daisy8 Posted December 23, 2006 Report Share Posted December 23, 2006 Hi allI have a project and have a set of old style gauges I want to include in it. One of the gauges is a voltmeter but the gauge is not performing the way I would like.When power is supplied the gauge jumps to 12 volts and then bounces back and forth on the gauges internal spring. What I want is for the gauge to slowly rise to 12 volts when turned on and then slowly drop to zero when turned off. This would stop the gauge jittering around.The gauge is purely something interesting to look at a serves no practical purpose but I would like it to read the correct voltage.Any help would be appreciated. Thanks guysDaisy Quote Link to comment Share on other sites More sharing options...
audioguru Posted December 24, 2006 Report Share Posted December 24, 2006 Hi Daisy,If the meter is actually a current meter with a series resistor converting it to read volts, then just add an electrolytic capacitor in parallel with the meter to slow it down. Quote Link to comment Share on other sites More sharing options...
daisy8 Posted December 24, 2006 Author Report Share Posted December 24, 2006 Thanks audioNo I have tried a capacitor in that way but it does nothing to improve the gauge. Anything else ?Daisy Quote Link to comment Share on other sites More sharing options...
audioguru Posted December 24, 2006 Report Share Posted December 24, 2006 An opamp can drive a voltmerter as slowly as you want. But the opamp would need a supply voltage anout 2V higher than the max voltage the meter is measuring. Quote Link to comment Share on other sites More sharing options...
daisy8 Posted December 24, 2006 Author Report Share Posted December 24, 2006 Thanks againAll I really need is to slow down the increase in voltage across the volt gauge. A linear increase from zero the 12 when the power comes on and then the reverse when the power goes off.I need an automatic pot. If I could somehow start with lots of resistance that decreases after power is given then I would be set !I have just tried to use a really slow triangle wave generator that latches when the output hits 12 volts but had no real luck with it.Thanks againDaisy Quote Link to comment Share on other sites More sharing options...
ante Posted December 26, 2006 Report Share Posted December 26, 2006 Thanks audioNo I have tried a capacitor in that way but it does nothing to improve the gauge. Anything else ?DaisyHave you tried to use both a capacitor in parallel and a resistor in series with the meter? Quote Link to comment Share on other sites More sharing options...
daisy8 Posted December 27, 2006 Author Report Share Posted December 27, 2006 Hey AnteThanks for the response.I have tried just tried what you suggest. A resistor in series lowers the reading on the gauge. The gauge may only be for show but I still want it to read 12v. A capacitor in parallel has no effect on start up. It has a tiny effect on shut down though but only noticable with a 1000 mic cap. The effect it shows is to delay the gauge from dropping to zero immediately. However it has no effect on the spped the needle moves.What I really want is to have the needle slowly rise to 12v when the power goes on and to slowly go back to zero when the power goes off.Any other ideas ? I do have the design for a triangle wave generator (check the light fader thread) that I might be able to latch once it reaches 12v but I am not having any luck with it yet and would rather use something a little simpler.Thanks again and don't be scared to offer other suggestions - I'll try anything.Daisy Quote Link to comment Share on other sites More sharing options...
aniruddha Posted December 27, 2006 Report Share Posted December 27, 2006 you said:="I need an automatic pot. If I could somehow start with lots of resistance that decreases after power is given then I would be set !"What about using an inductor? You could also connect a tiny resistance in series. ;) Just trying to give a suggestion. ;D Quote Link to comment Share on other sites More sharing options...
ante Posted December 27, 2006 Report Share Posted December 27, 2006 Hi Daisy,If the resistor lowers the reading its value is too high. If the capacitor makes no difference its value is too low. It all depends on the internal resistance of the meter. If you use a cap without a resistor the cap will charge very fast on power up and discharge fast through the loads when power is removed i.e. no effect. You have to choose a resistor that influences the meter as little as possible and a cap which is large enough to give you the desired effect. Quote Link to comment Share on other sites More sharing options...
Cabwood Posted December 27, 2006 Report Share Posted December 27, 2006 Daisy, I believe you are connecting the capacitor across the whole gauge (resistor and galvanometer together), effectively putting it in parallel with the power supply, which is why it doesn't slow the rise to 12, but does slow the drop to zero.What Audioguru correctly suggested was to connect the capacitor (100uF should make a significant difference), across the galvanometer itself. Only the galvanometer part. Inside the gauge's case there should be a resistor in series with the galvanometer's coil. Do not connect the capacitor across this resistor. Do not connect it across the galvanometer/resistor pair. Connect it only across the galvanometer's coil connections. Quote Link to comment Share on other sites More sharing options...
daisy8 Posted December 28, 2006 Author Report Share Posted December 28, 2006 Hey guys, thanks for all the reponses.aniruddha thanks, will give it try.Ante I have found a resistor that doesn't lower the gauge reading (1 Ohm) but even with 4700 uF cap power up on the gauge is fast. Shut down is perfect though ! Nice and slow.Cabwood I have openned the gauge up and I can't find any internal resistor. The gauges connections are linked straight to the coil that operates the needle. You are right though that I have connected the cap across the power supply. This causes another problem - shutdown of the gauge looks great but the rest of the circuit shuts down slowly too.So any further suggestions ? I have included a diagram of what I have connected now. All I really need to do is get the slow power down to be a slow power up instead.Thanks again guysDaisy Quote Link to comment Share on other sites More sharing options...
ante Posted December 28, 2006 Report Share Posted December 28, 2006 We don’t know the data for your meter but what would happen if you increase the value of the capacitor even more? Quote Link to comment Share on other sites More sharing options...
Cabwood Posted December 28, 2006 Report Share Posted December 28, 2006 If you can measure the resistance of the coil for me, I'll figure something out. This is no ordinary gauge, methinks, it's an interesting one. Quote Link to comment Share on other sites More sharing options...
daisy8 Posted December 30, 2006 Author Report Share Posted December 30, 2006 Hi again !Ante, increasing the capacitor only slows the shutdown further. (The biggest I have is a 4700 so I wired 2 in parallel).Cabwood the resistance of the gauge is 554 Ohms both ways.ThanksDaisy Quote Link to comment Share on other sites More sharing options...
Cabwood Posted December 30, 2006 Report Share Posted December 30, 2006 What would make this REALLY easy - can you use a 24V supply instead of 12V? Or, really, any supply higher than 12V? Quote Link to comment Share on other sites More sharing options...
daisy8 Posted January 1, 2007 Author Report Share Posted January 1, 2007 Hey CabwoodActually the circuit has a 170 volt section that drives Nixie tubes so I could use this to run the gauge I guess.Daisy Quote Link to comment Share on other sites More sharing options...
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