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Built a digital sync and you can, too! After reading this forum about installing an aftermarket TCI and in other places about easy to use microprocessing platforms, it occurred to me that one might be able to use multiple MAP sensors to set the carb sync on a bike. I'm no expert on either motorcycles or electronics, so it had to be easy if I was going to do it. And it was easy. The hardest thing for me was figuring out what certain connectors are called and then finding a reasonable source. Point your search engine at “arduino” or go directly to this link: www.arduino.cc to get an idea for the microprocessing end of this. I used the Arduino Uno R3. You can use any, but you'll have to modify my program or write your own. In particular, if you use the kind of LCD display connection I did (IIC) it interferes with two of the ports on the board. On the Uno it's analog 4 and 5, leaving a nice grouping of 0-3 for my 4 sensors to connect. My end goal is to remove the LCD and use a wireless smartphone as the display. When I get that working then this thing could do a 6 carb bike. Goldwing heaven! (On the Leonardo board it's digital 2 and 3.) Here's the parts list. I'll edit this post to improve accuracy as I can. The hard parts (for me): MAP sensors. I found 6 old GM 1 bar MAP sensors for $40 on Ebay and was quite happy. 6 3-tower GM weather-pack housings with male connectors. Spendy with rip-off shipping. You don't really need the plastic housing. You can just solder wires to loose male connectors, and maybe use some heat shrink to tidy up. Save big $$. The rest: Arduino Uno R3. $23. Arduino IDE software (free download). Sensor shield (optional - makes connections easier). $10. LCD IIC display 4x20. $7. 4 count 3-wire board connectors with one end removed and soldered to the weather-packs. $5. 1 count 4-wire board connector to attach the LCD with the +/- polarity rewired. $2. 2 feet 1/4” hose. Cut into 6” lengths and attached to the MAPs. 10 feet 3/16” hose. 4 count ¼ to 3/16 connectors. $5. 4 count caps for the 3/16 hose. $3. The Arduino IDE includes sample programs. I modified one that keeps a running average for input smoothing to load arrays of readings for each cylinder and calculate the peak and average readings. I'm an old software guy but never something like this and never in C. But those old skills came in handy and I wasn't shy about this part. The Arduino doesn't report overflow errors at compile or run time, so I had to do a little digging to debug odd results. For example, if I set the readings array to more than 180, the LCD stopped working. What I figured out was that the sensitivity scale of the readings multiplied by the number of readings had to be less than the max integer value (32k) or it would overflow. If the array got too big the RAM would overflow. I could change to long integers or floating point math I suppose. I could change to a chip or board with more memory because there is a memory size limitation. My rainy weather project will be to go back through and clean up the code. Basically, I just hacked my way forward and didn't worry about the elegance of the code like I did when I was working in software. I didn't know how the compiler or board really worked so why worry about style. The key thing I did was code a self-calibration step. The first time through loading the reading array (with the bike not running), it takes an average of the average of all the MAPS and uses that to establish a calibration adjustment to be applied to all subsequent readings. This way all the MAP sensor circuits are normed to a constant value. It could be normed to zero, but then negative numbers would be more common. To test this live, I hooked up all 4 MAP sensors in turn to the same cylinder on a running bike to see if it would return a consistent value. It did. The nice thing is that build precision is less of a factor which is great for me. It just works with what you have for MAP sensors, wire harness and soldering skills. Assembly is just plugging the shield into the top of the Uno, then plugging in the LCD and the 4 MAP sensors. For power I plugged in a cigarette adapter into my battery maintainer plug, plugged a USB converter into that, and ran a USB cable to the Uno. There are other ways but I had all this handy. The software was already loaded; you just plug the USB into the computer running the IDE and upload. At power up it does the calibration and when you hit the reset button. Nothing to lose by trying. I hooked up 4 hoses to the bike and capped them. Then I tested #1 against all 4 sensors. It read the same, about 159 peak. Then I hooked all 4 up. The bike was in good sync, which I knew because it runs good. But I tweaked all 3 sync adjustments to get them the same. Everything ended up peaking at 158-159. Then I capped the hoses and tested #3 against all 4 sensors. All the same. After that I took it for a ride. Seemed smoother but it was running great already. The numbers don't really mean anything. They depend on how 'sensitive' the software is set. The MAP sensors run at 5v and drop the signal voltage from that as vacuum increases. The UNO board reads an analog voltage and returns a range of integer values. The rest is software. One nice thing - you can crack the throttle without worries. In fact, since you can compare manifold pressure at higher RPMs you may get some diagnostic value if you've got pin holes in a diaphragm or a sticky slide. Hopefully, some engine experts will weigh in on that notion or with better ideas. Things to consider. If you can't find cheap MAP sensors, don't bother. They should all be the same or similar, but the calibration step allows for variances. Try to get the weather-pack connectors included because you'll go broke if you have to buy a small quantity at full retail. If anyone has a better source please let me know. Late 80's GM cars in a junkyard may be a good place to start. There are also less expensive vacuum sensors available for non-automotive applications that are not as rugged. Everything you need can be bought online if you know what to call it. The board connector names still elude me. I just bought stuff until I had something that worked. I'll post the code in a subsequent post. I will be glad for suggestions. I will be especially interested in a) how to build a cool enclosure and b) thoughts about better analysis techniques. I would never post it anywhere else, because the purists would flame you. But this forum is different. Best $12 ever! Lots of pix. If there's a better way to post them I don't know it. Tom
