I have a PCB powered by an IRM-30-12 power supply (230VAC to 12VDC). On this PCB, I have a MRF24J40MD from Microchip and a Udooneo to drive it + a 5VDC regulator and the 3.3VDC of the Udooneo.

After installing over 300 units in different places, I noticed that some old fluorescent tubes are resetting the MRF24J40MD when someone switches the fluorescent tubes on or off. Replacing the old fluorescent tube with a new one make the trick and I have no more issue with the MRF24J40MD. But this takes lot of time.

My goal would be to design a protection circuit against this that I can plug or solder on the PCB on the 230VAC parts or 12VDC, 5VDC or 3.3VDC parts to protect my MRF24J40MD against resetting. Sadly, I have no idea how to manage this.

I could reproduce the bug at home with a Philips TMX 200 LS fluorescent tube and a Philips S10 starter. After some retries, the MRF24J40MD resets itself and doesn't communicate anymore if the PCB and the fluorescent tube are on the same plug.

EDIT: new measures with the oscilloscope following recommendations in the comments.

The 3.3VDC of the MRF24J40MD comes from the Udooneo. There's a separate power supply for the GSM parts.

With an oscilloscope, I could mesure the perturbations at the 3.3VDC/GND of MRF24J40MD. I made the same measures on the output of main power supply (12VDC) and the perturbations are exactly the same. Here's the result on 3.3VDC/GND with new measurement setup (see below for probe setup):

Tube switched off 1 Tube switched off 2

The probe :


Some schematics (MRF24J40MD and 3.3VDC output of Udooneo):

3.3VDC output from Udooneo MRF24J40MD

Hope this isn't a too noob question and someone could suggest some ideas to help me solve this. For the little story, the PCB was designed by a group of junior engineers in a school. I'm a software engineer. That's why I'm struggling with this kind of problem and I can't reach the original designers anymore...

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    \$\begingroup\$ Not at all noob! You can spend lifetime learning and perfecting EMI. Sounds like you have poor EMI rejection. Show layout! What’s your ground plane situation? Decoupling of every IC? Series resistances on critical nodes? CM chokes? Also, show your probe setup for your oscillogram. \$\endgroup\$ – winny May 13 at 18:00
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    \$\begingroup\$ As above, the probe setup is important. While there is no question that your problem is EMI related, the scope traces can be very misleading. A 4" or 6" ground lead on a scope probe acts as a loop antenna, making a bad problem appear even worse. \$\endgroup\$ – AnalogKid May 13 at 18:15
  • \$\begingroup\$ Resonance above 20MHz is likely the probe ground inductance. Re-scope and verify to avoid loops > 2cm and coil probe coax, which may also help. Then add low ESR decoupling caps. Resonance at 12MHz is also LC related. Either add ground plane or better CM choke pi filter. Supply noise is best measured with AC coupled to 50 Ohm load \$\endgroup\$ – Tony Stewart Sunnyskyguy EE75 May 13 at 18:34
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    \$\begingroup\$ Please post a schematic of the important stuff like power and MRF \$\endgroup\$ – MadHatter May 13 at 19:11
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    \$\begingroup\$ In my experience what reveals the culprit is this question: "Have you followed the Manufacturers' recommended schematic and PCB layout? It would be helpful if you could share with us the schematic and layout, or at least the sections relevant to this question. Additionally a first step is to understand the source of the vulnerability, i.e. if they are conducted or radiated emissions. If you can power your board with the battery, you can verify this, and be closer to knowing where to apply the fix. \$\endgroup\$ – Elmesito May 13 at 20:05

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