The Genii Hack

This is not really a Tesla related project, but it is related to the previously described Garage Minder effort.  It is a gentle hack that does not intrusively modify anything. 

We recently replaced our old garage door opener with a basic Genii belt drive unit.  The new opener is very quiet and works well with the Garage Minder controls.  It comes with a feature called Safe-T-Beam which must be installed for the opener to work.  It transmits an IR beam across the doorway to a matching receiver and an obstruction is detected whenever the beam is blocked.  I really didn't want this feature and hate it when other people try to force their philosophies on me, though I must admit that it is very well designed for idiot proof installations.  The Internet provides many lame suggestions for how to bypass it, typically by sticking the receiver and transmitter together.  I eventually found the one useful article about it by "Joel Ideas" here: https://www.youtube.com/watch?v=GbmufXgpl14&t=622s.  Joel also proposes a really elegant way to bypass the system.  Thanks Joel.  It turns out that the IR receiver places an active signal on the sensor wires.  This signal needs to be simulated to bypass the sensor.  Simply disconnecting the wires or shorting them will not work.  On the Genii model I have, the signal is a 330 Hz square wave with voltage levels ranging from 9V to 3V, as shown below.  When the beam is interrupted, the signal is a flat 9V level, as shown.  It looks like the receiver is pulling the 9V down to 3V whenever it senses the IR beam. The trace is shown inverted only because the striped sensor wire that Genii calls positive is actually at a lower voltage level.

I also looked into the voltage levels on the "Wall Console".  Besides the button to open/close the door, there is a switch to lock the door and a button to toggle the light on/off.  The circuit is as shown below.  Once I understood the opener's design, I got ideas for new features. 

  

Condition

BW to Gnd

Notes

Open

5.15 V

Wall Console LED disconnected

LED only

3.65 V

LED connected

S2 pressed

0 V

As expected

S1 (Lock) on

0.79 V

Genie out impedance = 453 Ohms ?

S3 (Light) pressed

1.94 V

Genie out impedance = 334 Ohms ?

 

 

 

Stop Light

A visible Stop light in the garage is useful to indicate when to stop driving forward while parking.  The Safe-T-Beam detects when the vehicle is completely inside the garage.  We had a tennis ball hanging from the ceiling to indicate this.  It is a pretty simple idea but our doggie always wanted that ball.  I wanted a red light to come on to indicate when the back end of the vehicle cleared the Safe-T-Beam. 

The red LED in the Wall Console button was an obvious choice for the stop light.  According to the Wall Console circuit, the LED can be turned on and off by placing an 82 ohm resistor across the console wire pair.  The Garage Minder Pi already had access to these wires.  Next, the Pi needed to recognize the signal from the Safe-T-Beam.  The red trace in the diagram below shows the 9V signal input.  To shape the signal, a capacitor gets rid of the DC offset.  The diode grounds most of the negative spike.  The 100K resistor attenuates the signal peak to about 2.3 volts.  The resulting signal (shown in blue) is suitable for the Pi.  There seem to be a few false edges detected, but it does not cause problems.  Configuring a software pull-up for the GPIO input fixes the false detection, but also wastes some current.

Software in the Pi detects the edge (blue trace).  If no edges are seen for 100 milli-secs, it implies that the entering vehicle is interrupting the beam, and a relay is turned on.  The relay bridges the "Panel Console" wires with an 82 ohm (1/4 watt) resistor, and this turns off the red LED in the Wall Console button.  When an edge is detected, it indicates that the vehicle has stopped interrupting the beam, and the relay is released.  This causes the red LED "Stop light" to come on.

Automatic garage lighting

The garage light was often left on inadvertently, so a motion detector triggered light seemed nice.  The "Wall Console" wires can be used to toggle the light on/off, and the Pi has access to these wires.  Three PIR sensors are distributed around the garage, wired in parallel.  If any one of them detects motion, it will pull up the signal line.  The Pi bridges a 202 ohm resistor on the "Panel Console" wires to toggle the light.  Unfortunately, there is no direct way to turn the light on or off, this only toggles it.  A light sensor detects if the illumination changes in the desired direction.  If it didn't then the state is toggled again.

Patent

A quick search found the following abandoned patent Garage parking assistant (US20100245127A1) which seems close.  The difference is that this note describes a method to use the existing sensor, wiring and indicator.

Acknowledgements

Many thanks to Joel for the initial idea.  You da dude.  Long may you live.

Also thanks to Pico Technology for making the really cool PC based oscilloscope.

All in fun

Sept 2021