July 25th, 2009

Silent Ceiling POV Display

Silent Ceiling POV Display

A persistence of vision (POV) display is a device that creates an apparently still image using rotating LEDs with great speed. The human eye is not able to distinguish every image individually, so the picture formed appears as a solid image. The POV phenomenon is not a new discovery and a lot of POV display projects have been made. However, this one right here has two different attributes that differentiate it from other POV displays: it is located on a fan placed on a ceiling and it’s silent.

This project uses a fan with 5 propeller blades and every blade has 32 LEDs mounted on it (that means a total of 160). These LEDs are connected to an Atmel microcontroller on an Arduino board. The POV display also uses 74HC595 8-bit serial-in, parallel-out shift registers that convert serial-in data into parallel-out data. The microcontroller generates the sequence in which the LEDs are lit, thus creating the image.

The location of the display makes it pretty cool and the fact that it’s attached to this kind of fan makes the whole device completely silent, which is quite different from most POV displays out there that are rather noisy. Having a thing like this blinking in your living room might seem like a good idea if you want to impress a guest audience, but other than that I can’t find a reason for actually using it.

Silent Ceiling POV Display: [Link]

January 29th, 2009

Advanced LED display board

Advanced LED display

Like I promised earlier, this is a solution for larger LED displays, with as few as possible pin costs, my solution uses only 7 micro controller pins, and controls 128 LED’s, this can be scaled up to 2048-4096 without problems (check the schematic).


The heart of the schematic is a simple serial to parallel conversion, in other words a shift register (IC1,IC2) this can be connected directly to the SPI of the ATmega88, or to any SPI master. To further optimize the pin count I used a 3 to 8 decoder (IC3), since only one row is powered at any given time there is no use to directly connect the rows to micro controller pins. The schematic contains also the power buffer, which is made with discrete transistors, basically this is also a row to column addressing solution, to prevent the LED’s from flashing when the shift registers are updated the row’s must be disabled for a short time, this can be made with LEN input (IC6 pin6).

Example of a sequence: disable the rows, by pulling LEN to logic 0, update the shit registers via SPI, select the row, enable the row by setting LEN to logic 1. Between the row updates it is usefull to place a delay, makes no sense to have a refresh with a few kHz, this makes the display ligth fade, if the delay is to large the image won’t be steady, you must experiment the optimum refresh rate, my advice is that 50Hz-100Hz of image refresh is enough, this result in 400-800Hz row refresh.

By inserting more shift registers or decoders the resolution of the display can be increased, the only limit is the refresh rate, if you have a large display and you want to make some complicated animation which need a lot of computing and considering also the SPI frequency, the refresh rate could became to slow and the display will flicker.

Advanced LED display board.

January 26th, 2009

Simple LED display board

simple led display board

This project is for beginners, but even people with experience can find it interesting the solution for doubling the columns of the display. They say that a picture worth a hundred words, then what would worth a movie? I recall when i was learning micro controller programming, after i made the led blink, and a few led animations the next step was to build a display suited for text or animation, at this moment everybody tries to power each led individually but since you can’t use a 150 pin micro controller you look for more clever solutions, which is the row-column addressing.

On the video the author explains step by step how to control 120 LED’s with just 16 pins, with normal row-column addressing you can control only 64 LED’s, by using a simple trick you can double your resolution. Although they omitted the fact that you need to use some buffer circuit, or limit the total current of your LED’s in a row, be aware that a micro controller pin can handle only 20mA.

If you will be interested, I can post a more advanced method which uses only 7 pins and can control a display with a few thousand LED’s.

Simple LED display board: [via][Link]

June 2nd, 2008

ATtiny2313 Thermometer

ATtiny2313 Thermometer

The brain of this project is an AT90S2313 that controls the LED Display thus showing the temperature read from a DS182 temperature sensor. The temperature sensor chip, DS1820 is connected to PD1 with a 4.7k pull-up resistor. The circuit presented here uses only one sensor, but you may tie multiple sensors on the same line and modify the program to read it with the help of internal chip ID.

ATtiny2313 Thermometer: [Link]

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