Hello All:
I don't have any BT or BLE experience with the 181A but I was very disappointed to find that I had no easy way of getting useful data off the meter, that had been saved in the data logging mode. This was really frustrating, because the supplied utility is .XLS aware, but only provides that if the data is collected in real time.
Soooo, this led me down a reverse engineering path that turned into a real time vampire. The upside is that I have a moderate understanding of how the meter communicates.
I used the supplied utility and Wireshark with the USB plug-in to watch the data stream. It's cumbersome and I ended up exporting it as text and wrote a post processor to remove the USB overhead and extract the actual data. I think the Microsoft Message Analyzer would be better but I couldn't get it to work reliably on USB, so rather than fight to find out why, Wireshark it is.
The data packet is fairly complete, letting you know just about everything going on in the meter, but unfortunately, it is highly variable depending on the mode and function selected.
The "05" mentioned above is a command ID, in this case, read real-time data (What you see on the meter) The byte following that is the read mode:
Assuming the meter has just booted, it is in normal mode and if you send 0x05 0x00 it will return a single reading. If you send a 0x05 0x01, it will then send readings continuously at ~ 10/sec. If you send a 0x05 0x00 while in automatic mode, it will return to normal mode.
There is no other sample rate available.
One interesting thing I noticed is that if you continuously request data in the normal mode, the main data updates as it does on the display, and the secondary data for the bargraph changes rapidly. However, the main data does a proper update when in automatic.
As previously noted, the bar graph data has lower resolution but is MUCH faster, and if you look at the chipset datasheet, there are actually 2 separate A/D's.
By that, I mean that the conversion, and sample and hold appear to accurately support the higher data rate, it's not fudged or interpolated.
The USB communication is an HID class but does not enumerate to anything specific, so you need to interpret the data in raw mode. The chip is a CP2110 by Silicon Labs. Thankfully, their documentation is excellent and they provide 2 DLL's for communication and doing stuff like identifying the device and setting up baud rate. The same libraries are used by the Uni-T Utility, but are more recent on the SL website.
Hope this helps.
Bob