Soundless Horn Source section

Astable Multivibrator 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 atable multivibrator.

Source section

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.

Monostable multivbrator #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 monostable multivibrator.

Monostable multivbrator #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 monostable multivibrator #2. Similarly based on the gap between the bursts reqiured the Off time should be adjusted.

Monostable multivbrator #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