Arduino help and advice for projects?

[TableLeg]

I'm new to it, and in trying to learn and get help joined the Arduino forum and I have to say, I have never met such a bunch of unhelpful people in a forum

I believe there are a few members on here that know their way around Arduinos so I hope they might be able to add their wisdom to mainly very simple questions relating to small projects.

I would like to ask some questions and hope somebody can enlighten me.

My Ecu has map switching. Simple in operation the Ecu supplies a +5v supply to a switch (can be single, 2 way or 3 way), in my case the switch is 3 way. This gives me 3 different maps to switch between. The other side of the switch on the 3 connections are as follows:
1, is left unconnected therefore giving 0v
2, is connected to ground via 1k resistor and gives 2.5v
3, is connect direct to ground and gives 5v.

The Ecu software for map switching looks for between 0v and less than 1.5v for map 1, 1.5v to 3.5v for map 2 and above 3.5v for map 3.

I was looking to see if I could control the map switching with a single push button (I have written a sketch that operates 3 Led's with one push button one at a time, the theory being once proved with Led's these could be substituted for other things such as relay etc), but I have a question regarding this.
Can I use the 5v supply from the Ecu to the switch but then use the Arduino ground to complete the circuits?
Ultimately I want to use a 16x2 Lcd screen and output the options onto the screen e.g. "Map 1 - Maximum Power selected"

I've also been looking at simple Menus lately and they seem a great way to incorporate various options, some of these using a rotary encoder but at this moment my lack of coding skills means I am struggling to understand what some of the various parts of the code are doing. Until I can understand some of these I can't work out how to change the code to meet my needs.

Any tips or advice great fully received.

 

[Kit Car Electronics]

So long as you keep the Arduino ground common with the ECU ground, you can do whatever you want within the 5V range. 

Tip1: grab Electrodroid Android App- very handy for quick calcs on Ohms law for example

Tip2: be careful to stay within the current rating for the Arduino pins (20mA is safe) - for 5V that means always keeping a 270 Ohm resistor on the pin if you're unsure of what you're doing

Yes you can use the Arduino to directly ground the ECU 5V switch circuit as you suggest- it sounds like the ECU might use an internal 1K pull up, so the current would be below the pin limit. Obviously you can probe the switch voltages easily.

 

[Kit Car Electronics]

Oh, and most forums don't seem to have the polite members we have. Don't even think of mentioning cars on an electronics forum - it's a banned subject for various reasons 

[TableLeg]

1 minute ago, Kit Car Electronics said:

So long as you keep the Arduino ground common with the ECU ground, you can do whatever you want within the 5V range. 

Tip1: grab Electrodroid Android App- very handy for quick calcs on Ohms law for example

Tip2: be careful to stay within the current rating for the Arduino pins (20mA is safe) - for 5V that means always keeping a 270 Ohm resistor on the pin if you're unsure of what you're doing

Yes you can use the Arduino to directly ground the ECU 5V switch circuit as you suggest- it sounds like the ECU might use an internal 1K pull up, so the current would be below the pin limit. Obviously you can probe the switch voltages easily.

 

Many thanks Mike

You are indeed right, the Ecu has a 1k pullup resistor then a second 1k resistor on the 2.5v leg of the switch.

I already have Electrodroid on my phone and you're right it is very useful

 

[TableLeg]

My current setup is 2x 3 way rotary switches. Each map has 3 traction control settings also accessed by a 3 way switch. I'd like to have just 2 push to make buttons and utilise an arduino to have one button cycle through each map and the other to cycle through each TC setting for each map. The selections to show as text on the Lcd display.

Not impossible right? even for a noob

[Kit Car Electronics]

Sounds like a perfect project for starters. When you pick your display, also look at serial OLED graphical ones - they are very visible in daylight and easy to wire up and create pretty graphics. 

[TableLeg]

Thanks again Mike,

I have a Hitachi HD44780 I was planning to use, had it for a while. I've avoided the display shield with buttons as I want the buttons to be slightly away from the display itself on the dash.

Maybe once I get the hang of it I'll look at a nicer display