LED Bike Light

This was a small little project I worked on in the summer of 2016.  While taking my first circuits class, I wanted to experiment with placing some LEDs on my bike.  During this time the weatherproof WS2812 addressable RGB LED strips hit the Sparkfun store and I wanted to place a meter strip on my bike!

Like I said, this was while I was taking EE201: Electric Circuits, so my knowledge of designing circuits was minimal.  Thankfully there’s this beautiful thing called the internet, so whatever I didn’t yet learn from the classroom could be discovered by a quick Google search.

The overall design of the circuit was fairly minimal.  A Sparkfun Pro Micro, which is a ATmega32U4 placed on a breakout board with a USB programmer, was used to control the LED strip.  A Sparkfun Power Cell board was used to both charge the Lithium Polymer battery and step up the 3.7 V output to the 5 V needed to power the board and LEDs.  The biggest problem with using the Power Cell was that the DC-DC boost converter was limited to 500 mA of current draw, which was about half of the current needed for the meter of LEDs to display peak brightness.  Besides these two boards, a capacitor was added as a voltage buffer for the output from the DC-DC converter.  A switch was also added to turn the output on or off from the converter.  A resistor was also added to the signal line for the LED strips.  The components were then soldered to a prototype board that was way to big for what I needed.  I was still a soldering greenhorn at the time and did a slightly less than mediocre job at soldering the board together.  You can see my work below.

My less than perfect soldering job for the board.

The majority of the project was spent debugging my solder job.  I ended up having to learn how to use a spring loaded solder vacuum to clean some of the traces, as a short was the cause of most of my problems.  Once the soldering was finished.  Code was uploaded to the Micro and I had a pretty rad looking bike.  The final product can be seen below.

IR Remote and Receiver

In EE230, Electronic Circuits & Systems, we were assigned two projects in the semester.  Both projects were centered around active and passive filters.

The first project involved designing and building a three-channel crossover network for audio.  The low-pass channel needed to have the ability for the user to be able to increase the amplitude of the signal, or drop the bass.

The second project was slightly more complicated, where we were asked to build an analog infrared transmitter and receiver that would be capable of sending two different signals.  In demonstrate the correct behavior of the system, each signal would light up an individual LED.

Our design was fairly simple.  For the transmitter we used two op-amps on an LM324 for two oscillators, with one oscillating at 1 kHz and the other at 20 kHz.  Two switches would output the signal from the oscillator through an infrared LED.  A circuit diagram of the transmitter can be seen below.

Infrared transmitter circuit

For the receiver, an infrared photo-diode was connected between an op-amp terminal and the negative voltage.  Because the output from the photodiode was very weak, one op-amp in the circuit acted as a preamplifier for the high and low-pass filters that separated the input for each LED. To determine what LED should be lit from input, we used a high-pass filter to block the 1 kHz signal to one LED, while a low-pass filter blocked the 20 kHz signal from the other LED.  The single-order active low-pass filter was designed with a corner frequency of roughly 2 kHz and a 0 Hz gain of 10 v/v.  The output from this filter was sent to an AC rectifier, where the DC output was passed to a small resistor and LED. For the 20 kHz signal we decided to build a second-order filter with an infinite frequency gain of 10 v/v and a corner frequency of 10 kHz. The output from the high-pass filter was passed to a non-inverting amplifier of 10 v/v before being output to the other LED and small resistor.

This was the second circuit class I have taken at Iowa State in a planned sequence of three.  Circuit design and analysis are two skills that I have really enjoyed learning.  The skills have proven to be very useful on personal projects and also in a past co-op.

A video of the final solution for the project is shown below…