This simple to-construct and-use cell phone hostile to robbery alert is a ultra-straightforward security gadget that appends a security link from a cell phone to an item, hence discouraging the potential burglary of a cell phone in open regions, for example, air terminals, railroad stations, and cafeterias. Since the gliding end of the security link has a standard smaller scale USB connector, you can undoubtedly append it to the USB in a hurry (OTG) port of your cell phone in the wake of circling the security link around a table/seat leg to keep the cell phone set up. At whatever point somebody attempts to withdraw the security link from the cell phone, the cell phone hostile to robbery caution gadget, bolted to a similar leg, alarms you quickly with a thundering cautioning signal!
Prepare some useful parts
As you can see in the above schematic drawing, only a handful of components are needed to build the entire system. The key component here is an extremely popular (and cheap) hex inverter MC14069UB (IC1), fabricated with MOS P−channel and N−channel enhancement-mode devices in a single monolithic structure. The combination of the first three gates (A/B/C) of the hex inverter forms a low-frequency oscillator to make a small (35-mm) 8R/500-mW loudspeaker (LS1) cry a little below 2 kHz with the component values used. For the rest of it, there is a small-signal transistor T1 (BC547) for driving the loudspeaker and a pair of resistors (R1 and R2) with a 1N4148 diode (D1) to disable the tone maker when a 5-Vdc supply from the USB OTG port of a smartphone appears across the input terminals. The whole circuitry is configured to work with a low-current 3-Vdc supply rendered by any appropriate battery.
You can make the security link (the security circle) by taking a miniaturized scale USB information link of adequate length. The USB “A” male connector shaped toward one side of the link isn’t vital here, so simply chopped it down with a cutting edge or scissors however protect the wires inside the link, as you’ll require the VBUS/VCC, GND, and ID leads of the USB link later. You can likewise set up your own security link with the assistance of an adaptable three-center/two-center sound/screened link and one small scale USB male connector. Generally, such a male attachment has three weld cushions on one side and the other two on the contrary side. The beneath commented on figure will enable you to weld the essential wire associations appropriately. Keep in mind, erroneous/inappropriate bind joints may slaughter your cell phone’s USB OTG gadgets — be cautious!
Note that to get the smartphone to enter into USB OTG mode, you need to short Pins 4 and 5. You can choose to short them permanently by either soldering them together (then you need just a two-core security cable) or soldering wires to each of the required pins and extending those outwards from the connector (a three-core security cable is essential), which can then be soldered to your circuit board. Once done, the security cable is ready for use. Just to ensure that you do not end up frying your smartphone, double-check the new security cable with a multimeter or continuity tester immediately after its preparation.
Brisk note on USB OTG
USB OTG is a detail that empowers gadgets to go about as either an essential or optional host, and jobs of the essential and auxiliary hosts can change as indicated by the convention. The greater part of the present Android telephones and tablets support USB OTG, along these lines enabling clients to connect standard USB input gadgets, for example, a USB console and mouse, or even expand the capacity utilizing an ordinary USB stick. You need to do it according to the list:
- Check if your device is compatible
- Check if you have enough power
- Advantages and disadvantages of USB OTG
- Buy an OTG USB cable
- Connect your USB drive or accessory to your tablet
- What else can I do with USB OTG?
Even though I built and tested my primitive model on a breadboard (see images shown below), it’s highly advised to use a small perfboard for the final build. Soldering and modeling will not be too difficult, but pay attention to keep the length of circuit wires/tracks as short as possible.
After fruitful development, put the all out gadgets gathering (counting battery and amplifier) inside a sealed tiny metal fenced in area, ideally with an instant/independent latch system. The nook requires reasonable gaps for the power switch and the security link. What’s more, there must be prolonged openings for the amplifier. Powerful alert fenced in areas come in numerous shapes and sizes, so I can’t give a standard formula for making the last model. Be that as it may, it is anything but an ill-conceived notion to deliberate with the fine art of my “cooked up” model, demonstrated as follows, when you begin the procedure. Continuously recollect that an uncovered power on/off switch will render the security ineffectual!
Over on the hardware side, there’s a low-voltage, diode-gated, ordinary CMOS oscillator with default running recurrence near 750 Hz. Observe: The 1-nF capacitor is the fundamental recurrence choosing segment of the oscillator circuit. On the off chance that you need to hear an a lot higher tone yield (~1.5 kHz), simply evacuate the weld joint between Pins 1 and 2 of the patch jumper (SJ1) however scaffold Pins 2 and 3 together with a bind mass.
As referenced before, the oscillator is gated by a “dropped” 5-Vdc supply accessible from the USB OTG port through the security link. The last yield of the oscillator will be “low” (0 V) when the oscillator is crippled by the gating diode (see beneath documentation)
Furthermore, note that only three gates of the hex inverter are utilized here, so all of its unused inputs must be tied to the ground rail (unused outputs must be left open).
As to utilization, it doesn’t generally make a difference in light of the fact that the framework pulls immaterial current from a 3-V battery in the inactive express that may shoot up to 50 to 60 mA in the dynamic state (i.e., during the caution time). Moreover, the nearly higher worth potential divider (R1 and R2) draws peripheral current from the 5-V USB OTG interface and hence won’t stack the associated cell phone or channel its interior battery to an extreme. It’s anything but difficult to catalyst the framework with an arrangement associated pair (1.5 V × 2) of standard AA or AAA dry cells.
One last comment on development is about the battery. Since the hardware needs at least 3 V, it ought to wind up important to utilize new, dry cells toward the begin to guarantee agreeable activity of the security caution framework. A little LiPo battery (see next figure) will be a feasible choice here. Assuming this is the case, you can include a little battery charger segment to the current principle hardware too. Consider it!
In the event that you have to charge a solitary cell LiPo battery, this straightforward charger circuit dependent on MCP73831 will do only that and do it securely. Then again, shoddy, pre-wired USB LiPo charger modules (see beneath) permit “apathetic” creators to set up fundamental chargers for charging their 3.7-V LiPo batteries, normally at a rate of 100 mA or 500 mA for every hour.
Remaining over innovation is hazardously costly, particularly in the side interest hardware world. Regularly, you have to purchase at any rate one new segment for another task, and normally, numerous old segments kick the bucket in the garbage box. In any case, this doesn’t imply that you can’t construct fascinating or helpful circuits with more established parts from your garbage box. The circuit presented here is a genuine model, and it’s a lot easier than it looks. With a touch of training, you can without much of a stretch figure out how to make it a solid match for an assortment of productive applications.