Author Topic: RFM69HW at lower power?  (Read 1636 times)

TheOddler

  • Newbie
  • *
  • Posts: 3
RFM69HW at lower power?
« on: May 16, 2017, 03:49:53 AM »
I'm looking at the RFM69W and RFM69HW transceivers. Low power is very important, so the non-H version seems the best for me. However, my local stores only have the RFM69HW transceiver. So I was wondering, can the RFM69HW transceiver also send at lower power?

I read that RFM69W uses 45 mA when sending at +13 dBm. Whereas RFM69HW uses 130 mA at +20 dBm. Is it possible for the latter to send at only +13 dBm and also just use 45mA?

Thanks!

ChemE

  • Sr. Member
  • ****
  • Posts: 419
  • Country: us
Re: RFM69HW at lower power?
« Reply #1 on: May 16, 2017, 07:18:08 AM »
The RFM69W uses 16mA when transmitting at 0dBm.  I believe that the absolute minimum the RFM69HW can transmit at is 45mA.  This is one reason why I decided to go with all Ws.  The other is my lot is only 200' long so there is no scenario in which the W cannot reach a gateway on my lot.

TheOddler

  • Newbie
  • *
  • Posts: 3
Re: RFM69HW at lower power?
« Reply #2 on: May 16, 2017, 07:40:59 AM »
Ah, so it is possible to send at lower power, for less range? And do you know if the range of a RFM69W and RFM69HW are the same at 45 or less mA? Or that's just something I'll have to try.

Felix

  • Administrator
  • Hero Member
  • *****
  • Posts: 6370
  • Country: us
    • LowPowerLab
Re: RFM69HW at lower power?
« Reply #3 on: May 16, 2017, 09:38:14 AM »
You can lower output power but if you're not getting anything across it's useless.
So use RFM69_ATC (see examples). Set your target RSSI around -80 or so to get a good signal. Then your output power is auto adjusted.

perky

  • Hero Member
  • *****
  • Posts: 873
  • Country: gb
Re: RFM69HW at lower power?
« Reply #4 on: May 17, 2017, 11:10:16 AM »
The RFM69W uses 16mA when transmitting at 0dBm.  I believe that the absolute minimum the RFM69HW can transmit at is 45mA.  This is one reason why I decided to go with all Ws.  The other is my lot is only 200' long so there is no scenario in which the W cannot reach a gateway on my lot.
Not according to this document, which suggests only enabling PA1 for lower power where the current is around 16mA:
https://andrehessling.de/2015/02/07/figuring-out-the-power-level-settings-of-hoperfs-rfm69-hwhcw-modules/
 Mark.

WhiteHare

  • Hero Member
  • *****
  • Posts: 1296
  • Country: us
Re: RFM69HW at lower power?
« Reply #5 on: May 17, 2017, 11:48:24 AM »
Not according to this document, which suggests only enabling PA1 for lower power where the current is around 16mA:
https://andrehessling.de/2015/02/07/figuring-out-the-power-level-settings-of-hoperfs-rfm69-hwhcw-modules/
 Mark.

In a different thread, JoeLucid says he was able to make that work, but didn't have demo code.  Well, he had sorta partial code, but I was busy with something else at the time and so I gave up after only one quick attempt.  Maybe ChemE can make it work, and then post the code?  Sounds like it would be right up ChemE's alley. 
« Last Edit: May 17, 2017, 11:55:26 AM by WhiteHare »

TheOddler

  • Newbie
  • *
  • Posts: 3
Re: RFM69HW at lower power?
« Reply #6 on: May 17, 2017, 12:09:23 PM »
Not according to this document, which suggests only enabling PA1 for lower power where the current is around 16mA:
https://andrehessling.de/2015/02/07/figuring-out-the-power-level-settings-of-hoperfs-rfm69-hwhcw-modules/
 Mark.

Thanks for this! After reading this, and looking specifically at the last plot (current consumptions vs. different calculated output power), the answer to my orriginal question seems to be 'yes'. Yes I can use the H modules at lower power settings and get roughly the same output strenght for the same current consumption. The non-H module however can go even lower in power if the distance between sender and receiver is very small, but that's not the case I think (though the article doesn't say what a 'very small distance' is).

Thanks to everyone in this topic! I think the H modules are fine for what I need, so I don't have to go looking for non-H's anywhere.

WhiteHare

  • Hero Member
  • *****
  • Posts: 1296
  • Country: us
Re: RFM69HW at lower power?
« Reply #7 on: May 17, 2017, 01:08:28 PM »
Thanks for this! After reading this, and looking specifically at the last plot (current consumptions vs. different calculated output power), the answer to my orriginal question seems to be 'yes'. Yes I can use the H modules at lower power settings and get roughly the same output strenght for the same current consumption. The non-H module however can go even lower in power if the distance between sender and receiver is very small, but that's not the case I think (though the article doesn't say what a 'very small distance' is).

Thanks to everyone in this topic! I think the H modules are fine for what I need, so I don't have to go looking for non-H's anywhere.

Yes, but there's still the riddle of exactly how to do it.

ChemE

  • Sr. Member
  • ****
  • Posts: 419
  • Country: us
Re: RFM69HW at lower power?
« Reply #8 on: May 17, 2017, 04:30:19 PM »
Maybe ChemE can make it work, and then post the code?  Sounds like it would be right up ChemE's alley.

I don't think I could verify my results even if I could get it to go since I don't have an oscilloscope.  Correct me if I'm wrong but I think the TX power spike would be too transient for a uPower/multimeter to pick up accurately right?  Can an Arduino be used as a psuedo-oscilloscope for capturing a trace from a uPower?  I'm also a little distracted right now since I'm just starting to build a temperature controller for my Big Green Egg :)

WhiteHare

  • Hero Member
  • *****
  • Posts: 1296
  • Country: us
Re: RFM69HW at lower power?
« Reply #9 on: May 17, 2017, 05:11:41 PM »
Oscilloscope is the only way I know of, though maybe if you were to Tx in continuous mode (i.e. not packet mode) a uCurrent would suffice.

I don't know what a Big Green Egg is.  Does it go with a Big Ham?

ChemE

  • Sr. Member
  • ****
  • Posts: 419
  • Country: us
Re: RFM69HW at lower power?
« Reply #10 on: May 17, 2017, 06:55:33 PM »
Nice one but no.  It is a lump charcoal fired grill/smoker so I'm getting to fool around with thermistors, MOSFETs, and servos to implement PID control over a grill.  And part of me is wondering if I can do it low power, like one set of AAs to control a few cooks which can be 16+ hours each.  Now that I've totally derailed the thread, I plan to build an RFM69CW into my controller because again no need to the H's range and power draw.