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Topic: Analog vintage gauges - Controlling amperage? (Read 680 times) previous topic - next topic

mdweezer

After seeing the analog gauge clock project on Makezine.com last week I got inspired and hit up my local surplus electronics shop and bought 4 really cool and very solid metal gauges made by Weston.  Each gauge is for a different measurement but they seem to be very solid and there's no reason why they shouldn't function correctly.

1 gauge measures between 0 and 1 amps; how would I easily control this?  I figure I'll be using the PWM pins like the other maker but what would be the best method to control that amperage?

The other gauges are for various measurements so I'll be doing a lot of experimenting to see how to appropriately get the pins on these gauges moving.

Any tips or suggestions would be greatly appreciated, once I get home I'll be getting the measurements that the gauges are meant to display and will do some further googling.

The goal is for a nice clock, I plan on mounting in a nice wooden enclosure.  

gradbert

The output pins on the arduino can only supply up to 40mA of current.  So there is no way to directly drive those meters.  You will have to use a transistor of some sort to allow the arduino to control that much current.  You would be better off if you can find meters that work down in the mili-amp range

westfw

Just because the scale on a meter says "1A" doesn't mean that the meter movement actually takes 1A to make it move full scale.  The fundamental meter mechanism is quite sensitive and has it's deflection controlled by current through the meter coil.  This means that a meter designed to register volts will probably have a series resistor of appropriate value, and a high-current meter will have a parallel low-value resistor "shunt", so that only a fraction of the applied current goes through the meter coil.  The shunts and/or series resistors MIGHT be  built into the meter, or the might be expected to be provided externally.  A close examination and/or partial disassembly should show for sure.  The shunt on your 1A meter may be easily replaced with a value more appropriate to the Arduino output, or removed entirely, or may not even be present.

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