Time-of-Flight Imaging: Low-cost sensing with ams/OSRAM TMF8828 and Pi Pico

RE: Time-of-Flight Imaging: Low-cost sensing with ams/OSRAM TMF8828 and Pi Pico

shabaz — Mon, 16 Dec 2024 05:14:31 GMT

I was thinking about applications. I think I have a genuine use-case; I wish to make a gesture sensor to remove the need for a cord switch in the bathroom (I'm renovating that, so it's the perfect time). Maybe swipe up to turn on the lights. I'll definitely need a cover glass! And maybe even warm the glass a little bit (e.g. from the internal electronics naturally running warm) to prevent condensation on the surface.

It is possible to buy non-contact switches (some look very basic!), but this would still be an interesting challenge, and if it fails, I can always swap out to a ready-made switch.

The 8x8 array seems great for (relatively speaking) high-res sensing of the environment, but not so great for fast gesture sensing, because of the four separate sub-captures which need to be meshed. Each sub-capture occurs at a slightly different time of course, so you're not getting an 8x8 snapshot at a single precise time, but rather it is blurred in time.

Reading some more, I decided there's no need for such granularity for the simple gestures I'm thinking of. I'd rather reduce the number of pixels ("zones" in ams OSRAM terminology).

According to the user docs, it is possible to switch the TMF8828 into a different mode where it behaves like a TMF8820 or TMF8821 device, to run in 3x3 or 4x4 modes (which are single snapshots, with no meshing). I wasn't sure if that meant uploading different firmware into the microcontroller inside the TMF8828 device, but I found the latest firmware files (Intel Hex format), and spent some time converting them into C arrays that the Pi Pico can automatically push to the TMF8828 RAM on startup each time. And initially failed miserably, I thought I had damaged the TMF8828 by using the TMF8820/21 firmware!

But, it turned out I had made mistakes in the Intel Hex to C array conversion. Once I fixed that, I ran it, and now I'm in a very fast (I believe 30 Hz) mode with a 3x3 array, which I think will be more than sufficient for the gestures I'm thinking of. The web app now shows the grid very smoothly.

Next step: try to implement a simple gesture detection in code! I'm going to aim for it to detect a vertical swipe from up to 50 cm away, just for want of a hopefully achievable goal.

Maybe this could be useful for others too, if they wish to operate some electronics in kitchen/bathroom etc.

All ideas/suggestions/cautions welcome, since I'm just brainstorming currently.

RE: Time-of-Flight Imaging: Low-cost sensing with ams/OSRAM TMF8828 and Pi Pico

DAB — Sun, 15 Dec 2024 20:44:55 GMT

Very interesting post.

Well done.

RE: Time-of-Flight Imaging: Low-cost sensing with ams/OSRAM TMF8828 and Pi Pico

michaelkellett — Thu, 12 Dec 2024 11:25:07 GMT

Great blog. And an interesting part.

RE: Time-of-Flight Imaging: Low-cost sensing with ams/OSRAM TMF8828 and Pi Pico

genebren — Wed, 11 Dec 2024 15:19:16 GMT

Great blog on a highly interesting subject. I have completed a few designs utilizing a PIR detector for motion sensing. I can see where a Time-Of-Flight sensor might be a huge improvement. I will have to consider using this sort of sensor on my next project and requires motion or environment sensing. Thanks for sharing.

RE: Time-of-Flight Imaging: Low-cost sensing with ams/OSRAM TMF8828 and Pi Pico

shabaz — Wed, 11 Dec 2024 15:14:51 GMT

Speeding up the rate ended up being quite simple. I modified the Pi Pico code by adding the following to the main.c file (can't add a hyperlink! https://github.com/shabaz123/TMF8828/blob/main/tmf8828_experiment_board/main.c ) (it is obvious by inspection where to place this, around line 875):

if (strcmp(token, "F") == 0) { // Fast mode
    tmf8828Configure( TMF8828_A, configPeriod[0], configKiloIter[0],(uint8_t) dumpHistogramOn );
    PRINT_STR("#Conf Fast"); PRINT_LN();
    token_progress = TOKEN_PROGRESS_NONE;
    return TOKEN_RESULT_LINE_COMPLETE;
}
if (strcmp(token, "S") == 0) { // Slow mode
    tmf8828Configure( TMF8828_A, configPeriod[2], configKiloIter[2],(uint8_t) dumpHistogramOn );
    PRINT_STR("#Conf Slow"); PRINT_LN();
    token_progress = TOKEN_PROGRESS_NONE;
    return TOKEN_RESULT_LINE_COMPLETE;
}
if (strcmp(token, "M") == 0) { // Medium speed mode
    tmf8828Configure( TMF8828_A, configPeriod[1], configKiloIter[1],(uint8_t) dumpHistogramOn );
    PRINT_STR("#Conf Medium"); PRINT_LN();
    token_progress = TOKEN_PROGRESS_NONE;
    return TOKEN_RESULT_LINE_COMPLETE;
}

Then, in the JavaScript code app.js file ( https://github.com/shabaz123/TMF8828/blob/main/tmf8828_viewer/js/app.js ), I added:

Send('F\n'); // set to the fast configuration

just before the line:

deviceInitialized = true;

near line 244, in the function:

document.getElementById('btnStart').addEventListener('click', function() {

Now it's more responsive.

RE: Time-of-Flight Imaging: Low-cost sensing with ams/OSRAM TMF8828 and Pi Pico

obones — Wed, 11 Dec 2024 09:11:04 GMT

Thanks for this very detailed run through, the device looks quite capable!
What I'm wondering though, is how you get to have a PCB manufactured for 2$, I have looked at various options and for a delivery to France, I'm always at 20/30€ for PCBs.