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1216  Forum 2005-2010 (read only) / Interfacing / Re: 4-20mA analog input to serial out on: October 23, 2010, 04:12:06 am
Firstly your device is not a sensor, it is a controller that needs mains power and suitable sensors connected.

It outputs both an analogue current (4 to 20ma) based on controller computation and a dry relay contact for use as an alarm or switching facility.

I cannot determine what it means by stating the relay is a 5volt unit unless it also outputs a 5 volt on/off signla for an external relay.  A copy of the operating manual should clarify this for you.

The device outputs 4 to 20 ma but can only do so if you present it with a load resistor.  I suggest you connect a 250ohm resistor between the terminals marked as 4-20 then connect the arduino input and ground across the resistor.  The 4-20 output will now produce a voltage signal of 1.0 to 5.0 volts across the resistor for the arduino to read.  Getting hold of a 250 ohm resistor might be problematic so use a 220 ohm and scale the arduino such that 0.88 volts equals 0% span and 4.40 volts equates to 100% span.

Jack
1217  Forum 2005-2010 (read only) / Interfacing / Re: Interpolation methods for predicting future on: November 16, 2010, 06:37:42 am
Don't wish to be picky, but prediction of future data is "extrapolation".  Interpolation is the assessment of data between two measured points.  ie it relates to history.
jack
1218  Forum 2005-2010 (read only) / Interfacing / Re: How to decrease voltage? on: November 14, 2010, 01:45:59 pm
By magic !  it's all done with smoke and mirrors.

A cars electrical system is a self contained system.  Battery output to device, out of device and back to battery.

Do not confuse the term "ground" with a stake driven into planet earth.  Thos devices are the preserve of vampires.
1219  Forum 2005-2010 (read only) / Interfacing / Re: Arduino with zener diode on: November 14, 2010, 01:36:07 pm
On the basis that the arduino can output only 40ma without going into self destruct the maximum zener required power rating is
5 x 0.04 = 200mW.   That's based on using a 5 volt zener  feeding into a dead short with 100% duty cycle of the PWM.  To protect the arduino one should fit a resistor in the output of the zener to limit current to 40ma.  The maximum resistor required is 5 / 0.04 = 120ohm. Again this is based on 100% duty cycle feeding a dead short but this time with the zener voltage set to zero volts
jack
1220  Forum 2005-2010 (read only) / Interfacing / Re: Arduino with zener diode on: November 13, 2010, 02:17:33 pm
Here's a simple circuit using a zener  (click on the image to see it)


The PWM output is a 5 volt signal of varying duty cycle (mark to space ratio).   The zener diode subtracts its voltage rating from the 5 volt output to produce a reduced output.  For example, if the zener is rated at 2.1volts the output will be 2.9 volts.

jack
1221  Forum 2005-2010 (read only) / Interfacing / Re: +-10V Analog input on: October 20, 2010, 04:36:55 pm
Apollo
Please tell us what language you are using and what software translator you are using to create the english translation.  If you send your last message, about curtain rods, in your original language we may be able to try a different translator.
jack
1222  Forum 2005-2010 (read only) / Interfacing / Re: +-10V Analog input on: October 17, 2010, 03:43:05 am
A simple voltage divider using a pair of resistors, say 2 resistors in series each of 3k3ohms  (that's 3300).  One end of the chain to your 10 volt output, the other end to the arduino 0volts and the centre to the arduino analogue input.  You also need to connect your cnc 0volts to the arduino 0volts
1223  Forum 2005-2010 (read only) / Interfacing / Re: Image Broadcast using Handheld radio on: November 04, 2010, 08:55:37 am
Isn't that called a fax machine ?
1224  Forum 2005-2010 (read only) / Interfacing / Re: High Amperage Circut on: October 08, 2010, 02:09:41 pm
Suggest you might also want to include a "Time Out" function which interupts the procedure after a predetermined period has passed and a launch has not been initiated.  This will prevent the system being left in a "Ready to Launch" mode if the operator becomes distracted by something nice passing across his line of vision.

Such a concept is quite common in industrial types of "initiation" control circuits

jack
1225  Forum 2005-2010 (read only) / Interfacing / Re: Calculating correct values for pulsating voltages on: October 29, 2010, 05:26:56 am
I should also have added that charging currents should be shown as negative values but you will have a problem with the charging voltages since the voltage measured during charge will not be the true battery voltage.  True battery voltage can only be measured after termination of the charge process and the battery has been given time - say a couple of hours - to "settle".  Hence charge power will always appear to be very much greater than discharge power.  You can only really measure instantaneous charge AH rather than charge power.

jack
1226  Forum 2005-2010 (read only) / Interfacing / Re: Calculating correct values for pulsating voltages on: October 29, 2010, 05:20:25 am
You need to integrate snap-shots of current and voltage during the adjacent snap-shots.

Take current and voltage readings as fast as you can.  compute watts consumed between adjacent snapshots, then add together all your snapshots.

For example say take snapshots at 1 millisecond intervals.

T1  I=10.4 amps  V=12.6 volts
T2  I=2.3 amps    V=12.8 volts
T3  I=4.2 amps    V=12.8 volts

From T1 to T2 you assume current remained constant at 10.4 amps and voltage remained constant at 12.6 volts.  Therefore AH consumed = 10.4 x 0.001 / 3600  =  2.8miroAH  and power = 35.28 microwatts

From T2 to T3 you assume current remained constant at 2.3 amps and voltage remaned constant at 12.8 volts.  Therefore AH consumed = 2.3 x 0.001 /3600 = 0.6389 microAH and power = 8.178 microwatts.

Now you simply add together all the iterations.  In this case from AH for     T1 + T2 = 2.8 + 0.6389    = 3.4389 microAH and
Watts for T1 + T2 =  35.28 + 8.178 = 43.458 microWatts

Note that the measurements at T3 don't come into consideration until you consider the time element from T3 to T4

Yes you are dealing with very small instantaneous numbers and there is a great deal of "averaging" going on but that's what integration is all about.  The gains balance out the losses.

Jack
1227  Forum 2005-2010 (read only) / Interfacing / Re: Help with connecting LED's on: October 30, 2010, 04:40:01 pm
Connect 2.7k resistor to digital out pin  - connect LED anode to resistor  -  connect LED cathode to arduino ground.  Do that for as many LEDs you have or the number of output output pins (whichever is the lesser)  

There are ways of using very many more lEDs but let's learn to crawl first !
1228  Forum 2005-2010 (read only) / Interfacing / Re: sensing up to 100 voltages on a single arduino on: October 22, 2010, 04:53:22 pm
Tango

If you're still considering this project then, as previously mentioned, double pole switched relays (1 per cell) is definitely what's required.  Because of the possibility - however remote - of creating a battery short circuit, the installation of fuses in each cell sampling line is essential.

The "outputs" of all the relays are commoned together and feed into a single isolation amplifier such as this http://www.prelectronics.com/prefiles/2204/Datablad/2204uk.pdf   The output of the amplifier then feeds into the arduino.

However, such an amplifier can be quite expensive so you might have to search around to get one at a cost you can afford.  Such a device is definitely not a DIY project.

jack
1229  Forum 2005-2010 (read only) / Interfacing / Re: sensing up to 100 voltages on a single arduino on: October 22, 2010, 06:45:16 am
Mike
I appreciate that but you misunderstand my comment.

On page 1 of this topic you'll see I was the one who advocated the use of relays to connect the cell under measure to the arduino.  

My latest comment was aimed at those who are showing concern about the fact that as they go up the cell structure the voltage to "ground" progressively increases, mot only beyond the capabilities of the measuring ICs but also presenting a safety hazard.  

If the bank is floating then there is no increase relative to ground - in effect all cells will appear to have the same potential which is determined by leakage resistance alone, which on industrial applications is usually limited to 10kohms, but preferably much higher.

Of course to maintain the "float" one would either have to galvanically isolate the cell under examination, from the measuring system by using a 1:1 galvanic isolator (as typically used in I.S. installations) or have the arduino and all its ancillaries, including power supply and display, fully floating (which will be much more difficult).  

jack
1230  Forum 2005-2010 (read only) / Interfacing / Re: sensing up to 100 voltages on a single arduino on: October 22, 2010, 04:10:32 am
Hold on guys, you're all making the assumption that the 100+cells are connected to a reference ground at some point.  

Is this actually the case.  

On DC switching control circuits and high power UPS systems, which used upwards of 240volts, we always ensured that the batteries were completely floating.  By this means we removed the electrocution hazard and also the possibility of false switching by leakage currents.

Can the originator of this topic please confirm if his system is floating or grounded; and if grounded, why.

jack
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