The global COVID-19 Pandemic and the resulting lockdown imposed is what got me to think along the lines of doing something with the Arduino bits and pieces I had with me. So though this is a very simple instructable, I say this and another instructable I am about to post titled (COVID-19 inspired voice controlled home automation) was truely inspired by COVID-19 lock down.

Going forward with the huge job losses and economic downturn after we emerge from the pandemic as survivors, I am sure it will be in everyone interest to cut costs in every possible way. One doable way at home is by reducing the power consumption. Small saving you might think but then many a drop make a mighty ocean doesn't it?

Step 1: Components Required

Making this simple instructable requires the following:-

(a) Solar panel capable of delivering about 30 watts of power at 12 volts

(b) Arduino Uno

(c) 4 or 8 relay module

(d) one 16x2 or 20x4 LCD display module (remember to modify the code accordingly)

(e) 3 wire shield for the LCD module from https://www.amazon.in/gp/product/B01669R204/ref=ppx_yo_dt_b_asin_title_o03_s01?ie=UTF8&psc=1

(f) one DS3231 clock module

(g) one HC-SR04 module

(h) wires and connectors as you deem fit

Step 2: About

So this instructable is really about making something that is intelligent enough to turn off the supplies when not required (and there are a million such designs on the net) and to the extent possible minimise the dependance on power supplies from the utility company (without the use of an inverter or a battery bank).

Note: Though I mentioned a solar panel in the list of components required, what is implied is that you try to use the solar panel that you already have at home (with your solar inverter assembly).

Ok so here goes....

Step 3: Connections

Basically I ran two wires from the terminal of a 100 watts solar panel to the bathroom on the ground floor. The bathroom was the designated place for the arduino control panel and the distribution and also for one of three LED lamp assemblies.

As a test case initially I used a 10 volt 5 watt solar panel but found that it did not have enough capacity to take the load of two LED assemblies and the arduino boards et al. If I were to scale things up I needed a solar panel that was capable of giving out more. So with a 500 watt solar panel set up at home to power up the lamps and fans in every room, I decided to tap the required 30 to 35 watts (approximately) from one of the 100 watt panels.

Now the challenge was how do i step the 16 to 18 volts to a more manageable 10 to 12 volts. Just when I was thinking of a DC-DC step down circuit, it occurred to me to take the tap out of the left most and centre terminal of the solar panel - my Eureka moment if you like.

The rest of the connections are elaborated in the sketch and reproduced below:-

CLOCK Module
GND to Arduino Ground Vcc to Arduino +5V SCL to Arduino A5 SDA to Arduino A4

LCD Module GND to Arduino Ground

Vcc to Arduino +5V

SCK to Arduino D11

CLK to Arduino D12

D to Arduino D10

RELAYS 4 relays connected from D2 to D5

DISTANCE Sensor use pins D0 and D1 as shown:- Echo - D8 Trig - D7

Step 4: Working

Ok so basically the light and the exhaust fan in the bathroom was powered on by the same switch. I wanted the light to stay off during the day between 10 AM and 5 PM. However I wanted the exhaust fan to come on if someone spent more than 30 seconds in the bathroom. Also I wanted the exhaust fan and the LED lights that came on to go off after approximately 2 minutes if it senses no activity in the bathroom.

The bedrooms in my 85 year old ancestral house,on the other hand, had the LED lamps coming on at around 8 AM or so and staying lit till about 5 PM or so. I didn't want any switching ON and OFF here because these room are pretty dark without any light and I felt a light in each of these otherwise dark rooms will curb the first natural reaction to reach for the wall switch and turn the lights on.

So at the end of it all, I am quite pleased it works and above all it minimises the need to reach for that switch. How much of savings this will translate into.....I will have to wait and watch.