Saturday, March 23, 2019

Programmable light controller

The main objective of this project is to design a maintenance free and low-cost light which automatically turns on and off at the predetermined time of the day.

To meet the above requirement I designed this controller using ATmega8 MCU and DS1307 RTC. The driver stage of this light controller is intended to work with commonly available 7W LED modules.

PCB of the programmable light controller.

The core component of this programmable light is ATmega8 low power CMOS microcontroller. The main reason to select this microcontroller is it’s lower cost and higher availability. Except for the above two reasons this microcontroller also bundled with a rich set of peripherals which including 23 GPIOs, 3 independent timers, Two-wire serial interface, EEPROM, etc.

Apart from ATmega8 microcontroller, this system uses DS1307 real time clock to maintain system time. Like ATmega8, DS1307 is also a very popular RTC in the market.

This controller is designed to work with a 24V DC power supply. The main reason to select 24V is that most of the medium power LED modules in the market are designed to work with that voltage. During my search all the medium power LED modules which I found are designed to work with 20V - 28V range. Out of those LED modules, the majority of modules are rated for 24V input.

The bottom side of the programmable light controller board.

For this circuit, the recommended power supply is 24V 1.5 A portable switch mode power supply. Except for the LED driver stage the all other parts of this light controller is designed to work with 5V. MC34063 DC-to-DC converter is used to supply 5V to those components.

To reduce the size of the PCB I design this system using surface-mounted components, but this system can also build using through-hole type components. At the prototype stages, I build this system entirely on a breadboard using through-hole type parts.

To build 7W light, I used LED lamp parts available in the market which including Warm white 7W LED panel, aluminum lamp shell (heatsink) and diffusing cap (lamp cover).

All the design files and source code related to this project are available at The complete documentation of this project is also available at Github Wiki.

Monday, March 11, 2019

Lightning arrester installation

Recently I build my new house near Maharagama town. While building this house I allocate space for my antennas and observation equipment. Before installing antennas, I decided to install a lightning rod into the house. The main reason to install a lightning rod is because of the height of the building. It nearly 48 feet (approximately 15m) high, and located in open space, because of those reasons there is a very high probability to hit lightning into my antennas and other equipment.

Installed lightning rod

At the time of this writing, in here in Sri Lanka mainly two types of lightning arrestor systems are in use. The first type is a conventional lightning rod. This type of lightning rod is very common in Sri Lanka and it made with copper rods. The second type is ESE (Early Streamer Emission) type lighting arrestor. This ESE type is now getting popular in here and I saw it in a couple of new buildings. As I noticed most of the lightning arrestor installation companies are now moving into this ESE type solutions.

After reviewing lighting rods in the market, I decided to move into the conventional light rod. The main reason to select conventional light rod is because of its cost. Based on my findings decent quality ESE type lightning arrester costs around LKR 70,000 - LKR 120,000. Again this price further varies with its effective range. The conventional lightning rod costs LKR 9000 only. Also, the effectiveness of ESE type is still in debate. By considering everything I decided to stick to the low-cost conventional method.

Components of the lightning rod.

Friday, March 1, 2019

TCS230 based Bluetooth color picker

This is TCS230 based Bluetooth color picker prototype which we build to test the concept. In here the idea is to extract color from any physical object and transfer it to PC / mobile. To test this concept, we use low-cost TCS230 color sensor.

A prototype version of color picker on a tiny breadboard.

TCS230 is programmable color light-to-frequency convert IC. This chip produces square wave output with frequency directly proportional to the light intensity. To drive this sensor and capture its output we used PIC16F628A microcontroller. The processed output is then transferred to the host using the HC-05 Bluetooth SPP (Serial Port Protocol) module.

In PC we wrote small Python script to display captured value and color in a Window.

In this design, we drive the TCS230 sensor with 20% frequency scaling. The entire circuit is built using commonly available modules and components. For the color sensor, we use the 8-pin TCS230 sensor module which is commonly found in eBay and other online electronic component stores. This module comes with 4 white LEDs and because of that, we don’t need a separate circuit for LEDs.

Minimum frequency readout from TCS230 for green color.

Maximum frequency readout from TCS230 for green color.

Sunday, February 24, 2019

13.8V 5A Power Supply

13.8V power supplies are commonly used in armature radio experiments. Most of the portable armature radio transceivers are designed to work with a 13.8V power source. We mainly build this power supply unit to power some of our armature radio circuits and modules.

This design is based on the popular LM338 5A voltage regulator. We choose this regulator because of to it’s higher current rating, short-circuit protection feature and higher availability.

The prototype version of 13.8V - 5A power supply unit.

Apart from that, we include MC3423 based crowbar sensing circuit to preventing an over-voltage condition of a power supply unit.

We design this circuit by using commonly available 18V×2 (5A) + 12V (1A) transformer. This transformer is available in the market because it’s commonly used with some AF power amplifier systems/kits. We use its 12V terminal to drive 120mm - 12V cooling fan.