DIY Mares InfraRed Cable for AirLab/M1/Dacor Darwin -- Works!

[PanamaMike]

I successfully made my own IR cable for Mares infra red
dive computers. I used the information at www.ektm.de
and www.cardew.org/edward on this. I made one with yet
more generic parts than they used. I've got a documentation
package that include a schematic(that simulates in the free
circuit simulator LTspice), a layout for perf board as it
uses no surface mount devices, some photos, and some
information on the communications protocol used. The zip
file is 372K. Is there a place here at Scubaboard that
I can share this with? Below is the ReadMe.txt file from
the .zip file

Regards,

--Mike


This is the documentation for a DIY infrared interface cable for use the
Mares dive computers that use IR instead of wire connection. The design
is based in part on information obtained from http://www.ektm.de and
http://www.cardew.org/edward. Inasmuch as some of that is copylefted,
that would impact this design. I have no interest in any copyright of
this material. I only claim that I wrote it, build it and it works. I'm
posting it because someone else might find it useful or interesting.

I didn't follow those designs mentioned above exactly because they used
parts that I would have had to have mail ordered and are increasing
difficult to obtain in through-hole versions. For example, instead of
using high voltage CMOS for the transmitter logic, I used a couple of
cross-coupled 2N3904's which also eliminated a crystal oscillator.

The IR xmit and receive diodes were taken from a piece of defunct consumer
audio equipment. I think the most critical part of the design is to use
a receiver diode that doesn't have too much capacitance. The one I found
has 1nF which is a lot but still works.

The schematic and layout are drawn in LTspice/SwitcherCAD III, an unlimited,
free high performance SPICE program that you can get from Linear's home
page, http://www.linear.com. Put all of the files in the same directory
to be able to view the layout in LTspice.

Distribution File Contents
Application.jpg A photo using the cable with an AirLab
DesignNotes.txt Design notes
IRD.asy A symbol used in Layout.asc
LGcap.asy A symbol used in Layout.asc
LT1018dip.asy A symbol used in Layout.asc
Layout.asc A layout that you can simulate
Photo.jpg A photo graph of the circuit
RN55.asy A symbol used in Layout.asc
RN55upright.asy A symbol used in Layout.asc
ReadMe.txt This file
SMcap.asy A symbol used in Layout.asc
SMdiode.asy A symbol used in Layout.asc
Schematic.asc An LTspice schematic file that simulates.
Schematic.wmf An Windows Meta File image of the schematic
TO92.asy A symbol used in Layout.asc
coaxCap.asy A symbol used in Layout.asc
header9.asy A symbol used in Layout.asc

 

[allegfede]

You could use rapidshare.de to upload the files it's free and rapid for little zips

Federico

 

[PanamaMike]

Federico,

> You could use rapidshare.de to upload the
> files. It's free and rapid for little zips

Thanks, I might do that. Right now you can
get my release package from the Download
section of http://www.ektm.de, but I believe
you have to register there to get the files.

Regards,

--Mike

 

[PanamaMike]

Federico,

> You could use rapidshare.de to upload the
> files. It's free and rapid for little zips

Thanks, I might do that. Right now you can
get my release package from the Download
section of http://www.ektm.de, but I believe
you have to register there to get the files.

Regards,

--Mike

I did a redesign of this cable(version 2) and it is now documented
at a Yahoo users' group dedicated to my local diving(Monterey, CA).
http://groups.yahoo.com/group/ba_diving/files/DIYmaresIRcableVer2.zip
I don't know if you have to join the group to download files or not.

Regards,

--Mike

 

[Waterskier1]

Mike,

Thank you for the work done. I have been looking for something like this. I looked at the ektm.de site when I first got my Mares M2 computer. I didn't do sufficient research to find that the Mares iris didn't follow generic protocol. I bought an inexpensive USB IRAD, but never could get it to work with any ir devices. I thought I could "talk" to the builting in ir in my Garmin iQue (Plam-type PDA/GPS) or my notebook computer directly. I found that isn't true.

Can you provide me with any more details on the IT diodes? I plan to purchase most, if not all the parts for this. Also, what is the difference between the Cstray and the Layout drawings? They look similiar. Do you have any other tricks or hints or advise in construction? I don't plan on canabalizing anything, so most everything will be purchased specifically for this project. Do you have any recommended sources?

Thanks,

-Rick

 

[PanamaMike]

Rick,

> Thank you for the work done. I have been looking
> for something like this.

I'm glad someone appreciates that I did this. It
was all such an old ball thing to do for SCUBA.
Now I'm glad I documented and posted the info.

> I didn't do sufficient research to find that the
> Mares iris didn't follow generic protocol.

Yeah, it is a simple but odd protocol. Most IR
communication(like TV remote controls) use a
protocol that allows an effective AGC circuit no
matter what binary data is sent, i.e., there's just
as many blips for a '0' as a '1'. But the Mares
encoding scheme just keys an oscillator with the
bits out of a UART. The only reason it works at
all is that it only sends the characters 0-9, A-F
and '<''>' which have enough 0's and 1's in them
to keep the AGC happy.

> Can you provide me with any more details on
> the IT diodes?

I used an unmarked diode from a TV remote control,
but any IR emitter diode should work. A PIN photo
diode receiver is sensitive to a very broad band
of light waves. Their bandwidth is determined by
the plastic package which at best filters out most
visible light but isn't selective within the
infrared band.

> Also, what is the difference between the Cstray
> and the Layout drawings? They look similar.

The difference is that the Cstray version includes
a 200 femtoFarad capacitance between the Transmit
and receive sides for the simulation. This is a
not a component soldered in but just a result of
them being laid-out close to each other. It is
this capacitance that loops back the transmit data
to the receive side. This cable loop back is
required as part of the communication protocol.
The oscillogram shows the signal due to this
capacitance. If you don't add this stray capacitance
to the simulation, the simulations doesn't behave
like the physical circuit.

> Do you have any other tricks or hints or advise
> in construction?

I don't think layout is too critical. I put it
on perf board without a ground plane. My layout
drawings were done to make my wiring it less error
prone. Normally I only simulate circuits, this
is is the only circuit I've actually soldered
together in many years.

> I plan to purchase most, if not all the parts
> for this...I don't plan on canabalizing anything,
> so most everything will be purchased specifically
> for this project. Do you have any recommended
> sources?

I went the DIY route on this because (i) this was
for the wife's computer and I had absolutely
no domestic budget for this project, (ii) I could
find no sales information that the Mares IR cable
that is sold worked with the AirLab and (iii) it
looked like it would be an interesting little
circuit to try. Frankly, if I had to buy the parts,
I would be better off just buying the cable from
from, e.g., Scubatoys for $99(before the ScubaBoard
discount). The only part I had to procure was the
IR receiver, a Vishay PIN photo diode that they
graciously gave and shipped to me as a free sample.
I just filled out the form on their web page. BTW,
Mares now has the more desirable USB cable but I
don't know what that costs and I've not seen it for
sale in the US. However, you're right, the parts
are all pretty cheap, a few cents a piece even in
quantity 1 except for the 50¢ diodes. Usual low
volume distributors are DigiKey, Mouser, and Jameco.
So if you like playing with circuits, it is a fun
little thing to get running. I spent more time on
the design then building it, so you might not have
the vanishing small per hour pay back that I got on
this then I got. In any case, where you buy or build
the cable the little software program in the release
package I posted is worth its weight in gold in
debugging how sensitive a cable is to positioning.

Let me know if there's any other help I can give
you on it.

--Mike

 

[linuxbaba]

I did a redesign of this cable(version 2) and it is now documented
at a Yahoo users' group dedicated to my local diving(Monterey, CA).
http://groups.yahoo.com/group/ba_diving/files/DIYmaresIRcableVer2.zip
I don't know if you have to join the group to download files or not.

Regards,

--Mike

May I know how to join your group. I click many many time on the link but still cannot get it.

 

[scubatoys]

If you want to email it to me, I'll post it up on the ScubaToys site - then people could get it from there.

 

[PanamaMike]

If you want to email it to me, I'll post it up on the ScubaToys site - then people could get it from there.

Very well, it should be now in your larry@... address. Hope that was the
right one to use.

Regards,

--Mike

 

[linuxbaba]

Very well, it should be now in your larry@... address. Hope that was the
right one to use.

Regards,

--Mike

Hi PanamaMike,

Where is larry@... address. I would like to get this DIYmaresIRcableVer2.zip for study.
I cannot get the Yahoo Web Access wrok.
Or, If you have another location to let us download it. That is great.
Please help.