I've decided to have a go at PIC Microprocessor programming, and after having a drive in a friends RX-8, I liked the idea of the gear shift reminder beep.

Great idea I thought and started doing some digging, initially looking at using a frequency to voltage converter. Then I found a thread where by someone was going to use a microprocessor to correct the Speedo after changing the car's gearing (I think). Now that idea I like, I haven

 

It depends on where you pull the signal from, I suppose. Don't quote me on this, but it should be 1 pulse per every other revolution if you pull it from one of the coil packs, and 1 pulse per revolution if you pull it from the RPM test connector.

Let me know if you run into any problems learning the PIC and could use some pointers... I've been working with them for about 7-8 years now.

 

I'm going for pin 5 on connector 204 as per: http://www.baustnet.com/honda/mods/shift/Redline.pdf
This is listed as NEP (Engine Pulse), with the stated output voltage as 3V-6V, with reference to Ground. So in which case I may need to pull up the voltage input as 3V may be too low.

Thanks for the offer of help with the PIC. I'll probably take you up on that offer and send you whatever I create for feedback.

I still haven't decided if I'm going to use assembler or cheat a little and try and use a high level language like JAL.

 

I always use assembler, that way I know exactly what's going on.

You may want to add in an adjustable voltage divider... 6V will start deteriorating your input if you're running off of a 5V supply.

As far as the 3V level goes, it will depend on which input type you go with. A Schmitt trigger input won't work, as that requires at least 0.8Vdd (or 4V for a 5V supply). A TTL input, however, should work... it only needs 0.25Vdd + 0.8V for a high level (or 2.05V for a 5V supply).

 

I had been thinking of using the PIC16F628, using the T0CKI as the input for the tach pulse. Checking the datasheet shows that this and most of the other ports are Schmitt Triggers.

I was thinking that it may be necessary to buffer the input somehow, either using a simple transistor, feeding the base with the tach pulse, or perhaps it would be better to buffer the input via a high impedance buffer say using an CA3140 (mosfet op-amp). Going down the latter route may be a safer option since the high Z will reduce any potential impact on anything else that looks at the tach pulse.

I'm also considering taking the VTEC wire and possibly speed pulse as inputs, so extend the project further, albeit I'll start simple 1st.

 

Tach pulse signal is rpm/30, and at the wires noted in my instructions it is a 12v P-P perfect square wave signal.

My first shift beeper did use a F-V converter, worked great, but didn't have the fancy features and required a pot+guess method to set it.

It will be fun for the first 40 hours, after that, who knows. I had a professional micro-controller programmer help me with the code for the Redline module. Good thing he's a life-long friend or I'd still be in debt for the software.

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12V P-P - Hmm, that's good to know as that's not what the ESM says that pin should be outputting (3v-6v). Got my scope now, but probe is missing, so new one on order so I can take some readings.

Any chance you want to share more information like what's:
a) Output on speed pulse wire?
b) Output on VTEC engaged wire? (think this might be covered on your website, I'll check later).
c) Are you willing to share any informaiton on how you buffered the input, simple resistor voltage divider, a transitor, or a op-amp buffer?

If you don't ask you don't get

From my reading so far, creating the intial shift alert shouldn't be too complicated since it's basically a PIC frequency counter of which there are reference designs available.

Turning it into a data logger with lots of wizzy advanced features is gonna take a while longer (if ever). I view this project as a means of learning PIC programming if nothing else.