Fast enough for rotating LED clock?

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amewsaj

Member
I was wondering if the PICAXE microcontrollers (28x1) would be quick enough for a simple version of a rotating LED clock?

http://www.youtube.com/watch?v=no2_M_b059g

Not neccesarely as advanced, but would the calculation speed be fast enough to display anything?

I guess I have to get up to 60 rounds per second?
Assuming I have 60 places per round, I have to update the LEDs 60 times per round.

That would be 60*60 updates per second = 3600 updates per second = 3,6/ms

Am I right that the picaxe is not fast enough?
 
S

SilentScreamer

Senior Member
At a rough guess id say its just about possible with an X2 running at 64Mhz. Note only the 3V 28X2, 3V 40X2 and 20X2 can run at 64Mhz.
 
hippy

hippy

Ex-Staff (retired)
You can use lower refresh rates than 60Hz. 3600 updates per second is about 270us per update; an 08M can manage that at 4MHz.

Take a look at the Spacewriter Kit (AXE135S) which uses a 20M.
 
T

tiscando

Senior Member
I was planning to create a cylinderical RGB POV with 192 LEDs in total, and 480 columns per revolution.

I was going to make use of a multi-part video head spinner (the heads come off, leaving the rotating part of the signal inductor), to clock in SPI to the shift register LED drivers at 16MHz from a logic circuit controlled by a picaxe.
The picaxe would send a 'read' command to a SPI memory, enable the logic circuit to, after the index pulse from an encoder, start clocking the data to the display.
etc.
 
hippy

hippy

Ex-Staff (retired)
Large numbers of 'pixels' should work but one thing to consider is how bright the LED will be. For 480 columns that means a pixel will only be on for 1/480th of the time. To get the equivalent brightness of a fixed LED you'd have to drive it quite a lot brighter for that time and, if it happens to need to be on for the full revolution, you have to make sure you have a LED capable of being driven that bright for the full time. High brightness often means huge current which has to get to the display somehow.
 
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tiscando

Senior Member
I think I will be using very bright miniature leds.

Ok hippy, I would probably go for having double the LEDs, which means 240 columns for half a rev, and the spinner would be at half it's speed.

Anyway, before this, more info: there would be 32 LEDs on a vertical strip, and 64 LEDs on a visual column, which means for each colour, there would be 2 strips on the other side of each other, and the second strips would be slightly higher than the first ones. This means interlaced but fast scanning.

EDIT: to be more specific, I am likely to use these 1.8mm high power (red, grn, blu) LEDs in water clear package on rapidonline.com. They are about 40 times brighter than the standard types when driven at 20mA (a further x1.5 when driven at 30mA)
 
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