On Fri, 2008-02-08 at 17:18 -0600, Javid Butler wrote: > 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
Thanks for the reply, Javid. I'll have to check out the Exar's. Part of my problem is that I know very little about opamps. All of my VFD's and the KBIC use 10 Volt inputs with a couple able to use 5 Volts, so I decided 10 Volts was the output to have. The LTC1257 allowed me to do what I needed, at the voltage I needed, with allot of the detail work done by Linear. I was wondering how I could try to protect the DAC output. I had a current limit resistor on the output for the first tests, but I found that one of the VFD's drew enough current to drop about a Volt across it, so I had 9 Volts at full scale. The datasheet indicates that the output is rated for a continuous short, so I took the limit resistor out. The datasheet also has an application note showing the RC filter on the output that I currently have on my schematic. I am thinking I may have the same voltage drop. But if the drop shows up in testing, I can just replace the resistor with a jumper. Another thought was to have a Zener across the output to clamp it. Though, I am tending towards leaving it as is right now, and see how it works out. -- 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
