Why would you add a separate knock system if you just need to add a simple resistor and diode to the "proto area" of your MegaSquirt system? Your board fully supports it (yes MegaSquirt 1 and 2 both have the ability) and will read your OEM knock sensor (requiring a simple calibration). I have a full DIY on it, and I already helped my friend on his MR2 Turbo install it with his MegaSquirt and it works 100% (only took 15 minutes to install it).
All you need to do is the following:
On the proto area of your your board (which is the expansion board allowing you to add additional abilities (ie knock sense, water control for meth, N20 ability etc).
(Note proto area on the bottom left of the board)
1.) Add a 1k Ohm resistor (1 / 4 or 1 / 8) watt which will be soldered to a wire which connects to the
JS4 socket.
2.) Do the same on another area on the proto area (with a resistor), however this one go's to the
SPR3 circuit.
Then, locate a simple GM knock sensor module, which will be added inline to the existing knock sensor:
Once this is said and done, you can do the following:
Knock Control:
Disabled: do not use knock feedback for ignition advance control.
Safe Mode: use knock retard, but keep the advance below that which caused knock. This backs the advance 1 small step back and leaves it at that until TPS or MAP changes - or knock comes back. This is "safe mode" scheme is the safest thing for a DIY set-up.
Aggressive Mode: use knock retard, but keep advance at threshold of knock occurring. That is, the program advances (up to the timing table value) if it doesn't see knock, and retards if does see knock. The difference from safe mode is that the timing can be advance all the way to the table value after knock, not just up to one step below knock. This may result in the knock returning, in which case the timing is retarded again, then advanced slowly, and so on.
Threshold Direction: This sets whether MegaSquirt® recognizes a voltage above the threshold (see next item) or below the threshold is considered knock.
Threshold (V): The is the voltage from the knock sensor module which defines whether there is knock occurring or not. Note that you can define a 6-element table of rpm versus voltage instead of a single value. You define this table under 'Settings/Knock Threshold'. The GM sensor/module signal is ON/OFF, but the knock threshold value/table is there in case someone has a system they can calibrate to their car by a threshold.
Peak (V): the maximum expected voltage value on the knock signal, used in some configurations where the difference between the signal level and the maximum levels indicates the degree of knocking.
Knock Count (knocks): number knock detects required for valid detection
No Knock Above MAP (kPa): no knock retard is implemented above this MAP
No Knock Below RPM (rpm): no knock retard is implemented below this rpm
No Knock Above RPM (rpm): no knock retard is implemented above this rpm, which may be desirable if valve train noise triggers the knock sensor when knock isn't actually occurring.
Maximum Retard (deg): maximum total retard when knock occurs. This can be useful to prevent timing from being excessively retarded (avoiding potential overheating issues) if the senor malfunctions or there are other problems with the knock sensing system.
Retard Check Time (sec): this is the time between knock retard corrections, allows short time step to quickly retard
Retard Step Size (deg): ignition retard step size when 1st knock or after stopped, make it large to quickly retard the timing and stop knock
Advance Check Time (sec): this is the time between knock advance correction (I.e., timing return to 'normal')
Advance Step Size (deg): ignition advance steps after knock has stopped
Recovery Advance (deg)): this is the change in table advance required to restart advance until knock or reach table value (0 knock retard) process. This only applies in 'Safe Mode'
For more information, visit this link:
http://www.megamanual.com/ms2/knock.htm
Note: This article was written before support was written for the MegaSquirt 1 board, but is used on many models, so ignore the area stating that it was tested only on the bench (ive even scene it used as well).
I don't see a purpose to spending more than what you have to because your system already has it. It will also be easier to tune your car, because you'll have an active knock gauge on your tuning software, which you can specify how much timing to pull when knock is sensed (also if you're using your megasquirt as a boost controller, you can pull boost away by a specified amount on top of pulling timing).