Alright I've ordered a compatible Hitachi HD44780 LCD for the project. Now i just have to play the waiting game til it arrives...

Ill keep you updated

David

 

Wow... that took forever to get!

Well i finally got it and hooked it all up

So now i need a 4.7u to protect the pin and 3k-10k for it?

David

 

I'm ready to hook it up. Was what i posted in my last post correct?

David

 

Breaking out my drawing skills again

David

 

Why don't you try my suggested code(see below) for starters.

Hook up pin 14 (Analog 0) of your arduino to the tach wire through a 1M resistor and run a 330K resistor from that pin to ground along with a 100 pf cap.

void loop () {
 while (digitalRead(14)==HIGH) {} //spin til no tach pulse
 while (digitalRead(14)==LOW) {} //spin til 1st tach pulse begins
 unsigned long pulse1=millis(); //track time when 1st pulse begins
 while (digitalRead(14)==HIGH) {} //spin til 1st tach pulse ends
 while (digitalRead(14)==LOW) {} //spin til next tach pulse begins 
 unsigned long pulse2=millis(); 
 int rpms=30000/(pulse2-pulse1);  
 Serial.print(rpms);
}

I don't think you could hurt the arduino doing this and if your LCD is hooked up you can use that to print the rpms value. If it doesn't seem to work, just replace the guts of the loop with an analogRead of pin 0 and see what that shows.

 

once you have that working you can package it in a function call with a timeout for if the engine's not running.

 

I currently do not have a 100 pf cap. only a 100v .1uf, 50v 1.0uf and 10v 100uf.

Will any of those work?

David

 

I currently do not have a 100 pf cap. only a 100v .1uf, 50v 1.0uf and 10v 100uf.

Will any of those work?

David

I actually don't think so. The value's not critical but the electrolytic caps would be way too big. If you're in a radio shack sometime just look for a small ceramic cap. Just leave it out for now and let's try to get it working.

 

Alright.

I'm testing it out using a little over 12v.

This is what i get from the voltmeter: 4.3 and it keeps going lower and lower.

However, once hooked to the arduino analogpin 0, i get nothing on the LCD.

Here is the code:

#include <LiquidCrystal.h>
LiquidCrystal lcd(8, 11, 7, 6, 5, 4, 3);

void setup()
{
  //attachInterrupt(0, tachPulse, RISING);
  //time = millis();
}

void loop () {
 while (digitalRead(14)==HIGH) {} //spin til no tach pulse
 while (digitalRead(14)==LOW) {} //spin til 1st tach pulse begins
 unsigned long pulse1=millis(); //track time when 1st pulse begins
 while (digitalRead(14)==HIGH) {} //spin til 1st tach pulse ends
 while (digitalRead(14)==LOW) {} //spin til next tach pulse begins 
 unsigned long pulse2=millis(); 
 int rpms=30000/(pulse2-pulse1);  
 //Serial.print(rpms);
 
 lcd.clear();
    lcd.print(rpms);
}

David

 

so 12V-->1M-->*A*-->330K-->Ground.

a voltmeter at *A* should show about 3 volts and it shouldn't change. There's no capacitor - right?

 

Its about 3.52 steady and yes, without the cap.

But still nothing displays on the LCD.

David

 

looking at the code, the attachinterrupt isn't needed this time and it won't work with a steady voltage. To get a result printed you'll need to repeatedly cycle the voltage from 12v to 0 (assuming you're doing this on a workbench rather than pulugging it into the tach lead).

 

ok thanks for the pic. that's great.

is the tach wire actually going to the running engine? If so we should see something.

Assuming you've verified that you can print on the LCD and see a result. Replace the body of the loop with:

int v=analogRead(0);
LCD.print(v);

caveat: I've never used the LCD stuff.

 

Yes the lcd works just fine. I replace the code and it shows "0" on it constantly... I commented out the attachinterrupt and time = millis(); already.

the tach wire is hooked up to 12v right now for testing.

I did the 12v to 0v then back again a couple times and got -1 and sometimes 6000. 14, 30000, 144, 283, 1071, 7500, 3333, 1000, 75....

David

 

I did the 12v to 0v then back again a couple times and got -1 and sometimes 6000. 14, 30000, 144....

David

bingo - just toggling it by hand will bounce like mad and give erratic results. You could try the tach now if it's convenient.

If you want to try something else on the bench you could hook up the .1uf cap to the "tach" input or in parallel with the 330K and do a deliberate one per second make/break and you might get something more sensible. Do NOT use the big cap when you hook it up to the real car circuit.

 

for future reference though, you should be able to see a value like 600-700 or so on the analog read.

 

ok let me go out and see if i can hook it up real quick.

David

 

Im getting nothing when i hook it up to the tach

David

 

Put the v=analogRead(0); print(v); code back in the loop and hold the lead to 12V.
Do you get a reading?

 

i get 610 when hooking it up to the 12v

David