working a real gauge without PMSys.

[Jackpilot]

http://i24.photobucket.com/albums/c29/jackpilot/gauge.jpg

(This works only with electrical gauges)
Wired this way, the pointer moves from zero to full when the pot is rotated from zero to max.
The pot can be preset so that the pointer goes to a target value when power is applied and reverts to zero when power is off.
Can be used that way for brake pressure with a microswitch on the brakes pedal.

Now the question !!
What kind of little electonic circuit could be used so that the pointer would creep slowly to the target value when power is applied. Could be used for Hyd pressure on engine start, or APU spooling up, or temperature going up etc... No link with any software and sort of eye candy but good enough for secondary systems and dirt cheap!

Any idea?

[rottenlungs]

I get the feeling a dirty great electrolytic capacitor would be involved somehow - a smoothing cap from a power supply maybe? This is the kind of thing used to provide soft on-off functions on courtesy lights etc..

Put the capacitor in parallel with the gauge and it would rise & fall slowly I think - though my analogue electronics skills are crude in the extreme and I would suggest waiting for confirmation / debunking of my theory..

Cheers

James

[Matt Olieman]

This is a good one for Mike Powell :) :) :) I'm willing to bet he has the answer :)

Matt Olieman

[Jackpilot]

Actually, was trying to get his attention...lol...
James, I thought about the capacitor but as I remember these things accumulate and release in a burst....may I am wrong/rusted too! I'll try it tomorrow anyway...and report.

[AndyT]

The curcuit will work as drawn as long as the power supply is exactly in the correct range for the guage. Otherwise, you are going to need to adjust it with resistors. You will also want a diode in there to prevent reversing the polarity by accident and blowing the guage and the rest of the circuit.

[Jackpilot]

It works, I actually tested it on a 747 Hyd pressure gauge.
One AA 1.5v is enough. I tested up to 5v. The pot acts as a resistor itself and just needs a new adjustment to get the pointer where it should be when the voltage is increased.

What I would really like is a progressive "spool up" like 3 seconds..in other words inserting an electronic circuit that would have the same effect as turning slowly the pot's shaft . In fact decreasing a resitor value slowly over a few seconds when power is applied and vice versa.
Maybe a transistor can do that...my knowledge is insufficient!!

[Mike.Powell]

I think we can come up with a simple circuit to do that. First I need to know something about the gauge sensitivity. Can you make some voltage and current measurements?

[Jackpilot]

Yes if you tell me how to do it...with a multimeter I suppose.
I have two wires identified as + and - and three unknown ones.
For the moment I power it with a 1.5v AA and it deflects fully with the pot half way.

All ears.
Jack

[Mike.Powell]

I need the voltage across the gauge when the pot is set for full gauge deflection. This is done with the multi-meter leads plugged into the + and - jacks.

I also need the current through the gauge with the pot set to get the same gauge needle deflection. For this you need to put the multimeter leads in series with the gauge. You may have to tweak the pot to get the same gauge deflection.

[Jackpilot]

will do and report
Thanks mike

[Trevor Hale]

Actually, was trying to get his attention...lol...
James, I thought about the capacitor but as I remember these things accumulate and release in a burst....may I am wrong/rusted too! I'll try it tomorrow anyway...and report.

Guys,

If you place a resistor in series with the capacitor you can control the speed to which the capacitor will charge. you would be required to use something like a 2500 Micro farad capacitor and try like a 10K resistor to start.

You would have some playing to do, (I am sure Mike could give you the formula), however I think you would find that it would work to your satisfaction.

Trev

[Jackpilot]

Thanks Trev. will try that too.
For the moment I tried what Mike asked for and either I do it wrong or my multim is not sophisticated enough (probably) but here is what I get.

http://i24.photobucket.com/albums/c29/jackpilot/multi.jpg


On item 2 (serie) I get a neg on the multi and a positive move of the pointer if I insert the multi on one side (pos or neg do not rmemeber) and vice versa.


Would be so nice to have those few analog gauges on the NG become alive with a little bit of ingenuity and a very thin budget.

[737NUT]

Allot of those gauges are D'Arsonval movements and work on VERY low current. I expieremented using 3V source and cap and resistors. IT was impossible to get smooth movement, it would bounce real bad.

[Mike.Powell]

On item 2 (serie) I get a neg on the multi and a positive move of the pointer if I insert the multi on one side (pos or neg do not rmemeber) and vice versa.



You can get a positive reading on the multimeter by reversing the leads connected to it.

When you measured 1.5 for the voltage reading, what position was the multimeter selector switch set at?

What sort of multimeter are you using? Is it digital or a moving needle type?

[Jackpilot]

When you measured 1.5 for the voltage reading, what position was the multimeter selector switch set at?

Lowest range 15v »DC

What sort of multimeter are you using? Is it digital or a moving needle type?

Needle...think I need a better one.

[mauriceb]

A while back, I posted this circuit. The gauge could be there instead of a voltmeter as shown in circuit. The Values for R1-R2 & C1 depend on the time constant you want to achieve. Also, instead of the switch, there could be relay switches instead so that the whole operation could be automatic when the power is applied ore removed.

http://i32.photobucket.com/albums/d38/mau_ben/Circuit.jpg

Here is an explanation from Wikipedia:
In an RC circuit, the value of the time constant (in seconds) is equal to the product of the circuit resistance (in ohms) and the circuit capacitance (in farads), i.e. τ = R × C. It is the time required to charge the capacitor, through the resistor, to 63.2 (≈ 63) percent of full charge; or to discharge it to 36.8 (≈ 37) percent of its initial voltage. These values are derived from the mathematical constant e, specifically 1 − e − 1 and e − 1 respectively.

A convenient short-cut is that the same formula works if R is in megohms (MΩ) and F is in microfarads (μF).

Maurice

[Jackpilot]

I assume that the R1 circuit is for ON (gauge spooling up) and R2 for OFF and spool down
R1 and R2 being Pots
Acordingly in T= R X C
R= R1+R3 or =R2+R3 if spool up and down are the same duration.
Correct ?

[mauriceb]

I assume that the R1 circuit is for ON (gauge spooling up) and R2 for OFF and spool down
R1 and R2 being Pots
Acordingly in T= R X C
R= R1+R3 or =R2+R3 if spool up and down are the same duration.
Correct ?


No, R3 does not enter in the RC picture and should be very high resistance. You may have to experiment with the value but the higher the better (try 10 Megohms) . It is just there so that C1 does not discharge via the gauge (I'm assuming the gauge does not have a high resistance value like a voltmeter has).

So RC should be R1 x C1 for spool up and R2 x C1 for spool sown.

Maurice

[Mike.Powell]

When you measured 1.5 for the voltage reading, what position was the multimeter selector switch set at?

Lowest range 15v »DC

What sort of multimeter are you using? Is it digital or a moving needle type?

Needle...think I need a better one.

Were you able to make the current reading with the multimeter leads reversed?

If we know the voltage across the gauge and the current through it at full scale we can calculate the gauge resistance and know its sensitivity so we can select the right circuit values.

[Jackpilot]

Were you able to make the current reading with the multimeter leads reversed?

.

Yes. ....still reads 1.5 but the gauge needle moves 1/10 of its travel and even by turning the pot (100K) full , the gauge pointer does not move much further.
??

[Mike.Powell]

Okay, so for the voltage reading made in parallel with the gauge, the multimeter was set to the 15V scale and the reading is 1.5V

For the current reading made in series with the gauge, the reading was also 1.5? and the multimeter was set to what current scale?

[Jackpilot]

Mike

Bought a nice digital Unitrend multi...mine was really primitive

Here we are

AA Battery alone 1.594V
Parallel reading 1.593V
Series reading 1.02 mA

How's that
Jack

[Matt Olieman]

Hooray Jack.... You did it... Congratulations :) :) :) You graduated from analog to digital.

This seems like a fun project, very curious how it is going end up working. Look forward to seeing the end results Jack. :)

Matt Olieman

[mauriceb]

Hooray Jack.... You did it... Congratulations :) :) :) You graduated from analog to digital.


And the next logical step is to move up to FS98 :p :mrgreen:

Maurice

[Jackpilot]

Mau

One more like that and I switch to Airbus !!!

[mauriceb]

Mau

One more like that and I switch to Airbus !!!


And what would you do with all those nice mechanical gauges in an Airbus? :D

Maurice

[Mike.Powell]

Mike

Bought a nice digital Unitrend multi...mine was really primitive

Here we are

AA Battery alone 1.594V
Parallel reading 1.593V
Series reading 1.02 mA

How's that
Jack

Looks to me like your gauge is a moving coil style meter likely with an internal resistor to boost the total resistance to roughly 1.5KOhms. Nominal sensitivity is 1 ma full scale.

If you put a standard 3.3KOhm resistor in series with it and connect the resistor to a switched 5 volt source, you should see the gauge swing slightly over full scale. If you put a 1000 microFarad capacitor directly across the gauge, this gives a time constant of about 1 second. (If you use the time constant formula posted earlier, the resistance you use is the parallel combination of the 3.3K series resistor and the 1.5K resistance of the gauge,or about 1K.)

Adjust the value of the 3.3K resistor to change the final deflection of the gauge pointer. I wouldn't go any lower than 3K if you connect to 5 volts. Don't want to toast the gauge.

Adjust the value of the cap to change the time constant. 2000 microFarad will give you 2 seconds, 3000 gives you 3, and so on.

[Jackpilot]

Mike

Confirm this is OK.

[Mike.Powell]

That's it, but one issue with using a pot is it leaves room for turning it to too low a value.

If you are going to connect to 5 volts, I'd feel more comfortable seeing a 3K (or there abouts) resistor in series with the pot. It's just a bit occupational paranoia. Maybe once, possibly twice :roll:, I've let the magic smoke out by not being careful enough.

[rottenlungs]

See I knew a big fat capacitor would be there somewhere!

Drifting of topic one of my early memories is of my dad demonstrating what happens when you put +400vdc through a 63v rated electrolytic cap. after a fraction of a second there`s a big bang and a snowstorm of (no doubt highly toxic) dust raining down. Apparently this was the prank of choice at London Underground`s signalling workshops back in the 1960`s! I also had fun as a kid wiring every cap I could find in parallel and using this thing as a makeshift spot-welder!

Ah nostalgia - it just ain`t what it used to be! lol


Looks to me like your gauge is a moving coil style meter likely with an internal resistor to boost the total resistance to roughly 1.5KOhms. Nominal sensitivity is 1 ma full scale.

If you put a standard 3.3KOhm resistor in series with it and connect the resistor to a switched 5 volt source, you should see the gauge swing slightly over full scale. If you put a 1000 microFarad capacitor directly across the gauge, this gives a time constant of about 1 second. (If you use the time constant formula posted earlier, the resistance you use is the parallel combination of the 3.3K series resistor and the 1.5K resistance of the gauge,or about 1K.)

Adjust the value of the 3.3K resistor to change the final deflection of the gauge pointer. I wouldn't go any lower than 3K if you connect to 5 volts. Don't want to toast the gauge.

Adjust the value of the cap to change the time constant. 2000 microFarad will give you 2 seconds, 3000 gives you 3, and so on.

[mauriceb]

Just a reminder folks that the time constant formula is Megohms x Microfarads and not K ohms. With the values shown, the capacitor would charge pretty much instantly.

Maurice

[Jackpilot]

so.... I do not want to smoke my gauge!!??

[mauriceb]

so.... I do not want to smoke my gauge!!??


so.... I do not want to smoke my gauge!!??

???? No idea what else you want to smoke ;) , but if this is in response to my comment about megohms, the higher the resistance, the less current through the gauge and less possibility of smoking the gauge.

Having said that, I don't think this circuit will accomplish what you want to do, namely have the needle go up slowly. With the values that you showed, the capacitor would charge pretty much instantly and once the capacitor is charged, the gauge would receive all the current that goes through the pot .

No harm in trying though and the only chance of damage to the gauge is if the pot goes to zero ohms or close to it, so as Mike said, you need a resistor in series with the pot to avoid that possibility.

Maurice

[Jackpilot]

Check Y.ca

[Matt Olieman]

and.... after you get this monster working.... we want to see pics or better yet video :) :) :) :) :)

Matt Olieman

[Jackpilot]

You bet!!!

Posted another crazy idea for the trim gauge too....

Having fun anyway,,,

[Mike.Powell]

Just a reminder folks that the time constant formula is Megohms x Microfarads and not K ohms. With the values shown, the capacitor would charge pretty much instantly.

Maurice

Even though the resistance is in KOhms and the cap's in microFarads, the time constant is about a second because it's a big cap.

1 K * 1,000 mFd -> 10E3 * 10E3 * 10E(-6) -> 1

[mauriceb]

Even though the resistance is in KOhms and the cap's in microFarads, the time constant is about a second because it's a big cap.

1 K * 1,000 mFd -> 10E3 * 10E3 * 10E(-6) -> 1

My mistake :oops:. For some crazy reason, I missed the 3 zero's following the 1. Need more diet coke to wake me up :D

Maurice

[Jackpilot]

IT WORKS FINE

made a video but what I have is a .MOV format
Do not know how to upload it

Very happy...will allow populating the NG with live analogs..brake pressure/Hydraulic/ temperatures/ APU EGT/Oxygen etc...

Parts cost about $5, gauges average $20 on EBay

[Matt Olieman]

Jack, upload it at www.MyCockpitVideos.com (http://www.MyCockpitVideos.com) if you haven't' registered there yet, you'll need to do that. Pretty simple to upload it.

Then you can link it to one of your post here, or I can do that for you.

Matt Olieman

[Jackpilot]

Here it is , powered by 5V DC.
Thanks Mike Mau Matt (all M's)


<embed width="448" height="361" type="application/x-shockwave-flash" wmode="transparent" src="http://i24.photobucket.com/player.swf?file=http://vid24.photobucket.com/albums/c29/jackpilot/000_1990.flv">

[Matt Olieman]

Slicker then you know what :) :) :) Thanks Jack and all others for this group effort :)

Matt Olieman

[Jackpilot]

Forgot to thank James who had a clue from the start of this thread..!!
Cheers

[Michael Carter]

Cool stuff!!!

[kondrat]

Jackpilot,

Can you post your final connection scheme for you pressure gauge?

Thank you in advance,
Denis.