TL84, LM35 electronics
This block contains the LM35 sensor. It receives 9V supply from a battery and delivers an output voltage signal that ranges between 0 and 500 mV depending on temperature,
0V at 0ºC and 500mV at 50ºC increasing linearly in between. It may deliver more than
500 mV when the temperature is higher than 50ºC , but it is useless since the conditioning system has a ceiling temperature of 50ºC beyond which sticks displaying as if it was 50ºC. It has a RC damper of 1uA capacitance and 100Ω resistor connected from output to ground to improve capacitance tolerance as advised in its datasheet. [1]
The LM35 has a possible deviation of up to 1.25ºC in our range (0-50ºC) as stated in its datasheet that cannot be avoided and would affect the accuracy of the whole system. [1]
This block only drains 60 uA from its supply. [1]
3
This block receives the 0-500mV signal directly from the sensor and amplifies 15.4 times so that its output ranges from 0 to 7.7 V, being supplied by a 9V battery. Since
Gain= 1+R2/R1 for a non-inverting amplifier, R2 = 14.4 R1. Maximum precision in the
R2/R1 resistance ratio is achieved using a potentiometer instead so it can be adjusted exactly to the desired output.
This signal will be read from Arduino with a full scale of 5V and then, Arduino decides which output pin activate to supply the voltage divider chain. Since the voltage to be read can be higher than 5V, the measure is taken divided by two taking advantage of the voltage divider of the following differential amplifier (between R2 and Rg in figure 3, in the differential amplifier block).
It is a non-essential block to comply with the specifications of the product, although it collaborates in improving the resolution of the system.
The cost is not very huge since it consists only of a potentiometer and an operational amplifier which will be used afterwards for the differential amplifier. Its current consumption therefore, can be estimated together with the differential
0V at 0ºC and 500mV at 50ºC increasing linearly in between. It may deliver more than
500 mV when the temperature is higher than 50ºC , but it is useless since the conditioning system has a ceiling temperature of 50ºC beyond which sticks displaying as if it was 50ºC. It has a RC damper of 1uA capacitance and 100Ω resistor connected from output to ground to improve capacitance tolerance as advised in its datasheet. [1]
The LM35 has a possible deviation of up to 1.25ºC in our range (0-50ºC) as stated in its datasheet that cannot be avoided and would affect the accuracy of the whole system. [1]
This block only drains 60 uA from its supply. [1]
3
This block receives the 0-500mV signal directly from the sensor and amplifies 15.4 times so that its output ranges from 0 to 7.7 V, being supplied by a 9V battery. Since
Gain= 1+R2/R1 for a non-inverting amplifier, R2 = 14.4 R1. Maximum precision in the
R2/R1 resistance ratio is achieved using a potentiometer instead so it can be adjusted exactly to the desired output.
This signal will be read from Arduino with a full scale of 5V and then, Arduino decides which output pin activate to supply the voltage divider chain. Since the voltage to be read can be higher than 5V, the measure is taken divided by two taking advantage of the voltage divider of the following differential amplifier (between R2 and Rg in figure 3, in the differential amplifier block).
It is a non-essential block to comply with the specifications of the product, although it collaborates in improving the resolution of the system.
The cost is not very huge since it consists only of a potentiometer and an operational amplifier which will be used afterwards for the differential amplifier. Its current consumption therefore, can be estimated together with the differential