DIY Solar Mitra

DIY Moon Phase and Menstrual Data tracking

Posted on February 25, 2025May 30, 2025 by Tathagata Mitra

Despite the website being about solar 🙂 Today I write about the moon. The recent moon game doodle by google got me further intrigued by the magic of moon phases on earth. Moon doodle

Coincidentally, there was an article in make magazine which used PCB(Printed circuit board) and moon like arrangement of LEDs specifically to indicate the moon phases, there are a lot of software apps that track this type of information on the web but few on hardware…Having a moon calendar, indicating full and no moon every month seemed cool.

The project captures a way to display major phases of the moon – like a full moon(poornima), no moon(amavasya), 1st quarter and last quarter. It also has an option to manually add period data. The thought of gifting this project primarily to my daughter and wife made this interesting

I also wanted to check the pricing of hardware manufacturing in 2024/2025 sourced to India, so I got working on this project

The Project in pictures

Moon Tracker Assembled PCB with RP2040 Solder party Stamp

Example month with moon and menstrual data

Lets go over the layout of the LEDs in moon pattern. As you can see on the hardware, there are 30 circular – moon like arrangement of LEDs

6 moons on each row and – 5 rows in total – making 6×5 = 30 days to represent moon phases

Each circular pattern of LEDs from the top left represents a day in the calendar, so each row represents – 6 days going from top left to right and then subsequent bottom

Bright blue colour is being used to represent the full moon, 1st and and last quarter. Light blue represents new moon and reddish pink colour represent dates matching with the menstrual cycle

In the above example month – 2nd day of the month is new moon; 17th day of the month is full moon; 10th day is 1st quarter and 24th day is the last quarter; Menstrual cycle dates are highlighted in reddish pink colour

Hardware build

Thanks to the detailed walkthrough – by @artur0182 and Anuradha Reddy, it was a breeze to order PCB and components from an online PCB vendor- this was a four layer board, designed in KICAD – open source PCB software. The PCB was primarily comprised of about 250 RGB LEDs and 500 Capacitors surface mount type.

I ordered the brains of the project in the form of an RP2040 stamp and a carrier from solderparty which came in from Sweden

The components and PCB arrived in under 2 weeks and I started inspecting for scope for hand soldering the components. The thought of hand-soldering for 250 LEDs and 500 capacitor, despite being tedious and the risk of looking slightly unprofessional output, is extremely cost effective. Its an added plus if you enjoy this as a hobby 🙂

However on close inspection of the boards, the PCB pads for soldering was just enough to accommodate the terminals of the LEDs and components. Tried to solder a few LEDs with my trusty not so professional soldering rod, my soldering did not inspire confidence on the electrical contact. So I started to look for local professional assembling service – inclined towards automated assembly. Part of the reason I wanted to check the pricing for automated assembly

It took almost a month for an automated assembled board to work- primarily due to the requirement of framed stencils for assembly and slight issues in the assembly process.

The build and code repository

The hardware design involved Kicad and code was based on Micropython. Following are the links to the repositories

https://github.com/arturo182/strange_leds_hw

https://github.com/anu1905/Islamic-Geometry

Powering through a 5 V supply – even PC USB port is enough to power the board – highlighting the low power requirements

Improvements to be thought

Auto update full and new moon based on moon calendar of particular location
Enhance the functionality to include period tracking with an easy to update interface- Currently this feature is available through circuit python -need an easier hardware interface for user friendly operation
Modify the layout for DIY friendly soldering – this would meet the estimated cost mentioned in the magazine… Currently its considerably more due to automated assembly one time setup cost
Create a 3D printed case to hang the moon tracker – meanwhile I came up with a DIY case made out of multiple cable ties surrounding the PCB to keep this out of playful hands of my kid 🙂
- this could be hung on a peg on the wall
- was kind of pleasantly surprised by how quick and robust was the solution – hung the solderparty RP20240 stamp adjacent the PCB with the cable tie as well – could be easily programmed by the laptop connected to this

Moon Tracker hung on the wall — Moon Tracker on the wall

Few Insights gained from the moon in general

Its amazing depending on your location on earth and day of the year, the Parts of the moon are lit and it changes ever so slightly every day throughout the month ..

The impact the Moon has on earth is quite evident with tides that we see in coastal areas with high and low tides…I also feel the phases of the moon have an effect on my body physiology.. I feel energetic on full moon days/ no moon days

From the google doodle, the phases of the moon have different names such as the Waning gibbous, waxing gibbous – At first I thought of them as some animal species names, but these are different phases of the moon 🙂

Do you know the lunar calender months vary from 28-30 days? Ancient calendars based their lives around cycles of the moon.. the 28 -30 day cycle – hence 6×5 =30 moons is sufficient to represent the phases in any given month

Also the same side of the moon faces the earth, the other side is not visible from the earth, the same side is lit gradually everyday. This is also known as tidal lock…observed in other moons of other planets in the solar system as well. The moon due to long being inorbit with the earth has become a bit elliptical instead of a perfect sphere. The center of rotation is lower than the geometric centre, thereby making same face of moon face the earth irrespective of the rotation

Hardware sourcing

Incase you would like to order – I do have the sourcing starting from PCB to automated assembly – all figured out in India and ready to be shipped, feel free to contact for more details

I would like to thank @artur0182 and anuradha reddy for the detailed flow which enabled quick prototype and build.

Pigeon Scarer

Posted on July 7, 2024July 7, 2024 by Tathagata Mitra

What do you do with an old Arduino Uno, small speaker and PIR sensor lying in your electronics dump? My family always thinks the wires and electronics stuff lying in the cupboard are a waste of space….😅

I recently came across an article in make magazine which utilized the above items in a project, and I thought, it’s time to dust them out of my electronics dump and finally utilize them..

The project consisted of a PIR sensor coupled with an arduino to detect movement and trigger a capture of the person/moving object using a camera connected to a raspberry pi. Credit -Eben Kouao – Open Smart Cam Make Magazine — The step by step build is presented here https://www.youtube.com/watch?app=desktop&v=lFr-kprnpdA

*Functioning of PIR Sensor: A PIR sensor specifically used was HC-SR501 sensor. PIR Sensors are Infrared sensors used in various applications like Automatic floodlights; Automatic car park lights; CCTV cameras; They have an ability to detect motion even in complete darkness

The Passive infrared sensor works on heat signatures amplified with a lens; any movement even in dark is detected. There are 2 pyroelectric sensors next to each other… Any movement even in the dark would be detected by the difference in readings of the 2 sensors.

My problem statement:

I had some pigeons eat the plants in my mother’s place. Needed to scare them away, not capture these destructive moments !!

I decided to use part of the project – the PIR sensor coupled with an arduino and L293d driver shield to drive an annoying speaker … I thought, great, let me get this built… This could be done in a weeks time , or so I thought… I highly underestimated the project build 🙂 I ran into some issues which lead to missing the 1 week deadline

The Issue

When you couple L293D Driver shield with Arduino… the output signal to the buzzer seems okay.. but at the input side, the connection between the PIR sensor through the driver shield to the Arduino seems to get drowned in noise..The shield between the PIR sensor and the Arduino seems to corrupt the digital signal. This results in no obstacle detection and no buzzer…I was disappointed.. I had prepped for a week’s deadline hoping to finish the build and make it ready to save the plants…. now with no hardware solution, completing it in my parent’s place was tough

PIR Sensor+L293d shield with arduino and loudspeaker

Now back at my workplace, I thought about how to solve this issue. I experimented with PIR sensor directly connected to the arduino through a female-female berg connector… and it worked flawlessly to detect a moving object… I decided to remove the L293D driver shield board and go through with an external relay powering the loudspeaker module

This way the arduino to PIR sensor pathway was clear and also, I had the circuit powering the loudspeaker circuit isolated.

Block Diagram

The following are the steps followed

Setup the arduino to receive a digital input from the PIR sensor- Test the human movement – simulating the pesky pigeon eating Ma’s plants
write an if else statement to trigger the relay powering Loudspeaker when the pigeon is detected and turn off when no further movement is detected

The building of the Proof of concept

PIR Sensor PVC Pipe — PIR Sensor embedded on PVC Pipe

PVC End cap with small speaker — Speaker inside PVC End cap tied with cable ties

Bottom view – speaker inside PVC end Cap

Complete Build

Working of Pigeon Scarer

Components to make the build

PVC Pipe 63 mm diameter with end caps
Arduino
5V relay board
Couple of cable ties
HC–SR501 PIR Sensor
Small Loudspeaker
Small switch – According to amazon its DPDT on off switch – small rocker boat switch

Room for improvement

Following are few areas you could consider to improve

5 V supply derived from the solar panel charging a Li-ion battery; Currently solution involves powering setup from a power Bank/ 5V
Single source of power supply- Currently the Arduino powering the PIR and Relay board is powered by a rechargeable 5 V power bank; The Speaker is powered by a separate 9V battery; Eventually I would like the entire setup to be powered by a single 9V rechargeable battery from Solar
To make this extra scary both in light and dark. Add a parallel LED, or just LEDs without the speaker to scare rats /cats underneath the car
Need to actually test with a live pigeon/rat 🙂

My interests currently

Posted on June 5, 2024 by Tathagata Mitra

I am fascinated by the art of making PCB and assembling parts and programming them to achieve any goal perceived valuable for a person

Multiple tools and vendors come into force at various levels, some are paid and some free. For instance, for PCB designing there is a free and powerful tool like the KICAD used by poineering organizations like CERN and also a paid edition of Altium – used by many commercial firms. Usage is dominated by the familiarly and ease of using the tool

This is exactly what is the building block from say a mobile phone to say a solar inverter – PCB manufacturing/ assembling and programming and testing; report generation

The basic process for building the above products is the same… I recently became aware of the level of testing these products go through before the customer gets their hands on the product. Often there are multiple configurations and testing them becomes tedious unless there is automation. Interested in simplifying and accelerating such testing and report genrationthrough python is also of interest

Often testing against the requirements is differentiator between a good and a great product with great brand recall say for instance apple

I am also fascinated by the progress of the products in commercial /industrial levels governed by standards like IEEE 1547 – pioneering the stability of the grid with solar and NEM3.0 – pioneering great savings for the customer for not only solar but with solar + storage configuration with capability to export to grid to earn disproportionately more than solar alone installs

I believe in DIY approach and avid fan of Make magazine to inspire my creative juices to make a few side projects to keep the hunger alive

In my previous roles I have been in solar designing, permitting and technical sales… would love to explore more in these verticals as well

I am interested in creating both building blocks for hardware design and software/firmware code which just work out of the box. Also, a setup to automate testing to achieve the quality and scale will simplify the process

In the coming posts I would like to venture into each of the above interests and document the flows

Robust Enclosure for LED light

Posted on April 23, 2023May 13, 2023 by Tathagata Mitra

In my previous post I discussed about PVC pipes enclosing electronics.

Here is an example of a painted PVC enclosure consisting of 2 end caps

PVC-Enclosure-with-double-end-cap-painted-black — PVC Enclosure with double end cap painted black

PVC-enclosure-spray-painted-black — PVC enclosure spray painted black

PVC_enclosure-side-compared-to-human-hand — PVC enclosure side compared to human hand

Based on the size of the electronics to enclose, one could experiment with the size of PVC pipe. Here I have used 63 cm wide PVC with end caps spray painted black.

They are the perfect DIY solution to weatherproof your electronics.

Even a Resort in Coorg agreed with me 🙂

Yes, the lights that you see are all supported by PVC Pipes 🙂 and they are not painted and look great.. I have zoomed one for you below

And no they are not temporary solutions, the base foundation is on concrete mixture, made to last the life of PVC pipe

This made me wonder, okay, for electronics we have the the perfect enclosure, but what about an LED light I would like to weatherproof?

The PVC end cap seems to perfectly fit a round LED panel. As seen below

Fitment is one thing, but protecting from the elements of nature– tough, when I want light to emanate from an opaque PVC pipe 🙂

I knew I needed something to be transparent and also kind of weather proof. I searched google for transparent PVC pipe, and found that its a thing!! However the price of a transparent one is about 4 times as expensive and less common in the hardware shops.

That’s when it dawned on me that I could use a test tube that we used in chemistry lab for enclosing the LEDs 🙂 . 4V LED strips are kind of available inexpensively and would easily fit into the test tube. Lets combine Electricity with chemistry:)

I quickly searched amazon and found plastic test tubes. Perfect even for a single Li ion battery powered LEDs. An elegant solution

Here are few snapshots of few solutions for the same

On further exploring the idea, it struck me that one could use 20 INR used Mountain dew(soft drink) bottle for the same 🙂

The following are the sub steps involved in making the above Assembled LED light

Firstly drill the end cap with a drill machine to allow perfect fit of PG7 IP68 Gland

Soft drink top cap with PG7 Gland with Wire

Secondly create filament type surround lighting using 4 V Led Strips soldered together on a single side perf board as seen in the below video

Thirdly Solder and assemble and connect to a power source outputting 4 V 3W. Here is the assembled version of the same

Here is me making a filament type surround lighting using 4 V Led Strips soldered together on a single side perf board.

One added benefit to the greenish yellow tint of the above used soft drink bottle is a warmer glow to cool white LEDs.

This is an extremely rugged and low cost lighting solution and I plan to use them to my upcoming camping expeditions coupled with a rugged solar powered lithium battery charging solution.

please let me know how important are following features in a portable LED light

Light Use

What features would you value the most in a portable solar powered light?(Multiple selection allowed)

Size

price/cost effectiveness

battery life 4 Hours

battery life 8 Hours

Brightness

more features- mobile charging

charging time under 3 hours

Min votes count should be 1

Please fill out the form:

These would help me prioritize development of the same

Stay tuned for the rugged Low cost DIY Solar Li ion Charging solution!!!

Best Enclosure for DIY solar electronics projects

Posted on January 16, 2023January 17, 2023 by Tathagata Mitra

Over the past 5 years, I have been experimenting with enclosures available online to protect electronic circuitry mostly from dust and to bring an elegance to my mess of wires in the project.

I started out with a Simple Solar Li ion battery charging circuitry which had 1 18650 cell of Li ion battery with the associated circuitry as a personal project. I had assembled a printed circuit board(PCB) and soldered the components using a locally bought soldering kit

I first ventured out to digikey.com and mouser.com, the popular US websites for procuring electronics at hobby and professional manufacturing.

At that time I was also professionally involved in procurement of electronic components for products to make for Indian market, we were heavily dependent on these online electronics distributers from the US to run a small batch of manufacturing prototypes and testing in India.

I checked the dimension of the PCB, associated battery and Connectors and and after careful consideration picked the most economical amongst them. Funny thing about enclosures is that there are no predefined holes for cable through fare!! One has to drill holes according to ones requirement.

Here is a snapshot of the invoice of the enclosure I had procured in 2017

Enclosure Invoice

This enclosure kind of fit in my hand

Here are some of the modifications I did on the enclosure I did for cable and connector management, with help of a drill machine

Enclosure with Cable gland and connectors and LED holder

Assembled Enclosure with Cable and Circuitry

Internal View of Circuitry with Enclosure

This was about 5 years back, looking currently at the digikey website I was kind of presently surprised of its availability still now

https://www.digikey.in/en/products/detail/hammond-manufacturing/1591GFLBK/409885?s=N4IgTCBcDaIBIFkAcBWFBaAcgERAXQF8g

Here is a snapshot of the current pricing as of 15th Jan 2023

I can see the bump in price by a dollar from the price I had access in 2017

(Kind of expected with COVID scenario)

On the hindsight, I calculated the Price of electronics components including PCBs and the enclosure and saw that the humble enclosure made up almost 50% of the prototype cost. Also the fact that I was being charged customs and shipping fee in order of 40% did not further make this option appealing as a hobbyist

Over the period of 5 years, I have tried to optimize the size of the PCB and also experimented with several enclosure from different sources to optimize the cost

I sourced few enclosure from aliexpress of China in early 2018, the delivery times seemed erratic and quality questionable

I also tried sunrom electronics based out of Ahmedabad, India

https://www.sunrom.com/p/enclosure-90x70x28mm

However the material seemed to be brittle and drilling holes for cable management would often result in cracks in the enclosure

After loads of experimentation, Do you know the best enclosure I found after these 5 years?

Its the humble PVC pipe with end cap!!

Not only will this protect your hobby projects from dust at times with the right adhesive can also protect from water(After all there is a reason these are employed to transport water)

Here is an example of how I modified a PVC endcap to house a circular LED powered by Li ion battery to function as a portable emergency lamp

PVC End Cap Enclosure with Old Selfie Phone holder

Pros of PVC as Electronic Enclosure

Easily available in local hardware shops throughout India
They are available in all sizes / diameters.
I can later spray paint the PVC with any colour to make it aesthetically appealing and the over all cost is very nominal compared to online sources
Can become water proof with right adhesives

So now I am in love with these PVC pipes as enclosure for my personal projects. you would see lot more experiments on them moving forward from 2023

Credits

https://www.digikey.in/

https://www.sunrom.com/