On Thu, Sep 30, 2010 at 9:16 AM, Mark E. Skeels wrote: > =A0List, > > I have need of a couple of inexpensive (hopefully) dmm's for a test > fixture I am designing. By inexpensive, I mean <$150 USD. > > I am going to use them to measure DC current at 1-10A (mostly >5A) and > interface them with a PC. > > They should have the following features: > > =A0 =A0* I could live with better 2-3% accuracy in the range of 5-10 amps= DC. > =A0 =A0* Ability to disable auto-shutoff feature > =A0 =A0* battery powered, portable form factor is fine > =A0 =A0* Optical isolation of PC link would be nice, but not necessary > =A0 =A0* Can be directly interfaced (includes a spec) by a user-created > =A0 =A0 =A0program through serial port or USB; does not require use of > =A0 =A0 =A0special logging software. > =A0 =A0* If USB, it must look like a serial port to the PC, or come with = a > =A0 =A0 =A0compatible, easy to use driver, since I am going to write the > =A0 =A0 =A0interface program in Delphi under WindowsXP, using Async Profe= ssional. All your specs are met by, e.g. $30 MAS-345. (except perhaps "reasonable quality") http://www.web-tronics.com/indmmwrspcin.html I started a thread about this a year or so ago: http://old.nabble.com/Interfacing-with-Chinese-RS232-DMMs--tt16355946.html Now that I have some experience, let me add a couple things: - The portable battery-powered meters that I have experience with use an infrared LED to accomplish optical isolation. Combined with the auto-shutoff being disabled in RS-232 mode, this leads to pretty short battery life, a few days of measurements and it is done. - I ended up writing Python code to interface to the meters using pyserial. The serial interfacing isn't too difficult. I'm happy to share the code if it helps. (Python code is generally easy to read.) - I got tired of the meters eating batteries, so I designed a simple ammeter into my test circuit. An ammeter is straightforward to build: pass your current through a shunt resistance and read the voltage across it with an opamp and ADC. Use a chopper amp to keep the burden voltage low. There are some eevblog podcasts about this. Regards, Mark markrages@gmail --=20 Mark Rages, Engineer Midwest Telecine LLC markrages@midwesttelecine.com --=20 http://www.piclist.com PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist .