Problem with testing current using a multimeter

Thread Starter

alexx

Joined May 29, 2011
29
this is great stuff, I'll buy those parts and make a regulated 5V power supply, does this mean that i dont need to measure the current going to the viewfinder anymore? it sounds like if i do the regulated 5V power supply I dont need to worry about current

As for the diagram, I confused because it looks like the input in the drawing only has one terminal, so how could you connect the + and - to it ? attached is my understanding of the diagram in the pdf you shared:

http://www.youtube.com/watch?v=qj6aGaSluWM

that is probably wrong but its a start. i know that 3 is the ground but doesnt that symbol at 3 mean 'negative'? so thats why i think the negative wires connect to 3. and at 1 there is an extra terminal in the middle that im not sure what to do with
 

Thread Starter

alexx

Joined May 29, 2011
29
To measure an unknown current:
1. Move red lead to 10A connection.
2. Set dial on meter to 20m/10A
2. Connect meter in series with load. (Like your set-up 3 or 2)
3. Look at value on meter.

If reading is above 200mA (.2A) This is your value. You are done.

If reading is between 20mA (.02A) and 200ma (.2A):
1. Disconnect meter from circuit
2. Change red lead to mA connection
3. Set dial to 200m
4. Connect meter in series with load. (Like your set-up 3 or 2)
5. Look at value on meter. If value is above 20mA this is yor value
you are done.

I did the first step and my multimeter said .13, so i moved to the next step (not to mention replaced the fuse i blew before :p) and it said 217.1. so the final results are:

Voltage = 5.04
current = 217.1 mA

with this, would it be better to set up a 5V regulator of use 4 double a's with the approperate resistor?

thanks!
 

Thread Starter

alexx

Joined May 29, 2011
29
that current was from set up 2 in my diagram ( multimeter in series with viewfinder)

when i measured the current using set up 3 i got:
current being supplied from battery with viewfinder --> .79
current being supplied from battery without viewfinder --> .67
_______
.12
these were measure in the 10 A terminal at 20 m/10A
 

Pencil

Joined Dec 8, 2009
272
attached is my understanding of the diagram in the pdf you shared:
I think you have input and output reversed. Check pin locations.

i know that 3 is the ground but doesnt that symbol at 3 mean 'negative'? so thats why i think the negative wires connect to 3. and at 1 there is an extra terminal in the middle that im not sure what to do with
Ground and negative are the same thing in this instance.
Mounting tab and middle pin are the same function. Use either one or both.

I forgot one item to make this board "deluxe" add these, otherwise
just solder wires for input and output.
Wire to board connectors

Look at attachment for connections/possible layout.
ALWAYS check your components yourself to verify correct pin locations and connections.
Different manufacturers/models may have different pinouts.
 

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CDRIVE

Joined Jul 1, 2008
2,219
The odds are that three 1.5V (AA or AAA) batteries wired in series will power your view finder with no regulator needed.
 

Pencil

Joined Dec 8, 2009
272
The odds are that three 1.5V (AA or AAA) batteries wired in series will power your view finder with no regulator needed.
I agree.

Although his final goal may need 2 different voltage supplies (9V and 5V).

Also to add another thought, if the current requirements
are as he posted, alkaline batteries may give suitable operating time.

Maybe both supplies could be done without a regulator from a single battery pack.
 

Thread Starter

alexx

Joined May 29, 2011
29
3 aa batteries in series give a reading of between 7 - 8 on the multimeter in the 10 A terminal at 20m/10A, are you sure this much current wouldnt kill the viewfinder?

this means 7-8 amps right? and the viewfinder only needs about 217 mA
 

Pencil

Joined Dec 8, 2009
272
3 aa batteries in series give a reading of between 7 - 8 on the multimeter in the 10 A terminal at 20m/10A, are you sure this much current wouldnt kill the viewfinder?
Do not ever connect your meter across the + and - of a battery
when it is set to measure amps!!!

Treat your meter when set up to measure current (Amps) as if it is a solid
piece of wire. Do not connect things together that you would not connect
with a piece of wire. For your safety, and the safety of the equipment.

Now, using the DC setting test the voltage of 3 AA batteries in series.
You will probably need a new set. The other set you shorted out with your
meter is probably dead. Your reading (on fresh batteries) will probably
be 4.5-4.8V.

For good info look at the AAC books that are linked at the top of this
page. A little reading will get you far, start with VOL. 1 DC, it will enlighten
you to some basic principals.

Simplisticly speaking:
Most devices need a specific VOLTAGE. They will draw only the current
they need, no more, no less, if the proper Voltage is provided.

Concentrate on figuring out the voltage requirements needed.
Don't worry so much about Amps, yet.

Hang in there buddy, you'll get it. Be careful and keep asking questions.
 

CDRIVE

Joined Jul 1, 2008
2,219
I thought that you finally understood the difference between voltage measurements and current measurements. I can't believe that you did the same thing again! It's a miracle that you haven't destroyed anything yet, or have you? :eek:
 

Thread Starter

alexx

Joined May 29, 2011
29
dam, i forgot that current has to be measured in series with a load because i was too curious to see what the current from the batteries was. truth is i would rather my multimeter bust then the viewfinder anyways.. but Ill think about it next time before I test things. I dont think anythings broken, maybe some dead batteries but thats okay. I think im going to use 3 alkaline aa batteries and test the voltage to make sure its near 5V, then attach it to the viewfinder with out a resistor since the viewfinder will only take the current it needs. The reason i was scared to put all the curent to the viewfinder is because I put a lot of current into IR LED's and they all broke because they took more then what they needed, but it sounds like viewfinders and electronic devices do only take what they need so that makes things easier
 

CDRIVE

Joined Jul 1, 2008
2,219
Please....... Before you connect the battery pack to your view finder check and double check that the polarity is correct. It would really bum me out to read that it's now toast.
 

CDRIVE

Joined Jul 1, 2008
2,219
STOP!!! ALTO!!! HALT!!!

It has occurred to me that the information regarding this device has been too meager and insufficient for us to make any recommendations. You also stated that the camera jack has three pins. This may mean nothing or it may mean a very significant something!

Before you connect your view finder to anything other than your camera please post the manufacturer's link or a distributors link to this device. If it has a data plate on it please post what it states. If you have any pertinent user documentation, scan it and attach it to post.
 

Pencil

Joined Dec 8, 2009
272
This is getting long and confusing.

Let's do a recap. Please point out any incorrect information.

1. The viewfinder is from a Sony camera.
2. The OP wants to connect the viewfinder to another device.
3. The viewfinder has three terminals.
4. The three terminals are suspected to be V+, V-, and video out.
5. Voltage measured from camera across suspected V+ and V- pins
going to viewfinder was approx 5V.
6. The view finder drew either .13A or 217mA depending on meter setting.
Note: There is an inconsistancy here between the readings. (Let's not
worry about the reason for inconsistancy, this will only derail the discussion)
7.The general consensus is more information needed to proceed.

For anyone interested: Other information given by OP
 
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Pencil

Joined Dec 8, 2009
272
Night vision I am guessing.

After looking around I can say that it appears
"messing with salvaged viewfinders" is not as
uncommon as I would think.

I found this and this that lead me to believe the
input to the viewfinder was : V+, V-, and video IN.
There were a few instances that showed how to simply
identify the wires.

Your schematic in video shows you using a camera battery.
Is this battery 9V?
You mentioned the pinhole camera was powered by 9V.

Anyway, my recommendation for experimental purposes is
attached. I omitted any fuse(s) and switches for simplicity.
This is based on my understanding of your information.

Depending on battery type you may not get very good operating
time, but the best way to find out is to start experimenting.

Double, Triple check everything.

But my inability to imagine doesn't make it a fact. There's always some risk in repurposing a circuit, in assuming you "know" something.
Good luck and use caution at every step.
 

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Thread Starter

alexx

Joined May 29, 2011
29
okay thanks so much!!! Everything makes sense now and even my testing is solid because i can expect what the meter will say before i test. Iv'e learnt a lot But i do have only two more questions, last ones I promise!

good news: i double checked the current going to the viewfinder with the multimeter in series with the viewfinder, it was .13 A (130 mA). so this clears up the inconsistancy because the previous reading from subtracting the difference supplied from the battery was also .13 A

My first question is, which of the following do you recomend to attach the the viewfinder:

OPTION 1) 3 aa batteries (measured to be 4.54 V) in series with four 1/8watt, 5%, 10 ohm Carbon resistors giving a final measured voltage of 4.45 and a current of .11 A. I know you said never measure current with out a load and i was confident that the 40 ohm resistance can definatly be conisedered a load + nothing was getting hot

or


OPTION 2) the 5V regulator (i will add in a fuse too, side question :p --> is there such thing as a 130 mA fuse?) with four 1/8watt, 5%, 10 ohm Carbon resistors. which will give a final voltage of about 5V and a current of: I = 5V/40 ohm = .13 A


question 2:

should i use the 1/8watt, 5%, carbon resistors which only sell in 10 ohm, 22ohm, etc. making me have to use four 10 ohm's........... or can i use 1/4watt, 5%, carbon resistors which are bigger but are sold with a 39 ohm resistor. i figured for less then or equal to 9 volts the 1/8 watt were more appropreate?


and to answer you question in your last post: yes the camera battery was going to be a 9V because of the pin hole camera.... but i went to spytech and a pin hole camera is 150 dollers!!!! so i am going to attemp to use a web cam by hooking up the video wire to the viewfinder. apparently lap tops supply DC 5V through the usb which is very convienient because the viewfinder takes 5V DC so i will use the same 'OPTION 1 or 2' to power the webcam but i will use a different approperate resistor. in other words, solder a seperate wire after the 3 aa batteries or after the regulator (depending on which option we choose) and put the 40 ohm resistance on the viewfinder wire and a different resistor on the wire leading to the webcam. only problem is that in physic's class i remember something like the voltage splits evenly at a junction but the current will decrease by half? hope thats not true because it will throw everything off
 

Pencil

Joined Dec 8, 2009
272
Instead of responding to option 1 or option 2 and getting into
the resistors in series etc... let me say this.

I understand that you blew up some LED's due to not using a
current limiting resistor. This is making you believe that you must
current limit devices for proper operation/safety. Am I correct?

The general consensus is that you will not need current limiting
to the viewfinder. This statement was always followed up by
a disclaimer because there is no way to know absolutely unless
the person is directly familiar with the exact circuits involved. You
are not likely to find someone who knows the exact circuit on that
exact model, that information is just not readily available. This is
where the risk in repurposing a circuit comes into play.

Didn't you short the V+ and V- pins going to the viewfinder with
your meter? You stated:
my camera makes a weird sound when i do this
Oh that explains why the camera was getting hot!
I'm guessing no current limiting going to viewfinder.

Once again, I have got to issue the standard disclaimer that something
may go wrong, I am not there, nor am I an expert on the Sony CCD-V9
 

Pencil

Joined Dec 8, 2009
272
One more quick note.

Webcam compatability with viewfinder:
I think I saw something about the signal to the
viewfinder was possibly NTSC. I do not know
anything about video, but this would seem to be
the way to see if you have the right signal from
the webcam. One possibility.

Dangit now I have inadvertantly learned something.:D
 

Thread Starter

alexx

Joined May 29, 2011
29
yes your correct, and oh okay i see what your saying. i just dont think i want to risk the small chance of it frying if all it takes to prevent is some 10 ohm resistors. probably just paranioa but old viewfinders are hard to come by (n)

in not to sure what NTSC means :p but your saying the webcam is a good way to go right? I will probably post another thread when i get to the web cam issues because I feel that this thread will get too long for people to catch up
 

Pencil

Joined Dec 8, 2009
272
Its your experiment. Do whatever makes you confortable.

Watch closely for any strange results or hot components.

There is risk whatever you try. No getting around that fact.
 
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