Hi all, another idea i need to judge the practicality of.. i need to control the intensity of a laser beam which will be scanned rapidly. obviously PWM is problematic since if the beam is moving, you see the pulses quite easily.

cheap analog laser drivers exist, for example:

https://shop.stanwaxlaser.co.uk/lovell-laser-diode-driver-677-p.asp

however they require an analog control signal on the input.

Since i wish to control these using a standard addressable LED protocol, the control signal will be pwm at between 1.5khz and 10 khz (depending on protocol chosen)

i assume the correct method would be to use a DAC to convert from pwm to analog voltage, however my knowledge kinda hits its limits here. If the resulting circuit is too complex/expensive its unlikely ill have time/budget to proceed. However if there is a simple solution (LC filter?) it might be doable.

any help from experts, as always, most appreciated. I know ive been asking about lots of stuff recently here, but im currently trying to put together a list of proposals for a client who wants "cool lights" and i need to understand the practicality/cost of each option before proposing them.

 

Hi all, another idea i need to judge the practicality of.. i need to control the intensity of a laser beam which will be scanned rapidly. obviously PWM is problematic since if the beam is moving, you see the pulses quite easily.

cheap analog laser drivers exist, for example:

https://shop.stanwaxlaser.co.uk/lovell-laser-diode-driver-677-p.asp

however they require an analog control signal on the input.

Since i wish to control these using a standard addressable LED protocol, the control signal will be pwm at between 1.5khz and 10 khz (depending on protocol chosen)

i assume the correct method would be to use a DAC to convert from pwm to analog voltage, however my knowledge kinda hits its limits here. If the resulting circuit is too complex/expensive its unlikely ill have time/budget to proceed. However if there is a simple solution (LC filter?) it might be doable.

any help from experts, as always, most appreciated. I know ive been asking about lots of stuff recently here, but im currently trying to put together a list of proposals for a client who wants "cool lights" and i need to understand the practicality/cost of each option before proposing them.

Use an RCRC filter to convert the PWM to analogue, but first make sure that your PWM signal is a known voltage.

 

Use an RCRC filter to convert the PWM to analogue, but first make sure that your PWM signal is a known voltage.

ok that specific laser driver requires 0-5v control signal. the adressable led controller outputs 10khz pwm at between 7 and 24 v, depending on what supply voltage i use.

 

I assume that you are using a single laser to draw images on a wall.
PWM is the usual method to control the intensity. You don’t need to filter the signal. Just make sure that the PWM frequency is not synchronized with the scanning frequency.

 

I assume that you are using a single laser to draw images on a wall.
PWM is the usual method to control the intensity. You don’t need to filter the signal. Just make sure that the PWM frequency is not synchronized with the scanning frequency.

hi its actually an RGB laser, and currently has 3 ttl drivers which allows each diode to be either on or off, giving 7 colours. literally every laser forum ive seen says that if you want dimming on each diode giving many more colours, you need an analogue driver, otherwise you wont get proper color mixing but just individual coloured dashes on the wall as the galvo scans.

 

Is the entire image of one colour or you are trying to draw a multicoloured image?

 

Is the entire image of one colour or you are trying to draw a multicoloured image?

i would like the freedom to do multicoloured images, or single colour.

 

ok that specific laser driver requires 0-5v control signal. the adressable led controller outputs 10khz pwm at between 7 and 24 v, depending on what supply voltage i use.

Then clamp the signal to 5V by buffering it with any HCMOS gate powered by 5V, and attenuating the PWM input so it is between 3.5V and 5V.
You may also need to buffer the output of the RCRC filter using an op-amp.

 

Educate me, please ? --- Is there a lasing voltage threshold that must be overcome for a laser diode to 'lase' - emit the beam ? If under that value, the laser does not dim nor emit; it is then off, or it it is on above that value. Being above that threshold the only range where some dimming can happen; so any PWM would have to be above that voltage value ? ?

Am trying to extend the life of a laser to ~12/7/365 and in doubt that I should use a much higher powered one and under drive (continuous wave) it to achieve longevity or there is another method ?

 

If the PWM frequency is much higher than the scan frequency so that the scan doesn't mover perceptually between PWM pulses, then you won't see any flashing or smearing of the colors.

 

Educate me, please ? --- Is there a lasing voltage threshold that must be overcome for a laser diode to 'lase' - emit the beam ? If under that value, the laser does not dim nor emit; it is then off, or it it is on above that value. Being above that threshold the only range where some dimming can happen; so any PWM would have to be above that voltage value ? ?

Am trying to extend the life of a laser to ~12/7/365 and in doubt that I should use a much higher powered one and under drive (continuous wave) it to achieve longevity or there is another method ?

It will be driven by a constant current source.

 

Being above that threshold the only range where some dimming can happen; so any PWM would have to be above that voltage value ?

Yes.
The on level of the PWM signal would be brightness level you want when the Laser is fully on.

Am trying to extend the life of a laser to 12/7 and in doubt that I should use a much higher powered one and under drive it to achieve longevity or there is another method ?

If the Laser is kept below its max rated current, and properly cooled, then it should have a very long life.

 

The problem with lasers and LEDs is that there is very little persistence.
I think if you want to achieve more that eight colours, you will have to PWM each of the RGB lasers with independent PWM signals.

If you want to avoid seeing dashed lines, you will have to freeze the scanning while the dot is being generated. Now you will have to settle with pixels instead of vector graphics.

The entire image has to be generated in under 20 ms in order to avoid flicker.

 

The problem with lasers and LEDs is that there is very little persistence.
I think if you want to achieve more that eight colours, you will have to PWM each of the RGB lasers with independent PWM signals.

If you want to avoid seeing dashed lines, you will have to freeze the scanning while the dot is being generated. Now you will have to settle with pixels instead of vector graphics.

The entire image has to be generated in under 20 ms in order to avoid flicker.

I believe the standard approach for full colour laser displays (of the professional variety)is analogue control of laser brightness using a DAC and analogue drivers with min and max current levels set to match the diode.

 

I believe the standard approach for full colour laser displays (of the professional variety)is analogue control of laser brightness using a DAC and analogue drivers with min and max current levels set to match the diode.

I am under the impression that the laser in question does not have analogue control on the input.

 

i have not specified a laser diode yet, only the driver (which was provided as an example, not necessarily the one i would use, but a reasonable choice given it does what i want and does not cost much)

https://shop.stanwaxlaser.co.uk/lovell-laser-diode-driver-677-p.asp



its fully analogue with min and max current settings and a 0-5v analogue signal input for intensity control.

 

Yes.
The on level of the PWM signal would be brightness level you want when the Laser is fully on.
If the Laser is kept below its max rated current, and properly cooled, then it should have a very long life.

Lasers DO last a sort of long while, BUT THEY CERTAINLY DO LOSE BRIGHTNESS! I cautioned one customer about that, and stated very specificly that the lasers did have a finite life time. The FOOLS insisted on leaving the lasers burn 24/7, and used up the lifetime much earlier than they needed to. Now they have an array of $5000 dollar paperweights. Their electronics repair shop has no clue as to how to diagnose problems.

My point being that "a long life" is not nearly "forever."