Panel meter confusion

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steve_j83

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For a project that i am working on i will need to buy x6 1mA panel meters. After scouting around for a while i found the cheapest ones availible to be over £5 each (usually much more).

Is it just me or are they really that expensive?

I can pick up a cheap multimeter for around £2.50 it seems that i would be better just to hard wire 6 of them into the project (something i'd rather not do), i understand the quality will not be as good but i cant really see the point in forking out more for less.

tcmtech

Banned
Ive done that many times. A good factory made digital panel meter can run between $50 -$150 in the USA. A cheap digital multimeter can be purchased for less than $6 on sale. I strip them down to a bare circuit board and just wire the multimeters rotary conections together at what voltage or current setting I want them to read and power them with a regulated 9 volt power pack.$1 at garage sales!

With a little dremel tool work they can even be fit right into a panel and look professional too!

They seem to work well and have never given me any long term running problems doing it that way.

MikeMl

Well-Known Member
...Is there another way where i could use a roatry switch to do the same?
Are the six circuits tied to a common circuit node, like ground or a battery?
When reading one; what should the other five to be doing?

tcmtech

Banned
I see the panel meter prices are still up there even at mouser.

Those Cen-tech are the ones I strip down and convert to single application use. I just run them off a regulated 9 volt power pack.

I picked up 16 of them one time when they were on sale for \$2.99. I gave away about half of them! Anyone that wanted to borrow a meter just got to keep it!
Far as I know they are all still working too!

If you using them for higher range voltage or amperage reading you do have to switch a few of ther resistors out for larger ones. The factory ones will heat up too much and the readings drift.

If I remember correctly the circuitry in them is referanced to the common battery neg line. If your using a independent and isolated power source it doesnt matter.
Being they are so low of power draw a simple hf transformer driven from a 555 timer IC could power a dozen without any problems.
Using several independent secondary windings with a single diode and capacitor works well. Just phase half of the output windings one way and the other half of them the other way to keep the load even on the 555 IC.

steve_j83

New Member
You obviously haven't bought a new analog panel meter recently.
Have never bought one... Im new to all this

Are the six circuits tied to a common circuit node, like ground or a battery?
When reading one; what should the other five to be doing?
Basically i want to make 6 or these (see below). They will need to run simaltaniously but i am happy to take the reading from the meter one at a time.

I assumed i could use a SPDT switch on each so that i can keep the circuit closed and just divert the current of each circuit through the meter when needed.

Hence why i was asking if i could use a rotary switch, it would be much neater. Can this be done?

As for the power. currently there are 3 9v batteries in each circuit. Ideally i would love to run all 6 off a single power supply but am struggling with the dual power supply. Is there a simple way to turn a 9v single regulated into a 9v dual? I am still very new to this so sorry if my questions seem a little silly.

Edit: ok so it seems i need to run a 9v ac supply then convert that into a regulated +/-9v dc, i will come back to that last.... but feel free to throw in any suggestions

Thanks

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Schematics.....

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steve_j83

New Member
And another question. I need a 50uf 10 volt cap, the closest i can find is 47uf 16v. I assume the voltage is ok but will i be fine with a 47uf of should i wire another one in series?

MikeMl

Well-Known Member
The 50uF capacitors are just for bypass. Not critical at all. Anything from 10uF to 100uF will work there. Voltage rating from 15V to 50V will work; not critical either.

For sharing one meter, try this. Get six 1/4" panel-mounted mono headphone jacks like this.

Attach a 1/4" mono plug, like this to the mA meter. Connect tip to meter + and barrel to meter-.

Wire the jack "Ground" to barrel, "Signal" to tip. To read one of six circuits, just plug the meter into the jack you want to read.

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steve_j83

New Member
Nice ideas with the leads... it is a bit fiddely though.
Can i use rotary switch though?

If not, and i went with your idea would i need to wire the circut closed where the meter would be or will it still function when the circuit is broken? ie when it is not plugged into the meter?

MikeMl

Well-Known Member
The voltage between the "signal" output and the circuit's "ground" will be effected by the meter resistance. The DC resistance of the typical milli-Amp meter is about 30Ω, so R14 and the meter resistance form a voltage-divider. With the meter in the circuit, the "output to Audurino" will be a few mV, while without the meter, the open-circuit output could be a couple of volts.

If you want the output to be constant, regardless of the meter being there or not, you will have to switch-in a resistor equal to the resistance of the actual meter you are using.

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steve_j83

New Member
ok well thats thrown a spanner in the works... Although it could be a good thing.... a couple of volts will be a much better reading for what i am doing (it will be read in a pc).... i guess i could drop the meter out all together. ok well back to the drawing board.

Cheers Mike

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