This summer I took a course called "Digital Electronics" at my college. I learnt about flip-flops, counters and much more. So I thought it would great If I do a project related to digital electronics and from there the project digital clock started. The project took about 2 weeks to get completed. I started off with TTL IC's and made a block diagram shown below but there came the problem with this design as you can see in the block diagram it uses too many IC's making project very expensive and would have taken lots of power and battery would drain quite early. Using this design you requires at least 3 or 4 breadboards which assures you to consume a lot of space.
If anyone still wants to do this project using TTL ICs I have uploaded the schematics of the minutes and second hand of the clock using 7490 and 7492 ICs.
Now I needed to use some other option so I made the clock using CMOS very famous 4026 IC.
Step 1: Specifications
- Clock should have hours, minutes and seconds display.
- Clock should be battery operated.
- It should be power efficient.
- It should have time setting mode.
- Parts should be easily available.
- Should consume less space.
Step 2: Parts Needed
- CD4026B IC *6
- CD4013 IC *2
- CD4060 IC *1
- CD4001 IC *1
- Common cathode 7 segment led *6
- crystal oscillator of frequency 32,768 Hz
- Resistor - 100k,10k*2, 1k*1, 470k*1, 1M*1
- capacitor - 0.01uf, 22pf*2
- push button *2
- battery 9v
- MOSFET 2N7000
Step 3: Circuit Description
I have uploaded schematic of the clock and now I will explain what each part of this clock does.
1. 4060 IC - This IC consists of 14 master−slave flip−flops and an oscillator with a frequency that is controlled either by a crystal or by an RC circuit connected externally. The output of each flip−flop feeds the next and the frequency at each output is half of that of the preceding one. The state of the counter advances on the negative−going edge of the Osc In. The active−high Reset is asynchronous and disables the oscillator to allow very low power consumption during stand−by operation. The timer circuit is built around the CD4060 which is 14 stage ripple carry binary counter, divider and an oscillator. Its built in oscillator is main feature of this IC that’s why it can be used in numerous application like flasher, clock generator in timer circuits. Image below shows the pin layout of the IC:
4060 circuit (IO1) divides crystal frequency 32 768 Hz using a 14-stage binary prescaler down to 2 Hz frequency. This 2Hz frequency is fed to the clock pin 1 of the 4026 IC.
The two switch are used to set the time and is achieved using 4060 pin by increasing the frequency that is being fed to 4026 IC.
The first switch which has lower frequency of the two is used to set the minutes in the clock.
The second switch which has higher frequency is used to set the hours in the clock.
2. CD4026B - This IC has four uses in the circuit
I) It is used for providing clock to the circuit.
2) It is used as decoder they have direct outputs for the 7-segment display. Unlike conventional BCD counters, they don't need a decoder from BCD to 7 segments
3) It is used as frequency divider.
4) They also have an additional output like "Ungated C segment", and "Carry Out" that is very useful for making clocks
NOTE - This IC has active high outputs so it can drive only common cathode seven segment LEDs so make sure you are using the same.
The 2Hz signal enters its CLK input (pin 1) through R3, R4, R5. Counting cycle 10 is shortened to 2 using reset input (pin 15). Since it doesn't have any BCD outputs, we connect the reset input to segment g output. Segment g is not active for the digits 0 and 1, but it is active (high) for the digit 2. Therefore, when the counter reaches state 2, it almost immediately resets and gets into state 0. Thus, only the digits 0 and 1 alternate with a frequency.
UNGATED C SEGMENT - This pin when given as the clock divides the internal frequency by 10.
CARRY OUT - This pin also does the same.
The only difference between them can be made by visualizing their timing diagram which I have uploaded.
4013 IC - This IC is used to reset the virtually identical seconds and minutes circuits. They
both use 1/2 of a 4013 to create a reset pulse when the tens of units reach six. This is accomplished when the "Carry Out" pin on the tens of units counter (4026) goes high with the "5" count follow by "Clock In" going high on the "6" count. This toggles the 4013's "Q not" output which then resets the 4026. It then counts from 0 to 5. The units counters are straight divide by ten or decade counters.
Step 4: This Step Is in Continuation of the Previous One
4013 - This IC is used twice in the circuit -
1) This IC is used with Seconds and minutes hand of the clock which are pretty much identical. both use 1/2 of a 4013 to create a reset pulse when the tens of units reach six. This is accomplished when the "Carry Out" pin on the tens of units counter (4026) goes high with the "5" count follow by "Clock In" going high on the "6" count. This toggles the 4013's "Q not" output which then resets the 4026. It then counts from 0 to 5. The units counters are straight divide by ten or decade counters.
2) To provide the 12 hour format, a 4013 counts tens of hours plus works with the 4001 to reset then insert an extra count into the units of hours when 13 hours is reached. This makes it count from 1 to 12 hours. Part of this is accomplished by utilizing a special output on the 4026, the "c" segment, that is available independent of the ED state. This "c" output is low only when the count is at "2" and goes high on count "3". This is how the hours count of "13" is detected.
4001 - This IC is used in conjunction with 4026 and 4013 to on the tens count of hours hand of clock and to reset the ones count of the hours hand of the clock to 1 instead of 0.
MOSFET 2N7000- This mosfet is used as a switch to switch on last seven segment led when the clock reaches a time of 9:59:59
Step 5: Some Pictures From the Project
Hope you have liked the project I have also uploaded the video if you have any regarding this project please put it in the comments down below I will be very happy to respond to it.