REUK Super Timer with Light Detector Override

Posted on May 28, 2014 by neil

Pictured below is a new device which mixes the features of the REUK Super Timer 3 and the REUK Dawn/Dusk Lighting Controller.

The timer can be programmed with different ON and OFF time durations from 1 second to 99 hours with various modes of operation available. When the time is ON, there is a 12V output (rated at up to 1A) which can be used to control up to 10-12 Watts of 12V devices, or used to switch a relay if higher currents or different voltages are to be switched.

The modification is the addition of a light detector (light dependent resistor) which is used to override the timer at night time. When the ambient light level is measured to be less than the user set threshold, then when the timer is ‘ON’ the output remains off.

This particular board is for an automatic fish feeder which directly drives a small motor, and the override is to prevent the feeder operating at night.

If you need a timer similar to this, email neil@reuk.co.uk with details of your exact requirements.

Low Voltage Disconnect with LCD Display

Posted on May 20, 2014 by neil

Pictured below is our latest low voltage disconnect circuit with LCD display.

As with our standard programmable low voltage disconnect (LVD), this device is designed to protect batteries from being discharged too deeply and permanently damaged. The user can set the low voltage at which the output loads will automatically be switched off, and also the higher cancellation voltage above which the output loads will be switched back on again.

This particular LVD has a backlit LCD on which system information is constantly displayed. It is also used when setting the low and high voltage thresholds which makes things a lot clearer and simpler than using LEDs or a rotary switch to programme those in.

As shown above the display shows the measured battery voltage updated multiple times per second and given to 2 decimal places of resolution (and calibrated to be accurate to within +/- 0.02 Volts across the range 10-16V).

The system status is usually ON or OFF, but can also be LOW or HIGH when the battery voltage is transitioning one of the thresholds about to change the state of the system. The high and low threshold voltages are also permanently displayed.

In order to avoid the output cycling on and off too often (particuarly as the battery voltages can spike or dip depending on the loads they are powering) there is a time delay during which the voltage must remain under/over the voltage threshold before the system will change from ON to OFF or OFF to ON respectively. During that time delay the backlight of the display flashes as a visual indicator that the threshold has been breached. We chose to flash the display itself rather than flashing an LED either on the board or on leads, since it is much easier to panel mount just the LCD than to mount both that and an LED indicator.

This particular client-tailored LVD has a MOSFET directly switching the output loads which can have a maximum total rating of 3 Amps. We can also make this with a relay fitted on board for direct switching, or a lower rated output which can be used to energise a high current (or high voltage) rated relay external to the board – e.g. an automotive relay or a solid state relay (SSR).

This low voltage voltage disconnect with LCD is now available direct from the REUK Shop. Click here to find out more or to purchase now: buy REUK Low Voltage Disconnect with LCD.

We will shortly be adding a very similar unit with the addition of datalogging functionality. Over the last couple of years we have sold many LVDs with built in dataloggers (see here for an example: Low Voltage Disconnect with Display and Datalogger), and we now have refined things to the point that the product is ready for general sale. In the meantime, if you have any requirement for a low voltage disconnect with or without a display and with or without datalogging, please email neil@reuk.co.uk with details of your requirements.

Frost Warning Thermostat with Temperature Indication

Posted on May 13, 2014 by neil

Pictured above is a project we have recently completed for a special thermometer thermostat for an automotive application. The requirement was for a device which would show the temperature using LEDs, and would sound a warning buzzer for a couple of seconds when the measured temperature falls to or below a user set temperature threshold (in this case chosen from within the range 3- 5 degrees Celcius).

A waterproof temperature sensor was required for this project, and good accuracy and reliability was also essential. Therefore we chose to use a stainless steel encased DS18B20 digital temperature probe – the same sensors we use in our swimming pool solar water heating pump controllers amongst other things.

The button on the circuit board can be pressed by the user to change the temperature at or below which the attached buzzer will sound. When the temperature is above 5 degrees, both red LEDs are on. When the temperature is below 3 degrees, both green LEDs are on. When the temperature is in the range 2.76 to 5.24 degrees the LED which corresponds to the nearest temperature to that measured it on.

If you need a thermometer or thermostat along similar lines to this unit, email neil@reuk.co.uk with details of your exact requirements. We can also add 16×2 LCDs (displays) upon request.

Solar Water Heating Swimming Pool Controller with Display

Posted on May 7, 2014 by neil

Pictured below is another of our solar water heating pump controllers – this time with digital waterproof temperature sensors (DS18B20), and an LCD to show the measured temperatures of the solar heating panel and swimming pool as well as system status and for the user to programme in the settings.

As this controller is to be used in sunny Australia it includes a pre-programmed maximum temperature override to prevent the swimming pool from getting too hot. When the pool is measured to 31 degrees Celcius or hotter, the pump will not to be turned on again until the pool temperature has fallen to 28 degrees.

Pictured above is the LCD showing the solar panel temperature of 26 degrees C, and the pool at 32 degrees C. Therefore the pool is too hot and even when the solar panel temperature increases, the pump will not turn on.

At the bottom of the circuit board is a pair of screw in terminals which will be connected to the output from a 12V programmable digital timer. In the winter, the customer for this controller wants to be able to automatically run the pump at the same time each day for a certain time just to circulate water around the system.

If you need a solar water heating controller for any application, with or without a display, email neil@reuk.co.uk with details of your exact requirements.

Raspberry Pi GPIO Sensor Readings to Twitter

Posted on April 17, 2014 by neil

We have just published a new article Publish Temperature Sensor Readings to Twitter with Raspberry Pi to the REUK.co.uk website which includes full details on how to get sensor measurements from a Raspberry Pi up to the internet for remote viewing.

We will soon be returning to this to look at how batteries can be monitored, solar generation can be monitored, and many other similar projects.

We will then be showing how devices can be controlled from Twitter – for example, you could turn on your immersion heater element with a Twitter message if your Twitter feed tells you that your water tank is cold and you are on the way home and would like a hot bath.

Arduino Datalogger Testing

Posted on April 15, 2014 by neil

We recently built and tested a very simple SD card datalogger based around an Arduino Pro Mini – the smallest and cheapest Arduino board commonly commercially available. We have previously described datalogging to an SD card with an Arduino in our blog post Arduino SD Card Datalogging (to log temperatures). In this example we are instead logging the voltage of a solar charged battery used to power the lights in a shed.

The Arduino Pro Mini (£3) was programmed from a PC via an FTDI breakout board (£5), and connected to an Arduino micro SD module (£1) fitted with a 1GB micro SD card (£3). Note that the unlabelled components in the image above are not required for this datalogger – we just built the controller so that it can later also be used as a low voltage disconnect.

We programmed the Arduino to read in the voltage of a 5Ah 12V SLA (via a 47K-10K voltage divider) and write it to a log file on the SD card once every second. The battery is connected to an 80 Watt PV solar panel via a solar charge controller. The battery is also connected to three 1W LED spotlight bulbs which were left permanently on so that the battery would drain over night and be recharged during the day.

The datalogger was left connected to the battery from around 10:30am one day to around noon the following day in mid-April with blue skies both days.

In order to view the data collected on the micro SD card we just needed a USB all-in-one memory card reader (£1). Plug the micro SD card into the reader, plug the reader into a PC via USB, and download the collected data.

The collected data file (which was simply a list of voltages measured to 2 decimal places) was 97070 lines long with a file size of 680 kB. Therefore our 1GB card could have logged the battery voltage once a second for 3-4 years.

Looking through the datalog in a text editor it was obvious that the battery voltage did not change very fast at all. Therefore logging the voltage every second was unnecessary for this application – every 30 seconds or every 60 seconds would have been adequate.

Knowing from experience that plotting 100,000+ data points with Excel is usually an unhappy experience, I first copied the log file over to my Raspberry Pi, and ran the following sed script to create a new smaller file containing just every 60th record from the log file. (This is equivalent to having set up the datalogger to log the voltage once per minute in the first place.)

sed -n '0~60p' logfile.txt > 60slogfile.txt

This command took just 0.24 seconds on the Raspberry Pi (thanks to the raw speed of sed) and I then dropped the new smaller (1617 records) log file into Excel and made the following plot of the results.

The vertical axis shows the measured voltage, and the horizontal axis shows time with the far left being 10:30am on day1 and the far right being noon on day2.

The plot shows how the solar charge controller carries out a bulk charge phase to rapidly charge the battery (peaking at 14.6V) and then maintains a float charge (around 13.6V) during the day while the solar generation far exceeded the charge used by the spotlights. At night the voltage of the battery drops rapidly down hitting a low of 11.95V before the sun rose high enough to start to charge the battery again.

If you need a voltage datalogger like this, a voltage datalogger with a built in low voltage disconnect to protect the battery from being too deeply discharged, or any other kind of single or multi-channel datalogger, please email neil@reuk.co.uk with details of your exact requirements.

Automatic Irrigation System with Moisture Probes

Posted on April 5, 2014 by neil

Pictured below is a controller we recently made to automate watering of plants depending on the moisture level of the soil in which they are growing.

This device measures the resistance between two stainless steel probes made from 1.6mm arc welding rods (pictured below) to which leads have been soldered, and inserted into the soil a few centimetres apart. When the soil is measured to be ‘dry’, a pump is turned on which waters the soil. When the soil is subsequently measured to be ‘wet’, the pump is turned off, but only if it has already run for a user programmable number of minutes first.

To provide default wet and dry thresholds, the resistance between the probes was measured at what the user considered to be the dry and the wet threshold. These values were 36.5 kOhms or lower for wet, and 229 kOhms or higher for dry (with the probes inserted 7cm into the soil, 6cm apart). Therefore we programmed the controller to turn on the pump after 5 continuous seconds of resistance measured to be below 36.5 kOhms, and turn off after 5 continuous second of resistance measured to be above 229 kOhms.

Since different growing mediums may be used in the future, we also made this controller so that the user can calibrate the wet and dry thresholds themselves or revert to the default values. Calibration is achieved simply by putting the probes into soil which the user considers to be at the wet or dry threshold, and pressing a button to save the measured resistance value in memory as the new threshold.

If you need an irrigation controller similar to this, please email neil@reuk.co.uk with details of your exact requirements.

Low Voltage Disconnect with Early Warning Alarm

Posted on February 19, 2014 by neil

Pictured below is another of our low voltage disconnect (LVD) circuits designed to protect batteries from being overly discharged.

This particular LVD has a few added features. First of all, to reduce power consumption by the LVD itself, it has been designed to work with a latching relay. The chosen relay (click here to download the latching relay datasheet) has two coils – one coil to latch the relay closed (set coil), and the other to release the relay (reset coil).

This controller can be programmed as per our standard REUK Programmble Low Voltage Disconnect with the disconnect voltage and cancellation voltage. While the voltage is good, the relay will be left latched closed, and then when the voltage falls below the disconnect voltage, it will be latched open.

As an added feature, when the measured battery voltage is 0.2V or less more than the disconnect voltage, the external LED (which can be panel mounted somewhere easily visible) turns on, and an on board piezo buzzer sounds briefly every half a minute until either the user starts to charge the battery, or the disconnect engages due to even lower measured voltage.

If you need any kind of low voltage disconnect circuit, email neil@reuk.co.uk with details of your exact requirements.

Dawn Dusk Automatic Hen House Door Controller

Posted on February 14, 2014 by neil

Pictured below is a hen house door controller which will automatically open the hen house door in the morning and close it again at night to protect the birds from foxes and other predators.

This controller is somewhat based around our Simple Hen House Door Controller which uses a low voltage programmable digital timer to set when the door should open and close.

This version instead takes an input from a light detector (click here for our article introducing Light Dependent Resistors), and uses this to detect dawn and dusk.

When dusk begins, the motor turns one way to lower the door until it presses against and closes the lower roller switch which acts as a limit switch. Similarly, when dawn begins the following morning, the motor turns the other way to raise the door until it closes the upper roller switch.

(For the explanation of how the polarity of the voltage sent to the motor is reversed see our introductory article: Automatic Hen House Door Controller).

In order for the user to set the light level threshold at which day becomes night and night becomes day, a programming button is provided on the circuit board. When the ambient light level is at the level considered by the user to be the threshold, they press this button while powering on the controller to save that measured light level as the new threshold. The threshold is stored in permanent memory and is therefore not lost even when the controller is subsequently disconnected from the power.

Pictured above is a functionally identical controller, but which is built around an Arduino Pro Mini instead of the PICAXE-18M2 used in the original. The instructions for this controller are available here: Dawn Dusk Henhouse Door Controller Instructions.

If you need any type of door controller contact neil@reuk.co.uk with details of your exact requirements.

Automatic Low Voltage UPS Shutdown

Posted on February 14, 2014 by neil

Pictured below is a special low voltage disconnect controller designed to switch off an uninterruptible power supply (UPS) when the battery bank to which it is connected is low on charge.

The system for which this controller was built is as follows. A 72V 2.3 kW solar PV array is connected to a 48V 50A MPPT solar charge controller. The charge controller charges a 48V battery bank (made up of an array of 12V batteries); and that feeds a 3.5 kW UPS which supplies electricity to the house.

The UPS does not have a low voltage disconnect feature and so from time to time the batteries were being discharged too far. Obviously the owner wanted to avoid this as the battery bank is a very expensive part of the system.

This particular UPS has a standard female USB port on it, and if its pin1 is shorted out with one of its other pins, the UPS switches off.

Therefore our controller is a slightly modified version of our standard programmable low voltage disconnect. One of the 12V batteries in the battery bank is constantly monitored. If the voltage measured stays below a user set low voltage threshold (e.g. 12.0V) for 10 seconds, the on board relay closes for 2 seconds which shorts two of pins in the USB socket and forces the UPS to switch off immediately. Therefore the battery bank is protected from being run down excessively.

REUK.co.uk

The Renewable Energy Website

Category Archives: electronics