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Thread: Power Supply grounding

  1. #21
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    You have to ZIP up the PDF - and then you are limited by the file size...

    By the looks of it, the signal lines from your CP/M computer to the opto isolators are completely isolated from the flexowriter. That's what I would expect - so the two shouldn't be interfering with each other electrically.

    You say there is a long cable between your CP/M machine and the flexowriter. Is this shielded and (if so) is the shield only connected at one end (preferably the CP/M computer end)?

    I assume your triangle symbol is the other end of the Flexowriter power supply and not the frame (which should be connected to your mains plug protective earth)?

    Here's the rub. If you have opto isolators going the other way (from the flexowriter to your CP/M machine) - then the opto isolators will be reacting to the un-smoothed DC power supply of the flexowriter and will be constantly switching on and off at 120 Hz. Is this what you are seeing I wonder?

    Everything else looks OK.

    Dave

  2. #22
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    Box.com wants $5/month. I'll look for a free one. Mike

  3. #23
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    How is this?

    https://filebin.net/f4nyxnwrz90771cg...pdf?t=4ply0l20

    Yes the referenced ground is not the Friden frame. AND I added a filter capacitor to smooth out the DC. It is not perfect, but the ripple is just a few volts which doesn't get through the opto isolator.

    I've been working on the reason why I can not get the Carriage return code from the friden. I believe it is because the punch magnet is not activated until the carriage return moves all the way back to home. The function is started when the carriage return key is pressed by I (the computer) has to wait about 100 mSec, before the code is sent. I will have to test this maybe tomorrow. Thanks Mike.

  4. #24

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    I'm a little concerned about where you've placed the filter capacitor. It should be on the LED side of the current limiting resistor. you don't want to significantly change the AC like ripple on the printer side as it can significantly increase the power in the coils. You might want to include a diode is on the printer side. I'm thinking what Daver2 said.

    Dwight

  5. #25
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    Suppose I should have been clearer. I placed the filter cap on the Firden Power supply, right after the rect bridge. It did raise the overall supply voltage. I suppose I should check the change in current in the actuating magnets. Didn't think about that. Thanks Mike.

  6. #26
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    But you stated back in post #1 that you placed the filter capacitor between the flexowriter negative AND frame ground?

    Dave

  7. #27
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    I do this in real time also, sometimes when I talk, i think I've said something and I didn't, or assume those who I'm talking with understand and see everything that I have. I meant to say the 1.0 uF capacitor was placed between the negative +8 VDC of the CP/M machine and it's frame. Sorry, sometimes I just can not help catching my pitch fork on my own pants. Mike

  8. #28
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    Excellent design, resolves all the issues of the hot DC side. How do you synchronize the word sent to the printer with itself? Would assume they use an AC sync motor to control speed but wonder if there is something required like a start bit or something to control when the word is sent to the printer? Or are you just sending the word to the printer and see what happens?
    I wasted lots of time connecting a paper tape reader to my Nova that transfers one byte at a time. Getting a strobe from the reader when it advanced to write the byte into a register that feed a second register that read the byte onto the data bus was a big deal.
    Until timing was worked out it was very frustrating.

  9. #29
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    Quote Originally Posted by Mike_Z View Post
    Box.com wants $5/month. I'll look for a free one. Mike
    No, it's free. The link defaults to the "business" plan, not the individual--you have to click on the "Individual" tab.

    Think of it like Amazon offering stuff for free shipping, but defaulting to paid shipping on checkout--unless you notice and click the "fast 'n' free" tab.

  10. #30
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    OK, I didn't see that part of box.com.

    The Friden is a machine that was designed to communicate with other Friden machines or to make paper tapes so as to make reproductions of documents. The Friden has a keyboard and writing machine, along with a punch and a reader. The keyboard is connected mechanically to the writing machine and to the code selector. The code selector contacts will punch a paper tape or output to another Friden (or my computer). The tape reader contacts are connected to the code translator or to the input of another Friden (or my computer). The translator operates the same as the keyboard would to type a character.

    My computer will parallel the reader contacts and operate the reader clutch, just as the reader would to operate the code translator and the writing machine. In this case my computer must first select the proper code, as the code selector would and then activate the reader magnet to initiate the writing.

    The keyboard operates the code selector contacts and the punch clutch magnet to make a paper tape. My computer is in parallel with the code selector contacts to receive characters. In this case my computer senses the punch magnet selections and the inputs when the punch magnet is selected.

    My computer has to deal with the timing of the Friden's mechanics. To print, first my computer sends out the proper key code and then a reader clutch signal. To input from the Friden, my computer waits for the punch magnet signal and then senses the punch magnet signals. Other than that my computer has to wait for the Friden to finish before sending more. AND it must wait for the next character, otherwise the computer will read the same character as a second, third or more character.

    There seems to be quite a bit of circular work here but the computer basically replaces the punch, output to the computer, replaces the reader as input to the writing machine.

    Hope this helps. Mike

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