Shop OBEX P1 Docs P2 Docs Learn Events
Heterodyning a signal — Parallax Forums

Heterodyning a signal

The NaffinThe Naffin Posts: 6
edited 2007-07-14 01:47 in General Discussion
I know this is a pretty simple subject, but I am still in search of some help.·

I am trying to heteryodyne two signals (one being the reference) of two 555 timers.· I would like to read the output (namely the difference of signals frequency)·by the basic stamp.· I am running the 555 timers at roughly 1.5 Megahertz.· So, my question is, what is the easiest/best method to do this?· Will a CD4070 be able to handle something like this?· Thank you for your help.

Comments

  • Beau SchwabeBeau Schwabe Posts: 6,568
    edited 2007-07-13 19:27
    What is·the frequency range of your·other signal?

    Are they both at about 1.5MHz?

    What it the upper and lower·beat frequency you are looking for?



    ▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔
    Beau Schwabe

    IC Layout Engineer
    Parallax, Inc.
  • The NaffinThe Naffin Posts: 6
    edited 2007-07-13 19:40
    Yes, they will both be running near 1.5MHz (actually, the other will be slightly higher, but barely). That should give a lower beat frequency of 1kHz and an upper of somewhere near 15-16kHz ideally.
  • BeanBean Posts: 8,129
    edited 2007-07-13 21:08
    I'd use an XOR gate, then a low-pass filter on the output. Because the output of the XOR gate will be the sum and the difference.
    The Low-pass filter will block the sum frequency.

    Bean.

    ▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔
    Teacher: What is the difference between ignorance and apathy ?
    Student: I don't know and I don't care
    Teacher: Correct !
    - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
    www.hittconsulting.com
    ·
  • The NaffinThe Naffin Posts: 6
    edited 2007-07-13 22:59
    Okay, that is kind of what I was thinking, but I forgot the low-pass filter. I was thinking I could do it with the XOR gate, but I hadn't thought how to filter it. That is so simple... stupid me. Thanks. Well then, I'll just throw that together with the CD4070 (XOR) and add a low-pass filter to the end. Thanks again.
  • Dave HeinDave Hein Posts: 6,347
    edited 2007-07-14 01:47
    I think the resulting waveform will be a triangle wave at the difference frequency.· Is that what you want?· You could convert this to a logic level by using a comparator with hysteresis.· The comparator could be a logic input set with a threshold of 50%.· I believe the stamp has a command to measure the duration of a pulse.· The stamp wouldn't be able to do anything else while it was measuring the pulse duration.
Sign In or Register to comment.