MicroSquirt.com read only forum (Jan.15,2018)

I am new to the forum.
I have a new microsquirt V3 3.83 firmware.
And a GM 7 terminal HEI
The documentation for 3.4 hardware manual states to connect R terminal to the pin 32 uS connector VR1IN+.
The diagram shows pin #30
The Picture on page

Connecting to pin #30 does not provide RPM signal during crank.
I did verify a 10 degree before TDC 12V+ Square pulse for each cylinder present at pin 30.

Another forum poster stated

I wired Option + to Href and wired Option - to the HEI "R" pin.

My question is What is correct? So none of these work
Pin 33 to R pin 32 Gnd VRIN
Pin 32 to R pin 33 floating VRIN
Pin 30 to R pin 31 floating OPTO
Pin 30 to R pin 31 to Gnd OPTO
Pin 30 to Vref pin 31 to R OPTO


I connected A Scope to the wire removed from the harness at the uS and I have an exceptional clean cranking signal.
Scope probe is set on 10x scope on 1x voltage is only 2v per division not 20v. So it is a clean 5V pulse. Really not liking this.

Checked R20 ok jumnpered pin 31 to OPTO - (cathod U4) and pin 30 to Opto + (Anode U4) built external filter 500ohm in series with .22uF and .001uF to GND tested still no signal to RPM TachIC.
Tomorrow I am setting up signal generator and tracking down the lost signal.
Really truely unhappy as a new user at this point.

I would try using the VR input instead of the optoisolated input. Some ignitions don't supply enough current to trigger the optoisolator.

Yep thought of that when I tried using pin33 and pin32 no joy.
Tonight I am looking directly at the opto isolator MOC205M.
I am going to try and trigger with a Gwinstek Function Generator and see if I can sort out a tach signal RPM.
THe GM HEI7 pin module easily lights 3 standard LEDs in parallel or at least 60mA I am thinking that the OPTO transistor may be shorted.
If it is not producing a signal at the Collector MOC205M pin6 then either the LED is dead or the transistor is shorted.
If transistor is emittor to collector shorted than it will also short the VR signal to ground.

If thats the case I will replace the MOC205M with a CNY651 that I know works reliably for other Tachometers I have built.

On the Microsquirt Module schematic that looks like the same for the Microsquirt in this area.
I see that the OPT+ and OPT- trigger the TachIC signal Inverted through U4.
VRIN+ triggers Q4 inverted to U10A that triggers Q2 inverting the signal again.
Looks like Q3 R22,R28,R54 form a 47 Gain feedback circuit with a .7V bias.
The only thing I can figure is that Q3 is providing some thermal stability and matching for Q4.

My opinion is that this could be done simpler and more robust.
VCC should be @5V+
A CNY651 opto with 20K between VCC and collector and emiter tied to ground.
The IR LED on the CNY651 driven at 5mA 5V switches 5uS on 3uS off with a .3uS hold time between so it provides enough filter for spuratic noise rejection. So a 100Ohm resistor in series with the IRLED is all thats needed for HEI DIS and FHID.

For the VR inputs a LMV321 op amp with the - input taken off a 1n4001 diode anode to ground cathode to 1Kohm resistor Vrin+ to the opposite lead of resistor. - input to LVM321 taken from cathode of diode. 1n4001 diode anode to ground cathode to 1kOhm resistor other lead of resistor to Opto + input.
100KOhm resistor from out to + input of opamp. Out of op amp to 2n2222A or N2907 transistor base emitter to ground collector to opto collector.
All of the noise and thermal stuff would be redundant as the 321 is a little slow and the diodes block any thing over .7V.

I have simulated tach signal at PW0 TACHIN and showing RPM on TunerSTudio.
Really disappointed at the amount of jiggering with a product to make it work.
Be advised this is not really a direct part for commercial resale but more of hobbiest or hacker level product.
I will reserve my total opinion once I have finished tuning the car.
I typically have used only GM 66ECU controllers found on pre1996 corvettes, caprice, lumina, camaro.
The earlier pre 1996 does not incorporate OBDII it is typically known as OBD1.5
I really considered changing my tuner platform to TunerStudio and the Microsquirt line of products due to the lack of WindowsXP compatable laptop hardware to continue using CatsTuner and GM66ECU.
I have one more project in my shop that is TBI I will attempt to use MicroSquirt Module instead of the Microsquirt.

What I had to do to get this Microsquirt to recognise a signal.

First the Software settings.

Ignition Set-up > Base Ignition Settings > General Ignition
Trigger Offset = 0.00
Skip Pulses = 1

Ignition Set-up > Base Ignition Settings > Prediction Settings
Predictor Algorythm = Last Interval

Ignition Set-up > Base Ignition Settings > Tach Signal Masking
Time Mask(msec) = 0
Percent Mask(%) = 50

Ignition Set-up > Base Ignition Settings > Next-Pulse Tolerance
Cranking(%) = 50
After-Start(%) = 70
Normal Running(%) = 25
Check Tach Sync Options = Check Only at Steady Speed
Ignition Input Capture = Rising Edge
Cranking Trigger = Trigger Rise
Coil Charging Scheme = Standard Coil Charge
Spark Output = Going Low (Normal)

Ignition Set-up > Dwell Settings
Maximum Dwell Duration(msec) = 3.1
Maximum Spark Duration(msec) = 2.0
Acceleration Compensation(msec) = 0.6

Ignition Set-up > Dwell Settings > Battery Voltage Compensation
Voltage 1 (V) = -4.0
Voltage 2 (V) = -2.0
Voltage 3 (V) = 0.0
Voltage 4 (V) = 2.0
Voltage 5 (V) = 4.0
Duration at Voltage 1 (msec) = 2.4
Duration at Voltage 2 (msec) = 0.9
Duration at Voltage 3 (msec) = 0.0
Duration at Voltage 4 (msec) = -0.5
Duration at Voltage 5 (msec) = -0.9

Ignition Set-up > Tach Signal Settings
TachOut Fixed PW(ms) = 2.0
TachOut Duty Cycle(%) = 50

Ignition Set-up > Dual/Multi Spark Ignition Options
Dual/Multi Spark Options = No Dual/Multi Spark
Auto Trigger Calculation = Disable Auto Trigger
Offset (advance) for Output #2(degrees) = 0.0

Ignition Set-up > Advanced Ignition Options
Trigger Wheel Teeth(teeth) = 0
Cam Tooth(teeth) = 0
Start IAT Retard (rpm) = 800
Full AIT Retard (rpm) = 1500
FET Output Delay (usec) = 0
VR Input Delay(usec/1000rpm) = 0

The crap I had to do to modify the hardware to get a propper signal at PW0 pin of ECU TACHIN.

I found that the filter assembly of D4 R20 C27 C28 idi not pass a signal to the U4 MOC205-M opto coupler,

The output of my ignition module is clean clear and undistorted at 5V 10% duty cycle.

Harness Adapter Board

Microsquirt with removed components of OPTION filter and test Leads soldered in place

The Filter on the Microsquirt V3 was removed by removing R20 C27 C28 D4.
Wiring was accomplished through connector at pin 30 and pin 31 by jumping from D4 anode to pin 1 of MOC205-M U4
Replacement Filter consists of 3mm LED with forward voltage drop of 1.3V in series with 470 OHM resistor accross HEI7 module pin R to GND.
a single .001Uf ceramic capacitor is wired accross in parallel to LED resistor combo.
Microsquirt Pin 30 is wired to Anode of 3mm LED and pin 31 is wired to GND

By putting an LED in parallel with the OPTO Isolator you provide Reverse polarity rejection and voltage limiting accross the OPTO Isolator LED.
The input current is limited to @ 10.6mA with the majority going to the Opto Isolator so the filter LED will not illuminate visibly.

You can see that the MOC205-M has a bit of slew about 100usec on The transistor Turn Off This will cause crappy ignition signals at higher RPM.
IMO I would select a different Opto Isolator than this one.
The cheaper Generic 651 common to most UPS and Computer Power supplies is two orders of magnitude faster 5-3Usec instead of 100usec, has a 13.9KV isolation voltage so it survives a wet distributor cap discharge that I think will blow the MOC205-M at only 300V.


Gwinstech Function Generator injecting signal


TunerStudio Dashboard showing RPM

Circuit for filter as described

I see many people have discussed issues with this area of the MEGASQUIRT MS2 that I understand is the basis for the Microsquirt V3 On the MEGA they use a 4N25 Opto that is somewhat better than the MOC205-M.
I think that the 651 would function better.

In motor drivers and other circuits where I have mixed voltage or high voltage interfaced with microcontrollers I typically use the 651 or A GOULD or COMDON OPTO Triac. I have a small dual scram jet controlled by two 651 triggering the MOSFETS on the fuel and on the ignitors. The circuit uses an arduino at 16Khz to trigger the fuel and spark and works well.
No real controll over variable load on a jet so its sort of like PWM to control output level.

Transistors are 2n2222
Caps are .001uF
The input on the left is from any reluctance coil pickup polarity shouldn't mater.
Output will be a 5V pulse on right side.
1n4001 clamps to .7V input if input is non zero output transistor is saturated.
I bread boarded and tried with Cadilac NorthStar Lower Crank Sensor and a screw driver. Output is clean.