I discovered my passion for electrical circuits when I was a child. For fun I would disassemble toys and electronics extracting their parts for my diverse experiments with electricity. As I constructed these projects my untrained soldering skills was definitely a limitation. I was also unaware that solder material available was composed of a high percentage of lead metal which is quite toxic for children if not handled with care.
Thankfully today, with STEM education becoming a national focus children have a multitude of solder-less electrical project options at their disposal such as the LittleBits eco-system. Every LittleBits module magnetically snaps together without solder. If you can build with LEGOs, one can now easily construct a working LittleBits circuit.
Since 2014, Silicon Labs has been increasing their focus on sponsoring STEM education in order to foster the next generation of technical innovation. This endeavor got me thinking about how to incorporate a Silicon Labs device into LittleBits. For this project I chose a Si1102 proximity sensor as its concept is pretty simple to understand: If an object is detected, assert a signal. Using the Si1102 will allow us to build a proximity alarm circuit.
Step 1: Getting the Materials
For this project most are found within LittleBits kits, however a few items had to be individually bought:
Step 2: Evaluating the Proximity Sensor
The Si1102 is very a simple device to setup. With the Si1102EK demo board, it is just a matter of powering it up and testing it. After flipping the power switch to on, wave your hand over the Si1102 and the blue LED in the upper corner of the board is activated.
To activate the LED the Si1102 proximity sensor has a PRX pin that asserts low to sink electrical current across the LED. This is the signal we want to bring into the LittleBits module. Along the bottom of the board is a single row header of every signal that connects to the Si1102’s 8-pin device. For the LittleBits module we will need VDD (power), GND (signal ground) and PRX (presence detected by pulling the output low). The Si1102 can operate with a power supply voltage from 2.0 to 5.25 V, which is great because LittleBits modules carry +5V across their circuit chain.
Step 3: Hacking the LittleBits Proximity Sensor Module
To make use of the LittleBits 5V as the power supply for the Si1102EK, I removed the CR2032 coin-cell battery located in the rear of the demo board.
Next, to incorporate the Si1102EK demo board into the LittleBits eco-system I have connected three wires to these signals and then connected them to the LittleBits proto module’s VDD and GND into the VDD (H1 pin 3) and GND (H1 pin 1) of the Si1102EK demo board. The Si1102EK’s PRX (H1 pin 4) is wired into the signal input of the proto module and depopulated the middle jumper the LittleBits proto module. Since PRX is an active low signal, I added a LittleBits inverter module to correct the signal polarity to make it friendlier to the LittleBits output modules which operate based on active-high input signaling. Also note it is important to leave the demo board’s switch to ON as this switch was to preserve the life of the coin-cell battery. In this setup, the only way for the module to receive power is if it is part of a LittleBits circuit connected to a power module.
Step 4: Building a proximity alarm circuit
Now that you have the proximity module created, it can be used in an alarm circuit. To complete this circuit, besides the power module I chose the bright LED and buzzer output modules as whenever a nearby object is detected, one wants visible and audible noise to draw attention. Waving your hand over the Si1102 proximity sensor device, now not only is the original LED activated, but now the downstream output modules within the LittleBits circuit are also activated as well.
Step 5: Final test
Once this is setup, the final test will be to get an excited LittleBits volunteer to try out the new module.
Watch the video: Creating a LittleBits Proximity Sensor
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