Arduino Automatic Coolant Temp Hack for Better MPG's

[TheForce]

This is the next version I'm working on for the automatic coolant temperature hack. This version is based on Bob Wilson's MSP430 micro controller hack. NHW11 Prius Temperature Hack I took Bob's code and schematic ( with his permission ) and translated it to the Arduino. I was just going to use Bob's design but I was unable to get it to work. Since I understand the Arduino code more than the MSP430 I decided to just port everything over.

What makes this different than the hardware based hack is that this hack will have both hot and cold protection. It will also keep the correct fake and start temperature no matter what the ambient temperature is since the logic is based on software and not hardware.

All the connections I'm using are pretty much the same as my previous ACTH as seen here. Automatic Coolant Temp Hack for Better MPGs

The only thing I'm using different is the voltage source. Instead of taking 5v from the ECU I'm taking the switched 12v from the 12v socket.

I started out using a resistor/cap like Bob's design to smooth out the PWM but decided to go with a digital pot. I have removed my original design and replaced it with this current one. If you read down through the thread and some things dont make since just skip to post 18. Post 18 is where I start with this current design.

Here is the schematic for this hack. This schematic can change at any time. You can use a DPDT or DPST switch. I just had a DPDT laying around and included it in the schematic.


Here it is working on the bench. The blue LED means its too cold to fake the temp.


I'm currently using an Arduino Nano on the bread board just for ease of use. When I get it fully working I will be using a regular Arduino in a Arduino project box.


Here is the source code for the Arduino. Version 0.11.03.30 The source code includes some serial output for diagnostics.
http://stuff.jaygroh.com/priuschat/acth/aacth.zip


If you have any ideas or input please feel free to post.

This design and source code is completely open source. Feel free to make modifications. If you do make any changes please post about it.

[nerfer]

When you say it doesn't "work right", what do you mean? The temperature doesn't get substituted, or the substituted temperature is too high or too low, or is substituted when it shouldn't be?

I assume the PWM controls the voltage that is read by the car as the current temperature. What units are those (I'm wondering why the cold temperature is higher than the target temp). Finally, I'm not familiar with the Arduino, how many bits is an int?

[macmaster05]

This is a very cool mod but it is just completely over my head. I have no idea what you're doing. LOL.

[TheForce]

The temperature does not stabilize which is a result of the average not stabilizing and jumping around. Its kind of hard to explain without seeing the debug output live while in the car. As if right now I don't understand why it works perfect on the bench but not in the car.

The PWM of the Arduino is 8 bit. The ADC is 10 bit. The voltage range for the temperature is we want is somewhere between 1.5v cold and .5v hot. In the Arduino the ADC is 0-5v and translates to 0-1023. Thats why the cold number is higher than the hot number. Its kind of confusing at first.

[nerfer]

Originally Posted by TheForce

The temperature does not stabilize which is a result of the average not stabilizing and jumping around. Its kind of hard to explain without seeing the debug output live while in the car. As if right now I don't understand why it works perfect on the bench but not in the car.

The PWM of the Arduino is 8 bit. The ADC is 10 bit. The voltage range for the temperature is we want is somewhere between 1.5v cold and .5v hot. In the Arduino the ADC is 0-5v and translates to 0-1023. Thats why the cold number is higher than the hot number. Its kind of confusing at first.

I looked it up, an int is two bytes, so 8 ADC values (8*1023) will fit (< 65536), I was thinking at first maybe you were losing bits off the top when summing your samples. Then I noticed you only read into ADC_value[7], which gets copied down one slot on each loop, so only after 6 times thru the averaging loop you'll be getting valid entries, but you check for that, so it's okay.

I don't see a problem in the averaging function, but you might want to print out the current ADC value and make sure it's not going over 1023. The code doesn't change between the bench and the car (I assume) and the problem is before your output, so I would bet the ADC input is different somehow.

[TheForce]

The ADC value on the bench and in the car should be the same 0-5v range. The car I dont think ever sees 5v because thats damn cold. Somehow when its in the car I think the resistor capacitor is not smoothing out the PWM like it is on the bench. I have not touched this since December so I cant really comment on what its really doing.

I'll start working on this as soon as I can sit in the car and debug with out freezing.

[PhazonPhobe]

Da huh?

[seilerts]

Originally Posted by TheForce

The only thing I'm using different is the voltage source. Instead of taking 5v from the ECU I'm taking the switched 12v from the 12v socket.

I wonder if putting an LM317 between the Arduino and the car 12V would help. The car 12V is not stable, especially at startup.

Cool project, thanks for the info.

[nerfer]

Originally Posted by macmaster05

This is a very cool mod but it is just completely over my head. I have no idea what you're doing. LOL.

I only knew what the purpose was because I had read some of the previous threads on this before. Follow the links in the first post for more info, but basically you're fooling the car into thinking it can go into stage 3 (and thus glide) before the engine fully warms to 157'F.

[TheForce]

Voltage should not be an issue. The Arduino has its own voltage regulator built into the board.