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And the homebrew PICAXE TCU project reawakens

robertbarr

robertbarr

Forum Sage
TGSR Superstar
Past Bard Award Winner
picaxe%20tcu.JPG


It's all soldered up on a perfboard about 2.5" x 4". There's a nice little project box that it fits into with no room to spare.

The project was delayed by the phenomenon known as 'decent weather'. Since we had a rather chilly weekend last week, I was able to put some time into it. The underside is something of a rat's nest of slender wires going here and there -- quite a mess, considering the total component count is 14 items. (There are three linear regulators -- the L7805's -- because the incoming signals from the bar control left & right are 12v, and would kill the PICAXE otherwise... I couldn't think of a dependable way around this. )

After a boatload of soldering, it was pretty satisfying to hook it up and have it work exactly as it was designed, right off the bat. To test the self-cancel, I still had to use a separate breadboarded PICAXE to simulate the pulses I'll get from the reed switch in the speedo.

After fighting for most of the project with a garbage Radio Shack soldering pencil that refused to tin, I broke down and bought a new Weller soldering station -- once I was about 90% finished. The new pencil is a dream to use, especially compared to the RS unit.

It's time to finish epoxying and squeeze this into its box with the OEM TCU's harness, so it plugs in where the original did. The second half is mostly hookup -- I'm replacing the '81-style bar control with a unit I reworked off of a '79 GS-something with self-cancels. The finishing touch will be to install a pair of super-bright LED arrays into the front signals; these will be wired to be on all the time as running lights (except, of course, when they're blinking).

The way this is set up, it's really not much of a stretch to conjure up a direct plug & play replacement for a deceased original TCU. Simpler than this unit, and certainly less money than an original -- provided you can even find one that's likely to work properly.
 
nice work mr. barr! now chef me up a replacement board for my electronic tach, willya?

greg
 
Robert,

Tell me about Picaxe.
I have some familiarity with op amps and with 7400 DIP (although that was 30 years ago).

Dave

.
 
Redman said:
Robert,

Tell me about Picaxe.
I have some familiarity with op amps and with 7400 DIP (although that was 30 years ago).

Dave

.
Click to expand...

Well, I could just show you:

The PIC is a microcontroller, the kind of gadget that operates your microwave oven or the like. A simple, dedicated computer. The PICAXE is a self-contained system on a single IC -- it includes the OS and storage, as well as analog-to-digital converters and so forth. All for a few dollars.

They are used (at least in the UK, and probably elsewhere) in elementary schools as teaching aids. They're simple enough that schoolkids can assemble and program microcontroller projects. They're not terribly versatile, and for my needs they really lack timing capabilities within their programming language, but they're beautifully simple and somewhat addictive.

There are many similar microcontroller systems out there. PICAXE is just one of a slew of them; support varies greatly, as do costs and add-on goodies.
 
Robert,

Thanks for the info and the link.
Thanks fro bringing me up to date on something I probably already should have known. SO was I 5 years out of date? 10? 15?

Thanks again,
Dave

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Dogma said:
Nice work! Time to break out the Eagle CAD and get some PCB's made for kits, right?
Click to expand...

That would be a fun but expensive wintertime effort, no doubt. I'm sure we could shrink its size by half, and save the wear on my eyesight by about 90%. The circuit is really shamefully simple.

I doubt I'd take it that far, but it sure would be satisfying to look at... someday. Hmm, a roll-your-own auto-cancel kit... not 100% out of the question.
 
Well, I was sorta hoping. I plan to replace all my indicator lamps with the LED towers Cliff found, and I'd rather not have to add resistors to the circuit to get the flasher to work. I could buy a new flasher, but those down't work with the auto-cancel, right?
 
Nice work but a question: if you needed a TCU why not just buy a good used one? The first generation TCU's are almost impossible to find in usable condition, but the second generation type that came out in 1980 are dime a dozen and reliable.
 
Dogma said:
I'd rather not have to add resistors to the circuit to get the flasher to work. I could buy a new flasher, but those don't work with the auto-cancel, right?
Click to expand...

Yes, you'd lose self-cancel. If yours works now, I'd just go with the resistors. It's not elegant, but it gets the job done simply & reliably. Easy to hide, cosmetically. Cost, of course, is overwhelmingly in favor of resistors.

In my case, my TCU is deceased and I absolutely hate the later bar control, so the PICAXE approach is a natural.

Do you have a link to the LED's you are considering?
 
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