I'll document my progress on the InputTrigger/NissanTrigger Helper Board here.
This is my current table setup:
The chip is the AtTiny2313.
The (ugly) schematic:
(I didn't have a AtTiny2313 component for the schematic, thus the older AT902313 is pictured, but the pinlayout is the same.)
The code is [here].
It will light up the corresponding green LED. I've never seen the LED used for decoding errors light up.
This purpose of this board is twofold; it should be able to input a trigger signal to VEMS but also supply a voltage used for the tachometer. This is something the stock ECU provides so I need something similar.
I decided on the [LM2917 chip], since the [datasheet] already had a trigger to tacho schematic. However, I can't seem to tap the signal without disturbing the input on the attiny.
Alternative solutions:
Soft-PWM from the attiny, no need for multipin DAC (see softpwm.c)
NE555 (or equivalent from other manufacturer) is the standard for simple pulse-shaping and timing.
If a monostable multivibrator makes a constant 1000usec output pulse for every input pulse, you get an output proportional to input freq in 0..1000Hz range. Directly measureable via DVM, or can drive an (inductive!) voltage gauge with just 2 diodes (no RC needed, but flyback is needed to protect the silicon output). RC low-pass filter is recommended if signal is measured with an ADC.
See eg. Philips AN170 page 8: if you put an R and C between VCC and GND, and connect the RC midpoint to NE555 pin 7 and 8, you get a monostable multivibrator with 1.1RC output pulse.
TODO:
- decide about the input-capture pin. Why isn't input capture utilized ?
- Please elaborate. I'm not sure I understand what you mean here.
- prefer a non-EOL (not obsolete) chip
- I'm not using the at902313, but the attiny2313. The schematic is wrong.
- Get a freq->voltage converter working.
- Change output to simple trigger + cam sync
- Get input on the solution
- Make a real board
- ?????
- Profit!!!