GSM Remote Control MotherBoard Schematic

Posted on Feb 6, 2014

The entire remote control is handled by a PIC that controls the GSM/GPRS module`s activity, reads the room temperature through a Dallas DS1820 smart probe, controls the logical state of two opto-isolated inputs, and gives commands to the two relays. In addition, the circuit is equipped with a DTMF decoder whose purpose it is to identify the bi-tones involved in the phone

GSM Remote Control MotherBoard Schematic
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selection found within modern telecommunication systems bi-tones which every phone emits and sends out on phone lines when its keyboard keys are pressed. The identifier is necessary in order for the DTMF functionality to work. Having said that, let`s take a better look at the electric scheme: power is supplied by continuous voltage, not always stabilized (applied to PWR + and -) at a value between 5 and 32V; such voltage is filtered at the bottom by the diode protecting against polarity inversion (D1) through condensers C1 and C2. Fuse F1 enables us to protect both the circuit and the power source in case of a short circuit in the integrated regulator discussed below, which is necessary to obtain the 4 volts needed for the rest of the circuit to work. The switching regulator is based on a MC34063 chip, utilized in the classic configuration of series PWM regulators charged by inductance, whose output voltage depends on the energy stored in L1; the regulator is stabilized by the component demoted from resistive divider R2/R3, which is needed to set at 4V the component leveled at the top of both C4 e C5. The 4 volts at the bottom of the abovementioned condensers are sufficiently filtered by other condensers placed on the power lines of the microcontroller and of the GSM module; which presents, during transmission, absorption peaks compensated for by C7, C8, C13, C14, C15 e C16, thus avoiding that an impulsive current request...

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