Greendome Tech

A cheap, DIY alternative to the PLA2216 logic probe

27/04/2024

Bram

I recently upgraded from my trusty Rigol DS1054Z to a Rigol DHO924 as I was in the market for a higher bandwidth 12-bit oscilloscope with logic analyzer capability. Whilst purchasing the oscilloscope, I noticed that the price of the logic analyzer it pairs with is above 300 euros, WAY too much for a function I was not going to use too often. I decided to scour the internet and find a DIY alternative.

That’s when I stumbled upon an EEVBlog forum and particularly this version of the DIY probe. When I inspected more closely, I noticed a few things that I could improve upon such as length and impedance matching, as well as routing the differential pairs more efficiently.

The schematic from Nikki Smith is completely fine, and thus copied for my PCB design.

The drivers for the signal are SN65LVDS391D which is a Quad LVDS Line Driver, they can tolerate input voltages up to 5 V, which is fine for my logic applications as they are mostly 3.3 V. This part specifically, is designed to drive 100 Ω differential pairs, which is what I based my impedance match on using the built-in calculator in KiCAD and the dielectric values from JLCPCBs FR4. The traces have been length matched up to 0.5 mm on the input side and 0.5 mm on the output side.

They are powered by the TLV743P33, which is a 3.3 V Low Dropout Linear Regulator.

The LED within the schematic is left unassembled for my purposes, but is included in the PCB design.

The designed PCB is a 2-layer PCB:

On Nikki’s website, I saw that the 50 pins connector had to be flipped for easy installation in the oscilloscope, this turned out not to be true after production. In the next revision, this will be corrected. Next to that, ground vias will be placed near differential pair vias to increase integrity. Overall, I am quite pleased with the PCB and its operation as it does work flawlessly. It has been tested up to 160 MHz and performed okay.

Over here, it can be seen in action with an 8-bit counter counting at 4 MHz, which leaves the LSB at 2 MHz.

Since there are still some things that need improving, it will be updated some time in the future, for now, the files can be downloaded below.

EDIT 15-09-2025: It seems someone made a case for it! https://www.thingiverse.com/thing:7015417/apps

Files Download

4 responses to “A cheap, DIY alternative to the PLA2216 logic probe”

basic

12/08/2025

Greetings,

Nice project, but in circuit board bottom side has more pads than top side?

Reply
1. Bram
  
  15/09/2025
  
  First of all sorry for the late reply. I’m unsure what you mean with the pads, but I assume you mean that the bottom side has more solderable pads than the top.
  
  This is due to the fact that SMD components are used, which means the components lay flat on the PCB and do not protrude it. Which in turn means that it only has to touch one side of the PCB, allowing for more efficient use of area.
  
  Reply
Ivan Ignath

29/08/2025

Are you able to complete the calibration process with this design? I just assembled Nikki’s version, but it’s stuck with the message “Please disconnect channel.” Otherwise, it works fine without calibration in the MHz range (DHO924S). If your version supports calibration, I would try it, as I have a lot of “spare” parts.

Reply
1. Bram
  
  15/09/2025
  
  I think that when I made this tool, the probe calibration was not yet implemented in firmware.
  
  I just tried to do it but the whole LA menu becomes unresponsive whenever I try to do so. I disabled all channels and they remain visible (also switching the size does not work, even turning off the scope does not). I think this is a bug within the firmware, however I can’t say for certain that it is not caused by this probe.
  
  I will reply to you if I know more.
  
  Reply

A cheap, DIY alternative to the PLA2216 logic probe

4 responses to “A cheap, DIY alternative to the PLA2216 logic probe”

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