Soundless Horn Source section
AstableMultivibrator • The TSOP 1738(IR sensor) requires an incident signal with a centre frequency of 38khz. • So the Infra red LED must be illuminated by a signal that has a frequency of 38khz. • This is accomplished by generating the required signal using an atablemultivibrator.
Advised data format • The main intricacy involved with the TSOP 1738 is that a continuous signal of 38khz is treated as noise. • There is a suggested data format of sending IR pulses to the sensor. • They should be in the form of bursts of cycles. • The bursts should have 10-70 cycles
Data format(contd.,) • There should be a gap of at least 14 cycles between the bursts. • While all these criteria being satisfied, the frequency of the pulse train must be kept at 38khz.
Monostablemultivbrator #2 • As the format consists of bursts, to produce a burst of cycles the astable should be on and for the gap between the bursts it should be off. • This can be achieved by drawing the supply(Vcc) of the astable from the output of the monostablemultivibrator.
Monostablemultivbrator #2(contd.,) • As there should be 10-70 cycles/burst based on the frequency of the astable output signal its time period can be calculated and hence the time required for 20 cycles is determined. • This becomes the on time of the monostablemultivibrator #2. • Similarly based on the gap between the bursts reqiured the Off time should be adjusted.
Monostablemultivbrator #1 • This multivibrator forms the initial block of the source section. • A driver while blowing a horn excites this multivibrator. This is nothing but the trigger to the multivibrator. • It generates a signal that sustains for a duration of 0.5 sec. • This forms the supply of the monostable #2.
Source section using Microcontroller • The circuit using multivibrators is only for testing purpose • For accuracy and to reduce bulkiness, the same can be implemented using Microcontroller