jerabaul29
commented
2 years ago Great to see you go in such details to check :) . Many thanks for raising this issue here :) .
TLDR: yes, I think you are right, and thanks for pointing this out :) .
cc:ing @gauteh here :) (Gaute should get credits for finding that the chip was available in this way, and helping me find out how to correctly wire it :) ).
A side note: @gauteh had looked in details at the datasheet for the ISM330DHCX itself for knowing which pins to connect or not, see the datasheet available at: https://www.st.com/en/mems-and-sensors/ism330dhcx.html section 3.1:)
Regarding your question: I think (I do not have the chip under the hand to double check; if you and / or @gauteh can confirm it would be perfect :) ) that you are right and that the pins to use are the pins connected to R3 and R5, ie pins P4 and P5, ie the SCx and SDx on the side of VDD and VDDIO rather than on the other side. I agree that it looks like the pins SCx and SDx on the other side of the breakout, i.e. pins P17 and P24, are only "connected" through a non-mounted resistor, ie not connected and not active. This is indeed very confusing (a bit tricky that ST built this STEval with 2 breakout pins marked SCx and 2 breakout pins marked SDx, where 1 is connected and one not for each "category"), and I will have to update the instructions as you say, to make it clear that the pins on the side of VDD and VDDIO should be used, and NOT the pins on the other side, when connecting SCx and SDx.
I was actually not really aware of this, I went a bit fast and was a bit sloppy myself, and I just connected to some "randomly chosen" SCx and SDx on my breakouts... It turns out that, since I am "luckily lazy", I connected the SCx and SDx corresponding to pins P4 and P5 to +3.3V, since these are the 2 close to VDD and VDDIO where I already have 3.3V, so I could cut a shorter jumper ^^ . This is actually (barely) visible on the picture https://github.com/jerabaul29/OpenMetBuoy-v2021a/blob/main/instrument_hardware/jpg/STEval_PCB.jpg . If you zoom there you can see that I did let the SCx and SDx on the SDA/SCL side unconnected, and I connected instead the SCx and SDx on the VDD and VDDIO side. Pure luck, but need some now and then ^^ :) .
As a side note:
- I tested relatively extensively my setup corresponding to the description above, and it seems to work very well
- I had initially not read the datasheet as I should have, and not connected SCx and SDx at all, and things were working fine if I remember well (though as @gauteh had pointed out then, floating inputs that should be clamped was not a good idea)
Having an extra pair of eyes on this would be great :) . So if you can read this being quite critical / not "trusting", and double check and confirm, would be great :) .
Let us confirm, keep the issue open, and I will update the readme :) .
gauteh
CatherineTaelman
A question about the intructions found here: https://github.com/jerabaul29/OpenMetBuoy-v2021a/blob/main/instrument_hardware/ST_eval_instructions.md .
Is it correct that we should be connecting the red qwiic cable (3.3V) to pin 4 for SCX and pin 5 for SDX?
Reason for confusion is the following: From the diagram found online (https://www.st.com/en/evaluation-tools/steval-mki207v1.html), it seems like SCX is connected to two pins (P4 and P24), but the connection to P24 had a resistor that says DNM, which we assume means 'do not mount'. So we concluded that the red cable should go to P4 for SCX. Same holds for SDX (with P5 and P17 as connected pins), where P17 had a DNM resistor, so the red cable for SDX should go to P5.
Might be nice for future users to add the schematic diagram of STEVAL-MKI207V1 as a link on 'ST_eval_instructions.md' page :)