Low cost logic analyzer

MFB

Senior Member
The current issue of Servo magazine has an interesting item on using the Stamp Logic Analyzer (from www.parallax.com) with non-Stamp microcomputers. It should be possible to monitor 16 lines and decode serial, I2C and SPI signals. The cost has been kept down to $79 by leaving out input buffers and test probe leads. Some kind of adaptor would therefore be required between the Stamp compatible header board and the PICAXE chip. Has anyone tried this approach to producing a low cost logic analyzer?
 

Brietech

Senior Member
Wow - i hadn't seen that before. That is a very cool product. Maybe you could build a "breakout" board for it, mount it all in a project enclosure, and have a pretty decent, cheap, computer-based logic analyzer. Given that even old logic analyzers are still incredibly expensive (as in, way more than 'scopes even!), this looks like a great deal.
 

MFB

Senior Member
Not sure about mounting this device in a box to produce a general purpose USB.2 based logic analyzer. This product is designed to plug directly into a DIL socket, with the Basic Stamp plugged on top. This keeps the input wiring between the microcontroller and the analyzer very short and avoids the possibility of miss-connection. The Stamp Analyzer does not therefore have the capacitance buffering and protection circuitry required for general use. Rather than a separate box, a small adaptor board would be needed to wire between the analyzer and a PICAXE socket. However, looking at the very powerful support software it would seem well worth the effort to produce an adaptor board for each type of PICAXE.
 

profmason

Member
Logic Analyzer

I just went on Ebay and bought a HP1631d. It is a 50 MHz bandwidth and 200 M sample/second 43 channel Logic Analyzer and 2 channel digitizing scope combo. So it is 20 years old, but it is what I used in college. These go for around $100 shipped in the US with a set of logic and state probes.

This will replace the 30 year old analog scope on the bench. I thought about the USBscope http://www.hobbylab.us/default.aspx but decided I would rather have all the nice probes and a stand alone instrument. When I need to get an image on the computer, I just use the digital camera to snap a picture of the screen and then upload it.

having a scope really helps in debugging!
mmason
 

womai

Senior Member
One thing I like about USB based instruments for hobby use - as opposed to older analog equipment - is that they tend to take up very little space (especially also when not in use!). An important feature in all those cases where the home office desk has to double as the electronics lab bench :)

I had a look at the hobbylab scope/logic analyzer. Seems a decent offering for logic analysis of SPI, I2C and USART. The scope mode unfortunately is rather a joke with its 200 ksamples/sec, translating to a usable analog bandwidth of maybe 30 kHz - enough for audio work, but not much more. The technical data and limitations (sample rate, 10 bit resolution etc) give away its core - must be a regular 8 bit microcontroller, as opposed to the FPGA that is used in the Velleman scope or the PCTestinstruments logic analyzer.

Wolfgang
 
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