555 digital stopwatch

Discussion in 'The Projects Forum' started by ro169, Oct 10, 2014.

  1. ro169

    Thread Starter Member

    Oct 10, 2014
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    Hi Guys.

    I've been working on a stopwatch project this week. Basically using a 555 astable to create a function with period 0.1s. This then goes to a 4510 and then a 4511 and finally a seven segment display. The stopwatch has 3 functions; namely start/stop, count forward/backward and reset.

    So far so good with simulating the project on Multi-Sim. However the issue Im having is with the counting down. I am using 4 seven seg displays, 1 for deciseconds. 1 for seconds, 1 for 10s of seconds and 1 for minutes. I have managed to use gate logic to implement the 10s of seconds to reset after 5 (so it doesn't display 60 seconds or more and rather displays these as minutes). However when counting down, the 10s of seconds counter starts at 9. I need it to start at 5.

    will uplo0ad a picture of my circuit from Multi Sim.
    please note that from top to bottom the displays are deciseconds, seconds, 10s of seconds, minutes.
    All comments and criticism welcome
    Thanks!
     
  2. ScottWang

    Moderator

    Aug 23, 2012
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    767
    The inputs of CD4510 where they connecting to Key-A, Key-B, Key-C should be connecting a 10K resistor to ground, you can't left them floating when the key was off, they may generating the noise to affecting where the inputs they are.
     
  3. ro169

    Thread Starter Member

    Oct 10, 2014
    60
    0
    Thanks ScottWang.
    have made those changes.

    also have solved my count shortening issue by using another AND gate with inputs from the LSB and MSB as to reset the counter when its at 1001.

    however i do have another issue; i have just been asked to change my input power to a battery. I oringally was going to use a rectifying PCB connected to AC source to produce a steady +5V input as i already have the rectifying PCB built. Now how would i change my inputs from that of a ground and +VCC to a positive and negative terminals of a battery?
     
  4. ScottWang

    Moderator

    Aug 23, 2012
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    You should be concern is the LEDs because they got the current limiting resistors to limited the voltage, otherwise the other IC as CD4510 and CD4511 and 555 can be working on a big voltage range.

    How is your battery (V/I, pcs)?
     
  5. ro169

    Thread Starter Member

    Oct 10, 2014
    60
    0
    oh good spot! well originally thought the circuit was going to use TTL and not CMOS. But yes i will be increasing the voltage to something between 5-15V.

    Sorry I don't understand your question regarding the battery?
     
  6. ro169

    Thread Starter Member

    Oct 10, 2014
    60
    0
    Also I have realized that my original problem with counting down isn't really solved. i thought that i could use an AND gate to reset the counter everytime it produced an output of 1001, but the counter resets to 0 instead of 5.

    I'm thinking I can actually use combinational gates to achieve a 0011 input to the BCD when the counter hits 1001, but not too sure about how to go about doing this. Any Ideas?
     
  7. ScottWang

    Moderator

    Aug 23, 2012
    4,855
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    The batteries voltage(V) and current(I) and how many piece in series together?
    Set the Key-C off.
    Using inverter as CD4069 or 74hC04 and 4 inputs AND gate as CD4021 to detecting 1001 of CD4510, and set P1(pin 4),P2(pin 12) to High, and P3(Pin 13), P4(pin 3) to GND, the output of CD4021 connecting to 0.01uf/50V(or 103/50V), and a 10K resistor connecting to GND, the RC common pin connecting to PE(Preset Enable, pin 1) of CD4510, here is using a CR differential circuit to generating a pulse to triggering the PE to load the number 0011.

    CD4510 datasheet, please check figure 13,14 on page 10 to see P1~P4, Q1~Q4, when PE=High.
     
  8. ro169

    Thread Starter Member

    Oct 10, 2014
    60
    0
    Hi ScottWang, just managed to solve this issue using your advice.

    used an AND gate to detect the output of 1001 and set the output of this to set pin PE to high. on the 4510 the pin settings are as follows: P1: High, P2: GND, P3: High, P4: GND. This is to output 0101 ensuring it doesn't output more than 59 seconds.

    Thank you so much! was quite puzzled as to how to input my own number to a 4510 prior to this..

    As for the power source. Most likely 9V, unsure of the current ratings as I have not bought it yet.

    My question is with regards to connection. How would i use the positive and negative terminals? take the positive as +VCC and the negative as?
     
  9. ScottWang

    Moderator

    Aug 23, 2012
    4,855
    767
    Because you didn't get used to it to see the datasheet, so you don't know what to do, I already told the method then next time you could try to solve the similar problem from the datasheet, you just don't forget to plus the C and R to make sure only generate a pulse not latch at the number.

    Are you using the small 9V cooky battery?
    If you using that kind of battery, the current could not support too large and it can't keep the circuit working too long, because the LEDs will draw too much current.

    You should draw the new circuit and attach it, otherwiese only you can see the circuit and judge it is correct or not.
     
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