RFM69HCW Enable/Disable to save power - Doesn't seem to wake

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TomHumbleAndHandsome
 
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RFM69HCW Enable/Disable to save power - Doesn't seem to wake

Post by TomHumbleAndHandsome »

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Hi,

I have two dirt simple sketches:

Sketch 1 sits in a tight loop and broadcasts a buffer every 5 seconds. This works perfectly as I can receive the buffer on another device.

Sketch 2 differs from Sketch 1 by bringing the "EN" line on the radio low when not in use, and bringing it high again when I broadcast the message. This runs ok (as seen when I put Serial debug statements in it) but the other device never gets the message.

Do I need to have a delay after bringing the EN high? Do I need to re-start the radio by going through the whole "setup" again?

Thanks in advance - debugging radios is confusing as all get out!

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TomHumbleAndHandsome
 
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Re: RFM69HCW Enable/Disable to save power - Doesn't seem to

Post by TomHumbleAndHandsome »

Since I made my initial post, I found that if I toggle the RST line, set the frequency, power and encryption key again after setting EN high, that the radio recovers and is once again fully operational. My problem is... solved... kind of? But it seems pointless to have to go through the entire initialization sequence again every time I enable the device. Why not just power it off and on again using Vin?

According to the only documentation I can find, the EN line "cuts power to the regulator." Since I could also cut power using Vin, one would assume that Adafruit added the EN input for some purpose other than to restart the board completely. My assumption (apparently incorrect) was that it was there to disable the device temporarily when not using it to save power. And then to use the device, all I'd need to do was simply raise EN high again and I'd be off and running without any additional initialization.

So Adafruit, what is EN used for? Does it do the same thing as if I were to bring Vin to LOW? Maybe it's a "low current" way to turn off the radio whereas connecting Vin directly to the CPU's output pin would draw too much power... But now I'm just guessing.

In case you're wondering, I don't mean to sound snarky; hardware is new to me so I'm trying to learn. I'm sure there's a perfectly good reason to have an EN pin (Lady A knows her stuff !!!), I just don't know what it is yet.

As for sounding snarky, forgive me, I have "engineer's disease" :-)

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bobtrex
 
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Re: RFM69HCW Enable/Disable to save power - Doesn't seem to

Post by bobtrex »

Hi

I happen to be playing with the RFM69HCW modules at the moment trying to get low power usage to last on battery for over a year.
For the Radio breakout the EN pin is connected direct to the 3.3V regulator En pin and and also pulled high to Vin by 100K. So should cut all the power to be board ( I am still seeing approx 33 micro amps ?). I guess the intent is this saves you having to have your own circuit to cut the power.

Regards
Robert

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TomHumbleAndHandsome
 
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Re: RFM69HCW Enable/Disable to save power - Doesn't seem to

Post by TomHumbleAndHandsome »

Thanks Bob.

As a software guy, understanding hardware can b a struggle.

Tell me something, why couldn't you just power the radio by connecting the radio's Vin to a GPIO output on the CPU? Wouldn't that do the same thing? Or does that require too much current from the GPIO output?

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bobtrex
 
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Re: RFM69HCW Enable/Disable to save power - Doesn't seem to

Post by bobtrex »

The Radio can draw 100+ milli Amps when transmitting and will damage the CPU.
As you have seen using the enable pin shuts down the LDO and gives around 33µA (which I believe comes from the 2x100K pullups).
I have tried the Sparkfun module which has no pullups, LDO or level conversion. This consumes 1.33µA in low power mode.
However you have to be able to supply adequate power to the module at 3.3V and only 3.3V I/O.

Regards

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TomHumbleAndHandsome
 
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Re: RFM69HCW Enable/Disable to save power - Doesn't seem to

Post by TomHumbleAndHandsome »

Significant difference. Good to know, thanks.

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