02 LogicAnalyzer Hardware
As the project target is to create the most cheap but useful device possible I have kept the minimum requirements to a minimum, so minimum that the most simple form of the device is... a Pico, nothing else, you can program the firmware, connect some wires to it and that's it, you have your logic analyzer ready to be used.
This presents some limitations as the Pico only supports 3.3v IO's, so I designed a couple of boards, one for the analyzer itself (basically to make it easier to connect/disconnect Dupont wires and connect it to the secondary board) and a level shifter board.
The level shifter board allows to use voltages that range from 1.6v to 5v, it is referenced by default to 5v but you can reconfigure it to accept an external reference voltage.
Also, the latest version of the analyzer board allows to daisy chain the analyzers so you can chain up to five of these and sample up to 120 channels at once, a massive ammount of channels for a logic analyzer.
To use the Pico (or another RP2040 based board like the RP2040 Zero) as logic analyzer you need to short the trigger pins, these two are reserved for the fast and complex triggers (more info on Firmware and Software sections).
Once you got these shorted upload the UF2 file to the board and the device is ready to be used.
The Pico pinout is this:
And the Zero pinout:
The PCB's are designed using KiCad 6.0, the projects are in the Electronics folder of the repository and contains everything you need to generate the gerber files to be sent to production.
I don't provide pre-configured gerber files as each manufacturer may have different requirements, so use the projects to create yours. You may find pre-generated gerber files inside the project, those are MY gerber files, the ones that I used to send to my provider to build the PCB's, so I would NOT recommend to use them as like I said each manufacturer may require different settings.
The analyzer board contains very little components: an horizontal pin header which contains the channels, ground, +3v3, +5v and two external trigger pins, two three-pin connectors (male and female) for daisy-chaining the analyzers, a resistor, a diode and the Pico itself.
The external trigger pins allow to trigger another devices like oscilloscopes using the same trigger pattern requested to the device, this only works for the fast and complex trigger as these are the ones that use the GPIO0/1 bridge to trigger the PIO machines (more info in the Firmware).
The pinout of the header is this:
The shifter board is also very easy to assemble, it contains six TXU0104 level shifters, some decoupling capacitors, the pins/headers to connect to the logic analyzer and the channel wires and a jumper to configure the voltage.
The shifters are distributed in both sides of the PCB to reduce the size and the trace length (I tried to keep as short as possible the traces to avoid interferences at higher frequencies, but these are also length-matched to avoid discordances in marginal cases) but they are very easy to assemble, I always solder these by hand using the drag method but it also should be no problem to solder them using an infrared oven.
The pinout of the shifter is exactly the same as the logic analyzer except if you remove the 5v reference jumper, in this case the 5v pin becomes the external reference voltage source.
| Qty | Item Detail | Example supplier code |
|---|---|---|
| 1 | Raspberry Pi Pico (or Pico W) | Raspberry Pi SC0915 (Pico) or SC0918 (Pico W) |
| 2 | 20 way straight pin headers 2.54mm (0.100") pitch | Adam Tech PH1-20-UA |
| 1 | 1N4148 General Purpose Diode, SOD80/Mini-MELF package | Onsemi LL4148 |
| 1 | 100K Resistor, 1%, 1/10W, SMD 0603 package | Vishay Dale CRCW0603100KFKEA |
| 1 | 30 pin dual row right angle header socket (2x15 pin) | Sullins Connector Solutions PPPC152LJBN-RC |
If you want to daisy-chain boards, also add the following:
| Qty | Item Detail | Example supplier code |
|---|---|---|
| 1 | 3 way right angle header socket (1x3) | Sullins Connector Solutions PPPC031LGBN-RC |
| 1 | 3 way right angle header pins (1x3) | Adam Tech PH1RA-03-UA |
| Qty | Item Detail | Example supplier code |
|---|---|---|
| 1 | 30 pin dual row right angle header socket (2x15 pin) | Sullins Connector Solutions PPPC152LJBN-RC |
| 1 | 30 pin dual row right angle header pins (2x15 pin) | Adam Tech PH2RA-30-UA |
| 12 | 0.1uF (100nF) Ceramic Capacitor 16V 10% SMD 0603 package | YAGEO CC0603KRX7R7BB104 |
| 6 | Texas Instruments TXU0104 IC Translator Unidirectional IC 14-TSSOP package | Texas Instruments TXU0104PWR |
Note
20 way headers are not necessary if you buy a Pico H/Pico WH, as the H suffix means they have the headers already soldered on. However, the cost difference may be more than just buying the headers would be and soldering them on yourself. You can also buy the headers in longer break-away lengths that may be cheaper (eg: a single 40 pin length snapped in half, etc). Also you can opt to solder the Pico directly to the board as it is prepared to use the castellated mounting holes.
Note
Device has been tested with a PCB thickness of 1.6mm