To do the simplest smart TRE you only have to put a 6.8kOms resistor anywhere on the pink wire
that goes from the GPS to the ECU, as the example shown on the fisrt attached picture.
- full benefits of the "classic" TRE and "smart" TRE
- no impact on the neutral map (no cold start problems)
- no intrusion on any other circuit (such as neutral light circuit)
- cheap and easy
- i don't see any...
if you want to know "how and why", please read my original post just below.
Below the original post, you may also read the "additional informations" which were gathered during the thread life (thanks to all participants)
ORIGINAL POST :
First of all, moderators may merge my post into the TRE thread if it is more appropriate. I thought this post deserved to be highlighted but i may be wrong.
And i'm sorry if this circuit has already been proposed on the board or somewhere else on the web but i definitly could'nt find it.
It is still on road testing stage but i think i found the simplest way to make a Smart TRE :
simply connecting a 6.8 KO resistor in series anywhere on the GPS pink wire
(as shown on the first attached diagram).
Here is the way i found this :
The GPS-ECU stock circuit is a voltage divisor circuit (not sure of the english name of it...) as shown on this page which everyone probably knows already : http://wotid.com/tls/content/view/17/47/
According to this, there is a small formula that allows to calculate the voltage drop depending on initial voltage (usualy arround 5VDC), internal ECU resistor (1KO) and external resistor (GPS resistors) :
Ve = Vi * (R2 / (R1 + R2))
where Ve is the voltage detected by the ECU (= pink wire voltage)
Vi is the initial voltage (= to pink wire voltage when bike is in neutral)
R1 is the internal 1KO resistor
R2 is the variable GPS resistor
On the attached sheet you can see the calculed voltages with Vi=5.26 VDC (which was mesured on my bike) for the stock circuit and also with the 6.8 kO resistor added : with the 6.8 kO res, all voltages are higher than the 5th gear stock voltage which means the ECU would always "think" it is at least in 5th gear even when the bike is in lower gears.
I've also tested most of these voltages with digital multimeter on my bike and they appeared to be almost exaclty the same as the calculated ones.
My only concern was the 6xt gear : what would "think" the ECU with 21.8 kO res and 5.03 VDC ? to get the answer, i connected a 21.8 kO res (15+6.8) in paralel between the pink and the black wire and did the idle clutch in/out test. The result was i clearly felt the revs difference between clutch in and clutch out, exactly as for the basic TRE with 15 kO resistor (which i also tested to make sure the ECU behavior was the same). That result means the ECU is still "thinking" it is in 6xt gear even with 21.8 kO res.
ADDITIONAL INFORMATIONS :
The resistor i used is a 6.8 kO, 1/4 W, 5%.
I used it because it's a standard resistor value, cheap and very easy to find here.
As mentioned by Trojan, you may find a pack of 100 for 1 USD on Ebay :
But if it's not a standard resistor value for you local dealer, you may use a resistor with different wattage characteristics or different %. These characteristics should not have any impact on the setup.
The thing to take care of is the Ohm value. But, as truly mentioned by Prophet, there is a range of value that works for this TRE setup : you may use a resistor value between 6.2 kO and 6.8kO
. This is a conservative range in which you will be 100% sure the setup will work.
As mentioned by several members, you may also combine different resistors to get the correct value within the range (such as two 3.3 kO resistors to get 6.6 kO for example).
Below the 6.2 kO value, the risk is that the TRE won't be efficent on fisrt gear (and maybe on second gear also).
Above 6.8 kO, here is my answer to Youngleadfoot who asked about using a higher value :
would there be aproblem using a higher rated resistor? Kcar said that he had none even though in sixth gear he makes more than the necesary resistance. if there is no downside you could use any resistor over 6.8kohms.
Yes, there may be a problem using a higher resistance. At a certain resistance threshold the ECU could "think" you're in neutral instead of sixt gear. And the neutral map is clearly not the one to ride with.
That's why i did a practical test in sixt gear with clutch in and out to make sure it doesn't switch to neutral map.