Topic: gauge face restoration, the HARD way!

[bistromath]

One of the things that really needed attention on my 550 was the tach: the face was cracked and faded, and it looked pretty beat up. I kept looking for reproduction gauge decals, but all the ones I found were goofy-looking "Cafe"-style, or really didn't look stock enough for me. So I got a screen printing kit and did it all myself. The green and red are color-matched spray paint, and the white is Jacquard screen printing ink. It was way too much work to consider doing again, but it sure looks sharp.

And, well, while I was in there, the guts of the tach were aging, and they weren't exactly accurate in 1975 when it was made, either. Plus, with all the time and money I have into my motor rebuild, I want to know something besides "Oil pressure" or "No oil pressure". So I figured I'd replace it with a more modern design and add some sensors. It's a custom printed circuit board of my own design, built around an ST ARM Cortex-M3 microcontroller and a snazzy OLED display. The needle is driven by the stepper motor from a Ford Mustang. It also measures oil pressure and cylinder head temperature. The oil pressure comes from a VDO 360009 gauge, and the CHT comes from a Westberg thermocouple which sits under the #3 spark plug.



I mean, why not? If you're going to do something, you might as well go all-out. No sense half-assing it.

If others are interested in doing something like this, I'd consider putting kits together. It wouldn't be cheap, but you could have the only CB on the block with an electronic tach. 

[johnyvilla]

That, is flippin slick.

[HondaDano]

That, is flippin slick.

+1!!! Thats freakin incredible

[Terry in Australia]

Very nice mate. The digits on the gauge face look a bit fuzzy though? Cheers, Terry.

[GammaFlat]

Very nice mate. The digits on the gauge face look a bit fuzzy though? Cheers, Terry.

Nope.  You and I both have a shrinking ever darkening world - we're getting old   Sorry Terry   

[mystic_1]

Holy crap!    Niiiice!

mystic_1

[bistromath]

Very nice mate. The digits on the gauge face look a bit fuzzy though? Cheers, Terry.

Well, it ain't perfect. But once I wet sand it down, and attack it with a small paintbrush, it ought to be close. 

[Kframe]

Wow, very impressive! 
It's really cool when people upgrade componentry while maintaining classic stock looks.
Good job!
-K

[campbmic]

Try backing off the idle screw a tad on your PC 

[ev0lve]

That, is flippin slick.

Yes, it is impressively flippin slick  You flippin flip!






More please...

[BobbyR]

Great work and extremely clever idea.

[MaaseyRacer]

Awesome mod.  I might be interested in a kit.  Now is there anyway to get a speedometer in there as well?

[cb350twin]

Awesome! I almost don't believe it. But I do Very neat!

[Hondell]

Nice work Bistro. Nice to see some advanced electronics on an old bike. Here's my LCD readout I  designed around a 16F876 pic micro. I needed Kilos per hour so decided to add more features. A hall effect gear counter counts spokes for the speed indicator. The oil temp toggles every 15 sec. and displays ambient air temp also. Voltage and a real time clock round out the display. In true junkbox designing, an LCD off an old Nortel phone is used. I origionally used a PLED display but it washed out in bright sunlight.

[Laminar]

Looks fantastic. Question - how quickly can the stepper motor move? I've only played with stuff like that a little bit but I'm pretty sure the servo I have couldn't move as quickly as the RPMs would when free-revving or in first gear. Any problems there?

[Bodi]

Very very few tachs will accurately track a free revved engine.
Pre-electronics, race engines used "chronometric" tachs, super accurate but not at all good at tracking changes: they counted revs for about half a second then the needle quickly moved to display the result. Somehow that was good enough for grand prix cars and bikes... so maybe tracking instantaneous RPM isn't vital?

[westondc]

Great work, that is just too cool for school! the like the electronic readout, you really know your sh*$!

[Laminar]

Alright, a couple more questions-
- I'm assuming you're getting your tach signal off of the coils, right? What are you doing to that signal to make it usable in your circuit?
- Did you plug the tach cable hole in the valve cover?

Theoretically, adding a speedometer would be really easy - use a bicycle speed sensor on the rear wheel, send that signal to the microcontroller, output the speed value to the display. eBay has 128x64 OLED displays for under $10. If you didn't want to go the route of making your own circuit board, I'm sure an Arduino or one of its stripped-down cousins would do great.

[bistromath]

Tach signal comes off the coil primary. I'm just using it to switch a transistor to ground through a large resistor, gives a real clean signal that's resistant to voltage spikes. Zener diode on it just in case. The tach cover is currently awaiting a plug. 

As far as tracking a free-revving engine, I don't know a tach that will, but the pointer on my tach definitely moves at least as fast as stock -- up to 720 degrees per second.

Arduino would definitely be the way to go if you're starting from scratch. I do this stuff for a living, so I had kit laying around as well as software.

[Laminar]

Awesome - more questions.

How did you route the signal wire from the thermocouple? Is this a two wire self-powered thermocouple? According to this document the self-powered thermo couples have the potential for a significant error depending on the outside temperature. That could pretty easily be solved by an ambient temperature sensor, though.

Any more info on the stepper motor? I found one on Sparkfun, but it doesn't mention its range (the last servo I got has a 180 degree range, so it wouldn't be suitable for a tach) and it mentions 1.8 degree steps. If your tach covers 12,000 rpm over 270 degrees, each step would be about 80rpm, or about 12 steps for each 1000rpm segment on the tach.

Any ideas what you have? Any reason you chose a stepper over a servo?

[bistromath]

It's a type J thermocouple. As with any thermocouple you have to correct for the temperature at the connector, since thermocouples only give a temperature reading proportional to the difference in temperature between their two ends. So I do use an ambient temp sensor (a thermistor, actually) to determine that error.

The stepper I used is a Swatch X25.591, for use in a Ford Mustang. X25 is the family, 591 is the options. I used a stepper because it's what everyone uses for pointers, and because you'd be hard pressed to find a servo with the range necessary to swing the 250 degree sweep that the tach uses.

[Laminar]

Thanks for the info. BTW, here's a servo with 360 degree rotation.

[bistromath]

Right, but it doesn't include position feedback, it just controls velocity. So you'd have to integrate velocity to get position, which incurs drift over time. Without using a Hall sensor or another rotary encoder, you wouldn't be able to control the pointer for long periods of time.

[Laminar]

Right, but it doesn't include position feedback, it just controls velocity. So you'd have to integrate velocity to get position, which incurs drift over time. Without using a Hall sensor or another rotary encoder, you wouldn't be able to control the pointer for long periods of time.

Gotcha. I didn't realize that by "continuous rotation" you no longer control position but speed instead.

So now that you are reliably counting RPMs, how hard would it be to wire in a relay to ground the coils once you hit a certain RPM - a spark-cut rev limiter?

[bistromath]

It'd be really easy. I thought about doing it, and decided I'd start slow. One thing at a time. =)