Building the VBA Curve Tracer, a sizeable project

SEEKING A CURVE TRACER FOR SEMICONDUCTORS

Recently I put together a curve tracer for vacuum tubes based on a design from xxxx yet almost no projects I work on use tubes any more. I am a big believer in the ability of a curve tracer to flag issues with components that simpler testers fail to find. However, the good instruments, even bought used and restored, are very expensive, typically in the thousands to tens of thousands of dollars. 

Much as with the tube tracer I built, I wondered if someone had designed and shared a suitably good tracer that I could build myself, saving money while enjoying the act of construction as a side benefit. I located a design, the VBA Curve Tracer Designer's blog about the device, which seemed to be sophisticated and accurate enough to handle all the devices I expected to work with. This includes junction and MOS transistors, plus diodes of all types. 

THE COSTS KEPT CLIMBING AS I BOUGHT THE COMPONENTS

I sent the four PCBs out to be fabricated at JLCPCB, then began ordering parts from the bill of materials (BOM) files for each of the four boards and the outer assembly. The costs grew as there are quite a few components involved in this very sophisticated design. Ultimately the costs for PCBs plus parts is around $900 including shipping, thus the savings over buying something like a Tektronix 576 were still present but not as big as I had hoped. 

Finding some of the parts was a challenge as they were out of stock everywhere and in some cases discontinued by their manufacturer. I had to carefully examine the specifications and other aspects of a part to determine whether I could substitute something else without impacting the working tracer. 

In two cases, I had to accept a different form or size for a part after checking whether I could make it fit onto the existing PCBs. One was simply a surface mount part that was a bit larger than the footprint on the board, but I could add a bodge wire to connect it properly. The design uses a -15V voltage regulator part in a surface mount shape that is absolutely unavailable across dozens of supply sources. There is room however for me to make use of a thru hole version of the part, build a small mount for it and then tack its leads onto the pads on the PCB. 

CURRENT STATUS

I have ordered every single part needed to build this per the BOMs. The PCBs are back from the fab and look great. My order from Mouser arrived as did one of the six orders from Digikey, with the rest of the Digikey shipments in the pipeline. One pair of parts had to be ordered from Aliexpress and is in transit now from China. I anticipate having everything in hand to start building within a week. 

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