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Location:
Lost in the K hole
Registered:
May 2002
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simple MAP sensor based switch...
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Wed, 10 September 2003 05:15
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I know shit all about electronics, so thought i'd post this to see what people thought...
im after a circuit which i can hook up to a 1bar MAP sensor, that will let me switch on a device when the output of the MAP sensor hits a certain voltage. the point at which the device is switched on needs to be adjustable for tuning purposes (ie an extra injector needs to be switched on at a given manifold pressure - but the pressure threshold at which the injector will switch on needs to be adjustable so i can tune the damn thing)
with that in mind - i found this:
http://minimopar.net/perf/eepc-fuel-map.html
heres the theory:
http://minimopar.net/perf/eepc-basic.html
what id like to know is: obviously that circuit is designed to switch on up to 4 injectors sequentially. it seems logical enough that it should be able to switch only one injector, and that it is adjustable.
is that correct?
will this cicuit do what i stated in the opening paragraph?
(and fwiw - i wont actually be switching an injector directly with this circuit, but rather a relay, which will then switch the injector - i dont think this matters really, but thought id mention it just in case it does)
and secondly, this circuit is based on a 2bar map sensor with an output of 0-5v. im guessing a 1bar sensor also has an output of 0-5v and thus can allso be used sucessfully (on an NA engine)
anyone know a CHEAP supplier of 1bar map sensors that would suit this circuit?
thanks y'all
cheers
ed
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Location:
was adelaide now newcastle
Registered:
February 2003
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Re: simple MAP sensor based switch...
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Wed, 10 September 2003 05:26
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have you thought about using a hobs pressure switch, they are adjustable for switching point.
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Location:
Lost in the K hole
Registered:
May 2002
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Re: simple MAP sensor based switch...
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Wed, 10 September 2003 05:35
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| JDM hachi wrote on Wed, 10 September 2003 15:26 |
have you thought about using a hobs pressure switch, they are adjustable for switching point.
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im using it on an NA engine, and the Hobbs vac switches arent adjustable. you buy them preset at the pressure switch point you want, and have inbuilt errors of ~2-3mmHg
there are other adj vac switches available, but theyre rather $$ and still not as graceful or user friendly as a MAP sensor output and controller...
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Location:
Lost in the K hole
Registered:
May 2002
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Re: simple MAP sensor based switch...
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Wed, 10 September 2003 05:54
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| ed_ma61 wrote on Wed, 10 September 2003 15:15 |
anyone know a CHEAP supplier of 1bar map sensors that would suit this circuit?
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d'oh! eBay, as usual 
cheers
ed
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Location:
Kita-Ku, Sapporo, Japan
Registered:
January 2003
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Location:
Lost in the K hole
Registered:
May 2002
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Re: simple MAP sensor based switch...
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Wed, 10 September 2003 07:14
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stewart - those ones you listed appear to be pressure sensors? ie 2-16psi absolute (positive) pressure? not negative pressure (ie vacuum) for an NA application? dunno, maybe im just dumb and dont get it?
dont suppose youll have any spare from that buy would you 
ebay (as usual) looks like the source of all things good anyway.
still... does anyone have any comments on the circuit above??
cheers
ed
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Location:
Kita-Ku, Sapporo, Japan
Registered:
January 2003
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Re: simple MAP sensor based switch...
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Wed, 10 September 2003 08:30
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they are "absolute" pressure sensors, so at atmospheric pressure they read 103kPa or whatever.
the one in the megasquirt is an MPX4250AP type, which reads from 5kpa to 250kpa absolute, ie 100kpa of vacuum, and 150kpa of boost (relative to atmospheric)
the "relative" sensors are referenced to atmospheric i believe.
there is a slim chance i could get hold of an MPX4115AP (5-115kpa absolute) or an MPX4250AP (5-250kpa) sensor as i haven't paid for the megasquirt partial kits yet.
i'll find out by email tonight or tomorrow. give me a call (if you still have my number) or pm me.
Cya, Stewart
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I supported Toymods
Banned User
Location:
Brisbane
Registered:
May 2002
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Location:
Kita-Ku, Sapporo, Japan
Registered:
January 2003
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Re: simple MAP sensor based switch...
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Wed, 10 September 2003 08:42
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as far as the circuit goes, it looks okay.
i would beef up the 'lash-back/flyback' portion, as the voltage spikes of closing injectors has proved to be larger than ppl usually expect. there is a flyback design on the main MS site (and i prolly have it somewhere)
but apart from that, it's a simple comparator circuit that will probably work okay.
concerns would be difficulties with latching on/off at the switching point... if it keeps flapping around, could be interesting, with voltage spikes and stuff.
if you are thinking of this for water injection, it looks good.
for extra fuel.. hmmmmm
but it looks pretty interesting and worth a go 
Cya, Stewart
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I supported Toymods
Banned User
Location:
Brisbane
Registered:
May 2002
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Re: simple MAP sensor based switch...
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Wed, 10 September 2003 09:02
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To me that circuit above is a little complex for what it does 
For just one output a simple adjustable voltage divider will do the job and do it rather well And I personally wouldn't use a relay to switch the injector, I would simply use a FET built into your main circuit. A FET will switch much much faster and has about a billion more operations than a relay!
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Location:
MACKAY
Registered:
May 2002
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Re: simple MAP sensor based switch...
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Wed, 10 September 2003 09:39
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ed
You can get a map sensor of a commodore , falcon XF , camira , or any Toyota they will all work for what you want but dont get the latter falcon type map sensor as they work with frequency rather than voltage , also you can run your extra injector by tapping into one of the existing injectors and switching the extra inj with the circuit this way you will have a better enrichment as the injector will increase fuel with revs as the standard injectors do , If you do it this way make sure you use an injector with the same resistance .
Trevor
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Location:
Brisbane
Registered:
February 2003
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Location:
Lost in the K hole
Registered:
May 2002
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Re: simple MAP sensor based switch...
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Wed, 10 September 2003 13:12
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| Cool1 wrote on Wed, 10 September 2003 18:39 |
Do you want to know what the switched level will be when you are adjusting it? Or will you have a reference else where?
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no, i dont need to know what the 'actual' level is when im adjusting it. it will be simply be adjusted as a preventative measure for knock elimination, so will be set subjectively against that (not any masurable manifold pressure or anything)...
| Cool1 wrote on Wed, 10 September 2003 18:39 |
For just one output a simple adjustable voltage divider will do the job and do it rather well Smile And I personally wouldn't use a relay to switch the injector, I would simply use a FET built into your main circuit.
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want to design me a circuit?
it really just needs to take a variable 0-5v dc input, and switch on an output at a given input voltage - which needs to be adjustable.
whats a FET? this thing is going to be hooke up to a bunch of other relays, so maybe a relay is easier - just so my simple mind can integrate the whole system?
cheers
ed
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Location:
Lost in the K hole
Registered:
May 2002
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Re: simple MAP sensor based switch...
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Wed, 10 September 2003 13:20
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| thechuckster wrote on Wed, 10 September 2003 21:12 |
hi ed,
if you tap into inject wiring, you might want to link to two injectors as the toyota ECUs i've seen run 2 banks of injectors (e.g. non-sequential).
but if you've got the time/enthusiasm, there's a few variations on the standard Megasquirt that supports the kind of thing you're after, e.g. dual table ECU (drive normal injectors on table one, and table two drive extra big injectors such as water/meth inject or a second bank of petrol inject for moments of panic/testosterone etc)
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thanks charles
thats getting all a little above and beyond in terms of complexity for a si ple water/methanol misting system
im running a shurflo 45psi pump and an industrial micro misting jet (50micron spray) rather than an injector per se.
switching it will be donr by a combination of an rpm switch, and a MAP switch. i just need to figure out the MAP switch circuit
cheers
ed
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I supported Toymods
Banned User
Location:
Brisbane
Registered:
May 2002
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Re: simple MAP sensor based switch...
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Thu, 11 September 2003 07:46
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What range do you want to adjust it over Ed? You obviously wont ever want it to be switching on at .6 of a volt!
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Location:
Lost in the K hole
Registered:
May 2002
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Re: simple MAP sensor based switch...
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Thu, 11 September 2003 09:14
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dont know
id be guessing somewhere in the middle like 1v-4v??, but im not sure what the output characteristics of the MAP sensors are ie; Pressure vs Voltage...
what restrictions are there in terms of the available range?
cheers
ed
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I supported Toymods
Banned User
Location:
Brisbane
Registered:
May 2002
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Re: simple MAP sensor based switch...
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Thu, 11 September 2003 09:22
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| ed_ma61 wrote on Thu, 11 September 2003 19:14 |
what restrictions are there in terms of the available range?
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Probably none  If i get time i'll try and knock up a circuit while i'm at tafe!
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Location:
Lost in the K hole
Registered:
May 2002
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Re: simple MAP sensor based switch...
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Thu, 11 September 2003 09:38
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lol, do some work ya bum
(hell, what am i saying? im the one who should do some work....)
dont stress too much on it though - that comparator circuit is looking ok - thanks stewart!
cheers
ed
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