On Wed, 2012-01-25 at 23:43 +0200, Viesturs Lācis wrote: > 2012/1/25 andy pugh <bodge...@gmail.com>: > > On 25 January 2012 21:07, Viesturs Lācis <viesturs.la...@gmail.com> wrote: > > > >> Kirk, I am getting totally confused... > >> What is the difference in schematics between both images in Your last > >> email? I cannot see any... > > > > The direction the arrow points in the transistor schematic symbol. > > Ok, thanks! > I do not understand - that is inside the BD139, right? What can I do > about it, if it is still the same BD139 transistor???
If your transistor is a BD139 it will be an NPN. As mentioned in another message, the pin number depends on the package TO or SOT. > I finally managed to get at least something working: > Short-circuiting +5V to 4N25's pin5 turns the laser power on and off > as required. It's jumping the 12 V supply to U1 pin 4 that should turn Q1 ON. If the 5 Volt supply turns Q1 ON, that means that your 12 Volt and 5 Volt supplies share the same ground, which is okay unless they need to be isolated, which is what opto-isolators (U1) allow you to do. > I am left with an impression that 4N25 is not working correctly. I concur. > Is that diode next to R1 mandatory? I will not have a time to obtain > one and solder in, before going to client. The general purpose diode next to R1 can tolerate a much higher reverse voltage. The opto-isolators internal LED has a reverse voltage tolerance a little over 5 volts, so hooking up the LED backwards or noise on the line could burn it out. The general purpose diode prevents the opto LED from being damaged. In addition, a regular LED can also placed in series with the general purpose diode, and will light up when the signal is ON. This can help with trouble shooting, and gives customers something watch while you are explaining how wonderful your machine is. > I just hope that I have spare 4N25... Me too. There may be some opt-isolators on junk telecom PC boards you might have laying around? > How sensitive to soldering heat are things like 4N25 optoisolators? > Maybe I have accidentally burned it? You might pull a trace up before damaging the opto-isolator, although sometimes heat can damage a component such that it still works but not very well, or not all the time. -- Kirk Wallace http://www.wallacecompany.com/machine_shop/ http://www.wallacecompany.com/E45/index.html California, USA ------------------------------------------------------------------------------ Keep Your Developer Skills Current with LearnDevNow! 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-d2d _______________________________________________ Emc-users mailing list Emc-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/emc-users
