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Old 02-25-2008, 07:34 PM #33
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Default Re: DIY Laser Power Meter Interface Module

Not at all... I'll PM payment info to you.


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Old 02-25-2008, 07:36 PM #34
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Default Re: DIY Laser Power Meter Interface Module

SWEET, i can build it and my LPM at the same time!
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Old 02-26-2008, 08:20 AM #35
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Default Re: DIY Laser Power Meter Interface Module

I think it is good to keep both the hardware and software simple.
The software could have just a few functions like power measurement, power vs. current and power vs time (that measures the power at a specific interval like once every minute to see long term stability) and the possibility to make and save data and graphs.
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Old 02-29-2008, 02:17 AM #36
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Default Re: DIY Laser Power Meter Interface Module

I finally received all the parts and the PCBs. *I'll be doing more testing the next couple of evenings and over the weekend but initial testing looks good. *If all goes as planned, I'll have kits ready to go out on Monday.
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Old 02-29-2008, 03:57 AM #37
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Default Re: DIY Laser Power Meter Interface Module

I've done some preliminary testing of the interface module and it appears to work perfectly.

There is one problem however and that is that the output from the LPM amp is a bit noisy for an A/D process with no other filtering. *The noise is only a few LSBs but I'm not happy with it. *I've made a preliminary fix by soldering a .1uf cap across the amplifier feedback resistor (between pins 2 & 6 of the LTC1050) and that definetely solves the problem. *I suppose I could write a software filter for the PIC and I'll have to consider that.

Also, I'm wondering if there shouldn't be some offset built into the interface to allow for a reliable zero. *The PIC can't convert a negative voltage and a negative voltage is the same as 0 to the A/D converter (actually it's clamped). *Because of this, it would be possible to inadvertently put some dead-band in the measurement if the offset was set below 0. *
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Old 02-29-2008, 04:13 AM #38
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Default Re: DIY Laser Power Meter Interface Module

Quote:
Originally Posted by knimrod
I've done some preliminary testing of the interface module and it appears to work perfectly.

There is one problem however and that is that the output from the LPM amp is a bit noisy for an A/D process with no other filtering. The noise is only a few LSBs but I'm not happy with it. I've made a preliminary fix by soldering a .1uf cap across the amplifier feedback resistor (between pins 2 & 6 of the LTC1050) and that definetely solves the problem. I suppose I could write a software filter for the PIC and I'll have to consider that.

Also, I'm wondering if there shouldn't be some offset built into the interface to allow for a reliable zero. The PIC can't convert a negative voltage and a negative voltage is the same as 0 to the A/D converter (actually it's clamped). Because of this, it would be possible to inadvertently put some dead-band in the measurement if the offset was set below 0.

solder a cap on the main board?? or on the interface module?

regards,

amk

P.S. LOOKS GOOD! and if the cap is on the interface module, can you revise the PCB's to accommodate this? if yes ill be in for one soon, for rev 2!
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Old 02-29-2008, 04:22 AM #39
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Default Re: DIY Laser Power Meter Interface Module

The cap modification would go on the original amplifier PCB as pictured above. *But I'm not sure it's necessary yet..
I'm looking into some simple software filtering.



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Old 02-29-2008, 05:02 AM #40
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Default Re: DIY Laser Power Meter Interface Module

do the 2 wires going to the interface module from the DPM out on the main PCB solder in parallel with the original DPM setup?
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Old 02-29-2008, 05:03 AM #41
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Default Re: DIY Laser Power Meter Interface Module

Quote:
Originally Posted by amkdeath
do the 2 wires going to the interface module from the DPM out on the main PCB solder in parallel with the original DPM setup?
Yes.
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Old 02-29-2008, 05:08 AM #42
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Default Re: DIY Laser Power Meter Interface Module

payment send to your paypal.

I also added some to support the project.
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Old 02-29-2008, 11:24 AM #43
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Default Re: DIY Laser Power Meter Interface Module

I would opt for the best hardware solution possible and keep the software simple. If a cap will solve a jitter problem
I would go for that. Deadband may be another problem.
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Old 02-29-2008, 05:48 PM #44
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Default Re: DIY Laser Power Meter Interface Module

Quote:
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I would opt for the best hardware solution possible and keep the software simple. If a cap will solve a jitter problem
I would go for that. Deadband may be another problem.
I think I'll put a filter in the firmware anyway but I'm convinced that adding that capacitor would be the best solution. *I'll include the extra cap as part of the kit. *I'll leave it up to the builder to decide whether to install it or not after seeing what kind of noise issues come up on a case-by-case basis.

As for the deadband, what I would propose is perhaps a one or two LSB -offset in the application software for determining end of range. *This would mean that the measurement from the DPM and the PC would disagree by a mW or two with respect to zero offset but it would make adjusting the zero offset via the PC more accurate. *The offset could always be disabled in software...
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Old 03-01-2008, 11:45 AM #45
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Default Re: DIY Laser Power Meter Interface Module

sounds reasonable to me.
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Old 03-02-2008, 04:38 PM #46
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Default Re: DIY Laser Power Meter Interface Module

Working on the PC application. The display seems noisy because the sensor is facing the window and I'm casting shadows. It's actually quite clean in subdued lighting.

[media width=480]http://www.youtube.com/watch?v=oC0vf8ooovQ[/media]

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Old 03-02-2008, 05:24 PM #47
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Default Re: DIY Laser Power Meter Interface Module

Great job!
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Old 03-02-2008, 06:02 PM #48
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Default Re: DIY Laser Power Meter Interface Module

OMG ILL TAKE ONE


see my PM


btw, I dont see what you mean by noise...
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