Welcome to Laser Pointer Forums - discuss green laser pointers, blue laser pointers, and all types of lasers

LPF Donation via Stripe | LPF Donation - Other Methods

Links below open in new window

ArcticMyst Security by Avery

DIY Thermal LPM for under $50

lasersbee

lasersbee

0
Joined
Sep 20, 2008
Messages
17,622
Points
113
Jufran88 said:
I actually built one of these about 2 months ago, but I failed:(. I gave up because I am waiting for summer break so I can figure out what went wrong.

I used MarioMaster's and Jib's schematics but the readings seem to fluctuate a lot. It worked for a moment and I went eat dinner came back and it didn't work :undecided::confused:
Schematic:
LPMscm.jpg


Board:
LPMbrd.jpg
Click to expand...

The reason your circuit is not working is that you have made
a one wring connection.
The connection on your Schematic and your Artwork between
pins 6 and 7 should be removed and put between pins 6 and 5...

BTW... the industry standard for PCB layout colors is Blue for
the component side (top) and red for the solder side (bottom)..


Jerry

You can contact us at any time on our Website: J.BAUER Electronics
 
Last edited:





Jufran88

Jufran88

0
Joined
Feb 9, 2011
Messages
578
Points
0
Benm said:
Since its there anyways, using it as a buffer or extra correction stage would be a good idea. Some people prefer multi-turn pots, others 2 'normal' pots for fine and course adjustment. The latter could easily be realized by adjusting the buffer amps gain slightly.

Also, if you are not using an opamp, dont connect both pins to ground and let the output remain unconnected. You should connect the output to the - input and the + input to ground.

Connecting both to ground results in amplifying offset voltages by infinity, which isnt good since those offsets can vary with temperature, possibly leaving the omamp output flappering between ground and supply voltage randomly.
Click to expand...

MarioMaster said:
Thanks, I will update the schematic when I have some time
Click to expand...

I just followed Benm's advice since that op amp isn't used. Maybe I could run 2 different boards one where both in2+ and in2- are grounded and out2 not connected. Or just completely not connect those pins, would that work? :confused:

The layer colors were given by eagle, I didn't change them or I don't think you can change them.
 
123splat

123splat

0
Joined
Jan 14, 2011
Messages
424
Points
0
Sounds like reversed polarity on the IC. That's close to the only thing you could do that should make the board hot. If so, you'll eventually burn a little hole in the IC, or short your supply. Dbbl check your circuit layout and the positioning of the IC (you know that if you hold the IC with the indention on the left, that pin 1 is the one on the bottom left, pin layout is 1,2,3,4 on the bottom left to right, 5,6,7,8 are on the top right to left? If there is no indention, there will be a dot or dimple over pin 1).

If that is it, your IC is indeed fried. Nothing else should be damaged.
 
Last edited:
Jufran88

Jufran88

0
Joined
Feb 9, 2011
Messages
578
Points
0
I don't know. I checked multiple times between the board layout, data sheet, schematic and acutal board. I built 2 boards both with new parts over 2 months ago. Same problem.

I'm going to be looking for different parts and I'll be cleaning up the schematic and hopefully that will work better.
 
lasersbee

lasersbee

0
Joined
Sep 20, 2008
Messages
17,622
Points
113
Jufran88 said:
I don't know. I checked multiple times between the board layout, data sheet, schematic and acutal board. I built 2 boards both with new parts over 2 months ago. Same problem.

I'm going to be looking for different parts and I'll be cleaning up the schematic and hopefully that will work better.
Click to expand...

The PCB is an exact copy of the Schematic... but you still have the
same error on both the Schematic and the PCB when you compare it
to jib77 schematic or MM's... (refer to post#289)

The 2nd OpAmp's output is tied to the input...and that OpAmp does
nothing.... (but pump it's output into one of the inputs)
The output should be floating... the +in should be to GND and the -in
should be tied to VCC.

I'll test that tomorrow when I'm in the shop...


Jerry

You can contact us at any time on our Website: J.BAUER Electronics
 
Last edited:
Jufran88

Jufran88

0
Joined
Feb 9, 2011
Messages
578
Points
0
Hmm, but if the second op amp (unused) does nothing would it matter if it was floating or tied to the input? :confused:

I used benm's advise on the second op amp.

I'll revise the board to set the second op amp floating and the 2nd inputs to ground.
 
lasersbee

lasersbee

0
Joined
Sep 20, 2008
Messages
17,622
Points
113
Yeah it matters....

If the inputs are floating that can pick up stray AC
like an antenna and amplify that signal and/or start
to oscillate drawing more current.
Since it is on the same die as the other OPAmp it can
induce errors/noise into the OpAmp being used.


Jerry

You can contact us at any time on our Website: J.BAUER Electronics
 
Last edited:
Jufran88

Jufran88

0
Joined
Feb 9, 2011
Messages
578
Points
0
I am enlightened.

Thanks for the explanation! I'll update my board soon to correct that error.

:beer:
 
Jufran88

Jufran88

0
Joined
Feb 9, 2011
Messages
578
Points
0
Actually, that's how mines was hooked up. The + was grounded and output connected to - on the unused op amp.

I just read through some data sheets of similar LM358s and stated that inputs should be grounded and outputs left open on unused op amps in a dual op amp package. And I also googled "unused op amps" and found a lot opposing that statement.

It's pretty confusing :confused:

But since the original design works, I'll stick with it.
 
HIMNL9

HIMNL9

0
Joined
May 26, 2009
Messages
5,318
Points
0
Someone use resistors, for do the connection, for avoid direct wiring and high loads in case of accidental short circuits ..... i mean, connecting the IN- to OUT through a 1K resistor, and the IN+ to GND through another 1K resistor.
 
qumefox

qumefox

0
Joined
Mar 26, 2010
Messages
3,220
Points
0
Jufran88 said:
Actually, that's how mines was hooked up. The + was grounded and output connected to - on the unused op amp.

I just read through some data sheets of similar LM358s and stated that inputs should be grounded and outputs left open on unused op amps in a dual op amp package. And I also googled "unused op amps" and found a lot opposing that statement.

It's pretty confusing :confused:

But since the original design works, I'll stick with it.
Click to expand...

Another option is to just build a two stage amp using both sides. Which is what I do. One side is a course adjust and the other is a lower gain fine adjust. But this leads to a more complicated circuit though.
 
HIMNL9

HIMNL9

0
Joined
May 26, 2009
Messages
5,318
Points
0
qumefox said:
Another option is to just build a two stage amp using both sides. Which is what I do. One side is a course adjust and the other is a lower gain fine adjust. But this leads to a more complicated circuit though.
Click to expand...

I do the same, but using 2 separated op-amps (usually 741) ..... this way, i can use offset regulation for trim the "zero" set of the output without have to use "strange" floating voltmeter connections at the GND :p

Also, you can improve a bit the "noise reduction", placing a resistor in parallel to the 100nF cap at the input, and another 1uF (NON electrolitic) capacitor in parallel on the voltmeter output points.
 
qumefox

qumefox

0
Joined
Mar 26, 2010
Messages
3,220
Points
0
Hehe. 741's.. Old school. :D They're kind of a pain for this application because you kind of have to jump through a few hoops to make them run single supply.
 
You must log in or register to reply here.




Top