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I need to generate a pulse each let's say 30 seconds. I don't need this period to be any precise (20...40 seconds fluctuation will be OK). The pulse duration should be about 1 ms.

I tried to implement NE555 for this but looks like NE555 don't intended for generation this low frequencies as it would need a relatively big capacitor (I'd like to stay within small and cheap CMD technology so 10uF cap is a maximum) and many MOhms resistors. This can lead me to the topology leakage problems.

So I tried to look for any counting solution but looks like that I will be able to get 100kHz divided by 64K as a maximum which is definitely not enough.

Next I tried to look at the watchdog timers. However after initial filtering I see that the longest period is 1.6 seconds and the lowest price is 33 cents.

Important note: I'd like to have this solution as cheap as possible. I hope to fit within 10-15 cents for BOM of this circuit.

Is there anything staying out of my sight? Any thoughts?

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    \$\begingroup\$ This site is not about recommnedations for particular components, however <cough> CD4060 </cough> \$\endgroup\$
    – Neil_UK
    Commented Oct 26, 2016 at 7:20
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    \$\begingroup\$ I went to mention CD4060 and see it has multiple mentions already. It will meet your need with ease. By using diode feedback from and output pin or multiple pins you can make it recucle or stop or pulse or ... at a given count. \$\endgroup\$
    – Russell McMahon
    Commented Oct 26, 2016 at 10:57
  • \$\begingroup\$ How much would it cost to point a laser at a literal wall clock and watch the dot? \$\endgroup\$ Commented Oct 26, 2016 at 12:27
  • \$\begingroup\$ Sorry, @JanDvorak, did not get your idea :) \$\endgroup\$ Commented Oct 26, 2016 at 12:36
  • \$\begingroup\$ Any particular spot on a wall clock gets passed by the minute hand once per minute. Outputting the brightness level of that spot will yield you your pulse. Two dots to get two pulses per minute. \$\endgroup\$ Commented Oct 26, 2016 at 12:39

3 Answers 3

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A counting solution is the way to go, if you start with a frequency of 1 kHz and use a 15 bit counter you will get 30.5 mHz. Using a 14 bit counter like CD4060 is also possible if you start with 500 Hz. A second NE555 may be used for the puls width of 1 ms.

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    \$\begingroup\$ So is that correct that I will be able to make the primary frequency lower that specified in digikey table? So this frequency can be considered as "maximum" and it is adjustable via RC on the inputs? \$\endgroup\$ Commented Oct 26, 2016 at 9:09
  • \$\begingroup\$ See figure 14 on page 12 of this datasheet ti.com/lit/ds/symlink/ne555.pdf how to get 1 kHz or 500 Hz. \$\endgroup\$
    – Uwe
    Commented Oct 26, 2016 at 10:57
  • \$\begingroup\$ Why did you mention NE555? Actually I hope that I will be able to use a counter like CD4060 without extra components (with exception of couple of resistors and caps of course!) \$\endgroup\$ Commented Oct 26, 2016 at 12:31
  • \$\begingroup\$ What will generate the clock? If you throw this into the equation, a microcontroller with a built in oscillator becomes a clear winner. \$\endgroup\$ Commented Oct 26, 2016 at 12:44
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    \$\begingroup\$ @Roman -- I stand a bit corrected. ti.com/product/CD4060B says it will work with an RC or crystal oscillator. \$\endgroup\$ Commented Oct 26, 2016 at 17:18
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If you don't mind using a microcontroller, the pic10f200 would be a cheap and easy solution. They're about 30 cents in bulk and would easily handle this task.

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  • \$\begingroup\$ I thought of this solution (did not mention it in the main topic). Howevet I can not take it seriously in my case as controller should be programmed (0.3 USD controller itself + programming roughly 0.5 USD in working time or for dealer work) \$\endgroup\$ Commented Oct 26, 2016 at 9:12
  • \$\begingroup\$ @roman Programming is only done once. Pretty sure you can spare 15 minutes (according to your cost estimate) typing a loop in assembly. \$\endgroup\$ Commented Oct 26, 2016 at 12:25
  • \$\begingroup\$ @JanDvorak I meant the HEX transfering to the controller. Of course I would create the code - it is not the problem. \$\endgroup\$ Commented Oct 26, 2016 at 12:35
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    \$\begingroup\$ @JanDvorak You could order the microcontroller pre-programmed as a value added option. Even after that cost, I suspect this is your least expensive solution. \$\endgroup\$ Commented Oct 26, 2016 at 12:45
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    \$\begingroup\$ @RomanMatveev -- try microchipdirect.com/programming/… It may not be perfectly straightforward. Delivery times might be long. As always, the bigger your count, the bigger bat you swing. \$\endgroup\$ Commented Oct 26, 2016 at 17:19
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If you don't mind using electromechanical, rather than pure electronic solutions, the simplest way to implement this would be a gear reduction motor turning a cam, which actuates a microswitch -- then using suitable electronics (555 as a one-shot, for instance) to generate your one millisecond pulse.

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    \$\begingroup\$ "Important note: I'd like to have this solution as cheap as possible. I hope to fit within 10-15 cents for BOM of this circuit." I doubt having gears and a motor is anywhere near cheap. \$\endgroup\$
    – Bradman175
    Commented Oct 26, 2016 at 12:16
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    \$\begingroup\$ Moreover I expect that this solution will be much less reliable. Thank you anyway for the idea! \$\endgroup\$ Commented Oct 26, 2016 at 12:29

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