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61  Using Arduino / Displays / Re: LCD drawing too much power? on: July 02, 2012, 07:26:06 am
What I'd do is :

put something like a 100-200 ohm resister in the 5V to the LCD and connect just that and GND, then measure the voltage drop across said resister.  That will give you the current with ohms law, if its much more than 4mA its a faulty LCD or a fault in your wiring. 
62  Topics / Home Automation and Networked Objects / Re: home thermostate on: June 29, 2012, 08:42:26 am
I have as well. Just heating although the arduino does a lot besides.  The arduino can autonomously maintain a temperature, a small server (a hacked NAS box) keeps score, draws pretty graphs and tells the arduino what temperature to maintain at whatever time of day/week. It can be overridden via the server's web site. 

http://pluggy.is-a-geek.com/index.html

 
63  Using Arduino / Displays / Re: 16*2 HD44780 LCD Not Working on: June 28, 2012, 04:33:04 am
If you haven't got the display of the line of blocks with just power,contrast and backlight, the code is entirely irrelevant.
64  Using Arduino / Programming Questions / Re: Is there a known speed limitation on the Uno USB UART? on: June 25, 2012, 03:34:31 pm
It is an early Uno BTW - A genuine Italian one.

The Duemilanove I took out and put back is a Chinese knock off I bought on Ebay.
65  Using Arduino / Programming Questions / Re: Is there a known speed limitation on the Uno USB UART? on: June 25, 2012, 03:13:08 pm
After seeing this thread and posting in it, I thought I'd hook up my Uno in place of the Duemilanove in my long running home monitoring sketch. All appeared well so I left it to it, came back to it several hours later to find numerous holes in my graphs and log files. Not many, but not the 100% perfect record the Duemilanove has been turning in.  I've put the Duemilanove back in place.  I've had numerous doubts about the Uno since I bought one, this hasn't exactly inspired my confidence..............
66  Using Arduino / Project Guidance / Re: My switches are acting weird on: June 25, 2012, 02:43:27 pm
You use something like a 10k resister between the pin and gnd or the pin and 5v to hold the pin one way or the other. You then wire the switch so it connects the pin the opposite way, if you have the resistor holding it to gnd, the switch connects it to 5V.  When you get used to it you can use code to activate the arduino's own internal resisters but thats for another day. Google pull up (or pull down) resisters...........
67  Using Arduino / Programming Questions / Re: Is there a known speed limitation on the Uno USB UART? on: June 25, 2012, 05:40:56 am
The BASH code I use

Code:
#!/bin/bash
arduinoport=`cat /root/arduinoport` # sets arduinoport to suit UNO or Duemilanove which is stored in /root/arduinoport

stty -F $arduinoport cs8 115200 ignbrk -brkint -icrnl -imaxbel -opost -onlcr -isig -icanon -iexten -echo -echoe -echok -echoctl -echoke noflsh -ixon -crtscts -clocal

cat $arduinoport|head -n 6|tail -n 4 > /root/arduino2

other than setting the device name  (/dev/ttyUSB0 for the Duemilanove) in /root/arduinoport that is the only change between the Uno and the Duemilanove. It has worked 100% once a minute over several years. Although I do use the Duemilanove most of the time. 
68  Using Arduino / Programming Questions / Re: Is there a known speed limitation on the Uno USB UART? on: June 25, 2012, 04:36:37 am
I use 115200 with Linux just redirecting the serial device to a file with BASH. It works fine on Uno or Duemilanove allowing for the different device name.
69  Using Arduino / General Electronics / Re: Arduino reading different voltages than a multimeter on: June 25, 2012, 04:22:57 am
Replace the resister if you want, but just jumpering the two ends with a piece of wire is quicker and easier and see what the change is. 

From what has already transpired in this thread, I think its safe to say that the voltage difference is the result of the Arduino having a higher internal impedance than your multimeter and it loads the tiny amount of current coming out of the LED less.  The voltage detected by the arduino will be closer than the multimeter, although what you're going to do with such a miniscule amount of electricity is open to question.  Use it as a light detector ?
70  Using Arduino / Project Guidance / Re: Bike Computer on: June 25, 2012, 04:02:50 am
I'd take it further than that. Work out by hand what 80 spokes a second comes out to in MPH (or whatever) and then divide spokes per second by a number that gives the correct MPH figure.  Then you just use that number for all spokes per second in arduino .  It minimises the impact of the limited precision of real numbers.

You said you can spin the wheel at 15MPH by another method, if that is the same as 80 spokes per second then you just divide  80 by 5.33 to get 15 miles per hour.  You divide any spokes per second by 5.33 to get the speed in MPH.  It avoids any contact with impossibly small numbers. 

Bear in mind a 26 inch wheel will not have a rolling distance of Pi times 26" , it needs to be determined by experiment with you sat on the bike.  Tyres and pressures affect the rolling distance.
71  Using Arduino / General Electronics / Re: Arduino reading different voltages than a multimeter on: June 24, 2012, 05:50:35 pm
Something must have changed since the meter reading has gone up, the arduino reading has come down significantly which was what I was expecting.  What do the readings do if with it set up as it is now you short circuit the resister with a piece of wire ?
72  Using Arduino / General Electronics / Re: Arduino reading different voltages than a multimeter on: June 24, 2012, 05:32:10 pm

Taking a second look at your circuit, you did have it right, since you have both 'implements' connected at once. 
73  Using Arduino / General Electronics / Re: Arduino reading different voltages than a multimeter on: June 24, 2012, 05:13:33 pm
No, connect the LED as you had it and the resister goes in the + lead to the measuring device.  It just adds extra impedance to the 'virtual voltage divider' ,formed between the LED and the measuring implement.  With no current flowing a resistor of any value will not affect the voltage, but since all "measuring implements" use some current they affect the voltage downstream from the resister. If you have an old analogue multimeter (needle and scale) you could try that, they have a much lower internal impedance and affect the voltage much more.  If using an LED as a light detector produces microamps as one poster has suggested, you probably wouldn't get a reading at all from an analogue meter.

A 1.8 M will do fine.
74  Using Arduino / General Electronics / Re: Possibly stupid question about supercapacitor voltages... on: June 24, 2012, 05:01:49 pm
I must have led a sheltered life........   
75  Using Arduino / Project Guidance / Re: Bike Computer on: June 24, 2012, 04:11:44 pm
Simplify it.  There is a linear correlation between the number of spokes passing the sensor and the road speed.  See how manys impulse you get in say a second, then come up with 1 number that when divided  into the impulse number gives the road speed in your units of choice.  With a bit of thinking outside the box it could all be done with integers. But 6 digits precision is plenty. 17.4532 MPH ?
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