Arduino based LPM using Ophir20C project

[Seoul_lasers]

So, I am just entering the world of programming and microcontrollers.
After seeing a demo online via the Photon-Lexicon page I became extremely interested. Not only are these little boards able to display mW/W, uR, mR, cpm, lux, lumens, mm, cm, pH...etc ..etc.. via programming code but they can record and timestamp a file for output to any computer for printing or graphing. ::
It's got me thinking. However, with a 5V Analog input limit, what kind of protection is needed to allow the Ophir20C to show a 15-20W laser measurement. Is it as simple as resistors? Or do I need some filtering as well. What do you suggest.

Potentially without protection a 5W measurement should be pretty easy? correct?

 

[Bionic-Badger]

You need to amplify the signal so the very low voltages you get from the sensor will use your full ADC range, and then also providing a zero-offset to ensure that the ambient input from your sensor reads 0V on the output of the amp.

A good example circuit is the correction amp Benm posted. You should learn how the op-amp circuit operates, however, before really diving into it, especially as that circuit was not meant to amplify very low voltage signals.

I've got some 20W or something Ophir head and could barely record much change when I held the head with my hand (on the back) to force some temperature changes, so you'll need some good amplification or a sensitive ADC (which the Arduino's is not).

A good place to start before working with a sensor (Ophir head) that has very little output is to use a more sensitive sensor such as a photodiode or phototransitor. Then you can see how the calibration works and make adjustments for other sensors. Nothing is more discouraging than seeing only zeros arrive from whatever you're measuring because the signal strength is too low to detect.

 

[Seoul_lasers]

hmm, any ideas about an off the shelf DMM breakout board for an Ophir sensor?
I didn't know the Arduino was unable to see mV across the analog input.
Good to know.

Thanks.

 

[Seoul_lasers]

Actually it got me thinking today, if the Arduino has such a voltage sag and poor resolution issue on the analog ports, I am wondering if I combine a (relatively cheap) 10/12bit DMM for voltage sensing and an arduino to take 14400 or faster data stream from the ADC to the digital pins, would that provide a greater data accuracy? Could this even work>
----->
I'd love to see the circuit for the LumenOS that Trevor was running for the Arduino.

 

[Trevor]

The ATMega328p on an Arduino is not fast enough to drive LumenOS R1... the framerate drops to unacceptable levels (full color LCD).

The circuit was just the analog signal from the Ophir sensor running to the board, traces and pulldowns for buttons, traces for the SPI to the screen, and drive circuitry for the sensor. All the interesting stuff is on the microcontroller.

Trevor

 

[Seoul_lasers]

Yes, after reading a little more, the arduino community mentioned about board issues
,sagging vref, and some other issues.
The maple boards sound great by comparison but look like they're gone now.

 

[Bionic-Badger]

I'm not a huge fan of the Maple's development platform. It's kind of a bastardized Arduino, and I'd just rather not even bother with "Arduinoism" if it's going to do that.

Really, your Arduino can still work fine as long as you have the signal sufficiently amplified and calibrated so that the sensing range is mapped to the full range of your ADC. Once you have that done, if you still need something even better you can use a dedicated ADC for sensing. The important thing for now is to getting the signal amplified to the point that you can do something with it, because otherwise you'll need more expensive or sensitive ADC chips to compensate.

 

[Trevor]

I'm not a huge fan of the Maple's development platform.

I love them just because I tend not to use shields, and I'm fine with using the more obtuse environment in exchange for the benefits I receive by using the Maple.

Trevor

 

[Seoul_lasers]

Yes, and the maple is running an ARM at about +4.5x the speed, and after Trevor's LUMEN OS demo utilizing this board, I'm hooked.
By the way, the Arduino forums mentioned that the analog input has an ADC built in, and as Trevor mentioned sees in 10bit resolution down to .1mV, so no need for an external ACD.
One major problem with the Arduino board is a sagging Vref, which throws of any measurements when using the battery input. (Using the external jack seems to correct this issue). But again, I am after a fast accurate reading with the capability of sending a signal over to a computer for printing.

 

[Bionic-Badger]

I love them just because I tend not to use shields, and I'm fine with using the more obtuse environment in exchange for the benefits I receive by using the Maple.

Well, my statement was more to say I'd rather have a complete break from Arduino, even with the IDE and stuff. I tend not to use shields either, but for the Maple the quasi-Arduino environment coupled with the whole clicking reset at the exact moment to get the device recognized just became really obnoxious for me, and I wished it were just some other programming mechanism. Maybe it's changed since then though (I had one of the first Maple revisions).

One major problem with the Arduino board is a sagging Vref, which throws of any measurements when using the battery input. (Using the external jack seems to correct this issue). But again, I am after a fast accurate reading with the capability of sending a signal over to a computer for printing.

That probably depends on what voltage you give it. The voltage regulator on the board should be keeping the voltage steady. You could also add your own voltage regulator to keep things steady.

 

[Things]

Don't forget with the Arduino, it has a built in 1.1V analog Vref, which will work fine with the Ophir heads for decent resolution

Put analogReference(INTERNAL); in your setup then your ADC swing will be 0-1.1V.

 

[Trevor]

Well, my statement was more to say I'd rather have a complete break from Arduino, even with the IDE and stuff. I tend not to use shields either, but for the Maple the quasi-Arduino environment coupled with the whole clicking reset at the exact moment to get the device recognized just became really obnoxious for me, and I wished it were just some other programming mechanism. Maybe it's changed since then though (I had one of the first Maple revisions).

I use the Mini. Fantastic placement of peripherals, highly usable IO port layout, the whole shebang.

Fantastic little board.

Trevor

 

[Bionic-Badger]

I use the Mini. Fantastic placement of peripherals, highly usable IO port layout, the whole shebang.

Fantastic little board.

Trevor

Oh that does look nice! I think I'll have to take a new look at these Leaflab offerings. Arduinos just feel like such child's play sometimes.

 

[Trevor]

Oh that does look nice! I think I'll have to take a new look at these Leaflab offerings. Arduinos just feel like such child's play sometimes.

Yeah... the Mini is all the power of an ARM Cortex M3... in a small package without the proprietary toolchain and with much better documentation.

Arduinos are definitely child's play in comparison.

Trevor

 

[Seoul_lasers]

yup thinking about getting the maple (leaf), and using that soon for my build.
Can't go wrong for $45.00, just need to find a color LCD with key breakout board. Unfortunately the one trevor used is no longer available. Sold out or not in production