# Archive for the ‘General’ Category

## Ferric chloride

Posted by doc on March 22, 2021

In order to etch my own printed circuit board, I bought some ferric chloride.

The seller instruction is to dissolve 40g in 110.5ml of water.

To concoct 1 molar solution of FeCl3, according to its molecular weight, one will need 162.2g for every 1L of water.

So with 100ml, 16.22g is needed.

40/110.5*100/16.22 = 2.232mol.

## Number of Wires.bas

Posted by doc on March 22, 2021

Rem W is the diameter of the wire in mm
Rem W = 0.35
Input “Diameter of wire in mm”,W

Rem H is the diameter of the hole in mm
Rem H = 8
Input “Diameter of hole in mm”,H

Input “Length per winding in mm”,L

Print “Winding calculator by Dr Liew”
Print “March 7th, 2021”
Print

Print “Diameter of wire = “;W;”mm”
Print
Print “Diameter of hole = “;H;”mm”
Print
Print “Length per winding = “;L;”mm”
Print

Rem t is the height of triangle
t = W/2

Rem A is the area of the hexagon
A = 2*sqrt(3)*(t^2)

Print “Area of hexagon = “; A;”mm²”
Print

Rem B is the area of the hole
B = 3.14159265354*((H/2)^2)

Print “Area of hole = “; B;”mm²”
Print

Print “Number of wires = “; int(B/A)
Print

Print “Length of wire required = “; int(B/A)*L;”mm”

## Winding a Toroid

Posted by doc on March 22, 2021

A ferrite core is prefered. A metal nut doesn’t really work. Magnetic property is just not the same.

More turns equal more Henry value of the coil.

But given the size of the hole, how to calculate roughly how many times a wire of given size can pass through it?

So first, we need to convert each round wire into a hexagon in order to fill up the gaps in between them.

Each hexagon will be composed of six equilateral triangles.

Each equilateral triangle will have a height of W/2.

The area of each equilateral triangle is then calculated.

Multiply the area of equilateral triangle by six will be the area of each hexagon.

The area of the hole H will can be obtained easily.

Divide the area of the hole with the area of one hexagon will give you a rough idea of how many wire can pass through said hole.

The thickness and the height of the cylindrical core will tell you the length of each winding. Multiply this with the number of times the wire can pass through will produce the total length of the wire needed.

But with more winding, the length of the wire each turn will increase. So you may need to take this into consideration if there is a very big hole to be filled.

Again, this is just a rough calculation, accuracy is more than enough for small projects.

Posted by doc on March 22, 2021

Another simple LED blinker using 1 NPN and 1 PNP transistor.

## Joule Thief

Posted by doc on March 22, 2021

Here is testing a Joule Thief circuit with a simple oscilloscope.

It can bring the voltage of a battery (with as low as 0.3V left) high enough to light up an LED.

## D-cell

Posted by doc on March 22, 2021

Switching the AA battery with a D-cell. I have changed one of the 100nF ceramic capacitor to a 10nF version. Thus the frequency is now 10Hz instead of 1Hz. So, it can still blink for 10 years. This Energizer Max D-cell has a shelf life of 10 years.

Need to find a housing for it.

The 4 screws holding the circuit board to the battery holder are 1.6mm glasses/watch screws.

I have also pulled away the LED so that it may be afixed somewhere else in its future housing.

Posted by doc on March 22, 2021

The same circuit on breadboard. This enables me to swap components with different values to test out different configurations. For example, to make the LED blink faster.

Don’t worry, I have tidied it up later, replacing those naked copper connections with proper jumper wires.

And the four jumper wires in the photo connects to a toroid elsewhere.

## Circuit Board

Posted by doc on March 22, 2021

I drew this circuit using Fritzing’s PCB view.

The result:

The problem with this circuit board is the gaps were too narrow. Even with a little moisture, where will be leaking current somewhere. However, with thorough cleaning (with dish washing paste) and drying (with a hot air gun), it worked without a problem. Hot components will make the LED blink faster.

Still need to wash and dry to get rid of leaking current.

I have also made a templates out of 2mm acrylic sheet. This will let me make more circuit board easily.

## 10-year LED Flasher

Posted by doc on March 22, 2021

I got this diagram from https://www.instructables.com/10-Year-LED-Flasher/.

There is another from https://www.hackster.io/simpletronic/10-year-led-flasher-398282 but I tried on breadboard and it didn’t seem to work.

The obvious difference is the lack of a diode 1N5819 in the later.

This circuit is supposed to light an LED bulb for 1/1000th of a second (1mS), every second, for 10 years, using an AA battery.

If you switch the AA battery with a D type battery, which carries 10 times the charge, it may blink up to 100 years, provided that the battery doesn’t deteriorate sooner.

## 我操

Posted by doc on February 12, 2021