LM3909 IC 1.5V LED Flasher Circuit

LM3909 IC 1.5V LED flasher circuit. A circuit that uses the now obsolete LM3909 IC to flash an LED from a single 1.5V cell. This IC and circuit is now a piece of history. I had one of these circuits running on a PCB for years, the circuit finally failed. My attempts to repair the circuit were unsuccessful. It appears that the IC finally failed. Read on for a look at some electronics history.

LM3909 1.5V LED Flasher Circuit Diagram

Below is the circuit diagram of an LM3909 LED flasher taken from an out of print electronics magazine. I built this circuit on a tiny PCB many years ago. The circuit operated from a single 1.5V cell, but could also operate from a single 1.2V rechargeable cell.

LM3909 1.5V LED Flasher Circuit Diagram

LM3909 1.5V LED Flasher Circuit Diagram

Flashing an LED from a Single Cell

I remember the LM3909 being expensive, costing many more times than a 555 IC. The problem with using a 555 is that it could not be used to flash an LED from a single 1.5V cell, but had to operate from a higher voltage. A 555 also drains a lot of current from a battery because of its internal voltage divider resistors.

When the LM3909 became available it was popular with hobbyists because an LED can not be lit up from a single 1.5V cell. Here was an IC that would flash an LED from a 1.5 or 1.2 volt cell, pretty impressive. The cell would last for a long time too.

LM3909 now Obsolete

Unfortunately the LM3909 is not available anymore. It was made obsolete several years ago and has no equivalent or replacement part. There are some transistor circuits available that will flash an LED from a single cell.

Attempting to Revive my LM3909 Circuit

The only LM3909 IC that I have was used in a LED flasher circuit built on a PCB. Fortunately I had used an 8-pin IC socket on the board, so could remove the IC to test it on breadboard. The PCB and breadboard test circuit are shown below. Notice that only two additional components are needed in the circuit – a capacitor and LED.

LM3909 PCB Circuit and Breadboard Circuit

LM3909 PCB Circuit and Breadboard Circuit

After many years of service, the LM3909 finally failed. After testing the PCB circuit with a new battery and then building the circuit on breadboard and testing it, the LM3909 was finally declared dead.


Choosing an Arduino for Beginners

In this blog post we look at how beginners wanting to start with Arduino can choose an Arduino board. Help is provided for beginners choosing an Arduino. The difference between an Arduino and AVR ATmega microcontroller is also covered.

Choosing an Arduino for Beginners

The recommended Arduino for beginners is usually the Arduino Uno. On the Starting Electronics website, the article on choosing an Arduino for beginners provides more information on which Arduino to choose when starting to learn about Arduino and writing sketches.

Difference Between Arduino and AVR

Many Arduino beginners are confused about the difference between Arduino and AVR, or Arduino and ATmega. Difference between Arduino and ATmega328 explains what the ATmega328 microcontroller is and how it relates to the Arduino Uno. The article also explains more about the AVR microcontroller found on most Arduino boards.

Update to Arduino Programming Course

The Arduino programming course originally started in 2014 is being updated and extended. Updates include using the newest version of the Arduino IDE and updating the videos in the course to HD video.

Currently parts 1 to 5 of the course have been updated which cover Arduino sketch structure and flow, Arduino main loop, calling functions, variables, arithmetic operators and relational operators.

Once updates have been completed the course will be extended to include new material and topics. Take a look at the Arduino programming course contents page to see the currently available tutorial parts of the course.


Atmel Software Framework Tutorial

The final part of the Atmel Software Framework tutorial is now available. It covers how to use the ASF help documentation and how to find and use example ASF code. The tutorial uses an Atmel ARM Cortex on an Atmel Xplained evaluation board.

A previous blog post listed the current articles in the tutorial at the time of posting. The tutorial series is now complete.

ASF – Atmel Software Framework Tutorial

The first part of the ASF tutorial series introduces ASF and shows the basic structure of ASF. Each part of the tutorial series explains various parts and usage of the ASF in easy to follow steps.

The final part of this series shows how to use the ASF documentation and ASF example projects in Atmel Studio 7.


ESP8266 ESP-05 WiFi Module – Getting Started

I recently purchased three ESP8266 ESP-05 WiFi modules. These are very cheap WiFi modules costing around $4 USD each, so are ideal for hobbyists, makers and hackers to use in various projects. My idea was to try to get an Arduino web server working on WiFi as a cheap alternative to using an Ethernet shield or WiFi shield.

Although the same module is available from several suppliers, the particular module that I bought was from SainSmart: SainSmart Neu ESP8266 Esp-05 Remote Serial Port WIFI Transceiver Wireless Module AP+STA

ESP8266 ESP-05 WiFi Module

ESP8266 ESP-05 WiFi Module

ESP8266 ESP-05 Pinout and Documentation

The supplier web page for the ESP8266 ESP-05 had no pinout for the module and no documentation. Some of the information on the web page for the module was also completely wrong, for example they state that the module has 5V compatible I/O, however this is wrong. The I/O pins only work with 3.3V logic and are not 5V tolerant.

They also state “on board antennae”, but this module does not have an on board antennae, it has a connector for an external antennae.

ESP8266 ESP-05 Pinout

After some searching on the web I found a pinout diagram for the 5 pin version of the ESP8266 ESP-05. A new article with pinout and power requirements for the ESP-05 is now available on the Starting Electronics website.

ESP8266 Documentation

The manufacturer of the ESP8266EX chip found on the ESP-05 and other modules is the Espressif company. Documentation for the module must be taken from the ESP8266EX datasheets on the Espressif website. Look under Documentation on the ESP8266 resource page where you will find datasheets, user guides, application notes, technical references, etc.

Getting Started with the ESP8266 ESP-05 WiFi Module

You bought a ESP8266 5-pin ESP-05 module, now what? Here are the steps necessary to get the module working for the first time. Once you have a basic understanding of the module and where to find further information you will be able to start your own project development.

Soldering the Header

The module comes with a separate 5-pin header that must be soldered into the module. After the header is soldered to the module it is easy to use the module in a breadboard.

ESP8266 ESP-05 with Header Soldered

ESP8266 ESP-05 with Header Soldered

The following video shows how to solder the header to the module.


Aerial / Antennae

I found that the module works fine without an aerial / antennae as long as it is near enough to the WiFi router that it is connecting to. Connecting a wire to the aerial connector does give it more range and picks up the second WiFi router that I have on the other side of the house.

Testing the Module

Use the pinout diagram to correctly connect the ESP8266 module power and UART data pins. An Arduino Due is ideal for testing the module. This is because a Due can supply enough current from its 3.3V pin and works with 3.3V logic. The Arduino Due is therefore completely compatible with the ESP8266 module.

The article on testing the ESP8266 ESP-05 module using an Arduino Due shows how to connect the ESP8266 module to the Due and test it. Use this article to get started with sending AT commands to the WiFi module.

Documentation and Staring your Own Projects

Once you have the ESP8266 module working, it is a matter of sending the correct AT commands to the module to set it up for your project.

Find example AT commands in the ESP8266 AT Command Examples document.

Find all of the AT commands in the ESP8266 Instruction Set document.