Hacking an alarm clock

The project involves bypassing the mechanical snooze switch of an alarm clock and replacing it with a more engaging method: physically striking the device. The objective is to impart useful techniques in reverse engineering that can be applied to future projects. This initiative targets intermediate electronics enthusiasts who are proficient with multimeters and comfortable with soldering complex circuits. The alarm clock selected for this project is designed to ensure that no mains voltages are accessible internally, although other models may have different layouts. Caution is advised; this project should only be attempted by individuals who are confident in their ability to work safely with mains electricity. The DE-ACCM sensor is preferred for this application, as it offers a continuous analog voltage proportional to vibration intensity, unlike mercury or reed switches which only provide binary outputs. This allows for a customizable trigger threshold based on vibration levels. The project requires identifying the ground and regulated positive voltage supply within the clock's circuitry to power additional circuits. Analyzing the snooze button switch is essential to understand its impact on the clock's circuitry. The examination will begin with the four wires connected to the snooze and alarm reset switches. A suitable voltage supply must be located first. Inside the clock, a small mains transformer reduces 120VAC to a lower AC voltage, which is then rectified to DC by a series of diodes and capacitors. The presence of resistors and transistors in this area raises questions about their functions. A large integrated circuit (IC) is responsible for powering the clock's LEDs, requiring a capacitor in parallel with its power pins for stability. The largest electrolytic capacitor in the circuit is likely connected to the ground plane and the filtered positive supply. Prior to re-energizing the clock, it is crucial to ensure no wires are misplaced or shorting. Upon reactivation, the voltage across the capacitor should be measured, which should read approximately 13V DC, with fluctuations depending on the LED activity. This voltage will serve as a power source for the additional circuit, with the capacitor's negative side acting as the ground reference for further voltage measurements. The next step involves analyzing the snooze button by using a multimeter's continuity function to identify the corresponding wire connections.

The project entails a detailed exploration of the alarm clock's internal circuitry, focusing on safety and functionality during modification. The DE-ACCM accelerometer is a core component, providing a continuous output that allows for precise adjustments to the triggering mechanism based on the intensity of the physical interaction. This flexibility surpasses traditional switches, which may not respond adequately to the desired level of user engagement.

The identification of the power supply is pivotal. The voltage supply derived from the main storage capacitor is critical for powering additional circuits that will be integrated into the alarm clock. The capacitor's role in stabilizing the voltage for the LED driver IC is vital, as it ensures consistent performance of the display, especially during variable load conditions.

To execute the modifications safely, it is necessary to maintain a clean workspace and ensure that all components are tested for continuity before reassembly. The multimeter will be an essential tool for verifying connections and ensuring that the modifications do not introduce any faults into the system. The analysis of the snooze button's wiring will reveal how the circuit responds to its activation, enabling the design of a new circuit that will replace the mechanical switch with a more interactive solution.

In conclusion, this project not only enhances the functionality of the alarm clock but also serves as a practical exercise in circuit modification and reverse engineering, providing valuable experience for intermediate electronics enthusiasts. Proper safety precautions and thorough analysis of the circuit are paramount to ensure a successful outcome.We will bypass the mechanical snooze switch on top, and instead turn the alarm clock off in a much more fun way: punching it! Hopefully along the way I will be able to teach you some techniques that are useful in reverse engineering, so you can apply them to future projects.

This project is aimed at intermediate electronics enthusiasts, who have mastered the art of the multimeter and are comfortable with soldering a complex circuit. This project involves working with a device that connects to mains voltages. The alarm clock I used just so happened to be designed so well that it was impossible to touch any mains voltages inside it. Other alarm clocks may not give you this comfort and will most likely have a different layout inside.

Do not attempt this project unless you are 100% sure you know you can do it safely! The DE-ACCM is a good choice for this project because other vibration sensors such as mercury switches or reed switches only provide open or closed switch outputs, whereas the DE-ACCM provides a continuous analog voltage directly proportional to the intensity of the vibrations. For example, a mercury switch might prove to be too insensitive to measure the small vibrations of someone banging on the table, or it might be so sensitive that it activates simply from the vibration of the alarm clock`s speaker.

With an accelerometer, you can easily design the circuit to trigger at any amount of vibration you want. We must find the ground and regulated positive voltage supply for the clock`s circuitry. We need this so we can power any additional circuits we design and insert into the clock. We must analyze the snooze button switch. When it opens/closes, what changes happen in the clock`s circuitry Knowing this information is necessary to design the circuit that will activate snooze.

You can see four wires leading to a board that contains the snooze` and alarm reset` switches. We will examine those wires very soon. Let us first hunt for a good voltage supply! Inside the main body of the clock, you can see a small mains transformer that steps 120VAC down to a lower AC voltage. The transformer`s wires lead to an area with a bunch of diodes and capacitors that rectify the AC waveform into DC.

But what are all those resistors doing there What is the deal with those transistors Things are getting too crowded in that area to easily probe around, so lets try another approach. Over on the right, you can see a large IC which is clearly responsible for driving all the LEDs on the clock`s screen.

Since the chip needs to supply the LEDs with a fair amount of current that could change at any second, it would need a capacitor connected directly in parallel with its power pins. Lo and behold, right next to the chip you will see the largest electrolytic capacitor in the whole circuit.

There is a very good chance that the negative side of this cap is connected to the circuit`s ground plane, and the positive side is connected to the filtered positive supply of the circuit. Before powering the clock again, we must double check that no wires are accidentally out of place and shorting each other out as a result of opening the clock up.

Once the clock is plugged in again, we can observe the voltage across the big capacitor when the clock is running. The meter reads about 13V DC, and the voltage fluctuates slightly depending on how many LEDs are on in the display at the time a clear sign that this is definitely the main storage capacitor for the IC.

We now know that we have a 13V supply we can work with to power our additional circuit. The negative side of the capacitor is the circuit ground, and we can use it as a reference point when measuring other voltages in the circuit. So now we can move on to analyzing the snooze button. After unplugging the clock, we can use the continuity function of our multimeter to see which pair of wires the snooze button is connected to.

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