Scaling the Hex Led Sensor circuit, discussed earlier, to control a large array of LEDs for active mirrors, etc is not practical.
With 10ms sensing times for each LED sensor input, multiplexing is not an option for reason of excessive flicker. And using a 18X for each 6 LED sensors would quickly run into $$$ for large display.
The physical bidirectional I/O function of the PICAXE to interface the LED sensor / display can be easily duplicated in discrete CMOS logic as shown here:
<A href='http://www.user.dccnet.com/wrigter/picaxe/ledsensordisplayv2.gif' Target=_Blank>External Web Link</a>
I have tested this design with two 74HC374 octal registers. Each register controls 8 LEDs and a single 08 picaxe can provide all the timing signals for as many registers as needed.
This design is scalable to virtually any size with no timing penalties and can be expanded to control a very large array of LEDs. In this design, the LED sensor to LED display conversion is processed by the registers themselves. The picaxe can only adjust the sensitivity of the threshold.
For a large instalation, the physical design of the circuit can be modular.
PCBs that are 4" x4" with eight 74HC374 chips controlling 64 LEDs in a 8x8 array spaced on 0.5" centers would be practical.
Each module would cost approximately $15
A mirror of 64 x 64 LEDs (4096) would be a respectable 32" x 32" and would require 64 modules all connected to a 3 wire bus which can be controlled by a single PICAXE 08M for this simple mirror application.
Alternatively each module can be separately controlled by a 08 or 08M which allows modules to be used in complex feedback installations in which multiple small mirrors reflect each other to generate recursive dynamical LED Display patterns.
With a modest 5 mA per LED and the typical 50% sample/display dutycycle, each module requires 5V @ 170mA.
For the large mirror a 10 amp power supply is required for all LEDs on.
wilf
Edited by - wilf_nv on 14/01/2007 09:37:17
With 10ms sensing times for each LED sensor input, multiplexing is not an option for reason of excessive flicker. And using a 18X for each 6 LED sensors would quickly run into $$$ for large display.
The physical bidirectional I/O function of the PICAXE to interface the LED sensor / display can be easily duplicated in discrete CMOS logic as shown here:
<A href='http://www.user.dccnet.com/wrigter/picaxe/ledsensordisplayv2.gif' Target=_Blank>External Web Link</a>
I have tested this design with two 74HC374 octal registers. Each register controls 8 LEDs and a single 08 picaxe can provide all the timing signals for as many registers as needed.
This design is scalable to virtually any size with no timing penalties and can be expanded to control a very large array of LEDs. In this design, the LED sensor to LED display conversion is processed by the registers themselves. The picaxe can only adjust the sensitivity of the threshold.
For a large instalation, the physical design of the circuit can be modular.
PCBs that are 4" x4" with eight 74HC374 chips controlling 64 LEDs in a 8x8 array spaced on 0.5" centers would be practical.
Each module would cost approximately $15
A mirror of 64 x 64 LEDs (4096) would be a respectable 32" x 32" and would require 64 modules all connected to a 3 wire bus which can be controlled by a single PICAXE 08M for this simple mirror application.
Alternatively each module can be separately controlled by a 08 or 08M which allows modules to be used in complex feedback installations in which multiple small mirrors reflect each other to generate recursive dynamical LED Display patterns.
With a modest 5 mA per LED and the typical 50% sample/display dutycycle, each module requires 5V @ 170mA.
For the large mirror a 10 amp power supply is required for all LEDs on.
wilf
Edited by - wilf_nv on 14/01/2007 09:37:17
