This page pretends to document my Logic Analyzer adventures. In the olden days, Logic Analyzer were large and expensive devices, inobtanium for low-cost hobbyists.
Forward to more modern times... With the advent of cheaper FPGA's Logic Analyzer became affordable. At one time I bought the Open Bench Logic Sniffer with the extra wing board. This board, with the Java based ols host software, makes a cheap workable Logic Analyzer. Alas, FPGA's also get dated very fast, so this platform is also hard to find. On the software side, it is supported by the sigrok/pulseview suite. The trigger mechanism in sigrok is quite rudimentary, but on the other hand, the decoder interface is very cool. This API allows a scripting language (typically Python) to read the sampled data and to add a higher level interpretation to the display. Here sets of signals can be interpreted as a data- or address-bus value, or even instruction opcodes.
The Open Bench Logic Sniffer (with wing) has 32 channels for data, each usable as trigger. 32 sounds a lot, but a simple Z80 CPU has 8 data lines, 16 address lines, and about 5 basic control lines. That leaves 3 lines for your project specific signals. More is better in the Logic Analyzer world.
IThe box is an implementation of my universal project box. Any project board that has all connections at just sides, can be put in this standardized box. The only effort is in designing the two I/O-panels.
Microcontrollers used to be slow and have limited capacity. But nowadays they are becoming fast enough to capture data in the 100 MHz range. That is more than fast enough for last century vintage computers. Somewhere in 2022, AgustÃn Gimenez Bernad (gusmanb) developed code for a Raspberry Pi Pico board (and a 5V adapter board, very useful for those vintage computers). The basic Pico does 100 MHz, the Pico 2 even 400 MHz (with more sample memory).
The basic board, has only 24 channels, but up to five boards can be connected together. For now I cannot imagine a project where 120 channels will be useful. But up to 48 is useful for 8-bit systems, 72 for most 16-bit systems. It also has to fit somehow on your computer display!
The board I use is a variant, the Jason YANG board, which includes the level shifter into the R.Pi Pico carrier board. A very cool feature of the PC-software is that it supports the same decoder scripts as the sigrok/pulseview suite.
Above is a three board device, the lower case contains an USB hub to simplify cabling. There is also an optional oscillator in this case to help test the boards.
One issue with the gusmanb type Logic Analyzers is that the channel organization is not very clear. Improving this with intermediate boards is possible, but an ongowing process. More on this later.
A nice feature of these small Logic Analyzers is they can be very close to the circuitry to test, so only short wires can be used. That simplifies wiring and all the transmission line complications relateds to long measurement wires. On any bus system, it can be a 'card on the bus' with just a USB cable to the host PC.
Last updated: 2025-05-24