Hello,
I am new to arduino and also posting for the first time to the forum.
Actually we are working with laser diodes and want to drive 16 laser diodes through arduino and read out the readings from a semiconductor chip. we need to operate laser diodes with voltages 2.0 to 3.3 volts. and driving current is around 30mA. For our purpose i found out that arduino mega 2560 is better choice as it has sufficient IO-ports where as other versions only have IO ports less than 16, and as i need to drive 16 diodes individually it won't be possible. I saw the technical list of this board but i couldnt figure out whats the output pin voltage will be as i need to change this voltage between 2-3.3 volts.So I want to ask
What is the value of output pin voltage for this circuit?
And is amplification of the reading signal be possible with this board?
(We want to read current from semiconductor which is very small current and we need to amplify it before evaluating it back on computer.)
Is driving laser diodes and at the same time reading current from the chip is possible with arduino mega 2560.
Thanks in advance for the help.
Actually I am using laser diode module so no problem in driving the diode that way but it requires less then 3.3 volt for operation and limiting current to 30mA. I also want to drive 16 laser diodes simultaneously but with different pins so to toggle each laser diode separately. For this I thought Arduino mega 2560 as it has 54 IO pins, but i don't know how to decease pin voltage to less than 3.3 for the pins driving laser diodes
Now I gather you want to power up just one laser diode at a time?
The output voltage of a pin will be the supply voltage in series with an effective resistor of about 80 to 100 Ohms if I recall.
I would advise just using a basic Arduino ("Nano" if USB needed, or Pro Micro if not) and two TPIC6B595 shift registers in series to control the 16 diodes as these are very capable of a lot more current.
If you want amplification of your sensor output, you will have to provide the op-amp/ instrumentation amplifier circuit.
we need to operate laser diodes with voltages 2.0 to 3.3 volts. and driving current is around 30mA.
I assume these are like LEDs and require a constant current source. (From what I've read, higher-power LASER diodes can be a bit trickier.)
That means you DON'T apply a fixed voltage to the LASER. You feed-in a constant current and the voltage "falls into place". Diodes are non-linear. Their resistance changes with voltage. At low voltage, the resistance is high and very little current flows. When you reach the breakdown voltage ("operating voltage" for an LED or LASER) the resistance suddenly drops. If you go over the breakdown voltage, resistance drops to almost zero, you get excessive current and something burns-up!
With low currents (30mA) a series resistor with a fixed-voltage can serve as a constant current source... If we know the applied voltage (5V) and the voltage across the LED/LASER (~2V) we know the remaining 3V are dropped across the resistor (Kirchhoff's Law). Since we know the required current* as well as the voltage across the resistor, we apply [u]Ohm's Law[/u] to determine the resistor value. Or, use an [u]Online LED Resistor Calculator[/u].
In a series circuit, the same current flows through all components (another of Kirchhoff's laws).
Actually I am using laser diode module so no problem in driving the diode that way but it requires less then 3.3 volt for operation and limiting current to 30mA. I also want to drive 16 laser diodes simultaneously but with different pins so to toggle each laser diode separately. So I think shift register won't serve the task. For this reason I thought Arduino mega 2560 as it has 54 IO pins, but i don't know how to decease pin voltage to less than 3.3 for the pins driving laser diodes.
And if I want to change voltage for all diodes do I need to use separate voltage regulators for each diode?
And as I asked previously like is it possible to drive laser diodes and at the same time reading current from the semiconductor chip?
strager_smz:
Actually I am using laser diode module so no problem in driving the diode that way but it requires less then 3.3 volt for operation and limiting current to 30mA.
You mean these I suspect:
Or something like these:
.
Or these:
They are a laser diode whose current is controlled by a series "chip" resistor on the back of the board. The diode has a voltage drop IIRC of about 1.8V and the resistor is about 56 ohms for 3.3 V or 91 ohms ("910") for a 5V diode. (I can see the "910" on those images; will check the 3.3 V version later.)
strager_smz:
I also want to drive 16 laser diodes simultaneously but with different pins so to toggle each laser diode separately. So I think shift register won't serve the task.
Actually, my suggestion of two TPIC6B595 shift registers in series to control the 16 diodes is exactly what you want for the reasons I specified.
strager_smz:
For this reason I thought Arduino mega 2560 as it has 54 IO pins, but i don't know how to decease pin voltage to less than 3.3 for the pins driving laser diodes.
To operate a "3.3 V" unit from 5 V you simply add the additional resistance in series to make it match the 5V version. But you need the shift registers, not the extra I/O pins if you want to operate multiple lasers simultaneously.
strager_smz:
And if I want to change voltage for all diodes do I need to use separate voltage regulators for each diode?
Yes, separate resistors.
strager_smz:
And as I asked previously like is it possible to drive laser diodes and at the same time reading current from the semiconductor chip?
You appear not to comprehend what a microcontroller is.
The I/O pins, once set as an output, continue to deliver either HIGH or LOW to that pin until you write a different value.
Once you write to the I/O port, whatever else you do afterward does not matter.
this is the link to data sheet of these laser diode.
But is it possible to turn some laser diodes on and some diodes off in alternative combination with these shift register?
I thought shift register can be used if we want to turn all diodes on and off at the same time but not in different toggling combination for every diode
They probably need a good stiff 3.3V supply to operate stably as they have circuitry on-board. Switch
them with NPN or n-MOSFETs on the negative terminal, common the +ve terminals to a 3.3V 1A
regulator (with input and output capacitors). You might get away driving them with a shift register,
or you might find the APC circuit oscillates/misbehaves (it has a feedback loop and amplifier internally)
strager_smz: this is the link to data sheet of these laser diode.
But is it possible to turn some laser diodes on and some diodes off in alternative combination with these shift register?
I keep giving you the link to the datasheet. Have you read it?
In fact, it is three things in one - a shift register, also a latch, and an output gate. You use the shift register to enter the data bits in a serial stream - which means you can chain any reasonable number together and shift in multiples of eight bits using only three control lines - then once all the bits are shifted in, you actuate the latch which holds the pattern until you have shifted another pattern in and then latched that.
Therefore since it only requires three control lines (or a fourth to initialise it to zeroes or disable it until you first load it), you can perfectly easily control it with a UNO, Nano or Pro Mini (or Leonardo, Pro Micro) and have plenty of port pins for other purposes.
Perhaps most importantly, it is rated to drive 150 mA on all outputs simultaneously, far more than the MEGA2650.
That laser does specify that it must not be powered at more than 3.3V, so you really need to use the TPIC6B595 because it does not care about the output voltage. You use it to control the cathodes of the laser diodes, and connect all the anodes to a 3.3V regulator.
I just purchased a laser "module" with "integrated APC" (VLM-650-03 LPA).
What exactly does "integrated APC" mean? Does it mean that I do not have to manage the votage and/or current? The spec sheet heading says that it covers both the LPA and LPT variants, but I cannot determine the difference between them - does anyone know?
I know what the acronym APC stands for, but I don't know what the Automatic Power Control circuit does exactly, or how it affects interfacing the module with devices like the Arduino.
but I don't know what the Automatic Power Control circuit does exactly
Well at a guess I would say that the power control was handled automatically.
If you had read the rules of this forum How to use this forum
you might have spotted that we don't encourage the resurrection of old threads, maybe if you obey the rules you would be treated a bit better.
raschemmel:
Oh, you didn't know his hobby was Arduinos ?
No, more likely hot air ballooning.
Kevin07003:
What exactly does "integrated APC" mean? Does it mean that I do not have to manage the voltage and/or current?
The spec sheet clearly states that you feed it with a voltage between 3 and 5, and depending on model, you may expect it to draw less than either 25 or 45 mA.
Please note that the APC may not tolerate rapid switching for modulation or PWM.
