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1  Using Arduino / Sensors / Re: Decoding thermistor characteristics table on: January 29, 2011, 10:39:50 pm
Granted TC are not as cheap as a NTC but, you don't need a $20 AD582 to used a TC either. Just a little thinking out of the box smiley. But, that's another post.
2  Using Arduino / Sensors / Re: Decoding thermistor characteristics table on: January 29, 2011, 09:56:23 pm
Thermistors are odd devices and its not a trivial task to get a precise temp reading with them. I've used them in the past for trip point applications. Anyways, you will need to use the Steinhart-Hart equation to calculate the temp.
Have a look at this site: http://www.facstaff.bucknell.edu/mastascu/elessonshtml/Sensors/TempR.html    I would use a thermocouple.
3  Forum 2005-2010 (read only) / Development / Re: Voltage regulator needed? Or not? Portable LED PWM on: January 19, 2011, 08:42:59 pm
All depends the the cells or batteries that are used. If you use a single cell and the Vf of the LEDs are 3 - 3.4v that's not going to work, you'll need a boost Reg. I would start with the easiest solution, maybe four AA's, resistors and MoFETS,  see what that gets ya. It will give you an idea of what the next step will be.
4  Forum 2005-2010 (read only) / Development / Re: Voltage regulator needed? Or not? Portable LED PWM on: January 19, 2011, 09:02:37 am
A lithium cell be a good choice. They have an excellent energy to weight ratio. Charging them safely maybe an issue. Lithium needs to be charged with a constant current/ constant voltage charger. constant current @ 1/3 C rate until the cell voltage reaches 4.2 volts and switch to constant voltage mode of ~ 4.5 volts to top off the cell About  20% of the energy in the topoff. Anything above 4.5volts and the cell may explode.  So, the voltage needs to be controlled.  

I did a white LED drive that used a single lithium cell a few years ago. I used two of these: http:// http://www.maxim-ic.com/datasheet/index.mvp/id/3025 and a buck/boost 5 volt regulator for the power supply. The regulator was programmed to shut off when the cell voltage dropped below 2.5 volts. Lithium doesn't like a deep discharge. PWM of the EN pin on the MAX1916, to control brightness, was done on an AVR.

    
5  Forum 2005-2010 (read only) / Development / Re: Help Newbie Project on: January 19, 2011, 09:55:29 am
First, you need to know what type of tag you will be reading. There are several different types that work on different frequencies. Then look here:http://www.sparkfun.com/categories/144 and see if any of the readers are compatible. Looks like most of these readers spit out a serial stream, be it USB or 232.  Use the Arduino to parse the data.  
6  Forum 2005-2010 (read only) / Development / Re: Help Newbie Project on: January 18, 2011, 01:54:56 pm
What type of "data" are you trying to acquire .....analog? ...... digital?.... What type of RFID?
near field?
We need more info...much  more
7  Forum 2005-2010 (read only) / Development / Re: Pellet stove controlelr. on: January 17, 2011, 03:10:25 pm
Wissy, you may want to look at a cheap PLC to get your prototype up and going. PLC would make the hardware interface easer.
8  Forum 2005-2010 (read only) / Development / Any interest in a 802.11 Shield for a Mega2560 ? on: January 17, 2011, 12:41:00 pm
Just putting out some feelers. Besides my full time design job, I also do contract design. I have just finished a PCB based on the ConnectOne - Wi2Wi. chipset for 802.11 communications. At my "real" job, I use Arduino for rapid prototyping and one offs. Anyways, I'm going to need 802.11 solution for a Ardino project. It will be interfaced to a Mega2560, so I thought I would reuse the design and change the form factor to a "shield".
I have attached a pic of one the prototype PCB's just for a look see.
The prototype is nothing more than ConnectOne's Secure Socket iWiFi with a PS and interface logic added. http://www.connectone.com/products.asp?did=73&pid=61
Pic:



The shield would be an interface for the module from ConnectOne and include:
Mega2560 form factor
3.3Volt power supply (maybe a 5.0V for the Mega)
3.3 to 5.0 volt level shifting for communication.
Headers for the Secure Socket iWiFi. (you buy your own from Mouser, ~$50
RS232 port for configuring the ConnectOne part off of the Mega via ConnectOne's tool.
Pass through headers for stacking the Mega2560.
various LED's and switches   smiley-wink

Any interest? If so, we'll work out the details later.

Thanks,
John

      
9  Forum 2005-2010 (read only) / Development / Re: (updated) building a circuit - can you look at it? on: January 17, 2011, 11:05:16 am
At a glance, I would add gnd connections to your connector(s) to the other devices (serial).
Add a few 0.1uF caps on the power - gnd of the connectors also.

I would move the diode to the input of your 7805.
10  Forum 2005-2010 (read only) / Frequently-Asked Questions / Re: Dealing with DC Motor Stall Current on: January 21, 2011, 01:00:52 pm
If you are still having an issue with inrush, try a power NTC thermistor.
11  Forum 2005-2010 (read only) / Frequently-Asked Questions / Re: Dealing with DC Motor Stall Current on: January 18, 2011, 04:25:24 pm
I think you need to implement a "soft" start as  Lefty suggested. What I have done in the past is kinda a dual PWM. Sorta like FM modulation if you will.

During the ON time, PWM at a high frequency. Hope that was clear.
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