MiniPOV3 Laser version?

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mlmforshypeople.com
 
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MiniPOV3 Laser version?

Post by mlmforshypeople.com »

Hi Forum,

I want to build a laser version of the miniPOV3. This is my first kit with Adafruit, so please excuse my inexperience.

Here is the scope of the project:
1. Replace LED's with either Pre-wired 3v laser modules or with Laser diodes (no driving circuit)
2. The Board will be stationary, but there will be a rotating or vibrating mirror that will "scan" the laser light onto the side of my house...

My question is, how much current can the MiniPOV3 board provide to the lasers? I assume its 3v? What is the current sinking limits into the control chip ? can I use a current limiting resistor to avoid damaging both the chip or the laser modules / diodes and still have a functional display?

My plan is to use green lasers. The diodes require 2.5v at 45ma to operate at the typical level. The complete modules would likely use 50 to 75ma...

Any suggestions or has anyone done this before?

(In case you are curious, I want to project some messages on the side of my house that can be read from the nearby freeway and street traffic. I am trying to save a huge colony of rabbits from being crushed or buried alive when a construction project gets approved by our city council. I would like them to do a capture and release / transplant program for the bunnies - an estimated 100 or so live on the existing lot. )

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adafruit_support_rick
 
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Re: MiniPOV3 Laser version?

Post by adafruit_support_rick »

MLMforShyPeople.com wrote:My question is, how much current can the MiniPOV3 board provide to the lasers? I assume its 3v? What is the current sinking limits into the control chip ? can I use a current limiting resistor to avoid damaging both the chip or the laser modules / diodes and still have a functional display?
3V is voltage, not current. For this chip, current is measured in milliAmps (mA). The chip is the Atmel ATtiny2313P microcontroller (datasheet is here)

Each I/O pin can source up to 40mA on a 5V supply (it will something less than that on a 3V supply). However, they can't all do that at the same time. According to the datasheet, the max steady-state current draw across all the I/O pins should not exceed 60mA. The MiniPOV exceeds this by running all 8 LEDs at 20mA, but gets away with it because the LEDs are always changing state.

If you want to substitute your lasers for the LEDs in the MiniPOV, change the 47ohm resistors to 27ohm resistors. That will maintain the same 20mA current used by the LEDs, while accounting for the difference in forward voltage of 2.5V vs 2.0V.

You might consider using NPN transistors to switch the lasers. The I/O pins from the ATtiny would connect to the transistor's base pins to switch 3V to the lasers on and off. Something like this:
laser_transistor.png
laser_transistor.png (29.32 KiB) Viewed 4058 times

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