Cheap solar battery + wireless IoT node

[Lgbeno 189]

For grins I made this to test out on my own https://upverter.com/imp-guru/f43d6e493161a233/picoSolar-Boost-Converter/

 

I'll probably put them on Tindie if anyone else is interested, otherwise feel free to grab the gerbers from upverter and order them yourself.  This time I used TPS61097A-33, it doesn't have this down conversion feature but my hope is that a NiCd in a 1xAAA unit won't exceed 3.8V. 

[Fred 453]

@@Lgbeno That TPS61020 looks interesting. The 10SON package isn't great as I like to etch my own boards. The TPS61097A looks nice though. I'll bear them in mind if I'm designing any battery operated boards.

[Lgbeno 189]

@@Lgbeno That TPS61020 looks interesting. The 10SON package isn't great as I like to etch my own boards. The TPS61097A looks nice though. I'll bear them in mind if I'm designing any battery operated boards.

Yeah it seems that lead less packages are here to stay. I'm getting to the point now where I always have a pipeline of boards in the queue at OSHpark so as they come out I solder them up and test.

 

I wish that TI would take this same concept for TPS61029 and make a family that uses fixed voltages and comes in SOT23-5

 

 

Sent from my iPhone using Tapatalk

[cubeberg 540]

@@Lgbeno - yes - 1xAA or 1xAAA.  I honestly couldn't find ones that had two batteries (at least not under $15).  

What do you think BOM cost would be for the board?  It would certainly let me drop to one solar charger per device.  

 

For now - I'm going to rip apart the solar charger and set it up so that the batteries are more secure - the battery holder in these are crap (but what do you expect at $1 each).  

[Lgbeno 189]

@@Lgbeno - yes - 1xAA or 1xAAA.  I honestly couldn't find ones that had two batteries (at least not under $15).  

What do you think BOM cost would be for the board?  It would certainly let me drop to one solar charger per device.  

 

For now - I'm going to rip apart the solar charger and set it up so that the batteries are more secure - the battery holder in these are crap (but what do you expect at $1 each).  

TPS61097A-33 is the lions share of the BOM cost right now, they are about $1.70 ea and then Inductor and cap are another dime.  Cost for the whole deal is around $2 if I build 50.

 

I'd list them on Tindie for $5 but of course I'd sell them to you at cost.  I think if I built in the 1000's then they would be a dollar but I don't think that it will be that big of a success.

 

Tearing these apart is quite the education on how to make something as cheap as possible.  The one that I have is just a single sided phenolic PCB with a single ASIC in a SIP package and some cheapo flimsy injection molding like you mentioned.

[cubeberg 540]

@@Lgbeno - I'd absolutely be in for a few - I could actually create something small enough to fit in the original light which would mean no need for an enclosure - or at least reduced project size.

 

I moved my sensor into a sealed container from the dollar store.  Expecting it to break down over time since it's probably not meant to be in the sun - but it's at least hot glued together for now and more stable (although the next problem will be that melting in the sun later in the year).  

[dubnet 238]

@@cubeberg    @@Lgbeno    I have been following this thread since it is of interest and, as a result, I have bought into a handful of the solar lights.  I am also intrigued with the idea of boosting a single unit to power a data collection node. 

 

I did some back of the envelope calculations to see how much power would be available with a single cell design since I would be interested in the possibility of running through the night (albeit at a much reduced duty cycle).  From the TI data sheet the TPS61097A-33 operates at about 80% efficiency at a 1.2V input and based on a fully charged AAA cell which is rated at 200mah (in my solar lights anyway and assuming it really is 200mah  ). So with those numbers I come up with: 1.2v x 200ma = 0.24W / 3.3V = 72.7mah x 80% = 58.1mah available to the electronics.  This of course assumes a fully charged battery and in my quick testing these don't charge well on overcast days (stating the obvious?).  So I am assuming that maybe half that number, 29mah, might be a more realistic planning number? 

 

With two batteries, efficiency goes up to about 87% with input voltage of 2.4V so you end up with about 131mah fully charged and perhaps an "overcast number" of 65mah. I realize that I haven't factored in the additional current available due to solar during the day.

 

What is cool is that the TPS61097A-33 will handle either a one or two charger approach. 

 

What do you guys think? Have I overlooked anything?

 

Lgbeno, I would also be interested in a few of the TPS61097A-33 boards.

[Lgbeno 189]

Calculations look good to me. The name of the game is to lower the avg power consumption as much as possible. I have not taken precise measurements but managed to get about 5 months out of 500mAh, thats like 140uA average

 

 

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[CorB 64]

@@Lgbeno,

 

How often do you transmit data from your nodes to get such low average consumption ?

[cubeberg 540]

I get a about month on a CR2032 transmitting every 20 seconds (honestly need to increase the interval) + a quick led blink - that's ~240mah - and that's for an energizer - not the crappy ones I buy off of Amazon which are likely .  That's all internal sensors except a light sensor - so it depends on what else you're adding to the device as well.  Charging is outpacing my device - but that's without lost efficiency and it's a two-cell solution.  

I've got other sensors running on 2 alkaline AA's - still have yet to replace those.  

[CorB 64]

@@cubeberg

 

In my nodes I have added code to increase the interval if the battery goes down. Currently my nodes sleep in LPM3 for 10 seconds, check if they need to send data (based on a programmed interval). Then send or directly go to sleep again. But during winter I see the nodes loosing energy when the sun is less strong and the skies are more often overcast. Without the solar-cell I am sure the nodes would not last that long.

[Lgbeno 189]

@@Lgbeno,

 

How often do you transmit data from your nodes to get such low average consumption ?

I transmit every 5 minutes, the payload is about 30 bytes and I don't have a protocol that ensures message delivery.  For me this is ok because it is just temperature and humidity data and it doesn't change very fast.

 

Honestly I was thinking 140uA was rather high, some day I would look into using LPM3 with VLO, that and the sleep current of the radio and sensor should get me into the 10's of uA.  It's all about current consumption when sleeping because thats what the sensor does 99% of the time

[Lgbeno 189]

Just got the boards from OSHpark today, it sort of caught me off guard because I didn't order parts yet!  Any way one massive Digikey order later (for about 4 other projects II'll be in action next week  Going to build 20 and see where that goes, I have a solar light to test it out on as well.

 

TPS61097A-33 = $1.81

Caps                 = $0.13

Inductor            = $0.125

PCB                  = $0.17

----------------------------

Total                    $2.235

 

For 43oh friends $3 each should be good plus $2 to ship as many as you buy in the US $3 for international.

 

Just leave a message on this thread if interested and PM me the shipping address.

[bluehash 1,581]

Just got the boards from OSHpark today, it sort of caught me off guard because I didn't order parts yet!  Any way one massive Digikey order later (for about 4 other projects II'll be in action next week  Going to build 20 and see where that goes, I have a solar light to test it out on as well.

 

TPS61097A-33 = $1.81

Caps                 = $0.13

Inductor            = $0.125

PCB                  = $0.17

----------------------------

Total                    $2.235

 

For 43oh friends $3 each should be good plus $2 to ship as many as you buy in the US $3 for international.

 

Just leave a message on this thread if interested and PM me the shipping address.

I kind of lost track in this thread. Which boards are these?

[vinicius.jlantunes 50]

@@bluehash, I think it's this one (see message 31).

 

 

 

There is this very under appreciated part from TI called TPS61020.  It is normally a boost converter (for stepping up 1.5V to 3.3V) but then if the input voltage exceeds 3.3V, it also has a step down mode where it acts like an LDO, pretty useful in these situations.