Project (part 2)

Images of blind interface with frame

Presently, work has begun on cadstar editor with the schematic designs of the main board containing the Basic Stamp microprocessor and two seperate boards for the H-bridge, one for each motor. Once they are complete they will be transfered to PCB design and built. 

Click on images to enlarge

Basic stamp control board schematic

This is an image of the schematic drawing that was designed on cadstar. From the basic stamp to components it shows pins 1-4 are connected to 9pin RS232 for interfacing to the stamp to upload program. Pins 5-7 are connected to a Light to Frequency converter,  and pins 8-10 are going to the DS1302 trickle charge time keeping chip. Pins 11 and 12 are for a remote control over ride switch which will be interfacd at a later date. Pins 13-15 are for the up down motion of the blind and pins 16-18 willcontrol the tilting of the blind. Pin 19 is an input from the revolution sensor at the motor that controls the up/down and pin 20 is inputing from the tilt motor.

H-Bridge schematic

This is a schematic for one of the H-Bridge circuits that will either control the tilt motor or the up/down motor. The Opto-coupler is used to send control signals to the transistors on the H Bridge as the basic stamp cannot source or sink sufficient current to drive the transistor. The schematic design on the next page shows the actual H-Bridge with the Opto-coupler so when appropriate binary commands are sent to the H-Bridge, depending on which code, the internal LED's will activate it to determine which motion to take. The KB847 (4channel) is optically coupled isolators containing a GaAS light emitting diode and an NPN silicon phototransistor. Below is a schematic of what the internals look like inside the KB847 chip.

Basic Stamp control board PCB artwork

This is an image of the PCB design for the Basic Stamp control board, showing both sides of the board including the components.

H-Bridge PCB artwork

An image of the PCB artwork for one of the H-Bridge boards, again showing both sides and all components.  There are two of these, one for tilting the blinds and the other to control the motor for raising and lowering the blinds.

In order to interface the motor to the blind, it proved difficult to find a suitable coupler nut so the idea I came up with was to strip the plastic off an electric joiner. Inside the plastic was the perfect soloution to the problem. As shown in the image's below, the way of the interfacing from the motor to the blind can be seen.

Here we have a pair of electric wire connectors.

Once the plastic was striped away, it shows a perfect part for the job. This will be used to lock the shaft of the blind to the dc motor.

The motor that was used for the tilting motion was sufficient enough at 100:1 ratio. The motor for raising the blind needed to be 250:1 ratio. This allowed a better pull for raising the blind fully.  While raising the blind the 250:1 ratio drew current from 0.23 amps to .6 amps at its max point.

The boards are now complete and all components are soldered in place. While debugging the H-bridge boards it was noticed that on the schematic design, the PNP transisters were not mirrored proparly. This caused some confusion but was easily fixed by twisting pin 2 to fit in pin 3's location and for pin 3's leg twisted to fit in pin 2's location. From furter testing this proved to fix the problem. A simple program was then written on the Basic Stamp editor to send a control for a forward motion and sent out through the RS232 connection on the main board, which proved successful. The same was done for the reverse motion. Now that the boards are working well together, the next thing will be to get the software up to scratch and to interface with the other components on the boards, such as the Light to Frequency converter and the time keeping chip. There is also a remote control over-ride to be interfaced and a thermistor.

12V Remote control On/off 2 Channel momentary relay

The Basic Stamp control board with the two H-bridge boards stacked on top of each other.

The image above shows the two H-Bridge boards stacked on top of each other and the main control board. The multi-colored wires connecting into the H-bridge boards are for the FWD, REV, and ENA controls from the basic stamp. Directly left are two brown wires which go to the 12V Remote control On/off 2 Channel momentary relay for the A and B buttons.

After creating some test programs to successfully run the motors on the blind the next step was to start mounting the boards in a housing unit. In the image below, you see a power supply coming into the board. This was made from a laptop lead that will transform the power from 240V down to 12V and 5V. The 12V is connected to the remote control receiver and the 5V will power the boards.

The two H-Bridge boards are stacked on top of each other and fixed in to the back of the unit and the  basic stamp control board is then fixed to the lid so that the light to frequency sensor and the RS232 serial connector will be on the outside of the unit, thus allowing an easier program change or upgrade.

 The complete unit was then fixed to the back of the frame and the motors connected from the back. Below is an image of the completed automation system unit, ready to use.

The main frame to display the blind was welded together with 20mm box iron and coated with red oxide paint to prevent rust before been sprayed matt black. A timber strut was fixed to the top rail of the frame to hold the blind. Once the blind was in place the motors were then positioned and fixed to the blind control mechanism.

Below is a movie clip of the automatic blind working with a gas lighter to simulate the sunlight at the light to frequency sensor and the remote control raising and lowering the blind.

Safety and Ethical Considerations of the Project

A major safety concern for non-automated blinds in the home is the cord which is a choking hazard for young children. However with the automated blind there is no cord so this hazard is eliminated.

Another hazard could be someone catching their hand in the blind when it was automatically moving. A simple over current protection circuit could be incorporated in the design that would cut off the power to the motors if such a scenario arose.

The other issue which was noticed during testing was the noise generated from the motor. This would need to be much lower for productions of multiple units.

It was also noted that different motor sizes would be needed depending on the size of the blind as a larger blind would require more current to drive the motor due to the weight of the blind as it was been raised. This would require a lot of research into standard blinds available on the market today and different motors that are readily available.

Before production of multiple units the automated blind would need an electrical safety classification and a rigorous safety test to be carried out.

A Final test procedure would need to be devised in order to have a Quality product.

Protection codes would need to written into the software in order to have better control of the blind e.g. No tilt allowed when blind is fully up. Alternately a sensor could be built into the blind to detect end stop positions.

Conclusions and Recommendations

It was a fantastic experience to work on this project over the past 7 months. The automatic blind now works under certain conditions in the software but could be extended a lot further which would take a considerable amount of time to finalize.

A thermistor circuit can be introduced at P14 and P15 on the BS2 which can be then used to read in the temperature with pre-set values. These values could then be implemented into the software code to control the blind motions depending on room temperature.

While de-bugging the boards during the testing stages an error was found on the schematic design for the H-Bridge in Cadstar. The PNP symbols were not properly mirrored thus placing pin 2 where pin 3 should be and visa versa. This was quickly corrected by twisting the legs on the transistors as a temporally solution.  As time was running out it was not feasible to remake these boards.

A lot was learned throughout this project and if it was to be re-designed, the following recommendations could be applied:

The basic stamp could be multiplexed to allow for extra sensors and applications.

PCB boards could be made a lot smaller and neater designs which would allow for a more convenient appliance to fit on the blind.

The motors used in this design would not be sufficient for anything bigger than the display model and are very noisy. This would allow for more research into a real world scenario where these issues could be solved.