2SCA transistor pinout, marking CA Sometimes the “2S” prefix is not marked on the package – the 2SCA transistor might be marked “CA”. BACKLIGHT: WITHOUT BACKLIGHT; LED; EL. 3. COLOR OF BACKLIGHT: Y/G; BLUE; WHITE. 5. POWER SUPPLY: V; V. 4. TEMPERATURE RANGE. CA ETC datasheet pdf data sheet FREE Datasheets (data sheet) search for integrated circuits (ic), semiconductors and other electronic components such.

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This is a security box for storing valuables. As functionality was changed, some components were not used. They may be integrated into a future revision of the device. This is to mainly illustrate an early phase of development. More detailed diagrams are provided later. Due to space limitations we had to remove it and use an external 12V DC power supply. A power distribution diagram is shown below:.

The shift register output signal Q7′ can be fed to the data input of additional shift registers. The shift register output feeds the input of an 8-bit output latch, which has a dedicated clock input. In this way you can shift any kind of data through the shift register chain without disturbing the actual output pins, and then only load data from the shift register to the output latch when necessary.

The output of the final shift register in the chain can be fed back into MISO for diagnostic purposes; while the shift registers are output-only devices, connecting the output to MISO allows you to verify that the data transmitted through the chain was correctly received.

This can help identify wiring errors or other problems early on and is a good diagnostic tool. While only two shift registers are used, more could be added. There is no practical limit other than the worst-case time it takes to change the last shift register is the time it takes to shift data through all shift registers in the chain. For high speed applications the chain should be kept short, but even then the 74HCT is rated to run up to 25 MHz, so with good wiring even a long chain can be updated rather quickly.

Other diagrams shown later will detail the low-level implementation between the shift registers and the peripherals they drive. The keypad is arranged as a 4×3 matrix. Where each row and column intersect is a switch, and a physical connection between the row and column is made when the switch is depressed.

Otherwise there is no connection when a switch is released, and the relationship between the row and the column at that point appears as an open circuit. As the keypad has no datasheet the first task was to disassemble the keypad and use the continuity test function of a multimeter to determine the pin assignments:. The notation of row vs.

S RFID Security Box – Embedded Systems Learning Academy

As the rows and columns are shorted when a key is pressed, it is important to never drive the rows and columns to complementary output levels. The rows should be inputs with internal pull-ups enabled, and the columns are outputs that are driven low or high or tri-stated.

For each column, drive the corresponding column output low e. Row bits will be 0 where the row and column intersect AND the key is pressed, or 1 where the key is released. Note that the keypad operation is fully mechanical like any switch, there is no ground datasheeh power connections necessary. This datasheer a legacy part that has a alike bus as follows:. C1627aa support devices with less GPIO such as 4-bit microcontrollers, the Datazheet has a 4-bit mode where only DB are used, and byte-sized data is transferred by writing four-bit nibbles twice in sequence.

However the documentation is sparse on the exact timing in this mode, and it was unreliable when the control signals d1627a slowly. To compensate, one of the shift registers was allocated to provide all 8 bits of data, and the remaining GPIO was used for the control signals.


The HD needs a certain amount of time to carry out actions, and will output a busy status flag on DB7 during a read cycle. As a output-only shift register was being used to drive the data bus it was not possible to read data. Dayasheet hardware solution was to place a 10K resistor in series with the shift register, such that Q7 of the shift register could pull DB7 low or high.

In this way the HD could still drive DB7 which was connected to a GPIO, allowing the busy status to be read regardless of how the datasyeet register was driving the pin. However the time it takes to complete operations is somewhat variable, and it varies further between different manufacturers. To be daatsheet lengthy delays must be used which waste valuable time. It seemed much more worthwhile to have a hardware solution to enable polling, in order to keep the software responsive.

Current limiting resistors are provided on the PCB and do not need to be added externally. By doing this the available current from the MIC regulator on the SJ one board isn’t impacted, as it is limited to mA, 60mA would have been a considerable portion of the current budget.

The available color range is black offred, green, blue, cyan, magenta, yellow, and white. The LCD display has a very finite viewing angle at which the display appears undistorted. To accommodate for other viewing angles the contrast may be adjusted using a 10K potentiometer.

In practice the user will be holding the control box and can tilt it for datashest clearest possible display, so a fixed contrast level was chosen that matched that use case.

The solenoid used Adafruit is designed to function similarly to the latch datashee a door. A spring pushes the metal slug outwards such that the door is locked when the system is turned off. The datasheft contains a coil that generates a magnetic field when energized, which draws the slug inwards against the force of the spring allowing the c627a to be opened. Thus the solenoid locks the door when off, and unlocks it when on.

When the solenoid is turned off after a period of activation, the magnetic field collapses, at which point the force of the internal spring overcomes the decreasing force of the magnetic field holding the slug in place, and the spring can then eject the slug to the outward position. When the magnetic field collapses current is induced in the coil, causing a large voltage spike that can be damaging to any digital datwsheet connected to it.

This provides a safe discharge path so that the voltage spike does not go into the digital circuitry.

Note that the ULN used has a built-in diode for this purpose, but during testing it was observed that the LCD display would flicker when the solenoid was turned off. Adding a large 1N diode across the solenoid eliminated this problem completely.

A Darlington transistor is a pair of transistors in series that can sink a large amount of current, and can interface to higher voltage signals such as 12V. The output is inverted with respect to the input, such that a high-level input sinks current on the output, and a low-level input makes the output go high impedance.

Accordingly, the output must have a pull-up resistor to prevent any oscillation or noise when in the high impedance state. Each channel of the ULN can handle mA. As there were multiple free channels available, three were used in parallel to provide up to 1.

Adafruit sells the solenoid with the slug oriented in 90 degrees from the desired position.

To correct this, the housing can be lifted up after removing two screws. There is a thin D-ring around the base of the slug which is quite hard to remove. Using a flat screwdriver head to push on one side of the ring while holding the other side in place with needle-nose pliers worked eventually. There may be some kind of dedicated tool c1672a D-ring removal which would simplify this process. The solenoid in the security box is connected to a RCA jack, which connects to a matching jack on the control box.


This was chosen as it was a inexpensive two-terminal cable that datasheett easily available. Ideally the wiring should be held in place by small fencing staples, but as a temporary solution electrical tape was used. The piezo buzzer is a thin plate that deflects when voltage is applied to it. This deflection is enough to datasbeet audible sound, and the plate is mounted in a plastic cavity for amplification.

The buzzer can be controlled by DC voltage such that dahasheet square-wave of a given frequency, such as Hz, creates a Hz tone. At very low frequencies the buzzer can be used to make simple clicking sounds, such as to augment the keypad entry with clicks as each key is pressed.

C1627 Datasheet PDF

This kind of feedback makes it easier for the user to tell if a key press was complete or not. This makes it susceptible to noise which can be heard as audible clicks. Holes were drilled out and slots were removed with a Dremel tool.

The printed circuit board was used to construct the circuit using wire-wrapping. Due to the low clearance underneath the PCB the sockets had to be cut down to fit, complicating wiring.

Mounting holes were made to connect the PCB to the case bottom using plastic standoffs and screws, and a similar system was employed to mount the SJ One board to the PCB. Ideally a number of identical length jumper wires would have been used so that wires could have had zip-ties applied and been mounted out of the way. In practice the jumper wires that were available were from miscellaneous sources and were hard to organize, while still allowing access to the circuitry inside the box.

This task scans the keypad matrix, storing the resulting data in a “key event” structure. When a key is pressed, the structure is loaded into the key queue. Application software can then unload key events and process them as necessary.

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This task advances the user interface through different screens based on criteria such as keypresses made, if a PIN was valid, if the door unlock countdown timer has expired, etc. Using a finite state machine makes the ‘initialization’ state transition and ‘running’ work done within a state easy to manage and trivial to expand to add more functionality. This task generates a square wave to activate the piezo vatasheet.

To provide uninterrupted sound it is a high priority task. To manage this shared resource a mutex is used such that each task cannot be pre-empted by the other during SSP0 bus access. The mutex is datashset during startup:.

The shift registers are abstracted as a chain of shift registers placed in series.

The “sreg” class is used to get the state of a shift register the last value written to itand set the new state as well.

The shift register update function actually updates the shift register chain with the new values. When the user enters data on the keypad this creates a key event.

The key event stores the current keypad state and indications of what has changed, such as if a key was pressed or released. Key events are placed into the key queue for other tasks to retrieve user input. This is used to play back beeps that are generated when the user presses buttons on the keypad.

For the most part the tone and key events are datsheet coupled, but the system was designed so that other sources could generate tones, such as RFID card swipe results which are independent of any key input. The finite state machine controls the different display screens and manages the PIN entry and door unlocking mechanism. It can be visualized as a flowchart as follows:. States from top to bottom: A line editor module was developed to allow complex data entry.

It support commands such as delete backspacecancel, and submit.