Timer Circuit

Discussion in 'General Electronics Chat' started by Guinness1759, Dec 10, 2010.

  1. Guinness1759

    Thread Starter Member

    Dec 10, 2010
    64
    0
    Hi,
    I'm looking for 1 or 2 IC's (preferably 1) that can do this job for me.

    I have 3 devices that I need to power, and I need to power them one at a time. Each of these devices has a Vdd pin that requires 3V and about 1-2mA. Obviously each device is on it's own line and whatever chip you recommend will need to be able to drive these devices. What I need is a 3V IC that powers these in succession at programmable frequency. For example, if I use a resistor to select a clock frequency of 1 Hz, this IC would do the following

    0-1 seconds : power device 1 by applying 3V to 1st output line
    1-2 seconds : power device 2 by applying 3V to 2nd output line
    2-3 seconds: power device 3 by applying 3V to 3rd output line
    3-4 seconds: power device 1 by applying 3V to 1st output line

    The only way I can think of doing this is to use a ring oscillator and then a frequency divider and also a multiplexor to get 4 different outputs. This is a very low power application so I'm trying to avoid using this many IC's. Also this works only with 4 and not 3.

    Ideally this chip could be scaled up to use more, for example in the future if I wanted to power 8 devices in this manner, I could just add more lines. That is not a requirement however for this project.
     
  2. nerdegutta

    Moderator

    Dec 15, 2009
    2,519
    786
    Hi,

    Could this be done with a 555 timer and a 4017? Just thinking loud....
     
    Guinness1759 likes this.
  3. Len Whistler

    Member

    Dec 10, 2010
    44
    3
    One problem using the 4017 is that you would have a delay from device #3 back to #1

    0-1 seconds : power device 1 by applying 3V to 1st output line
    1-2 seconds : power device 2 by applying 3V to 2nd output line
    2-3 seconds: power device 3 by applying 3V to 3rd output line
    3-4 seconds: N/A
    4-5 seconds: N/A
    5-6 seconds: N/A
    6-7 seconds: N/A
    7-8 seconds: N/A
    8-9 seconds: N/A
    9-10 seconds: N/A
    10-11 seconds: power device 1 by applying 3V to 1st output line

    To use the 4017 you need to be able to evenly divide the number of devices by 10. Example: 10, 5, 2 or 1 device(s)
     
    Last edited: Dec 10, 2010
  4. djsfantasi

    AAC Fanatic!

    Apr 11, 2010
    2,815
    834
    In each of the time periods, is power cut off from the previous devices? Is this a continuous loop, i.e. 1-2-3-1-1-2-3-1-1-...? Or do you want 1-2-3-1-2-3? You should be able to construct a 3 OR 4 stage ring counter using two CD4013 D flip-flops. If you are unfamiliar with the idea, All About Circuits has an explanation
     
    Guinness1759 likes this.
  5. Guinness1759

    Thread Starter Member

    Dec 10, 2010
    64
    0
    Thanks for the info, the ring counter should do the job. Can you recommend any low power D flip flops, perhaps 1.8V or 3V chips?

    Also it looks like the 555 timer is a bit power hungry. I'm looking for an timer that will operate at very slow frequencies, like 1/10 Hz. Can I do this without a timer chip to save power? Do you guys know of any low power low frequency timers? I'm trying to get this circuit to operate within a 50uA power.
     
  6. djsfantasi

    AAC Fanatic!

    Apr 11, 2010
    2,815
    834
    Search for the specification sheets. The CDE4013 will operate at 3V and the LMC555 will also operate at that voltage.
     
    Guinness1759 likes this.
  7. Wendy

    Moderator

    Mar 24, 2008
    20,766
    2,536
    Nope. If you read my article I explain how to tailor the count to what you want. Plus you can use two outputs for one device. This is very basic stuff.

    LEDs, 555s, Flashers, and Light Chasers

    Chapter 9 - Light Chasers

    You can also use a CMOS 555 down to that voltage.
     
    Guinness1759 likes this.
  8. Guinness1759

    Thread Starter Member

    Dec 10, 2010
    64
    0
    Thanks a lot for everyone's help on this. I decided to go with the 74HC74 and TS555. They seemed to consume the least amount of power. Regards,
     
  9. mtripoli

    New Member

    Feb 9, 2010
    44
    8
    Well, before I suggest anything we should qualify what you are looking for.

    Is this a low-cost, one-off project?
    Can you use an SMT device or does it have to be through-hole only?
    Does a 555 timer HAVE to be involved?

    These things are called Power Sequencing Controllers. Many companies make them. Here's one that I think does exactly what you want: http://www.intersil.com/data/fn/fn9005.pdf. However, know that it's an SMT device and costs about $7.00 in oneses from Digikey.

    Personally, I'd use a $0.60 Microchip uC and a few logic level FET's (granted requiring programming) but you can control everything exactly how you want with one IC.

    Mike T.
     
    Guinness1759 likes this.
  10. Guinness1759

    Thread Starter Member

    Dec 10, 2010
    64
    0
    Mike, thanks for the suggestion. At 3V it consumes a typical current of 140uA which is a bit on the high side. Which Microchip uC do you recommend and how much power does it consume? The main design criteria for me is scalability and power consumption. It seems like I can build this with d-flip flops and a timer and consume less power. No I do not need to use a 555 timer.
     
Loading...