Author Topic: WeatherShield R2 Idle Power Draw  (Read 2164 times)

muddyhikers

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WeatherShield R2 Idle Power Draw
« on: February 27, 2017, 11:47:48 AM »
I've been playing around with the weathershield R2 paired with a Moteino RFM69HW, however, I can't seem to get the weatherShield to draw less than 0.25mA at idle. (According to the blog post https://lowpowerlab.com/2016/09/09/weathershield-r2-released/ it should be 3.5uA).

Removing the weatherShield, the Moteino seems to draw 0.01 mA while sleeping.

Putting 3.6v on the WeatherShield vin + ground without being connected to the Moteino shows a draw of 0.25mA.

I suspect this may have something to do with voltage divider cct, but I would prefer to not cut it out of the cct.

Other than the power draw issue, the sensors appear to be all working good.

Thanks for any insight!

Felix

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Re: WeatherShield R2 Idle Power Draw
« Reply #1 on: February 27, 2017, 01:10:57 PM »
It's an artifact (or call it mistake) on my part when I assembled this batch of weather shields. Basically it's because of the choice of resistors used for the voltage divider on A7. If you cut the supply to those or just remove them, the power will be sub uA.
See a detailed analysis of this problem in this blog post.

sparky

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Re: WeatherShield R2 Idle Power Draw
« Reply #2 on: February 27, 2017, 03:36:23 PM »
Felix,

So are you still selling from the same batch?  I just recently purchased one (1/18) which has not been opened yet, would it have the same resister or has it been corrected?

Felix

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Re: WeatherShield R2 Idle Power Draw
« Reply #3 on: February 27, 2017, 04:22:45 PM »
The fix is rather simple and I reduced the price for this reason and people still want it and use it in various ways so ... yes the remaining stock is the same. And yes to your question. Let me know if I can assist but the article does a good job in describing how to get around the higher consumption.
I have to decide what I do with the next batch (same PCB), whether I remove the divider completely or I increase the resistor values to cause a ~3uA consumption.

muddyhikers

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Re: WeatherShield R2 Idle Power Draw
« Reply #4 on: February 27, 2017, 06:54:33 PM »
Thanks for the link! If I wanted to replace the angled resistor so the divider still works, what would you recommend for a value? Or would I also have to replace the one between VIN and A7 to a higher value as well to maintain the resolution?

Felix

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Re: WeatherShield R2 Idle Power Draw
« Reply #5 on: February 27, 2017, 08:06:31 PM »
Right now it's a 3.3v > 4.7K > A7 > 10K > GND  divider.
So you could replace it with 470k and 1Meg to have the same ratio and go down to 2.24uA constant draw through that divider network.

sparky

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Re: WeatherShield R2 Idle Power Draw
« Reply #6 on: February 28, 2017, 01:55:26 PM »
The fix is rather simple and I reduced the price for this reason and people still want it and use it in various ways so ... yes the remaining stock is the same. And yes to your question. Let me know if I can assist but the article does a good job in describing how to get around the higher consumption.
I have to decide what I do with the next batch (same PCB), whether I remove the divider completely or I increase the resistor values to cause a ~3uA consumption.

The only reason I ask is if I was to purchase another one for outdoor use it would be battery operated and the lower power draw would be great... and also, the less tiny microscopic work I have to do is better..  ;D  I will wait and watch for the next revision before I do anything else..

Thanks 

Felix

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Re: WeatherShield R2 Idle Power Draw
« Reply #7 on: February 28, 2017, 02:51:38 PM »
If you ask I can do it for you :), I can swap the 2 resistors with 470k/1M if you put it in the comments.
I try to cater for small needs like this in my otherwise crazy schedule, especially when I see people dont get grumpy at me for making more/less intentional mistakes.

sparky

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Re: WeatherShield R2 Idle Power Draw
« Reply #8 on: February 28, 2017, 02:57:36 PM »
Thanks for the offer..  after I build the latest kits I got from you I will consider that for my next project..  need to decide where I want it to be located, mailbox.. standalone..

Thanks again!

ssmall

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Re: WeatherShield R2 Idle Power Draw
« Reply #9 on: March 01, 2017, 02:10:25 PM »
Felix, out of curiosity why didn't you include the FET to turn the voltage divider on and off like the older model?

Felix

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Re: WeatherShield R2 Idle Power Draw
« Reply #10 on: March 01, 2017, 02:44:32 PM »
I can't remember now, I think because it was still leaking some current and folks didn't like that, it wasnt a true zero draw circuit. Then also the PowerShield has a divider on the same A7 and a lot of times people use both.