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Regulating power for RF24l01// PB with auto reset


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Hi,

 

Fot my sensor project i'm using rechargeable 2 AA batteries, so they start at 2.6 or 2.7 V. The MSP run between 1.8 and 3.4V and the RF24 between 1.9 to 3.6V with a on board current regulator.

 

First question : Does the entry voltage level had some consequences on the RX/TX capabilities of the RF24 ?

 

I could put an third AA battery to get a ~3.6V entry current. But there is also small 12V batteries (half a AA in size) and I would like to know which type of current regulation should I use to run both the RF24 and the MSP at 3.3 V (keeping in mind low power consumption)

 

Regards,

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Referring to the Nordic nRF24L01+ I assume?

If so, the voltage doesn't matter because internally the nRF24L01+ uses a voltage regulator (not current regulator) to provide a 1.9V reference to the chip's core.

The only thing I do recommend is making sure there's a little capacitance on its Vcc rail, maybe 10uF or so, to assist the transceiver during its startup & RF transitions.

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It's the Nordic one (+). Excuse for the confusion, so as I was thinking it regulate itself (but want to be sure, i'm pretty  new to the electronic field).

 

And what advice will you give me for a step-down from 12V to 3.3 or even 2V (as the RF's working below).

 

Oh, and what distance did you achieve between 2 nRF24L01+ in a house got on extended range with external antenna  http://hackspark.fr/en/nrf24l01-with-pa-and-lna-2-4ghz-rf-module-long-distance-antenna.html for the logger and a regular ones http://hackspark.fr/en/nrf24l01-2-4ghz-rf-module-improved-range.html for the sensor.

I did not see an dramatic range change when i change the raspberry one by the one with the antenna. I got something like ~12m (~40 feet) of range, I think with one door closed on the path. Did you achieve greater distance?

 

Regards,

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I guess A23 (Little 12v baterries) won't suit you. they will do 12v@80mah, down to 6~7v if i remeber correctly.  

Best way to power a msp if you have space limitations, would be a couple AAA's. a standard Alkaline AAA will do something like 1500Mah down to 0.8v, and Ni-MH ones will do 600~~1000Mah in the 1.2>>0.8v range



Quoting an old entry in the linux manual: Avoid buck converters like the plague.

In the world of small power budget, the worse thing one can do is to convert voltages.

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Thanks for your answer.

 

They are powered by rechargeable AAA cell (1200mah/1.2V) ,voltage regulator can bring longer running time, in everyday utilisation at home, AAA will do fine. But we have a countryside house which I wanted to supervise (temp, humidity, level in the rain water tank), and it could be several month between our visits.

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Quoting an old entry in the linux manual: Avoid buck converters like the plague.

In the world of small power budget, the worse thing one can do is to convert voltages.

This is not really true, though. There are intelligent micropower DC SMPS devices available now, which are especially good in WSN devices because there are moments of high power. The best example is the ST SPIRIT1 transceiver, which has one built-in. It eats the CC1xxx devices for breakfast. To give TI some credit, its BQ25570 is also a very efficient SMPS power manager for ULP devices. The net result I've seen is better than BQ25504, which lacks the buck converter on the output.

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I believe you refer to power pumps integrated into the silicon.
 I can't think of any discrete buck implementation that would yield beter results than direct operation, especially if your operating range matches the battery output.  

Maybe, in the very end of the alkalines life, when internal resistance starts to be a big problem during surge, upconverters could store enough energy in the decoupling capacitors so you can transmit your beacon (Low duty cycle). But again, the total loss during the other 90% of the discharge curve would compensate the extra juice extracted?

Ni-Mh's have a near flat discharge curve, so there is no point converting if the msp's operate in the range.

Off course, that is for low duty cycle, remote sensoring stuff.

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  • 2 weeks later...

Shhiiiiiiittt, just saw that DS18B20 is working between 3V an 5V (I'm an newbie doubled with a programmer, so I know: RTFM, but can't help trying not to...) and 2 AA are only giving 2.5V. When voltage drop around 2.4V  MSP goes berserk and reset itself in a loop....

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Hi,

 

Thanks, I got an sensor with RF24 and a ds18b20 which give me false reading since yesterday. It alternates between 0 and a very high value and sometime read some right values. Keep reseting itself too. Maybe the false reading came from the resetting. Got an other one keeping resetting itself but without wrong reading. The common thing is that the internal voltage reading is equal or under 2.5 V. The RF24l01 run from 1.9V and the MSP430G2553 from 1.8 so apart the ds18b20 I don't see what can draw to much power causing the MSP to reset itself.

 

EDIT: Just saw your edit. it says that under 2.7 it could got pb reading values, so i'm wondering if in case of difficulty to read it trigger the msp watchdog thus resulting in a reset...

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I'm a bit curious why two AA batteries are only giving you 2.5V ... are they alkaline?  Should work either way, but perhaps you just need to use some fresh batteries?

 

If they're rechargeable I can see that (2.4V typically for NiCd and NiMH) but it should still work.

 

Otherwise, try adding 1 more cell, make sure it never exceeds 3.6V and if it does, maybe try adding a simple 0.7V diode between the battery and circuit to hold the voltage down to the MSP430's comfort level.  Or a proper voltage regulator...

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