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1861  Using Arduino / General Electronics / Re: LM298 question on: August 04, 2012, 04:46:42 pm
Thank you Sir for that neat link. Last time I used those decicees I used the L293 to control an H bridge... Didn't want to but there was a need for a much larger motor and reworking the rest of the control network was out of the question. I did have to change out the Brake resistor though.

Doc
1862  Using Arduino / General Electronics / Re: atmega328 glitching on and off on: August 04, 2012, 03:59:33 pm
Winner you are DEAD WRONG the half wave rectifier has been successfully used without the strange effects you describe for nearly a hundred years, it's only drawback is the requirement for a large input filter.
I've used it for 50 years my self... Very successffully... When I was a WORKING PROFESSIONAL ENGINEER, You?

Docedison
1863  Using Arduino / General Electronics / Re: atmega328 glitching on and off on: August 04, 2012, 03:48:46 pm
This is a "No-Brainer", Really simple. However remember that an 8VA transformer has a secondary current capability of .3A and 300 mA can quickly be used if the transformer supplies other things.
One other thought is that If the transformer is used for other control it's secondary must not be common to your ground or negative PSU terminal.

Solution #1 use a 150 ohm 10 watt resistor from the HV to ground... Load it down to the equivalent RMS voltage.
Solution #2 use a half wave rectifier and 2200uF cap on the output of the diode. 1/2 of 24 V
Solution #3 is the transformer Center Tapped? if so use a halfwave bridge or tweo diodes cathodes common and + output... - output is the CT.
               or connect the bridge rectifier from one side of the secondary and the center tap... 12V Ac... now 1/2 of the transformer secondary is used
Solution #4 Connect a 12Volt 1 watt or better Zener diode in Series with the HV PSU cathode pointed to the HV side of the PSU... anode to the regulator.
                Polarity of the diode is important here the diode will work connected either way however only the way I mentioned will give you more than the
                nominal .6V diode drop. The Zener is used as a level shifter.
Solution #5 Get a 12V transformer... or see Solution #3 and find a 24V transformer with a center tap.

Doc
1864  Using Arduino / Programming Questions / Re: atoi() function where does it come from ? on: August 04, 2012, 03:25:55 pm
Tom Carpenter... Does that also include "sprintf"?

Doc
1865  Using Arduino / Displays / Re: need help connecting an LCD on: August 04, 2012, 12:53:18 am
You have an issue here it looks like you are reading information from the telephone PCB and not from the display PCB. If the display is integral to the main PCB you will have some serious issues connecting it...

Doc
1866  Using Arduino / Displays / Re: Trouble compiling examples for the UTFT Library on: August 04, 2012, 12:46:56 am
Good or bad?

Doc
1867  Using Arduino / General Electronics / Re: Trouble with a boost converter on: August 03, 2012, 11:58:36 pm
You could add a PNP transistor and 2 resistors to make the pin switch the main 5V source off and on as required or for that matter and better a P Ch Mosfet would be an even better choice. There are several made by Supertex that are in TO-92 packages and have Rdson values around 2 to 3 ohms require no heat sinking and are easy to use there are a lot of varying types of packages... Siliconix makes a whole family that are SOT-23 size in the same current range and bigger ones in SOT-223 packages as well as a different line of devices in SO-8 packages for still higher > - 5 A Id current loads.

Doc
1868  Using Arduino / General Electronics / Re: What kind of decoupling capacitors? on: August 03, 2012, 11:39:08 pm
If you use a battery for the 7805 you might well consider a minimum of 100uF on the input side with a .1 to  .33uF cap as a battery's internal resistance increases as it becomes depleted or needs charging. I start at 470uF and go as high as 1000 to 2200 uF depending on load and battery size. There is nothing wrong and a whole lot right in using Large value bypass capacitors they WILL prevent a lot of 'unpredictable' or 'unreliable' operation of electronics, don't cost a great deal more and don't draw any more current if they are bigger.
They will also extend a batteries useful life by reducing or eliminating the apparent higher internal resistance of a discharged battery (the main reason for larger values).
There are however better devices available called LDO regulators or Low Drop Out regulators. A 7805 requires a 2.5 to 3V higher source voltage than its output voltage and there are regulators that will go as low as 200 - 400 mV I/O differential and at currents equal to the 7805 (1A max).
If noise isn't a real issue like for anything non analog a switcher type regulator is a much better deal...
A linear regulator can be thought of as a voltage controlled resistor, It's load current and its quiescent current X the drop across the regulator is dissipated as heat.
For example consider a "Worst Case" scenario, a 24V supply driving a 7805 and a 3/4 A load.  24 source - 5V load = 19V drop across the regulator X .75A = 14.25 W as wasted heat and 3.75 W for the 5V 3/4 A load is almost 4X the power total power wasted as heat. An 80% efficient switcher will waste (.8 X 3.75) - 3.75 or .75 W as heat so the current drain from the 24V source is now 3.75W load + .75w loss/24V or 18 mA. .018A X 24V = 4.5W total power drawn from the source. In short a linear regulator regulates voltage and a switcher regulates power.... Efficiently.

Doc
1869  Using Arduino / General Electronics / Re: LM298 question on: August 03, 2012, 11:00:33 pm
There are 2 'drivers used, the 16 pin dip L293 and the Multiwatt package L298 the L293 can be used for really small motors and the L298 can be used for medium power motors, The 298 requires a heatsink and the lack of a heatsinkable package makes the 293 limited in power dissipation. Although driver transistors can be added for more power. A nice L298 shield is sold by Pololu and there are several others that stock or sell similar types.
The IC can be purchased from several sources including Dipmicro who sell the chip for $3.25 and a shield for an Arduino for $11.95. Dipmicro is useful as they have prices nearly as good as china, ship quickly (from Canada) and sell a lot of Arduino stuff not too high priced either...
The L298 is a 2A 46V device, the L2993 is a 36V 660 ma to 1A device with and W/O diodes and current sense B, D, E (20 pin W current sense)... WWW.dipmicro.com

Doc
1870  Using Arduino / Displays / Re: 4D Systems μLCD-μLED-μVGA Serial_LCD Library Suite on: August 03, 2012, 10:28:27 pm
Although pricey compared to a 3.2" TFT01 3.2WD and the UTFT lib's it is a really nice work horse 1 16 bit, or an 8 bit W/Flow control or2 8 bit ports or a 16 bit individual port all are bi-directional, 2 TTL RS232 serial Ports and a speaker. The device can communicate at up to 2.56 Mbaud comm rates on a dedicated TTL RS232 port and change that data rate on the fly so as to not get in the way of touch screen data and it's interactions the 32PT SGC device can do a lot... With a change in it's firmware it can be programmed to operate as a standalone terminal GFX mode and the program and stored data is easily accommodated by it's high capacity uSD card port 4GB + ... All for $69.00  from 4D Systems.AU... (79.00 @ Robot Shop and $84.00 @ Sparkfun) I bought one and the Backplane connector ($20 -30.00) for easy access to the additional I/O. Although a resistive touch screen the device I have is very responsive with the protective plastic still in place. In short it is a lot of display and while you can easily (now as the prices have fallen) buy 2 3.2 " displays for the same money you'll not find one that can do what it does 'naturally'. Maybe a Pro-Mini and a TFT01 and... but Not all in one with the SD card capacity this one has... The graphics are fast, clean and really good looking.
As much as this might sound an advert for 4D Systems... It isn't, The 32PT SGC IS a LOT of DISPLAY.

Doc
1871  Using Arduino / Programming Questions / Re: Adafruit DHT - Two sensors on: August 03, 2012, 09:42:19 pm
Define the pin numbers and call the function with the correct pin number:

  DHT11_PIN = pin 4  // define the pin on the fly
  int chk = DHT.read11(DHT11_PIN);  //Check Read Status
  do some more stuff with pin 4 DHT
 DHT11_PIN = pin 5  // re-define the pin on the fly
  int chk = DHT.read11(DHT11_PIN);  //Check Read Status
  do some more stuff with pin 5 DHT
  or define both and call each one as needed
Not recommended to put long wires on sensors like the DHT series W/O small value pull-ups  < 4K7,  > 2K2 ohms and even then not for more that a meter or maybe two as the Arduino pullls down the pin and waits 15uS then flips it to an input and waits for the DHT device to "release" the pin (let it go high) the time measured from flip to input to the falling edge of the "pin" determines a 1 or a 0. The whole transaction usually takes
< 50uS which is easy to "smear" or distort with extra capacity on the measurement pin).

Doc
1872  Using Arduino / Programming Questions / Re: Strange pushbutton behavior on: August 03, 2012, 09:11:53 pm
2 things that might help your issues are 1. Do you have the input pulled up or down as the logic requires and do you have a 100nF cap from the Pin to ground and 2. are you familiar with the bounce library or a delay without delay(). Both or either issue might well fix your problems.

Doc
1873  Using Arduino / Programming Questions / Re: AD conversion adjustments. Look up table? on: August 03, 2012, 08:10:01 pm
This is a simple issue to sort out...
The simplest change is the ground leg of the divider. a small BUT Proportionate value in series is required. If the reading is low and a bigger value in parallel if the  reading is high.
It's all easy math as all you are dealing with is a small but proportionate change in value. If the value read is 5% high reduce the current by 5% which would be 95% of the 'current' low end (divider) resistor value.
To do so is trivial...  For example the low end resistor is 1K ohms and it needs to be 95% of 1000 or 950 ohms so the resistor needs to be reduced in value. The simplest method is a parallel resistor. The easy two value (or more, just add more (1/Rx)... to the total before the final reciprocal) formula is Rt =  (1/(1/R1) + 1/R2))... so if R1 = 1000 and Rreq = 950ohms then Rp (R2) = (1/(R1) - (1/Rreq)) = (1/(1/1000) - (1/950)) = 19200 ohms and (1/(1/19200) +(1/1000)) =  950.4950495 ohms The decimal remainder is due to floating point errors... <BFG> This is the simplest correction I know of and since the voltage (another reason) is lowest here..
the power dissipation of the correction resistor/s is the "Correction" percentage or low in power.
   For safety's sake I might add a 5.1V low tolerance low leakage Zener diode from the Arduino analog input to ground and I would make VERY CERTAIN that ALL grounding is in a STAR pattern
so that the total divider current doesn't flow in the Arduino's ground return path because it will offset the A/D reading by the added voltage drop in the ground circuit...  Just an IMPORTANT thought and the reason why analog measurements are sometimes inaccurate when measured with an Arduino.
2 39K resistors of 5% accuracy  in parallel would be fine for the correction @ 19500 ohms, Their combined errors are divided by 2 and that error is added to the 5% term we were correcting for. There is method in my madness...    Making this change makes the device software independent.
There is another method and that is to use a 100 - 250 ohm pot and add it in series with the main divider and take the sense from the wiper of the pot. The first (series/parallel proportionate) method is what I would use as spot correction, the second was what I used when designing for production where > 5% accuracy was required.
Back in the day for really inexpensive correction a larger that required carbon resistor (5 - 10% and Not carbon or metal film) was placed in the ground leg of the divider ans "Notched" with a small triangular file until it was the "correct" value. I might add that it was a small change and the old carbon resistors lent themselves readily to that "method?". The notch was of course coated with a waterproof paint... Fingernail lacquer (usually bright red) to indicate a "Modified" resistor. But this techniquue hasn't been done in regular production in 50 years or more... Was an old geezer that taught it to me... along with the required math to do it the right way.

Doc
1874  Using Arduino / Displays / Re: [SOLVED] Arduino Leonardo not compatible with UTFT? on: August 02, 2012, 01:33:02 pm
Not for long I fear. The Curiosity that brought you to Arduino, then to Leonardo... Will Eventually bring you to the registers as well. There is an old expression that Might fit here...

A Journey of a Thousand Miles... Is Begun with a single step.

Been There, Done That.
 
I can tell you however that learning is its own reward, Expressing the leanings to others, One of the Greater Joys Life provides

From an Auld Phart...

Doc
1875  Using Arduino / Displays / Re: Trouble compiling examples for the UTFT Library on: August 02, 2012, 01:22:44 pm
The UTFT library is an example of very well written software, I bought one of those 3.2" 320X240 displays with a shield from Electrodragon ($14 or $15.00) compiled the examples for a Mega and was Very Pleasantly surprised. Everything works as advertised... I haven't tested the touch or SD card yet... But I am sure they will work as well as the rest does.

Doc
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