Electronics

I have been interested in electronics from early high school.  Over the years I've been several projects, etched 100s of PCBs and soldered possibly 1000s of kits.  Here you will find a small selection I've chosen to document and share - in the hope that they are useful to someone.

UV Exposure Box & Timer

posted Jan 9, 2012, 3:28 AM by Andrew Jessop   [ updated Jan 10, 2012, 2:59 AM ]

April 2006

I was getting into microcontrollers such as the AVRs and I needed a quicker, easier and more flexible way of building circuits. I have since seen some insane circuits built with veroboard and enamel copper wire, but I am too impatient to build circuits this way and I also like the neatness associated with PCBs.

I therefore set out to build a UV Exposure box to etch my own boards. I bought 4x18W fluorescent battens from Bunnings for $20.00 each and designed a box to fit them all in. I drew up the design in Autocad, which is basically a box with a small compartment on the side for the wiring and a timer to switch the tubes down the track. The drawing isn't dimensioned and some parts of the design changed while building, but the basics are the same. The tubes are mounted 75mm apart on their axis, and are 60mm below the glass plate. I purchased the sheet of glass for ~$20 to fit in on the top.

Here is a basic parts list of my box, and a picture of the box nearing completion.

2 x base/ lid 800 long x 350 wide
2 x front/back 165 high x 800 long
3 x sides 325 wide x 165 high
1 x plate of glass 650mm x 325mm x 4mm
2 x hinges



UV Exposure Box Timer

After building the exposure box, it was decided that a timer would speed up the PCB making process and help to control some of the variables when still learning. A suitable pre-made timing module was found at Jaycar Electronics (XC-0124) for reasonably cheap (around $10 if I remember correctly).

The circuit schematic is fairly simple and is based on standard parts. A 12v relay is connected to H2 and is switched after the time has elapsed. After looking at the simple data sheet provided, the timer required a 1.5v supply and would go high while the timer was counting down. When the counter had finished the output would go low again. To power the timer a small 12V AC transformer was mounted inside the wooden box. The circuit would then rectify and regulate this power to DC to run the timer, a relay to switch the UV lights and some leds to indicate power and when the UV lights were on or not.


A simple PCB of the circuit was made which can be used to create your own. A capture of the design is shown below.


A wiring diagram of the control and power of the box shows how the internals are connected.

Atmel AVR ATMEGA32 Development Board

posted Jan 9, 2012, 3:17 AM by Andrew Jessop   [ updated May 29, 2012, 8:47 PM ]

Jan 2008

This project has evolved over several AVR experimentation projects from the need for a more generic platform to enable EASY! AVR experimentation and project development. This same dev board is used for many of my projects including a uni project, RC car speed measurer, AC light dimmer etc, and has been a major part in other project development.

Hardware

This PCB holds an Atmel ATmega32 AVR that has 32Kbytes of Flash Program Memory, 2Kbytes of SRAM, and 1KByte of EEPROM. The chip has 4 x 8-bit General Purpose I/O ports, of which some have alternate functions. Other features include 8-bit and 16-bit hardware timers, a USART, SPI, I²C as a start.

Apart from the power regulator, the rest of the design is just headers and connectors for the I/O ports. As you can see from the picture, there are a row of screw terminals as well as a header in parallel for each port, which gives the user the option to connect other add on boards to this dev board such as switches, LEDs, LCD; or the user can wire their own project in via the screw terminals.

The PCB overlay is available to provide a better insight into the project.

Parts List

A basic parts list is available. ALL the parts were purchased from Jaycar Electronics but I am yet to add in catalogue numbers.

Add On Boards

  • Serial Board
  • LED Board
  • Switch Board
  • DIP Switch Board
  • Motor Driver Board (T.B.C.)
  • LCD Board

Digital Volume Control

posted Jan 9, 2012, 3:02 AM by Andrew Jessop   [ updated Jan 22, 2012, 5:17 PM ]

Documenting my work on a digital volume control.

Background:

I was fascinated with audio and speakers at an early age; even before my father purchased my first 1W Amp kit from Dick Smith Electronics at age 11.  I enjoyed the concept of being able to share my enjoyment of music from my walkman with my friends at school.  Ever since I built that first kit I have been on an electronic journey for knowledge and satisfaction of my original goal - to share my enjoyment of music with others in the best way possible.

This specific project started in around grade 11 after I was introduced to Atmel AVR Microcontrollers.  It has taken a good many years to acquire all the knowledge required to piece this project together.  It has been the cornerstone of my extra-curricular engineering learning and provided me with motivation, purpose and enjoyment since I started.

It has taken on many incarnations over the years, however I will be only describing the present (and ongoing) version here.

Features:

* 4 RCA audio input w/ CD4066 digital controlled input switching
* LM1972 Digitally controlled analogue volume chip
* Network accessible via HTTP and a REST architecture using either ENC28J60 or RTL8019AS + NXP LCP2148 ARM
* TSOP4838 [pdf] IR Remote Sensor
* Rotary Encoders for volume and source selection

Software:

* lwIP or uIP embedded TCP/IP stack

Hardware:

Prototype

LPC2148 Dev Board - purchased from eBay
ENC28J60 Dev Board - purchased from eBay
 
CD4066 Analogue Demultiplexer Prototype
 
Custom LM1972 Board  


AC Light Dimmer

posted Jan 9, 2012, 2:37 AM by Andrew Jessop   [ updated Jan 9, 2012, 2:41 AM ]

March 2006

This project came about because a friend of mine had something similar as a component for his final year electronic engineering project. We decided that we would have a kind of competition to see who could build an AVR based AC light dimmer the quickest. I was interested because I had always wanted to experiment with AC power control, and this was the perfect, simple little project.

AC Dimming Theory

Explanation to go here.

Hardware

The schematic for the dimmer is of a fairly simple design. The zero crossing detector is based on a diode bridge which rectifies the AC into full wave. This will go to zero each half cycle. The transistor is then used to switch the optocoupler on as the voltage rises above ~0.7v. The triac is the main switching device for the load since this is an AC dimmer. The control is fully isolated from the AC source so this circuit could be used to switch higher voltages as long as proper precautions are taken.



Software

The code for this project was written in BASCOM AVR - a BASIC compiler for the AVR microcontrollers. The code is fairly simple and is only two pages long.  The main loop just polls the port where the zero crossing detector is connected. If there is a zero crossing, then wait for a short time to give the voltage on the base of the transistor time to fall to zero instead of 0.7v, and start the timer.  The timer interrupt just coverts a brightness based on a 50Hz (or is it 100Hz due to rectification?) time period and turns the triac on. The triac will automatically turn off at the next zero crossing, so the timer is reset to maintain the brightness.

References

Silicon Chip

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