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Original question:

CD74HC4059: Creating a Frequency Divider

CD74HC4059: Strange Output of Frequency Divider

Gage Pelon
Prodigy 240 points
Part Number: CD74HC4059

Hello,

I have this frequency divider circuit (see below) that takes a sine wave input and divides the frequency by different values using jumpers. The signal looks clean and consistent through each device until it goes through the HC4059; after which the signal is very inconsistent. I've tried several different things and can't seem to find a fix. The only thing I can think of is maybe the small duty cycle is causing errors? Please help!

I've attached a small .docx file containing images and descriptions. 

Signal Conditioning Issue.docx

  • 0
    TI__Guru* 96862 points
    Hey Gage,
    The HC4059 should respond to clock pulses within just a few nanoseconds, so I don't think duty cycle is an issue.

    Can you get a scope shot of the supply pin of the HC4059 during operation? (preferably also showing the input signal). I'm wondering if there's enough decoupling with all the inductance running around that board.

    Looking at your breadboard setup, there's a lot going on! My next step would be to go through and start cleaning up things -- I'm not saying that your board is messy or anything... it actually looks amazing for so many wires on it. I just know from experience that breadboards can be iffy on connections and it's easy to make a mistake in wiring when there's so many connections running around. I can't see 100% of the connections in the image, so I don't know that I can be much help on verifying for you.
  • 0 in reply to Emrys Maier
    Prodigy 240 points

    Hey Emrys,

    The input is just a constant 5 V. Although, I did notice something strange; if you look at the 4th image in the .docx file, the reference voltage for the comparator rhythmically dips in voltage. The voltage is set for 0.3 V in that picture, and the dip gets larger and larger as RPM grows. 

    Thoughts?

  • 0 in reply to Gage Pelon
    TI__Guru* 96862 points
    Is the sensor input going straight into the comparator, or is it buffered first?

    I saw that the signal goes up then down (if I recall correctly), and if it goes beyond a rail, it's possible that it causes a shift of either ground or the supply.