Our EFI ECU outputs a 5v+ square wave signal, which is modulated for dwell by the ECU. The dwell, in this case, is the time between the rise and the fall of the signal. We wish to run that signal through the SSM box, which will monitor the square wave and report the rise and fall timing to a processor. The processor does nothing more than to delay the replication of each rise and fall event by a factor, which is found in a look up table that is stored in the SSM box in the processor’s flash memory. Every three waves is a revolution to calculate RPM.
The SSM box will also receive load data from a MAP sensor where 5v is no load and 0v is full load. The lookup table has a column for load. Delay values entered into the table records are therefore qualified by RPM and load. For example, load might be 0, 2.5 or 5 at a given frequency so there would be three possible delay offset values at a given RPM.
The SSM box has two outputs – one to each of two Coil Igniters. A Bosch Coil Igniter is a transistor that switches the coil on to charge, and when it switches off, the coil fires. The ECU varies the dwell time in order to compensate for fluctuations in voltage since the voltage affects the rate at which the coil will charge.
We need a Tuner Box SSM and a production SSM box:
The tuner box allows a tuner professional to designate various offsets for various RPM’s and loads. Our engine builder says that he wants to make an offset at every 200 RPM over a range beginning at 1,500 and ending at 6,000 RPM and at various loads – perhaps full and half load – and at less than half load, there is no offset. The SSM will calculate the engine RPM based on the time between falling edges of the input signal. The SSM tuner box would have a screen displaying the RPM and the load. It would have an up arrow button (to increase delay) and a down arrow button (to decrease delay) and an Enter button to send an offset value into the table.
The production SSM box would not have any display or buttons. It would simply receive a micro SD card that loads the lookup table into the processor’s flash memory. Once tested, we would need to buy these 25 at a time.
These boxes do not need sealed connectors because they will be inside the passenger compartment. We need a fixed price bid for this work. WeI have no idea how much time is involved. We have other projects to do after this one is done.