Sunday 22 December 2013

Remote control your electric heating by SMS - Review of the GSM-AUTO-AC

Packaging and accessories

SMS controlled relay

GSM SMS Controlled relay (2 relays to be precise):
  • Power: 110-240V AC
  • Power Consumption: Max 450mA, typically 60mA
  • Relay Contact: 2 x 230V @30Amp, Normally open and Normally Closed contacts(Form C), switching capacity 2.5Kw
  • GSM Bands: GSM 850/900/1800/1900Mhz
  • Operating Temperature: -20°C 60°C
  • Physical size: 130 x 100 x 50mm, 5 x 4 x 2inches
  • Protection: IP65 

Opening the packaging

The device called 'GSM-AUTO-AC' is professionally packaged, comes with a technical user manual in poor English (intelligible) and an cheap looking label. Probably yet another copied design.
Opening the SMS relay
The box also contains an external GSM antenna that I'm not going to use as well as two serial (RS232) programming cables which remain a mystery to me (no explanation or software provided).

Opening the device

As expected inside we find:
  • a GSM module and antenna (top left)
  • a power supply (black, bottom left)
  • two large 30A relays (the two large Tetris looking blue bricks)
  • a micro-controller (on top of the relays)
  • diagnostic leds (centred on top) with no indication of what they could be used for
  • two relay status led (on the right of the relays)
  • a programming port and unknown 'programming' button (top right)
  • 8 screw terminals (two for power and 3 per relay)

Little surprises

  • Terminals are mislabelled for both relays: 
    • NO should be understood as "this is contact is closed when the relay is OFF"
    • NC should be understood as "this contact will be closed when the relay is ON"
  • NO and NC terminals are not in the same order for both relays which can lead to errors
And some other small things:
  • One of the blastic box screws was a little shorter than the others for no apparent reason. This is nothing but makes the whole thing a little less well manufactured.
  • Relay 1 is on the right and Relay 2 on the left (which is confusing as I'm used to write from left to right.
  • The O-ring seal comes in two part. A single one would have probably been better.

Remote controlling relays

There are lots of features coming with a complicated syntax. Where you can do all sorts of complex tasks (such as switch relay 1 ON for XX seconds, wait YY seconds and sitch relay 2 ON for ZZ seconds. I sincerely do not see any uses for that (who knows). You will find hereunder the list of SMS commands (text messages) I find useful:

  • #PWD123456#CAP121212#CAP121212
    Sending this string will change the current password from 123456 to 121212 (note that you need to repeat/confirm the new password)
  • #PWD123456#RLY1=00060
    Sets relay 1 ON for 60 seconds (you need to use your password every time)
  • #PWD123456#RLOP1=ON
    Sets relay 1 ON permanently. You can use OFF in the command above to switch it off 
Note: There are some other interesting commands to check the signal strength, and receiving SMS confirmations, setting a whitelist...

Some very IMPORTANT remarks:
  • No CE or Rohs label: not certified for European electrical installations. It does not automatically mean it is dangerous. I suggest you take your responsibilities.
  • Do not get overexcited when texting your installation: SMSes take time to arrive and if you send too many of them, your relay will behave like it is possessed.
  • SMSes are not guaranteed to be delivered in the right order. Keep this in mind if you are remotely controlling energy hungry equipment or performing sensitive tasks.
  • Do not forget to remove the pin code protection for the sim card
  • Remember to top-up your card (if prepaid) to keep it alive or on some day your network might reject it !
If you're wondering where I got mine, I got it on aliexpress. You can try using keywords such as 'SMS' and 'RELAY'. Most solutions do not have an AC adapter built in and many have more than one or two channel. You can expect to pay something around 100$ shipping included.