Timer Comp

Discussion in 'General Electronics Chat' started by G207, Jun 18, 2014.

  1. G207

    Thread Starter New Member

    Jun 12, 2014
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    Does anyone know of any companies that produce pre made timer circuits for use in professional applications? The timer would be a pretty simple monostable device that drives less than 70 mA of current and would be run by 4 AA batteries. It would not need an enclosure. I would like it to be already on a printed circuit board. Ideally, it would be great to get several ideas so that I can weigh them out.
    Thank you in advance
     
  2. crutschow

    Expert

    Mar 14, 2008
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    There are such devices available from small electronic hobby companies on the web. What's your definition of "professional"?
     
  3. #12

    Expert

    Nov 30, 2010
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    This one would be fried by a set of new alkaline batteries at 1.59 volts each but you didn't say exactly which batteries you were using, so I gave it a try.
     
  4. samuel.whiskers

    Member

    Mar 17, 2014
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    70mA is a pretty generous current limit - is this standby current? because that would make short work of AA batteries.....
     
  5. Dodgydave

    Distinguished Member

    Jun 22, 2012
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    Ebay do a 555 timer kit, Velleman do kits. What output do you need relay or transistor?
     
  6. Alec_t

    AAC Fanatic!

    Sep 17, 2013
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    What time period is required? Milliseconds? Days? .....?
     
  7. G207

    Thread Starter New Member

    Jun 12, 2014
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    Sorry for the delay on getting back to this thread. I have limited access to the internet. Thank you for the replies so far.

    I am looking to put this timer in a device to market. I am considering designing the timer circuit myself, but was thinking it would save time if there was a device that could be used "off the shelf".

    I was thinking of using typical AA alkaline batteries, however, I could consider other power sources if it was absolutely necessary. The specific Linear Technologies timer block doesn't fit my specs, but I will have to look into their other products. Thank you for the lead...

    I was planning to have a momentary pushbutton trigger a timer circuit which would drive a motor load of approximately 40 to 70mA. It would run for about 5 minutes. There would be long "off" periods, so it would need to have low standby current to save on battery power. There would also need to be an LED indicator. It doesn't really matter whether it uses a relay or transistor as long as I can get it to meet the correct specifications. The motor is rated for 4 to 7 V.
    Thank you for your help and ideas. It is appreciated.
     
  8. Alec_t

    AAC Fanatic!

    Sep 17, 2013
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    Does the '5 minutes' need to be adjustable, and how accurate/consistent?
     
  9. G207

    Thread Starter New Member

    Jun 12, 2014
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    It does not need to be extremely accurate or consistent. It would be good enough to stay within 20 or 30 seconds on either side of 5 minutes.
    Thank you
     
  10. crutschow

    Expert

    Mar 14, 2008
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    A reasonably simple timer circuit can be made using a CD4060 counter which has a built-in oscillator circuit. The timer can drive a transistor to turn on the motor for the desired time as determined by the counter oscillator frequency and pickoff point. At the period end, the timer can be wired to shut itself off. It takes only a couple μA current when idle so the battery life will be mainly determined by the frequency of the motor operation.

    Here is a example of such a circuit. That circuit operates a relay after the interval which is not what you want. To change it to operate the motor during the interval, do the following:

    1. Replace the NPN transistor and relay with a logic-level type P-MOSFET.
    2. Connect the source to V+ and the drain to the motor plus terminal with the other motor lead to common (V-).
    3. Connect a small diode (1N4148 or similar) across the motor terminals (anode to common) for transient suppression.
    4. Connect the CD4060 pin 6 to the MOSFET gate (no resistor needed) and also to D1.
    5. Remove R1 and the associated diode.
    6. Connect a LED and series resistor across the motor for a indicator when the motor is powered.
    Pushing the Reset button starts the timed sequence.

    To adjust the timeout period you can monitor the output from Pin 7. Adjust pot R4 so pin 7 goes high in 1/8 the time you want at pin 6 (e.g. 37.5 seconds at pin 7 for 300 seconds at pin 6).
     
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  11. inwo

    Well-Known Member

    Nov 7, 2013
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  12. G207

    Thread Starter New Member

    Jun 12, 2014
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    Originally, when I posted this thread, I was looking for ready made devices already placed on a PCB board- somewhat like those posted by "Dodgydave", ( I am still open to more suggestions.) , however, it seems like there are so many different applications, the solutions probably have to be largely customized.
    Thank you for the design suggestion crutschow. The information is really helpful. I am a newbie to all of this, so the CD4060 chip idea, and even the suggestion about the logic level transistor was great. I understand the purpose of the diode across the motor and the LED with current limiting resistor being in parallel with that. However, I don't understand how the counting should be stopped.

    I am not sure how this is done...???
    I had looked at the CD4561, which has a somewhat similar function. It has the option of the Automatic Reset built in, however, on most of the brands of the chip this seems to have some additional leakage current and some voltage restrictions I may not want to deal with.
    Thanks again
     
    Last edited: Jun 30, 2014
  13. crutschow

    Expert

    Mar 14, 2008
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    The reference circuit I posted automatically stops when the selected output goes high. Diode D1 applies the voltage from the selected output to the oscillator pin 11 which stops the oscillator from counting. That freezes the count and thus any oscillator current so the circuit current draw is basically just the leakage current of the IC plus the small current through R5. Pushing the Reset sets all counts to zero and restarts the oscillator.
     
  14. jaclement

    Active Member

    Apr 15, 2009
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    The MC14541 timer IC is very usefull for longer time delays or slow astable oscillators. It can use its internal oscillator or an external drive. It then devides that clock by 2^8, 2^10, 2^13 or 2^16 selectable . The outpout can be a square wave or a one shot. I use it to time a light source (two 10 watt white LEDs) to expose PC board artwork. This gives me very consistant exposures. My time is about 30 seconds
     
  15. G207

    Thread Starter New Member

    Jun 12, 2014
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    Thanks for the help. I have been ordering parts and putting together a demo board. So far it is going well. Thanks again.
     
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