DLP Lightcrafter negative LED current

Hello WP,

First,GUI allowing entering negative value,

there is mistake in the GUI code, this number is actually be processed as a unsigned 16bit number for the current setting, so valid range is 0 - 1023, refer to the DLPC300 I2C programmer'g guide, I2C commands 0x12, 0x13 and 0x14.

I think your -78 is processed & sent as it is to the DLPC300 which is then processed as unsigned number, that results in very high value, so LEDs are turning oFF.

Secondly, best way to disable light output,

The LED_EN signals going into the LED driver circuit can be disabled, you can do this buy updating DLPC300 register as follows - 

Register[0x4B] = Bits31:24 = set to 0x00 to disable Red LED

Register[0x4C] = Bits7:4 & BITS3:0 = Set to 0x00 and 0x00 respectively to disable Blue and Green LED 

Note, you should retain rest of the bits untouched, so first Read the register into a 32bit variable, clear the bits as mentioned above to disable.

Let us know if it helped.

Regards,

Sanjeev

Hi Sanjeev,

Thanks for reply. I figured that out and now I understand how registers and commands work but I still have a few questions.

1. What about minimal current? Is it possible to lower that minimal 140mA value? I can't believe that driver prevents that. Must be something with software/firmware side.

2. Can I change default variable values? When lightcrafter starts up, device sets current to 633mA which stands for 274 variable value from that 0 - 1023 range.

I am asking for that because I need to change light source for smaller diodes that work on much lower current(below 100mA). It is not typical application but I need to figure  that out.

Regards,

WP

WP,

If you are not going to drive the LED, it is best to just disable the LED enables as Sanjeev suggested.

The LED driver was not designed for extremely low current, so do not set its value less than 5. It can produce an unstable power output since it has a hard time regulating and reading the feedback network for very low LED PWM settings.  

As far as low currents, the LED driver feedback network was designed to map a large current capabilities (up to 1A) of the LEDs to 1024 steps. You might need to remap this by changing the feedback resistor values. We have not experimented much with low values, but you would need to lower the bias resistor while increasing the PWM divider resistors. You might try:

• R50, R54, R49 = 174K
• R52, R56, R59 = 2.26K
• R51, R55, R58 = 84.5K
• Set GUI to LED current to 35, this will drive about 50mA.

I would recommend some experimentation and measuring of currents at several different values. The voltage and current capability of the LED might change the amount of current produced by the LED driver. Please note that this suggestion has not been extensively tested and any changes to the LightCrafter board are not guaranteed and could damage the board.

Moreover, you can also use the GUI to create a setting for LED currents and LED enables, then save that as a solution and make that the default solution. Those settings will load up as default on the next power up.

Hi,

I am returning to work after weekend and still have a few questions/problems.

1. First of all, solution creating in GUI doesn't work properly because to turn all diodes OFF I need to alter values in 0x4B and 0x4C register. After I do that and create gui solution, it doesn't save this values, only changed currents. The problem is that when I am restarting DLP device it turns all diodes back ON despite that I edited that registers.

How to disable all diodes permanently? Will DMD chip still be working after that?

WP

Hello Wojciech,

1. First of all, solution creating in GUI doesn't work properly because to turn all diodes OFF I need to alter values in0x4B and 0x4C register. After I do that and create gui solution, it doesn't save this values, only changed currents.

[Sanjeev] Very good point. The existing command handler application running on the DM365 don't have option to store the LED enable states. We could add this feature, let us know how urgent it is, like if you are building product or into ramp. 

How to disable all diodes permanently?

[Sanjeev] Ensuring the LED_EN signals not enabled. If your question is from the previous clarification i.e., disable the LEDs during power on, then the DM365 command handler application needs changes.

Will DMD chip still be working after that?

[Sanjeev] DMD is in active and running state if the Sequence is running i.e., DLPC300 register I2C: 0x82 bit0 is '1'. Now if the Sequence is not running, DMD stop updating/refreshing the data on it, but it will still be in power-on state.

Regards,

Sanjeev

Hello,

I would be grateful for a new version of firmware with permanent LED disabling feature. It is very urgent because I have deadline and I must do that on time. It is a part of my engineers degree final project and if I won't do that on time, I would be in trouble :D

Thanks for help,

WP

Hello WP,

Unfortunately it is not possible to implement your request in DM365 in this short period.

We would certainly keep your request in our database, and would add in future releases. As such there is no planned dates so we cannot comment on its availability.

Having said that, i have few other suggestions, see if it helps,

Suggestion-1:

Create a solution that is configured to display Internal Test Pattern set to "Solid Black", and make it as a 'default' solution. So whenever the kit is powered-on after displaying  start-up logos, it will not show any other pattern.

Suggestion-2:

Create solution - Pattern Sequence, with just 1 black pattern and configured to external trigger. Make it as default solution. This will also bring up the EVM  with nothing displayed.

Regards,

Sanjeev

Hello,

Thank you for your help Sanjeev. We already solved our problems by different approach. We reverse engineered that electronic module a bit and made our own electronic tape with resistors instead of LED diodes. Now we have same voltage drops so device works properly but without internal light source. We have our own laser-based external light and everything seems to work fine. But as always we have more questions :D

1. Is it possible to clear memory image buffer without turning off the device? I mean, when we tried to send one image to device and after that send another which was smaller than previous one, there was always background from the previous one left. I didn't find any easy solution for that.

I can always try to solve that with modifying the pc software but firstly I would like to know if there is another solution for that.

Cheers,

WP

Hello WP,

There is no direct command that could clear the DMD. 

The available options are (a) Load a ALL Black image i.e., send a black image before sending the new image, (b) Create a solution that is displaying black static image, before loading the new image you can load this solution, after this send the new image.

Regards,

Sanjeev