Experimenting w/ TLC5916/17

[MrDEB]

Eliminated a-lot of fluff so I can be "AT ONE" with this interesting chip. It sure makes a difference as far as led brightness and all the same intensity.
Using 8 leds to indicate what is happening inside the chip. In the simple schematic I failed to use pull ups on the SDI and CLOCK lines. seems to work without but probally a good practice to include.

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[MrDEB]

Using the posted schematic, the LEDs are drawing 18.9ma each but they seem really bright. WHY? your guess is just as good as mine. Maybe just imagining.

[bitfogav]

Just because it is recommended that the max of 20mA is used to operate a LED doesn't mean you have to run them at 20mA?, adjusting your Ext resistor to an higher value will adjust the brightness of the LED's..
Sometimes its about personal preference and I quite often use an higher value resistor to run my LED's at 10mA which usually give good results. But for the 8x8 matrix's that what Brad uses in his projects its always a good idea to use a lower value resistor especially when its driving several LED's at the same time..

[MrDEB]

This is a battery powered device and 1k resistor (measured at 18.9ma) is plenty I hope.
I find it hard to believe that if I turn OFF and ON at a fast rate (think PWM) that it conserves power?
Hopefully using the higher intensity LEDs matrix I can view from at least 50-75 feet aay in broad daylight. Might be asking to much but won't know until I try it.
Still tossing it around about using either the 8 channel version(TLC5916 or the 16 channel TLC5940. The new matrix has separate pins for anode and cathode so a total of 28 pins.
Either two-5916's or 1- 5940 OR one TD62783APG High side driver per color(total of two/-red & Green)
LOT's of choices to decide.
The 5940 is $3.78 per while the 5916 is $1.70 per.
The TD62783APG is .95 per
can't wait to see just how bright the mew matrix really is.

[brad]

What is your battery voltage? because if you are getting 18.9mA through a 1K resistor that's 18.9 Volts!

[MrDEB]

The 1k resistor is the external resistor that sets the current for each led. 16 channels = one resistor, 8 channels = 1 resistor.
here is screen shot of app note. This cuts down on part count and equalizes the LED intensity. There is a dot correction available as well.
Being the last person to ask about algebra I looked at the data sheet then decided on 1k seeing how a 720ohm = 26ma if I recall. Used the 1k and actually measured the current draw at 18.9ma. Contemplated using a 1k pot to find out EXACTLY but I haave a hunch the external resistor is involved on power up so one might not be able to change while the chip is powered. I might be wrong but thats the impression I get reading the data sheet.

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[brad]

Oh I get it - it's a programming resistor!

[MrDEB]

One really nice item I was expecting was the issue of the Green current draw different than the RED. I neeed to plow through my notes but I think the RED had 8-10 ma more current draw. Using a 750 ohm resistor I get 26.8ma per segment RED or Green. I had to use two TLC5916"s (one for Green and one for RED).
The issue I reared its ugly head was going from one color to the other I get a mix of Red and Green = orange.
Looks like I need to be able to clear the shift registers before changing colors.
Just disabling the output enable doesn't do the deed.
Thinking maybe use a clear byte (%00000000) in my const arrays.

[brad]

Are you sure you are disabling the output enable? It seems very strange that an output enable pin wouldn't actually disable the output.

[MrDEB]

Yes I am taking the OE pin HIGH as stated in the data sheet. Maybe the registers retain the last bytes and seeing how the SDI and CLK lines for both chips are tied together.
Another issue I am experiencing is upon powering the circuit I get one stray LED that blinks ON. Thinking of separating the SDI inputs and at the start of the code institute a LOW on the SDI lines as well as a HIGH on the OE lines.
Looks like Jon over at DDIY is getting into a similar chip.

[brad]

I have been looking through the data sheet and I really can't see why any LED's would stay on when you take the OE line high. I would be chasing down this fault before looking into anything else because the OE going high will not let any LED's turn on even if the data is retained within the registers.

[MrDEB]

The OE works but when I switch from one color to another I think the latches retain data because the SDI to both chiops are common as are the CL:K and LE. Only pins on the TLC5916 that are on seperate lines is the OE which works until I switch colors.

[brad]

I would have thought that you would tie the OE lines together and the clock connections together - then have the data lines separate. That way you can just send the data in all at once and then enable the output.

Are you trying to display just one color at a time with the way you are doing it?

[MrDEB]

yes only one color at a time. Am in process of house keeping the code (cleaning it up but need to work out an issue with my sub routines.

[brad]

I think that could be your problem then. I am confident that if you send the data out like I posted above, it would eliminate your problems