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Solar Driveway Light to MSP430 Wireless Sensor Node


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Just remembered something else--what part did you use for the Inductor?  Rereading your first post I think you used the one that came with the lamp.  The schematic states that it's 10uH, but can it handle the peak current required by the boost regulator (~200mA per the TPS61097-33 datasheet, page 14)?

 

FWIW, if you need to try something different I could mail you a couple 4.7uH's that's rated 650mA I think.  I've used it in my boost regulator projects (TPS61221 ~150mA output, needs up to 400mA switching current at the outlying max).  They are surface-mount (I think 1210-size).

 

Thanks for the response @@spirilis! I stuck a 22uF 25v capacitor on C4 and that didn't fix it.  

 

The inductor I am using is 10uh and I am not sure what it is rated to since it is the salvaged part from the light. It is a basic axial through hole and looking online those seems to range between 180 and 265ish mA.  I can see how this might be causing the issue.  

 

I just started getting into soldering surface-mounted components but I would like to start using those more.  My current PCB design uses through hole axial inductors so I might try to stick with those on these boards.  I appreciate the offer.  If you have a free oscilloscope laying around I would love one of those! ;-)   I can send you a board to troubleshoot if you want.  

 

I happen to work next to the Wireless Research Center of North Carolina...they have a great PhD electrical engineer with a background in wireless technology.  He gave me a tour of their wireless testing chambers at their lab...pretty darn cool.  I told him I would  harass him if I ran into problems.

 

Do you think it is smart to go to 10uH or should I go with 4.7uH.  The reason I used the 10uH is because the datasheet says it increases stability.  The battery I am using is a Ni-CD AA 1.2v 1000mAh.     

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Greetings!  I am new to the forum and this is my first solo microcontroller project.  Please be kind to me as I am a Geographer and by no means a programmer or electrical engineer.  Stupid questions s

Nice project & code!  One word of caution with the nRF24 handler code (your main while(1) loop)--   w_tx_payload(32, buf); msprf24_activate_tx(); LPM4; // Put the RF transceiver back

Baby boy was born and I have been sick for a week and a half so that has slowed my progress.  I did play with the bypass switch on the DC booster and came to the conclusion that I need to reduce the t

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I think 10uH is fine.  Also on another thought--the input stage of the DC-DC converter, you have a 10uF cap there, what type is it?  i.e. aluminum electrolytic (can) or ceramic?  Might be useful to have a ceramic-type (usually has low ESR) of as large a value as you can find on there to help source the switching current better... Mostly I'm just looking for any quick fixes you may have at your disposal to bolster it :)

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I think 10uH is fine. Also on another thought--the input stage of the DC-DC converter, you have a 10uF cap there, what type is it? i.e. aluminum electrolytic (can) or ceramic? Might be useful to have a ceramic-type (usually has low ESR) of as large a value as you can find on there to help source the switching current better... Mostly I'm just looking for any quick fixes you may have at your disposal to bolster it :smile:

The capacitors are ceramic 10uF 16v. I replaced them with 22uF 25v aluminum electrolytic to see if that would help and it didn't. Then I tried adding a 16uH inductor...no luck. I did hook up a 3.3v power supply to the battery terminals and it does work when you apply 3.3v. I tried using two 1.2v AAA's did not work. Grrrr. It seems like it wants more voltage.

 

Ready for this one? So I decide to set rf_speed_power = RF24_SPEED_MIN | RF24_POWER_MIN to see if it was a power issue because I think this code means slower transmission speeds and less power consumption but more range as I understand it. I am programming the TX chip while it is on my custom PCB using my launchpad, the RST and Test pinouts as shown on my schematic, and the VCC and VSS from the launchpad to the battery terminals. I compile in debug mode, press play, and the packets are successfully transmitted as expected. When I remove the power from the TX and add the battery it doesn't work. So I plug it back in re-flash the chip in debug mode again, plug the battery in while VSS and VCC are still plugged in (this causes the TX to stop working), then I pull the VSS and VCC connections from the battery terminal (with the battery still in) and it works. However, it will only let me go about 30 feet before it stops TX. As I get closer it picks back up. So, in conclusion, there is still a strange power issue. Can anyone explain this behavior?  Does that even make any sense?  

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Thanks again @@spirilis.  Sounds reasonable.  I am thinking of ordering these inductors:

 

http://www.mouser.com/ProductDetail/Bourns/78F4R7J-RC/?qs=sGAEpiMZZMsg%252by3WlYCkU1wbcydNIDvKD70RmuEuJkg%3d

 

http://www.mouser.com/ProductDetail/Fastron/SMCC-N-100J-01/?qs=sGAEpiMZZMsg%252by3WlYCkU8BLlVcluYKE51pm1lHTf0E%3d

 

These have higher current ratings and a resonable price.  What do you think? 

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  • 4 weeks later...

I like 'em, especially the 2nd one.  Might just grab a few of both at that price (and with Mouser's $5 economy shipping... probably worth padding it with more junk lol!)

I can't believe it has almost been a month since the last post...sorry!  I have the fortune of visiting former soviet republics a couple times of year for work so I have been out of town.

 

So I did install the new 10uH inductor with the two 10uF ceramic capacitors and it didn't work. Switched the Vin and Vout capacitors for cheap 22uF 16v electrolytic and it works sporadically.  I removed the 22uF from the Vout and replaced it with a 68uF 16v cheap electrolytic capacitors and I am getting better performance. I currently have the transmitter in the garden and the receiver in a window about 30 feet away. This seems to be the outer range limit with the current capcitors.   I think the new inductor helped but I also think I need to seriously upgrade the capacitance on the power circuit. TI recommends ceramic so maybe some larger low ESR ceramic capacitors (100uF) will help. More testing to come.  

 

 Is this issue something that I could troubleshoot with an oscilloscope? If so, how would the oscilloscope help? I am thinking of buying an oscilloscope.

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I can't believe it has almost been a month since the last post...sorry!  I have the fortune of visiting former soviet republics a couple times of year for work so I have been out of town.

 

So I did install the new 10uH inductor with the two 10uF ceramic capacitors and it didn't work. Switched the Vin and Vout capacitors for cheap 22uF 16v electrolytic and it works sporadically.  I removed the 22uF from the Vout and replaced it with a 68uF 16v cheap electrolytic capacitors and I am getting better performance. I currently have the transmitter in the garden and the receiver in a window about 30 feet away. This seems to be the outer range limit with the current capcitors.   I think the new inductor helped but I also think I need to seriously upgrade the capacitance on the power circuit. TI recommends ceramic so maybe some larger low ESR ceramic capacitors (100uF) will help. More testing to come.  

 

 Is this issue something that I could troubleshoot with an oscilloscope? If so, how would the oscilloscope help? I am thinking of buying an oscilloscope.

Hmmm!  Very interesting.  An oscilloscope would probably give some hints.  What is the boost converter using as its source again?  A rechargeable battery of some type inside the device?

I wonder what might happen if you put the 68uF electrolytic AND a 22uF ceramic on the Vin side of the boost converter.

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Hmmm!  Very interesting.  An oscilloscope would probably give some hints.  What is the boost converter using as its source again?  A rechargeable battery of some type inside the device?

I wonder what might happen if you put the 68uF electrolytic AND a 22uF ceramic on the Vin side of the boost converter.

Source is one AA rechargeable Ni-CD 800mAH.   Okay so you are thinking if I put the larger capacitance on the Vin side it will stabilize the input and thus provide a stable output?

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Source is one AA rechargeable Ni-CD 800mAH.   Okay so you are thinking if I put the larger capacitance on the Vin side it will stabilize the input and thus provide a stable output?

That's what I'm hoping.  Along the same line as the inductor, the idea is if you can't get switching current high enough you won't boost... that could be due to an inductor with too high of impedance (too low of saturating current) or a power source of too high of impedance too.  Input capacitance should bolster that I think.

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That's what I'm hoping.  Along the same line as the inductor, the idea is if you can't get switching current high enough you won't boost... that could be due to an inductor with too high of impedance (too low of saturating current) or a power source of too high of impedance too.  Input capacitance should bolster that I think.

Yep...I added a 100uF 10v capacitor to the Vin and was able to get another 25 feet of range with the receiver in the window facing the garden. I also tested in the house and got about 40 to 50-feet through 3 walls.  Is this range consistent with what you are getting on these wireless modules with the trace antenna?

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Yep...I added a 100uF 10v capacitor to the Vin and was able to get another 25 feet of range with the receiver in the window facing the garden. I also tested in the house and got about 40 to 50-feet through 3 walls.  Is this range consistent with what you are getting on these wireless modules with the trace antenna?

Yup!  That sounds about right.

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  • 3 weeks later...

Project update:

 

I have been casually testing the setup for the past couple weeks with mixed results. Most of the testing includes a screaming infant on my shoulder. You can imagine why this project is moving so slowly. The main issues with the current setup seems to be the range. It will transmits okay the first times but the signal seems to get weaker with subsequent transmissions.

 

I have purchased a NRF24L01+PA+LNA module to put on the receiver end. I am hoping this will get me a bit more distance so it is more usable. In the meantime I am going to work on the charting interface.  

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