Ultrasonic Movement Detector

Posted on Feb 6, 2014

This ultrasonic movement detector circuit uses a crystal locked circuit to get maximum performance from the ultrasonic transmitter. However, the detection circuit is different. think it is more sensitive. Check all the components against the parts list. It is generally easier to solder in the lowest height components first the resistors and di

Ultrasonic Movement Detector
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odes. Make sure to get the diodes in the correct way. The black circle or band on the diodes must match the bar of the diode symbol on the overlay. There are a lot of resistors. Use the resistor color code printed on the back of the header card to work out each value. The 40 kHz crystal can be inserted either way. Holes have been provided to secure its case to the PCB. Use one of the leads cut from the resistors. You can also quickly solder the wire to the case of the crystal. The ultrasonic transmitter has a T suffix on the number stampedunderneath it. The receiver has an R suffix. Each may be soldered either way around on the pads under the PCB. Make sure to get them both pointing straight out at 90o from the PCB. Battery operation is not recommended for this detector. As the battery potential decreases the sensitivity will change. This is partcuarly so if the unit is triggered often (as in detecting a door opening. ) It is better to use a power supply. Use 9V to 12V DC. You could go to a maximum of 15V but you may have to replace the 78L05 by a 7805. Immediately after you connect the power let the unit stand for at least 20 seconds so whole circuit will settle down electrically. The schematic shows that the setting of the trimpot value is critical to the operation of the detector. We provide a 1M trimpot. Set it to about 400K by eye. We have found that below about 300K the detector is too sensitive and will self-trigger....

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