What is it?

DIY Programmable relay with voltage sensor and real time clock for Raspberry Pi Pico. It can measure input voltage (max 30v dc) and has a high precision real time clock chip DS3231 (this chip is expensive atm). So you can program your relay based on voltage and/or time. Sample micropython code is provided for programming Raspberry Pi Pico (Pico not included). The circuit is powered by 5v-30v dc input and the relay can handle 110v/220v AC up to 6A.

Why did you make it?

Originally created as an automatic changeover switch for a small off-grid solar inverter ups system. It connects/disconnects grid when a threshold voltage is reached or at sunset/sunrise, whichever comes first. It serves live solar power in the day and reserves remaining battery power for blackouts in the night.

What makes it special?

Existing solutions are based only on voltage, but this one can also read time (supports coin cell battery backup). And if Pico W is used it can also read the weather data from internet. You might as well make a custom analytics tool out of it.

Whats included?

The fully assembled PCB contains the following components:

• Relay (Max 6A 220V/110V AC, 6A 30VDC)
• Female headers for Raspberry Pi Pico
• Genuine Maxim DS3231MZ+TRL RTC chip
• Battery holder for CR1220 Lithium coin cell battery
• Female headers for optional I2C display
• Female headers for optional UART Bluetooth module (amazon)
• Example program to read voltage/time and toggle relay

Add-ons

• Raspberry Pi Pico W (or you can program your own Pico)
• Coin cell battery
• OLED Display
• Enclosure box

Notes

• The relay is not intended for heavy loads like Dryer or AC or for powering your entire home.
• Take extreme caution when dealing with high volt AC lines! Get the help of a certified electrician.
• Please be mindful of polarity and do not exceed the input voltage limit or the components will get damaged.
• This DIY product is provided as is, the developer is not liable for any damages caused by it.