1. OCAU Merchandise now available! Check out our 20th Anniversary Mugs, Classic Logo Shirts and much more! Discussion here.
    Dismiss Notice

Dual Polarity Adjustable Voltage and Current Lab Power Supply Worklog

Discussion in 'Electronics & Electrics' started by nux, Mar 31, 2006.

  1. fredhoon

    fredhoon Member

    Joined:
    Jun 27, 2003
    Messages:
    2,643
    Location:
    Brisbane
    will the Op Amp buffer reduce the quality of the signal generators output by any chance (clip the signal)? What do you plan on connecting the function generator to that will require a moderate power draw?

    Purely for interest and laziness (i haven't looked over the schematics, not that i'd be able to understand them properly), will the signal generator allow you to change the output waveform?
     
  2. OP
    OP
    nux

    nux Member

    Joined:
    Jan 20, 2002
    Messages:
    16,780
    Location:
    Melbourne
    Well the Op-Amp I've ordered should be fast enough to not reduce the quality. I would make sure I dont amplify it too much so it gets clipped.

    I'm not sure what I'd be connecting it to that would need moderate power draw, but I dont know what the capabilities of the XR2206 is in terms of supply and things. I dont think its capable of driving say a large speaker or something.

    The XR2206 can do from 0.01Hz to 1MHz with Square, Sine and Triangle as the main outputs (you can do step and saw too but I cant be bothered :p).

    Mine will probably go from 1Hz to 1MHz with two selectable timing capacitors and 3 pots.

    I'm thinking of getting a PCB made up for each stage (Function Generator, Op-Amp and Counter) so each bit is seperated and I can mix and match things. I can post them up if you or anyone else is interested. But theyre pretty much what is in the datasheets.
     
  3. Goth

    Goth Grumpy Member

    Joined:
    Jun 22, 2002
    Messages:
    9,228
    Location:
    /dev/null
    Have you looked into making PCBs yourself instead of having them made?

    The PIC based frequency counters look fairly simple, IIRC Silicon Chip did a very similar project too.

    Say, you're at Melbourne Uni, right? How is teh swot-vac going?
     
  4. OP
    OP
    nux

    nux Member

    Joined:
    Jan 20, 2002
    Messages:
    16,780
    Location:
    Melbourne
    I have a few friends that make PCBs themself so I might give that a go. Already got a mostly working schematic in Eagle, just gotta work on getting it all single layered.

    I liked the PIC counter as I have a few homemade PIC Development boards that I had made from BatchPCB as well as quite a few spare LCDs.

    I am, Swot-Vac is going alright, havent really studied for exams yet though :p

    What do you think of using the LM318 for a buffer/amplifier?
     
    Last edited: May 31, 2006
  5. dakiller

    dakiller (Oscillating & Impeding)

    Joined:
    Jun 27, 2001
    Messages:
    8,069
    Location:
    3844
    Looks ok from here
    Only has about 20mA output
    Wouldn’t want to have much gain running it at up to 1 MHz, unity gain would be best
    You’ll need a minimum of 10V to run it, and probably a split supply too (not much of a problem with your new psu)
    just make sure you make a good pcb layout for it, keep the traces tight, keep power traces away from the signal and plenty of power supply decoupling as close as you can to the chip, 0.01uF ceramic and 10uF electrolytic on both rails to ground with the ceramic as close as you physically can put it (<5mm) and the electrolytic not far behind it
    Just for added value, low pass filter the opamp to about 5 MHz as well (cap across the feedback resistor) great to get rid of high frequency noise and ringing/overshoot on square waves
     
  6. OP
    OP
    nux

    nux Member

    Joined:
    Jan 20, 2002
    Messages:
    16,780
    Location:
    Melbourne
    Alright, I've just been designing this PCB layout in Eagle today. Made it single sided so I can make a prototype myself. I haven't worked out how to do a ground plane in Eagle, however not sure if its really needed.. Even on my Breadboard the output seems fine. I'll try and get one made up in the next week.

    [​IMG]
    Click to view full-sized image!

    I can post the schematic too if anyones interested.
     
  7. Goth

    Goth Grumpy Member

    Joined:
    Jun 22, 2002
    Messages:
    9,228
    Location:
    /dev/null
    You'll probably want 5k1 resistors, since 5k is not a standard value.

    There is a part in the standard Eagle libs for a vertically mounted resistor, i'm sure it's in the Discrete lib or somewhere like that.

    Looks good.
     
  8. OP
    OP
    nux

    nux Member

    Joined:
    Jan 20, 2002
    Messages:
    16,780
    Location:
    Melbourne
    Yeah I know, Im using 5.1K on the breadboard. The PDF specs 5k so hence I wrote that :p Its just used to create a 'phantom' ground I think. I did have vertical resistors in there before, but its easier to use these as I can run traces under them and stuff.

    All fits in a 2x2 square inch board, I might get a few made and try and sell some as kits.

    I've just nicened up all the silkscreening positions and am fiddling round with ground/power planes. Some of the planes need to be spaced a bit better but this is it so far:

    [​IMG]
    Click to view full-sized image!
     
    Last edited: Jun 8, 2006
  9. OP
    OP
    nux

    nux Member

    Joined:
    Jan 20, 2002
    Messages:
    16,780
    Location:
    Melbourne
    Update:

    [​IMG]
    Click to view full-sized image!

    Board made (left one). Studying for exams is too boring so I bought a PCB making kit from Jaycar. My new laser printer didnt want to do it properly (all the toner smeared and ran) but the old old one worked fine, albeit somewhat blotty and with a few streaks.
     
  10. Sadow

    Sadow Member

    Joined:
    Dec 25, 2001
    Messages:
    590
    Location:
    Brisbane, Springwood
    did you print directly onto the copper?
     
  11. OP
    OP
    nux

    nux Member

    Joined:
    Jan 20, 2002
    Messages:
    16,780
    Location:
    Melbourne
    Nope, toner transfer method: http://www.5bears.com/pcb.htm

    I wonder if I could print directly to it... My old laser has the paper going straight through..
     
  12. Goth

    Goth Grumpy Member

    Joined:
    Jun 22, 2002
    Messages:
    9,228
    Location:
    /dev/null
    The way a laser printer works, it won't print directly on to a conducting material.

    What kind of paper did you use for the toner transfer?
     
  13. OP
    OP
    nux

    nux Member

    Joined:
    Jan 20, 2002
    Messages:
    16,780
    Location:
    Melbourne
    I used this cheap glossy inkjet paper from Safeway, came in a 50 pack.

    Funny thing is my almost new Samsung CLP510 laser wouldnt print on the glossy paper, it just smeared and could be wiped off, but this old laser worked quite well for it. Maybe its because the old one is much hotter, or the paper doesnt go through as many rollers. It just has a problem with black marks every few cm and stuff.
     
  14. Goth

    Goth Grumpy Member

    Joined:
    Jun 22, 2002
    Messages:
    9,228
    Location:
    /dev/null
    How much was the paper?

    I was gonna buy some more Press'n'Peel, but might try the cheaper option.
     
  15. OP
    OP
    nux

    nux Member

    Joined:
    Jan 20, 2002
    Messages:
    16,780
    Location:
    Melbourne
    I think it was on special for under $20 for 50 sheets. I've wasted about 6 trying to get it to print right and stuff.

    I might buy some other types and see what works best. Most people say finding the right paper is key. Although this paper seems pretty good, only took 2 minutes or so to iron on and when I put it in water it basically fell straight off the board and left all the toner on the copper.
     
  16. Goth

    Goth Grumpy Member

    Joined:
    Jun 22, 2002
    Messages:
    9,228
    Location:
    /dev/null
    I reckon even if it is far less reliable than PnP, it would still be more cost effective.
     
  17. fredhoon

    fredhoon Member

    Joined:
    Jun 27, 2003
    Messages:
    2,643
    Location:
    Brisbane
    I vaugely using remember using OHT sheets. The transfer left bits out, but more like a speckled track rather than a missing track. I don't know if the mehtod has changed (been a few years since uni) but we inked over everything just to be on the safe side.

    Most laser printers should have an option to select OHT as the printing medium, they aslo should have a glossy or coated option as well.
     
  18. OP
    OP
    nux

    nux Member

    Joined:
    Jan 20, 2002
    Messages:
    16,780
    Location:
    Melbourne
    Yeah I might try with transparencies next.

    Okay PCB is etched and looking good! Now I just need to borrow someones drill press and drill some holes. SMD is looking very tempting for future boards.

    Etching:
    [​IMG]
    Click to view full-sized image!

    Finished:
    [​IMG]
    Click to view full-sized image!
    Some of the pads look funny but its just because theyre scratched and reflecting light funny. And the traces are actually copper, I just did a bad job in Photoshop with Auto Levels :p
     
    Last edited: Jun 20, 2006
  19. Dr feelgood

    Dr feelgood Member

    Joined:
    May 24, 2005
    Messages:
    1,727
    Location:
    Mornington peninsula
    looking good, keep the photo's coming. :thumbup:
     
  20. -KoMoD0-

    -KoMoD0- Member

    Joined:
    Dec 26, 2005
    Messages:
    9,033
    Location:
    Western Sydney
    looking good
     

Share This Page

Advertisement: