This listing includes the following:

• one TinyTracker HD single-axis solar tracking controller board
• Delrin stand-off and mounting screw, unassembled
• Hand assembled and tested in USA.

The TinyTracker HD is an efficient microprocessor powered, LED based sensor-and-controller-in-one meant for use with standard satellite dish linear actuators for PV and other solar tracking applications.

New Rev G firmware allows updating of EEPROM parameters with an Arduino based program (USBasp or similar AVR programmer required) including:

• Balance, daylight, sunlight, tracking period, max motor run time, max tracking run time, east-inhibit operation, secondary axis use, and pwm settings

Theory                                                                                               

The TinyTracker HD is named after the ATtiny85 microprocessor which controls its operation. The ATtiny85 is an 8 bit microprocessor with 8K of program memory, and is configured to run on its internal clock at only 1MHz to save power.  The microprocessor is equipped with 10 bit analog to digital converters (ADC) which read the voltage produced by light striking the LEDs.  Two digital outputs are utilized to control a standard H-Bridge motor driver circuit based on MOSFET devices. This allows the microprocessor to very efficiently control the direction of the current through the motor in an attempt to achieve a position where the light (voltage produced by the East and West LEDs) is equalized.

While it is commonly know that LED’s produce light from electricity, hence their name, it is less commonly known that they also produce a voltage in response to normal light striking the diode. Due to their size, LEDs produce an insignificant amount of power, but the voltage is easily read by a microcontroller.  Two LEDs at a 90 degree angle to each other form the core of the light sensor, while two additional LEDs provide a wider field of off-center light detection to help enable solar target acquisition.

Use of a microcontroller allows a minimum of electrical components and also enables the TinyTracker to be extremely energy efficient. The ATtiny85 chip draws less than 0.5 mA when the motor is not operating. By updating the motor position according to the Tracking Period, extraneous motor movements are avoided: reducing wear and also conserving energy.

TinyTracker operation may be affected by various environmental factors such as trees, clouds, ground color, reflections, and other extraneous light factors. The voltage from the LEDs and the 10bit resolution of the ADCs limit the theoretical resolution to slightly better than 0.5 degrees. The TinyTracker is primarily intended for PV tracking, and due to the factors mentioned, no minimum accuracy is appropriate.

Once light levels have fallen to “nighttime” levels, the TinyTracker will wait about 10 minutes (to make sure it’s not a solar eclipse or something else transitory), and then engage the “east-return” function. This causes the motor to run in an eastern direction until the limit switch is tripped. As the microprocessor has no knowledge of the actual array position, the east-return function runs for the specified Max Motor Run period. As long as your motor can at least return 50% from its western limit in this time, the TinyTracker should be able to reacquire the sun the following day.

Also note that the pulse output connections for positional sensing common to many linear actuators are not used by the TinyTracker. It is completely dependent upon limit switches stopping the flow of current to the motors when mechanical constraints prevent the unit from achieving the desired orientation, and the LEDs for determining what that orientation is.

In practice the TinyTracker often tends to return itself to a middle azimuth position (and horizontal panel position when used for elevation control) following sunset, and will acquire the sun the next day without issue. Battery power after dark must be supplied in order to enable the east-return function, if needed according to your mount and latitude.

Connections are minimal and should be made as per the illustration for your system. Note that a fuse and/or power switch may be desirable or required in many applications. Much of the documentation contains qualified statements because there are so many different situations with multiple solutions available.

When first turned on, the TinyTracker will run the connected motor West for aproximately 1 second, then East for 1 second. Reverse the motor wires if necessary to obtain the proper behavior. After approximately 10 seconds to stablize light readings, the first tracking action will be initiated, the next movement will occur after the regular tracking period has elapsed.

There are many types of tracking mounts where the TinyTracker can be used here are just a few:

Azimuth – these are the most common type of pole tracker.  Rotation is about the vertical axis, and the PV panel is usually set at a fixed angle.  The TinyTracker should preferably be positioned at the same angle as the panel, but may also be positioned vertically as best appropriate for your application.

Altitude-Azimuth – a second TinyTracker can be added to an Azimuth tracker to create a dual-axis tracker where the panel elevation angle is adjusted throughout the day as needed.

Polar – the axis of rotation is tilted from horizontal to match your latitude and point at the celestial North Pole. This is ideal for the TinyTracker.

Horizontal – this is a simplified version of the polar mount with a horizontal north-south axis. These are popular on flat rooftops and along north-south roof ridges. These work best at lower latitudes.

Light Vane: Use of light vane (not included) is optional according to your requirements. A properly designed external light vane can increase tracking accuracy. A longer vane will cause more of a shadow to fall on the LEDs which will increase sensitivity.

LEDs: the two LEDs that are 180 degrees apart (East and West) are intended to help increase the effective field of vision. This can help the tracker re-orient itself in the morning if the east-return function did not work due to lack of power after sunset (if the tracker is powered by PV instead of batteries); however, in some circumstances this may not be desirable. For instance: with a dual-axis controller using the TinyTracker for elevation control (rather than Azimuth or Right Ascension angle), movement will be 90 degrees maximum. In this situation using a piece of tape to cover the outside LEDs will improve performance.

Supply Voltage: The TinyTracker is designed to handle a wide range of input voltage to allow operation from unregulated 12v PV panel output; however, unregulated 24v PV output may exceed the maximum rating (30vdc) for the MOSFETs. The TinyTracker board features a blocking diode to prevent reverse polarity damage to the logic portion of the board, however the MOSFETS can still be damaged by reverse polarity. ALWAYS CHECK DC POLARITY before connecting power to avoid accidental damage.

If you are using an AC adapter power supply instead of PV or battery, then a 24vdc 5.0 amp rating is recommended.

Motor Amperage: The MOSFETs have very high current handling capability under ideal conditions. Inside a hot enclosure in the sun is not ideal, and obviously those conditions will vary.Good standard engineering practice is to de-rate by 50%. In this case we'll say approximately 8A max. More important than actual amps, are the watts used by your motor (Volts x Amps = Watts) as this will determine the actual heat dissipation factor for the electronics.  The maximum wattage recommended is 200. Remember we’re trying to make more energy, not use it all up with the tracker! The PMA linear actuators sold by HomeCSP, and other common satellite dish actuators, draw slightly less than 0.4A at 24vdc, while heavy duty actuators typically draw 5-7A peak under load, and the TinyTracker HD easily handles that. Solar tracking motors should move slowly. Your motor should take at least a minute to go from one side to the other.

PWM is now supported by the TinyTracker HD 2.06!.

Enclosure: Painted or opaque enclosures with a clear window tend to function as small solar ovens and increase the operating temperature for the electronics, and are not recommended.  The recommended enclosure for the TinyTracker is a clear PET plastic jar (16 oz, 3" opening, 3.25" tall) or similar container.  The TinyTracker is easily fastened to the lid with a small stand-off, and this provides excellent weather protection and visibility for the tracker. Make sure the enclosure is water tight. Waterproof conduit and fittings are recommended to protect the wiring as well. A small desiccant package of silica gel can help prevent dew point condensation on the inside of the enclosure, but is not intended for absorbing leakage. For best results bake the silica gel packet a low temperature to remove all moisture before sealing in the enclosure. For adjustment and alignment, make sure that you can rotate the enclosure as needed about an axis parallel to that which the TinyTracker will be controlling.

Location: For a south facing panel in the northern hemisphere, the north-east corner of the array is the generally preferred location to mount the TinyTracker. In the southern hemisphere, this becomes the south-east corner. East-West trackers should be mounted on the top or bottom, while elevation axis controllers should be mounted on the side.

Limit Switches: Most linear actuators come with built in limit switches. These prevent the motor from destroying itself or the mechanical components by moving the actuator too far.  Rocker switches are normally used and are configured in a Normally Closed manner. They are also used in conjunction in blocking diodes to allow the motor to reverse direction while the limit switch is open. If you are using a motor without built-in limit switches it is essential that you incorporate these into your design. Failure to properly adjust limits can result in mechanical damage as well as motor stall conditions which may damage electronics!