# Tweaking the Open ReVolt Controller



## EVfun (Mar 14, 2010)

0 volts is full throttle... is that a good idea? Zero volts can be the failure caused by a broken wire.


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## Bottomfeeder (Jun 13, 2008)

Good point. I could move the pull-up resistor so a broken wire will default to 5V not 0V. In fact, it may be easier to move the 5V being sent to the throttle to a ground, so that I wouldn't have to change the code at all...

Thanks for the idea EVfun...

-D


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## jackbauer (Jan 12, 2008)

You will need to change the code. The reason is that the revolt throttle input pin on the micro expects a floating throttle signal. It interprets 0v or 5v as a fault to prevent against shorted or open circuit throttle cables. 

I'm running a BMW E46 hall effect pedal in my E36. I had to make some mods to the hardware and paul holmes did a custom software build that allows any hall type throttle to work with the controller. It has a programmable fault zone also. My pedal outputs 0.7v at zero and 4.5v at full throttle. Here is a rather crappy video of the installation:
http://www.youtube.com/watch?v=XrigNHzXuEU

I have the details somewhere. I also went through some of the steps in this video:
http://www.youtube.com/watch?v=xA6hDvAcjgQ

Shoot me a pm with your email and i'll send you the custom code. Be aware its setup for 8khz so i'd ask paul to compile a 16khz version more suited to your mosfet power stage.


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## Bottomfeeder (Jun 13, 2008)

You're right, Jack. It's not as easy as I had hoped (it rarely is).

The schematic of the Throttle looks like this:


```
5v           Throttle Pot
        |     2k        0-5k
        ---\/\/\/\----\/\/\/\    Node1       4.7k     Node2
                          ^--------0-------\/\/\/\/-----0------ Pin23
                                   |                    |
                                   Z                    |
                        Resistor   Z 4.7kΩ              = .1µF
                                   Z                    |
                                   |                   Gnd
                                  Gnd
```
My EE skills are a bit rusty, but the since the input Pin has high impedance, I'm ignoring the second 4.7k resistor and .1µF cap, which are really just acting as a low pass filter.

At Node1 the voltage at no throttle (0Ω on the throttle pot) is 5v*4.7k/(4.7k+2k) = 3.51V

The Node1 voltage at full throttle (5kΩ on the throttle pot) is 5v*4.7k/(4.7k+2k+5k) = 2.0V

That's not what I had expected at all.

I'll be replacing the throttle pot and likely the 2k resistor with a 0-5V voltage source. I can change the offset and gain to be a different value.

I'm going to ask Paul to see if he can help with the code change.

Thanks for all help.


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