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1216  Forum 2005-2010 (read only) / Interfacing / Re: Arduino powersupply from 27V~ on: June 06, 2010, 06:36:52 pm
That point you are connected to with the +5volts is the VCC line and is intended as a 5 volt output point to drive sensor circuits. As far as I can determine it is not meant as a power input and feeding anything in there jeapordises the arduino. Also you are applying voltage to the output side of the power regulator with nothing on its input.  I am unaware as to how this might handle such a connection but I would think it bad practice.

I'd therefore suggest you change the 5 volt regulator for a 9 volt one and put the 9 volts power into the correct terminal (Vin) on the arduino.

Apart from that you still have to establish the problem with the 12volt overload.  Have you triedoperating one of the other relays yet ?

jack
1217  Forum 2005-2010 (read only) / Interfacing / Re: Arduino powersupply from 27V~ on: June 06, 2010, 05:01:28 pm
From the drop in the 12 volt line and the heat of your regulator it is evident that there is an overload condition.  Could the suppression diode be faulty.  Suggest you cut it out as a trial..

<ight be orth triggering one of the other relays first to see if you get the same results.

Your 5 volts remain good when triggering the uln so it appears that the arduino is overloading it.  can youadvise whichpins on the arduino you are connecting the 0v and 5v lines to.  I take it you are not connecting the USB lead at the same time.  Also is ita genuine arduino or a clone.

jack
1218  Forum 2005-2010 (read only) / Interfacing / Re: Arduino powersupply from 27V~ on: June 06, 2010, 04:24:26 pm
OK time for some basic testing. to determine where problem lies.

With nothing connected to the arduino,  connect the ULN input to the 5volt point (yellow to red)  Does the relay energise and does the voltages remain 12 and 5.

If all is good then problem is with your arduino connection.  If not good then advise what is happening so's we can go to step 2  - whatever that will be.

jack
1219  Forum 2005-2010 (read only) / Interfacing / Re: Arduino powersupply from 27V~ on: June 06, 2010, 04:10:01 pm
I take your arduino isn't goosed !
1220  Forum 2005-2010 (read only) / Interfacing / Re: Arduino powersupply from 27V~ on: June 06, 2010, 03:52:18 pm
Think I've got it.  From you're underside image it would appear feeding the +12 for ULN2803 and the relays through a common diode.  You previously mentioned (suggested) that you had fitted a suppression diode across the ULN2803.  The way it appears to be wired is not performing this function.  What type of diode is this.  Is it suitable for a 1 amp capacity.  Have you it the correct way round for feeding the circuit.  Either way I suggest you remove this diode.

With respect to the arduino supply.  It may be that you have a 3.3volt unit and when you are feeding it with 5 volts (are you connecting it correctly) the internal protection may be crow-barring the 5 volt supply.

jack
1221  Forum 2005-2010 (read only) / Interfacing / Re: Arduino powersupply from 27V~ on: June 06, 2010, 03:09:13 pm
Diodes look to be connected correct way round.

I take it that you are connecting the ULN2803 input to the 5volt supply to switch on the relay.

Your sketch looks OK.  If you've wired up on strip board are you certain that you've cut the relevant tracks OK and none are shorting.  An underside view of the board would be useful.

When you load the system, what happens to the 27V ac.  Does it droop excessively.  As long as it stays above 15 volts the circuit should work.

Previous comment that those relays will draw several amps is mistaken.  Even at 200ohm coils they are only going to draw 60ma each, which is well within the ratings of your regulators.

You mention the "transistor" gets hot, what transistor.

jack
1222  Forum 2005-2010 (read only) / Interfacing / Re: Arduino powersupply from 27V~ on: June 06, 2010, 02:17:01 pm
Sounds like you may have your inverse diodes connected the wrong way round.   The bar shown on the diode (cathode) must be connected to the positive side of your 12 volt rail.
As suggested, rough out a schematic and we'll be better able to interpret your problem.
jack
1223  Forum 2005-2010 (read only) / Interfacing / Re: Arduino powersupply from 27V~ on: June 06, 2010, 12:37:33 pm
You'll have to disconnect the 7805 from the 27 volt feed circuit and I'd even suggest that you remove the 7805 all together, otherwise you'll have two 5 volt regulators (yours and the arduino) trying to feed a single circuit without blocking diode isolation.  This could lead to instability.

Congrats on a neat build.

jack
1224  Forum 2005-2010 (read only) / Interfacing / Re: Arduino powersupply from 27V~ on: June 05, 2010, 05:55:35 pm
Without wishing to become embroiled in an argument about right and wrong circuit design, the 2803 has a potential weakness in that all 8 output suppression diodes are connected to a common pin.  If this pin, or its track becomes defective (even slighyly high resistance) the effectiveness of the onboard suppression diodes will be compromised.

The older generation of us will remember using lamp test circuits on control panel alarm lights,.by means of a common test button feeding banks of diodes to each indicator lamp. If any single diode failed short circuit, this acted as a common feed such that any circuit going into alarm would bring up all indicator lamps. - not much help when the bovine is hitting the fan.

ie a single failure mode can jeapordise all your circuits, so good design practice will endeavour to engineer out such common mode failures wherever possible.  For the price of a penny diode across each of the relay coils, your circuit integrity will be much improved.

jack
1225  Forum 2005-2010 (read only) / Interfacing / Re: Arduino powersupply from 27V~ on: June 05, 2010, 05:10:41 pm
Wasn't it the leming who said "I'm jumping off this cliff because everyone in front is doing so"    

Good engineering practice and/or common sense should never be substituted by "following the crowd"

jack
1226  Forum 2005-2010 (read only) / Interfacing / Re: Reading High Temps on: June 12, 2010, 04:05:01 pm
A type K thermocouple and one of these
http://www.sparkfun.com/commerce/product_info.php?products_id=306
will get you going
jack
1227  Forum 2005-2010 (read only) / Interfacing / Re: power level on: June 11, 2010, 12:33:11 pm
I appreciate this is the arduino site but sometimes there are simpler ways of doing things if you are in a hurry and not too confident about what you're doing.
Doesn't use an arduino (well not by name) but you could use a Turnigy unit which computes total power consumed as well as displaying both volts and amps.  Google the name to find further details.
jack
1228  Forum 2005-2010 (read only) / Interfacing / Re: How do I measure 8000 volts with Arduino? on: June 09, 2010, 02:50:30 am
Neons have a trigger voltage of around 90 volts or so and were once used as a form of constant voltage source, rather like zener diodes are currently used, so they'd be no good at providing an analogue value.

However you could build a simple potential divider system using high voltage resistors such as available here
http://www.willow.co.uk/html/high_voltage.html

Assuming you want a drop from say 20,000 volts to 5 volts (to allow for the pulsar giving more than 8Kv) you would need a division of 4,000:1 (OK not exactly but near enough)  with say 1000 ohms as the input or sense resistance, you'd therefore need 4000 x 1000 or 4 megohms as the main dropper resistor.  To ensure against track-over this could be made from 4 off 1meg resistors each rated at 10kv wired in series.

In effect you'd end up with a chain of 5 resistors, the lowest of which provides the ground and +5 volt sense to be input into the arduino.

Also place a diode across the 1k ohm detection resistor reverse biased to ensure you only detected a positive going pulse.

Cheap and cheerful with a known calibration factor.

jack
1229  Forum 2005-2010 (read only) / Interfacing / Re: General Soldering Advice on: June 02, 2010, 05:11:12 pm
Hooking wires together before soldering is excellent practice.   As a humble instrument apprentice, some 50 years ago, we were always taught that joints should be mechanically strong before soldering.   The practice of simply laying a wire alongside a component and soldering the two together is very poor workmanship.

jack
1230  Forum 2005-2010 (read only) / Interfacing / Re: General Soldering Advice on: June 02, 2010, 11:59:04 am
2muchnfo
I do work for a charity REMAP which invariably gets involved with problems like yours.  Sometimes we have to apply some lateral thinking and your particular case might need quite a bit of this.

Firstly you need a good iron and it must be clean and properly tinned.  A dirty iron will always fail to solder but will keep pumping heat into whatever you are working on.

Now to your problem.  On the basis that you have a hand tremor, the solution might well be to "eliminate" the tremor rather than develop a work-around.  Would it be possible to make some form of hand restraint that permitted you to use and manipulate a soldering iron but which would eliminate the tremor by virtue of the fact that your hand was restrained.  Say something like a U-shaped yolk you could lay on the work-bench, into which you could drop your hand but still permit some degree of manipulation of your fingers to control movement of the iron.

Alternately you may need to look at some means of fitting the iron into a mechanical frame which would guide it onto the job and effectively isolate its movement from that of your hand.

jack
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