Upgrading a cloned logic analyzer

In my last post the logic analyzer I built so many years ago was actually useful. I did have some problems though. Due to it not being in a case or protected at all it wound up not having all 8 functioning channels. For this project it wasn’t a big deal, but for the future I want to fix that. While I’m fixing that I might as well make an interesting upgrade: double the channels! The first hack was centered around cloning an existing device to use its software, that is no longer desirable. Pulseview is now plenty good for using on a regular basis and I have no need of any proprietary software. That being said, I still (had to?) write a cloned eeprom to this board to make it identify as what I wanted.

The one I chose is the Braintechnology USB-LPS, this device is auto-detected in Pulseview with 16 channels and therefore can do what I want. I tossed out the shield that I had made so many years ago and decided to use the onboard eeprom spot since I no longer want to be able to switch between USB identifiers.

The chip I used happens to be a 24LC16B, since I’m not trying to get around the Saleae copy protection I don’t have to worry about 16bit addressing. The formatting I determined from this site ended up being C0 (tells the board to use the eeprom’s following VID/PID/DID) D0 16 98 04 84 23 00. I don’t know what DID I should use but it doesn’t seem to matter. Note that the addressing is backward-endian so every other byte is swapped. These bytes need to be placed at address 0x00 and it will detect in windows properly.

I had assumed that the software would just sort itself out because of the USB Vid/Pid setup. That was not the case for me. I got the device show up as unidentified until I installed the Braintechnology USB-LPS driver. That went well but still resulted in it not showing up in Pulseview. I got the error “fx2lafw: Failed to open potential device with VID:PID 16d0:0498: LIBUSB_ERROR_NOT_SUPPORTED”. To fix it I had to run Zadig and force the device to use WinUSB driver. I find myself having to use that program a lot lately, still not really sure what the usb drivers it switches out are for.

The next step is input protection. For the last one I cloned the input stage of the Saleae directly, but I don’t think that is as important this time. Based on the above table I decided to go with 100R inline resistors and 74HC245 buffer chips (I don’t need the bidirectionality, but the layout of the 244 is just annoying). I’m socketing them so I can try out HC, HCT, and other families (or none). This time around I’m not limiting myself to the same footprint as the breakout since I need 16 channels plus a couple grounds. I think I’m going to omit the use of a power header like the USBee, I never used them before and usb ports can’t source that much power anyway.

Since my original design I replaced the cable that had cheap chinese micro grabbers hardwired to bits of ethernet cable with a higher quality one. The new one has 9 pins, 8 for data and one for ground, it is color coded in the resistor color order and terminates in female 0.1″ crimps so I can use brand name Tektronix micro grabbers or plug into board pins directly. The newest replacement uses the color scheme that Pulseview assigns to each of the 16 channels. 0-7 are black through purple and 8-15 are grey through green. This means that each of the standard rainbow colors are used and even reused, but I think it can be obvious the order it goes in. That is except for needing to have ground on different cables; the colors get even more confusing because black is used as a data color twice by Pulseview.

still need to crimp the second 8 conductor cable

One Response to “Upgrading a cloned logic analyzer”

  1. Logic analyzer breakout pcb | Evan's Techie-Blog Says:

    […] an additional logic analyzer, and that means I’m now making a board. I had the design from last time, but it didn’t exactly translate […]

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