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The alarm unit sits inside the safe and sounds an alarm if the safe door is opened unless the correct code is entered before the entry delay period expires. Hotel safe alarm for travellers Design by JOHN CLARKE Are you a frequent tourist? Then you will be familiar with the small safes in every room in most hotels and in the cabins on cruise ships. This Hotel Safe Alarm tells you if the safe has been opened in your absence and will also give the offender a very bad feeling that he or she has been detected. Their natural reaction will be to close the safe and abscond immediately. A NYONE WHO regularly travels on cruise ships or stays in hotels will be familiar with the ubiquitous room safe which is usually inside the wardrobe. The safe has a 4-digit LED Features • • • • • • • Powered by a lithium button cell Armed indication (green LED2) Entry indicator (red LED1) Piezo alarm Low current drain Adjustable entry delay period Adjustable alarm period 64  Silicon Chip display and a numeric keyboard to let you enter a 4-digit code before closing it and again when you wish to open it. They are very handy but it would be naive to think that these safes offer a high degree of safety for your valuables. After all, if you forget the code or the safe malfunctions, it is a straightforward exercise for the hotel staff to open them. That means that there could be people lurking about in hotel or ship corridors that don’t have your best interests at heart. And since they will attempt their nefarious activity while you are absent, how can you discourage them? The answer is to use our Hotel Safe Alarm. Of course, you could also use this alarm in a safe at home, or in a filing cabinet or desk drawer that you want to monitor. And you could use it to monitor a tool cupboard, pantry (against hungry teenagers marauding at night?) or whatever. The Hotel Safe Alarm is a small plastic box with two LEDs (red and green) and two pushbutton switches. A light dependent resistor (LDR) detects when the safe has been opened and it will react to room lighting or a torch. A LED starts blinking immediately and if you don’t enter in a code via the two buttons within 15 seconds, the inbuilt piezo transducer will start screaming at you (or the offender). The duration of the alarm is 60 secsiliconchip.com.au POWER LED1: ENTRY DETECTED LED2: ARMED JP1 470k D1 1N4004 3V LITHIUM CELL K 4 100nF 1 Vdd GP5 GP3/MC 330Ω 2 330Ω 7 A GP0 IC1 PIC12F675 -I/P 6 LDR1 λ GP4 GP2 Vss 8 A λ K LED2 100Ω GP1 5 LED1 λ K A 3 1k CODE S1 ENTRY 1k PIEZO 1 S2 LEDS SC 20 1 6 K A HOTEL SAFE ALARM Fig.1: the circuit is based on PIC microcontroller IC1, light dependent resistor LDR1, a couple of LEDs and a piezo transducer. If the safe is opened, LDR1’s resistance goes low and pulls pin 4 of IC1 low to start the alarm entry timer. The correct code then has to be entered within 15 seconds via pushbutton switches S1 & S2 to stop the alarm from sounding. Specifications • • • • • • Power: 3V at typically 2.5µA Alarm current: 0.5mA Alarm entry delay: adjustable from 1-60s in 1s steps; initial value is 15s Alarm period: 10s to 120s, in10s steps. Default value is 60s Alarm disable code: any code sequence from one to eight switch presses Alarm signal: 280ms bursts of 4-6kHz tone with a 220ms gap between bursts onds as the default setting but this can be set to between 10 seconds and 120 seconds, in 10-second increments. If your safe has been opened in your absence, the alarm will indicate that by alternately flashing the red and green LEDs. To clear this alarm condition, you just feed in the entry code by pushing the two buttons in the normal way. We’ll describe how you enter the code and various time settings later in this article. Circuit details The circuit is very simple; just an 8-pin PIC microcontroller, two LEDs, two pushbuttons and few other components – see Fig.1. It is powered by a 3V lithium button cell and is switched on via jumper link, JP1. This can be removed when you are not using the alarm, to save the battery. IC1 is a PIC12F675-I/P microcontroller and it is programmed with a siliconchip.com.au tricky bit of software that lets you enter the necessary settings with only two pushbuttons. Normally, IC1 is in sleep mode and its watch-dog timer wakes it about every 2.3 seconds and it briefly checks the ambient light via the LDR, as follows. Normally, IC1’s GP2 output at pin 5 is set high (at 3V), so there is no current flow through the 470kΩ resistor and the LDR. This is done to minimise current drawn from the 3V cell. When IC1 wakes up, it sets GP2 low (0V) and then monitors the voltage at input GP3 (pin 4). In darkness, the LDR resistance is high (well above 1MΩ) so the voltage at pin 4 will be high, at close to 3V, so IC1 (yawn) goes to sleep again. If it wakes and the LDR is exposed to ambient light, its resistance will be much lower, perhaps as little as 10kΩ in bright light. So the voltage at pin 4 will be low and IC1 starts to get excited. Well, perhaps not but it starts Parts List 1 double-sided PCB, code 03106161, 61 x 47mm 1 front panel label, 74 x 47mm 1 UB5 translucent clear or blue case, 83 x 54 x 31mm 1 20mm button cell holder (Jaycar PH-9238, Altronics S 5056) 1 CR2032 lithium cell (3V) 2 SPST PCB mount snap action switches (Jaycar SP-0723, Altronics S 1099) (S1,S2) 1 30mm diameter piezo transducer (Jaycar AB-2440, Altronics S 6140) 1 10kΩ light dependent resistor (Altronics Z 1621; Jaycar RD3480) (LDR1) 1 DIL8 IC socket 2 M3 tapped 12mm spacers 2 M3 tapped 6mm spacers 6 M3 x 6mm machine screws 2 M3 x 6mm machine screws 2 M3 x 6mm countersink screws 1 2-way pin header (2.54mm pin spacing) (JP1) 1 jumper shunt 2 PC stakes 1 25mm length of 2mm diameter heatshrink tubing Semiconductors 1 PIC12F675-l/P programmed with 0310616A.hex (IC1) 1 1N4004 diode (D1) 1 3mm red high brightness LED (LED1) 1 3mm green high brightness LED (LED2) Capacitor 1 100nF 63V or 100V MKT polyester or ceramic Resistors (0.25W, 1%) 1 470kΩ 2 330Ω 2 1kΩ 1 100Ω flashing green LED2 to indicate that the alarm is about to start sounding. Provided the valid code is now entered with the two pushbuttons during the 15-second delay period, the alarm is disabled. If no code or an invalid code is entered, the piezo transducer sounds, as pins 6 & 3 (GP1 & GP4) alternately go high and low, to deliver bursts of 4kHz signal. In the confined space of a hotel safe and at close quarters, this can be quite loud. Certainly, there is no mistaking that June 2016  65 Fig.2: the yellow & green traces show the complementary drive signals applied to the piezo transducer. The two signals are at 3.99kHz and have an amplitude that’s close to 3V peak to peak, not allowing for the overshoot spikes. The total signal applied to the transducer is shown in the red trace and is 6V peak to peak the miscreant has been “pinged”. As already mentioned, the alarm will sound for the default period of 60 seconds (unless programmed to do otherwise). The scope screen grabs of Fig.2 & Fig.3 show the complementary drive signals applied to the piezo transducer. In Fig.2, the two signals are at 3.99kHz and have an amplitude very close to 3V peak-to-peak, not allowing for the overshoot spikes. Therefore the total signal applied to the transducer will be very close to 6V peak-to-peak or about 3V RMS as shown in the red trace of Fig,2. Fig.3 shows the same complementary drive signals but at a much slower sweep speed of 100ms/div. This shows the signal bursts which are about 280ms long and separated by gaps of about 220ms. If the safe door is hastily closed again, the alarm will continue to sound for the remainder of the 60-second period and then go back to sleep. When the safe door is re-opened, the red and green LEDs will alternately flash for 15 seconds, unless you enter the valid code. If not, the piezo alarm will begin beeping again. And so the cycle goes . . . So as well as providing some deterrent by sounding the alarm if a valid code is not entered, it will also tell you that the safe has been opened in your absence, even if it has been closed after being detected. Button detection As well as providing the drive signal for the piezo transducer, pins 6 & 3 (GP1 & GP4) monitor the state of the two momentary contact pushbutton 66  Silicon Chip Fig.3: this scope grab shows the same complementary drive signals but at a much slower sweep speed of 100ms/ div. The signal bursts are about 280ms long and are separated by gaps of about 220ms. The red trace shows the total signal applied to the transducer and is 6V peak to peak. switches, S1 & S2. To do this, GP1 & GP4 are set as inputs which are normally high but they can be pulled low via the 1kΩ resistors in series with the switches. So if S1 is closed, pin 6 (GP1) will be pulled low. The 1kΩ resistors are included so that pressing the switches when the alarm is sounding will not short out the alarm signal to the piezo transducer. Battery power As already noted, the circuit is powered by a 3V button cell, via link JP1. When IC1 is in sleep mode, the current is quite low, at about 2.5µA. The current drain when the piezo alarm is sounding is 0.5mA. And while LED2 is flashing, the current is 1.5mA (for a cell voltage of 3V). Diode D1 is included as a safety measure to prevent damage to IC1 should the cell be connected incorrectly somehow. If the polarity is wrong, D1 will shunt the reverse current. Reverse cell polarity could happen if the cell holder is installed the wrong way round. Alternatively, if the cell holder is installed correctly, then the diode protects the circuit if the cell is installed incorrectly. Note that for the particular cell holder we used, there is no way the cell can be inserted incorrectly and make a connection to the circuit. IC1’s power supply is bypassed with a 100nF capacitor and IC1 runs using its internal 4MHz oscillator which is shut down during sleep mode. LED2’s brightness provides an indication of the cell voltage. At 3V supply, LED2 is quite bright but will be dim when the cell voltage drops to 2V, indicating that it should be changed. Programming trickery Note that the GP3 input of the PIC12F675 is usually configured as the MCLR input (master clear), which allows the microcontroller to have an external power-on reset. However, for our circuit we need to use this as a general purpose input for monitoring the LDR. When MCLR is set up as an input, the MCLR operation is switched to an internal connection within the microcontroller so the master clear power-on reset function is not lost. One disadvantage of using the MCLR pin as a general purpose input is that there can be a problem when programming the microcontroller. This occurs when the internal oscillator is also used to run the microcontroller (which we do). Similar to the Fridge Door Alarm presented in the April 2016 issue, we solved this problem in the software, as discussed in the programming panel. PCB assembly The parts are all installed on a small double-sided PCB coded 03106161 (61 x 47mm). This fits inside a small (UB5) plastic case. Note that the LEDs, switches, LDR and the piezo transducer are mounted on one side of the PCB, while the remaining components are mounted on the other side. Fig.4 shows the parts layouts for both sides of the PCB. Begin construction by installing the resistors, using a multimeter to check the value of each before inserting it into place. Table 1 siliconchip.com.au 16 03106161 1 6 0 1 3 0 C 2016 Rev.B 470k 4004 PIC12F675 03106161 LED1 JP1 D1 CR2032 BUTTON CELL HOLDER + IC1 330Ω 100nF LDR1 PIEZO 1 330Ω LED2 100Ω 1k 1k PCB STAKES S2 SAFE ALARM S1 Fig.4: the PCB layout diagram on the left shows how the parts are mounted on the rear of the board, while the layout at right shows the how the parts are mounted on the top side. Take care to ensure that all polarised parts are correctly orientated and note that the piezo transducer is supported on 6mm spacers and secured with M3 screws – see text. The PCB should only take about 30 minutes to assemble. Note that the LDR and the two LEDs must be mounted proud of the PCB – see text. also shows the resistor colour codes. Diode D1 can now be installed, taking care to orientate it correctly, then fit the IC socket, orientating its pin notch as shown in Fig.4. The 100nF capacitor is soldered in next and it can be positioned either way round. Then solder in the 2-way pin header for JP1 along with the cell holder. Make sure the plus terminal is orientated towards diode D1 on the PCB. LED1 (red) and LED2 (green) are mounted so the top of the LED lens is 14mm above the top surface of the PCB. Make sure the longer lead of each LED (the anode) is inserted in the “A” position on the PCB. The LDR is also mounted 14mm above the PCB surface. Once the LEDs are in, install switch- es S1 & S2, again taking care to ensure that they are correctly orientated (flat side positioned as shown). have red and black wires, the polarity of the connections is immaterial; you can connect it either way around. If you intend to program the PIC yourself, the file 0310616A.hex can be downloaded from the SILICON CHIP website. Check the programming panel on the following page for details on how to do this. Alternatively, you can purchase a pre-programmed PIC from the SILICON CHIP Online Shop. Be sure to insert IC1 into its socket with the correct orientation and make sure you don’t bend the pins under the IC. Then install the CR2032 cell in its holder and place the jumper link onto the 2-way header (JPI). If all is well, LED2 will begin to flash on and off after about three seconds, indicating Piezo transducer mounting The piezo transducer is mounted off the PCB, supported on M3 x 6mm spacers and secured with M3 screws. The mounting holes in the lugs of the piezo transducer will need to be drilled out to 3mm for these screws. The wires are soldered to the PC stakes marked “piezo” on the PCB. We used PC stakes for the piezo transducer wiring as this allows heatshrink tubing to be slid over the wires and PC stakes to help prevent the wires from breaking off. While the piezo transducer may Table 1: Resistor Colour Codes o o o o o siliconchip.com.au No.   1   2   2   1 Value 470kΩ 1kΩ 330Ω 100Ω 4-Band Code (1%) yellow violet yellow brown brown black red brown orange orange brown brown brown black brown brown 5-Band Code (1%) yellow violet black orange brown brown black black brown brown orange orange black black brown brown black black black brown June 2016  67 Programming The PIC Micro A programmed PIC for this project can be purchased from our on-line shop (www.siliconchip.com.au) or you may program one yourself. The software is also available from our website. If you are programming the microcontroller yourself, you may be presented with a warning by the programmer stating that programming is not supported when both the MCLR pin is set as a general purpose input and the internal oscillator is used. As with the Fridge Door Alarm presented in the April 2016 issue, you will be able to program the microcontroller successfully, so ignore this warning. That’s because any problems associated with this configuration is already solved by a software solution. Read on if you want more details. As mentioned, we set MCLR as a general purpose input and utilise the internal oscillator within IC1. This can present problems for a programmer during the process of verifying the software code after programming. The problem lies in the fact that as soon as the microcontroller is programmed, it that the LDR is exposed to light. The piezo transducer will then sound the alarm after the (default) entry delay period of around 15 seconds. Plastic case The PCB is installed inside a UB5 plastic case with the piezo transducer arranged to “fire through” a hole in the lid. You need to drill holes in the lid for the two LEDs, LDR, two switches and the piezo sound exit hole. In addition, two mounting holes, one either side of the two switches, are needed to secure the PCB to the lid, using spacers and screws. The holes for the two LEDs and two PCB mounting holes adjacent to S1 & S2 are 3mm, the switch holes and piezo sound exit hole are 10mm and the LDR hole is 5mm. The drilling template (Fig.5) can be downloaded from the SILICON CHIP website (www. siliconchip.com.au). Having drilled the holes, the label can be attached. This can be downloaded from the SILICON CHIP website, printed out (preferably onto photographic paper) and affixed to the lid using either glue or neutral-cure silicone. Another option is to print the panel onto either an A4-size “Dataflex” 68  Silicon Chip will begin executing its program. A typical program initially sets up the microcontroller with the general purpose lines set as inputs or outputs (I/O). This conflicts with the programmer needing to use the clock and data programming I/O lines for program verification. This problem does not happen if the MCLR pin is set as the external MCLR input because the programmer then has control over the microcontroller, stopping it from executing the programmed code. Note also that in order to run the code, the microcontroller has to have the internal oscillator configured instead of an external crystal, RC or external clock oscillator. The programming problem is solved in the software provided by including a 3-second delay at the start of the program. This delay is before the I/O lines are set as inputs or outputs. The I/O lines therefore remain as high-impedance inputs while the programmer verifies the internally programmed code using the clock and data programming lines. sticky label (for ink-jet printers) or a “Datapol” sticky label (for laser printers) and directly attach this to the case lid. These labels are available from http://www.blanklabels.com.au – see accompanying panel. Once the label is in position, cut out the holes using a sharp hobby knife. The PCB is stood off from the lid of the case using M3 x 12mm tapped spacers. M3 screws secure the PCB to these stand-offs, with countersink screws used to secure the spacers to the lid. Finally, attach the lid to the case using the four screws supplied with the case. Note that you can keep tabs on the condition of the lithium battery condition by observing LED2. If it flashes brightly, the cell is OK. As the cell discharges, the LED will become quite dim. Changing the settings There are three settings that can be altered on your Hotel Safe Alarm: entry delay, alarm duration and the entry code. These can only be altered after switching the alarm off by removing link JP1 and then pressing one or both switches while JP1 is reinstalled to connect power. A warning from the programmer will still be issued but the microcontroller can be programmed successfully and correctly verified by the programmer. Note that the PIC12F675 also needs special programming due to the fact that it has an oscillator calibration value (OSCAL) that is held within the PIC’s memory. This calibration value is individually programmed into each PIC by the manufacturer and provides a value that sets the PIC to run at an accurate 4MHz rate using the internal oscillator. This value must be read before erasure and programming so that it can be included with the rest of the code during programming. If this procedure is not done, then the oscillator could be off frequency and that will have an effect on the Hotel Safe Alarm’s sound. Most PIC programmers will automatically cater for this OSCAL value but it is worthwhile checking if your programmer correctly handles this, especially if you have difficulties. Finally, be aware that the PIC12F675 requires a 5V supply for programming, even though it happily runs from 3V in the circuit. Changing the entry delay and alarm period are optional and you can leave them at default settings of 15 and 60 seconds, respectively. However, you will need to set the entry code. Entry delay To set the entry delay, power the unit off by removing link JP1 and hold switch S1 down while JP1 is installed. Continue holding S1 down until you get a short beep from the piezo transducer (after about three seconds). Release S1 and another beep will sound. The delay period is now entered by pressing switch S2. This starts from one second (plus the initial wake-up time of 2.3 seconds) and each time you press S2 there is a very brief double beep from the piezo to indicate the entry delay has been incremented by one second. You can increase the delay to 60 seconds but we think that 15 seconds is quite adequate. You then store the entry delay setting by pressing S1 and this will be indicated by a short beep from the transducer. Alarm period The alarm period setting process is very similar to the entry delay but siliconchip.com.au Front Panel Labels The PCB is mounted on the case lid using two M3 x 12mm tapped spacers and M3 x 6mm screws. now we do it with switch S2. So to set the entry delay, power the unit off by removing link JP1 and hold switch S2 down while JP1 is installed. Continue holding S2 down until you get a short beep from the piezo transducer (after about three seconds). Release S2 and another beep will sound. The alarm period is entered by pressing switch S1. The alarm period starts at 10 seconds and each time you press S1 there is a very brief beep from the piezo to indicate that the alarm period has been incremented by 10 seconds. The alarm period can be adjusted from between 10 and 120 seconds in 10-second steps. When S2 is pressed, the entered alarm period will be stored and indicated by a short beep from the piezo transducer. membered, such as 1221. But it can be any sequence from 1-8 presses. To set the entry code, power the unit off by removing link JP1 and hold both switches S1 and S2 down while JP1 is installed. Continue holding S1 & S1 down until you get a short beep from the piezo transducer (after about three seconds). Release S1 and S2 and another beep will sound. The entry code is now entered in, with each switch press acknowledged by a brief piezo beep. The entered code will be stored after both switches are left open (ie, after none are pressed) for five seconds. An acknowledgement beep then sounds. Using the alarm The correct code needs to be entered during the entry delay period. Do not try to enter the code too quickly. Each time you push a button you need to wait for a short beep and then you press the next button. So for example, if your code is 1221, you do it in this sequence: 1 beep, 2 beep, 2 beep, 1 beep. If the code is correct, the alarm Entry code The entry code comprises a sequence of presses of S1 & S2. It can be as simple as 1, 2 or 2, 1 or it could be up to eight presses, such as 1 2 2 2 1 2 1 2. Most people will want to keep it reasonably short so that it is easily re- SILICON CHIP C + + A + C C will not sound (the green LED stops flashing as soon as a switch is pressed). If you make a mistake while entering the code, or you enter it too rapidly, the alarm will sound and the safe can be closed to muffle the alarm sound. Entering the valid code prevents the alarm sounding only if no more switches are pressed. Any further button pressing following the valid code will be greeted by an alarm. If an intrusion is detected, both LEDs will be flashing. They will cease flashing once one of the switches is pressed to begin the entry code sequence. The LEDs turning off may even give an intruder a false hope that the code entered was correct. The alarm is rearmed after it is placed in darkness, ie, when the safe door is closed. As soon as light shines on the LDR, you have to enter the code to stop the alarm from sounding. SC LID DRILLING TEMPLATE + + The front-panel label can be made by downloading the relevant PDF file from the SILICON CHIP website and then printing it out onto photographic paper. It can then be attached to the front panel using silicone adhesive. Alternatively, you can print onto a synthetic Data­ flex sticky label if using an inkjet printer or onto a Datapol sticky label if using a laser printer. (1) For Dataflex labels, go to: www.blanklabels.com.au/index. php?main_page=product_info& cPath=49_60&products_id=335 (2) For Datapol labels go to: www. blanklabels.com.au/index.php? main_page=product_info&cPath =49_55&products_id=326 + A A = 10mm B = 5mm C = 3mm + A Hotel Safe Alarm B Door Open/ Alarm Pending Enter Code + C Fig.5: this drilling template can be downloaded as a PDF file from the SILICON CHIP website. siliconchip.com.au Unauthorised Opening 1 2 Fig.6: this front panel artwork is also available as a PDF file on the SILICON CHIP website (see panel). June 2016  69