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1006  Using Arduino / General Electronics / Re: Dangerous Component ? on: June 08, 2011, 03:12:56 am
The crude way is to simply shorten it out with a piece of wire but this could damage the capacitor (high current) - and give you a fright if it is charged -  better to use a resistor (say 100ohms) and place this across the terminals.  However be aware that a high voltage one will could give you a kick so avoid using your fingers to hold the terminals of the resistor
1007  Using Arduino / General Electronics / Re: Battery Requirement Calculations - First Arduino Project on: June 08, 2011, 03:08:54 am
In that case use a half-sizeAA battery.  These are litium based and provide 3.6 volts.  So either 1 of these or several in parallel will meet your dimensional needs.  Google 1/2AA for information of these devices.

One query on your use of a test meter.  You say it was across +5 and ground and the system supplied 3.9mA.   Are you sure you know what you were doing or did you miss something out in your description.  You cannot measure current by applying a current measurement across a voltage supply, the meter MUST be in series with ONE of the power leads.
1008  Using Arduino / General Electronics / Re: Basic one this ... on: June 06, 2011, 07:43:54 am
There are only two variables in any electrical circuit, the primary (or independent) one is voltage, and the secondary (or dependent) one is current.  It is voltage which drives the current through whatever passive device is attached to the circuit, whether it be resistance, capacitance or inductance.  Again it is voltage which excites active devices (semiconductors etc), whether they be voltage or current driven.

Hence by measuring voltage (on an oscilloscope) with respect to time you can establish or analyse what is happening within any circuit.
1009  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.
1010  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.
1011  Using Arduino / General Electronics / Re: transistor (2N2222) dropping 15v to 2v?!?! on: May 29, 2011, 02:52:47 pm
Steve,
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.
1012  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.
1013  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 ?
1014  Using Arduino / General Electronics / Re: Solenoid cuircut in parallel on: May 28, 2011, 02:56:31 am
Show us your circuit !
1015  Using Arduino / General Electronics / Re: What would you use a "darlington current driver" for? on: May 26, 2011, 09:18:02 am
Awol
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.
1016  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
1017  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
1018  Using Arduino / General Electronics / Re: RTC 1307 Problem on: May 23, 2011, 03:26:45 am
Have you tried changing its battery ?
1019  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 ?)
1020  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.
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