OwlCircuits

Multiple flickering flames LED circuit

Pre-programmed microcontoller for controlling LED special effects

This microcontroller chip comes pre-programmed and provides 8 independently flickering outputs for use with LEDS. Each output flickers randomly compared to the others. User configurable for either slow or fast flicker. The default mode has all 8 outputs flickering continuously. By connecting one of the mode pins to ground, you can have the flickering LEDS start up one by one then turn off one by one. This can be used to simulate a burning building or forest fire scene.

PINOUT

Pin Name	Description
VDD	+3V to +5V DC supply
MODESEL1	Mode selection pin for configuring operation
MODESEL0	Mode selection pin for configuring operation
RESETb	Active low reset
FLICKER0 to FLICKER5	Flicker outputs for LEDS
NC	No Connection. Leave unconnected
VSS	Ground

Application notes:

Power supply

The microcontroller runs off 3V to 5V DC only. Using other voltages will destroy the microcontroller. For use with LEDS only. Make sure to provide the proper series resistors for the LEDS to limit the current to less than 20mA each.

You can run this microcontroller circuit off of 2 AA type batteries in series to get 3V operation. However, the preferred method is to run on 5V operation using a voltage regulator , for example the LM7805. Connect the VDD pin to 3-5V DC and the VSS pin to ground. A 0.1uF bypass capacitor is recommended to be placed across the power supply pins to minimize electrical noise.

Reset

The RESETb pin is active low. This means that when you connect RESETb to 0V or ground , the device will not operate and all the outputs will be off. For normal operation, RESETb should be connected to the same VDD voltage supply through a 10K ohm 1/4 watt resistor.

Mode Selection

This microcontroller has two mode selection pins that allow you to select different modes of operation by simply connecting the MODESEL pins to either power or ground. This allows you to chose different operating modes without having to use a computer or programmer.

Pulling the MODESEL pin to VDD (power) creates a logic 1. Connecting the MODESEL pin to VSS (ground) creates a logic 0.

The following shows the different operating modes depending if you connect the appropriate MODESEL pin to VDD (power) or VSS(ground).

MODESEL1	Operating mode
VDD (1)	Fast flicker
VSS (0)	Slow flicker

MODESEL0	Operating mode
VDD (1)	Continuous operation
VSS (0)	One by one startup and shutdown

Outputs

The 8 flicker outputs (Flicker0 to Flicker7) will drive the VDD supply to the LEDS. If you connect VDD to +3V DC , the outputs will drive 3V to the LEDS. If you connect VDD to 5V the outputs will drive 5V to the LEDS.

It is important to select a series resistor for each LED such that the maximum current is limited to less than 20mA. The micorcontroller can handle 20mA per output with a maximum total output of 200mA.

Example circuits

Below is an example circuit showing the typical way to hook up the microcontroller and LEDS. If you choose to remote mount the LEDS, use 22-24ga wire.

C1 is a bypass capacitor that helps to filter out electrical noise in the power going to the microcontroller.

By pulling the MODESEL pins up to VDD via a 10K ohm resistor, you will put a default value of VDD on the MODESEL pin. If you close the switch , it will pull the MODESEL pin to ground (VSS), selecting a different operating mode.

NOTE: The MODESEL pins are only read once when the device first gets power. Switching the value on the MODESEL pins during operation will have no effect. You need to power cycle or reset the microcontroller to select the new mode.

D1 to D8 are the LED flicker outputs. R4 to R11 should be selected to limit the current in the LEDS to less than 20mA.

Click for a larger circuit diagram image.

S2	Operating mode
Open (1)	Fast flicker
Closed (0)	Slow flicker

S1	Operating mode
Open (1)	Continuous operation
Closed (0)	One by one startup and shutdown