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
- 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
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.
- Good for internal install
- No signal problems
- Not strong
- Fewer locking options
- Poor appearance
Some examples are:
Option: Heavy Duty Polycarbonate or ABS
- Reasonable price
- Rust proof
- Can get a signal out!
- Probably weaker than steel
- Getting pricey, especially with a lock
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
- Robust and long lived
- Good appearance
- Steel reasonably priced for the quality
- Signal is degraded**
- SS is expensive.
See a typical catalogue. A typical unit costs $160
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!