Pico Projectors for Raspberry Pis20 May 2021
When building prototypes that require tiny projectors capable of projecting an okay-ish image over short to mid-sized distances, finding something decent is not easy. In my case I needed something that is as small as possible, has a wide field of view and should ideally be compatible with a small Raspberry Pi Zero.
Texas Instruments DLP LightCrafter Display 2000 EVM for BeagleBone Black
Thats an evaluation kit for the smallest of the TI “LightCrafter” projector units, meant to be used as a Beaglebone Black hat. Luckily with an adaptor PCB this can easily be adapted for a Raspberry Pi as well. The Raspberry Pis GPIO pins can be repurposed as a parallel display interface (DPI) to get the image data to the projector, so no HDMI is required.
Pinout and I2C commands to configure the projector interface can be found on the website of Frederick van den Bosch Another very nice build that includes an adapter board made by MickMake can be found on MickMake’s website
Keep in mind: we are talking here about a DLP projector, so manual adjustment of the focus plane is necessary.
This can be done with this ultra-unhandy tiny lever that moves a part of the optical assembly (there is no way to fix it in position).
A tiny laser projector, running at 1280x720 pixel. Full-sized HDMI input, requires 5V/1.5A via micro USB.
To save a lot of space, an HDMI-to-FFC adapter comes in handy, but may degrade the HDMI signal.
The tricky part is getting the HDMI settings right:
In ‘boot/config.txt’ the HDMI modes can be set. The Ultimems chipset supports (among others):
mode 4: 640x480@60Hz mode 8: 800x600@56Hz mode 14: 848x480@60Hz mode 85: 1280x720@60Hz
mode 85 results in some nasty glitches with cheap adapters and long FFC cables. That’s what worked well for me:
hdmi_force_hotplug=1 hdmi_drive=2 config_hdmi_boost=4 hdmi_group=2 hdmi_mode=14
One nice advantage of having separate modules for projector and control stage is to be able to just fold it for a close fit (removing the projector stage with the TI LightCrafter 2000 EVM is a pain since the cable is connecting cable is quite stiff).