The experiment is stopped. The Logger has malfunctioned and is in a location that I cannot access. I will fix it and resume as soon as possible.
I’ve previously wanted to know how much do cheap led strips last: turned out they don’t even pay for themselves over incandescent bulbs. I’ve decided to extend the experiment to more kinds of strips and address some concerns about the experiment expressed by the readers.
LED logger V 2
In short: 8 channels, internet connected for live data visible by anyone. The experiment is trying to measure the light intensity variation over time, while maintaining the environment conditions constant.
Power supply: all strips are designed by their manufacturer to be powered from 12V. A 12V stabilized supply is used to power everything. In the first experiment I have periodically checked the voltage across the strip and found it to be constant. Now, the voltage is measured and plotted.
Temperature: all the strips together will dissipate around 2-3W and are placed on a big aluminum plate which is the box front panel. With what I have so far (4 working nonstop) the temperature of the panel raises 6 degrees C above ambient. The whole box is placed in a well-ventilated area inside the house, with an ambient temperature around 25 deg C, with small variations throughout the year. Therefore the strips are well cooled and operate in a rather constant temperature.
Sensor degradation: in order to verify that the sensor is still reporting correctly I have installed a strip that will only be lit for a short time at each measurement to check that the sensor has not changed. By measuring a strip identical to the first I have found that the sensor produces identical results, so there is no degradation over the 1400 hour time first experiment.
Here’s how the current data looks like: https://cosm.com/feeds/82160 . For more information about the strips, see below.
NOTE: At the moment the software has 2 bugs: It sometimes stops updating, although the LEDs remain on. So the values for the LEDs are correct, but may be old; i’ll periodically reset the device to ensure fresh data is available. Also, the PSU voltage seems to have measurement errors at the first readout(I’ve checked with a voltmeter, there’s no fluctuation in the PSU). So, out of order values for PSU voltage should be ignored.
Meet the candidates
The control strip is identical to the strip used in the first experiment, except that is has not been used. It turns out that it produces the exact same readout as the first strip, meaning that the sensor has not been degraded over the 1400 hours of initial test. The control strip and the original strip are the best aligned to the sensor.
Strip 1 is the strip used in the first led logger. It starts with a 1400 hour usage.
Strip 2 is made by Optoflash, it’s similar to the others except that the light is cold white. It’s a bit more expensive, comes from TME and there are no details about lifetime in the datasheet, but at least there is some sort of datasheet.
Strip 3 is an Ikea ledberg strip. It’s rated at 20.000 hours, but without any info as to how this time is measured.
Strip 4 is actually a waterproof module from a local shop that I paid about 1 EUR for. I don’t know anything more.
Strips 5 to 7 will be determined and added later.
Its PCB is developed from that of the ego box, replacing the 7 segment drivers with 8 channel high power drivers. Everything is based on tuxgraphics.org web client and someone has already done the task of making it work with Cosm (ex Pachube).
Schematic is quite trivial, you have your micro, your Ethernet chip and some MOS transistors to drive and control the LED strips.
Everything is built around the same box used in the previous project. The three wires in the middle are for three extra channels.
The intensity of each channel is measured every hour by turing all channels OFF and then measuring each intensity. After that, all the strips except the control turn back on. Data is uploaded to Cosm and can be found here https://cosm.com/feeds/82160.
Now it only needs time to add data points and check how these strips compare.