I'm in a group who is thinking of using the Peggy 2.0(several of them) as part of a educational design project. The project is to build an outdoor solar power based 'commercial' quality sign.
We're trying to figure out what LEDs would be the best to use in harsh conditions like direct sunlight and be viewed from upwards of 50 feet away. Right now, it seems like
green diffused LEDs are what we should be getting (since our eyes are sensitive to green). I just have no idea how 'bright' they should be. Any suggestions?

An outdoor LED sign is a serious design challenge, especially if you want it to be visible in sunlight. Generally speaking, you'll want the brightest LEDs that you can get your hands on and you'll want to drive them as hard as they allow. Avoid diffused LEDs-- they will light up when the sunlight strikes them. Instead, what you want are LEDs with water-clear lenses. If you'll only need to really see the sign from 25+ feet away, you can get LEDs with narrow-angle (5-10 degree) lenses that have incredibly high (100,000 mCd +) luminous intensity (white, usually).

Peggy 2.0 is designed as a low power display-- it comes with a battery holder, and is designed to run for days on end on one set of batteries. However if you're willing to hack a bit it can be "hotwired" to drive the LEDs close to their limits instead, making a much brighter, but power-hungry display that might be suitable for use outdoors. (Note: Outdoors or in, keep Peggy dry!) This requires building it with a different set of transistors. I'd suggest type STX790A. They are expensive but awesome. These are not *exactly* pin compatible-- you need to insulate the middle pin with a few mm of heat-shrink tubing and then twist the middle and right pins (while able to read the label) to swap their positions before putting them into the board. If you do this mod, just forget about driving peggy with batteries-- it will eat D cells for breakfast. ("Primitive but nutritious!" Instead, plan to drive Peggy with a 5 V regulated power supply with at least 700 mA capacity.

As I understand it, to high power LEDs (like Luminex 1W or other brand 350ma), we would just replace the transistors with beefier ones, and lower the resistor values accordingly? Or would I have to replace all the components to be able to handle the larger current?

Alternatively I guess I could power the LEDs separately and have a transistor for each LED individually, that would take some time but I have minions to solder for me

Peggy is definitely *not* designed for LEDs like that. You can use them, but they'll only be driven up to the max of the current drivers, 100 mA at best. Driving a 625 W LED driver is *not* trivial-- you'd need *much* more expensive electronics, a *serious* power supply, and a *serious* fan. There's very little in common with the design between something like that and the Peggy.

What can be done with 40ma LEDs, for instance, that are brighter offboard and get dim when on the peggy ? Changing resistors/transistors/power supply would do ? What kind of calculations should I make for resistors (for transistors I have no clue, need help hehe )
I assembled a peggy with ~40ma high brightness LEDs and would like to mod the board so I can remove the diffuser.
I'm aware that if made wrong way I could reduce the LEDs lifetime and overall components, but I'm willing to try.
Thanks

If your LEDs are rated for 40 mA, then you can turn up the current limit on both LED drivers to 40 mA without special considerations. The current limits are controlled by the values of RA1 and RA2; look at the datasheet for the LED driver chip to see what resistor value to choose. If your board has the pots, turn those all the way up. You could also add a wire across the three pins of the pot to short circuit it and keep it turned up permanently.

If you want to turn it up further, all the way to 100 mA, it will be within the pulse current spec of your LEDs, but it may not be if the LEDs are on continuously during turn-on and programming.

On the topic of high power LEDs: Here's a good looking setup for 60W worth of LEDs:
http://blog.makezine.com/archive/2010/01/photon-blasting_60w_rgb_led_array.html

Imagine what it would have to look like to handle 625 W of LEDs in a similar amount of space!

The LEDs will definitely be off-board, and using ping pong balls as diffusers on a board that is at least 50"x50" . If they peggy is just used to switch (NPN?) transistors, and I cannibalize 5 computer power supplies to create a circuit for the LEDs, it at least that possible? Of course computer power supplies would require different resistors since they usually have 3.3v, 5v and 12v rails but at least the circuit would be isolated from the peggy2 circuit.

Summary: Use the peggy2 not to drive LEDs, but to switch transistors that drive other fun stuff.

@Windell: Thanks for being informative and taking the time to research and link to related projects.

I think that there are several different configurations being discussed here.

Yes, you can use the Peggy board to drive LEDs with higher brightness than in standard configurations, but it will still be a multiplexed display, where only one row is driven at a time. Effectively, you can drive 100 mA at a given time into one row, if the LEDs will handle it. For a row of 25 LEDs, that requires a current of 2.5 A. This is above the continuous rating of the 2stx2220 PNP transistors that we use to drive the rows, but it's actually below the pulse (peak) current spec of 3 A, so long as we rapidly scan through the rows. The saturation voltage of the transistors becomes more important at these high currents; you'll need to drive at a full 5 V, and you may want to consider switching to the STX790A transistors.

It's also at about the maximum that the Peggy board can handle in terms of current on the board and so forth. I'd recommend against trying to drive more than 100 mA per row, even if you were to find chips that can handle it.

You can, of course, move off board the LEDs, or even everything else-- you wouldn't be the first to replicate it from scratch to make a giant ping-pong ball array. If you really want higher power, you might want to build a non-multiplexed array, where each LED has a dedicated channel of a driver chip. It's not easy or cheap-- you'll need about 40 LED driver chips to do the full array, and buckets of power to drive it.

Hi Windell

This is above the continuous rating of the 2stx2220 PNP transistors that we use to drive the rows

In the manual of the Peggy2 I see 2N5401 transistors which have a different pinout (C & B switched). Is it a fault in the manual?

In the manual of the Peggy2 I see 2N5401 transistors which have a different pinout (C & B switched). Is it a fault in the manual?

No, it's a difference between different versions of the Peggy 2. Peggy 2 is currently on its fourth version, the Peggy 2.3, and ships with the 2stx2220 transistors. If you have an older version, you should definitely regard its manual-- that shipped with it --as the definitive document. Each kit comes with the appropriate BOM, manual, and schematics (or link to the correct schematics).

Thanks for clarification and so fast
I'm currently in the process of designing something similar and I'm a little bit lost which transistor to choose. But in my case i think the 2N5401 should be sufficient.
I aim for 16x16 LEDs, ~80x80cm, with flying wires (for private use not for resale) and Ping-Pongballs as diffuser.