Author Topic: RFM69HW, 8mhz Arduino pro mini, and Raspberry Pi power  (Read 3364 times)

dewoodruff

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RFM69HW, 8mhz Arduino pro mini, and Raspberry Pi power
« on: November 30, 2014, 10:21:30 PM »
Hi there! I've been lurking and learning for a while, but here goes my first post!

I have Raspberry Pi that is the heart of my home automation/monitoring. I am trying to hook up a Arduino pro mini with a RFM69HW strapped onto it, and power it all via the Pi's 3.3v pin.

The radio works reasonably well when I do not set High Power mode, but from my reading of this forum it seems not setting High Power mode can cause other problems with communications. I'm wondering if my MANY missed ACKs are the result of this...

However, when I set High Power mode, the Arduino browns out and resets when it attempts to send a packet. It seems the 3.3v from the Pi can't support the burst current needed by the HW amplifiers.

Can I solve this problem with a capacitor? If so, how large of a capacitor would I need?

If not, I have a separate 3.3v supply I could use to power the Arduino board and radio. Would that fry anything or cause any other problems - to have the Pi powered off one supply, connected to the Arduino via UART, which is powered by another supply?

Thanks in advance (and thanks Felix for the awesome library!)

Felix

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Re: RFM69HW, 8mhz Arduino pro mini, and Raspberry Pi power
« Reply #1 on: December 01, 2014, 08:48:53 AM »
Hi,
I'm not sure if you can do it with a cap, you might be able to with a large one maybe 1000mAh, but it might interfere with the 3.3V rail stability and cause your Pi to freeze/crash. Nothing bad in trying, the worst could happen is your SD card image going bad.
Is there a regulator on the Pro Mini? I'm wondering if that can supply the 130mA bursts from a 5V input.
I know for sure a Moteino will work if it's fed 5V from the Pi's 5V rail.

dewoodruff

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Re: RFM69HW, 8mhz Arduino pro mini, and Raspberry Pi power
« Reply #2 on: December 01, 2014, 11:52:13 AM »
Hello!
Yes, there is a regulator, however I've hooked the 3.3v right into Vcc, which I believe bypasses the regulator because it doesn't need to step down. The Arduino I have is a clone so I'll try to figure out what regulator they are using tonight then hook up the Pi's 5v to the RAW input on the Arduino and see if that might work better.

Alternatively, will things go up in smoke if I tried to power the Arduino from a separate supply? The setup would look like this:

                                step down board to 5v -> Pi
                         /                                                   \
12v power brick                                                        TX/RX back to Pi
                         \                                                   /
                          step down board to 3.3v -> Arduino

I already have the two step down boards in place doing other things so it is not additional hardware, I just want to make sure I don't cause some kind of feedback loop by doing that (I'm relatively new at all this electronics hardware stuff).

Thanks!

Felix

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Re: RFM69HW, 8mhz Arduino pro mini, and Raspberry Pi power
« Reply #3 on: December 01, 2014, 12:34:45 PM »
It should not, but make sure you have the same GND reference.

dewoodruff

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Re: RFM69HW, 8mhz Arduino pro mini, and Raspberry Pi power
« Reply #4 on: December 01, 2014, 09:28:31 PM »
It looks like the regulator on the Arduino clone is this: http://www.micrel.com/_PDF/mic5219.pdf
With a 500mA peak output. So my new plan for this weekend is to wire to the 5v pin of the Pi to the regulator and give that a try. I'll report back if it works in case it helps someone else in the future.

Thanks for talking it out with me.

dewoodruff

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Re: RFM69HW, 8mhz Arduino pro mini, and Raspberry Pi power
« Reply #5 on: December 07, 2014, 10:17:37 PM »
Wiring the RAW pin of the Arduino to the 5v pin of the Pi worked.

I ran into a snag with my bench Pi power supply, which is only a 700ma output. Depending on what the Pi was doing, that low current rating would occasionally result in the Arduino browning out when trying to send. What is strange is that when this happened, the temp reading from the RFM69-HW shot up really high - I saw 120F a few times. Normally, it is at 78F for me.

Once I got the Pi back on the wall with my higher output power supply, there were no more brownouts. It has been running since Wednesday sending ACKs to two nodes every 30 seconds.

Takeaways for me:
- Always run the HW with setHighPower(), otherwise transmissions will be unreliable.
- 3.3v pin from the Pi cannot provide enough current for the HW to transmit.
- Instead, use the 5v pin attached to RAW with a large enough (at least 1000ma) power supply for the Pi.

Thanks Felix!

Felix

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Re: RFM69HW, 8mhz Arduino pro mini, and Raspberry Pi power
« Reply #6 on: December 08, 2014, 09:41:49 AM »
Great, thanks for following up with your findings!

TomWS

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Re: RFM69HW, 8mhz Arduino pro mini, and Raspberry Pi power
« Reply #7 on: January 08, 2015, 10:34:25 PM »
Wiring the RAW pin of the Arduino to the 5v pin of the Pi worked.

I ran into a snag with my bench Pi power supply, which is only a 700ma output. Depending on what the Pi was doing, that low current rating would occasionally result in the Arduino browning out when trying to send. What is strange is that when this happened, the temp reading from the RFM69-HW shot up really high - I saw 120F a few times. Normally, it is at 78F for me.

Once I got the Pi back on the wall with my higher output power supply, there were no more brownouts. It has been running since Wednesday sending ACKs to two nodes every 30 seconds.

Takeaways for me:
- Always run the HW with setHighPower(), otherwise transmissions will be unreliable.
- 3.3v pin from the Pi cannot provide enough current for the HW to transmit.
- Instead, use the 5v pin attached to RAW with a large enough (at least 1000ma) power supply for the Pi.

Thanks Felix!
Are you running the Pi in desktop mode (with a display) or via ssh? The Pi will consume a lot of power if driving a display and not leave as much supply for peripherals.
Also, regarding your comment about setHighPower().  If using the RFM69HW (and the standard RFM69 library) you MUST set high power mode to get any rf signal.  This isn't an option.  The HW power amplifiers are turned off otherwise and you'll get nothing usable out.

Tom

dewoodruff

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Re: RFM69HW, 8mhz Arduino pro mini, and Raspberry Pi power
« Reply #8 on: January 09, 2015, 01:15:54 PM »

Are you running the Pi in desktop mode (with a display) or via ssh? The Pi will consume a lot of power if driving a display and not leave as much supply for peripherals.
Also, regarding your comment about setHighPower().  If using the RFM69HW (and the standard RFM69 library) you MUST set high power mode to get any rf signal.  This isn't an option.  The HW power amplifiers are turned off otherwise and you'll get nothing usable out.

Tom

I only ever use it via SSH as it is mounted to my wall in the basement, however, I never thought to disable HDMI to save extra power! I found this post with the command to run: https://glframebuffer.wordpress.com/2013/08/28/raspberrypi-how-to-turn-off-hdmi-from-raspberry-pi/ Is there a better method for disabling the display? If not, I'll just throw that in /etc/rc.local to run at boot.

I realize now that setHighPower() is required. However, when I was testing on the bench with a gateway and a node, the HW was working just fine over short distances which is why I didn't immediately realize it was required.

Thanks,
Dan