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Delay timer circuit for a motor.

Discussion in 'Sensors and Actuators' started by Alfie, Jan 15, 2015.

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  1. Alfie

    Alfie

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    Jan 15, 2015
    Hi everyone,

    I am currently trying to use this circuit to have a delay start, then run a motor for a selected period and then cut out after a given period.
    [​IMG]
    [​IMG]

    However it won't run a motor. It works perfectly well with LED's and a bleeper but even a 3V motor won't run on it. I even tried replacing the 9V battery with a 9V plug in power source and slowly upping the voltage but this just fried the LED's and the 555 timer.

    Does anyone have a different kind of circuit I can use or anything I can do to change this one to make it run a motor? I have currently only got the circuit in a breadboard.
     
  2. KrisBlueNZ

    KrisBlueNZ Sadly passed away in 2015

    8,393
    1,270
    Nov 28, 2011
    That circuit won't run the motor directly because the 555's output is rated for a maximum output current of 200 mA and your motor presumably needs more than that. If that's the case, you'll also need a bigger battery than a little PP3.

    Heavy loads can be switched using transistors or MOSFETs; MOSFETs are easier to drive and have better performance. An N-channel MOSFET such as an MTP3055 available from Farnell (http://uk.farnell.com/fairchild-semiconductor/mtp3055vl/n-channel-mosfet-60v-12a-to-220/dp/1845563) is suitable. Connect the MOSFET and motor as shown in the first schematic (the coloured one) at http://electronics.stackexchange.com/questions/96776/555-to-drive-a-mosfet.

    This circuit won't give you a delayed start though. As designed, the 555's output will go high immediately on power-up, then return low after a time determined by the potentiometer.

    I will design a circuit for you if you describe your project and requirements in detail. What power supply is available? What are the specifications of your motor? What are the timings you want? What is the adjustment range? Describe the purpose of the project, etc.
     
    bikemech likes this.
  3. Alfie

    Alfie

    4
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    Jan 15, 2015
    Thanks very much for this.
    The circuit is for my A-level engineering project. It needs to be able to run a dragster kit down a track and then after a time period of say 10 seconds, cut off. This is so you aren't running around the room chasing it. It also will need to have a slight delay start so that it won't take your fingers off when you turn it on and put it down.

    It'll need to run from a maximum of 9V as I don't have much room on the base to be chucking on loads of batteries. The motor I am currently using is also 9V but I can go higher if needed. I'd like the adjustment range to be between 10 and 30 seconds for having the motor running as I'm not quite sure yet on how far it will need to run and the delayed start to be around 5 seconds, if possible. Finally it needs LED indicators on it to tell when the circuit is on but not running the motor and then a different LED to tell me that the motor is or should be running.

    I hope I have provided all the information needed. Again thanks very much for this.
     
  4. BobK

    BobK

    7,682
    1,686
    Jan 5, 2010
    Well, you answered most of Kris' questions, but not this very important one:

    What are the specifications of your motor?

    Bob
     
  5. Alfie

    Alfie

    4
    0
    Jan 15, 2015
    Sorry I thought I had. It is a 9V motor not sure about the amps
     
  6. BobK

    BobK

    7,682
    1,686
    Jan 5, 2010
    Can you measure it?

    Bob
     
  7. Alfie

    Alfie

    4
    0
    Jan 15, 2015
    Yeah I'll go over to my electronics room and get a measurement.
     
  8. KrisBlueNZ

    KrisBlueNZ Sadly passed away in 2015

    8,393
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    Nov 28, 2011
    272254.001.GIF

    OK that's my suggestion. It's based on a CD4093B CMOS quad NAND gate with Schmitt trigger inputs. Search this forum or Google for other mentions of the 4093 for a detailed description of what it does.

    This IC is represented by the four D-shaped symbols on the diagram. Its positive supply and 0V connections are on pins 14 and 7 and must be decoupled by C2, a 100 nF ceramic capacitor, connected as closely and directly as possible between the pins.

    When power is applied to the circuit, C1 is discharged, so U1 pins 2 and 5 are low. U1 drives pin 3 high, which quickly charges C3 to the supply voltage.

    During this time, since pin 5 is low, pin 4 will be high, and pins 10 and 11 will be low, so Q1 will have no bias voltage on its gate and the motor will not run.

    After about one second from power-up (set by R1 and C1), U1 will consider pin 2 to be high and will drive pin 3 low, allowing C3 to start to discharge slowly through VR1.

    Also around this time, U1 will consider pin 5 to be high. (These events won't occur at exactly the same time, because the input thresholds of U1A and U1B won't be exactly the same, but this doesn't matter).

    When this happens, pins 5 and 6 will both be high simultaneously, so U1 will drive pin 4 low, and pins 10 and 11 high, turning on Q1 and starting the motor.

    C3 will now slowly discharge through VR1 until its voltage reaches the falling threshold of pin 6. At that time, U1B will drive pin 4 high, pins 10 and 11 will go low, and Q1 and the motor will turn OFF.

    D4 will conduct due to the inductive kickback from the motor when Q1 turns OFF and this will protect Q1 from possible overvoltage at this time.

    Two gates are used to drive Q1 for slightly improved switching times.

    D3 protects Q1 against any unusual gate voltage that might occur due to capacitive coupling from the drain.

    R3 and R4 are provided to prevent possible damage to U1 when the power supply is turned OFF and C1 and/or C3 are still charged.

    For best accuracy and consistency for the run time, C3 must be a low-leakage electrolytic such as the Nichicon KL series component listed - see http://www.digikey.com/product-detail/en/UKL1C101KPDANA/493-13396-ND/2598379

    VR1 can be a potentiometer or a preset potentiometer (aka "trimpot") - either a single-turn or a multiple-turn one.
     
    Alfie and Arouse1973 like this.
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