How to prevent Arduino Micro from delivering full power in TTL output during turn on?

I use Arduino Micro pro clone to provide TTL to a laser driver. When I turn the power on (both get the power simultaneously from the same power supply) the laser produces full power for a fraction of the second and then TTL kicks in and reduces laser output. I wander if there is a way to avoid this eruption of power during turn on.

Many power supplies overshoot the supply voltage when they turn on.

You might want to find a better power supply.

You should probably use a pullup or pulldown resistor on whatever signal controls the laser. The microcontroller resets with all the pins set to a high-impendence ("input") state, which lasts somewhere between several milliseconds (hardwre reset of the microcontroller itself) and a could of seconds (bootloader deciding that there is no new sketch to upload) that can be interpreted by external devices in "random" ways (actual TTL logic, if that's what you mean by TTL, will interpret a floating input as "high.")

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My bad I forgot to add the pull up resistor. I will add and check.

I tried 3 different power supplies with the same result and I doubt that turn on voltage spike would last more than microseconds and in my case I observe increase of laser intensity for a period close to 1 s.

We need to see how you are doing this.

Unfortunately I don't have schematics for the driver which I got from ebay. The circuit diagram is enclosed. The voltage regulator is LM340 T.
2W driver

No difference with the resistor.

Without any input or output capacitors!!

See
Laser diode driving
http://www.repairfaq.org/sam/laserdps.htm

As per data sheet input caps are not required when the source is close to the regulator. Also according to TI :" *Although no output capacitor is needed for stability, it does help transient response."
I had 100 uF cap and the result was the same.

Can you provide a link please?

And do you have a TI device?

For fixed voltage regulators each manufacturer has its own data sheet for its own device. There is no generic device. What you read in one manufactures data sheet will not apply to another.

The fact that you could not detect any difference was due to the fact that you probably never looked at the signal from the regulator with an oscilloscope to see if it was oscillating. There is a lot more to it rather than sticking one or was it two capacitors on the regulator. There is also the self resonant frequency of the capacitors, which is why a 0.1uF ceramic is often put in parallel across each electrolytic capacitors.

Just because you think is is no different is not to say they are not needed. We are trying to help you with what is wrong with your circuit but you seem reluctant to take any advice, one wonders why you posted in the first place.

We do not have your equipment we only have to go on what you tell us.
did you read that link on powering lasers? Did you understand it? Do you have any questions about what you read?

Hi,

So DRAW it as box with connections.
Please DRAW a circuit diagram, include power supplies, component names and pin labels.
A couple of images of your project would also help.

Which pin of the Micro is connected to the driver?

It is recommended that apart from the odd 47uF to 100uF capacitor that you also parallel them with 0.1uF capacitors as close as possible to the regulator.

If you disconnect the signal wire from the Micro to the driver board, does the fault still occur when you turn it on?

Can you please post a link to where you purchased the driver.

Please post your code?

Thanks.. Tom... :smiley: :+1: :coffee: :australia:

here is the link and started to think that the problem could be in the driver design.
Driver Board For 405/450/520/638/808/980nm Red Green Blue Laser Diode 12V 2W | eBay

[

## Driver Board For 405/450/520/638/808/980nm Red Green Blue Laser Diode 12...

Driving power for 405/445/450/520/638/808/980nm red, green and blue lasers. 1pc Power Supplies Board Driver for ...

](Driver Board For 405/450/520/638/808/980nm Red Green Blue Laser Diode 12V 2W | eBay)

I get the same result when I drive Arduino with 5V supply.

When I simultaneously connect the power to Arduino and the LD driver ( using 5V supply for Arduino and 12V supply for the driver or alternatively using 12 V power supply for both and LM340 T to regulate Arduino voltage) during first 2.5 s of operation the power of the laser set to the level that I get without TTL and after 2.5s TTL start working and the power goes down according to what I set.
If I don't use Arduino the power does not fluctuate.

I use Pin 9 for TTL

When the Arduino is operating, what do you do to turn the laser OFF?
Do you make the Arduino output high or low?

You need to connect a resistor to the Arduino output / laser driver input that will pull the input in the same direction before the Arduino becomes active.

My guess is it needs pulling low, as floating TTL inputs are seen as high - as westfw mentioned in post #3. He virtually gave you the answer, but you proceeded to do the exact opposite, with a pullup resistor.

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