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1  Using Arduino / Programming Questions / Re: Need some help with millis() and debouncing. Driving me nuts! on: September 04, 2012, 08:42:56 pm
Debouncing in hardware is not difficult. One gate, one diode, one cap and two resistors.
The circuit I use is from an EDN article from 2002. It is very clean and
has never failed.

The schematic is in the datasheet for my prototyping board at

(* jcl *)
2  Using Arduino / Microcontrollers / Re: Running Duemilanove at 12MHz - effect on delay() function? on: September 03, 2012, 09:05:15 pm
All of my boards are 3.3V and run at 12MHz. When I make the bootloader
I change F_CPU in the bootloader makefile. The delay function
works fine.

However, you could run into problems with some libraries. One customer
reported issues with NewSoftSerial. The issue was a timing
table that looks at F_CPU. There were constants for 8MHz and 16MHz
but none for 12MHz. I wrote a Perl script that added the constants
for 12MHz and the library works. The details are at --

There could be other libraries with similar issues. These are usually easy
to fix.

(* jcl *)
3  Using Arduino / Project Guidance / Re: Stuck on pcb design layout on: September 01, 2012, 12:40:35 pm
You can take a look at all my PCB layouts.

Check out the PICO boards at
The schematic, PCB layouts and BOMs are all in the datasheets.

(* jcl *)
4  Using Arduino / Programming Questions / Re: DS1307 RTC Giving Wrong Values After Running for a Few Days on: August 31, 2012, 06:11:25 am
That crystal is correct. It has the proper capacitance and low ESR.

Since these crystals are susceptible to noise I always use a ground
ring. Check out the layout in the datasheet at

It sounds like your error is reasonable predictable and occurs after
a long period of time so it is hard to explain this away as noise.
It is good design practice to guard high impedance circuits.

Have you tried running your circuit under more controlled conditions?
Indoors (25C) and off of a bench power supply?

(* jcl *)

5  Using Arduino / Programming Questions / Re: DS1307 RTC Giving Wrong Values After Running for a Few Days on: August 30, 2012, 08:20:25 pm
In the datasheets that I have the DS1337 (REV 080508) crystal specs are 6pF and 50KOhms
The DS1307 (REV 100208) is 12.5pF and 45KOhms.

(* jcl *)
6  Using Arduino / Programming Questions / Re: DS1307 RTC Giving Wrong Values After Running for a Few Days on: August 30, 2012, 07:34:02 pm
The temperature rating is 85C for the industrial version but 70C for the commercial.
If you are only at 55C at the DS1307 you are probably OK.

What is happening with your power supply?
Is there a derating on the battery at 55C?

How is your crystal connected? Did you use a guard plane or ring as called
out in the datasheet? Did you use a crystal with a maximum ESR of 45KOhms
and a CL of 12.5pF? There are a lot of watch crystals that will not work
with the DS1307. Also the DS1307 and DS1337 have different crystal
requirements.  smiley

(* jcl *)

7  Using Arduino / LEDs and Multiplexing / Re: Charlieplexing a row of LED's on: August 30, 2012, 07:14:29 pm
I have a charlie-plexing FAQ at

I also make an 8x8 and 10x10 and circular board that uses charlie-plexing. The schematics
are in the datasheets. The information on the 8x8 board is at

Information on the software is at

You may be able to adapt the schematics and software to work for your project.

(* jcl *)

8  Using Arduino / Project Guidance / Re: Choosing a logic analyzer... on: January 21, 2012, 09:25:12 am
I use the Saleae one too. It is worth the money.
Very convenient to keep in your laptop bag.

(* jcl *)
9  Using Arduino / Sensors / Re: new thermocouple interface: MAX31855 on: December 12, 2011, 08:34:33 pm
The wiblocks ZB2 TC interface board will work with J type thermocouples
if the MAX31855 is changed to a MAX31855J and the input connectors
are changed to J-type.

(* jcl *)
10  Community / Bar Sport / Re: Maker Faire New York 2011 on: September 25, 2011, 06:07:35 am
One of the problems with exhibiting was that I never got a chance to look round. Sorry I missed you.

Me too. I didn't realize you were venturing across the pond.

This year I decided to walk around and take some pictures before the open
and after the close.

(* jcl *)
11  Community / Bar Sport / Re: Maker Faire New York 2011 on: September 23, 2011, 05:16:52 am
FLA sounds like a nice warmup from Boston during Jan/Feb smiley

(* jcl *)
12  Community / Bar Sport / Maker Faire New York 2011 on: September 21, 2011, 06:10:04 pm
Starting to recover from MFNY11  smiley

My table was in the Arduino tent. It is nice to see more and more people interested
in building and creating rather than just buying and consuming.

Before the open and after the close I managed to walk around and take
pictures. My pictures are at

(* jcl *)
13  Using Arduino / Sensors / Re: new thermocouple interface: MAX31855 on: September 05, 2011, 10:58:11 am
The uncalibrated accuracy on the MAX31855 should around +-2degC. The repeatability should be
a bit better. When I did a quick test nn my new board I was getting +-2degC and a repeatability
of around +-0.25degC. I will doing some tests over the next few weeks.

I added two channels to the board and some terminal blocks for ADC channels, I2C and SPI
ports. I also added a 5V boost converter.

I will have the schematic and documentation done in the next few weeks.
Preliminary information is at
(* jcl *)
14  Using Arduino / Project Guidance / Re: Circuit simulation software on: August 25, 2011, 07:39:08 am
If you are on windows LTspice is very easy to get going.
There are models for all of the Linear Technology parts.

If you want an open-source package you can use gschem (gEDA package)
+ ngspice. Due to copyrights you have to download the models
from the manufacturer websites.

(* jcl *)
15  Using Arduino / Microcontrollers / Re: Boards file for 3.3v 12mhz atmega328p? on: August 24, 2011, 07:48:15 am
Assuming you are driving the uSD card from the SPI port the clock sign comes
from the SCK pin. The frequency is set by changing values in the SPCR.
The range of division values varies from 2 to 64 (by 2's).
The SPI freq is fosc / divisor (where fosc is the XTAL pin freq).

(* jcl *)
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