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1036  Using Arduino / Motors, Mechanics, and Power / Re: Measuring LiFe battery pack voltage with Arduino on: February 24, 2011, 11:30:36 am
Put 22k resistor in series with the input to the arduino.  Even if you totally screw things up, the resistor will limit the input current to a safe value of <1ma.  (13.2/22000 = 0.6ma) and there will be no need for the external zener

jack
1037  Using Arduino / General Electronics / Re: Nixie Tube Transformer on: February 23, 2011, 04:15:57 am
You will not be able to use a potentiometer to provide a stable voltage to power the unit since the pot output will collapse due to current draw.  A pot can only be effectively used to provide voltage at zero current.  I'd suggest trying to find a voltage convertor chip capable of running off the 5 volt system and providing the 1.5 you require.  Yes it is down-up-down but that's life.   
An even cheaper way might be to fit a 3.5 volt zener diode in series with your 5 volt supply line to the camera module.  This will drop the 5 down to 1.5 volts.  However the zener will probably need to be rated at say 1 watt minimum in order to handle the required current draw.
jack
1038  Using Arduino / Motors, Mechanics, and Power / Re: how to install dc motors?? on: February 21, 2011, 01:53:19 pm
May I suggest that you look for alternative servos.  The speed of a servo is determined by how fast you feed the translation (movement) signal to the motor and the gear ratio within the servo (if it has an inbuilt gearbox).  The servo is the ideal motor if you want open loop positional control (no feedback of actual position) with reliable movement dependant simply upon command.   A conventional DC motor is totally uncontrollable without a feedback system which will complicate your design and add little towards solving your problem without a lot of effort.

jack
1039  Using Arduino / General Electronics / Re: Read voltage across a resistor and use it as an input to an anlog pin. on: February 18, 2011, 07:05:44 pm
almost   you must also connect the circuit ground to the arduino ground.

in my previous posting i got the instructions about the arduino connection reversed.  sorry about that.

re how can 5 volts be dangerous  ::  you need to read the precondition.   if the resistor is connected to a circuit at 500 volts to ground, with 5 volts across it the other end will be at either 495 or 505 volts, depending upon current direction.  not all low level measurements are referenced to ground !

jack
1040  Using Arduino / General Electronics / Re: Read voltage across a resistor and use it as an input to an anlog pin. on: February 18, 2011, 05:10:08 pm
The following is based ONLY upon a situation where the resistors is not connected to the ground point of the circuit generating the current and providess a simple and cheap solution.

It is irrelevant what potential the resistor ends are with respect to circuit ground.  The point at which the current enters the resistor must be connected to the arduino ground and the end at which the current flows out goes to the arduino sense input.

This being the case the circuit ground reference must be and remain insulated from the arduino ground reference.

Note :  If the potential of either end of the resistor is relatively high with respect to true ground then you are working on a potentially hazardous system and you should not consider direct connection to the arduino.  If this is the case then you require a galvanic isolation module.

jack
1041  Using Arduino / General Electronics / Re: Trying to do load sensing - how? on: February 17, 2011, 04:12:09 pm
If you want to simply detect motor stall conditions, rather than trully monitoring motor current, then measure the primary variable (shaft speed), not a secondary one (motor current).  Look at shaft speed and when it stops turning, the motor has stalled   -  QED.

You could use either an optical sensor looking at an interrupted light through a vane wheel or a simple magnet mounted on each of the wheels to operate a reed switch.  Measuring the time interval between switch operations will determine when the wheel stops turning.

No voltage losses, no hall sensors and no opamps

jack
1042  Using Arduino / General Electronics / Re: Trying to do load sensing - how? on: February 17, 2011, 04:15:58 am
If you are sensing 2 motors then you need 2 resistors and 2 analogue input pins.  You cannot add the separate voltages together to produce 0.3 volts since each must be referenced to a common ground point. 
As the previous writer said, for maximum efficiency and measurement resolution you should go for hall type sensors.  These can be provided with a 0-5 volt output over the desired current range and are totally isolated from the current being measured.

jack
1043  Using Arduino / Motors, Mechanics, and Power / Re: How to Increase the PID Response time? on: February 15, 2011, 04:12:43 am
Adjustment of the P-param will affect the gain of the system and so alter the speed of response.  I am unsure whether the arduino software requires higher (>1) or lower value (<1) to increase gain but you'll soon find out.

P stands for Proportional action (gain) and is the amount of correction action applied based on the size of the error signal (a quantity relationship)
I stands for Integral action and applies correction based upon how long the error exists (a time relationship)
D stands for Derivative action and applies correction based upon how fast the error is changing (a speed relationship)

The proportional action is the main factor governing speed of response so this should be your first point of adjustment.  If you set the value too high (increasing gain) then the system will speed up but may become unstable (excessive overshoot or even oscillate)
Generally if your system has a large response mass, such as a water heating system, then you require less I action and more D action
Conversely, if your system has a low mass response, such as a motor speed control system, then you may require more I action and less (or no) D action.

jack
1044  Using Arduino / Motors, Mechanics, and Power / Re: Turning a motor into a servo on: February 14, 2011, 08:55:50 am
To interpret head movement why not use a 3-axis accelerometer chip.  This will give you the required three degrees of rotation.
jack
1045  Using Arduino / Motors, Mechanics, and Power / Re: How do i measure the maximum current of an AC variable power supply with resetib on: February 12, 2011, 05:11:01 pm
Puting it simply, there's no way you will get 5 amps out of this without also releasing the smoke genie

If you want 5 amps at 8 volts then you need 40 volt-amp

If you need 5 amps at 15 volts then you need 75 volt-amps

simples

The reason that ac power units are specified as volt-amps is because the supplier has no way of knowing what power factor your load will be.  At unity PF volt-amps is equal to watts.  However at reducing power factor the available watts is also reduced since watts is specified at the equivalent unity power factor.

Hence if the unit is specified as 40 volt amps with an 8 volt output then you will always get 5 amps out of it, even if you have a low power factor (inductive or capacitive load) only represent say 20 watts

jack

1046  Using Arduino / Motors, Mechanics, and Power / Re: How do i measure the maximum current of an AC variable power supply with resetib on: February 12, 2011, 03:35:47 pm
Do you mean "how do you measure the current it is being loaded at"  If so the simplest way is to buy a cheap clamp-on test meter.

If you mean, what can you load it to without causing it to trip, then simply read the rating plate.

The resettable trip is probably a simple thermal device, in which case it will have a non-linear current x time relationship, so the maximum load current for say 1 second is probably twice that for 5 seconds

jack
1047  Using Arduino / Motors, Mechanics, and Power / Re: Problem interfacing arduino and relay on: February 12, 2011, 11:59:56 am
If you have a meter I suggest you check the arduino output port to confirm it is going both Hi and Lo on demand.

Is your arduino a 5 volt unit.  If not then a 3.3 volt output is not within the specification of your relay board and will not be switching it.

If it is a 5 volt unit and you are getting 5 volts output then there is a possibility that the relay board isn't being switched - even though its specification states it should switch at 4 volts.

jack
1048  Using Arduino / General Electronics / Re: Zener diode??? on: February 12, 2011, 04:57:31 am
I fail to understand your circuit.  Where is your 9 volts coming from to drive the milliamps and where is the P/D resistor you mentioned in your opening query.

You really do need to provide the full information if you want informed and correct answers, rather than best guesses.

jack
1049  Using Arduino / Motors, Mechanics, and Power / Re: Motor Selection on: February 11, 2011, 02:40:14 pm
Not the answer to your question but for what it's worth :-
For that sort of application you really need an instantaneous release of energy.  "Unwinding" a motor will not give this as the motor inertia will effectively act as a brake, resulting in a slow release.  I'd advise you look at a trigger mechanism to release the "elastic" once it's been wound up.  The motor can then be run back to pick up and restretch the elastic.

jack
1050  Using Arduino / General Electronics / Re: Zener diode??? on: February 11, 2011, 07:34:30 am
You should be asking yourself where the 9 volts comes from and you could then solve the problem.

A 4-20 signal should feed into a 250ohm resistor (R in your drawing) to produce a 1-5 volt signal for feeding into your arduino.

If the unstated value of R is greater than 250 ohms then the sensor will drive the voltage higher in an endeavour to ensure that the current range remains within the 4 to 20 scale.

I suspect your value of R is much too large.

Having said that, the zener should have conducted to clamp the voltage so I suspect you've blown it and it no longer works.

jack
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