On Fri, 2008-02-08 at 12:22 -0800, f m wrote: > Kirk, > > A couple comments. You have the visible LED's in > series with the LED's in the optoisolators. The > threshold voltage of both LED's when on comes real > close to the 5V from the driver chips. It probably > works, but doesn't leave any margin. Would be better > to route the visible LED's to ground through separate > resistors.
You made me look at the datasheets. I assumed (Dooh) a diode drop of .6 Volts for each diode, but the SMT LED is rated at 2 Volts (2.8 V max.) and the coupler emitter at 1.2 Volts, giving around 3.5 Volts or 1.5 Volts across the resistor at 1K Ohms for 1.5 mA. I don't know what I was thinking, but I figure 10 mA would be good so theoretically 150 Ohms should work. But like you said giving each diode it's own resistor would be better. This would allow me to tailor the current for each diode on it's own. Now I have to find space on the board. > Also, have you thought about adding additional DAC's? > As you already have the isolation and power supplies, > it would be easy to add 3 more DAC's. (D_out of U3 to > D_in of the next DAC...) This would give a simple > board that would control 3 servos as well as a > spindle. > > Fred I did briefly look at multi-channel DAC's, But for me, I only needed one channel and the software would have gotten more complicated. Thinking aloud, the board may be around $15. The DAC's are about $9 each. The DC-DC converter and voltage reference are about $5 each. The rest ... a few dollars more. I guess adding more channels would be about $10 each. Currently, the DAC board may cost around $40 complete (for a batch of 10), adding three more channels makes it $70 and four single channel boards would be $160. So, if you need four channels, you are right, a single four channel board would be much less expensive. Adding the channels to the schematic and layout would not be much work. The software change would be minor. A multi-channel DAC would be cheaper still. The software is more complicated, but no big deal. I like the simplicity of the current board, so it would be nice to have both available. Thanks for the help Fred. -- Kirk Wallace (California, USA http://www.wallacecompany.com/machine_shop/ Hardinge HNC lathe, Bridgeport mill conversion, doing XY now, Zubal lathe conversion pending) ------------------------------------------------------------------------- This SF.net email is sponsored by: Microsoft Defy all challenges. Microsoft(R) Visual Studio 2008. http://clk.atdmt.com/MRT/go/vse0120000070mrt/direct/01/ _______________________________________________ Emc-users mailing list Emc-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/emc-users
