By now you may have noticed the videos and projects involving a robot made from a power chair.

This is the latest video. The PC board CHI series from picAxe is modified to support a Sonar SRF-08 which requires the SPI bus.

You can see from these tests, this is a remarkable ping unit. It should be. It costs 60 bucks or so! But it is smart and provides values directly into a register on chip. That allows you to allow the sensor to constantly run (samples every 65ms) while you do a "check value B-4 going forward" in a very fast processor loop to give smooth controls.

The video shows testing a single sonar shifted to one side or the other. Now the robot should follow the wall like the previous tests with this setup using IR.

You get to drill a hole in the back panel where the wires run out of the control unit.

Make sure you put the drill on an angle. I used 1/8 in drill. Make it small as you can. You just want four #24 gauge wires for power (which is very small) and control Forward Backward and Left Right, these are signal wires.

See how you feed the four wires through the new hole you drilled through the back of the joystick/controller.

Here are the connection points to the controller shown close-up so you can wire the cables between the picAxe control board and the SRF device.

Here are the things that will need changing on the board to allow the addition of the SCI stuff for the SRF-08.

These are the basic parts hooked up. Here is the software listing for the unit described and operating as in the video.

I wouldn`t release it as a product, and I believe the next rev is going to do more things better, we hope. This listing is for you to get started. It will, as shown, right wall-follow and do object avoidance, just like you`d get in a weekend project where you built a mouse-bot, or equivalent simple device. AND, it is a lot of fun.

And, you can already see the sneak preview of what is in the works, putting the rf remote, the IR remote together so you can choose between r/c, autonomous, even semi-autonomous combinations.

Next step - We go further...

; *******************************
; ***** Power Chair Robot *****
; *******************************
; Filename: using18m2.bas
; Date: 03/09/12
; File Version: 2.x
;
; Written by: Jim H
; Function: using nav and drive ctl
; Last Revision: 1
` ------------------------------------------------------------
` Compiler Directives
#picaxe 18m2
` ------------------------------------------------------------
`--------------------------------------------------
` PicAxe 18M2 pin diagram
`==================================================
`(DAC / Touch / ADC / Out / In) C.2 leg 1
`(SRQ / Out) Serial Out / C.3 leg 2
`(In) / Serial In / C.4 leg 3
`(In) old reset is now signal C.5 leg 4
`---------------------------------------
`(gnd) 0v leg 5
`---------------------------------------
`(SRI / Out / In) B.0 leg 6
`(i2c sda /Touch /ADC /Out /In) B.1 leg 7
`(hserin /Touch /ADC /Out / In) B.2 leg 8
`(pwm / Touch / ADC / Out / In) B.3 leg 9
`=======================================
`---- package bottom -- direction up ----------
`=======================================
`(i2c scl / Touch / ADC / Out / In) B.4 leg 10
`(hserout / Touch / ADC / Out / In) B.5 leg 11
`(pwm / Touch / ADC / Out / In) B.6 leg 12
`(Touch / ADC / Out / In) B.7 leg 13
`---------------------------------------
`(vcc) +v leg 14
`---------------------------------------
`(Out / In) C.6 leg 15
`(Out / In) C.7 leg 16
`(Touch / ADC / Out / In) C.0 leg 17
`(Touch / ADC / Out / In) C.1 leg 18
`
`===================================================

`--------------------------------------------------------------

#rem
1. Make it look when turning, only "Far Enough"
2. Look without drive for tuning the algorithm flag on/off
3.
#endrem

` set motor drivers to known position
` turn all motor enables OFF
symbol in3 = b.7 `FWD/BKWD
symbol en34 = b.2

symbol in1 = b.5 `L/R
symbol en12 = b.3

symbol i2csda = B.1
symbol i2cscl = B.4

symbol runFlag = b6
symbol SRF08SftwRev = b0
symbol LightSens = b2
symbol Range = w2


symbol minAmnt = 25
symbol maxAmnt = 35

` stop everything
low en34,in3,en12,in1, runFlag

` Define i2c slave address for the SRF08
hi2csetup i2cmaster,%11100000,i2cfast,i2cbyte

hangTime: `wait to push button to start this thing going
if pinC.5 = 1 then
goto hangTime
else
goto main
end if


main:
`inline checks of robot condition
`stop, analyze, react appropriately
`make this check so fast it is a blur
`monitor the pb, then start the mover forward until strategy

hi2cout 1,(0) ` cut analog gain to 200 ish
hi2cout 0,(80) ` Send Ranging command to get range in in
pause 100 ` Wait for ranging to complete
`hi2cin 0,(SRF08SftwRev) ` Read SRF08 Software Revision in b0
hi2cin 1,(LightSens) ` Read the Light Sensor into b2
hi2cin 2,(b5, b4) ` Read the Range, Note b5-b4 are w2 high-low bytes

hi2cin 2,(b5, b4) ` Read the Range, Note b5-b4 are w2 high-low bytes

if Range <= minAmnt then
high b.0
gosub stopFB
gosub stopTurn
pause 200
gosub moveBackward
pause 600
gosub stopFB
gosub turnLeft
pause 700
gosub stopTurn
else low b.0
end if


if Range > minAmnt AND Range < maxAmnt then
high b.0
gosub turnLeft
pause 350
gosub stopTurn
else low b.0
end if

gosub moveForward
pause 200

goto main



moveForward:
high in3
high en34
pause 10
return

moveBackward:
low in3
high en34
pause 10
return

stopFB: ` stop forward/backward motion
low en34 `drive off
pause 10
return

turnRight:
high in1
high en12
pause 10
return

turnLeft:
low in1
high en12
pause 10
return

stopTurn: ` stop right/left motion
low en12 `drive off
pause 10
return