Introduction

This is the design of a mechanical flower which is sensitive to light and moves in the direction of light. It is powered by a 5V 3600mAh battery which is charged by solar panels, but also can be externally charged. This PCB has connections for a Raspberry Pi Pico, DS1307 RTC module and ST7735 tft display. A Logic Level Convertor is also available for shifting from 5V logic of DS1307 to communicate with Raspberry Pi Pico. All the pins of the Raspberry Pi Pico are utilized so you can use this PCB for different kinds of projects implementing the above said modules. It has a power in of 5V which can power the Pico as well and four additions pairs of vcc/gnd for powering from external 5V. Originally in my project I used the three power rails for the following.

1 - 5V to power two 37g Analog Servos along with a 22 MicroFarad capacitor hooked between the positive and ground rails.

2 - 5V to power six 4.3g Digital Servos along with a 22 MicroFarad capacitor hooked between the positive and ground rails.

3 - 5v to power six Neopixels

4 - 5V to power a 24BYJ48 stepper motor with a reverse voltage prevention diode.

So as i said these can be utilized for any project. Also apart from the connected modules the other pins can be used as GPIO of your choice.

Parts For The Project

• 2 x ES3001 37g Analog Servos (Most hobby shops or RC Aircraft parts shops have these. I had them from an old project I worked on)
• 3D Printing Filament (Black, Red)
• Spray Paint (Yellow, Green) - I used them because i didn't have the color 3D filament.
• 3D Printer
• Hex Screws and Nuts (Diameter 2.5mm) 10mm and 15mm lengths
• Super Glue
• Radial Bearing (Inner Diameter 8mm)
• 6 x 4.3g Digital Servo (These also can be obtained from RC Aircraft parts shops)
• 5V Lipo Battery (3600 mAh)
• 5V 3A Solar Charge Controller
• 1 x Thrust Bearing (Inner Diameter: 8mm, Outer Diameter: 22mm, Height:7mm)
• 1 x Radial Bearing (Inner Diameter:8mm)
• 4 x 200mA Solar Panels (120mm x 60mm)
• 1 x 60mA Solar Panel (68mm x 37mm)
• 28AWG Electrical Wires
• 22AWG Electrical Wires
• 1 x Roller type Omron Limit Switch
• 2 x Push Buttons
• 1 x One Way On/Off switch
• 1 x Two Way On/Off switch
• 3 x Photo-resistors
• 3 x 10KOhm resistors
• 1 x IN5933 diode
• 1 x IN4007 diode
• 1 x Raspberry Pi Pico
• 1 x DS1307 RTC module
• 1 x Logic Level Convertor module
• 1 x ST7735 TFT display
• 1 x 24BYJ48 stepper motor
• 1 x ULN2003 stepper driver module

Flower Design

I started designing from the top of the flower as that would be the main weight which needed to be supported from the flower stem. That way I would be able to figure out the dimensions of the stem later on in the design stages. The hardware also needed to be tested before designing as changing the design later on would mean more trouble and work as every part fitted and assembled according to their dimensions. The analog servos were checked if the would be able to carry the load of the flower bud and the petals and their respective servos. It was also important to make room to route the wires coming from the servo up top from the petals all the way down to the flower pot where all the electronics were housed.

The flower was designed in such a way that three petals were located a bit inner to the center of the flower and the other three petals a bit outer. This allowed just enough room for the petals to move freely without mechanical interference. The mid section of the flower houses a pollen like tall structure which houses the three photo resistor which detect light. All three of them are covers on the sides so that when light hits an any one of the photo resistor it would block the light hitting on other two. This was it would be possible to get the direction of light which is the strongest or weakest for that matter.

As for the petals, the material used was 1.5mm thick rubber sheets which were cut in petal shape and fitted onto the structure which mounted the servos. Beneath them also were space that accommodate the Neo-pixels for each petal which lights up the petals.

Design of Flower Base

Each petal of the flower is held in place by a 4.3g servo hinged by servo arms that fitted into the slots on the flower base structure. A second smaller structure was slotted into the top of each servo holders of the petals. These smaller structures have cutouts to insert the flexible transparent material cutouts in the shape of petals. The Neo-pixels are placed beneath each petal at a 45 degree angle to diffuse the light onto the petals.

The mid section of the flower base would house the pollen structure which would be glued on later. The pollen structure has holes cutout to pass the legs of the photo resistors. Each of the servo holders for the petals are hinged on both sides for added support and the opposite side to the servo arm is supported by a small metal rod (6mm in length). The flower base structure has a cutout on the bottom to slot in the flower bud. The petals were spray painted in yellow color on the outer section avoiding the section where the Neo-pixels lights up.

Design of Flower Bud

The flower bud slots into the base structure of the flower and is then glued in position. The flower bud is designed in a way that it gives enough room for the movement of the petals. The base of the flower bud also has 5mm deep cutouts for the upper stem to slot in. All the wiring from the servos, Neo-pixels and routed from the sides of the flower bud and then through the gap between the flower bud and the upper stem structure. This was a bit tricky as I had glued in the upper stem for testing the flower stem servos before routing the wires. It would have been easier if I had routed the wires before gluing in the upper stem. The order of operations is very important as it would reduce the workload and possibly avoid making mistakes.

Finally after routing the wires through the upper stem things the 37g upper stem servo was fitted into the upper stem slot and screwed in. I used a round servo horn for the stem servos as there would more mechanical engagement on the structures.

Design of Flower Stem

The flower stem was designed in three parts. The two upper parts are able to move and the lower part of the stem gives the height of the stem. The upper and lower parts are designed with a slant which gives a more natural look. Each part of the stem has holes cutout from the top to the bottom where wires can be routed through the stem. This was necessary to keep the flower agile but also for better looks. The second section of the stem is designed to hold a small leaf. The protruding arm like structures has holes to fit in the small leaf. The small leaf has a 60mA solar panel fitted on top of it.

Design of Flower Leaves

The mid stem section has a smaller leaf and the bottom stem section has four bigger leaves. The bottom leaves each houses a 200mA 120mm x 60mm solar panel. The leaves are designed with cutouts at the bottom for the wires to go through. The leaves are also designed with a slight slant to give a more natural look. Once designed and 3D printed, I sprayed green spray paint on it. The leaves were fitted in to the slots on the stem and glued in later on.

The smaller leaf does not provide much current but there was a more significant reason to place it there besides the power needs and looks. It provides a counter balance for the mid section stem servo when it hinges. This would reduce the load on the mid section servo as it would be supporting the whole flower structure as well as the upper stem. There are certain limitations to the movement of the servo such as going backwards less than 10 degrees would mechanically interfere so those angles should be avoided.

Design of Flower Root

The root of the flower is glued to the end of the bottom stem and all the wires from the top route down to the flower pot through the flower root. The bottom of the root has a protruding shaft with a 4mm hole to insert a metal rod for strength. This was necessary as the shaft is plastic and the metal rod would prevent from it bending and failing owing to axial loads when the flower rotates. The limit switch pusher is screwed to one side of the flower root which comes in contact with the limit switch when it rotates to a certain angle.

The lower end of the shaft is designed with a hex shape which can fit into the top part of the top coupler. The top coupler has a hex shape cutout where the bottom end of it fits into the strut which is bolted to the coupler at the bottom that is fixed to the shaft of the stepper motor which turn the flower. The top coupler sits on top of the thrust bearing which takes on the axial loads from the total weight of the flower and its components. A radial bearing in placed above the coupler to counter radial loads when the stem moves outwards.

Design of Bearing Enclosure

The bearing enclosure was designed in two piece and bolted together after the components were put in place. It houses the radial bearing, thrust bearing and the coupler. The legs of the enclosure are bolted to the top half of the flower pot. Once again it is important to note the order of operations as the shaft needs to fitted in through the radial bearing, coupler and the thrust bearing with one half of the enclosure. Once all the parts are seated in the enclosure, the other half can then be bolted on to the opposite half of the enclosure. The limit switch is fixed to one half of the bearing enclosure so that when the limit switch pusher on the flower root turns as the stepper motor turns it comes in contact to determine the starting position. The limit switch is necessary as continuous turning without limiting would cause the wires to get entangled with the flower stem and limit the motion of the flower as it turns.

I could have made the design more robust and mechanically stable by using aluminum rods instead of plastic shaft to fit in the bearings. Even though the plastic shaft is fitted with a 4mm metal rod, the properties of plastic allows to give more tolerances owing to mechanical vibrations and deformations when in action.

Design of Flower Pot

The flower pot is designed in three parts. The bottom part, the top part and the lid. The bottom part houses the battery, solar charge controller, and the ULN2003 stepper motor driver. On the sides of the bottom part there are two switches, one to turn the power on to the flower and another to switch between solar charging and external charging. In addition to this there is micro USB charge port for charging the battery externally.

The top part of the flower pot houses the PCB for all the electrical connections. The bearing enclosure is also fixed to the top part of the flower pot. The stepper motor is also fixed on the top part of the flower pot. It has holes cutout to guide the wires from the bottom part of the flower pot to the top part and vice versa.

The flower pot lid houses two push buttons. One is to activate and deactivate the light following mode of the flower. The other switch can be programmed to do various functions such as to move the petals in a certain pattern or close up or open up the petals depending on certain lighting conditions. It can also be programmed to show different color gradients from the Neo-pixels depending on the time of the day (The RTC module provides the date and time information). The flower lid also has the ST7735 TFT display housing fixed which gives the date and time information. The top part and the bottom part of the flower pot are bolted in and the lid finally bolted in to the top part.

Electronics and PCB Design

The flower is powered by a 5V Lipo battery which can be charged using the solar panels as well as externally if required. It is controlled by a Raspberry Pi Pico and all its GPIO pins are utilized in this project. The real time clock (RTC) module (DS1307) communicates with the Pico using the I2C protocol and requires to shift its logic level voltage as the RTC is a 5V logic module and the pins on Pico are 3.3V tolerant. Therefore a logic level convertor is used to shit the logic when communicating.

The ST7735 TFT display communicates with the PICO via SPI protocol and is used to display the time and date information on the display. It is also capable of showing bitmap images and is limited to the storage capacity of the Raspberry Pi Pico which is 1MB. The display itself has an SD Card slot but to communicate with the Pico it would require more GPIO pins which in this case was not an option as all the pins were already in use.

The three photo resistors are connected with 10KOhm pull down resistors on each and the readings obtained are from 0 to 65536 with higher values indicating more light and lower indicating less light. Its a bit surprising that the results show a 16 bit ADC (Analog to Digital Convertor) reading although the Pico has a 12 bit ADC.

There are two capacitors of 22 MicroFarad placed between the positive and negative terminals leading to the power rails of the six smaller servos (4.3g) which moves the petals and two bigger servos (37g) which moves the two upper parts of the flower stem.

In order to prevent reverse voltage spikes from the stepper motor flowing back to the Pico, a diode (IN4007) has been placed between the common ground whereby only current can flow into the motor and not the other way around.

A one way power on/off switch connects the battery to the power rail of all the components. Another two way switch is used to switch between charging modes. Switching the in one direction allows for charging of the battery using the solar panels and switching to the other direction allows to charge the battery externally through the micro USB port. This would come handy as solar charging might sometimes take some time while charging externally would require less time. To be fair this switching was most handy during the testing period where you would drain the battery often times faster than recharging and in conditions with inadequate lighting. The schematic is attached if anyone is interested in having a look.

The circuit schematic was designed using EasyEda software and the PCB design was created once the schematic was finalized. The EasyEda software has a rich library of components which can be easily searched and deployed in any of your projects. They also have a numerous amount of user contributed components which their footprint match most of the available components in the market.

Connecting Electronics

After receiving the PCB, it was time to make all the connections. Before mounting the PCB to the flower pot all the wires were soldered on the PCB and since they were all labeled there was little chance of making any mistake. Pin headers were soldered initially to the PCB for mounting the Raspberry Pi Pico and the DS1307 module. All the other components such as the logic level shifter and the wires leading to the ST7735 display were directly soldered onto to the PCB. The two push buttons were glued onto the flower pot lid and their leads soldered to the PCB.

Programming the Flower

Circuit Python which is a fork of Micro Python was used to program the Raspberry Pi Pico as they already have an abundance of libraries which support the many hardware components. Its ease of use makes it simpler for testing prototyping fast. Some of the external libraries used are adafruit_register, adafruit_motor, adafruit_display_text, adafruit_bus_device, adafruit_ds1307, adafruit_pixelbuf, adafruit_st7735r, adafruit_ticks, neopixel libraries. I will provide the code snippets in the sections below.

Conclusion

I enjoyed making this project and thank PCBWay for providing me the PCB. I hope I can keep making projects like this with their support and also the community benefitted in someway and this post was of some use to someone. Regarding the build one of my concerns is about the charging speed using the solar panels. I haven't had the chance to fully test it since these days the lighting conditions are inadequate and normally I get to work on these projects during the late hours in the night. I had tested 3 of the four solar panels used as leaves connected in parallel to hook it up to my phone it does charge so I presume in good lighting conditions it would be able to charge the battery. It would definitely take awhile but that's a known given the battery is 3.6Ah and the solar panels provide just below an Amp.

Since this build has more room for improvement, I have several ideas for added functions such as to show appropriate colors from the Neo-pixels during different times of the day since it has an RTC module. Another such function could be to display the level of happiness of the flower depending on the brightness of sunlight it could move the stem up or down and petals in or out. If you have any ideas please share it here and I would also be happy to give my opinion. Thanks!

Watch on YouTube - Mechanical Flower

Watch on YouTube - Light Sensitive Flower