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[Reply #15 on:]

Okay thanks! 
Seeing as how you have done this, you must've wired it all up in a parallel circuit, correct?

Parallel?  I'm not sure I understand.  I simply daisy-chained them together as shown at http://tlc5940arduino.googlecode.com/svn/wiki/images/breadboard-arduino-tlc5940.png

How did you wire up the atmega and the tlc5940s so that they didn't draw too much voltage (how did you put them in a parallel?)

I just wired them all to the same 5v source?  Maybe I did it wrong, but I thought the big concern about power draw was when you try and power the TLC5940 from an Arduino and not from an external power supply (assuming it's big enough).

I (shamefully) didn't use a voltage regulator of any kind and simply attached a 3.7v LiPo to my board (w/ a MAX1555 for charging) and ran at 3.7 volts.  That was my first board and I'd do things differently today.

I hope this is helpful and not misleading,

Brad (KF7FER)

[Reply #16 on:]

no it helps alot!
What were the issues?  Nothing blew up, right? 
Did anything get SUPER hot?

[Reply #17 on:]

I (shamefully) didn't use a voltage regulator of any kind and simply attached a 3.7v LiPo to my board (w/ a MAX1555 for charging) and ran at 3.7 volts.  That was my first board and I'd do things differently today.

Not sure what's wrong with that. I haven't used LiPo batteries, but have run several projects directly on AA cells. I am careful to set the system clock speed according to the supply voltage, but other than that, I'm not aware of major issues. Heck, I think these MCUs were intended for such applications.

[Reply #18 on:]

no it helps alot!
What were the issues?  Nothing blew up, right? 
Did anything get SUPER hot?

No issues, nothing smoked nor got hot.  It simply worked. 

I would add a 0.1uF ceramic cap near the TLC5940 (not shown in the playground entry) between the power/ground pins just in case though (for decoupling).

My design also simply passed 20mA to each LED and drove a string of 32 LEDs (a pair of the TLC5940's) in a rotating pattern (lighting 5 LEDs in a PWM fade) along with toggling the 16 LEDs on the final TLC5940.

Not high duty cycle, nor high power, but it shouldn't matter.

I hope this helps,

Brad (KF7FER).

[Reply #19 on:]

Not sure what's wrong with that. I haven't used LiPo batteries, but have run several projects directly on AA cells. I am careful to set the system clock speed according to the supply voltage, but other than that, I'm not aware of major issues.

I guess I struggle a bit with the idea of simply running off of batteries - just seems wrong somehow.  I know it's ok (as long as you're within the spec of the hardware you're using) but it... well... it's just a mind thing I guess. I'll just have to work on that :-)

Heck, I think these MCUs were intended for such applications.

You're probably right.  Sure a large range of acceptable voltages.  And they are are hardy little buggers too.

Brad.

[Reply #20 on:]

I guess I struggle a bit with the idea of simply running off of batteries - just seems wrong somehow.  I know it's ok (as long as you're within the spec of the hardware you're using) but it... well... it's just a mind thing I guess. I'll just have to work on that :-)

You're probably right.  Sure a large range of acceptable voltages.  And they are are hardy little buggers too.

The datasheet does caution against letting the supply voltage get too low, memory can be corrupted, but they have the solution built-in, namely the brown-out detector. Set the fuses so that it kicks in at a reasonable point given supply voltage and clock frequency.

[Reply #21 on:]

Yup, I run 2xAA's, 8MHz crystal, BOD at 1.8V, and I've had units lasting for months.

[Reply #22 on:]

I guess I struggle a bit with the idea of simply running off of batteries - just seems wrong somehow.  I know it's ok (as long as you're within the spec of the hardware you're using) but it... well... it's just a mind thing I guess. I'll just have to work on that :-)

You're probably right.  Sure a large range of acceptable voltages.  And they are are hardy little buggers too.

The datasheet does caution against letting the supply voltage get too low, memory can be corrupted, but they have the solution built-in, namely the brown-out detector. Set the fuses so that it kicks in at a reasonable point given supply voltage and clock frequency.

I think this is mostly a problem if you are writing to flash to eeprom during a low voltage condition.
My personal experience is that they go into a reset loop about 15% below the datasheet minimum for that frequency.

[Reply #23 on:]

Oh wow lots of input!
The project that i'm doing seems almost identical to brads.

I am careful to set the system clock speed according to the supply voltage, but other than that, I'm not aware of major issues.

So how would i do that?  Would i just upload my program and then the chip runs at the speed according to the supply voltage it is getting?

[Reply #24 on:]

Oh wow lots of input!
The project that i'm doing seems almost identical to brads.

I am careful to set the system clock speed according to the supply voltage, but other than that, I'm not aware of major issues.

So how would i do that?  Would i just upload my program and then the chip runs at the speed according to the supply voltage it is getting?

You have to set the clock speed for the lowest voltage you intend to operate at.

[Reply #25 on:]

By clock, you mean the frequency thingy?  like 8Hz?
I intend to run int at 8Hz because i don't wanna use an external crystal.

[Reply #26 on:]

By clock, you mean the frequency thingy?  like 8Hz?
I intend to run int at 8Hz because i don't wanna use an external crystal.

I assume you mean 8MHz
You could always either set the clock prescaler or use the 128khz internal oscillator.
This will provide a lower clock rate without an external crystal.
Be-careful because clocks below about 2Mhz will require slow SPI for programming.

[Reply #27 on:]

So I just want to make sure, I can use just the atmega and run it at 8Mhz using the internal oscillator, correct?
And that doesn't require any additional programming, correct?

[Reply #28 on:]

So I just want to make sure, I can use just the atmega and run it at 8Mhz using the internal oscillator, correct?
And that doesn't require any additional programming, correct?

But not at 1.8v
8mhz is too high to reliably run at 1.8v. It may or may not work and long term stability not guaranteed.

[Reply #29 on:]

Oh thats right,  Well since i want to wire this whole thing up in parallel, I would have 3.7v running through it, which is enough for it to reliably run at 8Mhz? correct?