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1  Using Arduino / General Electronics / Re: Simplest LED blinker on: April 14, 2011, 03:28:33 pm
Hooray!  Thats a wonderful list of options to explore!  Thanks so much!  I'll go through all of your suggestions and see what I can suit to my project... very excited.

I'll post the results once I get them.

Thanks again all!
2  Using Arduino / General Electronics / Re: Simplest LED blinker on: April 08, 2011, 08:58:23 pm
Thanks for the replies all!  Looks like this circuit won't work for me, as I am hoping to install the LEDs into several balloons and therefor hoping to keep the cost/size per circuit as small as possible (and also why I am looking for independent units opposed to several connected and controlled by Arduino).  "Blinking LEDs" are an option, but I am hoping to get a slower blink rate (maybe around 1 second on, 1 second off).  Is it time to look at control chips like the 555??  Is there a cheap method?

westfw, could you write more about your 2 transistor blinker if you think it might function for my balloon scenario?

thanks again,

3  Using Arduino / General Electronics / Simplest LED blinker on: April 07, 2011, 01:44:58 pm
Hello friends,

So, I have found a circuit designed by Dick Cappels for a simple LED blinker (no Arduino involved).  I have tested the circuit and gotten it to work with a 9V power supply. 

"In this implementation, a common NPN transistor is used.  In the circuit, a 1k resistor charged the 330 uf capacitor until the voltage became large enough to get the emitter-base junction to avelanche. In the oscilloscope image,  it can be seen that the peak voltage (yellow trace) was a little bit less than 9 volts. At this point transistor turned on quickly and partially discharged the 330 uf capacitor through the LED and the 100 Ohm current limiting resistor."

Now I am hoping to scale down the power supply to a 3.5V battery or lower, which seems not to work with the circuit as it currently stands (the LED does not turn on at all).  Can someone help suggest what parts of the circuit I should look at changing to allow it to function off a lower voltage?  Smaller capacitor?  Different transistor?

Thanks in advance,


4  Using Arduino / General Electronics / Re: TLC5940 and 74HC595 Shift Register on: March 19, 2011, 05:19:12 pm
I was thinking of pulling from one of "Grumpy Mike's" monome projects he had posted on his website  (  

His schematic (located halfway down the page, and downloadable in pdf) shows him using TCP6108 MOSFETS for the rows triggered by the Arduino pins (I think?)... To quote:

"The TLC5940 controls the LEDs by means of a current sink, that is, it pulls the LED to earth. Therefore, in order to multiplex it we have to connect four cathodes, one on each row, to the input of the driver chip and the other end of the LEDs have to be pulled up to 5V when it is time to light up that row. This can be done with a p-channel FET, when it’s gate is a 5V then the FET is off or high resistance, when the gate is at earth then it is turned on, or has a very low resistance. The Arduino drives these FETs by pulling one low at any one time."
Mike Cook

I must admit, my growing but rudimentary understanding of diagrams is slowing me in fully understanding his layout.  I don't think I quite understand how the current is flowing here.  These are common cathode RGB LED's, right?  Where is the current flowing from?  Is it Arduino Pin 15 - 18?  I'm a little lost...

ps:  Terry, thanks very much for you post!  It's wonderful having you weigh in on the topic, as many of your enlightening postings all over the forum have been integral in getting me this far.

5  Using Arduino / General Electronics / Re: TLC5940 and 74HC595 Shift Register on: March 19, 2011, 03:39:21 am
Thanks for the correction James!  Good point about being able to do an 8x8 with just the Arduino's outputs, as well.  I guess I am looking down the road hardware-wise, as I hope to eventually use common cathode RGB led's to make a similar matrix with (which I think should require 48 pins for an 8x8???  Might start with a 4x4 for those).

Thanks again,

6  Using Arduino / LEDs and Multiplexing / Re: 595 series Shift Register Simulator on: March 18, 2011, 09:46:51 pm
Very cool!!  Agreed, this is a great asset for the beginner.  Thanks Meden!
7  Using Arduino / General Electronics / Re: TLC5940 and 74HC595 Shift Register on: March 18, 2011, 06:20:11 pm
So, my current understanding is that the TLC5940 and the 74HC595 are both types of shift registers, but the TLC5940 is specially designed as a LED driver (it combines a high-power, low-side switch and a shift register... but can only be used to sink current, whereas the 74HC595 can be wired through a high-side switch to send current???).  I am pulling this from this video (4:20 - 5:35)... Am I understanding this correctly??

I will then be unable to form a matrix using only TLC5940's because they are only low-side, and unable to send current?

Many thanks to all who have replied to this thread... datasheetcatalogue has been a big help!

8  Using Arduino / General Electronics / TLC5940 and 74HC595 Shift Register on: March 07, 2011, 07:48:09 pm
Hello forum,

First post here, and I am just looking for some help in understanding how these two components - the TLC5940 and the 74HC595 Shift Register - differ from one another.  I am just getting started with my first few projects with Arduino, working towards building a 8x8 LED grid.  Seems like one, or both, of these components should be helpful... do they essentially do the same thing?  I read some older posts where people are using both together, too.

Thanks in advance for sharing your knowledge.
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