Serial over wireless

I spent much of yesterday afternoon and night trying to locate a RS232 or RS485 to bluetooth circuit that needed to be, cheaper than $50 (the cost of running the cable myself), could be powered by a 9V battery or a combination of AA batteries, and the result at the other end had to be serial.

The idea being that the inverter I have can output RS485 which gives us details about how much it’s putting out, the temperature, and we can then measure efficiency and make any further adjustments to it to improve efficiency.

I’m not installing anything yet, as I’m still waiting on the gross meter to be installed (been a bit of time actually, getting impatient). The company contracted to do it claimed 2 weeks last week, so hopefully in the next 7 days we are grid connected.

Back to the serial idea though, I can take RS485, use an RS232 converter and that gives us the ability to get the data to the PC. A wireless transmitter and receiver is what would be needed, and Bluetooth being the most common, used in industrial applications for monitoring / controlling various machinery.

I’ve found a few candidates in my search yesterday:

This PS110W Wi-Fi Serial Device Server – 1 Port offers much of what is needed, including RJ45 if we later abandon wireless. Not sure on price though.

I then looked into the LTC100 which seems a better device. Pricing internationally puts it at about $50 AUD, but I’ve asked RF modules if they can provide a price and then I might get it via them.

The advantages of the LTC100 are that it can be port powered, which means I can supply it 9V via the serial port. Getting the data from it should be relatively easy, I’d need a bluetooth adapter, paired to it, and then using the SPP (Serial Port Profile) to create a virtual serial port. Attach that to my Virtual Server 2005 or VirtualBox virtual machine, and then probe the serial port in the virtual machine for the data.

Then, place that data into RRD Graphs and use that for comparison of day and seasonal changes, and to detect performance issues. Think MRTG Threshold alerts – “Your Solar System is performing worse than a drained AA battery”.

The hardware isn’t going to be IP65 rated like the inverter is, so I’ll pick up a IP65 enclosure from Jaycar, use that to hide the Cat6 cabling from the inverter, the bluetooth adapter. Whilst I’m getting the enclosure, I’ll get a battery terminal so that the wires don’t get damaged from replacing the battery.

I’ll have to figure out how much power it uses, considering the continual probes – although.. it won’t be continual if we shut it down after 9pm and wake it up around 5am, so that’ll save some of the battery.

I’m half tempted to get a Linutop or similar low powered PC to replace the current server, but the offerings out there so far are from $400 to $700 for something very low powered (1Ghz). Due to the virtual machine, it’d need two to be effective – which makes a new server all of a sudden worth while (extra computing power for the same price).

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