Boron with a Solar Panel

Firmware
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Wonder if I could get some advice on setting my Boron up with a solar panel.
My Boron is running 2.2.0. I see that the Adafruit Medium 6V 2W Solar panel - 2.0 Watt seems to be a good choice.

From what I read I could connect directly to VUSB input on the Boron. Is that true?
What would the pmic setting for this panel should I use?

Anything else I should be aware of? It will be in some pretty hot temps during the summer (New Mexico)

Thanks for your help.

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@Athnetix ,

I run my Boron devices using solar and you are on the right path.

  1. You can use a 2W panel but know that you will need to be focused on low power operations. I have made these work for devices that only need to connect a few times a day. For my larger deployments, I use the 6V 3.5W panel which supports hourly connections for 16 hours a day. Your milage will vary based on signal strength, you peripherals and your firmware.

  2. You can connect the panel directly to the Boron (6V panels only as they will reach 9V when not under load). Ideally, you should also put a bypass cap across the power lines to smooth out variations in solar intensity with clouds / leaves and all. I use a 470uF aluminum cap for this which is built onto my carrier board.

  3. There is a range of temperatures for safe charging of a LiPO battery. For this reason, I added a simple temp sensor on my carrier board and will regularly check to make sure the temperature inside the enclosure is in the safe charging range (>36F and <100F) the exact numbers can change based on how often you check the temperature, these values have worked well for me in NC.

  4. Just a suggestion, you will want to protect your Boron against reversed polarity. I chose to do this with polarized JST PH connector so the solar panel cannot be plugged in wrong. Otherwise, you may need a Schottky diode but you will loose some energy to your device. I also added a fuse and varistor as the cable to the panel can be long to protect against shorts.

Hope this helps,

Chip

3 Likes
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Thanks Chip Great Info.
Another question I have is I have read and understand that the Boron has a RTC (real time counter) rather than a real time clock. It seems during testing I’m doing as long as you sleep for short periods of time like 15 or 30 minutes the real time counter works just fine. Have you seen that and would you trust it for short periods of time?

Thanks again

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@Athnetix ,

I am not sure about the naming but, you are right in pointing out that the Boron does not have a Real Time Clock as the Electron did.

However, In my experience, you can use the Boron RTC to reliably wake from sleep for longer periods - my max sleep time is an hour - without issues as long as you don’t go into HIBERNATE sleep. There is not a big difference between HIBERNATE and ULTRA sleep in terms of power savings so, I don’t see this as a major limitation. For your use case of 15-30 minutes sleep, it should be fine.

I have also added a Real Time Clock and Watchdog to my carrier board primarily for two reasons.

  1. To allow me to power cycle my Boron, the cellular modem and peripherals as part of a recovery process.
  2. To support an external hardware watchdog timer.

I used this guide for the hardware and software design:

Hope this helps.

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Thanks

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