Recent content by Ch33f

  1. Ch33f

    +/- 12 V power supply acting weirdly(?)

    To elaborate a bit: If this was a simple resistor based voltage divider I would not have been surprised, because by drawing current asymetrically you basically change the impedance of half of the divider, thus shifting the VGND. BUT: To my knowledge the two resistors play only a minor part in...
  2. Ch33f

    +/- 12 V power supply acting weirdly(?)

    Ok, first problem found: Looking at asymetrical loads I found the following problem. I put a 470 Ω resistor between the + rail and the VGND => everything ist fine. I put a 470 Ω resistor between the - rail and the VGND => The VGND suddenly shifts massively and the + rail shows 21 V and the -...
  3. Ch33f

    +/- 12 V power supply acting weirdly(?)

    Ok, so I have looked into this a bit further and here are some of the possible aproaches: Create a virtual ground on the input side using resistors. Problems: It's a balancing act between wasing power and still having a fairly low impedance on the ground rail. Especially if you want +/-12V you...
  4. Ch33f

    +/- 12 V power supply acting weirdly(?)

    Huh... I guess I missed a core concept there. :oops: I thought that might work. Well one followup then: Would it work if I hook up two 1Megs two create the floating common? That way I should only waste/lose 12 μA and thus should still be able to supply a fair amount of current right? Edit1: I...
  5. Ch33f

    +/- 12 V power supply acting weirdly(?)

    Front: Input on the bottom: Red +30V; black 0V Output on top: Red +12; black GND; yellow -12V Each column is connected all the way from top to bottom and in green I added the invisible connections on the backside. I added the 1N4007 after I experienced the weird behaviour. It didn't change...
  6. Ch33f

    +/- 12 V power supply acting weirdly(?)

    First of all: Yes I know, you should always measure the performance of a power supply under load. BUT: I just conjured up a little +/- 12 V supply with a 7812 and a 7912. After soldering the thing together I just hooked it up to my 30V lab suplly (which has only one channel, hence the need for...
  7. Ch33f

    Using an oscilloscope without a probe. Good or bad idea?

    Thanks a lot! That will help me in my future projects! :)
  8. Ch33f

    Using an oscilloscope without a probe. Good or bad idea?

    Thanks for these quick answers! I'll try that out then. But I have a followup question: Do these two statements not contradict each other? Or am I misinterpreting the term "above earth"? From what I understand, according to Harald Knapp I should have the test circuit be floating because...
  9. Ch33f

    Using an oscilloscope without a probe. Good or bad idea?

    Hi there, I want to measure current with my oscilloscope. So far, so easy. Just bodge in a little and precise resistor, like 1 Ω or so and measure the voltage across it. But I don't want to bodge that, I want a nice sollution. Now here is my idea: I wanted to make a little resistor box e.g...
  10. Ch33f

    Controll for Seven-Segment-Displays

    Thanks again for finding these chips! :D I guess I'll be doing it from here. Thanks loads everyone! :D
  11. Ch33f

    Controll for Seven-Segment-Displays

    BTW. how do you find those chips? Are there some advanced search engines that do the trick or have I just not figured out how to google for ICs correctly yet? :confused:
  12. Ch33f

    Controll for Seven-Segment-Displays

    Sorry that replying took me so long. Had a really really busy week and a half! Amazing that you found it! Thanks!!! :D Only one problem: The MAX7221 is for common cathode and the displays I have are common anode. Does anyone know a comparable chip for common anode? Only chip I found is the...
  13. Ch33f

    Controll for Seven-Segment-Displays

    Ok, now it's coming all together. Sorry, I am still a bit slow in the field of electronics and still have to learn a lot. ;) And I think I mixed up anode and cathode earlier. :oops: So, I need to multiplex the displays because the segments of 2 or more digits share their cathodes (-). Because...
  14. Ch33f

    Controll for Seven-Segment-Displays

    And the "Bad" or "Good" sketches are what I learned about the general Idea of how to or how not to drive LEDs in general. And I don't know how this applies to the 7SD in question and its internal circuit.
  15. Ch33f

    Controll for Seven-Segment-Displays

    Ok... I have a feeling that we are running in some kind of either linguistic barrier. We are talking at cross purposes here. (Hoping this is the correct figure of speech.) I never thought the MAX7221 looked like that. The internal circuit I mentioned in post #7 was the internal circuit of the...
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