DIY Arduino LPM

[HIMNL9]

3181253 represents the position of our star in our galaxy. I made it up.

Shhhh ..... don't say it so loud ..... Vogons are still searching where we have hidden it .....

:crackup:

 

[wbp]

This thread is about using a microprocessor to build an LPM. You don't need to scale the voltage first, you can do the math in the micro. You guys are thinking in analog terms, fine for the other threads where a DPM is used, but this is a digital discussion, no?

I've built two control systems for the heater in the h-alpha filter in my solar telescope. The first one was analog and very similar to the TEC and DPM approach, complete with a DPM, an op-amp, and a thermistor. The second was full digital - used a Basic Stamp, an ADC, and an Analog Devices temperature chip. The first one displays the temperature of the filter's oven. Functional but not much information. The second one displays the frequency the filter is tuned to, in angstroms, and has set points, etc. It was the prototype for Daystar's current products.

There's nothing wrong with the analog approach - it's simpler and doesn't require any programming. But I'm a digital guy, I've been writing programs for over 40 years, I'm sorta used to thinking that way now... :tinfoil:

 

[wbp]

Shhhh ..... don't say it so loud ..... Vogons are still searching where we have hidden it .....

:crackup:

Oh, yeah, sorry! Maybe I should encrypt it... :thanks:

 

[HIMNL9]

Yes, i know that you're speaking about digital application, but, think just about this:

Take your 10mV for 150mW example ..... what can be more precise, in A/D conversion ..... have a 10 mV to convert in 150 different levels, or have a 150mV to convert in 150 different levels ? ..... also, very low voltage signals directly connected to high impedance inputs, can be much more influenced from noise, in percentage, than higher level signals coming from a low impedance sources ..... and also high frequency noise can be took away more easily in the analog part .....

Sure, you can scale the 10mV in 150 steps via software, but the precision, noise immunity and stability are worse than with a greater value .....

I'm not saying that the digital approach is wrong (i had planned one too, with graphical LCD panel, but my programming skill suck a bit, so nothing done ) ..... i'm just saying that analog can help simplifying and improving the digital applications a lot, sometimes (and, considering that in almost all the professional instruments, when a digital management of an analog signal is required, there's almost all the times an analog "conditioning" circuitry, before the digital part, maybe my idea is not completely wrong, after all :beer

 

[wbp]

I understand the idea of using the op-amp but that also adds its own problems. The ADC I referred appears to be designed to measure low voltages accurately, from what I read in the tech sheet. So in the end it might actually be lower noise and more stable than using an op-amp.

Oh, and think about having the ADC mounted on the heat sink, with an I2C interface. Doesn't matter how long the wires are between the sensor and the meter...

I'm interested enough that I'll probably order some parts and play with it a bit...

 

[XFast]

i know this is an old post but it is very interesting and exactly that what i search.
Is there anywhere a detailed instruction and the sketch for the arduino? Or elsewhere a newer arduino LPM Project?

 

[Bionic-Badger]

Why don't you make a new thread and refer to the old one, instead of dredging up old threads?

Anyway, just use the simple sensor reading sketch the Arduino comes with. You could even send it out to Processing if you want. Really, there's nothing special about using an Arduino to read from a sensor. The more important thing is knowing what the values you read correspond to as far as laser power.

 

[ARG]

Best to use an external ADC though, since the arduino one is 10bit. Check out the Delta isis (Sigh, the name has such a horrible connotation now). It's just an Arduino with an LTC2453 external ADC.

Can interface directly with MarioMasters <$50 LPM.

 

[Sigurthr]

(Sigh, the name has such a horrible connotation now).

This will always be the one true Isis to me: Isis - Wikipedia, the free encyclopedia


Reading over this thread; ah, Old Times. Whatever happened to HIMNL9?

 

[XFast]

Why don't you make a new thread and refer to the old one, instead of dredging up old threads?

Sorry

Anyway, just use the simple sensor reading sketch the Arduino comes with. You could even send it out to Processing if you want. Really, there's nothing special about using an Arduino to read from a sensor.

I know.

The more important thing is knowing what the values you read correspond to as far as laser power.

That is right, and that is the problem

Are there no canche to use an arduino and a diy tec sensor?? I know that is not a exact measure but i want to test my goggles and i think for that it is good enough.

 

[Sigurthr]

You can get a relative power check out of it, assuming you have a laser that is known to be sub 5mW to use as a reference.

 

[jasonmrc]

The pieces:

10x10mm TEC mounted on a TO220 heatsink and connected to a LM358 Amp circuit per this thread:
DIY Thermal LPM for under $50

Aduino Board:
DFRobot DFRduino USB Microcontroller (ATMega168) - RobotShop

DFRobot LCD/Keypad Shield:
DFRobot LCD Keypad Shield for Arduino - RobotShop



Assembly:

Amp Out+ => Arduino Analog input Pin1
Amp Out- => Arduino Analog input Pin2
Amp PWR+ => Arduino +5V Pin
Amp GND => Arduino GND Pin

Assembled with my sketch running:


The Analog input has only 10bit resolution for 0-5V, this means roughly 5mV per bit, which is not great but good enough for me. I could use the internal reference voltage and get about a 2mV per bit resolution, but this makes the keypad unusable since it uses Analog Pin0 assuming a 5V Vref. I am going to try redefining the keypad trigger values for the internal Vref at a later date.

The Select button starts the LPM sampling. Left starts dumping the LPM reading every second over the serial port so I can capture it in a terminal app to create a log. Right stops the data dump. Up resets the Max to zero and Down stops the LPM sampling. Reset is just a relocation of the reset on the Arduino board for convenience.

Here is a video of it in action. I still need to calibrate the amp as I don't have any metered lasers or calibrated LPMs.

Hi

Is this lpm software open source ? , i have both the shield and arduino and tec interface.. would like to test this.

thanks

 

[marcuspeh]

Hi

Is this lpm software open source ? , i have both the shield and arduino and tec interface.. would like to test this.

thanks

What do you mean by lpm software. If you are referring to the quote for the arduino, so a simple search below with the search bar and you should be able to find it. I believed Arg and Trevor posted it. Anyway, googling or starting a new thread will be better than posting on this old thread.
Edit: It is this thread

 

[jasonmrc]

I mean the arduino project for the laser power meter using the lcd shield. does it have a specific name ? i found the delta isis and openlpm projects but not the lcd versions.

 

[marcuspeh]

I mean the arduino project for the laser power meter using the lcd shield. does it have a specific name ? i found the delta isis and openlpm projects but not the lcd versions.

I have already included the link in my previous post for arduino with lcd