View Full Version : BS2 Car Starter Question

m dillon
01-07-2006, 06:20 AM
Hey everybody,

i'm restoring a 70 mustang fastback, and intead of a regular key ignition switch, i came up with a system that
uses rfid tags to determine who can start the car. i have a starter button that is on the dash so that it goes
through the bs2 and then to a relay to the actual starter solenoid, that way if the rfid tag is incorrect the car
cannot start. Since the bs2 is starting the engine i need it to know when to stop activating the starter, so i figured
i would use the PULSIN command on my tachometer cable which has a 12volt square wave signal with a 20% duty
cycle. I need help in using the command, and i want the bs2 to stop the starter motor at 800 rpm.


PJ Allen
01-07-2006, 10:10 AM
Have you considered using the RFID/STAMP (controlling a relay, etc.) as a·"gate circuit" for the starter and·not actually doing the starting [ i.e. the circuit between the starter switch, which would still be necessary, would go through the RFID/STAMP control. ]


m dillon
01-07-2006, 12:31 PM
Thanks PJ that is exactley what i will do, and a very simple solution, plus it is actually much better becuase then i'm controlling the starting
not the bs2 which wouldn't know to stop when you hear the engine catching... or knocks etc... Thanks!


m dillon
01-07-2006, 12:45 PM
but just for the sake of my question, and a possible future project http://forums.parallax.com/images/smilies/tongue.gif could someone please explain what
i would have to do to implement the pulsin cmd w/ the square wave and 20% duty cycle?


01-07-2006, 01:26 PM

Do you have an o-scope or a DVOM that will measure pulse width. I believe one thing you will need to know is what is the period of the HI or LOW time of the 20% duty cycle tach output.

With the engine off, or below your target 800 rpm, the length of the HI or LOW time will be longer than when above the target, so the time of the pulse is needed to use the BS2.

The pulsein command measures the length of a pulse (hi or low). Based on the pulse length you can determine if the engine speed is greater or less than your 800rpm target.


Post Edited (KenM) : 1/7/2006 6:29:25 AM GMT

01-07-2006, 04:44 PM
Some new cars control the start time via their PCM. Like my uncles Toyota Tundra. You can tap the starter position very quickly and it will continue cranking after you let off until it starts. It seems my Chevy work van does the same thing sometimes.

Anyway as a fellow motorhead, COOL CAR and I wish I had one :)

However, as someone who has made their very own anti theft system I'd interupt something else or as well.
Because as you know if that's all that your control prevents is the STARTER selenoid, then most ppl would know Ford has a very open selenoid to jumper with anything metal from under the hood :)

I'd do something sneaky. If it still uses POINTS ignition, run a hidden wire from the points to a controller than keeps the points GROUNDED so it will crank, but never get spark.

If it's electronic ignition, I'd just interupt the magnetic pickup. Again hiding the wire you tapped into.

On my '03 Dakota I spliced a wire in the wiring harness that goes to the fuel pump relay in the main control box. Funny thing is when I spliced that wire the starter doesn't crank either and an error comes across the odometer, making the anti theft thing even better.

I hid my wire very well in the wiring loom where I traced and spliced the circuit.

It is open until you turn the key on, and touch a hidden sensor with your finger and a latch circuit closes the circuit to the fuel pump relay.

It would take a LONG time to bypass that. It took me a long time to do it once. :P

No controller needed for that circuit. Just a few resistors, a transistor, and a dbl pole·N.O. relay.

Hope that helps.


Post Edited (paysonbadboy) : 1/7/2006 9:47:04 AM GMT

m dillon
01-07-2006, 09:22 PM
i'm using an msd ignition 6a to do my points ignition, and the stamp will be controlling another relay that will interupt the the connection of one of the msd's wires that they say should be grounded if you want to have the ignition disabled, but yes that solenoid is right there and all. Thanks for the suggestions, i don't have an O scope so i guess ill just try and figure it out without one, thanks everyone for the help.


01-08-2006, 12:09 AM

·I know their is a few remote car starters that can be wired to start off your QEM remote is senses when you press the lock button a couple of time in a certin amount of time and some of the starters have a input to start from and existing alarm that way you just pulse the starter· unit with your BS2 and the starter unit will monitor voltage drops to know when it is started and other conditions like stalls and no starts. If you fuel injection on the car that outputs a check engine light use it to stop the car after it has started if it comes on. If you use a carb and you dont use a starter unit you could get a window RPM switch from MSD and set it to output your idle RPM so you know when it is started. One last thing this websight is a real good DIY fuel injection sight I think you will like DIYAutoTune.com

Chris Savage
01-08-2006, 03:40 AM
m dillon said...(trimmed)
but just for the sake of my question, and a possible future project http://forums.parallax.com/images/smilies/tongue.gif could someone please explain what
i would have to do to implement the pulsin cmd w/ the square wave and 20% duty cycle?

·· Wouldn't the COUNT command be a better choice for simple RPM monitoring?· PULSIN will return the width of the pulse, not the number of times the pulse occurred within a period.

Chris Savage
Parallax Tech Support
csavage@parallax.com (mailto:csavage@parallax.com)

01-08-2006, 11:30 PM
Using pulsin simply measure the length of time on one high going, and one low going then add them together. V8 engine with 8 point rotor this will give you one 1/4 of the time it takes for a full revolution. 1/8 turn of the distributor = 1/4 turn of the engine due to the 2:1 ratio between the cam and crankshaft.

That comes out to 800 cranking rpms, divided by 2 for cam speed = 400 cam rpms

400 cam rpms times eight pulses per revolution gives you 3200 pulses per minute

1·minute divided by 3200 pulses gives you 53.3333333 pulses per second

1 second divided by 53.33333333 gives you 18.75 ms per pulse set <high and low added together>

So simply measure pulsin high, and pulsin low add together and if sum<18.75ms then your running.

The advantage to using pulsin over count in this instance is you can take a higher number of samples and do a compare. For example a 3 step loop where you sample 3 times and declare running only if all 3 samples are less than your set value. This would help eliminate spurious signals and faults. The time to perfom a count command 3 times with enough pulses to get an accuracy.

Count would require a period long enough to capture 10 pulses to get around 5% resolution which is 187.5 ms, performing that even twice would take 375 ms plus overhead time approaching a half second. It would take some experimenting to determine what the reaction time or the system would be, and what an acceptable lag time is but I would guess the reaction could be up to 3/4 of a second from the time the engine actually started when you include contact lag time etc. Of course with Count you may not need the redundancy of multiple samples since a single extra or missing pulse will have a smaller effect. So its probably a wash, personally I preffer the redundancy and speed that pulsin allows. As it also lets you capture events later that are much more time sensitive, like a shift light.