Enclosures for electronics and RF

Investigations into using ABS, polycarbonate and sheet metal enclosures to house electronics with a focus on getting that radio signal (wifi, 3G/4G) out of the box

Requirements

• Weatherproof. IP66 = no dust and no water even from jets. IP55 would be okay – it allows minimal ingress.
• UV Stable
• Can get a signal out for Wifi/etc
• Lockable: not bombproof, but light-tamper proof
• Robust: handle impacts (IKK08maybe) like balls, kids stepping
• 300x200x150D

Summary

A heavy-duty polycarbonate or ABS is $150. Appearance and durability is average. No signal problems.

A sheet metal box is $160 + $70 = $230 for antennas. Good option is extra durability and good appearance is required.

Option: Polycarbonate

Some examples are:

• See a typical catalogue

Option: Heavy Duty Polycarbonate or ABS

Some examples are:

• CamdenBoss in polycarb and ABS. Robust, but trying to get a lock latch.
• Ocean Controls in ABS. $72 with ‘plastic key’. Trying sample.
• Fibex in ABS, IK10, two bit key, $150. Good option.

Steel or Stainless

See a typical catalogue. A typical unit costs $160

** Signals

I tested a few options inside metal boxes.

• In a stainless box, the 3/4G router couldn’t connect. Outside it could. In plastic it could. Therefore, an external antenna is required, at about $70.
• In a steel metal box, the wifi signal was dropped by half (similiar to doubling the distance). This might be okay with a good signal. Otherwise, it’s a problem: the IoT device can’t fit an antenna. A solution is to install a RPi zero with a USB dongle (via USB OTG into RPi) with an SMA connector and add a cheap external antenna. Then use the onboard RPi Wifi as an AP for IoT device to connect to. Total cost maybe <$50 but another point of failure. Phew!
• Update 2023: testing with mild steel box 15m from a good router.
  • Recall: -50dBm is excellent, -70dBm is just ok, -80dBm is the absolute limit of usable.
  • dBm is 10 x log(power1 / power2). 3dBm is a doubling (or halving). 6dBm is a quartering.
• Raspi Zero, `wavemon` gives -48dBm in open open versus -54dBm in the box. Actual figure depends a lot on orientation.
  • -40 to -50dBm outside and -48 to -54dBm. On average a 7dBm difference.
  • Hence the steel box drops the signal from a nominal 100% to 25%.
  • In practice, if we start with <-68dBm in open air, we’ll just be okay to get reception within the box. In the box this will be -75dBm, probably quite flaky.
• ESP8266 IotaWatt: use webapp (needs 9VAC reference to work!):
  • -72 to -62dBm outside, say average -67dBm
  • -78 to -72dBm inside, say 75dBm average
  • Same difference: 8 dBm
  • So same deal, except the ESP8266 antennae is rubbish so starts from a lower reception.
• My Android phone (Galaxy A8, from 2018?):
  • -40? dBm outside…. ? Can’t get a good reading 🙁
  • -56dBm inside
• This boils down to:
  • 3 bars (on my phone) required for ESP8266 in a steel box
  • 2 bars (on my phone) probably just ok too, but check orientation!