Kirk- If the DACs are $9 each you might want to look for alternatives. I've used some Sipex DACs before they were bought by Exar with good results. An Exar XRD5412 12-bit serial addressed DAC is only about $3-4 in small quantities. Almost the same pinout as what you are using, although 5V power supply.
Which leads to my next thought. If you operate off 5V you might be able to eliminate R7-R9 by taking the emitters of the optos to isolated DC GND and taking signal off the collectors. Last thought is to buffer the output with an op-amp, with the inputs to the op-amp clamped. This would allow you to take a 0-5V output and amplify it to 0-10V. That way if the real world throws some trash at the board the $.25 op-amp takes the hit, not the DAC. If you are only going to be sourcing current instead of sinking it you can also put a diode such as a 1N4004 in series with R10. Just my $.02 USD Javid ----- Original Message ----- From: "Kirk Wallace" <[EMAIL PROTECTED]> To: "Enhanced Machine Controller (EMC)" <[email protected]> Sent: Friday, February 08, 2008 3:47 PM Subject: Re: [Emc-users] Serial DAC Board > 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 > [email protected] > https://lists.sourceforge.net/lists/listinfo/emc-users > ------------------------------------------------------------------------- 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 [email protected] https://lists.sourceforge.net/lists/listinfo/emc-users
