The crystal oscillator will be the ideal solution for this problem. We won't talk about the oscillator section briefly any longer in this article since this 1 Hz oscillator circuit will do a pretty good job for our DIY timing project. You can always use other 1Hz clock generator circuits instead of the crystal , provided your application has some tolerance on accuracy.
The display block uses 4 common cathode 7 segments to display count seconds and minutes. The 7 segments marked as "S" for seconds and "M" for displaying minutes in the circuit diagram above. Use a 9v battery to power this pad. Activate "ON/OFF" to turn the meter on or off. Use the START/STOP switch to start and stop the stopwatch counting.
Four IC 4026 (decade counter with decoder that converts counter values to 7 segment outputs) were used to drive each of the 7 segment displays. The 1Hz oscillator clock is fed to the CLK pin of U1. With each incoming pulse into the CLK pin of this IC, the counter increases by one which in turn is decoded and displays the value in 7 segments accordingly. When the count reaches the maximum value of 9, a high signal has been sent from pin 5 CO of U1. The clock will go into the next IC U2. So when U1 segment counts up to 9 CO signals will be sent to U2. Then it starts displaying the value 1 in its segment.
The segment associated with U2 counts up to 9 before returning to 0. But to stay up to the 60 second limit, we must stop U2 before reaching 6 points. So here comes along another IC 4017 (the Johnson counter tilts the count values from Q0 to Q9 with each incoming input pulse) which is used to reset IC U2 before reaching mark 6 in its segment . To do this, we connected the Q6 pin to the reset (MR) pin of U2 and to the reset pin of U5 itself. U1's clock was used by U2 and U5 to keep the number similar to provide the correct reset point. When the count in U2 and U5 reaches from 0 to 6, the Q6 pin in U5 resets and U2. Thus, this sets the 60 second limit for our stopwatch.
The output of Q6 acts as a clock source for IC U3. So when the 60 second count is up, the minute segment associated with the U3 increments equals 1. When that U3 counts to 9, the CO pin goes high, which powers the clock on the U4 chip. This is similar to how U1 fed the clock to U2. Then U4 starts counting from 1 with each CO clock input of U3 and can count up to 9. So the combined U3 and U4 segment can count up to 99. Therefore this DIY stopwatch has a limit counting 99 minutes after it starts counting 0 minutes again.
NOTICED:
Use 470 ohm current limiting resistors to connect the 7 segment pins of IC 4026. I omitted it from the circuit diagram for simplicity.
Use pull-up resistors R1 and R2 to hold the pins at ground potential and prevent chips from shorting.
You can extend this stopwatch to display hours by adding two segments and 4026 more.
Hope you have fun building this stopwatch. Please comment below if you have any comments, suggestions and improvements with this project.
The crystal oscillator will be the ideal solution for this problem. We won't talk about the oscillator section briefly any longer in this article since this 1 Hz oscillator circuit will do a pretty good job for our DIY timing project. You can always use other 1Hz clock generator circuits instead of the crystal , provided your application has some tolerance on accuracy.
The display block uses 4 common cathode 7 segments to display count seconds and minutes. The 7 segments marked as "S" for seconds and "M" for displaying minutes in the circuit diagram above. Use a 9v battery to power this pad. Activate "ON/OFF" to turn the meter on or off. Use the START/STOP switch to start and stop the stopwatch counting.
Four IC 4026 (decade counter with decoder that converts counter values to 7 segment outputs) were used to drive each of the 7 segment displays. The 1Hz oscillator clock is fed to the CLK pin of U1. With each incoming pulse into the CLK pin of this IC, the counter increases by one which in turn is decoded and displays the value in 7 segments accordingly. When the count reaches the maximum value of 9, a high signal has been sent from pin 5 CO of U1. The clock will go into the next IC U2. So when U1 segment counts up to 9 CO signals will be sent to U2. Then it starts displaying the value 1 in its segment.
The segment associated with U2 counts up to 9 before returning to 0. But to stay up to the 60 second limit, we must stop U2 before reaching 6 points. So here comes along another IC 4017 (the Johnson counter tilts the count values from Q0 to Q9 with each incoming input pulse) which is used to reset IC U2 before reaching mark 6 in its segment . To do this, we connected the Q6 pin to the reset (MR) pin of U2 and to the reset pin of U5 itself. U1's clock was used by U2 and U5 to keep the number similar to provide the correct reset point. When the count in U2 and U5 reaches from 0 to 6, the Q6 pin in U5 resets and U2. Thus, this sets the 60 second limit for our stopwatch.
The output of Q6 acts as a clock source for IC U3. So when the 60 second count is up, the minute segment associated with the U3 increments equals 1. When that U3 counts to 9, the CO pin goes high, which powers the clock on the U4 chip. This is similar to how U1 fed the clock to U2. Then U4 starts counting from 1 with each CO clock input of U3 and can count up to 9. So the combined U3 and U4 segment can count up to 99. Therefore this DIY stopwatch has a limit counting 99 minutes after it starts counting 0 minutes again.
NOTICED:
Use 470 ohm current limiting resistors to connect the 7 segment pins of IC 4026. I omitted it from the circuit diagram for simplicity.
Use pull-up resistors R1 and R2 to hold the pins at ground potential and prevent chips from shorting.
You can extend this stopwatch to display hours by adding two segments and 4026 more.
Hope you have fun building this stopwatch. Please comment below if you have any comments, suggestions and improvements with this project.
No comments:
Post a Comment