On Friday, January 27, 2012 10:07:52 AM Viesturs Lācis did opine: > 2012/1/26 Kirk Wallace <[email protected]>: > > On Thu, 2012-01-26 at 08:40 +0200, Viesturs Lؤپcis wrote: > > An off-the-shelf solid state relay might do the job too. > > The relay was my first idea, but it turned out pretty quickly that > there are no such relays that could be driven directly by Mesa card - > even those with 5V coils on control side would require too much > current for gpio pin to sink - I think that smallest I found was > around 100 mA. > > > I just wanted to tell that I resoldered optoisolator and now it is > kind of working correctly. > Laser is shining. > The problem is that it is not burning the wood. > Is the voltage drop in the wiring too high? > How can I help there - use thicker wire leads? That could be one bit of help, but I would be making measurements to determine where the loss is. The idea being to grease the loudest squeek first. :)
Does it burn wood if your circuit is bypassed? How much voltage is the supply making when the laser is on by bypassing your circuit? Measure at the supply, and at the laser to get an idea of the wiring losses. More than a .05 volt difference and I would up the wire gage. If loss in your circuit is the difference in whether it burns wood at a usable feed rate or not, then how much on state voltage loss there is in that output transistor?, which could be anything from 150 to 6 or 700 milli volts. This is one of the reasons I suggested the use of a power hexfet device earlier in this thread, which when forward biased by at least 5 volts, could reduce that particular loss to 10 or 20 milli volts as they have on resistances in the milli-ohm range. It (the hexfet) also switches states 10 to 1000 times faster than a 2n3055 when given adequately low impedance gate drive. When switching at high rates, which you aren't here, the hexfet runs cool, not hot. The gate of a hexfet can look like driving a .1 microfarad capacitor for the really big ones, so lots of drive is needed to prevent as much as possible, the heat surge when it is in the middle of the switching transition. Even small ones can be effectively a .005 u-f capacitor. This means the driver stage will need large, low impedance bypass capacitors right on its power pins, 2 u-f paper/mylar would not be overkill in higher current circuits. Because old faded to too low a voltage computer PSU's are replaced 99% of the time because the capacitors have failed, they can be an excellent source of power hexfet's for a circuit like this. You can have a suitable hexfet in your hand in half an hour, but while extracting it, wrap some bare wire wrapping wire around all 3 pins so that it is shorted and won't be blown by static. Don't remove the shorting wire until it is in your new circuit. You can usually use the numbers stamped on these devices to look them up and download the data sheet pdf, I have been able to at least. A good driver for a hexfet can be cobbled up out of a 4000 family cmos hex invertor by using all 6 gates in the package in parallel, and your 4n2x can drive it direct with a suitable pullup resistor to the 5 volt rail & let the 4n2x pull that point to ground when on. That will drive the outputs of the hex invertor high going all the way to the + rail, turning on the hexfet at the same time to 4n2x is on. I would expect that today, there are better devices than the 4000 family cmos to do such a job, but the 4000 families ability to work at supply rail voltages well above their nominal 15 volt rating has been amazing to me. I once used a 4028 hex decoder to add edging signals to a character generator at a tv station in about 1979, bearing in mind they get faster at the higher voltages. It worked well but slightly warm at 28 volts for many years. What I am saying here is that my knowledge of available parts to do a certain job is dated, like me. :) What is the current in amps this laser needs from its nominally 5 volt supply? Cheers, Gene -- "There are four boxes to be used in defense of liberty: soap, ballot, jury, and ammo. Please use in that order." -Ed Howdershelt (Author) My web page: <http://coyoteden.dyndns-free.com:85/gene> Be sure to evaluate the bird-hand/bush ratio. ------------------------------------------------------------------------------ Try before you buy = See our experts in action! The most comprehensive online learning library for Microsoft developers is just $99.99! Visual Studio, SharePoint, SQL - plus HTML5, CSS3, MVC3, Metro Style Apps, more. Free future releases when you subscribe now! http://p.sf.net/sfu/learndevnow-dev2 _______________________________________________ Emc-users mailing list [email protected] https://lists.sourceforge.net/lists/listinfo/emc-users
