On 09/28/2013 05:38 AM, Charles Steinkuehler wrote: > On 9/28/2013 4:45 AM, Richard Thornton wrote: >> Hi, >> >> I have seen a bunch of info on using BBB with capes and a lot of 3D >> printing specific stuff like Replicape and BeBoPr++. >> >> My thought was can the BBB replace the PC in LinuxCNC and drive the G540 >> directly? > > The gecko will happily work with 3.3V signals (as will just about > anything designed to connect to a standard PC parallel port...they have > all had 3.3V signaling for ages). So if you want, you can just hook up > some wires from the BeagleBone connectors to a DB25, maybe using a > prototype "cape" if you want to be fancy: > > http://www.adafruit.com/products/572
The bottom line is, that for some G540 inputs one only needs to turn on and off the LED in a LTV846 opto-coupler. http://www.wallacecompany.com/machine_shop/G540/G540_upper_bottom-2.jpg http://media.digikey.com/pdf/Data%20Sheets/Lite-On%20PDFs/LTV-8x6.pdf The forward voltage for the LTV is typically 1.2 V. there is a 200 Ohm resistor in series with the input which will also need to be considered. At 3.3 V, V=IR, I=V/R, I=(3.3 - 1.2)/200=0.0105 A= 10.5mA. It looks like 5mA should be enough to drive the LED, so if the BBB output can drive 10mA and survive, a direct connection should work. The charge pump signal is different. http://www.wallacecompany.com/machine_shop/G540/G540_upper_bottom_z-1b.png The input charges a capacitor and diode bridge which needs a lot more current and is more sensitive to voltage, frequency and duty. This shows a parallel port signal in 5 V SPP (low drive) mode, which doesn't work: http://www.wallacecompany.com/machine_shop/G540/g540_mb_spp.jpg Here it is in 5 V EPP (high drive) mode, which does work: http://www.wallacecompany.com/machine_shop/G540/g540_mb_spp.jpg This signal peaks at just over 3 Volts and takes its time getting there. The SPP signal peaks at 2 Volts. The situation gets more difficult when one considers the length and type of cable used. Noise can put significant + and - voltages on the signal, so reverse voltage protection, filtering, conditioning and termination will need to be considered. So direct connecting a BBB and a G540? ... It depends. -- Kirk Wallace http://www.wallacecompany.com/machine_shop/ http://www.wallacecompany.com/E45/ ------------------------------------------------------------------------------ October Webinars: Code for Performance Free Intel webinars can help you accelerate application performance. Explore tips for MPI, OpenMP, advanced profiling, and more. Get the most from the latest Intel processors and coprocessors. See abstracts and register > http://pubads.g.doubleclick.net/gampad/clk?id=60133471&iu=/4140/ostg.clktrk _______________________________________________ Emc-users mailing list Emc-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/emc-users
