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Thread: DirkCheap 817 and ESP Thing

  1. #11
    Junior Elf member
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    Yeah they are 1k but 5% tolerance. All channels are doing the same.

    I can try running 5v vs 12v.


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  2. #12
    DIGWDF Engineer member dirknerkle's Avatar
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    I'm a little baffled why you're having trouble with this. You can always send it to me and I'll check it over. You might reflash the PIC though just to double-check on the firmware. It needs to be a DC build, not an AC build.

    Here's a HEX file that's set up for start_address 1 at 57,600 baud which ought to work.
    Attached Files Attached Files
    Even though the DIGWDF Store has closed, it's still awesome! Thanks to all who have supported us through nearly 7 years of excitement!
    Parts of the store will remain open for downloading documentation, firmware and other files: http://digwdf.com/store


  3. #13
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    Same results on 5v. My guess is maybe I bought the wrong PC817 Photocoupler. Mouser showed the part as discontinued here is a link to the one I bought on Tayda: https://www.taydaelectronics.com/pc8...output-ic.html

  4. #14
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    Quote Originally Posted by kguyot View Post
    Same results on 5v. My guess is maybe I bought the wrong PC817 Photocoupler. Mouser showed the part as discontinued here is a link to the one I bought on Tayda: https://www.taydaelectronics.com/pc8...output-ic.html
    I went a head and ordered the K847PH. Lets see if that fixes it.

  5. #15
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    Quote Originally Posted by kguyot View Post
    I went a head and ordered the K847PH. Lets see if that fixes it.
    Well that did it work. If using 5v What should the voltage be before and after the 330 ohm resistors?




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  6. #16
    DIGWDF Engineer member dirknerkle's Avatar
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    On the left side of the column of PC817 chips should be 680ohm resistors. On the right side, a 680 if running at 5vdc and a 1K-1.5K if running at 12vdc. The last row of four resistors that control the transistors should be 330 if running 5v and actually, I've had success using the same 330's if using 12vdc, but more correctly, you probably want to go to about 750ohms if using 12v.

    Note also that the DirkCheap817+ was a somewhat experimental design that allowed for 2 transistors per channel mounted in parallel. This isn't generally a good idea but in our testing, we found it to work providing the transistors were closely matched. The result was that the transistors ran a little cooler when pushed at 2A/channel. However, if one of the pair of the transistors is "weak," it may conduct current on its own and the result is that the channel appears as if it's still "on" because one of the two transistors is letting current through. And even though we put in the mounting holes for the extra transistors this is why it's still not a great idea to actually use them. Sounds kind of crazy -- but it does work when the transistors are closely matched. YMMV....
    Even though the DIGWDF Store has closed, it's still awesome! Thanks to all who have supported us through nearly 7 years of excitement!
    Parts of the store will remain open for downloading documentation, firmware and other files: http://digwdf.com/store


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