Adjustment for the ultrasonic alarm (2)

Adjustment of the transmission frequency

In case of mounting and removal of the ICs, always make a power OFF.

The ultrasonic sensor has a peculiar resonant frequency (about 40 KHz). The oscillation frequency of the transmitter must be adjusted to the resonant frequency.
The adjustment procedure of the frequency is shown below.

	Remove IC1 from the IC socket and connect the 1st and the 3rd pin of the socket.By this, the oscillation of IC2 is continuously done and the adjustment becomes easy.
	Monitor the 1st pin of IC4 of the receiver circuit by the simple high frequency detector or the oscillo scope.
	Turn VR1 of the transmitter circuit and the output with the receiver circuit maximizes.

Above, the adjustment of the transmission frequency is ending.
Remove the short circuit line of the IC1 and mount the IC1.

Operation confirmation of the detector

	Connect the VR2 and the LED temporarily.
	Set VR2 in the maximum.
	Place an obstacle in the about 1-m distance from the sensor and confirm that the LED goes out.
	Turn VR2 to resistance value's decreasing and confirm that the LED lights up.
	Return to VR2 resistance value's becoming big a little and turn off an LED.
	Remove an obstacle and confirm that the LED lights up again.

The normally operation of the alarm signal can be confirmed by above-mentioned operation.

The photograph on the left is the one to have observed a voltage change in the case that the reflected wave of the ultrasonic is the outside of the detection range.
Most the top is the one to have observed the reception wave of the ultrasonic and is the wave from of the 1st pin of IC4. A transmission wave and a reception wave are observed.
The 2nd is the one to have observed the transmission timing pulse and is the wave form of the 1st pin of IC8.
The 3rd is the one to have observed the output of the alarm detector and is the wave from of the 11th pin of IC8. You can confirm that the timer has started from the transmission timing.
The 4th is the one to have observed the output of the alarm detector and is the wave from of the 10th pin of IC8. The output of the alarm detector is as the H level because a reflected wave is received before the time-out of the alarm detection timer and the reflected wave detection gate is closed. In this condition, alarm output isn't presented.

The photograph on the left is the one to have observed the voltage change of each part when the reflected wave of the ultrasonic is the inside of the detection range.
The observation position of each signal is the same as above-mentioned photograph.
As shown at the 3rd photograph, a reflected wave is received after the time-out of the alarm detection timer. Because the reflected wave detection gate isn't closed at the time of the time-out of the alarm detection timer, at the point, the output of the alarm detector becomes an L level. (The 4th wave from)
This L level signal becomes the trigger signal of the timer of the alarm output circuit and an alarm is output outside.