# Dumb newbie question combining voltage

Discussion in 'General Electronics Discussion' started by ramjet, Aug 13, 2011.

1. ### ramjet

6
0
Aug 5, 2011
Hello,

1 is 1.75 - 2 VDC
1 is 1.75 - 2 VDC
1 Is Ground

I need 3 VDC to power a simple laser so my question is does electricity run concurrent or consecutive. In other words if I joined my two 1.75 leads together would I have 3.5 or 1.75 VDC?

Logic tells me that I would have 3.5 so I would then need a resistor to smooth out the voltage to a steady 3VDC???

However the specs say: "operating range 2.8-5VDC" so I won't need a resistor??
The specs also say: "Current consumption is 7ma at 3.2VDC"

So again I am new to this field so just running with logic I take that to mean that the laser will consume 7ma at 3.2VDC and a higher input voltage will consume more amps off your total circuit.

Thanks for the help
JB

If it matters here is the laser I got.

2. ### Resqueline

2,848
2
Jul 31, 2009
If one of the leads had the opposite polarity of the other then you'd have 3.5V but if it's the same polarity you only get 1.75V.
As to driving the laser it depends if it's a bare laser diode (which would need a resistor) or a complete laser with driver electronics.

3. ### ramjet

6
0
Aug 5, 2011
Well since they share the same ground I'm going to assume they have the same polarity (just read about polarity on wikipedia). Is there a way to check with a multi-meter. For example if both read 1.75 then they would have the same polarity. If one read 1.75 and the other read -1.75 then they would have opposite polarity correct?

4. ### poor mystic

1,074
33
Apr 8, 2011
Hi Ramjet
You're right, there's only one way to check - use your meter.
Check the voltage between the 2 low-voltage leads. If you can find a voltage between them, perhaps it'll be enough to run your laser.

5. ### ramjet

6
0
Aug 5, 2011
Hello,

I'm reading that pretty literally so I would connect one lead to red on multi and the other lead to black (normally to ground) and I'm not sure how that would work other than to maybee blow a fuse in the multi????

6. ### poor mystic

1,074
33
Apr 8, 2011
Hi
you need to measure voltage. Here's a safe way to use your multimeter.
Start by setting the meter to its highest AC voltage setting. Then connect the leads and read the scale of the meter. If the voltage is small compared to full-scale, choose the next more sensitive setting on the multimeter and look again. Progressively work your way down through the scale until you're sure there is no significant AC component in the reading. This is important for your application.
Then set the meter to read DC volts. Start once again at a high setting, and click down through the scales until you reach the optimum scale - where you find the voltage reading at its most precise.
Presto!