Independant flashing leds

Graham Stabler

This is going to be one of those annoying threads where I ask a question without telling you what it is for, sorry but I promise I will later and it should be worth it.

I need to make some flashing leds, probably about 32 of them, each should have it's own little battery and will not be connected to the rest. The thing is I need them to flash in a sequence, 4 at a time at 200hz. So there will be 8 groups of 4 leds that flash together, the first group will flash for 1/200 of a second, then the second set of 4 etc etc.

The propeller needs to know which group of leds are which so it needs to set them flashing in the first place.

So I'm thinking some sort of docking station connected to the propeller, the propeller gives each little LED circuit a kick to get it flashing, after that they must stay in sync by their own clock accuracy for as long as possible.

I'm open to other suggestions such as using a beacon from the prop from which each led can sync itself but it needs to be cheap so probably no RF.

Graham

Leon

I'd use IR links and give each group of LEDs it's own MCU, like a small PIC or AVR.

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Leon Heller
Amateur radio callsign: G1HSM

StefanL38

hi Graham,

by flashing independant do you mean there is NO electrical connection between the 8 groups of LEDs?

could there be an OPTICAL connection between the LEDs?

guess so as you mentioned a beacon

yes why not using a beacon and then each LED-group has a monoflop with different delays

or the second LED-group has two monoflops one for the beacon one for the flash of the first group

depending on the optical conditions the third group has three monoflops beacon 1st group 2nd groud etc.
or the second groud has a special and focused beacon towards the 3rd group


or maybe shiftregisters with parallel outputs. In each shiftregister a single high-bit is shifted to a different position and then the beacon shifts the bit in circles
through the register. Meaning the highest bit is connected to the serial input of the register

If the LEDs are connected to the different bits the LEDs are switched on only every 8th clock-signal but in sequence
to make the pulse short its combined with a monoflop that creates a short single pulse.

I also have a raw idea of a special re-sync circuit which counts the beacon-signals and if the circuit missed a beacon signal there will be a difference when
the next beacon-cycle is through and the low-high-pattern of the shiftregister (=wrong single bit is high making the re-sync circuit clear the register sift in the high-bit to the right position
and waiting for the next beacon-cycle to be finished to start cycling again. I guess this would require a really small MCU for each LED-group

best regards

Stefan

Graham Stabler

Leon,

all of the LEDs must stand alone even if they are flashing together and in fact LEDs in groups will be placed far apart on purpose. I should have also mentioned that the LEDs themselves will be IR (if they ever arrive).

Stefan,

That's right once up and running I would want each led to be a separate unit. I like the idea of the monostable delays triggered by a global beacon, the problem would be making sure that the LEDs did not reset each other although I could assume that all leds could see the beacon I could not assume they could see each other. Normally I would just use IR for the beacon but the LEDs are also IR. I could possibly use a modulated beacon and IR detectors to match.

Graham

rjo_

Graham,

Everything you do is worth looking at.

If it were me, I think I would use a photoresistor or phototransistor on the LED side and then strobe those from the Prop. You didn't say how much you wanted to spend... that is a constraint, which makes the conversations interesting[noparse]:)[/noparse]

Rich