Remote Switch

Last week, Netaji Subhas University of Technology (NSUT) was preparing for the Convocation of the graduating batch of 2025. One of the requirements was a reliable and simple interface to trigger the inauguration videos at the hands of the Chief Guest, the Hon’ble Lieutenant Governor of Delhi, who also serves as the Chancellor of NSUT.

I offered to design and fabricate a custom remote switch using the rapid prototyping facilities available at the Centre for Electronics Design and Technology (CEDT). My student, Harshvardhan Gupta, volunteered to take up the fabrication and testing. Within a week, the design was finalized, fabricated, and thoroughly tested.

On 13 December, the device was used by the Lieutenant Governor and the Chief Minister of Delhi in the presence of other distinguished dignitaries.

This outcome was possible due to the strong institutional support provided by our Vice Chancellor,  Anand Srivastava. 

For those interested in the Remote Switch, here are the details. 

 The circuit is really very simple - an Arduino, an HC05 Bluetooth interface and a suitable power supply together with pushbuttons to trigger the switch and LEDs for status. A python script on a laptop received suitable codes from the triggered Arduino and played the requisite video. The breadboard version was tested in a day. 

 The devil was in the details. Which power supply? Which pushbuttons? Which box to enclose it in? 

I wanted to keep the power supply very simple. For that we measured the current consumption of the Bluetooth module. The datasheet says 30-40 mA but in reality, it consumes ~200mA when sending data which is quite infrequent. So, instead of a lithium battery and it's retinue of boost converter, charging circuit, USB interface, I opted for a 9V alkaline battery connected to the Vin input of the Arduino. A good (Duracell) battery has ~600 mAh capacity that would last more than 10 hours in the circuit. 

 Next dilemma was which pushbutton? I didn't want a simple pushbutton that one could accidentally press several times. I decided to use an emergency stop switch. Normally it is used to turn off the power to an equipment or machinery in the case of an emergency, it has to be armed once it is pressed - perfect for our needs. A regular,  large pushbutton was used to cycle through the options for the videos and the selected option was  indicated on LEDs. 

 We found a large IP65 capable plastic box in the lab big enough to accommodate the circuit and some more. The circuit was fabricated on a zero board as there was no time to fabricate a custom PCB. The LEDs were hotglued to the box (not a good idea but works in the short term as a prototype). The decals for the box were 3D printed (thanks to Naman Puri for his help) and stuck with drops of Elfy. 

Once fully assembled, the Remote Switch was extensively tested for range and battery endurance. It was also tested many times at the venue during rehearsal day and the actual day of the event. The anxiety such an event creates, is simply unbelievable. Thankfully, the choices I made for the design and extensive testing it underwent, ensured that it worked flawlessly.

Apart from its main purpose, this project helped me teach the intricacies to a budding engineer and that to me as an educator is deeply satisfying.