Powering LEDs from the dev kit

Dev Kit Support
1

Hi, this is Riva Gulassa, I’m with the Whalefall project.

We’re trying to turn on a strip of LEDs only for one specific hour every night. The LED strip draws 1.6A of current at 12VDC (~20W), however I’ve been able to get it to still produce adequate light at 8VDC drawing 0.6A (~5W) so Bristlemouth could handle it. I realize this is right on the edge of what it could provide before needing to recharge the next day, I’m hoping with the sunny weather we should be able to just barely sustain the lights or have slow diminishing returns…

Anyway I’ve been attempting to use the Spotter/dev kit like a power supply, essentially just tapping into the 12VDC Vout from the dev kit. I have a voltage regulator to drop it down to 8V, and a mechanical timer to activate the 1hr/day LED window. With this config, the 12V needs to be supplied continuously at Vout even if the timer/LEDs aren’t drawing it.

I could use some help with the following:

  1. First is there a better way to approach this or do you have any suggestions? Has anything been done like this before?
  2. Based on some threads I saw I’m putting these into the command line to enable the Vbus and what I think might be Vout but I’m getting 24V output not 12V for some reason? I thought 12V was the default output?
    gpio clr vbus_bf_en
    gpio clr bf_pl_buck_en
  3. To flash a very simple code to enable this in the field, can I use Bristlefin for example bristlefin.enableVbus() and bristlefin.enableVout() to get the 12V to be supplied continuously from Vout? Are there failsafes or different modes that would prevent continuous power output?

Thanks in advance!
-Riva
[edit to tag @VincentSmith ]
(PS hi @estackpole!)

2

Hi @zachary, is this possible with the current configuration or do we need to move in another direction? Thank you

3

Hi @riva_g_deepdive and @VincentSmith! :waving_hand: :smiley:

The max continuous power Spotter is specified to provide is 3W, and brief spikes up to 10W are OK. The overcurrent cutoff for VOUT is 3A. First, main thing: You definitely need to get your continuous power draw below 3W.

Just in case it’s helpful, I want to mention this option: By default VOUT is 12V, and it can be adjusted to 9V by soldering a 1.15 MΩ resistor parallel to R14 on Bristlefin.

Another helpful tip: Keep an eye on your power logs in the bm folder on Spotter’s SD card. The power monitor at address 67 measures power delivered to VOUT before the buck converters.

You should carefully read the dev kit superuser PDF slides from BristleCon 2023! I think you’ll find them enlightening.

To be able to only enable VOUT when you want to turn on the LEDs, here’s one way I might suggest to accomplish what you’re describing.

Set your bridge configs like this:

bridgePowerControllerEnabled 1
sampleIntervalMs 3600000
sampleDurationMs 3595000
subsampleEnabled 0

(Let us know if you need more guidance on how to do that.)

This will let Spotter control the timing, turning off the whole Bristlemouth bus for 5 seconds right before the clock strikes each hour, and letting the mote boot at the top of each hour.

Side note: If you need to turn on the lights not exactly at the top of an hour, like 2:15-3:15am them you could have the sample interval be 15 minutes, and you’d just get brief lights out time in the middle of your hour of lights on.

Mote code on boot in the setup function should by default keep VOUT disabled with bristlefin.disableVout(). You could call isRTCSet() every second or so (waiting for a message from Spotter), and then only once the RTC is actually set, (meaning the mote received GPS time from Spotter) check whether the time corresponds to when you want the lights to be on. If so, call bristlefin.enableVout(). After that point, as far as I know from your description, it seems mote code doesn’t need to do anything.

I hope that’s helpful. Good luck!

4

Okay got it, thank you so much!! The power distribution system is different than I thought, that document is super helpful with the visuals.

Yeah I just have a small buck converter but it doesn’t regulate current so if we need to stay under 3W (I don’t know where I got 5W from?) I definitely need that resistor. However the LEDs won’t actually turn on at less than 8V and it definitely draws more than .375A so if that’s the spec I’ll need to redesign the system or at least switch LEDs.

What do you think of the idea of using the spotter to instead charge a 12V battery? Maybe I can run the LEDs off the battery and just use the spotter to recharge it when not in use by the LEDs.

Timing through the spotter and treating it like a sampler makes total sense, way better than the mechanical timer. Hopefully we’ll be able to use this… if I can get the power situation under control.

Thanks again!

1 Like
5

Regarding your question about charging a 12V battery, I know @mjbella has lots of experience thinking about how to manage power issues like this. Any recommendations Michael?

6

I may be doing something wrong but wouldn’t i.e. 12V/100Ah battery last for ~8 months without charging considering a duty cycle of 5W for an hour a day?

About charging battery from Spotter, wouldn’t a DC/DC converter with adjustable voltage and current work here?