Roomba 620 infrared signals

Having been pondering it for a while, I recently bought an iRobot Roomba vacuum cleaner - the Roomba 620 which is the current entry model. For fun I took some photos with an infrared sensitive webcam (a trusty XBox Live Vision), and then measured some of the IR signal codes with my Raspberry Pi.

Note the four downward facing IR LEDs (cliff sensors)

Does the Roomba use IR illumination to follow walls?

Initially it might seem like the Roomba explores blindly until it bumps into things, but it does have some open space detection as you can obverse speed changes. Having seen how it lights up where it is going with four IR LEDs (and another four pointing down which I assume are the cliff detectors) this is less mysterious.

Roomba Home Base

I've already done some background reading, so I was expecting to be able to see three IR LEDs on the Roomba Home Base or "Docking Station" - the top one is a unidirectional emitter visible from all sides of the dock (and behind it) referred to as the "Force Field" which normally repels the Roomba. The other two emit angled beams used to guide the Roomba to its "Home Base" for recharging.

Roomba Docking Station, with three IR LEDs (and glare)

Roomba coming in to dock using infrared

From Roomba iRobot Create Open Interface

This works like the port and starboard (red and green) lateral buoys in used to guide ships into harbour. By keeping the "Green buoy" to port (left), and the "Red Buoy" to starboard (right), the Roomba can find its way home. Of course, here the LEDs are not different colours (although I'd guess the original prototypes probably were), rather they emit different pulsed signals - which I should now be able to detect and decode with my newly fitted Raspberry Pi infrared receiver.

Published Roomba IR Codes

I used iRobot Create Open Interface v2 (PDF) to compile the following table, specifically page 18 which has the above diagram, and which covers the remote codes indirectly when talking about the Roomba serial interface - iRobot have been very positive about people hacking their robots for technology projects.

Each of these remote codes is 8 bits (1 bytes) which can be represented as a decimal number, a hexadecimal number, or a string of eight bits (hereafter the first bit in the signal being the most significant bit in the numerical code).

Sent by

Dec  

Hex

Binary

Meaning

Remote Control

129

0x81

1000 0001

Left

130

0x82

1000 0010

Forward

131

0x83

1000 0011

Right

132

0x84

1000 0100

Spot

133

0x85

1000 0101

Max / Dock

134

0x86

1000 0110

Small

135

0x87

1000 0111

Medium

136

0x88

1000 1000

Large / Clean

137

0x89

1000 1001

Pause

138

0x8A

1000 1010

Power

139

0x8B

1000 1011

Arc-forward-left

140

0x8C

1000 1100

Arc-forward-right

141

0x8D

1000 1101

Drive-stop

Scheduling Remote

142

0x8E

1000 1110

Download / Send All

143

0x8F

1000 1111

Seek Dock

Roomba 400
Home Base

240

0xF0

1111 0000

Reserved

242

0xF2

1111 0010

Behind / Force Field

244

0xF4

1111 0100

Green Buoy (meaning Starboard, or Right)

246

0xF6

1111 0110

Right Close / Green Buoy & Force Field

248

0xF8

1111 1000

Red Buoy (meaning Port, or Left)

250

0xFA

1111 1010

Left Close / Red Buoy & Force Field

252

0xFC

1111 1100

Middle / Red Buoy & Green Buoy

254

0xFE

1111 1110

Middle Close / Red Buoy, Green Buoy & Force Field

The IR codes from the Home Base make sense with a bit each for the "Red Buoy" (Port, right LED beam), "Green Buoy" (Starboard, left LED beam) and the "Force Field" (unidirectional close range LED).

It would be my guess that the composite signals are not actually broadcast explicitly, but are the overlap of the output from the two to three separate LEDs which must therefore be time synchronised. Time to find out…

Recording Roomba 620 Home Base IR codes

I recently setup an infrared receiver in my Raspberry Pi which can be used to record IR signals from remote controls. I was able to use the same procedure to record the signals from the each of the three separate LEDs of the Roomba Home Base by blocking the others with card and tape.

The IR codes are documented as emitted at 940nm using a form of pulse-width modulation (PWM), modulated with a carrier frequency around 38KHz. Each code consists of a sequence of eight bits, encoded as:

• Bit 0 - 1ms on, 3 ms off
• Bit 1 - 3ms on, 1 ms off

I started by watching just the "Force Field" LED, from the back (while Roomba was away in another room), it was clear that (with some variation in the long pauses), there was a simple repeating pattern. For example, where the numbers are in micro-seconds (1000 is 1ms):

$ mode2 -d /dev/lirc0
...
space 33098
pulse 2947
space 965
pulse 1016
space 2865
pulse 3086
space 826
pulse 1044
space 2869
pulse 1015
space 2894
pulse 1015
space 2868
pulse 1035
space 2873
pulse 2953
space 99558
pulse 2947
space 969
...

(long pause)

1
.
0
.
1
.
0
.
0
.
0
.
0
.
1
(long pause)
1
.

This repeating pattern was 1010 0001, or 161 (decimal), or 0xA1 in hex, which is not is listed in the current iRobot documentation (see table above).

Decoding that by hand was tedious, so I wrote a little Python script to decode the Roomba IR codes for me:

$ mode2 -d /dev/lirc0 | python decode_roomba_ir.py
10100001 - 161 - 0xA1
10100001 - 161 - 0xA1
10100001 - 161 - 0xA1
10100001 - 161 - 0xA1
...

Attempting to watch the "Force Field" IR LED only, from the back, gave a nice clean simple repeat. Using some tape to securely mask the two buoy LEDs I could get the same clean signal from the front of the dock:

• 10100001 - 161 - 0xA1

With just the right LED and the top LED, there were apparently two codes:

• 10100001 - 161 - 0xA1
• 10101000 - 168 - 0xA8

Just the left LED and the top LED, again I saw two codes:

• 10100001 - 161 - 0xA1
• 10100100 - 164 - 0xA4

All three LEDs from front, in some locations it was hard to decode the 5 and 6th bits - but usually there was a blend of 0xA4 and 0xA8 giving 0xAC as a recognisable code:

• 10100001 - 161 - 0xA1
• 10101100 - 172 - 0xAC

It seems that with the 600 series Roomba have changed the Home Base IR codes (compared to the Roomba 400 series). While the left and right IR LEDs seem to be synchronised so that when you see both their individual signals 0xA1 and 0xA4 overlap to register as 0xAC, I wasn't able to get them to blend with the "Force Field" LED as well - maybe my sensor is at the wrong height?

Sent by

Dec  

Hex

Binary

Meaning

Roomba 500/600
Drive-on charger/Home Base

161

0xA1

1010 0001

Force Field

164

0xA4

1010 1000

Green Buoy (meaning Starboard, or Right)

168

0xA8

1010 0100

Red Buoy (meaning Port, or Left)

172

0xAC

1010 1100

Middle / Red Buoy & Green Buoy

Roomba 500 Virtual Wall

162

0xA2

1010 0010

Virtual Wall

The first four bits match João Figueiredo's Roomba Virtual Wall (1010 0010, or 162 decimal, 0xA2 in hex), which seems to hint at a new scheme. Curious.

Update - More official documentation

I've now found the iRobot Roomba 500 Open Interface Specification online (alternative link), which confirms these codes - and indicated I should be able to get a blend of the three IR LEDs.

See also the next blog post, where I could control the Roomba with a Raspberry Pi and an IR LED.