Gladiolus

a GreatFET neighbor for Software Defined Infrared (SDIR)

Required KiCad dependency:

https://github.com/greatscottgadgets/gsg-kicad-lib

If you are using git, the preferred way to install gsg-kicad-lib is to use the submodule:

git submodule init && git submodule update

Concept

Gladiolus is an infrared (IR) transceiver in the style of Software Defined Radio (SDR), enabling implementation of arbitrary IR protocols. In every known over-the-air IR implementation, only the amplitude of the optical signal is modulated, so we detect/modulate the amplitude with a single ADC/DAC.

Example Targets

20 to 60 kHz IR remote control systems
IrDA up to 4 Mbps
Bosch Integrus audio broadcast over IR (DQPSK over AM)
proximity sensors

Wavelength

Though many IR-over-fiber implementations use longer wavelengths, all over-the-air targets we've identified use wavelengths between 850 and 950 nm. Gladiolus detects and produces IR in that range.

Getting Started with Gladiolus

For receive, we have brought the signal into GNU Radio via a pipe. So:

mkfifo /tmp/fifo
greatfet_sdir -r -S 10200000 -f /tmp/fifo

That's going to capture at 10.2 MSps. In GNU Radio Companion connect a file source (pointed at /tmp/fifo with Byte type) through UChar to Float and into visualization blocks such as a QT GUI Time Sink or QT GUI Frequency Sink. If they're too strong or weak, the gain can be controlled by a DAC.

To replay a capture: greatfet_sdir -S 10200000 -f

If you want to transmit from a GRC flowgraph: greatfet_sdir -S 10200000 -f /tmp/fifo

AC or DC coupling

The receive photodiode is AC-coupled by default for immunity to ambient light such as sunlight, but it can be switched into DC-coupled mode.

photodiode

We use the Everlight PD204-6B through-hole photodiode (840-1100 nm). As an option, we have included pads for the Vishay VBPW34FASR (used in IRis) which has very high sensitivity due to large surface area but is somewhat slow.

DAC Bypass

Many applications use On-Off Keying (OOK), so the transmit DAC is not needed. It is possible to bypass the DAC and control the TX LED(s) with one pin.