Archaeology Resistivity Meter

Hi Michael,

I had these initial thoughts, but I've not had time to think things through (I have some time late Wednesday to do that):

There was mention of more sense probes, but maybe the expansion interface is sufficient for that, since one could drive (say) a latching relay via that. Or maybe space for on-board relay?

A minor point was, for the USB UART, for MCP2221 I already have Android code. But FTDI is totally fine too, i.e. if you've already got the schematic entered for that portion then it's quicker for me to just hunt for demo code for FTDI, if you let me know the chip number. Below is the the schematic I've used previously for the MCP2221 (it needs an external 3.3V regulator which probably the FTDI device doesn't, and has 4kV protection which likely isn't enough, I didn't place any additional ESD protection on this schematic).

One other thought was for a test facility, if there was were four jumpers or four DIP switches on the board which would connect a potential divider across the source (two switches for that) and two switches to connect the sense wires to the divider. Maybe jumpers are easier. But probably there will be test points on the board for easy soldering of a mini test harness during software development anyway.

Yes, you are quite right.

And although I don't like the HAL I know it well - so I use it but mostly as a reference, but sometimes as intended.

There is a lightweight HAL but I don't think you can make the Cube tools generate a project based on it.

MK

Hi Michael and Rob,

Sorry you had a bad experience with this.

My current status is to try the code design as a paper exercise, and then some skeleton using the ST dev environment, but I'll simultaneously get code running on Mbed too if I can, just in case.

The architecture can be nicer with the OS, but I'll use a more traditional implementation with the ST dev environment.

Two bits of reference code could be a benefit, I cannot tell how large and how many features could be desired for later add-on. 

Mbed is C/C++, so direct writing to registers etc isn't an issue. The Mbed benefits are the diverse libraries for adding new features and the task handling (and it works well with interrupt handling) that is available.

I've been involved with bare-metal mil-customer projects too, custom-written RTOS, and Linux+huge middleware+C++ (which suits a very different sized project). I am excited about (say) one day add-ons (such as sending data in real-time via a network, or adding different tasks) then Mbed has got a lot covered, but it's unnecessary for the core functions.

That's a weird error, the output shows that MbedStudio is defaulting to an ARM-supplied compiler. With Linux, I can default to GCC with Mbed.

Bad that MbedStudio didn't work by default though.

I tried to compile the blinky on Linux with Mbed with GCC, and the particular errors in your comment refers to symbols in particular files, but the GCC-made version of the file I checked doesn't contain that symbol at all.

Regarding unwanted code, it is possible to delete some of it (for instance unused peripheral code), but by default Mbed will add it.

This is output for the blinky project on the command line with Linux, it's interesting to see which things took the code space (there is a normal map output too, this is just the summary output on the command line after the build).

The output shows the C library used almost half the total code, and about 13 kbytes was used for the basic peripherals (mbed-os/targets entry), OS consumed 6 kbyte, and the user-typed blinky code took 80 bytes, etc. I think this is reasonable (and no messing about having to struggle with 'lighter' versions with reduced printf formatting etc., but is a shift from only having code in there that is known to execute (but as you say that's rare to accomplish).

| Module           |         .text |       .data |        .bss |
|------------------|---------------|-------------|-------------|
| [fill]           |     102(+102) |       8(+8) |     19(+19) |
| [lib]/c.a        | 27372(+27372) | 2472(+2472) |     89(+89) |
| [lib]/gcc.a      |   3116(+3116) |       0(+0) |       0(+0) |
| [lib]/misc       |     180(+180) |       4(+4) |     28(+28) |
| mbed-os/drivers  |     174(+174) |       0(+0) |       0(+0) |
| mbed-os/hal      |   1672(+1672) |       8(+8) |   130(+130) |
| mbed-os/platform |   4228(+4228) |   260(+260) |   280(+280) |
| mbed-os/rtos     |   6880(+6880) |   168(+168) | 6228(+6228) |
| mbed-os/targets  | 13320(+13320) |       8(+8) | 1078(+1078) |
| test.o           |       80(+80) |       0(+0) |     28(+28) |
| Subtotals        | 57124(+57124) | 2928(+2928) | 7880(+7880) |
Total Static RAM memory (data + bss): 10808(+10808) bytes
Total Flash memory (text + data): 60052(+60052) bytes


Image: ./BUILD/NUCLEO_L4R5ZI/GCC_ARM/testprog.bin

Anyway, I'll concentrate on the high-level code design, this was just out of curiosity to check the ST-targetted Mbed can work on linux.

I built the bare metal one on a windows box and got the same errors as Michael:

It's a brand new MBED Studio install from last weekend, not fiddled with any settings.

Nice to know it's not just me !

I have my Nucleo board so I'll see if it will play with the ST tools.

MK

Unfortunately I don't know how to troubleshoot that, I'm a lot happier with Linux+GCC since I've used that.

It's a fundamental issue though, since it's related to heap settings expected somewhere... but could be a bug in the ARM-developed toolchain or (perhaps more likely) MbedStudio.

I think it's more likely MbedStudio, because I tried the online cloud version of Mbed to compile the blinky program, and that worked. It took 10 minutes, which was 5 minutes longer than usual, because there's only one example for the Nucleo board, and the blinky example was slightly incorrect (for C++) so it needed correcting.

I don't have the Nucleo board just yet (ordered it today), but I had a F746G board (quite powerful too!) and out of curiosity I tried running a filter. It was unfortunately unrealistic (I pretended to sample at 10kHz, which was a typo, I'd wanted 1 kHz) but the results were nice.. with 255 coefficients though!

This was the expected result (simulating 5Hz wanted in red (would be zero Hz wanted of course), and 82 Hz unwanted, with a cut-off at 10 Hz (unrealistic amplitudes too, since the wanted signal could be much smaller than the unwanted):

:

and this was the result with mbed-dsp (guessing is just a wrapper of CMSIS DSP functions, so should be identical to doing it on the ST environment, I just have not investigated that yet). This was with printf to output the values to a serial terminal, and then put them in matlab to plot them) - blue is output, and green was the expected result, I didn't plot them aligned:

I didn't get any timing since this was just a late-night coding experiment, but it's extremely impressive how much processing power these devices have. To think this wasn't possible with low-power microcontrollers maybe just a decade ago.

It will be better to use Matlab tools I guess for designing the filter (I'm not knowledgeable on filter design at all) and for now the filter was calculated using a Python program found online (can write that up). Anyway this is all premature coding experimentation, but does give comfort that ARM DSP capabilities are nice!

There has been an ominous silence since I published the input amplifier design a couple of weeks ago.

(You can find it by searching the armp tag.)

MK

Hi Michael I think it’s back to the problem of us requiring a group. There is certainly a lot of work in there thank you. I will try and set it up in LT Spice.

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