Hey all i am trying to make a tach that i can read the cars RPM's. I am only looking for the chip to see what the RPM's are and not display it out to the user.I've draw up how i think it should be hooked up but I'm still now 100% sure.
I am using the LM2907 chip and tapping into the tach wire from the ECU of the car. I'm looking at it as if the RPM's are 200+ (200,300,400,...1000, whichever) then the car is started. I would guess that any number above 50 would be considered started as 0 would indicate that the engine is not running. I'm checking because i will be remote starting the car and need to know when the stop cranking it.
Hi,
if your tack wire is already giving pulse.
Just make sure it is 0-5Volt signal and directly enter it on pin 2 or 3 and make a interrupt on raising.
you could easily make it work without the LM chips
Hi,
if your tack wire is already giving pulse.
Just make sure it is 0-5Volt signal and directly enter it on pin 2 or 3 and make a interrupt on raising.
you could easily make it work without the LM chips
I would like to use the analog input to detect this. Could i use a 4.7u capacitor between the analog pin 1 and the tach wire?
I was able to get a crude tacho hooked up using the following code and a simple voltage divider:
/*
Tachometer circuit:
Low tension from distributor >---24k-o-> input 2
|
11K
|
0v
*/
volatile int tachCount = 0;
long time;
long rpm = 0;
void setup()
{
attachInterrupt(0, tachPulse, RISING);
time = millis();
}
void loop()
{
//Runs every 1/4 second
if (millis() - time >= 250)
{
// rpm = number of interrupts counted in 250ms
// *4 to make per second
// *60 to make per minute
// /2 for 2 pulses per rotation (4 cylinder)
// /10 for some reason???
rpm = (((tachCount*4)*60)/2)/10;
//Do things with the RPM value here (update display etc)...
//
tachCount = 0;
time = millis();
}
}
void tachPulse()
{
++tachCount;
}
I'm waiting for a couple of chips (bootloaded Atmegas) to finish the project (with a nice display etc) and I haven't added prtoection to the input (zeners etc) yet.
I'm in the middle of cooking dinner but here's a link to a bit of really bad quality video I took on my phone last year of it working with just the resistors and without a zener (I didn't damage the board as I'm still using it!)