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1036  Using Arduino / General Electronics / Re: hex inverters - help with what's what in a circuit symbol? on: June 01, 2011, 04:33:38 pm
The left hex is acting as an oscillator driver to "excite" the crystal oscillator.  The hex on the right is acting as an impedance buffer to prevent the IR sensor circuit unduly loading the crystal oscillator. From the data sheet the diagram clearly shows the "A" is the input to the hex circuit and the "Y" is the output.  1A and 1Y are the respective inputs and outputs for hex unit number 1,  2A and 2Y for hex unit number 2 etc.  It matters not which hex units you use in the circuit.  Simply pick a couple and leave the others redundant.  It's usual to ground the input ports of the unused units to prevent any possibility of them oscillating.
1037  Using Arduino / Motors, Mechanics, and Power / Re: Arduino drawing too much current? on: May 31, 2011, 01:51:40 pm
You need to measure your 9 volt supply from the AAs to ensure they are giving adequate voltage output.  It is possible that your earlier trials have drain the cells.  If both arduino and motor are powered from the same 9 volt supply, it's unlikely that the arduino is drawing excess current, more like the servo (or whatever) that's doing the rotation.
1038  Using Arduino / General Electronics / Re: transistor (2N2222) dropping 15v to 2v?!?! on: May 29, 2011, 02:52:47 pm
You will note that I used the term "simple" when I inferred that care needs to be taken when paralleling transistors.  From your suggestion I presumed you were suggesting connecting base-to-base, emitter-to-emitter and collector-to-collector.  (My definition of "simple")

There are various techniques which do permit effective paralleling of transistors, amongst which are :

a) intimate thermal contact between transistors by either mounting within a solid metal block or a common heatsink
b) multiple devices on the same chip (as per the IC you suggested)
      - from both of the above, any temperature rise in one causes a similar rise in the other -
c) fitting emitter resistors (which automatically act as a negative feedback device to ensure balancing of current loads)

As regards FETs, you can "simply" couple up like terminals to share load - as may be seem in most RC speed controls which have numerous FETs coupled in parallel.
1039  Using Arduino / General Electronics / Re: transistor (2N2222) dropping 15v to 2v?!?! on: May 29, 2011, 03:38:29 am
Unlike FETs, NPNs and PNPs fitted in "simple" parallel do not share the load evenly.  As one heats up it takes even more of the load which heats it even further until self destruction is achieved.
1040  Using Arduino / General Electronics / Re: Simple Transistor Question on: May 28, 2011, 06:03:55 am
Do you have a base current limiting resistor (say 4k7) in the transistor base connection.  If not then the base junction is causing a (almost) dead short across the supply line.  Why would you want to connect the base to the 5volt line ?
1041  Using Arduino / General Electronics / Re: Solenoid cuircut in parallel on: May 28, 2011, 02:56:31 am
Show us your circuit !
1042  Using Arduino / General Electronics / Re: What would you use a "darlington current driver" for? on: May 26, 2011, 09:18:02 am
I presume what you meant was that you would need twice the base drive voltage over what a "normal" transistor would need (ie somewhere around 1.4 volts)  The collector-emitter voltage drop (circa 0.7 volts) would remain the same as normal.
1043  Using Arduino / General Electronics / Re: RTC 1307 Problem on: May 25, 2011, 02:48:10 am
Have you tried salvaging a crystal from an old watch - don't know what their frequency is but they are free
1044  Using Arduino / Motors, Mechanics, and Power / Re: Controlling 6V-200RPM-Torque-Gear-Box-Motor on: May 23, 2011, 03:29:28 am
If all you want to do is change its direction using a simple and cheap solution then use a manually operated DPDT switch
1045  Using Arduino / General Electronics / Re: RTC 1307 Problem on: May 23, 2011, 03:26:45 am
Have you tried changing its battery ?
1046  Using Arduino / General Electronics / Re: Question about solid state relays on: May 18, 2011, 06:00:37 am
And many of the DC ones operate in the microsecond speed range so no problems with PWM switching frequency either.  Not quite as cheap as a simple FET but the way to go if you are unsure about the circuitry.  Just make sure you get the 5 volt logic driven ones (TTL in old money ?)
1047  Using Arduino / General Electronics / Re: Question about solid state relays on: May 18, 2011, 02:52:53 am
There are also speed limitations on how fast you can pulse SSR units, typically 10s of milliseconds to turn on or off - see the spec sheets for the model you're interested in.  This may well relate to the period of the mains frequency that the SSR is controlling (20mS @ 50Hz) You'd probably be better going for a simple FET driver to control your solenoid.
1048  Using Arduino / General Electronics / Re: Heat and Resistive Circuit elements on: May 11, 2011, 04:20:41 pm
You cannot equate dissipated power to resistance value (High versus Low) without also considering one of the other required variables  (current or voltage).

Let us say the resistor is 1kohm (what you might call "high")

With 10 volts across it the power dissipated equates to 0.1 watts - cold
With 100 volts the power is 10 watts - warm
with 1000 volts the power is 1000 watts - hot
with 10,000 volts the power is 100kW - !!!!

So "high" resistance (whatever that means) can dissipate appreciable power if the voltage is correspondingly high.  

You cannot simply state low resistance dissipates high power whilst high resistance does not - unless of course you are considering the resistors applied across the same voltage.

If however you consider the same current flowing through the two resistors then the power dissipated across the high resistor is greater than that across the low.

1049  Using Arduino / Motors, Mechanics, and Power / Re: 12v DC PC PSU to 9V DV on: May 10, 2011, 07:26:26 am
The arduino will run quite happily from a 12 volt supply, so why do you want 9 volts.   If you really do want 9 then use a simple voltage regulator such as an LM7809
1050  Using Arduino / General Electronics / Re: Isolated N to N volts on: May 09, 2011, 03:03:50 am
It's might be even easier to solve than you think.  An in-line capacitor will block the DC supply but permit the data signal to pass through.
Might not be the exact answer to your question but may add to the thought process
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