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jwolf123

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Jul 21, 2010
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Or maybe I'm not using the oscilloscope properly.
I have a coax connected to the chan1 input, which I stripped and connected to the output of the driver where the laser diode would go.
I tried it with just the scope, and also with a dummy load attached but get nothing.
Multimeter is showing a very small reading which I am interpreting as a low state output, so it seems like I should see something on the scope.... but its a flat line. If i turn the time interval of the scope to Chan1, its a steady dot... 1div interval is a flat line.
Leader brand, model LBO-522 scope.
I found a PDF manual online and thought I had set it up correctly, but I am inexperienced with scopes. Any advice?
 
Last edited:





rev0

rev0

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May 5, 2010
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jwolf123 said:
Or maybe I'm not using the oscilloscope properly.
I have a coax connected to the chan1 input, which I stripped and connected to the output of the driver where the laser diode would go.
I tried it with just the scope, and also with a dummy load attached but get nothing.
Multimeter is showing a very small reading which I am interpreting as a low state output, so it seems like I should see something on the scope.... but its a flat line. If i turn the time interval of the scope to Chan1, its a steady dot... 1div interval is a flat line.
Leader brand, model LBO-522 scope.
I found a PDF manual online and thought I had set it up correctly, but I am inexperienced with scopes. Any advice?
Click to expand...

Your oscilloscope measures a voltage applied across a 1M ohm resistor, essentially. So by putting the cable across the output of the driver will just show the open circuit (full) voltage of the driver, since it's trying to push whatever current you set through 1 million ohms of resistance. To measure the current that the driver would output, you can build a dummy load like this: http://www.rog8811.com/test load01.jpg
Hook up the dummy load where the laser diode would go and connect the oscilloscope across the 1 ohm resistor. According to ohm's law, V = I*R, the current will be exactly equal to the voltage (V = I * 1 ohm), so if your oscilloscope measures 400mV, you have 400mA going through the test load.
 
mojo_1234

mojo_1234

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Joined
May 1, 2009
Messages
181
Points
28
Do you have a somekind of schematic? It's difficult for me to exactly get your setup.

To build a dummy load for 445nm just put 6 diodes in series (PN type with 0.7 voltage drop) and connect them to the driver. No need for additional resistors etc. Just measure the voltage drop on the shunt resistor.

R = U / I --> I = U / R

e.g.
R = 0.56 Ohm
Umeasured = 280 mV

Itotal = 500mA


jwolf123 said:
My DC power supply is adjustable but jumps from 4.5v to 6vdc @ 1amp.
From the DC PSU I hooked + to one side of a 10k pot and - to the other side of the 10k pot... the middle pin I connected to a 1kohm resistor. The other side of the resistor was then connected to the analog mod input but doesnt seem to be doing anything at either 4.5v or 6v.
I misinterpret something?
Click to expand...
 
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