braun@m10ux.UUCP (MHx7079 mh) (10/14/87)
I noticed in a new Heathkit catalog that Heath sells a kit for an oscilloscope add-on for a PC. It has two 50 MHz channels with 256-bit resolution, and connects to a PC (or any other computer) via a rs-232 port. There are no controls on the box, just 2 BNC sockets for the probes. The specs indicate that it has a good range of capabilities in the areas of triggering and adjustable horizontal sweep times and vertical sensitivities. It comes with source code (in Basic) for the software. It cost $400. This sounds neat. Has anyone seen or used one? How much would a comparable real scope cost? Does anyone know anything about similar products on the market? -- Doug Braun AT+T Bell Labs, Murray Hill, NJ m10ux!braun 201 582-7039
wtm@neoucom.UUCP (Bill Mayhew) (10/16/87)
I built the Heath scope for my lab here at work. I built the fancier model with the pushbuttons on the fron that can operate in standalone mode without the computer, if desisred. The unit is best as an audio bandwidth storage oscilloscope. The inputs are sampled through an 8 bit ADC. They traces are displayed on a cheap slave oscilloscope via a 10 bit DAC so that there is some lattitude to move the display around on the screen. The number of samples per channel is fixed at 512. Two current and two stored traces are possible. Data is shipped back to the host computer via a standard RS 232 port with jumper selected baud rates from 300 to 9600. The communications protocol is quite simple and easy to program in basic or c. The software included is written in microsoft basic with a couple of routines written in 8088 masm. They also give you a .exe version compiled with the microsoft basic compiler. Sweep rates above about 50 uS per division are sampled in "equivalent time", meaning that the display is useless unless you are looking at a steady-state waveform. There is no delay line, so the triggering event is lost at high sweep rates-- generally, this isn't a problem since only repetative steady-state signals can be viewed at high sweep rates anyway. All in all, the heath digital scope is pretty good, as long as you understand its limitations. I needed to look at some very slow signals, and I didn't have a storage scope, so this was perfect for me. I have a tektronix 2445 that I have to look at higher speed stuff and use as a slave scope for the heath unit. If you don't have a scope to begin with I think that the B&K model 2520 20 MHz digital storage scope would be a pretty good choice. The 2520 features dual trace and a very flexible timebase and triggering modes. It costs about $1800. We recently replaced a raft of 8 year old Tek 912s in our student labs with the B&Ks. We find that the B&Ks are much nicer instruments, especially for storage. Students can also make hard copy plots on an X-Y recorder with the B&K. It seems that for scopes, the rule of you get what you pay for pretty much applies. Bill Mayhew Electrical Engineering Division of Basic Medical Sciences Northeastern Ohio Universities' College of Medicine Rootstown, OH 44272-9989 USA phone: 216-325-2511 (wtm@neoucom.UUCP ...!cbosgd!neoucom!wtm)