New Solar Water Heating Pump Controller with Waterproof Sensors

Posted on July 16, 2013 by neil

Pictured below is our new solar water heating pump controller with waterproof sensors. It is heavily based around our standard 2013 Solar Water Heating Pump Controller, but modified to use waterproof DS18B20 digital temperature sensors in place of the LM335 analog temperature sensors we normally use.

Solar water heating pump controller with waterproof temperature sensors As it can take up to 0.75 seconds for the controller to get a reading from a DS18B20 sensor, and since sometimes digital sensors output spurious data, there have been some modifications made to the logic which decides when the circulation pump should be turned on and off, but all the original functionality of the 2013 controller has been retained.

This controller is ideally suited for use with swimming pool and hot tub solar water heating systems as well as many other applications where having waterproof temperature sensors is essential.

We will shortly be adding this new product to the REUK Shop, but in the meantime, if you are interested in purchasing this controller or something similar to meet your exact requirements, email neil@reuk.co.uk.

Project of the Day – Low Voltage Disconnect for Powered Snorkel

Posted on June 26, 2013 by neil

Today’s project was a very particular low voltage disconnect for a powered snorkel system for recreational divers. The diver’s face mask is connected to a 5 metre long hose which is in turn connected to a buoy floating on the surface. A 12V battery powered diaphragm pump forces air from the surface down to the diver to breathe. Using such a system as opposed to scuba has the benefit of requiring no certification, gives a safe fixed maximum diving depth, and is lightweight and non-polluting.

The system is powered by two series-connected 6V 8Ah AGM batteries (a type of deep cycle battery which is sealed and can be used inverted) and gives 1 hour of dive time before needing to be recharged. The problem is how to let the diver know that the battery is low and protect the batteries from being overly discharged.

A piezo type warning buzzer could not be used since in a group of divers underwater it would be very difficult to ascertain whose buzzer was sounding, and a warning light would not work since this system would be used in tropical waters in bright daylight at shallow depths.

A generic low voltage disconnect could also not be used since it would just cut off the pump and therefore the air to the diver with no warning when the battery voltage breeched the set low voltage level. Instead something was required which would over the course of a few minutes cycle the pump on and off to reduce the air pressure to the diver forcing them up to the surface. (The system is an open circuit with a rebreather bag, and so turning the pump on and off reduces the pressure of the air supplied, but does not result in there being sufficient air one second, and then no air at all the next.)

There are commercial PWM (pulse width modulation) solutions available, but they are very expensive and could not give the exact shut down sequence desired – bringing the air pressure down to 90%, 80%, 70%, 60%…and so on over three minutes when the battery voltage gets low.

Therefore we made the special low voltage disconnect controller pictured above. This device constantly monitors the battery voltage, and when it falls and remains below a set threshold (11.2 Volts) the shut down sequence begins.

For 20 seconds the pump is off for 1 second then on for 9 seconds, off for 1s then on for 9s. Then for the next 20 seconds the pump is off for 2 seconds on for 8 seconds, off for 2s on for 8s. This process is repeated every 20 seconds increasing the pump off time and therefore reducing the air pressure to the diver so they have to surface, but can do so safely and without panicking.

Project of the Day – Digital Competitive Shooting Range Timer

Posted on June 26, 2013 by neil

We have just finished working on a digital timer for competitive shooters to use at the range, but this type of timer could be turned to many different applications with minimal alteration.

In front of the shooter is a table with a pressure pad which detects the presence of a gun resting upon it. When the gun is lifted, the timer starts and the shooter attempts to hit each of five targets in turn. When the fifth and final target is hit, the target closes a micro-switch which stops the timer, and the time taken to hit the five targets is displayed.

In order to complete this project we needed an accurate timer and minimal wiring complexity, so we used the Arduino system but using its ATmega328 microcontroller chip as a standalone with external 16MHz clock crystal and capacitors, and an L7805 5V voltage regulator instead of using a full Arduino board.

The maximum time to be recorded by the timer is 90 seconds. (Typically shooters will have a limit of 50 seconds to hit all five targets, but may take up to 90 seconds initially.) We therefore needed a 4-digit display to show the seconds and hundredths of seconds of the elapsed time up to a maximum of 90:00.

We chose the excellent Adafruit 7-segment 4-digit i2c display with Backpack. This device has its own chip which does all the hard work and means that only two output pins from the Arduino are needed to drive the display (clock and data) together with a 5V and 0V connection to power it.

The accuracy of the timer comes from using the Arduino millis() function which returns the number of milliseconds the sketch (program) has been running. The exact time when the gun is lifted from the pressure pad is noted, and each time the display is refreshed (every tenth of a second) the start time is subtracted from the current time to display the time elapsed since the shooter picked up the gun. When the final target is hit, the start time is subtracted from that time and left on the display until everything is reset for the next shooter.

If you need something like this please email neil@reuk.co.uk.

Offer of the Day – 88Ah Deep Cycle Battery £56.95

Posted on June 18, 2013 by neil

Our recommended offer of the day is this 12V 88Ah deep cycle battery offered in the UK at just £56.95 including delivery (to mainland UK locations south of Glasgow/Edinburgh). As the image above shows, order this battery before 4pm to have it delivered next day, and it comes with a 4 year warranty.

This battery has dimensions of 257 x 172 x 220mm and is suitable for solar charging as well as for general leisure and marine usage.

Click here for more information or to buy this 88Ah 12V battery now at this low price.

Bricking a Beaglebone Black

Posted on June 14, 2013 by neil

In a previous article we introduced the Beaglebone Black – a low power, low cost, credit card sized Linux computer available in the UK for around £35 and just $45 in the USA. We have been using the Raspberry Pi since it was first released in early 2012, so we were very interested to try out this similarly priced alternative which promised greater processor speed, 2GB of on board eMMC flash memory for the operating system, and most importantly for the work we do, 7 analog (ADC) inputs compared to zero on Raspberry Pi.

We received our Beaglebone Black (pictured above) around a week ago, and have been playing around with it in any spare time. Getting it set up was very quick and easy following the instructions served up as a webpage from the BBB itself. But then today something went wrong.

While looking on the internet to find any recommendations/suggestions for a VNC (virtual networked computing) server for the BBB I found this recent blog posting by Roger Meike which went through the steps he took to successfully install the X11 VNC server on his Beaglebone Black. This enabled him to interact with its full graphical interface / desktop through his Mac instead of having to hook the BBB up to a separate monitor or TV or only being able to use the command-line interface terminal via SSH.

So, step one, connect the Beaglebone Black to the ethernet cable and USB cable – check everything is working as it should via SSH. Step two, update and upgrade the Ångstrom Linux distribution installed on the Beaglebone. So far so good – seemingly. The command opkg update took very little time to run to completion; the command opkg upgrade took the best part of an hour and a half to run, but didn’t show any errors, and after it was completed everything was working as it had previously – no problems evidenced at all.

Before embarking on the X11 VNC server installation I decided to reboot the Beaglebone Black, so I entered the reboot command. Next time I looked at the BBB a few minutes later 3 of the 4 user indicator LEDs were fixed on instead of their usual flashing. I attempted to SSH in but could not connect, and entering http://192.168.7.2 via my web browser (which is the usual way of accessing the BBB when it is connected to your computer via USB) resulted in ‘This webpage is not available’ error message.

It appeared that something had gone wrong somewhere, but the start up guide mentioned that the LEDs are fixed on while the eMMC is being flashed with a new distribution from the SD card and that process can take up to 45 minutes. On the off chance that upgrading the distribution without the SD card results in the same thing (and not wanting to turn it off if it was actually doing something), I left the BBB alone for a couple of hours, but the LEDs just stayed on.

I next pressed the on board reset button. The LEDs turned off, then one turned on (PWR LED), then another turned on (labelled D2), and then a few seconds later LEDs D3 and D4 turned on and stayed on permanently.

Next I unplugged the USB cable and left the Beaglebone Black disconnected from the power that cable supplies for a few minutes. When I reconnected the USB cable to the computer, nothing happened – the computer could not see the BBB whereas it previously recognised it immediately as a USB mass storage device when it was connected. But the LEDs still came on.

I tested there was nothing wrong with the USB port on the computer – it was fine; I tried connecting the BBB to alternative USB ports on the computer, and still nothing, just the LEDs permanently fixed on.

I then hooked the BBB to a monitor via HDMI, but still nothing. It seems that it has turned into an illuminated brick.

Looking around on the internet I found this guide to unbricking Beaglebone Black without Erasing eMMC, as well as comments from other people who have run into similar problems with their BBB. It seems the only way to fix this is to download the latest Ångstrom distribution on another computer, unzip it, get an image writer for Windows, write the image to the SD card, boot from the SD card, and then wait for the image to be copied across to the eMMC. But, this requires a microSD card which I don’t have, and a lot more time. Also, quite a few stories of people going through this process and ending up with an un-bootable BBB. Is it necessary to do this every time the distribution needs updating??

I’ve never had any problems with any Raspberry Pi, and I have some which have been running continuously for months without crashing or any other issues. Therefore this bricked Beaglebone Black is going to be returned – not to be exchanged for another Beaglebone, not for a refund, but for another Raspberry Pi. Sometimes the grass is not greener on the other side – I just wish that the Raspberry Pi GPIO included some analog inputs!

As Nigel D wrote regarding the advantage of Pi over BBB: having the boot stuff and OS on removable media means that bricking the board is that much more difficult, makes it easier to experiment between different operating systems, and makes full backup and recovery easier.

Project of the Day – 12V High Power Regulator with LT1084CP-12

Posted on June 13, 2013 by neil

We supply a lot of low dropout 12V regulators – primarily for use with LED lighting when powered from 12V batteries (particularly in vehicles) to get a clean 12.0V output. These regulators are limited to around 0.7 Amps maximum output.

HIgh current 12V regulator based around Linear LT1084CP-12 regulator

The regulator pictured above is a special order 2 Amp rated low dropout regulator for someone who was unable to split a lighting circuit into multiple lower current circuits for regulation with our standard regulators.

It is based around the LT1084CP-12 low dropout regulator from Linear Technology. This IC is rated to supply up to 5 Amps, but it has a higher maximum rated dropout (the voltage difference between target voltage and input voltage below which output voltage falls below target voltage) than the LM2940 chips we use in our regular 12V regulators – 1.5V compared to just 0.5V with the LM2940. (The recommended minimum input voltage for the LT1084CP-12 is 13.5V.)

This higher dropout will not be a problem in this particular application since a) power will be coming from a vehicle battery – therefore maintained constantly at near full charge and voltage, b) only 2 Amps at most will be drawn from the regulator resulting in a dropout of 1V at most, and c) the output is to power LED lighting so if the voltage of the battery were ever to fall to a low charge level, the lighting would just be a a tiny bit dimmer – no harm done.

Click here for the LT1084CP-12 datasheet for more information, or here to purchase this chip: buy LT1084CP-12.

Raspberry Pi Temperature Datalogger with DS18B20 Sensor

Posted on June 12, 2013 by neil

We’ve been adding more Raspberry Pi related articles to the REUK.co.uk website over the last week covering GPIO – connecting sensors to the Pi, and also controlling relays connected to the Pi from the internet

Now we have moved on to cover temperature sensors, a very important part of the work we do relating to solar water heating systems. Being able to control a pump based on the temperature of one or more sensors is very powerful, but Raspberry Pi makes it (relatively easy) to also monitor those sensors over the internet and track the exact state of the system in real time remotely while also logging the data.

We have recently added this article on using the DS18B20 1-wire digital temperature sensor with Raspberry Pi: DS18B20 and Raspberry Pi. (Note that Raspberry Pi only has digital, no analog inputs – therefore we use digital temperature sensors with Pi rather than the analog LM335 temperature sensors we use with our primary solar water heating pump controller product.)

We also added a second article which shows how you can feed the temperature readings from the DS18B20 connected to the Raspberry Pi for to be logged and visualised by cloud service Xively: Raspberry Pi Temperature Datalogger with Xively.

When we have finished publishing these introductory Raspberry Pi articles, we’ll then move on to articles showing how to pull the techniques explored together to make renewable energy related devices with Raspberry Pi – e.g. wind speed dataloggers, solar controllers, energy monitors, energy saving automation devices, and much more.

New Raspberry Pi Category on REUK.co.uk Website

Posted on June 5, 2013 by neil

We have been doing a lot of work recently with Raspberry Pi so we have decided to start uploading a collection of new articles on Raspberry Pi and its uses in renewable energy and other projects.

There is already a lot of information out there on the internet, but we will be covering the first steps from opening the box to doing useful work with Raspberry Pi.

Our first article in this series is here: Connecting to Raspberry Pi from PC via SSH in which we show you how to interact with a Raspberry Pi from a Windows PC so that you do not need to invest in an HDMI cable, extra keyboard, and mouse. Click here for the Raspberry Pi category article list.

Special Offer of the Day – 20W PV Solar Panel £25.99

Posted on May 29, 2013 by neil

While the price per Watt of PV solar panels has been tumbling, the cost of smaller solar panels (<30 Watt) have remained relatively high in most cases because of the fixed costs of postage, and manufacturing without the benefit of scale.

Smaller panels are particularly useful for battery powered outdoor projects such as shed lighting, electric fencing, irrigation systems, and much more.

Pictured above is our special offer recommendation of the day – a high quality 20 Watt monocrystalline PV solar panel for just £25.99 plus £2.99 postage (and no extra postage if you purchase 2 or more of these panels).

This panel is 363mm x 529mm x 25mm in size and 2.5Kg in weight, and is fitted with 1.5 metres of cable and a bypass diode to prevent reverse discharge at night.

Click here for more information or to snap up one of these panels now: 20 Watt PV Solar Panel Offer.

Reducing Reflectivity of PV Solar Panels to Increase Efficiency

Posted on May 25, 2013 by neil

The US Department of Energy’s National Renewable Energy Laboratory (NREL) is carrying out research on reducing the reflectivity of PV solar panels to increase their efficiency.

Standard silicon solar cells (out of which solar panels are built) reflect around 35% of all the light which hits them – therefore one third of the solar energy hitting them is immediately lost. To reduce these losses, commercial solar cells receive an anti-reflective coating (gas molecule deposition) which brings down reflectivity to 7-10% typically. (It is this coating which makes solar cells appear blue). This process is toxic and the equipment used to achieve it is very expensive. Therefore NREL are looking at ways to reduces reflectivity of solar cells while at the same time reducing costs of manufacture.

NREL’s solution called black silicon uses an acid bath with a silver nitrate catalyst to put trillions of tiny holes into the surface of each 6×6 inch solar cell. These holes trap the photons of sunlight increasing the chance they will be absorbed by the solar cell and converted into electricity. With this technique reflectivity is reduced to less than 1.5% (which results in solar cells which appear black).

An added benefit is that solar cells treated in this way perform better in the morning and afternoon when the angle of the sun is further from the optimum (perpendicular), and they also perform well in overcast conditions.

NREL have exclusively licensed this black silicon technology to Natcore Technology specialists in thin film solar panel manufacturing. With further development they hope to make more efficient and cheaper solar panels than anything on the market today.