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1006  Using Arduino / General Electronics / Re: Where to find precision R2R ladder? on: June 11, 2011, 03:22:42 pm
Assuming you want to power your control from the same supply as the telescope motoring device, and you want to read any combination of 6 switches then you will need to effectively create a 6 bit binary word where each bit (0 or 1) is an individual switch.  These you feed into a 6 input (binary) logic device which will read the respective binary word and produce a single analogue value.  As such you will need 3 wires for your hand control, 2 to supply power to the switches, DAC etc and one to return the respective analogue value.

However, 8 core security alarm cable is both flexible and of very small diameter so you might be trying to overcomplicating your requirements, when you could very neatly feed all 6 switches from your hand control back to the telescope.

1007  Using Arduino / General Electronics / Re: Correct capacitors for Voltage Regulator ? on: June 10, 2011, 02:17:50 am
Yes they will work but VASTLY overpriced and over-rated for what you need.  These are rated at 850volts DC.  All you need are something rated at 50 volts maximum - you'll find 100 volts or so pretty standard and cost less than £1 each. Something like this, though you'll find them much cheaper at the likes of Maplins 

1008  Using Arduino / Project Guidance / Re: Current measurement from Solar Panels on: June 09, 2011, 04:49:20 pm
DC hall current sensor is what's required with 0-5 volts DC output such as a CSLA2C or similarfor direct feeding into the arduino.
1009  Using Arduino / Project Guidance / Re: A variety of different frequency motors on: June 09, 2011, 07:51:31 am
This is really bouncing concepts off the wall. 
How about stripping out a musical box to salvage the reed assembly.  These are made of high tensile steel and are therefore magnetic.  Now, if you place a wound ferro magnetic coil adjacent to the reeds and excite this at various frequencies, only the reed which matches the excitation frequency will vibrate.
1010  Using Arduino / Project Guidance / Re: variable frequency motors on: June 08, 2011, 04:29:22 pm
The only problem with changing motor speed is there is also a rapid change in amplitude, ie at lower speed there will be a gross reduction in amplitude and at higher speed a gross increase since the vibration is induced by an out-of-balance spinning mass.

One alternative is to use the natural frequency of a vibrating strip of metal.  Differing frequency of vibration gives you the required haptic feedback.  Use a coil to excite the strip.  Alter the natural frequency by driving a damper finger along the strip by use of a small servo motor.
1011  Using Arduino / General Electronics / Re: Battery Requirement Calculations - First Arduino Project on: June 08, 2011, 05:19:11 am
+5 on supply (battery or whatever) to ground on supply is OK for measuring voltage  -  but NOT current.  To measure current you need to connect meter +ve lead to +5 on supply and meter -ve lead to the +ve terminal of your device (arduino or whatever).  The device -ve lead connects to the supply ground
1012  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
1013  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.
1014  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.
1015  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.
1016  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.
1017  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.
1018  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.
1019  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 ?
1020  Using Arduino / General Electronics / Re: Solenoid cuircut in parallel on: May 28, 2011, 02:56:31 am
Show us your circuit !
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