Electronic schematics, circuit designs
Squelch schematic
Squelch is a circuit that acts to suppress the audio (or video) output of a receiver in the absence of a sufficiently strong desired input signal. This squelch circuit is simple and has an amplification for sufficiently large to be incorporated into an assembly of automatically control from a wide range of radio receivers. The input signal derived from the RAA circuit from a receiver is tempered by the network R1-R2-P1. The signal from the mouse’s P1 is picked frm the entry of inverses operational amplifier A1, connected as comparator. At the non-inverted entrance is applied a voltage reference of 200 mV, through voltage divider R9-R10.
Read the rest of this entry »
Lead-acid battery charger
This circuit delivers an initial voltage of 2.5V per cell to rapidly charge a battery. The charging current decreases as the battery charges and when the current drops to 180 mA the charging circuit reduces the output voltage to 2.35 V per cell, leaving the battery in a fully charged state. This lower voltage prevents the battery from overcharching, which will shorten its life.
The LM301A compares the voltage drop across R1 with a 18 mV reference set by R2. The comparator’s output controls the voltage regulator, forcing it to produce the lower float voltage when the battery-charging current, passing through R1, drops bellow 180 mA.
Read the rest of this entry »
Radio beacon 2m 144 MHz
The transmitter on 2 meters 144 MHz was designed mainly for use by radio amateurs as radio beacon and to this end, it produces a signal of good quality and without unwanted harmonics. T1 transistor, in association with cristall X1, works as oscillator on 36 MHz. L1-C3 filter eliminates any tendency of the circuit oscillation on 12MHz (fundamental frequency of the crystal).
L2-C4 circuit is tuned on the fourth harmonic of oscillator signal (144 MHz). This signal reaches the antenna after passing through a buffer consisting of T2, a FET with 2 gates. The signal modulator (amplitude) is applied to the second gate of the buffer.
Read the rest of this entry »
