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Precision Timer

Nicola Salvi
Prodigy 20 points
Other Parts Discussed in Thread: SE555-SP, NE555, TPL5010, TPL5110, BQ32000, BQ32002

Hi, everyone.

I am running a project in which I need a very precise square wave generated with the use of 1 external Capacitor. I know that NE555 would make the job, but I really think it is not enough accurate to be used in my application, in which Accuracy and Precision are mandatory. Of course the TI's flagship Timer SE555-SP is Space-addressed, so it is not available to be purchased by "common" users, therefore I would like to have some reccomendations to sort my problem out; it does not have to be necessarily a 555 timer, as the only very important feature it must have is to be capable to work with only 1 external Capacitor. Furthermore, I would like it to have simple Frequency Formulas, in order to compress multiple Capacitor values decades in just as much Frequency decades.

Thank you in advance for your advices and time.

Nicola.

  • 0
    TI__Mastermind 18070 points

    Hello Nicola,

    Can you please start your question with NE555 or SE555-SP and repost the question? This thread has been directed to a wrong group. We don't have precision timers in our portfolio. We do have real time clocks (BQ32000 and BQ32002) and nano timer (TPL5010 and TPL5110) if you are interested.

    Regards,
    Hao

  • 0
    TI__Guru**** 165526 points

    Nicola,

    I have a few questions.

    1. Are you trying to say that you want to convert capacitance into frequency?  The NE555 does the the inverse; it converts 1/C into F.
    2. Is the output frequency the final output or does frequency get converted into something else?
    3. Are space products really needed?
    4. Is there a reference or calibration capacitor available?
    5. How many samples per second or any other conversion speed measure?

  • 0 in reply to Ron Michallick
    Prodigy 20 points

    Hi Ron, I'm glad to answer your questions.

    Firstlt, I wanted to clear about the Space products. My project does not have to go into Space, but its environment of work will be really extreme, full of moisture, a dense air and very low temperatures, at which only a very particular and extreme product would work.

    The main idea is to have a frequency proportional to the Capacitance of one, and one only, Capacitor. It does not matter whether the proportion is direct, inverse, square or others, I only need these two parametres (Capacitance and Frequency) to be proportional by each other. At the beginning, I thought to realise my project using two op-amps, one as an Inverting Integrator (in which the Capacitor is positioned) and the other as a Non-Inverting Schmitt Trigger. Keep in mind that the measure of frequency would be executed by a Microcontroller, so it would be very important to have low frequency values in order to have a higher precision.

    As for the Calibration Capacitor, it does not exist, as it would be almost impossible in my environment of work to get a precise reference. The Capacitor range is very very large, and goes from 20 picoFarads to 20 milliFarads.

  • 0 in reply to Nicola Salvi
    TI__Guru**** 165526 points

    Nicola,

    Your last post was helpful but still very mysterious. 

    I suggest using the charging time of the capacitor as a the measure of the capacitance. Charge the capacitor with a choice series resistors whose value scales with the range of capacitance being measured. Use a comparator to stop the time clock. The microcontroller should have a timer inside that can be started and stopped by external pin.