This project aims to be a somewhat lower performance but significantly cheaper alternative to Rigol's PLA2216 logic analyzer probe for MSO5000-series oscilloscopes.
The project is based on the design published by Gandalf_Sr on EEVBlog forum, with the most notable difference being that it should allow input signal threshold selection from the oscilloscope.
The project consists of two PCBs:
- connector-pcb which plugs into oscilloscope,
- 2x probe-pcb's which connect to the aforementioned PCB via 24-pin IDC cables.
As the original design, it aims to support ~1-5V logic levels up to 100MHz. The probe PCBs can be built with two different TI level-shifters:
- SN74AXC8T245 with specified input range of 0.65-3.6V (4.2V abs. max).
- SN74LXC8T245 with specified input range of 1.1-5.5V (6.2V abs. max).
Do note that the propagation delay for lower input voltages can limit the observable signal's bandwidth!
Revision 0 of both PCBAs has been assembled and passed basic function checks. The only required change was that series resistor for ProbeDet signal was apparently too high (10K->100R).
Do keep in mind that the threshold level set in scope is not executed faitfhully- it's essentially amplified with a gain of 16.8 and provided as Vcc for SN74AXC8T245. See the datasheet of SN74AXC8T245 and connector-pcb/threshold-vcc-gain-calc.ods spreadsheet for details.
