Tesla coils are fun, but not everyone dare to build them. This is mainly because to build large Tesla coils you need some knowledge about power electronics and they can be dangerous if you don’t know what you are doing. Anyway if you are looking for smaller scale solutions that would be safe enough, easy to build and wouldn’t require lots of knowledge, then check out this palm sized design introduced by Lucid Science. It uses few components like single transistor, LED indicator and simple custom made coil. It is powered from standard 9V battery. All parts you need probably you already have, so you can start right away. Despite its small size miniature Tesla coil is capable of lighting fluorescent bulbs and tubes. This guarantees some fun play while building and trying things out.
Most microcontrollers have ADC input which can sample an analog signal, including sound. Even using Arduino, you can do many cool projects using audio information. For instance, you can make a voice controlled devices such as Audio Recorder, voice-activated switch, and more exciting audio related projects. In this post, I want to focus a bit on the microphone part – the circuit required between the electret condenser microphone and MCU ADC input. Generally speaking, you cannot connect electret microphone directly to ADC pin and expect it to work. The part needed here is called an electret condenser microphone amplifier circuit. Electret microphone with preamplifier stage Condenser microphones require power from a battery or external source. The resulting audio signal is a stronger signal comparing to a dynamic microphone. First of all, the electret microphone isn’t only a condenser inside. It already has a preamplifier inside usually made of FET transistor, which is connected in common source configuration: First, the electret microphone needs to be powered through the drain pull-up resistor. Its value depends on the power supply voltage. Rule of thumb is to add 1kΩ per +1V of the power supply. Up to 10V 10kΩ resistor will work fine.
Joule thief circuit is popular among electronics enthusiasts. It has many implementations but probably most common is very minimalist voltage booster based on NPN transistor, coil, resistor, and LED. Its primary intent is to squeeze the remaining juice of dying batteries to light a LED. Since a pile of dying batteries keeps growing, I decided to give it a try. Instead of building the real circuit blindly, I decided to understand what is going on inside the circuit. So I made this circuit on LTSpice simulator. You may find some difficulties when adding a transformer to the circuit, there is an excellent video on how to do this (LTSpice Transformer).
Different logic levels are common problem in various circuits. For instance Arduino boards come powered from 5V or 3.3V. Raspberry Pi for is powered at 3.3V and it accepts and generates 3.3V signals on its GPIO. This is fine until you need to connect 5V peripheral to 3.3V device. This can be simple LCD. Of course you can get 3.3V LCDs, but this is not always the solution. Sometimes it is handy to build a voltage level converter. It can be a special buffer IC like SN74LVCC3245A. These work great as bidirectional voltage translators. But in many cases there is no need for another IC in your circuit. Hobbyists like to go with simpler solutions. Simplest way is to use resistors where signal levels differ. The fact is that in most cases devices have clamping diodes on the inputs that are meant to protect further circuit from over-voltages. For instance clamping diode inside 3.3v device will try limit input voltage to 3.3V. This is why a series resistor necessary in order to limit current flowing through diode. Using resistors, doesn’t guarantee safe operation. First of all you must be sure that 3.3V device has clamping diodes. Second thing is that…
In most small audio project hobbyist are using specialized audio amplifier chips. That’s really fine you get high quality amplification without scratching your head. Some probably don’t care how these things work. But don’t forget that amplifiers can be built out of discrete electronics components like bipolar transistors. Check out this great hackaweek project where Dino builds class AB audio amplifier out of three bipolar transistors and other passive components. He slightly goes through theory of operation and of course demonstrates its working in following video.
When you hear a word “relay”, probably you think of mechanical relay that can be activated with electromagnet inside. All you need to apply some amount of current across relay coil to operate switch. This way you can control large loads with small signals. But there are some disadvantages of using mechanical relays – they aren’t reliable, they wear off and are slow. So more and more they are replaced by electronic relays with no moving parts. These are called Solid State Relays (SSR) and can be purchased as blocks. If you have a pile of various electronics parts lying around, you can build a SSR relay and pay no money as these are quite expensive. Follow the Solid State Relay schematic provided by electronics-diy and you will be able to understand and DIY Solid State Relay out of distinct parts. Once finished SSR can be attached to your project like other normal relay that has to switch high AC loads.