Unicorpse - so I tried the 3.3V and basically went back to basics, even resoldering one of the resistor dividers and trying the different voltage out pins etc, still with no change.
I take it this means that it didn't work powering from 3.3V ? Ok, but that was worth trying.
Unicorpse However and I hope this isn't me being dumb from the very start... But I tried powering one of the sensors from the analog 5V, and the second sensor separately powered from the P9.07 pin - and it worked! (Still resistor divider on each sensor echo out).
That does not make any sense, I have no idea what is going on here.
Unicorpse Both sensors are a teeny bit delayed it seems but I'm over the moon that they are both working and sending readable data! I
Not sure how any of the above would make any difference in terms of delay, but again, I don't understand what the problem was /is.
Unicorpse What do you think? Is this performing as expected - was I supposed to do this from the very start?? Vice versa are there any reasons why I shouldn't do this?
I am very surprised it didn't work otherwise. If it works... good for you! but I am very confused.
Unicorpse Thank you so much again for all your help with this - there's no way I would have kept pushing on without your suggestions or support and I've learned a lot in the process.
ha, you are welcome. In the process I lost a lot of confidence in determinism and science
Unicorpse But I tried powering one of the sensors from the analog 5V, and the second sensor separately powered from the P9.07 pin - and it worked!
I mean ... maybe there is one explanation, but it will sound very silly. Let's say you that [for whatever reason], you have exactly 29mA spare current available from the 5V supply. Now:
- if you connect the two sensors to P9.07, they will draw 30mA total (15mA each) and therefore will not work.
- If you connect only one sensor at the 5V from the analog out header, this will actually be underpowered at 3.5V, and draw less current, 10.5mA, but nevertheless work.
- If you connect both sensors there, then the voltage will be so low that they will both stop working (even though they do not exceed the available current).
- if you plug one on P9.07 and one on the analog out, they will absorb 15mA and 10.5mA respectively, so everything will work fine
However:
- I would expect you to have far more than 29mA available on the 5V rail (there should be at least 200mA, I estimate)
- if you were actually overloading the 5V rail, I would expect the power management IC to just shut down everything.
- this does not explain why connecting only one sensor to P9.07 does not work.
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