A simple cyclic timer

Discussion in 'The Projects Forum' started by GiovaGiov, May 24, 2015.

  1. GiovaGiov

    Thread Starter Member

    Apr 3, 2015
    30
    0
    Hi,

    I'm looking for a circuit to make a simple cyclic timer.
    With "simple" I mean that every on/off cycle should be equal. Example: 2 mins "on" and 2 mins "off", continuously; would be also nice to insert a trimmer resistor to set, as I wish, the time of both cycles.

    Obviously this timer must activate a relay.
    The power supply will be 12 or 15 volt (this is due to the fact that I have various power adapters, which I can use for various needs).

    I would prefer to keep it simple also in regards of the used components: here I have some NE555: can someone suggest me some schematics to achieve this kind of timer?

    I also have one CD4060 IC: from what I can understand, should be be better to make a timer. Am I right?

    Thank you.
     
  2. MikeML

    AAC Fanatic!

    Oct 2, 2009
    5,450
    1,066
    Yes. 2min on+2min off = 4min = 240sec. If you use Q14 as the output, the oscillator will be running 16384/240 ~= 82Hz.

    Here is the data sheet. Fig 12 shows how to make an RC oscillator.
     
  3. Alec_t

    AAC Fanatic!

    Sep 17, 2013
    5,775
    1,103
    There's no 'obviously' about it ;). Relays gobble current to drive the coil, and a 4060 can't provide enough current for that. You would have to use a relay driver stage. An alternative (depending what load you intended to switch with the relay) is to use e.g. a MOSFET or bipolar transistor to switch the load.
     
  4. AnalogKid

    Distinguished Member

    Aug 1, 2013
    4,516
    1,246
    The 4060 is a great part within limits. As mentioned, it won't drive anything directly much bigger than a dim LED. The size of the relay determines the size of the driver transistor. What is this circuit for, and what relays are you considering?

    Also, while the 4060 is much better than 555's in long-period applications, the chip itself is not as accurate. The cycle lengths are dependent on the CMOS transition voltages, which can vary +/-25% over temperature. So if this is outdoors, in a garage, in an attic, or anywhere else without controlled temperatures, your 2 minute periods will wander.

    ak
     
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