When beginning with electronics you’ll get introduced to alot of beginner projects. One of those probably uses the 555 timer IC to generate pulses that make LEDs flash or speakers buzz. This generation of pulses is called oscillation and is used in electronics everywhere.
A more primitive way to get oscillation is with a very ancient circuit called the ‘transistor LED flasher’. This circuit uses a very nifty way to create oscillation. Also notice how the circuit is perfectly symmetrical.
R1 and R4 limit the current through the LED and R2+C1 and R3+C2 determine the speed in which the capacitors loads and thus determines the switching speed of the transistor. The speed (frequency) at which the oscillator ‘vibrates’ goes up when R2 and/or R3 go lower in value or when the capacitors go lower in value.
The values to choose for the components depend on the supply voltage. In this case with a 9 volt power supply (like a battery) the current limiting resistor for the LED’s (20mA) should be:
R1 & R4 = U / I = 9-2.8 / 20mA = 7 / 20mA = 350 Ohm. (Subtract 2.8 volts because of the forward voltage of the LEDs and transistor internal diode!)
The frequency of the circuit where C1=C2 and R2=R3 is given by:
f = 0.72 / RC
For example we use 68k Ohm as R2=R3 and 4.7 uF as C1=C2 then the frequency is:
f = 0.72 / 68000 * (4.7*10^-6) = 2.25 Hz
If the values of C1 != C2 and R2 != R3, then the following equation applies:
f = 1 / (0.693 * (R2*C1 + R3*C2))
Applying this equation to the same values give:
f = 1/(0.693 * (68000*(4.7*10^-6) + 68000*(4.7*10^-6))) = 2.25 Hz
The circuit above has been transferred to the following PCB:
As you can see I forgot that ground planes were a thing. Using ground planes would’ve got rid of a lot of unneeded traces and would’ve made the PCB single sided instead of two sided. Also the fancy edge cutting wasn’t necessary but I like to make the boards look odd. The 3D render proves that
After finishing the 3 component modules I wanted more of a challenge. I looked up the datasheet of the infamous LM386 audio opamp that is featured in many cheap audio applications.
Datasheets from IC’s like opamps often contain a ‘typical application’. These are circuits that show off the basic configuration of the IC or a simple implementation of the IC for various applications. For the LM386 I took the typical application for an audio amplifier with bass boost.
I took the schematic and remade it in KiCAD
Then I laid down the PCB
Also added a little silkscreen text to show who the creator is. The 3D render is pure art
Feedback is always welcome!
When looking at different electronics webshops that sell modules to make life easier, I got shocked by the way they turn any electrical component into a module. Then I thought let’s keep going with the easy modules and I made a module for an RGB LED.
The schematic is as easy as can be:
The labeling is a bit messy but the idea is there. The left connector represents male pin headers and the right connector represents the RGB LED. The resistors are used to limit the current to each LED. Note that every LED need a different value resistor.
The PCB layout is quite artistic again. I noticed how the solder pads for ground are rectangular and the others are circular. After a bit of research I found out that the positive voltages always use rectangular pads. Well, let’s call it a small design flaw then.
The 3D render looks pleasing again
Any feedback is welcome!
When starting with KiCAD I found out it was fairly easy to design PCB’s. To keep training my skills I did some small projects. One of these projects is a module that simply contains a buzzer, a potentiometer and some male headers. The module could be used as speaker with volume control.
The schematic is fairly simple
The module uses two male headers as signal input. The current gets limited by the potentiometer. From here on I continued laying down the PCB.
The end result is quite pleasing
Any feedback is welcome!