Off The Shelf PoE Adaptor Brings Success to our Power Problems
Some times it’s best to let someone else work things out! Making our own PoE and voltage regulator was perhaps a step too far when this off the shelf PoE adaptor is so inexpensive and easy to use. It was fun to try and make our own. Except for the time I clamped the device in my crocodile clips to test the voltage which of course resulted in a puff of smoke because I shorted the whole thing! I learnt a little more about the importance of heat sinks and neat soldering. But perhaps our time would have been better spent on more important elements of the project.
These TP-Link devices come with a 48v supply and converts down to 12V, 9V, or 5V DC over a 100 meters of Ethernet. I had to make my own Micro USB to 5V adaptor to power the Pi – only because that’s it’s a simple bit of bodging and I have loads of USB cables I could hack into.
The unit we’re using in the CDC Weather Station, the TP-Link POE150S, isn’t available any more. The replacement is the TP-POE10R – which costs around £10.00 – worth every penny!
Power Over Ethernet (PoE) Introduces It’s Own Problems.
To run data and power down a network cable you need to use a PoE injector. Often implemented when you need to power wireless routers throughout a building but don’t want the cost of putting a 13amp socket next to each one as well. At the CDC Weather Station we hit a problem with distance. Running a DC current down a 90 meter cable using a PoE injector will get some voltage to the end, but the drop off due to resistants in the cable is significant. Just like watering the garden; the longer the hose the more the water trickles out at the other end.
Using the voltage drop calculator below we determined we’d need to send 24 volts down the cable to guarantee a decent output at the other end. We were potentially facing a 50% drop in voltage. The Raspberry Pi only needs 5v consistently, no computer likes a varying current. As other factors such as kinks in the cable and change in temperature could play a part we’ve given ourselves some headroom so 24v should get us to around 12v, which in reality is probably going to be more like 7v or 8v.
CDC: Time to Install The Hardware
At this point in the project I’ve managed to prove I can program a Raspberry Pi to read the data from a Bosch BMP180 sensor and upload that data to Plot.ly and the Met Office. Alas the BMP180 sensor isn’t applicable to the Creekside Discovery Centre installation. Although I could weather proof the sensor I still need to measure water temperature. I have managed to buy, install and code the Pi to see the i2c bus that attaches to the GPIO pins and run some simple Python script that displays temperature readings from the Pi’s ROM. But I haven’t managed to crack publishing the data . But as someone once said…
“Time and Tide Wait for no Man”
CDC Pi Weather Station Has A New Sensor The 1Wire DS18B20
Second setup of the CDC Pi Weather Station
Time to tackle the 1Wire sensor
After the furore of last weeks success we’re back down to earth with a bit of a bang. We’re now trying to code the Raspberry Pi so it will read, and more importantly broadcast the readings from the 1Wire sensors to Plot.ly, the MET office or an alternative means of hosting the data online. The 1Wire sensor is already waterproof and designed to run in series with other 1Wire sensors which would greatly help with the expansion plans for the project. Although the Bosch BMP180 and the associated code worked, the sensor isn’t designed to be outdoors and nor does it measure water temperature. So I’ve turned to the 1Wire system.
CDC: First Test is a Success!
It’s taken two days of fault finding but we succeeded!
Success is a great word! Admittedly this is only the first stage and not even the sensor I eventually hope to use. But success it is! Main issue was an error using SSH with Python Version 2.7.3 which comes preinstalled on the Pi. It took a long time for this bit of code to work.
sudo pip install pyopenssl ndg-httpsclient pyasn1
I then found some other errors – but with line numbers I worked out I’d simply entered an extra digital in the AWS key. It’s hard to explain how excited I am!!
CDC Weather Station Is Coming To Life
I’ve been waiting on a simple bit of ribbon cable. I could have just ordered some, but my partner in crime the fabulous Jon San, had some spare. I was unashamedly excited to receive this simple bit of kit and immediately put it to use. Although I have to admit I didn’t notice or consider the relevance of the pink, zig-zag patten on one side of the ribbon. Although it didn’t slow me down, I’m pleased to now know that’s pin 1!
26 Pin Ribbon Cable used to connected the sensor to the GPIO pins on the Raspberry Pi.
CDC Pi Weather Station Build
The Creekside Discovery Centre Weather Station
Following the excellent work already done by Romilly Close, who setup the Sheffield Pi Station, I’m now embarking on my own ‘Deptford Pi Station’ at the Creekside Discovery Centre (CDC). The image captures some of the basic hardware I’ve invested in. Added to this will be a ribbon cable and perhaps a breadboard to help connect everything. The Pi will feed the data via ethernet back to a server and onto the web. Everything will be photographed, labeled and uploaded soon. But so far there’s…
Beginnings of the ‘Deptford Pi Weather Station’
Proposal For CDC Weather Station
This is the first draft of the proposal for a Weather Station at the Creekside Discovery Centre.
I did enthusiastically explain the idea for a weather to Creekside Discovery Centre staff. Indeed the idea had already been mooted by my co-geek Jon San. But nothing speaks of intention like a document with a cover page and an index! So a proposal was drafted and sent.
Creekside Discovery Centre Deptford
The proposal explains what we intend to do, when, rough costs and an outline of phase two. I hope it’s informative and eye-catching . I hope it inspires it’s intended recipients and other visitors to this site who may be interested in having their own weather station.
The proposal is just that, a proposal. I’ve never installed a weather station so there’s bound to be something I’ve not covered. As this installation is part of my Masters I’m providing most of the hardware and labour, the costs involved aren’t being passed on the Creekside Discovery Centre. As with most projects it’s actually labour that’s are often the largest overhead. The centre is supported by a fantastic body of volunteers and I see no reason not to join them. So it’s really just the hardware costs that become fixed. Raspberry Pi’s sell for under £20.00!! What a brilliant price point for such a phenomenal computer. The DS18B20 sensors are around £2.00 – The CAT6 network cable is probably the biggest outlay at around £100 – but luckily the Creekside Centre had a drum of it already.
So hopefully the proposal will inspire them to give me the go ahead. CDC-Install-DFT-001