Infra red stair lift project advice please.

[john2051]

Hi, my wife and I have to use a stair lift. It is made by a company called Meditek. It can be controlled by
infra red remote controllers which are supplied. There are two buttons on them, up and down!
The buttons have to remain pressed until the lift reaches either limit. What I have in mind is a picaxe
controlled infra red device which again has two buttons, but what I want them to do is:
press button once, and lift will go up or down until it reaches the limits without having to keep the buttons pressed.
This would make it so much easier carrying things up and downstairs.
My question really concerns the IR signal itself. What would be the best way to analyse the signal to find out the
sequence?. I have access to scopes, and I have a logic analyser. Could I just use an ordinary IR diode?
I suppose I could look on a scope to see if there is a carrier signal, like the IR receiver on the axe091.
If someone could point me in the right direction, I would be very grateful, as I've never done anything before using infra red!
regards john

 

[srnet]

The buttons have to remain pressed until the lift reaches either limit

Cant you think of a reason why Meditek designed it so that someone had to be there, keeping the button pressed, for the remote to work ?

 

[MPep]

Seems crazy to me too.
Imagine, if you will, that your remote's battery goes flat half way up!

@John,
If a standard LED can be used to receive a signal, then surely an IR LED would do the same. Haven't tried it.
If you amplified it, looked on a 'scope, and looks okay, then connect to LogAn to see if it makes sense .

 

[BeanieBots]

After answering srnet's question, you will need to use an IR detector hooked up to your 'scope.
You will need to know the carrier frequency and the bit pattern for each command.
Once you have those, it's then just a question of replicating the signal with a PICAXE.
For the carrier, PWMout will very likely do what is required.
For the bit pattern, this will almost certainly need to be bit banged out.
Then just AND the two signals together into an IR LED.

 

[hippy]

A link provided previously by 'vttom' ...

http://www.ostan.cz/IR_protocol_analyzer

That worked well when I tried it. 0V and 5V to the IR receiver. and simply connect the IR receiver output to the sound card input without any pull-up.

 

[john2051]

Hi , thanks for all your info.
srnet: there are several reasons why this is so, but after speaking to meditek, they have told us that this is to incorporated inn future models.
Unfortunately these things aren't cheap, and this one is going to have to last. As for safety concerns, there are dozens of cutouts, ranging from four on the footplate, some on the
plastic cover and three on the arm rails. Its just that to carry anything that requires two hands, a tray for instance ( meal tray) needs both hands.
The whole point of this lift was that it gave us independence from having to rely on others to carry things for us. Obviously weight has to be considered.
The vertical lifts installed for some disabled people are a press and wait button.
Mpep: If I manage to implement this idea the 'remote' is fixed at either end, and could run off mains or battery backup. Thanks to Beaniebots and hippy.
I have downloaded the program from the link, and will see what I can find out. With my wife and I, it is only waist down joints that don't function due to
arthritis and spondylosis. Our hands at the moment work ok, but I do appreciate peoples safety concerns.
Thanks again john

 

[geoff07]

If the remotes are not too expensive or inaccessible there is the option of modifying a remote so that a Picaxe 'presses' the button for you. It may be that the button acts as a pull-down so a Picaxe logic level 0 would do the same. It would take a bit of research but could simplify things considerably.

 

[hippy]

after speaking to meditek, they have told us that this is to incorporated inn future models.

If you have found a contact at meditek willing to talk it may be worth simply asking what the IR protocol is.

I would expect it is a simple protocol but they may have re-purposed some other key fob controller which might have some checksumming or other complexity to it.

 

[Rick100]

I am finishing up a similar project to control a Deskpets tankbot with a picaxe 08M2 via IR . I used the IR receiver on the AXE091 board , hooked to an
arduino mega running logic analyser software to decode the bitstream . The software on the PC was OLS 9.7 with a 50 kHz sampling rate . This setup won't show the carrier frequency , so I just assumed it was 38 or 56 kilohertz . I did several captures on each IR command to make sure the data was consistant . After I had a good capture , I used the the measurement tools in OLS to get the time of each high and low in the bitstream . If you only want to play back the commands this is probably all the info you will need . The Ir protocol of the tankbot was simple and I was able to convert each command into a 6 bit value .

For play back , the bitstream for each command was recreated from the 6 bit value and stored in memory with the bptr , as a series of high and low times .The PWM was set at 38 kHz 50% . Pulsout was used for each low time of the IR signal . Pauseus was used for high times . The 08M2 has a DSM (data signal modulator) , so I used Hippy's DSM code to mix the PWM signal with the pulsout output pin . This saved a external component but you could use an AND gate as BeanieBots said . The bit stream was played back with inline code for more accurate timing . After getting the transmitter outputing to the IR led , I used the AXE091 IR receiver and logic analyser setup to examine its output . The timing for the pulsout and pauseus was adjusted until the output of the picaxe transmitter was close to the original signal . The pulsout timing was pretty close to the original low time , but the pauseus timing needed significant adjustment for the high times .

If you have a logic analyser or digital scope and the IR protocol is not to complex , you can probably make it work . Which picaxe are you planning on using ?

Good luck
Rick

 

[john2051]

Hi
Hippy; The nearest I got to speaking to an engineer at meditek, was a member of their sales team!
I did find an infra red photo diode in a moulded plastic box, with a 3.5mm lead on it. My luck, wired wrong way for sound card
ir analyser!. Adapter in progress. I did connect this to my scope, and you can see the bitstream, just a repeating sequence
as long as the buttons are held.
Next step is to try out this logic analyser (scanalogic 100).
Rick: thanks for the info, as for picaxes, I have quite a range, but I would like to use one that will just do the job hopefully an 08m2.

regards john