Problem driving a laser pointer

[Louis Cimon]

Hi,

As a beginner, I am trying to drive a laser pointer from a PIC16F84 using this simple program:

-----------
loop: High 0 'Turn on LED connected to RB0
Pause 1000 'Delay for 1 second

Low 0 'Turn off LED connected to RB0
Pause 500 'Delay for 0,5 seconds

GoTo loop 'Go back to loop and blink LED forever
End
----------

For sure it flashes but it looses much brightness.

I tried to drive the laser pointer from a TIL111
using the following circuit but it still looses much brightness.

http://www3.sympatico.ca/louiscimon/varia/Laser%20pointer%20on%209v%2016f84.pdf

I suppose that "High" is in fact an oscillation that is not a continuously "on".

I have the same difficulty trying to drive a piezzo buzzer
(Velleman SV10) : it looses much loudness in the process, even driving it from 18 v
with the TIL111.

I would like to understand and find a solution.

Thank you very much

Louis Cimon
Québec, QC
Canada
http://www3.sympatico.ca/louiscimon/

[Jumper]

Hi,

Are you sure the TIL is fully open? 4.7k as the LED resistor seems a bit much.

Bring out your DMM and measure the voltage on the TIL to see what is happening.
/me

[Louis Cimon]

Hi Jumper,

Thank you for your input.

I changed the resistor for a 470 ohm.

I am reading 4,92 v between rb0 and ground
and 4,92 v between TIL111 pin 1 and ground

I am reading 8,35v between TIL 5 and battery and the battery produces 8,35 v.

I tested my piezzo on two 9v batteries in series and the sound output is greatly reduced when I drive it with the TIL111 compared to driving it directly with the batteries. The voltage readings of the batteries and the TIL11 output are the same.

Solution?

[Jumper]

Hi,

Why do you want to use this optocoupler? If you just want to switch something on with the PIC I would go for a FET solution.

ULN2001 is a favorite at this forum and if you only want to handle up to 500 mA this will do fine.. IF you need more you can use more channels in this chip in parallell.

You can also try to measure the current thru the laser to compare it with and without the TIL.

/me