09-01-2020, 09:27 PM
All that information is overwhelming to say the least! But it's really helpful. It seems that if I want to make something that works I would need a scope. I looked up some boat anchors 
as you call them on the local websites where people sell their stuff, but they seem to be asking over $200 for some old Russian scopes that have a screen the same size as a calculator's.
Then I found some guy selling these Chinese scopes for a very decent price:
https://www.aliexpress.com/item/32878694...web201603_
They are rated for 200Khz but he says in his listing that for sine wave they seem to be around 100Khz max. It doesn't hurt to try, so I might get one of them.
You gave me way too many tips, almost feels like cheating!
So first order of business is, make the needle move. I seem to have lost the arduino sketch that I wrote to generate the frequencies, so I'll try to write up a new one, and hopefully test it with a scope to make sure it works!
I am kind of familiar with interrupts, since I tried to build an arduino rev limiter a while back which used the time between 2 interrupts to calculate the RPM at any given time. I did it on my MK2 golf which had an RPM output pin on the coil itself which was about 7v so I used a resistor divider and it worked fine.
The J18 ECU has an RPM output pin, I guess it doesn't hurt testing it with a scope to see the frequency at a given engine speed. I might use that as an input to the circuit.
So, make the needle move, then make the arduino count the rpm correct, then make the arduino drive the tach correctly. I better get to work! Thank you so much for the help so far, but I'm afraid I might need some more. I'll keep you updated!
as you call them on the local websites where people sell their stuff, but they seem to be asking over $200 for some old Russian scopes that have a screen the same size as a calculator's. Then I found some guy selling these Chinese scopes for a very decent price:
https://www.aliexpress.com/item/32878694...web201603_
They are rated for 200Khz but he says in his listing that for sine wave they seem to be around 100Khz max. It doesn't hurt to try, so I might get one of them.
You gave me way too many tips, almost feels like cheating!
So first order of business is, make the needle move. I seem to have lost the arduino sketch that I wrote to generate the frequencies, so I'll try to write up a new one, and hopefully test it with a scope to make sure it works!
I am kind of familiar with interrupts, since I tried to build an arduino rev limiter a while back which used the time between 2 interrupts to calculate the RPM at any given time. I did it on my MK2 golf which had an RPM output pin on the coil itself which was about 7v so I used a resistor divider and it worked fine.
The J18 ECU has an RPM output pin, I guess it doesn't hurt testing it with a scope to see the frequency at a given engine speed. I might use that as an input to the circuit.
So, make the needle move, then make the arduino count the rpm correct, then make the arduino drive the tach correctly. I better get to work! Thank you so much for the help so far, but I'm afraid I might need some more. I'll keep you updated!