Why Get an Analyser?
Logic analysers are a very important tool when working with digital systems as they record the logic levels of multiple points simultaneously over a period of time. They also have the ability to decode the information they log so, for example, the analyser could be connected to an I2C bus and it would not only show the data / clock lines, but also decode the individual byte transactions and acknowledge bits.
- How much should you spend on an analyser?
- What brand should you buy?
- What are the speed requirements?
These are important questions to ask but if your answers to these three questions are 1) £10, 2) Don’t care and 3) Less than 24MHz, then there is a great product which is remarkably powerful considering its cost and size.
The Budget Analyser
HobbyComponents is currently selling a USB 8 channel 24MHz logic analyser for only £8.99. So when I needed a logic analyser a month ago for the ZBM Project, I purchased one and can say that it really packs a punch!
When my kit arrived (I paid £13.00), it came with both wires with jumper sockets and wires with clips for grabbing pins. The wires were a little on the thin side and some of the wires snapped off the clips. But, being an engineer, I replaced the jumper ends and used thicker multi-core wire.
The clips have a mechanism whereby squeezing the clip like an injection results in a protruding metal claw that closes when you release the clip. The clips are exceptionally resilient when gripping an IC leg!
Example of clips : Gabotronics
Software - Sigrok
The software needed to use this analyzer is called Sigrok, which is freeware and open source. Sigrok is a complete package for this device as it not only allows you to set the frequency / number of samples but also has the decoding features built in.
What makes the software impressive is the amount of decoding options, which range from serial busses (I2C, SPI, UART) to parallel busses (Parallel, Z80).
UART decoding in Sigrok : HobbyComponents
ARM ETMv3 example : HobbyComponents
There are some features missing from this product, such as triggering. But for simple projects, this is not typically important.
As the USB device is micro-based (CY7C68013A), there are also speed limits so working beyond 16Mhz with this device will result in small capture times (as compared to lower speed option).
When I first used this product, I noticed that if you do not select a high enough sample frequency, it will miss data. So if your fastest frequency is 2Mhz, it is best to go for a frequency of at least 8Mhz to guarantee each capture. You should also be cautious about going beyond 4Mhz as the speed of the capture also becomes dependent on the speed of your computer and USB ports.
Overall this logic analyser really punches above its weight and is not far from being par with other logic analysers which start from £50 and up. Along with the free open source software, it can log, decode, and debug most hobby systems while keeping the price low.