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Thread: Schematic for Frequency Counter

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    Senior Member+ Frank B's Avatar
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    Schematic for Frequency Counter

    I am looking for an input circuit with divider for a self-made frequency counter. As the main part should serve the Teensy 4, the necessary program I write myself.
    Does anyone have a link for a reliable circuit? I need the input stage only. It should be reliable enough to work with it. Maybe for 1.8 + 3V logic?
    Without too small SMDs, please..

    200MHZ-250MHz should be feasible - by the way, I don't have big demands on the accuracy. in the 200MHz range +-100Hz (or a bit more) are sufficient for me. But that should be controllable via the gate time, I think.


    Thanks in advance for good links!

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    Senior Member+ Frank B's Avatar
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    This seems to be easy to build: https://www.sprut.de/electronic/pic/projekte/frequenz/2015/counter2015_sch_300.png
    Click image for larger version. 

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    It's 5 V (because of the PIC and the U813BS, I think) - but I could just use a Teensy 3.2 which is 5v tolerant.

    Is that circuit OK?
    The 50MHZ input connects directly to the CPU - I don't like that much. Is there a better way? (for 1.8V + 3V logic)

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    Senior Member+ Frank B's Avatar
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    Thanks

    If found a very cheap module "PLJ8-LED"
    https://www.youtube.com/watch?v=WWy0821JLUQ

    Not the best, but OK for me.

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    That circuit has 2 big red flags for me - directly driving relay coils from the processor pins and no flyback diodes. It also seems odd to be using relays to drive LEDs but that may just my bad German.

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    Senior Member+ Frank B's Avatar
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    Quote Originally Posted by PhilB View Post
    That circuit has 2 big red flags for me - directly driving relay coils from the processor pins and no flyback diodes. It also seems odd to be using relays to drive LEDs but that may just my bad German.
    Relay: Yes, that's what I thought too. Seems that the PIC pins can drive relays. Maybe the diodes are actually not necessary. The relays are used to connect one of the three inputs to the PIC counter pin.
    These PIC chips seem to be quite popular for this type of application. The cheap counter I bought uses it too.

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    Senior Member+ Frank B's Avatar
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    The " PLJ8-LED " counter I bought (will arrive tomorrow) seems to measure above 100kHz only. So I need an additional thing for lower frequencies.
    Does the part with the LT1016 work with 1.8V ..TTL Levels <100kHz?
    Does it need to be a LT1016? Its quite expensive. The SMD Version is >7EUR here.

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    Relay: Yes, that's what I thought too. Seems that the PIC pins can drive relays.
    Those reed relays (HE3621) have the flyback diodes integrated and a DC resistance of 500R. Seems to be OK to directly drive them from a processor pin !?!

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    Quote Originally Posted by Frank B View Post
    I am looking for an input circuit with divider for a self-made frequency counter. As the main part should serve the Teensy 4, the necessary program I write myself.
    Does anyone have a link for a reliable circuit? I need the input stage only. It should be reliable enough to work with it. Maybe for 1.8 + 3V logic?
    Without too small SMDs, please..

    200MHZ-250MHz should be feasible - by the way, I don't have big demands on the accuracy. in the 200MHz range +-100Hz (or a bit more) are sufficient for me. But that should be controllable via the gate time, I think.


    Thanks in advance for good links!
    I quite liked this article and have bought the components for when I get round to making a Teensy version. Can be switched between count and period modes. The counting and timing is independent of the processor, avoiding latency issues, the micro just handles control and the data. Looks to be capable of high resolution, I intend to scale up the counter by adding more chips, maybe adding parallel to serial conversion to read and write the counter bus efficiently.

    https://www.nutsvolts.com/magazine/a...h2015_Teixeira

    Steve

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    Senior Member+ Frank B's Avatar
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    Thanks for the link, Steve, that looks interesting!
    I plan to use parts of it for the 1MHz counter.

    My ultra-cheap counter arrived:
    Click image for larger version. 

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    It was way off, and I had to add a resistor to the VCO. I "shorted" the switched 5V voltage regulator, too, to be able to use USB power.
    It was a bit of work, but now, it's usable.
    On the picture, it is 1 Hz off and should show 5,644,800Hz. That's very OK for a 15€ Counter (incl. shipping withing 2 days)
    However, I ordered it with blue display - and it came with a red display...

    edit: VC-TXCO, not VCO
    Last edited by Frank B; 02-05-2021 at 08:30 PM.

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    Quote Originally Posted by Frank B View Post
    Thanks for the link, Steve, that looks interesting!
    I plan to use parts of it for the 1MHz counter.

    My ultra-cheap counter arrived:
    Click image for larger version. 

Name:	counter.png 
Views:	18 
Size:	252.3 KB 
ID:	23598

    It was way off, and I had to add a resistor to the VCO. I "shorted" the switched 5V voltage regulator, too, to be able to use USB power.
    It was a bit of work, but now, it's usable.
    On the picture, it is 1 Hz off and should show 5,644,800Hz. That's very OK for a 15 Counter (incl. shipping withing 2 days)
    However, I ordered it with blue display - and it came with a red display...

    edit: VC-TXCO, not VCO
    I played with one of those too. Very good for the incredibly low cost. A lot more accurate after I adjusted the trimmer using a 10MHz standard!

    Steve

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