PCA20014 solar beacon fimware and HW questions

RE: PCA20014 solar beacon fimware and HW questions

Bjørn Kvaale — Tue, 17 Oct 2017 13:05:52 GMT

I would start with the battery free solution first, if I were you. A little less complex to start with. Should be able to charge up a coin cell battery (not a CR coin cell battery, as this is a disposable battery, see here). Not sure how difficult it is to charge a coin cell battery, but it would be a cool project! Good luck with your project!

RE: PCA20014 solar beacon fimware and HW questions

MANGO — Tue, 17 Oct 2017 12:38:50 GMT

What are you planning to do if there is no sunlight, i.e. no input voltage from solar cell? Do you want to hook up a battery or will no sound play?

My purpose was to create a battery-free product; I planned for the system to be shut down when there is no light; no beacon and no sound.

I learned a lot from you! Hooking up a battery sounds cool (if you meant that battery like CR2032 is used if there is no sunlight).

I will consider that scenario!

-Best Regards

RE: PCA20014 solar beacon fimware and HW questions

Bjørn Kvaale — Tue, 17 Oct 2017 08:59:05 GMT

I will sum up the comments as one answer:

Is there a reason for drawing the solar cell as an LED?

Yes, this is quite common, as the LED refers to a photodiode (see this article). A solar cell is just a large area photodiode.

Is there a reverse polarity issue while using the solar cell?

There can be a reverse polarity issue if multiple solar cells are connected in series (see this forum & this link). Since the solar cell you refer to is most likely a single solar cell, I believe this will not be an issue for you. But just to be certain, check with your supplier or the manufacturer directly.

Do these MOSFET works as a voltage regulator?

I believe not because the nrf52832 has an integrated DC-DC converter (see here under Section "Flexible Power Management").

I don't see any DC-DC converter or voltage regulators in the schematic. Does this mean that the voltage provided to the nRF MCU and the pressure fluctuates if the light level changes?

No, see above answer.

Since I will be adding an I2S amp, using a bigger solar cell and adding a buck converter will be better for me instead of using the above MOSFETs, right?

You might want to use a bigger solar cell. That is up to you. Just make sure the solar cell is within the supply voltage of the nrf52832 (i.e. 1.7-3.6 V). If you are using multiple solar cells in series, you might want to checkup on any possible reverse polarity issues. I am unsure whether you will need a Buck converter for the I2S amp. This is probably a good idea since the input supply will fluctuate due to changing light intensity (the I2S amp you refer to can handle 2.5-5.5 V input supply voltage).

As for these questions: Can you check other things such as

is PCA20014 using one or multi-solar cell(s)
need for DC-DC converter for nRF MCU and I2S amp
PCA20014 firmware code

I believe the PCA20014 is a single solar cell, but check with your supplier or manufacturer to be certain. There is no need for a DC-DC converter for the nrf52832 (see answer above), but this might be useful for the I2S amp. Talk to Adafruit tech support to confirm this for the I2S amp. The PCA20014 solar beacon firmware code can be found here.

Does this mean that this firmware doesn't use the Nordic's SoftDevice and turns on and off the 32MHz, the high-frequency clock, for power saving in the application?

I am quite certain that this firmware does not use the SoftDevice. In the Infocenter, I saw these statements at the bottom: "The beacon saves power by putting the CPU to sleep between every step in the firmware sequence shown above. It also saves power by switching off the crystal oscillator and the power to the sensor chip and the TWI."

I hope I answered all of your questions. :)

RE: PCA20014 solar beacon fimware and HW questions

Bjørn Kvaale — Tue, 17 Oct 2017 08:50:06 GMT

As for your question regarding not seeing any DC-DC converters in the schematic, the nrf52832 chip has an integrated DC-DC converter (see here, under section "Flexible Power Management".) So therefore I do not think that the Mosfets work as voltage regulators. Due to the integrated DC-DC converter in the nrf52832, the voltage level will not fluctuate if light intensity fluctuates (make sure the input voltage is within supply voltage of nrf52832, see here)

RE: PCA20014 solar beacon fimware and HW questions

Bjørn Kvaale — Tue, 17 Oct 2017 08:44:16 GMT

I am pretty sure the Amorton AM-1417CA is one solar cell, so reverse polarity might not be such a big issue. In the description, it says solar cell and not solar cells. But you could send digikey, another supplier or the manufacturer a quick message to be certain. The PCA20014 firmware code can be found here. Since the nrf52832 has an integrated DC-DC converter, you will not need any power management for the PCA20014. As for the I2S amp, you might need a DC-DC converter (the I2s amp you refer to can handle 2.5-5.5 V input supply, see here). Consider sending Adafruit tech support a quick message to confirm. What are you planning to do if there is no sunlight, i.e. no input voltage from solar cell? Do you want to hook up a battery or will no sound play?

RE: PCA20014 solar beacon fimware and HW questions

MANGO — Mon, 16 Oct 2017 08:58:39 GMT

Hi, Bjørn Kvaale. That's really interesting! I have learned a lot from the devteam.

Can you check other things such as

is PCA20014 using one or multi-solar cell(s)
need for DC-DC converter for nRF MCU and I2S amp
PCA20014 firmware code

If this is a multi-cell solar cell, I think I should consider the reverse polarity.

-Best Regards

RE: PCA20014 solar beacon fimware and HW questions

Bjørn Kvaale — Fri, 13 Oct 2017 09:10:41 GMT

Figured out why the solar cell is drawn as a diode. Have a look at this wikipedia article on photodiodes. A solar cell is just a large area photodiode!

RE: PCA20014 solar beacon fimware and HW questions

Bjørn Kvaale — Fri, 13 Oct 2017 07:37:07 GMT

Hi Mango,

Still slightly uncertain why the solar cell is being drawn as a diode. I will get back to you on that. From what I've seen, solar cells tend to be drawn like a battery, but with an arrow pointing towards them to signify that it is a solar cell & is dependent on sunlight, unlike a normal battery.

As for the reverse polarity issue, it seems this can become an issue, especially when multiple solar cells are connected in series (see this forum & this link). Since you are only using one solar cell (am I correct?), I am still a bit uncertain whether you will require a bypass diode.