This project is highly intriguing and boasts numerous practical applications in security and alarm systems for residences, stores, and vehicles. It comprises a pair of ultrasonic radar components, consisting of a transmitter and a receiver, both operating at the same frequency. When there is movement within the circuit’s coverage area, it disrupts the circuit’s delicate balance, leading to the activation of the alarm. The circuit exhibits remarkable sensitivity and can be customized to either reset automatically or remain in the triggered state until manually reset after an alarm event.
Technical Specifications – Characteristics
Working voltage: 12V DC
Current: 30 mA
How it Works
As previously mentioned, this circuit comprises both an ultrasonic transmitter and a receiver, both operating at the same frequency. They employ ultrasonic piezoelectric transducers as their output and input components, respectively, and their operational frequency is determined by the specific transducers utilized.
The transmitter section is constructed using two NAND gates from the IC3, configured as inverters. In this specific arrangement, they create a multivibrator whose output drives the transducer. To ensure optimal efficiency, trimmer P2 is adjusted to match the resonance frequency of the transducers being used.
On the receiver side, a transducer captures signals reflected back to it, and its output is amplified by both transistor TR3 and IC1, which is a 741 op-amp. The output of IC1 is directed to the non-inverting input of IC2, whose amplification factor can be fine-tuned using P1. The circuit is set up to maintain equilibrium as long as the transmitter’s output frequency remains the same. If there is any motion within the area covered by the ultrasonic emissions, it distorts the signal returning to the receiver, causing the circuit to lose balance.
This imbalance triggers a sudden change in the output of IC2, which subsequently activates the Schmitt trigger circuit built around the remaining two gates in IC3. This, in turn, drives the output transistors TR1 and TR2, which can either signal the alarm system directly or, if a relay is connected to the circuit in series with TR1’s collector, activate the relay. The circuit operates within a voltage range of 9-12 VDC and can be powered by either batteries or an external power supply.
First, let’s explore some fundamental principles of constructing electronic circuits on a printed circuit board (PCB). The PCB consists of a thin insulating material coated with a layer of conductive copper, shaped to create the necessary connections between various circuit components. Using a well-designed PCB greatly expedites construction and minimizes the risk of errors. Smart Kit PCBs come pre-drilled and feature component outlines and labels on the component side, facilitating assembly.
To safeguard the PCB from oxidation during storage and ensure it reaches you in pristine condition, the copper is tinned during manufacturing and coated with a special varnish that prevents oxidation and eases soldering. Soldering is the sole method for building your circuit, and your success or failure hinges significantly on your soldering technique. While not overly complex, following some guidelines will help you avoid issues.
Select a soldering iron with a power rating not exceeding 25 Watts and a fine, cleanable tip. Specially designed sponges kept moist prove quite handy for periodically wiping the hot tip, removing accumulated residues. Do not file or sandpaper a dirty or worn-out tip; replace it if cleaning doesn’t suffice. Various solder types are available; opt for good-quality solder containing essential flux for consistently excellent joints.
Avoid using additional soldering flux beyond what’s already included in your solder. Excessive flux can lead to numerous problems and is a common cause of circuit malfunctions. However, if you must use extra flux, such as when tinning copper wires, thoroughly clean it after your work. To correctly solder a component, follow these steps:
- Clean the component leads with a small piece of emery paper.
- Bend the leads at the appropriate distance from the component’s body and insert it into its designated spot on the PCB.
- If you encounter a component with thicker leads than usual, making it too thick to fit into the PCB holes, use a mini-drill to slightly enlarge the holes. Be cautious not to make the holes too large, as this can complicate soldering later.
- Apply the hot soldering iron’s tip to the component lead while holding the solder wire’s end where the lead emerges from the PCB. The iron tip should lightly touch the lead just above the PCB surface.
- When the solder begins to melt and flow, wait until it evenly coats the area around the hole, and the flux bubbles out from beneath the solder. This entire operation should take no more than 5 seconds. Remove the iron and allow the solder to cool naturally, without blowing on it or moving the component. If executed correctly, the joint’s surface should exhibit a bright metallic finish, with smooth edges connecting the component lead and the PCB track. If the solder appears dull, cracked, or forms a blob, you’ve created a dry joint and should remove the solder (using a pump or solder wick) and redo it.
- Take care not to overheat the PCB tracks, as they can easily detach from the board and break.
- When soldering sensitive components, it’s a good practice to hold the lead from the component side of the PCB with a pair of long-nose pliers to divert any heat that could potentially damage the component.
- Ensure you don’t use more solder than necessary, as this increases the risk of short-circuiting adjacent tracks on the PCB, especially if they are closely spaced.
- After completing your work, trim excess component leads and thoroughly clean the PCB with an appropriate solvent to remove any remaining flux residues.
With numerous components in the circuit, be careful to avoid errors that could be challenging to trace and rectify later. Begin by soldering the pins and IC sockets, then follow the parts list, soldering the resistors, trimmers, and capacitors while paying close attention to the correct orientation of electrolytic capacitors. Next, solder the transistors and diodes, ensuring they aren’t overheated during soldering. Position the transducers in a way that avoids direct interference with each other, as this can diminish the circuit’s efficiency. After soldering, double-check your work to ensure it’s done correctly, then insert the ICs into their sockets, taking care with IC3, which is a CMOS type sensitive to static discharges.
Do not remove it from its aluminum foil wrapper until you’re ready to insert it into its socket. Ground the PCB and yourself to discharge static electricity, and then cautiously place the IC in its socket. In the kit, you’ll find an LED and a 560-ohm resistor, which will assist in making necessary adjustments to the circuit. Connect the resistor in series with the LED and then connect them between point 9 (positive supply rail) and point 1 of the circuit.
To power the circuit, connect the power supply across points 1 (positive) and 2 (negative) on the PCB. Initially, set P1 to roughly the middle position. Slowly adjust P2 until the LED illuminates when you move your fingers slightly in front of the transducers. If you have a frequency counter, you can achieve a more accurate adjustment. Connect the frequency counter to the transducer and adjust P2 until the oscillator’s frequency matches the resonant frequency of the transducer precisely. Then, adjust P1 for maximum sensitivity. If you wish to keep the circuit triggered until manually reset after an alarm, connect pins 7 and 8 on the PCB, which can be beneficial for detecting intrusion attempts in protected areas.
This kit does not need any adjustments if you follow the building instructions.
If these components are integrated into a larger system and any harm or damage occurs, our company assumes no liability. When working with electrical components, exercise extreme caution and adhere to safety guidelines in accordance with international specifications and regulations when handling power supplies and equipment.
If it does not work
Inspect your work for potential dry solder joints, solder bridges connecting adjacent tracks, or any lingering soldering flux residues, as these issues often lead to problems. Additionally, review all external connections to and from the circuit to identify any potential mistakes in this regard.
Ensure that no components are missing or incorrectly placed.
Verify that all polarized components have been soldered with the correct orientation.
Confirm that the power supply provides the correct voltage and is connected properly to your circuit.
Thoroughly examine your project for any faulty or damaged components.
If, after performing these checks, your project still fails to function, please contact your retailer, and the Smart Kit Service will be available to assist with repairs.
R1 180 KOhm
R2 12 KOhm
R3, 8 47 KOhm
R4 3,9 KOhm
R5, 6, 16 10 KOhm
R7, 10, 12, 14, 17 100 KΩ
R9, 11 1 MOhm
R13, 15 3,3 KOhm
C1, C6 10uF/16V
C3 4,7 pF
C4, C7 1 nF
C8, C11 4,7 uF/16V
C10 100 nF
C12 2,2 uF/16V
TR1, 2, 3 BC547 , BC548
P1 10 KOhm trimmer
P2 47 KOhm trimmer
IC1, 2 741 OP-AMP
IC3 4093 C-MOS
R TRANSDUCER 40KHz
T TRANSDUCER 40KHz
D1, 2, 3, 4 1N4148