Electron: Hardware Discussion

Hardware
42

What types of PCB antenna’s are available for portable applications? How small can these become?

For space constrained applications (such as cellular phones) the manufacturers, make custom integrated antennas within the case, but these solutions require expert designers and $$$$ equipment.

43

Found a really small pcb flexible antenna just for 3G!
12.7mm8.4mm0.24mm

FXP29.07.0070A

http://www.digikey.com/product-detail/en/FXP29.07.0070A/931-1320-ND/4849886

1 Like
44

Update!

We are getting close to locking down the hardware with every passing day! @satishgn just finished routing the latest version of the Electron sans the power supply, giving us the flexibility to test it with multiple options. Current design challenges include using buried/blind vias. While commonly used in the industry, the turnaround time for such prototype PCBs is about 5 times longer, making it a challenge to quickly iterate on designs.

We have also started to receive early sourcing feedback on parts at quantity. As a design engineer you always want the best and most optimal parts at your disposal. It gets a little interesting when you hear back that the leads times for them are at 16 weeks. Getting an early head start is alway a plus.

4 Likes
45

It’s been a month and the time just flew by. Time for an update!

Here’s whats happening in the land of Electrons:

  1. We have tested the functional prototypes of the Electron without the intergrated power regulator. Things are looking good!

  1. We have finalized the power management unit and the secondary regulator. We have also started purchasing parts in volumes for the beta release.
  • PMIC: BQ24195 (4.5A of charge current!)
  • 3V3 Regulator: LM3281 (1.2A peak current)
  1. @satishgn finished routing the complete Electron and the PCBs are enroute. I can’t wait to bake them later this week!
  2. We are cleaning up the design repository and it should be made public shortly.

Happy Monday!

5 Likes
46

@mohit @satishgn So it looks like 36 pins on a 40 pin footprint. Can we get an image of the pinout so we can see how it matches up to the Photon? And what voltage supplies will it be needing?

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One thing… The USB connector seems to be in a different place than the Photon’s. That means that if I design a case with a custom USB opening, a ‘universal’ Photon / Electron PCB will not line up.

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@Awake Good eyes!

  1. First 12 pair of pins (beginning from the USB side) match up with the Core as well as the Photon. The extra pin mapping should be available in the upcoming documentation. Things are constantly evolving though!
  2. The VIN is rated at 3.9 to 17VDC (2.2A and above). You can also use the USB to power it as long as you have a battery connected (to take care of current transients).
  3. Yes, we had to move the USB connector to the side in order to make room for the battery JST connector.
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@mohit - Given the VIN, does this mean that the JST connector is not meant for single cell 3.7V LiPo batteries? Or are the VIN and JST circuits separate? Does the JST connector get repeated on one of the additional pins?

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The VIN/USB are used to charge the battery and power the system. In the absence of it, the Electron will be powered by the battery automatically.

The JST connector is not yet repeated on any pins.

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@mohit Sorry, just read the BQ24195 datasheet, and it looks like you have included a great integrated battery charger in your design! Fantastic and unexpected! So it looks like we will be able to charge the battery via the USB port on the Electron without additional circuitry. Wow! Thank you!

3 Likes
53

@mohit, Is there a way to utilize the onboard battery management system and use a solar panel for charging? For example a 6V (250mA) solar panel with blocking diode tied to Vin? That should charge the battery (slowly) during the day? I believe when the voltage on the solar panel drops below 4V the charge management IC will shutdown charging and 3.3V rail will be maintained by the battery?

Thanks!

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That is possible. The only tricky thing here is that if the system is consuming more than 250mA, the battery would never charge. You’ll need to put the Electron in deep sleep mode for majority of the time to let the battery charge during the day.

1 Like
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@mohit Thanks! The device will be sleeping 99% of the time. BTW is there any measured current draw of the Electron in deep sleep mode yet? I measured the photon to be around 68uA after the 0.4.4 update. I’m hoping the sleep current is similar to the photon.

Is there a trick to getting the entire schematic of the Electron to show up in Eagle? I only see headers, reset and mode buttons, and charge management IC. I mentioned that I would use a 6V (250mA) tied to Vin through a diode. I know the charge management IC is capable of this voltage (up to 17V from the data sheet) but I’m not sure what else is going on at the the VIN pin. It would also be nice to see how the 3V3 rail is handled from the battery JST connector. A complete schematic would be handy :smile:

Thanks.

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This is on my task list for this week. Please ping me if I don't post the results by the end of this week.

What version of eagle are you using to view the files? We also have the PDF version of the schematic available on the repo: https://github.com/spark/electron/tree/master/pdfs/particle-electron_v012

1 Like
57

@awake, Sorry you have already answered the question about Vin max/min.

When you say...

Does this happen when Vin drops below 3.9V?

If I use a 6V (OC) 100mA (SC) solar panel in my design to supply Vin for charging the battery. If the solar panel is delivering 6V to Vin, when the radio attempts to transmit, will the battery help with the transient current?

I have Eagle 7.4.0 with the Standard license. The PDF will work great until I figure out the multiple page schematic thing. Thanks for the help!

58

The Vin minimum is programmable from 3.88 to 5.08, and the default is at 4.36V

That is correct. If possible, I'd still recommend going for a solar cell with higher current output.

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Given the two power sources, is there a recommended way to add hardware power on/off capabilities, or will it always need to rely on firmware and some deep sleep state instead of “off” ?

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For our targeted enclosure a 100mA panel is all we can fit. If we are sleeping most of the time (on for 20 seconds a day) and sleeping anywhere in the uA range, we should have plenty panel unless I'm not thinking it all the way through. The only exception I can think of is if the radio depended on the current supply of the panel alone. I wish I had an Electron! @mohit, thanks for the advice!

61

The least intrusive way is through the firmware. I suppose one can always add an additional ultra low power time driven switch to achieve extreme low power modes. Things will be more clear as I spend time measuring current consumption in deep sleep for the electron.

4 Likes
62

One suggestion (idea from Cores with headers soldered on the wrong side)…might it be possible to offer an upside-down Electron? Having the SIM card on the underside of the board will make changing it very difficult when the Electron is soldered down on a PCB without a socket. But maybe that’s the point…