working a real gauge without PMSys.

[Jackpilot]

(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