RFM22B and Arduino Pro Mini 3,3v, reliability

[AxelRM]

Hi!

I just got two RFM22B working attached to Arduino Pro mini 3,3v. I have got the ones without the shields(hence the 3,3v arduino). I got about 400m range with my two modules using the "server" and "client" programs. I tried to increase the power of the modules but they doesnt seem to handle it. At 20Dbm they dont work att al, at 17 they work for about 10s and at 14 they work sometimes, and sometimes not so good.

What power do i get when i just simply run the client/server program without adjusting the TX-power? Is it possible that the RFM22 draws more current than the arduino mini can supply?

[Mike McCauley]

Hi,

Are you sure your modules are high-power capable?

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[AxelRM]

Im not sure because, i got them from Ebay as "arduino compatible" they have a voltage regulator marked "9827" The only spec i got on the current is 40mA/pin. The highest possible stable setting is 11Dbm.

[Mike McCauley]

Hi,

the highest power available on RF22B is RH_RF22_TXPOW_11DBM (11dBm)
Higher powers are only available on RF23BP, and then only with adequate power
supply.

I have updated the documentation in the next release of RadioHead to clarify
this.

Cheers.

[AxelRM]

Only 11dbm? They are sold as 20dbm, https://www.sparkfun.com/products/10153 I tried to meassure current when my module was transmitting with 17 and compared to 11 and saw a 30mA increase in power.

[stevech]

I have several RFM22's. Run at max power setting. Haven't had issues.
Which variation of the Arduino mini are you using... there are many.

[AxelRM]

I managed to get it working with external power suply, so its probably the onboard voltage regulator that doesnt give enough current. Does anyone know what the maximum power is? The data sheet, and Sparkfun say they are 20Dbm(100mW), other sources say 11dbm and 17. Does anyone know?

[Mike McCauley]

On Monday, May 05, 2014 12:54:23 PM AxelRM wrote:
> I managed to get it working with external power suply, so its probably the
> onboard voltage regulator that doesnt give enough current. Does anyone know
> what the maximum power is? The data sheet, and Sparkfun say they are
> 20Dbm(100mW), other sources say 11dbm and 17. Does anyone know?

It depends entirely on exactly which RFM22 variant is on your boards.
Look at that first.

Cheers.

>
> On Monday, May 5, 2014 9:37:41 PM UTC+2, stevech wrote:
> > I have several RFM22's. Run at max power setting. Haven't had issues.
> > Which variation of the Arduino mini are you using... there are many.
> >
> > On Monday, May 5, 2014 3:12:21 AM UTC-7, AxelRM wrote:
> >> Hi!
> >>
> >> I just got two RFM22B working attached to Arduino Pro mini 3,3v. I have
> >> got the ones without the shields(hence the 3,3v arduino). I got about
> >> 400m
> >> range with my two modules using the "server" and "client" programs. I
> >> tried
> >> to increase the power of the modules but they doesnt seem to handle it.
> >> At
> >> 20Dbm they dont work att al, at 17 they work for about 10s and at 14 they
> >> work sometimes, and sometimes not so good.
> >>
> >> What power do i get when i just simply run the client/server program
> >> without adjusting the TX-power? Is it possible that the RFM22 draws more
> >> current than the arduino mini can supply?

[Mike McCauley]

Hi,

On Monday, May 05, 2014 04:16:05 AM AxelRM wrote:
> Only 11dbm? They are sold as 20dbm, https://www.sparkfun.com/products/10153
> I tried to meassure current when my module was transmitting with 17 and
> compared to 11 and saw a 30mA increase in power.

Ooops, sorry you are right.

Max power on RF22B is 20dBm. Max on RF23BP is 30dBm.

Cheers.

[stevech]

RFM22B (note "B") spec says 100mW power out. That's with the power register set to 7.
 Your antenna choice might reduce that - since  cheapie antennas often have negative gain. Those springy-coil looking antennas - are far worse (terrible) than just 1/4 wave length of wire (wave length times 0.7 or so). But bad antennas are OK if the range goal is short (like 100 ft.) and depends as ever on how non-line-of-sight things are.

Don't run the RFM22B on 5V; it's designed for 3.3V, and  spec. sheet says 3.6V max.

I've run the RFM22B's on the 3.3V@100mA output of the Teensy 3 MCUs.

steve

[AxelRM]

I have connected the arduino to an external power source, capable of 800mA in 3,3v but i stil cant get stable operation over 14dbm. At 17dbm i get only 3 sending "blinks" with the client example program, and with 20 i get nothing. Its a strange problem, do i need to ad capacitors to prevent voltage drop?

[stevech]

Capacitors... I doubt it. But if that power source is a "wall wart" power transformer, some are badly engineered. I'd try a different one.
Can you please show how this is all wired? Ground in common with MCU.

maybe it's not a power problem, but rather RF getting into your MCU wiring or its crystal PCB circuits. Try max separation. Keep antenna away from MCU.

Just guessing.

[shorted neuron]

Axel do you have access to an oscilloscope to watch the power supply?  Trigger on downward slope at 3.2V, if it triggers, that may well be your problem.  Running the thing from a LiPo may help if you are a victim of crappy wall warts or USB that cannot handle it.  I had a similar behavior once, and a big, low ESR cap fixed it if I recall.

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[AxelRM]

I dont have acess to an osciloscope sadly, but here is a picture of one of my two modules, they are both identical.

[shorted neuron]

I would throw .1uF and 1000uF caps right next to the radio power inputs and see if it helps.  If not downsize the big one to 100uF and keep em.

[AxelRM]

I tried to use .1uf, and .1uf/470uf and .1uf/100uf solderd directly onto the vcc/gnd  on the board, but there isnt any change. At 11dbm it works flawlessly, but with 14/17dbm it works sometimes, but only for about 2-10s. At 20dbm it simply blinks once, then dies.

[stevech]

Did you try cures for possible RF field strength getting into the MCU clock pins or other pins that are floating. A famous one is leaving the RESET pin floating rather than having a pullup or connection to MCU.

[Alexander Ranstam]

I have connected the pins according to the arduino library, hopefully that will do it. I presume that the Arduino Pro Mini has the reset button on a pull-upp.

I have now tested to run the RFM22b with a arduino uno,  it gives me the exact same results strange enough.

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[stevech]

From earlier in this thread, the problem was that operation failed as the transmitter power choice was increased to 100mW. So I'm on the track that this is not a software issue.
Can you try these:
1. remove the antenna and try operating. This won't damage the radio, but of course the range is rather short.
2. if the antenna is merely a short length of wire, try using a pencil to shape it into a small coil. This makes it a less efficient radiator and may reduce the RF signal strength that may be entering the MCU's I/O or clock pins.

I don't have that Arduino or I'd try to reproduce the issue. What I have is RFM22b's on a separate PCB that is 2 in. or so away from the MCU which isn't an AVR (it's a Teensy 3).