Last year I started getting into building electronic circuits. I have a few ideas on a large project I eventually want to create, but it requires some knowledge of circuit development, so I started on a relatively easy project, a dub siren.
Since I’ve already finished with this project, I’ll show the final results, and explain how it all works. I’ll start with the schematic, and then the board diagram, and end with the printed circuit and assembly.
This is the schematic of my dub siren, designed using Eagle. There are 4 sub-systems in the design that I will describe in more detail. Broadly, the circuit allows for the adjustment of 5 aspects of the generated audio signal: Waveform, rate, modulation, frequency, and volume. The first three of these aspects are controlled by one sub-system, and the last two by two other sub-systems.
The power sub-system consists of a 9V barrel jack, an on/off switch, a diode, resistor, and capacitor. This provides a clean and protected 9V source of power to the rest of the circuit.
This is the heart of the circuit, and consists of a 555 timer, an op-amp, 3 potentiometers, and a few resistors and capacitors that all work together to determine the shape of the signal sent to the rest of the circuit. It also has an LED sub-circuit that shows the rate of modulation, if it’s active.
This sub-system contains another 555 timer, a potentiometer, a couple resistors and a capacitor, which all work together to modify the frequency of the input signal by either compressing or expanding the wave.
This sub-system consists of a switch, a momentary push-button, a potentiometer, a 1/4in TRS jack, and a resistor and a couple of capacitors (as well as an LED sub-circuit). This provides a way to connect the entire circuit to some external audio interface, allows the amplitude of the signal to be adjusted, and allows the user to either have a continuous signal sent to output, or only sent when the button is pressed down.
After the circuit was designed, I moved on to designing the board to layout the components and have something that I could have printed out for assembly onto. This involves placing the physical components on a board of a certain dimension, and routing all the traces between each of the components so that the power, ground, and signal all go where they are supposed to. This is an art all to itself, and this is my first attempt at laying out a board. I think I did a pretty good job, all things considered.
The board I designed is two-sided, and so allowed for 2 ground planes, as well as routing some traces on the back side. It may have been possible to do all my routing on one side, if I really looked at the flow of power and signal, but it may have required a larger footprint.
I placed all the connections for the off-board components around the edges of the board to make soldering the wires easier. I clustered the IC chips at the bottom, and the LED assemblies in the middle. The power assembly is up at the top-left corner, and the output assembly is at the top-right. The resistors and capacitors for the signal tuning are above their ICs.
After designing the board layout, I sent the files off to a circuit printing company. A few weeks later, I received a delivery with my circuit board(s)! I ordered 5, since the printing was cheap and shipping wasn’t.
It was then just a matter of placing the components in the correct spots, and soldering them in. This is the circuit board with all the non-external components soldered in.
All that was left was to attach the external components: the potentiometers, power, audio jack, switches, and LEDs.
I still need to place the assembly into a case so that it can be used, and protected. I’m planning on using wood for this, and will probably get the supplies at the end of the summer so I can work on it through the fall. I will definitely track the progress of the build here.