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Alastair Senior Member Joined: 03/04/2017 Location: AustraliaPosts: 161
Posted: 07:21am 12 Dec 2017
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I have built a central data collection unit based around an MM+ back pack. It has been working fine for several months except that every now and again I have found that it has been hung up and just cycling on the watchdog.
The unit communicates with several nodes via HC-12 links through 2 brick walls. The first node is only about 10m away.
When the base is powered up it initialises itself and then talks to each node sending the correct time from the base RTC. It then asks each node to send data when it wants it.
I finally got around to looking at it and have found that it runs perfectly when powered by a usb line to the PC. It hangs when powered by the Li-ion battery pack. It does not matter if the charger is connected to the external power or not. The 5v power to the system comes from a boost module (1A max) from the 4v Li-ion. The 5v line has some noise but is quite similar to the pc feed. The voltage is very stable.
If I move the unit slightly closer to the node it works. With the pc power I can move it anywhere to the limit of the cable.
After some fiddling and inserting debugs I have found the system hangs when it sends the first message on the HC-12.
My first thought was that the lack of a ground connection was limiting the range. Connecting the battery ground to the pc earth made no difference. Tried a piece of metal as a ground plane but no difference. Given the 430Mhz freq I would not expect it to make a difference.
The problem only occurs when on battery power so even though the 5v looked fine I have fiddled with capacitors etc to improve the 5v line to no avail.
It appears that on the battery the system is at its range limit and worked initially because it was in a slightly different place.
Any suggestions? Edited by Alastair 2017-12-13Cheers, Alastair
retepsnikrep Senior Member Joined: 31/12/2007 Location: United KingdomPosts: 134
Posted: 07:51am 12 Dec 2017
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Switch mode voltage boost things can be horribly electrically/rf noisy.
Perhaps that's killing the HC-12 in certain circs like when it increases current to transmit from idle state.. Gen1 Honda Insights.
GoodToGo! Senior Member Joined: 23/04/2017 Location: AustraliaPosts: 188
Posted: 08:55am 12 Dec 2017
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Have to agree with reteP above, it looks like the boost module is rf noisy and interfering with your transmissions. Can you try another type of boost module? Have you tried just running it off the li-ion battery direct?
Cheers, GTG! ...... Don't worry mate, it'll be GoodToGo!
kg4pid Regular Member Joined: 08/03/2015 Location: United StatesPosts: 50
Posted: 03:46pm 12 Dec 2017
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While your problem is likely dirty power, another problem to be aware of is the antenna itself. Using only the coiled antenna with no ground plane causes rf to flow on any conductor underneath the antenna. Adding a couple of 1/4 wave radials to the ground connections at the base of the coil will increase range and eliminate the commom mode currents. Want even better range? Don't use the little coiled antenna and replace it with a 1/4 wavelength piece of wire. The length of a 1/4 wave at 433mhz is about 6.5 inches or 16.5 cm.
Max
palcal Guru Joined: 12/10/2011 Location: AustraliaPosts: 2006
Posted: 07:40pm 12 Dec 2017
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Why not use 2 Li-ion cells and a 5v. regulator. Paul."It is better to be ignorant and ask a stupid question than to be plain Stupid and not ask at all"
Alastair Senior Member Joined: 03/04/2017 Location: AustraliaPosts: 161
Posted: 03:33am 14 Dec 2017
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Had things to do but now back on the case.
I had a proper look at the output of the boost module and as suggested there was a lot of noise over a wide frequency range. The peak noise was only about 200mv with the majority of the power below 40MHz according to the fft on my scope.
I tried a few different boost modules but the problem persisted. I tried various capacitors on the output but strangely it seemed to have little benefit the high freq stuff stayed.
I increased the voltage of the boost module and put it into a 78L05. This worked ok but the HF components were still there and hard to filter and still caused the problem.
As suggested by GTG instead of a 5v supply I connected the battery direct so it was only getting 4.0v when the charge module was on and 3.8 when it was on idle. Everything seemed fine with that. The MM+, display, RTC and HC-12 all seemed happy. There is still significant noise but the power is mostly below 10Mhz.
For the moment I am going to run things on the battery and fiddle with the boost modules to get more understanding of their behaviour. I have used then quite a bit in the past and not had problems. The ones I have at the moment are different and I need to understand why I can't filter out the hf components in the usual way.
Thanks for the suggestions shedders. I knew about the boost module noise issues but clearly the HC-12 really doesn't like HF interference. I am going to spend some time trying to work out a simple way to utilise the boost modules or just dump them and try something better.
My ESP-01s modules arrived yesterday and I was hoping to start playing with them for the wifi update link as discussed in another thread. I will be disciplined for a while and finalise this issue first. Cheers, Alastair
srnet Senior Member Joined: 08/08/2014 Location: United KingdomPosts: 164
Posted: 04:44am 14 Dec 2017
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Boost modules can and do affect radio modules, USB power banks are among the worse offenders.
Symptoms of the problem are significantly reduced range and\or corrupt data.
If your application is hanging, it may not be dealing with corrupt data in a fail safe manner, which is important for any UHF radio system..
$50SAT is Silent but probably still working. For information on LoRa visit http://www.loratracker.uk/
robert.rozee Guru Joined: 31/12/2012 Location: New ZealandPosts: 2462
Posted: 06:45am 14 Dec 2017
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what capacitors did you try? an electrolytic will only filter out very low-frequency stuff, while small ceramic capacitors are needed for higher frequency noise. it is not uncommon to see a design with a number of different capacitors paralled up (3 ceramic caps of 100pf, 10nf, 1uf in parallel and right next to each other). each one serves to stomp on a different frequency span.
a small RF inductors in series with the supply line will also act to block noise. combine this with a ceramic filter capacitor to ground on the HC-12 side of the inductor (there is no harm in having identical capacitors on both side of the inductor). wikipaedia should have a few good articles with examples.
cheers, rob :-)
Azure Guru Joined: 09/11/2017 Location: AustraliaPosts: 446
Posted: 08:56am 14 Dec 2017
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I agree with rob, very common to have an inductor on supply rail of good smps with multiple caps to reduce hf noise on rails.
srnet Senior Member Joined: 08/08/2014 Location: United KingdomPosts: 164
Posted: 11:41am 14 Dec 2017
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In tests I have done with some RF modules, the EMI is radiated from the switcher and being directly picked up by the antenna.
You wont get rid of that by filtering the power supply, but the sensitivity reduction goes away completely if the antenna is remote from the receiver\powersupply or the receiver\powersupply is screened effectively.
It did surprise me that switchers can radiate so much EMI.
$50SAT is Silent but probably still working. For information on LoRa visit http://www.loratracker.uk/
Grogster Admin Group Joined: 31/12/2012 Location: New ZealandPosts: 9750
Posted: 03:06am 15 Dec 2017
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......all of which is why I still use linear regulators for any RF stuff. Switchers are small and efficient, but as mentioned, they can play merry hell with RFI. Not a problem, if you are not using any RF link etc, but if you are......Smoke makes things work. When the smoke gets out, it stops!
Alastair Senior Member Joined: 03/04/2017 Location: AustraliaPosts: 161
Posted: 12:15am 16 Dec 2017
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Thanks for all the above. When I have time I am going to investigate the buck modules and try things like inductors. I have tried combinations of capacitors but have little success. I suspect srnet is on the money as all the modules are in close proximity ie cms and I am sure radiated noise is the problem cause. Cheers, Alastair
Notice. New forum software under development. It's going to miss a few functions and look a bit ugly for a while, but I'm working on it full time now as the old forum was too unstable. Couple days, all good. If you notice any issues, please contact me.
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