4.8V 700mAH battery not enough for LPD8806?
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4.8V 700mAH battery not enough for LPD8806?

by LostLess on Thu Jan 31, 2013 3:18 am

Hello! I am currently building a project that involves a Maple Mini, a BlueSmirf Silver bluetooth, and six segments of an LPD8806 strip. The Maple Mini will consume a maximum of 30mA, the BlueSmirf will consume 25mA, and the six segments should consume 24mA (I calculate 24mA like this: Each segment will consume 4mA, as I am sending color values that are 1/30th of maximum brightness (120 mA)). When I have the system powered via PC USB (that is, the Maple Mini is powered by my PC's USB port), everything works. When I swap to use my 4.8V 700mAH battery or 5VDC @ 2A power supply, only the Maple Mini and the BlueSmirf seem to receive power-the LEDs do not light up as they should at all.

What might be the problem?

Here are descriptions of each wiring diagram. I am attaching pictures as well so you can see. There's a copy of the Maple Mini schematic at Github: https://github.com/leaflabs/maplemini

Working configuration
Maple GND -> negative column on breadboard
Maple Rx -> BlueSmirf Tx
Maple Tx -> BlueSmirf Rx
Segment GND -> negative column on breadboard
Segment Vin -> Maple Mini Vin (when Maple Mini is powered by USB, this acts as 5V out)
Segment Clock Input -> Maple SCLK
Segment Data Input -> Maple MOSI
BlueSmirf Vin -> Maple Mini Vin
BlueSmirf GND -> negative column on breadboard
Power is driven from Maple Mini USB port.

What should also work (but does not)
Maple GND -> negative column on breadboard
Maple Rx -> BlueSmirf Tx
Maple Tx -> BlueSmirf Rx
Segment GND -> negative column on breadboard
Segment Vin ->positive column on breadboard
Segment Clock Input -> Maple SCLK
Segment Data Input -> Maple MOSI
BlueSmirf Vin -> positive column on breadboard
BlueSmirf GND -> negative column on breadboard
Power is driven from either 4.8V 700mAh battery or 5V @ 2A power supply whose leads are connected to the negative and positive columns on breadboard.

Thanks for your help! :)
Attachments
not_working.jpg
This is the setup that does not work.
not_working.jpg (100.51 KiB) Viewed 699 times
working.jpg
This is the setup that works.
working.jpg (99.51 KiB) Viewed 699 times
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Re: 4.8V 700mAH battery not enough for LPD8806?

by pburgess on Thu Jan 31, 2013 4:14 am

In the not-working case, what is the Maple VIN connected to?
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Re: 4.8V 700mAH battery not enough for LPD8806?

by LostLess on Thu Jan 31, 2013 4:30 am

In the non-working case, the Maple VIN is connected to the positive column of the breadboard. This is also the same for the modem and the segments.
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Re: 4.8V 700mAH battery not enough for LPD8806?

by pburgess on Thu Jan 31, 2013 12:32 pm

Strangeness! Do you have a meter to test the actual voltage coming from the battery pack? Is it freshly-charged?
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Re: 4.8V 700mAH battery not enough for LPD8806?

by LostLess on Thu Jan 31, 2013 5:13 pm

Isn't it? When I get a chance, I will check the voltage coming from the battery. This still does not explain why a 5V @ 2A adapter won't work either.

However, I've just read something about the Maple Mini that might explain why...but even then, it does not make sense to me in this context: according to the master pin map (http://leaflabs.com/docs/hardware/maple-mini.html#maple-mini-gpios), 1_MOSI and 1_SCK, the two SPI pins I am using (the chip has two SPIs) are not 5V tolerant, but the second set are. This does not make sense to me because that simply means that the pins can take 5V if applied to them...does not mean anything about output voltage from those pins.

I'm beginning to think that the voltage may not be high enough on those pins when a non-USB power supply is put in, but then, why would the voltage drop like that in that case? I am going to pose this question at the LeafLabs (the people who made the Maple Mini) forum to see if I might find any insight there.
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Re: 4.8V 700mAH battery not enough for LPD8806?

by adafruit_support_bill on Fri Feb 01, 2013 8:09 am

That is pretty weird. I don't know why the 5v USB supply would be "better" than your 5v/2A adapter. Let us know what LeafLabs has to say.
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Re: 4.8V 700mAH battery not enough for LPD8806?

by LostLess on Fri Feb 01, 2013 4:49 pm

Ok, I have been talking to the folks over at LeafLabs. They say that the SPI pins of the Maple Mini only output between 0-3.3V unless one provides external electronics (at least a pull-up resistor, or some sort of voltage-level shift). So, what may be happening is that the voltage is not high enough to register a data high (according to the data sheet, there's something about a minimum of 3.8V for a data high on the LPD8806). This is strange to me, because if this were true, wouldn't the LEDs never light up?

So it looks like I need to pull the voltage up. I've been looking at some of the logic level converters here. Does anyone know if this (https://www.adafruit.com/products/735) works or this (https://www.adafruit.com/products/757) would work?
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Re: 4.8V 700mAH battery not enough for LPD8806?

by LostLess on Sat Feb 09, 2013 10:39 pm

Update, 2/9/13:

After speaking with some of the people at LeafLabs, they suggested that the logic voltage may be too low: the mini outputs @ 3.3V, while the LPD8806 expects 5V. I ordered a logic level converter that does 3.3 to 5V (here are the specs: https://www.sparkfun.com/products/8745). The logic level converter requires two power sources: one at the lower voltage, the other at the higher voltage. For the higher voltage source, I am using the 5V adapter. For the lower voltage, I am using a 3V CR2032 battery. I connected the SCLK and MOSI pins to the TX lower voltage lines, and I connected the LPD8806 CI and DI pins to the TX lines of the higher voltage. It sounds contradictory to do so, but according to the description of the converter:

Pins are labeled as Inputs and Outputs. These are relative to the board. A digital one going into the RXI pin on the 5V side will show up on the RXO pin on the 3.3V side as 3.3V. A digital one going into the TXI pin on the 3.3V side will show up on the TXO pin on the 5V side as 5V.


Given that, still no joy. However, I think there may be a newer problem. The CR2032 is outputting closer to 4V (the last readout was something like 3.89V). Might it be that the power supply for the lower voltage is too high for the output of the Maple Mini?
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Re: 4.8V 700mAH battery not enough for LPD8806?

by LostLess on Fri Feb 15, 2013 2:41 pm

Ok, after several days of going back and forth on the LeafLabs forums, I narrowed the problem down to the initial code that I wrote: the setup works fine, and there was no need to involve logic level converters.

Along the way, the Adafruit library for the LPD8806 was ported to Maple Mini. If anyone is interested, here is the link:

http://github.com/crenn/LPD8806
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