Digital Alarm Clock Circuit Diagram
Faustina Bartsch
The advantage of digital alarm clocks over analogue alarm clocks is that they require less power, the time can be set or reset easily and displays the time in digits. Design of a simple digital alarm clock is explained here.
Using this digital alarm clock, time can be displayed in 24 HR format using an LED display and alarm can be set to a specific time. Alternatively, the digital alarm clock circuit can also be used to turn ON/OFF and electrical appliance after a specific time.
The heart of the digital alarm clock is the IC LM8560. It is an alarm equipped digital clock IC. The drivers required to drive a duplex LED display to show the time are in-built to the IC. The functions of the IC LM8560 are display of current time, alarm support, snooze function and supports 12 HR and 24 HR time format.
In the digital alarm clock, to display the information like current time, alarm notification etc. we use a duplex LED display. There is no need for any extra drivers to drive the display unit as all the required drivers are built in to the digital clock IC.
Diode D1 in combination with the capacitor C1 will produce a DC voltage that is supplied to the IC1 (LM8560). Diodes D2 and D3 act as switch signal generator to the cathode of the duplex display. They work in relation to the input of the LM8560.
A digital alarm clock is a very useful device as it can display the current time as well as function as an alarming device. The circuit shown above can act as a simple digital alarm clock without requirement of any programming.
As explained in the component description, the heart of the digital alarm clock circuit is the digital clock IC LM8560. The input from the mains is given to the transformer which converts the input voltage to 12V AC.
In relation to the input of the IC1, corresponding inputs to the cathode of the display are given through the diodes (D2 and D3). After switching on the power, we need to set the time. This is the current time to be displayed. In order to set the current time, we use the switches S1 and S2.
Once the time is set, we can set the alarm using the switches S1, S2 and S3. In order to differentiate between the setting of current time and alarm time in the digital alarm clock, we use the switch S3 which internally triggers the alarm display of the LM8560.
In order to set the alarm, we need to hold the switch S3 and set the Hour and Minutes of the alarm time by using switches S1 and S2 respectively. Once the alarm is set successfully, the digital clock IC waits for the alarm time and once the alarm time is reached, an alarm output at the Pin 3 is generated.
This can be connected to a small buzzer directly for alarm output. But in order to get special alarm tones from the digital alarm clock, we can use special alarm signals. But to drive these special buzzers, we need an audio power amplifier. Hence, the IC LM386, which is a power audio amplifier, is used in the digital alarm clock circuit.
The alarm output of the IC1 (LM8560) is given to the input (Pin 3) of the IC2 (LM386) through a potentiometer P1. The potentiometer is used to control the volume and pressure of the alarm signal from the buzzer.
This digital alarm clock can also be provided with snooze and repeat alarm facilities. Additional Pins of the IC1 (LM8560) have to be used in the digital alarm clock circuit in order to use these functionalities.
When you hear about the alarm clock circuit, the first thing that may come to mind is the alarm clock. No doubt, you're correct, but the device also works for other applications we'll discuss later in the article.
The IC1 is one of the basic concepts of the circuit as its drivers help activate the duplex LED digital display signal that displays the time. So, the LM 8560 supports 12 and 24 HR time formats, and it shows snooze function, current time, and alarm support.
This component comes in handy for showing different information like alarm notification, current time, etc. So, the LED display saves you the stress of using extra drivers with electronic systems to initiate the display unit. And it's because all the drivers you need are in the alarm clock IC.
With the (S1, S2, S3, and S4), you can do three essential things: turn off the alarm, set time, and set the alarm. Further, you can also use these components to set your alarm time in hours and minutes separately.
Further, the diodes (D2 and D3) give conforming inputs to the display's cathode. So, it's necessary to set a time when you switch on the power source. At this point, you should see the current time. And you can set it by using S1 & S2.
The first switch (S1) helps you set the hours, while S2 helps you develop minutes. With this, the IC will activate the display linked to it automatically. Also, you'll see the time on the duplex LED display.
To do that, you can use the S3 switch because it helps to initiate the LM 8560's alarm display internally. In addition, you can set the alarm time by holding S3. Then, you can select the hour with S1 and the minutes with S2.
Once you finish that, the IC will be on standby for the alarm time. So, when the alarm time is due, Pin 3 will produce an alarm output signal. With this, you can make a direct connection with a small buzzer for the alarm output.
The potentiometer P1 helps you control the alarm signal's pressure and volume from the buzzer. And the potentiometer allows you to receive the alarm output signal from IC1 and IC2's Pin 3. To cancel the alarm before it triggers, you can use the S4 switch, and plus, you can use the S4 button also to stop the alarm any time before it activates.
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It's pretty easy to build circuits with a microcontroller but we totally forget the tons of work that a microcontroller had to go through to complete a simple task(even for blinking an led). So, how hard would it be to make a digital clock completely from scratch? No coding and no microcontroller and to make it real HARDCORE how about build the circuit in a perf-board without using any printed circuit boards.
This project was inspired by this instructable (author: hp07) back in 2018, which would be insanely hard to build in a perf-board because of the number of connections and the components used. So, I did a bit of digging online to reduce the complexity but still make it fairly basic and difficult to build in a perf-board.
The solution to this problem is quite simple (If you think of yourself as a rebellious teenager and just pretend over a century physicists never scratched there head about it). The way we are going to approach this solution might be counter-intuitive, where first we'll see how we can keep track of time and then later define time.
Consider the clock as a counter which can count numbers up to 0-60 and 0-24 (let's just worry only about 24hr clock for now) whenever this value exceeds it just carry over to the next higher designation [Seconds -> Minutes ->Hours ->Days->Months->Years ].
Anyway, for simplicity, we'll just assume it's the time taken for a cesium atom to vibrate 9 billion times. Now when you increment the counter every one second or time is taken for a cesium atom to vibrate 9 billion times you got yourself a clock-sort-of-thing! To this, if we could just add logic in such a way that seconds carry over to minutes and minutes carry over to hours when they reach 60 (and hours reset on 24). This will give us a fully functional clock that we are expecting.
Let's first figure out the way to display the number(or time). The 7-segment displays should be perfect for this build because it gives a retro look, and it is also one of the simplest display that's available on the market, it's so simple that it's just made of 7 LEDs (8 LEDs, if the point LED, was counted in) placed in a clever way to show alphanumeric values that can be placed in adjacent with multiple 7-segment displays to show a larger value.
COMMON CATHODE: All the -ve terminal of the led is connected to a common point, and then this common point is connected to the ground(GND). Now, to turn on any part of the segment a +ve voltage is applied to the corresponding +ve pin of that segment.
CATHODE ANODE: All the +ve terminal of the led is connected to a common point, and then this common point is connected to the VCC. Now, to turn on any part of the segment a -ve voltage is applied to the corresponding -ve pin of that segment.
Each segment of this display is named from A to G in a clockwise direction and the dot (or point) on the display is marked as 'p', remember the segments with their corresponding alphabets, which will be handy while connecting it to the digital IC's.
This step is going to be a bit tricky because finding the exact size of the perf-board is quite difficult and you might not find one. If that's the case you can combine 2 perf-board to make a larger one.
Placing the 7-segment display is quite simple, just place the display evenly with right spacing so you can differentiate the seconds, minutes, and hours (refer the image for the placement of the led).
If you noticed by now I'm using a bunch of 100ohm resistors for each pin of the display, this is totally for aesthetics and it's not necessary to use these many resistors. If you can place a 470ohm resistor between the common pin of the 7-segment display and the ground that should be good enough. (These resistors are used to limit the current that's going to go through the LED)
Since this circuit has a lot to solder and to make sure not to lose track of what I'm doing, I soldered the 7-segment display pins in an alphabetical sequence to the resistors and the ground to the top of the circuit. It seems useless and complicated, but trust me this will make your job way easier.
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