Battery powered IoT lightning sensor shielding

Question

I have a low-power wireless solar powered IoT sensor that has a Geiger counter (400V SBM20 tube) on board and is controlled by ATmega328P, sitting outside. This set-up has been working great for almost 7 years but recently I've started experiencing random lock-ups of the MCU where it just does not respond to anything until being reset. This started happening about once every 10 days. My suspicion is that Geiger tube EMI has a long term impact on the MCU, degrading its performance and causing this issue. This suspicion has been further strengthened when I had the idea to add an AS3935 lightning module inside of the enclosure, but found out that every time the Geiger tube records a "hit", the lightning module picks up EMI from it and registers it as a lightning strike, so the AS module needs to be at least 1m away not to pick up this EMI.

Since I started experiencing this issue of the MCU locking up, I have decided to redesign the whole board and add AS3935 module to the original design but wire it approximately 1-1.5m away from the MCU/Geiger counter enclosure. The lightning sensor communicates via i2C so I cannot wire it too far from the MCU.

With this new design in mind, I'd like to get your suggestions on shielding of things. Basically my first idea was to add a metal RF shield can over the MCU to protect it from Geiger EMI. I understand I'd have to attach one contact of this shield to the GND of the board to make it effective. The board itself would have as much GND pour as possible.

The other idea I had is to also use shielded wires that would run to solar panel and AS3935, and attach the shielding of the wire to the GND of the MCU board. I live in an aree of high frequency lightning strikes. Would this be a decent solution to protect this device within reason?

Would adding ESD protection ICs to the i2c and power lines running outside of the main enclosure be beneficial in this case?

In Short:

1. Will adding grounded metal can RF shield help protect the MCU?
2. Will adding shielded wire, connected to ground of the main board be beneficial? (I'm afraid this shielding will become an antenna itself causing ground issues, but at the same time I'd still have to run ground wires to the solar panel and the AS module.)
3. Would adding ESD protection to those lines be of any benefit? (ICs for USB ESD protection type.)

Attaching diagram of my device for ease of understanding the set-up.

Answer 1

EMI (electromagnetic interference) generated by using a Geiger counter can cause MCU lockup issues. You can take the following measures to improve the EMI shielding and interference resistance of the circuit:

1. Add a grounded metal RF shield

Effectiveness: Adding a metal RF shield to the MCU is an effective measure to reduce the impact of external electromagnetic interference on the MCU. The shield can prevent EMI from directly interfering with the operation of the MCU. Implementation: Make sure that the shield is in good contact with the GND of the circuit board. Use a full GND plane whenever possible to provide better shielding and lower noise coupling. Note: When designing the shield, make sure it does not affect thermal management, that is, maintain adequate ventilation or use thermally conductive materials to prevent overheating.

2. Add a shielded wire

Benefit: Using a shielded wire and connecting it to the GND of the motherboard helps reduce the possibility of the cable acting as an antenna to pick up EMI. This is especially important because long wires are prone to induction of EMI. Considerations: Make sure the shield is grounded at only one point (usually at the PCB end) to avoid forming a ground loop. This can reduce the coupling of ground current noise on the cable. Design Tips: Twist signal lines inside shields to increase common-mode noise resistance.

3. Add ESD protection to externally running i2c and power lines

Benefits: Adding ESD protection ICs can prevent transient voltage spikes caused by electrostatic discharge from damaging your circuits, especially for lines exposed to the external environment. Applicability: ESD protection is particularly suitable for I/O ports or any connection entering from the outside of the motherboard (such as power lines, I2C buses). Implementation: Choose low-capacitance ESD protection devices suitable for data transmission speeds to avoid affecting signal integrity.

Other Tips

Power filtering: Adding appropriate filtering capacitors to the power input of the MCU may help smooth out any power noise caused by EMI. Line routing: Keep the routing distance of high-frequency signals and power lines as short as possible and avoid unnecessary loop area. Isolate Geiger counter: Consider isolating the Geiger counter circuit in a separate metal shielded box to minimize its impact on the MCU and other sensitive electronic components.

By combining the above measures, you can effectively improve your system's ability to resist EMI, thereby reducing the possibility of MCU lockup and improving the reliability of the device.