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Old 12-19-2014, 03:08 AM #1
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Default Modulating a green diode in a handheld build

I'm planning a handheld build using a green diode (PL520) and li-ion batteries for power. Normally, I would just use one li-ion and a boost driver except that I would like to modulate the laser (at fairly slow rates of 1 - 20Hz).

Ideally, I would provide a pwm signal from an Arduino board so I could program a variety of patterns. However, this would require quite a bit of voltage for a handheld. The Arduino would require 7V and since I can't find a TTL capable boost driver, I'd need to supply an additional ~7V for the LD and 1.5V for a linear driver.

Could I get away with pulsing power to the driver since the frequencies are low? If so, I could just use a boost driver and the Arduino, lowering the required voltage. I could power the driver from Arduino's 5V regulator and use a transistor controlled by one of the digital I/O pins to switch power on/off to the driver. I would then only need to provide the 7V power for the Arduino.

Thoughts? Anyone know of a TTL capable boost driver? That would solve all my problems…

Thanks in advance...


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Old 12-19-2014, 04:09 AM #2
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Default Re: Modulating a green diode in a handheld build

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Originally Posted by Stereo Joe View Post
I would like to modulate the laser (at fairly slow rates of 1 - 20Hz).
Why? I thought the point of a handheld was no wires, and since you'll be stringing the modulation signal to the thing... why not add one more wire for power?



With frequencies that low, you can use a FET to switch the power to the driver, and control the FET with your arduino.
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Old 12-19-2014, 02:44 PM #3
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Default Re: Modulating a green diode in a handheld build

Why not just use an ATTiny85 with a PWM output pin connected to a buck driver's PWM input, and then a cheap SOT23 5V regulator on the buck's input?

That seems like the most elegant, but more importantly, the smallest, approach.
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Old 12-19-2014, 03:15 PM #4
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Default Re: Modulating a green diode in a handheld build

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Originally Posted by Cyparagon View Post
Why? I thought the point of a handheld was no wires, and since you'll be stringing the modulation signal to the thing... why not add one more wire for power?



With frequencies that low, you can use a FET to switch the power to the driver, and control the FET with your arduino.
I'd use a small on-board Arduino like a Digispark. The idea is that everything would be battery powered and I would only connect to the Arduino to try a new sketch.

I've been looking into the FET - thanks for the suggestion! I'm very new to Arduino and electronic circuit design so I appreciate the input. A main goal of this build for me is the learning potential.
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Old 12-19-2014, 03:18 PM #5
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Default Re: Modulating a green diode in a handheld build

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Originally Posted by rhd View Post
Why not just use an ATTiny85 with a PWM output pin connected to a buck driver's PWM input, and then a cheap SOT23 5V regulator on the buck's input?

That seems like the most elegant, but more importantly, the smallest, approach.
Hmm. Very interesting... I like small and elegant! I'm reading about the ATTiny85 and SOT23 although I'm not sure about the buck driver. Wouldn't that increase my voltage requirements?
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