheet on page 23: The gain is R_FB/RSR_S, where RFB R_FB = 1/(1/RREF1 R_REF1 + 1/RREF2R_REF2). To find the right gain the first thing is to look into the maximal voltage drop which can be induced by the shunt resistor for current measurement. This is because of the shunt resistance of 2mOhm is about 24mV at 12A current. Since the target voltage range for the built-in ADC of the Arduino is 0-3.3V a gain of 100 is chosen. This would convert the 0-12A to 0-2.4V. To reach this gain value first of all the RFB R_FB has to be chosen, 100kOhm is a good choice in such cases. The next value is then RSR_S, which is RFBR_FB/GAIN or 100kOhm/100 = 1kOhm. Dropping this into the equation for RFBR_FB, one gets 200kOhm for RREF1 R_REF1 = RREF2R_REF2. This also means that the over current treshold threshold is at about 25A. To sum up: R31 = R32 = 1kOhm, R33 = R34 = 100kOhm and R35 = 200kOhm. For the second channel the same values are used.

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