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Cameras: External Trigger on GS: Please check voltage #3237

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njhollinghurst opened this issue Oct 25, 2023 · 8 comments · Fixed by #3273
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Cameras: External Trigger on GS: Please check voltage #3237

njhollinghurst opened this issue Oct 25, 2023 · 8 comments · Fixed by #3273
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@aallan
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bug camera 📷 linked pull request Has a linked Pull Request that will close the issue. urgent

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@njhollinghurst
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Another one like #3146

https://www.raspberrypi.com/documentation/accessories/camera.html#external-trigger-on-the-gs-camera

According to the IMX296 datasheet, XTRIG should be limited to OVDD+0.3V where OVDD=1.8V; but the documentation suggests it's safe to apply 3.3V to XTRIG.

The GPIO->XTRIG connection on the camera board uses a level shifter, but if R11 is removed as instructed then there will be neither level shifter nor pull-up, so it is hard to see how this can safely be driven from a Pico.

Asked on forum here https://forums.raspberrypi.com/viewtopic.php?t=358276#p2148485
@aallan aallan self-assigned this Oct 26, 2023
@njhollinghurst
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njhollinghurst commented Oct 26, 2023 •
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It's definitely dodgy, the question is what is the most elegant circuit to recommend in the doc. Need to decide whether to recommend a level shifter or if another resistor divider will suffice (maybe with smaller resistances, e.g. 680R or 1K, as it's now the Pico that's providing the current).

By the way, Pico can't conveniently do PWM + Open Drain (except using PIO), so an OD/Pull-up style is no good here.

@naushir @6by9 might have comments.

[Edit: Not sure why the doc calls for a Pico here rather than a Pi. Just for variety I suppose.]

@aallan
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aallan commented Oct 26, 2023

[Edit: Not sure why the doc calls for a Pico here rather than a Pi. Just for variety I suppose.]

That's what Simon's summer intern used I think?

@simon-martin-rpi
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Speaking to Nick. We keep the docs the same, i.e. remove R11. This guy needs to add a resistor divider to his output to reduce 3.3V to 1.8V. I suggest 18K to GND and 15K input resistor. Since the whole task needs soldering, I guess they will be Ok with it. I hope to respin this board and put a proper connector on it which accepts any voltage at high impedance one day. We have a lot of units with the wrong circuit to sell first though.

@aallan aallan removed the waiting for comment Awaiting a response label Nov 1, 2023
@njhollinghurst
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njhollinghurst commented Nov 1, 2023 •
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Got it. So we advise removing R11 in all cases (not just if Q2 fitted), then can use a divider (need to change picture).
Will we need to revise the documentation for the new new board version?

@njhollinghurst
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njhollinghurst commented Nov 1, 2023 •
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Nitpick: The current text is also wrong where it says "This connects GP0 to XTR", since this is GPIO1.

Perhaps the entire paragraph should be something like: "You will need to remove R11, shown in red below, to enable external trigger input."

Somewhere or other we should state clearly that it's a 1.8V signal.

@njhollinghurst
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I'll attempt a PR for this.

Still wondering about resistor values in #3146 -- it would be paradoxical for us to recommend much larger resistances for a driven signal than for an idle pull-up -- so I might revisit that as well. Will do some testing first!

@aallan
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aallan commented Nov 10, 2023

I'll attempt a PR for this.

Thanks @njhollinghurst!

@njhollinghurst
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njhollinghurst commented Nov 13, 2023 •
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This guy needs to add a resistor divider to his output to reduce 3.3V to 1.8V. I suggest 18K to GND and 15K input resistor.

@simon-martin-rpi Those resistor values seem high compared to the (entirely unrelated) pull-up we suggest here. Can I reduce them to (say) 1.8K and 1.5K? That would draw 1mA from the RP2040.

njhollinghurst added a commit to njhollinghurst/documentation that referenced this issue Nov 13, 2023
@njhollinghurst
GS Camera external trigger: fix for raspberrypi#3237
c030a66 
Clarify that R11 must always be removed in the current board version
(regardless of whether Q2 is fitted). Specify a potential divider of
10K:12K to reduce the high logic level from 3.3V to 1.8V.

Elsewhere, increase the suggested resistor values for the 1.65V
divider used to pull up XVS (to avoid the paradoxical situation
where we suggest higher impedence for a driver than for a pull-up).

Figures were hand-edited and may need to be regenerated by Fritzing.
@aallan aallan linked a pull request Nov 13, 2023 that will close this issue
GS Camera external trigger: fix for #3237 #3273
Merged
@aallan aallan added the linked pull request Has a linked Pull Request that will close the issue. label Nov 13, 2023
njhollinghurst added a commit to njhollinghurst/documentation that referenced this issue Nov 14, 2023
@njhollinghurst
GS Camera external trigger: fix for raspberrypi#3237
f34f633 
Clarify that R11 must always be removed in the current board version
(regardless of whether Q2 is fitted). Specify a potential divider of
10K:12K to reduce the high logic level from 3.3V to 1.8V.

Elsewhere, increase the suggested resistor values for the 1.65V
divider used to pull up XVS (to avoid the paradoxical situation
where we suggest higher impedence for a driver than for a pull-up).

Figures were hand-edited and may need to be regenerated by Fritzing.
njhollinghurst added a commit to njhollinghurst/documentation that referenced this issue Nov 14, 2023
@njhollinghurst
GS Camera external trigger: fix for raspberrypi#3237
eeeefff 
Clarify that R11 must always be removed in the current board version
(regardless of whether Q2 is fitted). Specify a potential divider of
1.5K:1.8K to reduce the high logic level from 3.3V to 1.8V.

Elsewhere, increase the suggested resistor values for the 1.65V
divider used to pull up XVS (to avoid the paradoxical situation
where we suggest higher impedence for a driver than for a pull-up).

Figures were hand-edited and may need to be regenerated by Fritzing.
njhollinghurst added a commit to njhollinghurst/documentation that referenced this issue Nov 16, 2023
@njhollinghurst
GS Camera external trigger: fix for raspberrypi#3237
b61da48 
Clarify that XTR is a 1.8V signal, and show a potential divier
with 1.5K and 1.8K resistors to generate it. Minor correction
that XTRIG would have been driven by GP1 (not GP0).

(Retain the instruction to remove R11 only if Q2 was fitted.)

Elsewhere, increase the suggested resistor values for the 1.65V
divider used to pull up XVS (2.2K was unnecessarily small).

Figures were hand-edited and may need to be regenerated by Fritzing.
aallan pushed a commit that referenced this issue Nov 16, 2023
Merge pull request #3273 from njhollinghurst/xvs-voltage
7bd9700 
GS Camera external trigger: fix for #3237
@njhollinghurst njhollinghurst mentioned this issue Dec 7, 2023
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GS Camera external trigger: fix for #3237 njhollinghurst/documentation
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