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PWM controlls, best chip for several at once? AVR or PIC

Discussion in 'Microcontrollers' started by Triode, May 3, 2009.

  1. Sceadwian

    Sceadwian Banned

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    They're called pick and place machines Triode.
    You can get them for about 10-15 grand off e-bay...
    You still need to reflow them after.
     
  2. Triode

    Triode Member

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    Yeah, I know what those are, but that's like if there weren't printers for home and you were like "they have it, its called a news press"
     
  3. Sceadwian

    Sceadwian Banned

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    The economy of scale doesn't work for a pick and place machine. MILLIONS of people need to print stuff every day. Not that many need a precision robot to place parts every day =) Maybe a few hundred. So the cost of development and what needs to be charged to make a profit is... very different. Even though the precision placement of the microscopic dots of ink is 'better' than a pick and place machine.
     
  4. dave

    Dave New Member

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  5. Triode

    Triode Member

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    Just cause I said I wanted it doesn't mean i think it makes sense. I'd like a zeppelin too.
     
  6. Mr RB

    Mr RB Well-Known Member

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    These days I can hand solder SOIC with a pointy tip soldering iron quicker than I can solder a DIP chip. And 0805 resistors etc about the same speed as through hole resistors, but no need to bend legs and chop the legs off after.

    Still takes a little time to make the PCB but. :(
     
  7. 3v0

    3v0 Coop Build Coordinator Forum Supporter

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    Sort of funny how that works. Took forever to solder that first 805.
     
  8. Triode

    Triode Member

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    I actually like working with surface mount better, but other than soldering them on to a dip mount is there any good way to prototype with them? Its not like many people here are doing production. Except for blueroom.
     
  9. 3v0

    3v0 Coop Build Coordinator Forum Supporter

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    It is not hard to make toner transfer PCBs if you use PulsarProFx. Harder if you do not. If you have a laser printer and a laminator you can get started for about $30 and the PCB stock. The cost of the paper and foil work out to somthing like 2 cents per sq inch.

    I cut clear plastic solder paste stencils on a cricut and reflow in a fry pan. Works great. So far I have only done SOICs with the stencils.

    When I make PCBs for my class I make 10 or 12 of each.
     
  10. Triode

    Triode Member

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    I guess I just never found perf boards to be all that bad. But I don't make anything really complex, mostly motor drivers of various kinds.
     
  11. 3v0

    3v0 Coop Build Coordinator Forum Supporter

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    To each his own.

    I use eagle for the layout. Start by editing the schematic. The schematic forces the board layout to have the same nets.

    It is very nice to have the good schematics and use eagle to relate them to the foil pattern when debugging.
     
  12. dougy83

    dougy83 Well-Known Member

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    Printable over-head transparencies (plastic sheet for over head projectors) works very well; just stick the whole board in the freezer after ironing, and all the toner transfers when you peel off the plastic sheet.
     
  13. jeremygaughan

    jeremygaughan New Member

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    Nigel, This is a little late but I was out of town.... Thanks for posting that code in assembler. It's been an interesting study. A lot more complex than I thought it would be, but I guess that's what happens when you know how to do it right. Do you have a listing somewhere that shows what all your commands mean? There are some assembler commands that you use that I'm not familiar with and can't figure out.

    Sorry not the assembler commands but things like var8+1 I see that var8 is defined but I didn't see var8+1...... Is it just like my logic is telling me, and it puts it in the next folder?
     
    Last edited: May 16, 2009
  14. Nigel Goodwin

    Nigel Goodwin Super Moderator Most Helpful Member

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    You need to consider how an assembler works, it's far less complicated than you may think - machine code is nothing but numbers, and instructions like BCF, ADDLW etc. are simply converted into numbers during the first pass, using the values listed in the INC file (it's essentially a simple search and replace, like you would do in a word processor). Likewise any names YOU define are also converted to numbers, so if you declare something like 'avariable' equals 35, then each occurance of 'avariable' in the program will be replaced by 35. If you refer to avariable+1, then avariable will be replaced by 35 and have 1 added to it, making 36. So +1 after a variable just refers to the next higher GPR.

    This is all explained in the helpfiles for MPLAB/MPASM.
     
  15. Triode

    Triode Member

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    I'm still reading up on what I'm going to need for my prohject. Now I'm starting to think I want to use a chip with a premade H-Bridge instead of building it, I'm very result oriented. I have an L298N, would that work right with a PWM input to adjust the speed of the motor? It seems like it should but I don't want to assume when I'm not very knowledgeable about these chips.
     
  16. Nigel Goodwin

    Nigel Goodwin Super Moderator Most Helpful Member

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    Depends on your motors, and what power they require, the L298 can only feed VERY small motors.
     
  17. Triode

    Triode Member

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    well for now we are talking about very small motors, the kind you would find in toys, like lego motors. Infact I plan to build one with lego connections that can drive two motors at variable speed in both directions by remote, for tank syle drive RCs, I figure its a good starter project for RC robots because its small and the legos provide most of the structure.
    I have nothing against buying new ICs either, and later I will want to drive the kind of motors that are in a racing RC, and of course it would be a good idea to make them able to handle the more powerfull ones in that range. But the main considerations now in choosing new driver ICs to order is that they can be used for variable speed and direction drive, preferably of two motors, but I can just use two chips if not. I realize theres several ways to do this though, and I'm reading about all the projects already out there that do this, theres pleny of info in those. But I'm still mentioning it here cause most of the time when I come up with my own way of doing stuff off of projects I find out its out of date, or that I'm using something wrong, and you guys are always helpful. I'm guessing what I want is a full bridge driver, but I don't know the full range of whats availble.
     
  18. Nigel Goodwin

    Nigel Goodwin Super Moderator Most Helpful Member

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    You might check the stall and start currents, I suspect you may be VERY surprised by how large they are.
     
  19. Triode

    Triode Member

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    I found a website that actually compares all the lego motors with some pretty thorough statistics.
    http://www.philohome.com/motors/motorcomp.htm
    It looks like the lego technic motors draw up to 12 V@0.12A and the older ungeard ones draw up to 12v@0.33A. They are brushed motors, no surprise there. There isnt any stall or start current listed. But they did run these tests loaded.

    I'm having a harder time than I thought finding these chips, but mainly because the big suppliers often only want to sell in 500s. Anyway, I found this one:jamco catalog page, datasheet, it looks kinda good, and all the inputs look to me like they would be easy to control with a PIC, except for the speed control. with a varable voltage input I'm not sure how I would go about making this work, also it seems to take out some of the point when the control input has to be 0 to 12v and the output from the chip to the motor is 0 to 12v, but I guess it handles more current. Any sugestions on how I could supply this from the pic? Of course I could still just build a FET h bridge, I'm not really sure at this point if I'll use an IC designed for motor control or just put it together myself.


    by the way for anyone following this trying to do something similar I've found these documents usefull:
    Tips 'n Tricks DC Motor Control PICmicro
    Low-Cost Bidirectional Brushed DC Motor Control
    Using the PIC16F684

    determining mosfet driver for motor operation
     
    Last edited: May 18, 2009

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