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1156  Forum 2005-2010 (read only) / Interfacing / Re: Pressure transmitter 4-20mA with arduino on: December 21, 2010, 02:18:44 pm
You have not defined exactly which model of 3100 transducer you are intending to use.  You mention 4-20ma but I believe that is because you are unaware that the three wire device is voltage output, whereas the 4-20 device is a 2-wire device.  You talk about 4-20 (2-wires) but your drawing shows 3-wires (voltage output)

Until you define exactly which you intend to use, we might be giving false guidance.

We will give you the correct answer to your question but only when you give sufficient information on which to base the answer.

kind regards

jack
1157  Forum 2005-2010 (read only) / Interfacing / Re: Getting odd readings from hacked digital scale. on: November 29, 2010, 04:16:49 am
You may be failing to appreciate that strain guages are dual action.  That is, as well as pushing down on them you can also pull up on them.  In effect their full range is from minus-weight to plus-weight.  So in effect, in a body mass device you are spanning over only half the weight range.

Also because the op-amps can only span from 0 volts to +5 volts they need to be set to mid range at zero load to match the strain guage capability.

You have proven that you can vary gain by twiddling the adjustable pot.  What you now need is a zero off-set adjustment so that you effectively blank out the -ve range capability of the strain guage and the mid-voltage offset of the op-amp.

There again I may be talking a load of bull.

jack
1158  Forum 2005-2010 (read only) / Interfacing / Re: Small submarine powered by Arduino Nano on: December 11, 2010, 05:11:00 pm
You could cheat and simply fix some stiff but flexible transparent plastic "whiskers" to the front and sides of your sub.  These will touch the walls and so keep the body away and with luck won't be seen when submerged
jack
1159  Forum 2005-2010 (read only) / Interfacing / Re: detecting obstructions on the sea on: November 17, 2010, 09:46:31 am
The first thing you need to do is define the size, shape and material of the obstructions that you are attempting to avoid.

Needless to say a "barn door" standing vertical on a raft will be much easier to detect than a small log partially submerged but still afloat on the water.

Once you have defined the obstruction specification you can then start looking at what you need to "see" it.

The Doppler effect radar detectors work on the principal of detecting the relative frequency shift between the transmitted signal and the reflected signal from the object.  If there is no relative movement, there is no frequency shift and hence no detection.  You therefore should be looking at a device that will sense actual reflected signal rather than frequency shift (Doppler)

jack
1160  Forum 2005-2010 (read only) / Interfacing / Re: detecting obstructions on the sea on: November 17, 2010, 09:07:31 am
How about something along this line - excuse the pun

http://www.tycoelectronics.com/aboutus/news/prodinnov.aspx?id=976

jack
1161  Forum 2005-2010 (read only) / Interfacing / Re: detecting obstructions on the sea on: November 17, 2010, 08:46:58 am
OK back to my original statement.  Not suicidal as no person at risk but could be financially crippling as system will be unreliable, at best.

You could put a big rubber tyre round it to act as a fender

jack
1162  Forum 2005-2010 (read only) / Interfacing / Re: detecting obstructions on the sea on: November 17, 2010, 08:37:26 am
Does USV = Submarine

If so, and if it's underwater obstructions you are concerned with,  then ultrasonic detectors are exactly what you need.
Howevre you need to get hold of the type used in echo sounders, which for obvious reasons are waterproof.  I believe they work at somewhat lower frequency than the "air" ones.  Somewhere in the order of 22kHz, I think.

jack
1163  Forum 2005-2010 (read only) / Interfacing / Re: detecting obstructions on the sea on: November 17, 2010, 08:13:11 am
Ultrasonic detectors such as you suggest will be totally useless in this application.  Firstly their range is very short - in the order of say 10 metres maximim.  On a pitching boat their ability to detect an obstruction in anything other than a dead flat calm will be questionable. And lastly, placing ones life (at full speed - your quote -) on a device that will not work is suicidal.
Radar is what you need !

jack
1164  Forum 2005-2010 (read only) / Interfacing / Re: Testing a Relay on: December 08, 2010, 06:52:47 am
In a word - Yes

The output contacts have no electrical relationship to the driving voltage so you can happily operate the coil with no output devices or circuits connected
jack
1165  Forum 2005-2010 (read only) / Interfacing / Re: Voltage divider + Thermistor on: December 06, 2010, 05:38:35 pm
Good on you Nerdy,

You've thought about and eliminated the obvious simple route to provide for extra facilities.  I like the idea of feeding back by telemetry.

Have you thought about also adding an infrared sensor so's you can "see" the location of the heat source in thick black smoke.

The 100 ohm RTD may give too poor a resolution since the buffer resistor to control bias current is so small, so the use of higher value units (1000 ohm) might be a better option.  Rather than using a simple tapped voltage divider, you'd be better to use a bridge configuration.  That way you can bias the arduino input with a reference voltage that is independant of battery voltage (to eliminate drift as the battery voltage drifts or varies. This would require a supply voltage separate from that which drives the arduino but this could easily be achieved by using a dc/dc convertor chip  driven by the same battery that drives the arduino.

jack
1166  Forum 2005-2010 (read only) / Interfacing / Re: Voltage divider + Thermistor on: December 06, 2010, 01:28:49 pm
Great to see someone thinking of using an arduino for a serious project.  A fibre optic type bendy line could present the colours to the user's preferred eye-line without having to place bulky components in his field of vision (though you can get some amazingly small LEDs these days)  Note also that you may need some conditioning system to brighten LEDs in daylight and dim them in black darkness.  Any extraneous light will be undesirable.

However you may be using a sledge hammer to crack quite a small nut

Have you considered using an LM3914 LED driver chip to do exactly what you want.  See http://www.national.com/ds/LM/LM3914.pdf for details.

jack
1167  Forum 2005-2010 (read only) / Interfacing / Re: Relays switched and loaded from same power source? on: November 29, 2010, 04:59:13 am
Your base current may be too low to fully turn on the transistors - you do not specify type of transistor.  What voltage do you have on relay coils when turned on.  Suggest you lower the 33k to 10k.
jack
1168  Forum 2005-2010 (read only) / Interfacing / Re: Relays switched and loaded from same power source? on: November 29, 2010, 04:56:27 am
What are the loads, resistive or inductive ?

What is the AH capacity of the battery ?

Why are you feeding the transistor collectors with a bleed resistor/diode arrangement across the relay coils ?

Where does the Arduino get its power from ?

So many questions, so little upfront information

1169  Forum 2005-2010 (read only) / Interfacing / Re: Strange dc motor behaviour on: December 03, 2010, 05:51:03 pm
Suspect that your wall-wart power supply is being dragged down by the motor attempting to increase speed.  Suggest you try repeating the exercise but use a 12volt sla type battery or similar.  The board is rated at 2A maximum so fit a 1amp fuse into the power line to protect your board.
jack
1170  Forum 2005-2010 (read only) / Interfacing / Re: Reading RPM from wire coiled round spark plug lead on: December 03, 2010, 08:05:10 am
Hi Mike,
Off topic, but as you mentioned using miniature neons, here's a little story.

Around 50 years ago the cheaper models of vessel echo sounder used a rotating neon light to indicate water depth.  One flash at 12o'clock as the zero reference then as the lamp rotated it would be re-struck to indicate depth.

One of the problems was that the neons were fired with a sharp pulse and would eventually blacken on the side of the glass such that they couldn't be seen.  One of the jobs I used to do, as a youngster, for local fishermen was to replace these neons.

Some varieties wouldn't stike successfully but I found that shining a torch light onto them, made them fire OK.  Grey cells into gear and doing some research, I found that any form of photon "exciting" would do the trick - so I ended up painting a little blob of luminous paint onto the back side of the neons.  In those days it was mildly radio-active !!  

These types of neons were also widely used as high voltage satbilisers, their stricking voltage being around 90 volts.  But that was in the days when 120 volt primary cell radio batteries were available.

jack
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