Helios - Open source, low cost DAC

[Grix]

I'd like to see a video of this in action.
Have you used it or the sole purpose is to sell it ?

I made a quick video here: https://www.youtube.com/watch?v=Yq_16HsXrRI&feature=youtu.be

I do use it as my main DAC now, for the programs that support it at least

 

[Benm]

That looks pretty good.

I presume the green is a DPSS and therefor misses output on the lower brightness levels. This is not the DAC at fault at all, but i suppose you should set some bias for that green to make it light up a bit better at the low end.

 

[Grix]

Yeah the projector is cheap with both pretty bad modules and scanners. Any errors you see in the video should be either their, the software or the camera's fault. It looks the same in real life as any other DAC I've tested, and I've previously verified that the output is correct on an oscilloscope.

That looks pretty good.

I presume the green is a DPSS and therefor misses output on the lower brightness levels. This is not the DAC at fault at all, but i suppose you should set some bias for that green to make it light up a bit better at the low end.

 

[OldNo7]

Yeah 16 seconds is way more time than you should ever need. Measure the time it takes to execute your main loop then add some buffer in case any interupts occur. Just make sure you reset the watchdog at the begining of the loop.

I'm not sure using the same chip to do all the work and check if everyting is okay is the best of ideas though. If something (like a big nasty voltage spike on the supply rail) caused the main uC to misbehave, isn't it likely that this could affect the watchdog timer too?

Yes, It would be better to use an external watchdog chip. For one it could also reset the DACs at the same time. I don't think the internal watchdog timer toggles the reset pin. In that case the DACs would maintain the last setpoint until the uC finished reseting (assuming the init code zero's the DAC channels). None of that really matters though since the hardware is already done internal watchdog is the only option. I would just make sure and zero the DACs early in the initialization code.

Then again scan-fail detection can go pretty far. You can look at galvo feedback signals to assert the mirror is actually moving, and detect if it was not moving with correct drive signals intact.

I didn't think there was a way to monitor the feedback signals from the ilda connector. I think that function should be left to the projector. One DAC can control multiple projectors. The DAC shouldn't shut off because a projector is malfunctioning. That projector should shut itself off while the other projectors continued working.

 

[OldNo7]

On another note have you looked at LaserShark and OpenLase? LaserShark also uses LibUsb. It may be worth porting his jack host app to work with your DAC in order making it compatible with the OpenLase framework as well.

LaserShark
OpenLase

 

[Grix]

The internal watchdog does fully reset the mcu as if the reset pin was driven low.

Openlase support has always been a plan, but I haven't had the time for it yet and don't quite know when I will.. There are a bunch of stuff like that I want to support eventually, like openframeworks too.

 

[Benm]

I didn't think there was a way to monitor the feedback signals from the ilda connector. I think that function should be left to the projector. One DAC can control multiple projectors. The DAC shouldn't shut off because a projector is malfunctioning. That projector should shut itself off while the other projectors continued working.

You're right about that.

Often the whole thing is on one box though: usb interface, dac, scanner modules etc.

For a strictly usb-to-ilda converter monitoring scanfails is not a task, but at this price point i can see plenty of situations of this board just ending up as part of what is basically a self-contained usb-laserprojector. In that application it would be nice if it had some failure detection, but since the product is a usb-to-ilda board this is not strictly your problem or responsibility.

As for the video and the green laser: They all do that to some extent, unless you use laser driver units that allow you to run the treshold current with zero input. This in itself is not uncommon, but because it is thermally sensitive on DPSS lasers the threshold current is often set a bit low on these since you would be unable to completely turn the laser off in warm/cold environments otherwise.

 

[OldNo7]

The internal watchdog does fully reset the mcu as if the reset pin was driven low.

The question I had was if a watchdog reset occurs does it drive the reset pin low? If so then you can/should tie it to the reset pin on the external DAC (with a pull up resistor). So that the lasers shut off as soon as reset starts.

 

[Benm]

That could be a good idea, i suppose the DAC's used have an enable or /enable input?

Could be an easy way to shut down the output in such an event.

 

[Grix]

The question I had was if a watchdog reset occurs does it drive the reset pin low? If so then you can/should tie it to the reset pin on the external DAC (with a pull up resistor). So that the lasers shut off as soon as reset starts.

Ah, I'm not sure but it should be configurable as the reset pin is bidirectional. However it doesn't matter as there is no reset pin on the external DAC. Only way to null the outputs is to send an SPI signal. The uc does this as it powers up and it powers up in less than a millisecond so it shouldn't matter much in practice I think

 

[OldNo7]

Ah, I'm not sure but it should be configurable as the reset pin is bidirectional. However it doesn't matter as there is no reset pin on the external DAC. Only way to null the outputs is to send an SPI signal. The uc does this as it powers up and it powers up in less than a millisecond so it shouldn't matter much in practice I think

I just looked and the datasheet for the ATSAM4S2B does have a timing diagram that shows the pin toggle during a watchdog timeout. It doesn't mention it occuring anywhere else. However if the DAC doesn't have a reset or clear pin than it doesn't really matter.

I just purchased one from bitlasers. When i get it I'll try to get it working with Openlase.

 

[Grix]

I just purchased one from bitlasers. When i get it I'll try to get it working with Openlase.

That would be awesome,
I just shipped the order for you.

 

[Grix]

Helios is now working with the legendary software LSX
To quote Andrew the support is in alpha mode right now, there is a small issue we are working on.

Also the ones of you who own the DAC might want to update the firmware, there has been a few updates since it was first released, increasing performance and adding features. (For example the watchdog we talked about in this thread is fixed, it's now set to reset after 500ms). To upgrade firmware, see the simple guide on bottom of the info page: Helios Laser DAC - Projects

 

[Benm]

Sounds like another move in the right direction

 

[AngelG]

@Grix
I like the video you posted What kind of laser projector does it need (not something like NEC P502HL I guess) ?

 

[Grix]

@Grix
I like the video you posted What kind of laser projector does it need (not something like NEC P502HL I guess) ?

No, it's not for video projectors, but show lasers with ILDA ports. Like these: ilda projector | eBay